patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
description | This application is a continuation of U.S. patent application Ser. No. 13/320,216, filed on Feb. 21, 2012, currently allowed, which is a national stage filing under 35 U.S.C. §371 of International Application No. PCT/US2009/002998, filed May 13, 2009, which was published under PCT Article 21(2) in English, the entire contents of each of which are incorporated herein by reference. 1. Field Aspects of the present invention relate to a radionuclide generator having a column assembly that may be terminally sterilized without the introduction of excess moisture. 2. Discussion of Related Art Radionuclide generators include a column that has media for retaining a long-lived parent radionuclide that spontaneously decays into a daughter radionuclide that has a relatively short-lived life. The column may be incorporated into a column assembly that has a needle-like outlet port that receives an evacuated vial to draw saline or other eluant liquid, provided to a needle-like inlet port, through a flow path of the column assembly, including the column itself. This liquid may elute and deliver daughter radionuclide from the column and to the evacuated vial for subsequent use in nuclear medical imaging applications, among other uses. One example of a generator is shown and described in U.S. Pat. No. 5,109,160, owned by Lantheus Medical Imaging, Inc., and which is incorporated by reference herein in its entirety. Sterilization to some degree is generally performed on radionuclide generators that are used in the medical industry. Sterilization may be performed by exposing a column assembly of a radionuclide generator, having a column loaded with parent radionuclide, to a saturated steam environment. During this process, liquid that resides in the column assembly, including the column and tubes that extend between the column and the inlet and outlet ports may be heated to vapor form (e.g., steam) to kill and/or inactivate contaminants. A vent may be included at the outlet port to allow both the introduction of steam and the release of vapors from the column during the sterilization process. As discussed in U.S. Pat. No. 5,109,160, it may be desirable to provide a radionuclide generator as a terminally sterile product—that is, a product that is sterilized in its final container, or at least that is sterilized with the flow path between the inlet port, the column, and the outlet port assembled in its final form, including any vented or non-vented vented caps over the inlet and outlet ports. This may be contrasted with aseptic sterilization where at least some of the individual components that make up the flow path between the inlet port, the column, and the outlet port are sterilized separately and subsequently assembled together. Providing a vented outlet cover at the outlet port of a column assembly during sterilization, instead of assembling a cap or cover after sterilization, may help a product achieve terminal sterilization. The applicant has discovered, however, that vented outlet covers may, in some instances, provide an entranceway to the flow path of a column assembly for unwanted liquid, despite the presence of a filter at the vent opening of a vented outlet cover. In fact, the applicant observed that a filter on a upwardly facing vent opening has provided a surface on which condensate may accumulate during or after steam sterilization. The accumulated condensate was found to breach the filter and enter the column assembly flow path, in some cases, and to be the cause of reductions in product life (i.e., elution efficiency) and in radioactive integrity (i.e., column assemblies emitting an amount of radiation that exceeds a threshold level), prior to product shipment. These reductions, until the present invention, were unexplained for years. According to one aspect, a column assembly of a radionuclide generator includes a column having an interior containing a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide. The column assembly includes an inlet port in fluid communication with the interior of the column and an outlet port in fluid communication with the interior of the column. The column assembly includes a vent opening that provides fluid access to the interior of the column via the outlet port. The vent opening is configured to provide fluid access and to prevent condensate from entering the vent opening or outlet port. According to another aspect, a method is provided for producing a terminally sterile column assembly of a radionuclide generator. The method comprises providing a column assembly of a radionuclide generator that includes a column having a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide. The column assembly also includes an inlet port in fluid communication with the column and an outlet port in fluid communication with the column. The outlet port includes a vent opening that provides fluid access to the column. The column assembly is positioned in an orientation with the vent opening facing downwardly to prevent condensate from entering the vent from above. The column assembly is also exposed to steam for sterilization. According to at least some embodiments, an outlet cover at least partially covers the outlet port and includes the vent opening. The outlet port may include a needle structure and the outlet cover may include a pierceable membrane that receives the needle structure of the outlet port. In some embodiments, the outlet cover includes a body portion and a removable cap. The vent opening may be defined as an annular space to between the removable cap and the body portion. According to some embodiments, a filter is in the outlet cover. The filter may be bacteria retentive, according to some embodiments. The filter may be positioned at the vent opening. According to some embodiments, a filter may be positioned between and in fluid communication with the outlet port and the column. In some embodiments, the inlet port may be accessible from outside of a shielded package that receives the column assembly, when the column is inside of the shielded package. The column assembly may be provided in combination with the shielded package. A plug may be removably attached to the inlet port to block fluid communication to the inlet port from an atmosphere outside of the column assembly, according to some embodiments. The medium in the column may include alumina, according to some embodiments. The column assembly may be provided in combination with the long-lived parent radionuclide and the relatively short-lived daughter radionuclide, according to some embodiments, and the long-lived parent nuclide may include molybdenum-99 and the relatively short-lived daughter radionuclide may include technetium-99m. According to some embodiments, a plurality of column assemblies may be exposed to a steam environment at a common time for one or more sterilization cycles. In some embodiments, exposing the plurality of column assemblies to steam for a single sterilization cycle results in an amount of remaining liquid that varies by 5% or less (relative standard deviation). In other embodiments, exposing the plurality of column assemblies to steam for two sterilization cycles results in an amount of remaining liquid that varies by 15% or less (relative standard deviation). According to another aspect, a column assembly of a radionuclide generator is provided that includes a column and an outlet port. The column has a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide. The outlet port is in fluid communication with the column and is covered with a vented outlet cover to provide a terminally sterilizable column assembly. The vented outlet cover has a vent opening that provides fluid access to the column and that prevents the ingress of gravity-driven liquid (condensate) to produce a column assembly that consistently exhibits high yield and that prevents migration of parent radionuclide away from the column. According to another aspect, a column assembly of a radionuclide generator includes a column and an outlet port. The column has a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide. The outlet port is in fluid communication with the column and is covered with a vented outlet cover to provide a terminally sterilizable column assembly. Means are provided to prevent the ingress of gravity-driven liquid to produce a column assembly that consistently exhibits high yield and that prevents migration of parent radionuclide away from the column. According to some embodiments, the means comprises a vent opening that provides fluid access to the column and that prevents the ingress of gravity-driven liquid. The vent opening may face toward the column, according to some embodiments. Broadly speaking, a radionuclide generator includes a column that retains a parent radionuclide which spontaneously decays to a relatively short-lived daughter radionuclide. The column may be incorporated into a column assembly that includes a fluid path extending from an inlet port, through the column, and then to an outlet port from which daughter radionuclide may be delivered for use. The column assembly is typically positioned within a shielded package. Some aspects described herein provide for improved retention of parent radionuclide in the column where radioactive shielding is typically the greatest. This may be accomplished by venting a column assembly in a manner that prevents the ingress of liquids during sterilization, yet that allows for the exchange of steam and/or other vapors. This, in turn, may reliably prevent excess liquid from being introduced to portions of the column assembly, such as portions of the inlet and outlet tubes where the presence of excess liquid might provide a pathway for unwanted migration of radionuclide. Other aspects of the invention relate to reliably preventing excess moisture from coalescing in or about the column, which may adversely impact column chemistry and lead to reduced yield of daughter radionuclide. Parent radionuclide is typically provided to a column in a fluid charge, where the radionuclide selectively binds to media in the column while the fluid charge is drawn through the column along a flow path of a column assembly. During sterilization there is an exchange of vapors, through the vented outlet cover, between heated, residual charging fluid residing in the column assembly flow path and the saturated steam present in a sterilization chamber. During the cooling process that follows sterilization, steam may condense about a column assembly and may enter the column assembly, as liquid, through an outlet port (absent features to prevent the ingress of gravity-driven liquid), resulting in excess liquid in the column assembly flow path. Excess liquid that may reside in the column or other portions of the flow path between the inlet port and outlet port of a radionuclide generator column assembly may provide a path along which parent radionuclide may migrate. Migration, in some instances, may occur to areas of a flow path that are shielded to a lesser degree than the column itself, which may result in radiation being emitted at a level that exceeds a threshold level. Aspects of the invention described herein relate to controlling the moisture content of a column assembly during and/or after steam sterilization so as to prevent excess liquid in the flow path of a column assembly, along which radionuclide may migrate. Excess moisture in the column or column assembly of a radionuclide generator may result from the entry of liquid into the column assembly during or after steam sterilization, and may adversely impact column chemistry, resulting in reduced yield of daughter radionuclide. Aspects of the invention relate to controlling the amount and/or phase state of moisture that may enter a column during or after sterilization to promote the production of a high yield radionuclide generator. It many instances, it may be desirable to provide a radionuclide generator that is terminally sterile. This involves sterilizing the column assembly, including the flow path between inlet port, column, and the outlet port, and any plugs or vented covers positioned on the inlet and outlet ports, when assembled together in final form, at least prior to being installed in a shielded container. Aspects of the invention relate to providing a terminally sterile product, including sterilization after fully assembling any plugs and vented covers to the flow path, while also reliably controlling the amount of moisture in the flow path of the column assembly. Turning now to the Figures, and initially FIG. 1, one embodiment of a column assembly 10 of a radionuclide generator is shown. The column assembly 10 includes a column 12 having a media 13 and that is fluidly connected at one end to an inlet port 14 and a charge port 16 through an inlet line 18 and a charge line 20, respectively. As shown, the inlet port 14 and charge port 16 are each covered with a plug 22, 24. A vent port 26 that communications fluidly with an eluant vent 28 is positioned adjacent to the inlet port 14, and may, in operation, provide a vent to a vial or bottle of eluant connected to the inlet port, as described in greater detail herein. The column assembly 10 also includes an outlet port 30 that is fluidly connected to the bottom of the column 12 through an outlet line 32. A filter assembly 34 is incorporated into the outlet line, and the outlet port 30 is covered with a vented outlet cover 36 that also includes a filter, as described in greater detail below. Various aspects of the illustrated embodiment of the column assembly are described in greater detail in U.S. Pat. No. 5,109,610 (Evers), owned by Lantheus Medical Imaging, Inc, which is hereby incorporated by reference in its entirety. Additionally, column construction materials and operation are described in U.S. Pat. No. 3,476,998 (Deutsch) and U.S. Pat. No. 3,774,035 (Litt), each of which is also hereby incorporated by reference in its entirety. Manufacture of a radionuclide generator, according to some embodiments, includes charging the column with a parent radionuclide after the column assembly has been assembled. This may be accomplished by providing a vial or bottle that includes a parent radionuclide, such as molybdenum-99 (Mo-99) in solution, to the charge port 16. The Mo-99 in solution is then drawn to the column, either by applying a vacuum at the outlet port 30 or by driving the fluid to the column under pressure provided at the charge port 16. The parent radionuclide in solution passes through a medium 13 in the column, such as alumina, that has an affinity for and that retains parent radionuclide therein. It is to be appreciated that embodiments of the column assembly may be charged with parent radionuclide other than molybdenum-99 (which produces technetium-99m as a daughter radionuclide). By way of non-limiting example, column assemblies may be charged with germanuim-68 as a parent radionuclide to produce gallium-68 as a daughter radionuclide or with tungsten-188 as a parent radionuclide to produce rhenium-188 as a daughter radionuclide. FIG. 2 illustrates portions of a column assembly configured for charging the column with parent radionuclide. Having a charge line 20 and charge port 16 that are separate from the inlet line 18 and inlet port 14 (as shown in FIG. 1), which are typically plugged as the column 12 is charged, may prevent radionuclide from entering the inlet line 18 of the column assembly 10. A plug 24, which may be permanent, may be placed over the charge port 16 after charging the column to prevent migration of radionuclide back up the charge line 20 from the column. After charging, a vented outlet cover 36 may be positioned over the outlet port 30 (as shown in FIG. 1). Other plugs and features, including a vent cap 38 positioned over the eluant vent 28, may be assembled to the column assembly 10 prior to or after charging the column to ready the device for sterilization. The flow path of the column assembly 10, including the inlet port 14, inlet line 18, column 12, outlet line 32, and outlet port 30, among other features, may be sterilized with the inlet plug 22 and vented outlet cover 36 in position, and prior to the column assembly being placed in a shielded package 40 (as shown in FIG. 4). Sterilization of the column assembly in this manner may provide for a terminally sterile column assembly, given that no further manipulations of customer access points (i.e., the inlet port and the outlet port) or internal portions of the flow path therebetween may be performed subsequent to sterilization and prior to the radionuclide generator being accessed by an end user. Alternatively, the column assembly may merely be assembled into a shielded package to complete assembly of a radionuclide generator, as discussed in greater detail herein, and readied for shipment. According to some embodiments, sterilization includes exposing the column assembly 10 to a saturated steam environment. This may involve placing one or more column assemblies into a sterilization chamber, each assembly having a plug 22 positioned over the inlet port and optionally over the vent port 26, and a vented outlet cover 36 positioned over the outlet port 30. Steam is provided to the sterilization chamber as the pressure of the chamber is increased until a desired temperature and pressure are achieved. According to some embodiments, column assemblies are exposed to a saturated steam environment at a pressure higher than atmospheric. It is to be appreciated that sterilization may involve various combinations of temperature and pressure values, such as combinations of pressure and temperature associated with a saturated steam environment, as may be determined from a psychrometric chart, and that types of sterilization other than saturated steam may also be used, as the embodiments are not limited to the sterilization techniques described herein. Additionally, different combinations of plugs and/or vented covers may be positioned over the inlet, outlet, and/or other access points, and in some embodiments, access points may be uncovered during sterilization. A column assembly may be oriented during sterilization to help retain radionuclide activity within the column and/or portions of the flow path near the column. According to some embodiments, the column assembly 10 may be oriented in a similar way, typically with the column assembly lower than other portions of the flow path, both during sterilization and when placed in a shielded package 40 for delivery and/or use. As shown in the embodiment of FIG. 1, the column 12 may be positioned near a lower portion of a column assembly 10, such that any liquid within the system is directed by gravity toward the column or portions of the flow path that are near the column, where shielding of a shielded package is generally thicker. The inlet and outlet lines 18, 32 may be oriented substantially vertically or diagonally downward at all points, lacking dips or horizontal sections that might otherwise trap liquid containing radionuclide after charging, elution, and/or during sterilization. It is to be appreciated that the embodiment of FIG. 1 shows but one configuration of inlet and outlet lines, and other others are also possible, including for instance lines that are configured differently from that shown in FIG. 1, but that are generally ramped downward toward an area near the column at all points along their length. During steam sterilization, residual fluid used in charging the column with radionuclide is heated to a vapor form (e.g., steam) to kill and/or inactivate contaminants. The vapor may be driven at least partially from the column assembly while steam also enters the column assembly from the saturated steam environment within the sterilization chamber, such that there may be minimal or no net change in moisture content of a column assembly during sterilization. At least one vent opening, typically positioned at the outlet port, and that may optionally include a filter, may be left open between the column and the steam environment during the sterilization process to allow for the ingress and egress of steam to the column. Although moisture exchange occurs between the flow path of the column assembly, including the column itself, and the environment during sterilization, no net change or a minimal net change in the amount of moisture in the column assembly may generally be desirable. Condensation may occur as the environment about the column assembly cools to room temperature and/or returns to atmospheric pressure after sterilization. Such condensation may collect on surfaces of the column assembly, and particularly horizontal surfaces, such as the top 42 of the vented outlet cover 36 (or equivalently the filter 37 of vented outlet cover 36, absent cap 48 and top surface 42 as shown in FIG. 3). Additionally or alternatively, particular positions within a sterilization chamber may be more prone to the production of condensation, due to air flow within the chamber, or by virtue of being positioned under features from which condensate may drip, among other factors. The applicant has appreciated that while the flow of saturated steam both to and from the flow path of a column assembly may prove beneficial in the sterilization process, that the introduction of fluid in a liquid state, such as condensate, to the flow path during or after sterilization may not be desirable. Steam or fluid in vapor form may naturally flow to and from the flow path of a column assembly at equivalent rates and/or equivalent amounts, such that there is minimal or no net change in moisture content of a column assembly during sterilization. On the other hand, fluid that may enter the flow path of a column in liquid form, particularly after the sterilization process, may not find a way back to the external environment, resulting in a net gain of moisture content in a column assembly subsequent to sterilization. Embodiments of the vented outlet cover 36 may include one or more features to prevent the ingress of fluid in liquid form, while allowing, the ingress and egress of fluid in a vapor form (e.g., steam). In one illustrative embodiment shown in FIG. 3, the cover 36 includes a vent opening 44 that faces substantially downwardly, such that condensate, when driven by gravity, will not enter the vent opening 44, but instead be shed downward toward lower, external portions of the column assembly or away from the column assembly 10 altogether. It is to be appreciated that the term “downwardly” as used herein with respect to a column assembly refers to a direction in which the pull of gravity draws a mass in relation to a column assembly that is oriented for use. In the illustrated embodiment, the vent opening 44 has an annular shape that is defined between a body portion 46 of the cover and a removable cap 48 positioned on the body portion. The cap 48 includes a liquid impermeable top surface 42 that is positioned above the vent opening 44, when assembled, and prevents water from entering the vent from above. Components of the vented outlet cover represented by FIG. 3 may be acquired from Filtertek, Inc. of Hebron, Ill. It is to be appreciated that FIG. 3 shows one embodiment of a vented outlet cover, and that other embodiments are also possible. By way of example, the vented outlet cover may include a vent opening that is oriented to prevent water from entering the vent without the vent opening facing directly downward. According to some embodiments, the vent opening may be oriented to face substantially sideways and still prevent liquid from entering the vent opening, and the flow pathway of a column assembly. It is to be appreciated that the term “vent opening” or equivalently “vent”, as used herein, refers to a space or opening delimited by portions of the column assembly and through which steam may pass from an environment external to the column assembly, through the outlet port, and into the interior of a column assembly. Whether an upward facing vent opening, of a column assembly is exposed to liquid during sterilization may be a result of the column assembly being positioned in particular places within a sterilizer and/or by chance, as one of skill in the art is to appreciate. In this respect, it is possible that column assemblies with upwardly facing vent openings may be sterilized without the introduction of excess liquid. The introduction of liquid to such column assemblies, however, may prove to be unpredictable. In contrast, column assemblies having vent openings facing downwardly may prevent or reduce the introduction of liquid and/or excessive moisture into the column. According to some embodiments, the liquid content amongst a plurality of column assemblies, after a single sterilization cycle, may vary as measured in standard deviation by fewer than 0.015 grams, fewer than 0.010 grams, fewer than 0.005 grams, or by an even lesser amount. According to some embodiments, column assemblies with an average of 0.040 grams of liquid may vary in liquid content by 0.002 grams or fewer (standard deviation) after a single sterilization cycle. Similarly, the liquid content may vary by less than 40%, less than 30%, less than 20%, less than 10%, less than 5%, less than 4%, less than 3%, less than 2%, or even less than 1%, as measured in relative standard deviation, after a single sterilization cycle. These reductions in standard deviation and relative standard deviation may represent greater than a 25% reduction, a 50% reduction, a 75% reduction, or even greater than a 90% reduction as compared to column assemblies that lack vent openings that face downwardly (e.g., that have vent openings facing upwardly). The liquid content amongst the same plurality of column assemblies, after a second sterilization cycle, may vary as measured in standard deviation by fewer than 0.100 grams, fewer than 0.050 grams, fewer than 0.010 grams, or by an even lesser amount. In some embodiments, column assemblies with an average of 0.039 grams of liquid may vary in liquid content by 0.006 grams or fewer (standard deviation) after two sterilization cycles. Similarly, the liquid content may vary by less than 200%, less than 100%, less than 50%, less than 15%, less than 10%, less than 5%, less than 4%, less than 3%, less than 2%, or even less than 1%, as measured in relative standard deviation, after two sterilization cycles. These reductions in standard deviation and relative standard deviation may represent greater than a 25% reduction, a 50% reduction, a 75% reduction, or even greater than a 90% reduction as compared to column assemblies that lack vent openings that face downwardly (e.g., that have vent openings facing upwardly). The cap 48 of the vented outlet cover shown in FIG. 3 is configured to be removable from the body portion 46 of the vented outlet cover. As shown, the cap 48 includes tabs 35 that mate with corresponding features of the body portion 46 to hold the cap in place. Removable caps may be configured to mate to other portions of the vented outlet cover in other ways, such as with threaded connections, press fit connections, and the like, according to some embodiments. According to other embodiments, the vented outlet cover may lack a removable cap while still having a vent opening that faces substantially downward. The outlet port, according to some embodiments, may additionally or alternatively be configured to prevent the ingress of gravity-driven liquid, such as condensate, when a column assembly is oriented with a column positioned lower than the outlet port for sterilization, shipment, and/or use. By way of example, according to some embodiments, the outlet port itself may act as a vent opening and face substantially downwardly, such that gravity-driven liquid may not enter the vent opening from above. Such embodiments may be sterilized without a vented outlet cover assembled to the column assembly, and may additionally be shipped for use without a vented outlet cover. The vented outlet cover 36 may connect to the outlet port 30 in different manners. In the embodiment of FIG. 1, the outlet port 30 includes a needle-like structure, and the vented outlet cover 36 includes a pierceable membrane 50 (as shown in FIG. 3) that may receive the needle-like structure to provide a seal therebetween and to retain the outlet cover in place. Other types of connections, however, are also possible, including screw type connections and/or press type fit connections, to name a few. Filters may be incorporated into the flow path of a column assembly, according to some embodiments. The embodiment of FIG. 1 includes a filter 34 assembly positioned in the outlet line 32 to prevent the egress of particulates from the column and to maintain sterility of the radionuclide generator eluate. Similar filters may additionally or alternatively be positioned elsewhere in the flow path of a column assembly. For example, a filter 37 may be positioned within a vented outlet cover 36, as shown in FIG. 3, or even directly at the opening of the vent, according to some embodiments. The filter may include a glass matrix sandwiched between cellulose layers that hold the glass matrix in place, and may be configured to retain bacteria, rather than solely preventing bacteria passage. The column assembly 10 may be positioned in a package 40 that includes shielding to prevent the emission of radiation from the column assembly above a threshold value. By way of example, FIG. 4 shows the column assembly 10 of FIG. 1 assembled into a package 40 that has a lead shield base 54 or shield of other suitable material, such as tungsten or depleted uranium, held in position by a spacer 56. The package receives the column assembly with a column shield 58 positioned around the column 12 and a shield plug 60 positioned about portions of the inlet and outlet lines of the flow path. As may be appreciated, the thickest and thus greatest amount of shielding may typically exist around the column 12, where radionuclide is expected to reside. The inlet and outlet lines 18, 32 are also shielded, but to a lesser degree. The package 40 additionally includes a charge well 62 about the inlet port 14 and the vent port 26 where an eluant bottle may be received when daughter radionuclide are to be eluted. The package may also include a collection well 64 about the outlet port 30 that may be accessed by a shielded, evacuated vial or other container when radionuclide are retrieved from the column assembly 10, as discussed in greater detail herein. A dust cover 66 may be removably positioned over the charge well 62 and collection well 64, and the package may include a handle 68, as shown in FIG. 4. Embodiments of column assemblies may be configured to prevent radiation emission from exceeding different threshold levels, according to varying criteria. By way of non-limiting example, according to some embodiments, a common threshold level may be defined for column assemblies, regardless of a charge level, as measured in Curies, of a radionuclide generator. According to one embodiment, a threshold limit of 200 mR/hr may be set as a threshold limit, as measured outside of a square corrugated carton having side edges of about 14″ in length and that encloses a column assembly positioned inside of a shielded package. Other values of threshold limits may alternatively be set, such as at lower threshold limits as the embodiments described herein are not limited to any one threshold value. According to other embodiments, threshold limits may depend on the degree to which a column assembly is charged with parent radionuclide. Some examples of threshold levels associated with different charge levels, are shown below in Table 1. TABLE 1Examples of Threshold LimitsCharge Level (mCi)Threshold Limit (mR/hr)1000272000412500463000364000464500505000546000637500761000098125001211500014018000159 To retrieve daughter radionuclide from the generator, the dust cover 66 is first removed, and then the inlet port plug 22 is removed from the inlet port 14 and vent port 26. The vented outlet cover 36 is also removed from the outlet port 30. A bottle (not shown) including eluant, such as saline, is then placed in fluid communication with the inlet port 14 and vent port 26. As shown, the vent port 26 and inlet port 14 may comprise needles that puncture and then seal against a diaphragm of the bottle, although other connections are also possible as embodiments are not limited to that which is illustrated in the figures. A shielded, evacuated collection vial (not shown), having a connection similar to that of the eluant bottle, is then connected to the outlet port 30. The negative pressure of the evacuated vial draws eluant from the eluant bottle and through the flow pathway, including the column, to elute daughter radionuclide for delivery through the outlet port and to the shielded, evacuated vial. The vent allows air to enter the eluant bottle through the vent port to prevent negative pressure in the eluant bottle that might otherwise impede the flow of eluant through the flow pathway. After having eluted daughter radionuclide from the column, the shielded, evacuated collection vial is removed from the outlet port of the generator, and a vial containing a preservative (not shown), having a connection similar to that of the eluant bottle and collection vial is inserted onto the outlet port. The radionuclide generator may then be stored until radionuclide is again to be eluted. The foregoing written specification is considered to be sufficient to enable one skilled in the art to practice the invention. The present invention is not to be limited in scope by examples provided, since the examples are intended as a single illustration of one aspect of the invention and other functionally equivalent embodiments are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the invention. The advantages and objects of the invention are not necessarily encompassed by each embodiment of the invention. The present invention is further illustrated by the following Examples, which in no way should be construed as further limiting. Production of column assemblies configured as shown in FIG. 1, but with a vented outlet cover having a vent that opens upwardly rather than downwardly (e.g., a column assembly like that of FIG. 1 but with the cap 48 removed), was monitored to identify column assemblies that exceeded an upper threshold radiation limit, as may be associated with a parent radionuclide present in an outlet or inlet line. Radionuclide was eluted from the column assemblies that exceeded the upper threshold limit. Elution efficiency (Tc-99m yield) was then measured for these column assemblies. For some of the column assemblies, residual moisture levels were tested prior to measuring elution efficiency, while for others, elution efficiency was measured, without testing residual moisture levels. The elution efficiency results for all column assemblies are shown in FIG. 5. The elution efficiency is the ratio of the actual yield of daughter radionuclide to the expected yield of daughter radionuclide, corrected for the elapsed time between elutions. Typically, the Tc-99m elution efficiency is 85%-95%. The Tc-99m yield for the column assemblies that exceeded a threshold limit was impacted for approximately 80% of the column assemblies that were tested for elution efficiency, with 58% of the column assemblies tested exhibiting less than 10% elution efficiency. For comparison, five non-high dose column assemblies (#1815-181B) are also shown in FIG. 5, and have elution efficiency values that exceed 85%. The results of this example suggest a correlation between exceeding upper threshold radiation limits and exhibiting elution efficiency less than 85%. Production of column assemblies configured as shown in FIG. 1, but with a vented outlet cover having a vent that opens upwardly rather than downwardly (e.g., a column assembly like that of FIG. 1, but with the cap 48 removed), was monitored to identify column assemblies that exceeded an upper threshold radiation limit, as may be associated with a parent radionuclide present in an outlet or inlet line. Column assemblies that exceeded the upper threshold limit were checked for residual moisture, as were column assemblies that did not exceed the upper threshold limit. Residual moisture was measured using an evacuated vial connected to the outlet port to recover moisture from the fluid path between the inlet port and outlet port, including the column. The results, shown in FIGS. 6a and 6b, show that column assemblies found to exceed the upper threshold limit consistently exhibited moisture levels at or in excess of 0.5 grams, while column assemblies that did not exceed the upper limit exhibited moisture levels typically less than 0.05 grams. These results suggest that increased residual moisture in the column assembly may promote the movement of radionuclide to to less shielded areas of a column assembly, including the outlet line and/or inlet line, which may result in a column assembly exceeding an upper threshold limit for radiation. Furthermore, excess moisture may reduce elution efficiency (Tc-99m yield) as discussed in Example 1. Positions were identified within a steam sterilizer where column assemblies having vents oriented upwardly were previously found to have relatively wide range of residual moisture levels following sterilization. Column assemblies configured as shown in FIG. 1, but with a vented outlet cover having a vent that opens upwardly rather than downwardly (e.g., a column assembly like that of FIG. 1, but with the cap 48 removed), were charged with eluant lacking radionuclide. Column assemblies were charged with different amounts of eluant so as to represent different size (i.e., Mo-99 activity levels) of radionuclide generators that are typically produced. The column assemblies were weighed, and placed in the identified positions within the sterilizer for steam sterilization. The column assemblies were subjected to steam sterilization, and then again weighed after sterilization. A change in column assembly weight was calculated. Results of this test are shown in FIG. 7. The test was then repeated with column assemblies configured as shown in FIG. 1, including a vented outlet cover with a vent that opens downwardly. The results of this test are shown in FIG. 8. The mean recovered liquid from the column assemblies having vents that open downwardly was 0.040 grams, a 25% reduction from the 0.053 grams of the column assemblies having vents that open upwardly. Additionally, the standard deviation of liquid recovered from column assemblies having vents that open downwardly was 0.002 grams, as opposed to 0.024 grams for column assemblies having vents that open upwardly. Similarly, the relative standard deviation of liquid recovered from column assemblies having vents that open downwardly was 5.0%, as opposed to 45.3% for column assemblies having vents that open upwardly, a reduction of 90.0%. The procedures described above with respect to Example 3 were repeated, except that column assemblies were subjected to two complete steam sterilizations, as may occur in the production of radionuclide generators when a steam sterilization is interrupted, such as due to a power outage, and may need to be repeated. The results for column assemblies configured as shown in FIG. 1, but with a vented outlet cover having a vent that opens upwardly rather than downwardly, are shown in FIG. 9. The results for column assemblies configured as shown in FIG. 1, including a vented outlet cover with a vent that opens downwardly, are shown in FIG. 10. The mean recovered liquid from the column assemblies having vents that open downwardly was 0.039 grams, a 64% reduction from the 0.108 grams of the column assemblies having vents that open upwardly. Additionally, the standard deviation of liquid recovered from column assemblies having vents that open downwardly was 0.006 grams, as opposed to 0.231 grams for column assemblies having vents that open upwardly. Similarly, the relative standard deviation of liquid recovered from column assemblies having vents that open downwardly was 15.4%, as opposed to 214.0% for column assemblies having vents that open upwardly, a reduction of 92.8%. This Example suggests that a vented outlet cover with a vent that opens downwardly may prevent the ingress of excess liquid, even after multiple steam sterilizations. Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only. |
|
summary | ||
061047732 | abstract | A fuel rod for a nuclear reactor includes a metal cladding tube being filled with nuclear fuel and having ends, an outer surface, and a longitudinal axis. A metal seal plug is welded to one of the ends of the cladding tube at a transition point, defining an annular bead disposed on the outer surface of the cladding tube at the transition point. The annular bead has a cylindrical outer jacket surface extending substantially parallel to the longitudinal axis of the cladding tube. The annular bead has material being formed of the metal of the cladding tube and the metal of the seal plug. A welding apparatus for producing the fuel rod includes an electrode having a through bore formed therein for receiving one end of a cladding tube. A counter electrode is displaceable relative to the electrode for holding a seal plug to be welded to the one end of the cladding tube. The electrode has a cylindrical step formed therein at an end of the through bore facing toward the counter electrode. The cylindrical step has a diameter being greater than the diameter of the through bore. |
summary | ||
description | Embodiments of the invention relate generally to a manufacturing method, which is used to manufacture high melting point metal based objects. Here, the “high melting point metal” related to a kind of metal whose melting point is higher than 2500 degrees Celsius, such as molybdenum, tungsten, tantalum, or their alloys. Three-dimensional (3D) objects such as collimators used in x-ray imaging devices can be manufactured by using laser rapid manufacturing technology. One laser rapid manufacturing approach uses a laser beam to scan across and selectively sinter/melt metal powder to build up a prototype layer-by-layer from a predetermined model of the 3D object. Laser sintering/melting is a process in which the temperature of a powdered material is raised to its melting/softening point by thermal heating with a laser beam, thereby causing the particles of the powder to fuse together in the heated region. However, if the melting point of the powdered material is very high, such as tungsten (about 3410 degrees Celsius), it may not melt the powdered material completely through the normal laser. To solve this problem, one conventional method may use a high power laser to manufacture the 3D objects. But, the high power laser will require significant energy input during the manufacturing process which may increase the costs. Another conventional method may use low melting point binders, for example including nonmetallic binders such as nylon and silicate and metallic binders such as iron and nickel, to add into the high melting point metal or alloys to improve the forming capability for manufacturing. For example, nickel is used as a binder for tungsten to manufacture collimators through laser cladding. However, when the nickel content in the powder mixture is low (for example, lower than 50 vol %), the powder mixture also has a poor forming capability. When the nickel content in the powder mixture is high (for example, higher than 50 vol %) to ensure forming capability for manufacturing by laser cladding, the collimator may be deficient in its absorbing capability. For these and other reasons, there is a need for manufacturing 3D objects which are made of high melting point metal without binders or only with low proportion of binders. In accordance with an embodiment of the invention, a method for manufacturing a high melting point metal based object is provided. The method includes: providing pure high melting point metal based powder; fabricating a green object from the powder, by way of a laser sintering technique; providing infiltration treatment to the green object; and providing heating pressure treatment to the green object. The temperature to the green object is controlled to the re-sintering point of the green object. In accordance with another embodiment of the invention, a method for manufacturing a high melting point metal based object is provided. The method includes: providing powder mixture comprising high melting point metal and balanced with low melting point metal binder; fabricating a green object from the powder mixture, by way of a laser sintering technique; and providing heating pressure treatment to the green object. The high melting point metal is greater than 50 vol %. The temperature to the green object is controlled to the re-sintering point of the green object. Embodiments of the invention relate to a method for manufacturing a high melting point metal based object. The method includes: providing pure high melting point metal based powder; fabricating a green object from the powder, by way of a laser sintering technique; providing infiltration treatment to the green object; and providing heating pressure treatment to the green object. The temperature to the green object is controlled to the re-sintering point of the green object. Embodiments of the present disclosure will be described with reference to the accompanying drawings. In the subsequent description, well-known functions or constructions are not described in detail to avoid obscuring the disclosure in unnecessary detail. Furthermore, the term “high melting metal based objects” refers to a type of objects which is made of high melting metal material, for example the object may be made of pure tungsten, or is made of high melting metal material balanced with binders and the high melting point metal is greater than 50 vol %. For example the object may be made of tungsten and balanced with nickel. The term “pure” refers to a type of high melting metal material with less than 1% impurity, for example 99.0% tungsten; in an embodiment, the level of impurity is less than or equal to 0.1%, for example, 99.9% tungsten. Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” is not to be limited to the precise value specified. In certain embodiments, the term “about” means plus or minus ten percent (10%) of a value. For example, “about 100” would refer to any number between 90 and 110. Additionally, when using an expression of “about a first value—a second value,” the about is intended to modify both values. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value or values. Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, more particularly from 20 to 80, more particularly from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items, and terms such as “front”, “back”, “bottom”, and/or “top”, unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation. Moreover, the terms “coupled” and “connected” are not intended to distinguish between a direct or indirect coupling/connection between two components. Rather, such components may be directly or indirectly coupled/connected unless otherwise indicated. Referring to FIG. 1, an exemplary laser rapid manufacturing device 10 for rapid manufacturing objects such as 3D objects is shown. As an example, the laser rapid manufacturing device 10 is a selective laser sintering/melting device. The laser rapid manufacturing device 10 mainly includes a fabrication bed 12, a control unit 14, and a laser scanning unit 16. Similar configurations may be used. The fabrication bed 12 may include a powder delivery unit 122 and a fabrication unit 124. The powder delivery system 122 may include a powder delivery platform 1222, powder 1224 located on the powder delivery platform 1222, and a roller 1226 used to push the powder 1224 into the fabrication unit 124. The fabrication unit 124 may include a fabrication platform 1242 used to receive the power 1224 delivered by the powder delivery unit 122. The laser scanning unit 16 may include a laser 162 and a scanner mirror 164. The laser 162 is used to generate a laser beam 166, and then the laser beam 166 is deflected by the scanner mirror 164 to selective laser sinter/melt the powder 1224 which is located on the fabrication platform 1242 layer by layer to form a green 3D object 1244 according to the control commands from the control unit 14. The term “green” refers to one or more intermediate states of the object 1244, prior to its completed state as will be described hereafter. Referring to FIG. 2, after the green object 1244 is formed by the laser rapid manufacturing device 10, the green object 1244 is further positioned in a heating pressure device such as an oven 20. The oven 20 may then be used to further treat the green object 1244, to improve its mechanical properties. In one embodiment, the oven 20 may include an oven case 22, a temperature controller 24, and a pressure controller 26. The oven case 22 is used to contain the green object 1244 to be treated. The temperature controller 24 is used to control temperature in the oven case 22. The pressure controller 26 is used to control pressure in the oven case 22. After the heating pressure treatment by the oven 20, a completed object 1244 is finished according to needs. Referring to FIG. 3 together with FIGS. 1 and 2, a flowchart 30 of manufacturing the 3D object 1244 is shown. The manufacturing process typically includes the following steps. Step (31): applying a thin layer of the powder 1224 on the fabrication platform 1242. As shown in FIG. 1, the control unit 14 controls the powder delivery platform 1222 move up a predetermined distance along the shown arrow direction according to control commands from the control unit 14. And then, the control unit 14 controls the roller 1226 to push the powder 1224 onto the fabrication platform 1242 of the fabrication unit 124. The thickness of thin layer may be controlled from 2060 microns in one embodiment. Step (32): scanning the layer by the laser beam 166 to selective sinter/melt the layer of the powder 1224. As shown, the control unit 14 controls the laser scanning unit 16 to scan across and selectively sinter/melt the powder 1224 on the fabrication platform 1242 to build up a corresponding layer of a prototype from a predetermined model of the 3D object 1244. The scanning speed may be controlled from about 100 mm/s to about 500 mm/s. The laser power of the laser beam 166 may be controlled from 50-400 W. The predetermined model is prestored in a memory of the control unit 14. Step (33): lowering the fabrication platform 1242 for a predetermined distance. As shown, the control unit 14 controls the fabrication platform 1242 in moving down a predetermined distance along the shown arrow direction according to control commands from the control unit 14. Step (34): determining whether the green object 1244 is finished/completed. In certain embodiments, the process continues to step (35). In other embodiments, the process may be repeated, with step (31) until the green object 1244 is finished. The control unit 14 determines whether all of layers of the powder 1224 are applied according to predetermined manufacturing program stored in the control unit 14 in advance. In certain embodiments, the above manufacturing processes of the green object 1244 may be subjected to a laser sintering process. In still other embodiments, the manufacturing processes of the green object 1244 may be subjected to other suitable laser sintering processes. Step (36): providing heating pressure treatment to the green object 1244 under a predetermined condition. These above steps are also illustrated in FIG. 5. Referring to FIG. 4, after the green object 1244 is formed by the laser rapid manufacturing device 10, the green object 1244 may be further positioned in an infiltration/penetration device 40. The infiltration device 40 may be used to further treat the green object 1244, to improve its mechanical properties, and then the green object 1244 is treated by the oven 20 as described above. In one embodiment, the infiltration device 40 may include a container 42 used to contain infiltration solution 44, such as Cu solution or Ni solution and the Cu or Ni is completely dissolved. During the infiltration process, illustrated as step (35) in FIG. 5, the green object 1244 is positioned in the container 42, and the infiltration solution 44 is added into the container 42 until it excesses the highest point of the green object 1244. After the infiltration treatment, the green object 1244 is returned to the oven 22 for further heating pressure treatment through the step (36). After the infiltration treatment and heating pressure treatment, a completed object 1244 may be finished according to needs. The FIG. 4 illustrates the infiltration device 40. In other embodiments, other control devices may be used, including but not limited to vacuum-pressureless control. In general, the high melting point metal balanced with low melting point metal binder is subjected to the method illustrated in FIG. 3 without the infiltration treatment step (35). A pure high melting point metal is often used by the method of FIG. 5 with the infiltration treatment step (35). In one embodiment, the manufacturing process may be used to fabricate a collimator used in a medical imaging device. The situation when recording an x-ray image of a patient 3 in x-ray diagnosis is represented schematically in FIG. 6. The patient 3 lies between the tube focus 1 of an x-ray tube, which may be regarded as an approximately point x-ray source, and a detector surface 7. The x-rays 2 emitted from the focus 1 of the x-ray source propagate in a straight line in the direction of the x-ray detector 7, and in doing so pass through the patient 3. The primary beams 2a striking the detector surface 7, which pass through the patient 3 on a straight line starting from the x-ray focus 1, cause, on the detector surface 7, a positionally resolved attenuation value distribution for the patient 3. Some of the x-ray beams 2 emitted from the x-ray focus 1 are scattered in the patient 3. The scattered beams 2b created in this case do not contribute to the desired image information and, when they strike the detector 7, they significantly impair the signal-to-noise ratio. In order to improve the image quality, a collimator (or collimator array, or 2D collimator) 4 is therefore arranged in front of the detector 7. With reference to FIGS. 6 and 7, the collimator 4 includes transmission channels 5 and absorbing regions 6 forming a grid arrangement. The transmission channels 5 are aligned in the direction of the tube focus 1, so that they allow the incident primary radiation 2a on a straight-line path to strike the detector surface 7. Beams not incident in this direction, in particular the scattered beams 2b, are blocked or significantly attenuated by the absorbing regions 6. Collimators usually need to be made from high melting point and high density metals or alloys such as molybdenum, tungsten, tantalum, lead or their alloys, which have a high absorption capacity for X-ray and gamma radiation. Moreover, usually there are specific geometry requirements for collimators. For example, the collimator walls may be required to have very small thicknesses. With such material and geometric requirements, it is very difficult to manufacture collimators by conventional laser sintering process. For example, the green object 1244 fabricated by the steps (31) to (34) may not satisfy the requirement of the high melting point metal based objects, like the collimators 4. For achieving a high melting point metal based object, having the geometric requirements needed, the above heating pressure treatment process, namely the step (36), may be used to further treat the green object 1244. In addition, quality may be further improved before the heating pressure treatment process, by using an infiltration treatment process. For example, a collimator may be made by the method shown in FIG. 3 and FIG. 5 from a metal powder that may include pure tungsten (W) or include tungsten balanced with nickel (Ni). In the tungsten and nickel mixture, the tungsten functions as a radiation-absorbing metal and the nickel functions as a binder, and the proportion of the tungsten is greater than 50 vol % to ensure radiation absorbing ability of the collimator. In other embodiments, other high melting point metals, such as molybdenum, tantalum, or their alloys may be used in place of tungsten, and other low melting point metal binders, such as Ti, Cu, Pb, Fe, may be used in place of nickel. As illustrated in FIG. 8, in an embodiment where the metal powder is provided in a form of W—Ni powder mixture, the nickel powder, after absorbing the laser energy, can be completely melted as a binding phase at least partially surrounding the un-melted/partially melted tungsten powder due to the melting point of the tungsten powder is higher than temperature of the laser melting pool. The tungsten powder adjacent to the melted nickel is partially dissolved into the melted nickel to form W—Ni compound. Furthermore, the tungsten particles are not arranged uniformly in the W—Ni compound because the laser energy is not uniform and thus the flow dynamic in the laser melting pool is uneven. However, after the heating pressure treatment by the step (36) mentioned above in FIG. 3, the green object is reheated to the re-sintering, point, and pressured to reorganize the element distribution in the laser printed part to make sure the tungsten particle distribution is uniform in the W—Ni compound. Furthermore, the heating pressure treatment process also enhances the mechanical strength and increases the density to the completed object. In an embodiment, the green object is a collimator; said collimator is made of tungsten and balanced with nickel, the thickness of the collimator is about 0.1-0.2 mm, and the tungsten and nickel mixture may have various particle sizes ranging from about 5-50 microns. Said collimator (green object) may be treated by a heating pressure process where temperature is controlled between 1000-1300 degrees Celsius and pressure is controlled above 100 MPa, for about 2-4 hours. In other embodiments, the manufacturing process also can fabricate other objects which at least have a thin part which ranging from about between 0.1-0.5 mm. In other embodiments, the metal powder may be provided in the form of tungsten powder coated with nickel, or other forms. As illustrated in FIG. 9, in an embodiment where the metal powder is provided in a form of pure tungsten powder, after absorbing the laser energy, the pure tungsten powder cannot be completely melted because the melting point is very high. Therefore, the tungsten particles cannot completely dissolve together which results in a compromising of the mechanical strength of the melted tungsten structure. However, after the infiltration treatment, such as that shown instep (35), and the heating pressure treatment by the step (36) mentioned above in FIG. 5, the first green object at the step (35) is infiltrated by the metal solution 44, and then the second green object at the step (36) is reheated to the re-sintering point Additionally, with the application of pressure, the tungsten particles may be dissolved together with the metal from the metal solution 44. Thus, the infiltration treatment and the heating pressure treatment processes enhance the mechanical strength, and increases density of the completed object. Further, by using the heating pressure treatment process and the infiltration treatment process, the laser power in the laser sintering process can be reduced. This may reduce cost. In an embodiment, the green object is a collimator; said collimator is made of pure tungsten, the thickness of the collimator is about between 0.1-0.2 mm, and the tungsten may have various particle sizes ranging from about 5-50 microns. Said collimator (green object) may be treated by a heating pressure process where temperature is controlled between 2300-3000 degrees Celsius and pressure is controlled above 100 MPa, for about 2-4 hours. “Particle size” as used herein, equals the diameter of the sphere that has the same volume as a given particle. In other embodiments, the manufacturing process also can fabricate other objects which at least have a thin part which ranging from about between 0.1-0.5 mm. After finishing the collimator object, post processing may be applied to the collimator object. The applicable post processing may include, but is not limited to sandblasting, mechanical polishing, abrasive flowing machining, magnetic polishing, electric chemical machining and chemical etching. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments flailing within the scope of the appended claims. It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. |
|
claims | 1. A high voltage insulating radiation enclosure comprising:a first truncated cone section and a second truncated cone section;the two truncated cone sections secured together at their respective bases by an overlap joint;an interior space defined by the two truncated cones sections;the first and second truncated cone sections having walls, the walls made of a material comprising:a) a polymer matrix andb) barium sulfate within the polymer matrix in an approximate amount of at least 10% by volume;a first emission port passing through at least one wall;a second electrical port passing through at least one walls. 2. The high voltage insulating radiation enclosure of claim 1, further comprising an X-ray tube disposed within the hollow body. 3. The high voltage insulating radiation enclosure of claim 1, further comprising at least one oil port passing through the walls. 4. The high voltage insulating radiation enclosure of claim 1, wherein the polymer matrix comprises at least one member selected from the following group: epoxy, polyester, polyurethane, silicone rubber, bismaleimides, polyimides, vinylesters, urethane hybrids, polyurea elastomer, phenolics, cyanates, cellulose, flouro-polymer, ethylene inter-polymer alloy elastomer, ethylene vinyl acetate, nylon, polyetherimide, polyester elastomer, polyester sulfone, polyphenyl amide, polypropylene, polyvinylidene flouride, acrylic, homopolymers, acetates, copolymers, acrlonitrile-butadiene-stryene, flouropolymers, ionimers, polyamides, polyamide-imides, polyacrylates, polyether ketones, polyaryl-sulfones, polybenzimidazoles, polycarbonates, polybutylene, terephthalates, polyether sulfones, thermoplastic polyimides, thermoplastic polyurethanes, polyphenylene sulfides, polyethylene, polypropylene, polysulfones, polyvinylchlorides, stryrene acrylonitriles, polystyrenes, polyphenylene, ether blends, styrene maleic anhydrides, allyls, aminos, polyphenylene oxide, and combinations thereof. 5. The high voltage insulating radiation enclosure of claim 1, wherein the polymer matrix comprises epoxy resin is an approximate amount of 50% to 70% by volume. 6. The high voltage insulating radiation enclosure of claim 1, further comprising:c) a third material. 7. The high voltage insulating radiation enclosure of claim 6, wherein the third material comprises at least one member selected from the following group: electrically insulating materials, binders, high density materials and combinations thereof. 8. The high voltage insulating radiation enclosure of claim 6, wherein the third material comprises at least one member selected from the following group: tungsten, lead, platinum, gold, silver, tantalum, calcium carbonate, hydrated alumina, tabular alumina, silica, glass beads, glass fibers, magnesium oxide/sulfate, wollastonite, stainless steel fibers, copper, carbonyl iron, iron, molybdenum, nickel and combinations thereof. 9. An electrical insulator for an ion source, the insulator comprising:a generally annular body having a diameter of at least 6 inches;the body having at least one vacuum sealing surface dimensioned and configured to provide a tight seal;at least one alignment pin projecting from the vacuum sealing surface of the insulator;at least one metal insert secured to the body;the body made of a material comprising:a. a polymer matrix andb. barium sulfate within the polymer matrix in an approximate amount of at least 35% by volume. 10. The electrical insulator of claim 9, further comprising at least one element selected from alignment pins projecting from the vacuum sealing surface of the insulator, metal inserts secured to the body, and combinations thereof. 11. The electrical insulator of claim 9, further comprising a third material selected from the group consisting of electrically insulating materials, binders, high density materials, and combinations thereof. 12. The electrical insulator of claim 11, wherein the third material comprises at least one member selected from the group of tungsten, lead, platinum, gold, silver, tantalum, calcium carbonate, hydrated alumina, tabular alumina, silica, glass beads, glass fibers, magnesium oxide/sulfate, wollastonite, stainless steel fibers, copper, carbonyl iron, iron, molybdenum, nickel and combinations thereof. 13. The electrical insulator of claim 9, wherein the polymer matrix comprises at least one member selected from the following group: epoxy, polyester, polyurethane, silicone rubber, bismaleimides, polyimides, vinylesters, urethane hybrids, polyurea elastomer, phenolics, cyanates, cellulose, flouro-polymer, ethylene inter-polymer alloy elastomer, ethylene vinyl acetate, nylon, polyetherimide, polyester elastomer, polyester sulfone, polyphenyl amide, polypropylene, polyvinylidene flouride, acrylic, homopolymers, acetates, copolymers, acrylonitrile-butadiene-styrene, flouropolymers, ionimers, polyamides, polyamide-imides, polyacrylates, polyether ketones, polyaryl-sulfones, polybenzimidazoles, polycarbonates, polybutylene, terephthalates, polyether sulfones, thermoplastic polyimides, thermoplastic polyurethanes, polyphenylene sulfides, polyethylene, polypropylene, polysulfones, polyvinylchlorides, stryrene acrylonitriles, polystyrenes, polyphenylene, ether blends, styrene maleic anhydrides, allyls, aminos, polyphenylene oxide, and combinations thereof. 14. The electrical insulator of claim 9, wherein the polymer matrix comprises epoxy resin in an approximate amount between about 50% and about 70% by volume. 15. A high voltage insulating radiation enclosure comprising:a first truncated cone section and a second truncated cone section;the two truncated cone sections secured together at their respective bases by an overlap joint;an interior space defined by the two truncated cone sections;the first and second truncated cone sections having walls, the walls made of a material comprising:a) a polymer matrix; andb) barium sulfate within the polymer matrix in an approximate amount of at least 10% by volume;a first emission port passing through at least one wall; anda second electrical port passing through at least one wall. 16. The high voltage insulating radiation enclosure of claim 15, further comprising an X-ray tube disposed within the hollow body. 17. The high voltage insulating radiation enclosure of claim 15, further comprising at least one oil port passing through at least one wall. 18. The high voltage insulating radiation enclosure of claim 15, wherein the polymer matrix comprises at least one member selected from the following group: epoxy, polyester, polyurethane, silicone rubber, bismaleimides, polyimides, vinylesters, urethane hybrids, polyurea elastomer, phenolics, cyanates, cellulose, flouro-polymer, ethylene inter-polymer alloy elastomer, ethylene vinyl acetate, nylon, polyetherimide, polyester elastomer, polyester sulfone, polyphenyl amide, polypropylene, polyvinylidene flouride, acrylic, homopolymers, acetates, copolymers, acrlonitrile-butadiene-styrene, flouropolymers, ionimers, polyamides, polyamide-imides, polyacrylates, polyether ketones, polyaryl-sulfones, polybenzimidazoles, polycarbonates, polybutylene, terephthalates, polyether sulfones, thermoplastic polyimides, thermoplastic polyurethanes, polyphenylene sulfides, polyethylene, polypropylene, polysulfones, polyvinylchlorides, stryrene acrylonitriles, polystyrenes, polyphenylene, ether blends, styrene maleic anhydrides, allyls, aminos, polyphenylene oxide, and combinations thereof. 19. The high voltage insulating radiation enclosure of claim 15, wherein the polymer matrix comprises epoxy resin is an approximate amount of 50% to 70% by volume. 20. The high voltage insulating radiation enclosure of claim 15, further comprising:c) a third material. 21. The high voltage insulating radiation enclosure of claim 20, wherein the third material comprises at least one member selected from the following group: electrically insulating materials, binders, high density materials and combinations thereof. 22. The high voltage insulating radiation enclosure of claim 20, wherein the third material comprises at least one member selected from the following group: tungsten, lead, platinum, gold, silver, tantalum, calcium carbonate, hydrated alumina, tabular alumina, silica, glass beads, glass fibers, magnesium oxide/sulfate, wollastonite, stainless steel fibers, copper, carbonyl iron, molybdenum, nickel and combinations thereof. |
|
042082064 | summary | This application relates in general to the manufacture of metal castings, and more particularly to a method for improving the quality of castings by pneumatically refining the melt prior to casting. Metal articles are generally divided into two product classifications depending on their method of manufacture, wrought products and cast products. Wrought products are made by first teeming molten metal into a mold, and then mechanically working or deforming the intermediate product by rolling, drawing, extruding or forging. In contrast, cast products are made without the second step. i.e., without the mechanical deformation of the solidified product. While cast products are generally heat treated, and may also be mechanically cleaned, machined or repaired subsequent to casting, they are not subject to plastic deformation. This difference between a wrought and a cast product, i.e., the presence of absence of mechanical deformation, is extremely important because it offers the manufacturer of wrought products opportunities to correct or eliminate various defects which may have occurred during solidification. For example, it is well known that while solidified ingots of rimmed steel have very good surface characteristics, they contain many small blow holes beneath the surface. Similarly, in most continously cast steel shapes, there is a center region containing shrinkage porosity. Nonetheless, these blow holes and regions of porosity are almost entirely eliminated during subsequent rolling, and the final wrought product contains virtually no evidence of the original porosity. Similarly, surface defects in ingots, slabs and billets are not a problem to the producer of wrought products, because these are intermediate products which undergo considerable mechanical reworking and plastic deformation prior to shipment. Furthermore, when surface defects occur, they can readily be removed by grinding or scarfing before further mechanical processing. In contrast, the surface quality of castings is very important because castings are a final product and any defect must be removed by costly and time consuming manual grinding, gauging or chipping. Then the cavity so caused must be rebuilt by welding or overlaying of metal. In addition, surface repair may diminish the dimensional accuracy and mechanical properties of the casting. It is evident, therefore, that since ingots, slabs and billets are intermediate products, certain surface and internal defects can be tolerated in them, while in castings such defects cannot, because castings are poured directly into their final shape. The metal founding industry has long been plagued with a number of difficult problems caused by unsatisfactory castings. These problems are due both to surface defects and to internal defects. While many surface defects can be remedied by the costly finishing operations mentioned above, internally defective castings frequently have to be scrapped, remelted and cast over. Some of the common surface flaws in casting include: hot tears, surface cracks, rough surface, and holes ranging in size from pinholes to gross blow holes. In general, the ultimate causes of these defects are not well understood. Consequently, melting and casting practices to produce satisfactory castings require a large amount of experience and empirical evaluation. Internal defects are due mainly to porosity and inclusions which adversely effect the mechanical properties of castings, i.e., its strength, ductility, toughness and impact resistance. The above-mentioned defects, as well as others such as embrittlement, age-hardening and the presence of fish-eyes or white spots, are believed to be related to the presence of uncontrolled amounts of oxygen, nitrogen, hydrogen, phosphorous and sulfur in the melt. Consequently, it has long been an objective of the foundry industry to produce sound castings with low or controlled levels of these five elements. In the production of stainless castings, where corrosion resistance is of paramount importance, it is often an additional objective to produce sound castings with low carbon levels. Casting defects are conventionally remedied during the so-called finishing operations. Most of these operations are highly labor intensive and consequently very costly. In addition, much of the finishing consists of grinding which causes dust that can be harmful to health. Some castings, however, cannot be repaired because the critical application for the part does not allow it. In such case, the defective casting must be scrapped. Consequently, the foundry art has long sought a method which would improve castings both in terms of their surface quality and physical properties. Various techniques have been used in the foundry art to refine melts prior to casting in order to improve the quality of the resultant castings. The final stage of melting often includes some form of purification or refining treatment intended to influence the microstructure and cleanliness of the casting. Such treatments usually involve the blowing of gases or the addition of certain reagents to the furnace or transfer ladle. These treatments may include decarburization, dephosphorization, deoxidation, desulfurization and degassing. Prior to the present invention, decarburization of molten steel for castings, was generally accomplished by blowing oxygen into the melt through a consumable lance inserted through an opening in the furnace. This technique of decarburization is, in the first place, dangerous to the operator because it exposes him to hot metal and sparks, and because the operator usually holds the lance manually, which is in itself hazardous. Secondly, this technique of decarburization is frequently inaccurate because all the oxygen does not always react with the bath. Hence, it is often necessary to reblow the molten steel because insufficient carbon was removed initially. Lastly, such prior art methods of decarburization tend to generate a great deal of fume and smoke which is hazardous to health and damaging to the environment. Because of the presence of oxygen is known to be detrimental to the properties of the castings, foundries generally deoxidize the molten metal prior to pouring. In addition, deoxidation is generally required to prevent the formation of blow holes during solidification. This is normally accomplished by the addition of well-known deoxidants such as silicon or aluminum, and also by the addition of special deoxidants, such as "Calcibar" and "Hypercal." The attainment of a well deoxidized melt prior to casting is essential for the production of sound, tough castings. Desulfurization of molten steel for castings, prior to this invention, has generally been accomplished by the formation of basic slags in the furnace, i.e., slags containing a high ratio of lime to silica or lime to alumina, and by subsequently mixing the slags with well deoxidized metal. Equilibrium between the slag and the metal causes the sulfur to be transferred from the metal to the slag. This process is very slow, often requiring several hours, particularly when very low (i.e., under 0.005%) sulfur is desired. Indeed, it is often necessary to remove the slag and to produce a new one. Sometimes this step has to be repeated several times in order to reach the desired low level of sulfur. This process is very laborious and time consuming, and unnecessarily exposes the furnace operators to molten metal and to unhealthy fumes. An alternative, and much more costly desulfurization technique is to add expensive sulfur scavenging elements, such as calcium, magnesium or the rare earth elements, to the furnace immediately prior to tapping or to the transfer ladle. The expense of this technique, as well as its non-reproducibility, militates against its general use. Known degassing treatments include vacuum melting, vacuum degassing, as well as degassing by bubbling scavenging gases, such as argon, through the melt. While argon degassing in the ladle, prior to casting, can improve the quality of castings by lowering the hydrogen and oxygen content of the melt, it does not remove all impurities or achieve low hydrogen levels in the limited time available. Because the time available for degassing is strictly limited by heat loss from the degassing vessel, it has been found that it is not possible to lower the dissolved gas content sufficiently for many applications. Furthermore, degassing by itself does not remove sulfur and may necessitate reheating the melt in order to obtain sufficient fluidity for casting. Prior to the present invention, therefore, the foundry art utilized the above-described techniques in an effort to produce defect-free castings. However, these prior art techniques are expensive, often inaccurate or non-reproducible, time-consuming, generally hazardous to the health of the operators, and by-and-large inadequate to the needs of the industry. Consequently, extensive post-solidification repair of castings is usually still required. In fact, in castings, for example, destined for nuclear applications, the cost of inspection and repair often exceeds the material value of the castings themselves. During the past twenty-five years, the manufacturers of wrought steel products have made large gains in upgrading their molten metal processing techniques through the adoption of one of several now well known refining processes such as the BOF, AOD, OBM or Q-BOP and LWS processes. U.S. Pat. Nos. illustrative of these processes, respectively, are: 2,800,631; 3,252,790; 3,706,549; 3,930,843 and 3,844,768. The production of wrought steels containing controlled levels of carbon, phosphorous, sulfur, oxygen, nitrogen and hydrogen is now readily and economically achievable through judicious selection of one, or a combination of more than one, of the above processes. In the foundry or cast metal industry, however, comparable advances have been absent. While the industry has, at various times, produced products with low or controlled levels of one or perhaps two of the above six elements, the manufacture of castings with low or controlled levels of all six elements has hitherto not been possible, and consequently, the value or advantages of being able to control all six elements have hitherto not been known. The pneumatic treatment of molten stainless steel for the production of wrought steel by the simultaneous injection of argon and oxygen into the melt, commonly referred to as the AOD process, has achieved wide commercial acceptance in stainless steel mills for the manufacture of wrought products. The basic AOD refining process is disclosed by Krivsky in U.S. Pat. No. 3,752,790. An improvement on Krivsky relating to the programmed blowing of the gases is disclosed in Nelson et al, U.S. Pat. No. 3,046,107. The use of nitrogen in combination with argon and oxygen to achieve predetermined nitrogen contents is disclosed in Saccomano et al in U.S. Pat. No. 3,754,894. A modification of the AOD process is also shown by Johnsson et al in U.S. Pat. No. 3,867,135 which utilizes steam or ammonia in combination with oxygen to refine molten metal. It is worthy of note that none of the above-mentioned pneumatic melt refining techniques have, prior to this invention, been used by the foundry art for the production of castings. OBJECTS It is an object of the present invention to improve the surface quality, internal quality and physical properties of castings. It is another object of this present invention to improve the method of producing castings by pneumatically refining the melt prior to casting. It is still another object of this invention to increase the yield of acceptable castings. SUMMARY It has now been discovered that by pneumatically refining the melt in a separate vessel prior to casting, castings of a quality superior to that heretofore obtainable can be produced. Such castings have unexpectedly superior surface quality and internal quality. The above, and other objects which will be apparent to those skilled in the art are achieved by the present invention which comprises: a process for producing metal castings having improved surface quality and internal quality by: melting selected charge materials in a furnace, teeming the melt into a mold, permitting the melt to solidify in the mold, and removing the casting from the mold, wherein the improvement comprises: (1) transferring the melt from the melting furnace into a refining vessel provided with at least one submerged tuyere, and (2) refining said melt by (a) injecting into the melt through said tuyere(s) an oxygen-containing gas containing up to 90% of a dilution gas, and (b) thereafter injecting a sparging gas into the melt through said tuyere(s). Preferably, the oxygen-containing gas stream is surrounded by an annular stream of protective fluid. The term "refining" as used in the present specification and claims is meant to include any one or more of the following effects: decarburization, dephosphorization, desulfurization, degassing, deoxidation, gaseous alloying, impurity oxidation, impurity volatilization, slag reduction and flotation and homogenization of non-metallic impurities. The present invention is applicable to refining of any iron, cobalt or nickle based alloy, and the term "metal" is used in that sense. The term "dilution gas" as used herein is intended to mean one or more gases that are added to the oxygen stream for the purpose of reducing the partial pressure of the carbon monoxide in the gas bubbles formed during decarburization of the melt, and/or for the purpose of altering the feed rate of oxygen to the melt without substantially altering the total injected gas flow rate. Suitable dilution gases include: argon, helium, hydrogen, nitrogen, carbon monoxide, carbon dioxide, steam and hydrocarbon gases, for example, methane, ethane, propane and natural gas. Argon is the most preferred dilution gas. The term "protective fluid" as used herein is meant to include one or more fluids which surround the oxygen containing gas and protect the tuyere and surrounding refractory lining from excessive wear. Suitable protective fluids include: argon, helium, nitrogen, hydrogen, carbon monoxide, carbon dioxide, hydrocarbon fluids (gas or liquid) and steam. Methane, ethane, propane or natural gas are suitable hydrocarbon gases. No. 2, diesel oil is a suitable hydrocarbon liquid. Argon is the most preferred protective fluid. The term "sparging gas" as used herein is intended to mean one or more gases which remove impurities from the melt by volatilization or transfer to the slag by entrapment or reaction with the slag. Suitable sparging gases include: argon, helium, nitrogen and steam. Argon is also the preferred sparging gas. Castings having improved surface quality are defined as castings which when compared to the prior art require reduced cleaning, grinding, chipping, welding or other repair. Such improved surface quality can be evidenced by a reduced level of defects determined during dye penetrant or magnaflux testing. Castings having improved internal quality are defined as castings which when compared to the prior art display one or more of the following characteristics: a lower level of inclusions, finer as-cast grain size, reduced internal porosity, reduced tendency for hydrogen flaking during machining, reduced evidence of defects when inspected by X-ray techniques or better physical properties such as toughness. |
description | Embodiments of the present invention relate to a passive containment cooling and filtered venting system of a nuclear power plant, and a nuclear power plant. An outline of a conventional passive containment cooling system of a nuclear power plant will be described with reference to FIGS. 11 to 14. FIG. 11 is a sectional elevational view showing an example of a configuration of the conventional passive containment cooling system. In FIG. 11, a core 1 is contained in a reactor pressure vessel 2. The reactor pressure vessel 2 is contained in a containment vessel 3. The containment vessel 3 has a cylindrical shape (see FIG. 12). The interior space in the containment vessel 3 is partitioned into a dry well 4, which contains the reactor pressure vessel 2, and a wet well 5. The dry well 4 and the wet well 5 each constitutes a part of the containment vessel 3. The wet well 5 forms a suppression pool 6 inside. A wet well gas phase 7 is formed above the suppression pool 6. The outer wall parts of the dry well 4 and the wet well 5 are integrated to constitute a cylindrical outer wall part of the containment vessel 3. The ceiling part of the dry well 4 is a flat plate, which will be referred to as a top slab 4a of the dry well 4. In the case of a boiling water reactor, the atmosphere in the containment vessel 3 is inerted by nitrogen and limited to a low oxygen concentration. In the case of the boiling water reactor, the containment vessel 3 is contained in a nuclear reactor building 100. In general, there are various types of containment vessels 3 depending on the materials. Examples include a steel containment vessel, a reinforced concrete containment vessel (RCCV), a pre-stressed concrete containment vessel (PCCV), and a steel concrete composite (SC composite) containment vessel (SCCV). In the cases of RCCV and PCCV, the inner surfaces are lined with a steel liner. FIG. 11 shows an example of an RCCV. As shown in FIG. 12, an RCCV has an outer wall part of cylindrical shape. The reactor pressure vessel 2 is supported by a cylindrical pedestal 61 via an RPV skirt 62 and an RPV support 63. The pedestal 61 may be made of steel, concrete, or a composite structure of both. In the dry well 4, the inside space of the pedestal 61, below the reactor pressure vessel 2 and surrounded by the cylindrical wall of the pedestal 61, is referred to as a pedestal cavity 61a. In the case of the RCCV of an ABWR, the cylindrical wall of the pedestal 61 forms a boundary wall between the wet well 5 and the dry well 4. The space is referred to as a lower dry well in particular. A containment vessel head 10 is arranged above the reactor pressure vessel 2. A water shield 11 is arranged over the containment vessel head 10. Main steam pipes 71 extend from the reactor pressure vessel 2 to outside the dry well 4. A safety relief valve (SRV) 72 is arranged on the main steam pipes 71. A discharge pipe 73 is arranged to be submerged in the suppression pool 6 so that the steam in the reactor pressure vessel 2 is released into the suppression pool 6 if the safety relief valve 72 is activated. The dry well 4 and the suppression pool 6 are connected by LOCA vent pipes 8. There are installed a plurality of, for example, ten LOCA vent pipes 8, whereas FIG. 11 shows only two of them (see FIG. 12). The LOCA vent pipes 8 have horizontal vent pipes 8a in the portions submerged in the pool water of the suppression pool 6. The horizontal vent pipes 8a open in the pool water. In the case of an RCCV, three horizontal vent pipes 8a are vertically arranged on each LOCA vent pipe 8. In the case of the RCCV the LOCA vent pipes 8 are installed through the cylindrical wall of the pedestal 61. In the case of the RCCV, the cylindrical wall of the pedestal 61 is thus also referred to as a vent wall. The vent wall is made of reinforced concrete with a thickness of approximately 1.7 m. The inner and outer surfaces are made of steel. The LOCA vent pipes 8 and the pedestal 61 constitute a part of the containment vessel 3. Vacuum breakers 9 are provided for the purpose of letting the gas in the wet well gas phase 7 flow back into the dry well 4. There are provided a plurality of, for example, eight vacuum breakers 9, whereas FIG. 11 shows only one of them. The vacuum breakers 9 may be formed on the wall surface of the wet well 5, on the ceiling of the wet well 5, and on the LOCA vent pipes 8. The vacuum breakers 9 are activated to open if the pressure in the wet well 5 exceeds that in the dry well 4 and the difference in pressure exceeds a set pressure difference. For example, the set pressure difference of the vacuum breakers 9 is approximately 2 psi (approximately 13.79 kPa). The vacuum breakers 9 constitute a part of the containment vessel 3. A cooling water pool 13 of a passive containment cooling system 12 is arranged outside the containment vessel 3. The cooling water pool 13 stores cooling water 14 inside. FIG. 11 shows an example of the cooling water pool 13 of a tank type, whereas the cooling water pool 13 may be of a pool type. In the case of the pool type, the cooling water pool 13 is covered with a lid from above. FIG. 11 shows an example where the cooling water pool 13 and the like are installed inside the nuclear reactor building 100. The cooling water pool 13 and the like may be installed in an adjacent auxiliary building or the like. An exhaust port 15 for releasing steam to the environment is extended from the gas phase above the water surface in the cooling water pool 13. An insect screen may be arranged on the outlet of the exhaust port 15. The cooling water pool 13 is usually located above the containment vessel 3. The cooling water pool 13 may be arranged beside the containment vessel 3. A heat exchanger 16 is installed in the cooling water pool 13 to be submerged at least in part in the cooling water 14. A plurality of the heat exchangers 16 may often be installed, although FIG. 11 shows only one heat exchanger 16. The heat exchanger 16 includes an inlet plenum 17, an outlet plenum 18, and heat exchanger tubes 19 (see FIG. 13). FIG. 11 shows an example in which only the heat exchanger tubes 19 are installed inside the cooling water pool 13, and the inlet plenum 17 and the outlet plenum 18 (FIG. 13) protrude out of the cooling water pool 13. However, the configuration is not limited to this example. For example, the entire heat exchanger 16, including the inlet plenum 17 and the outlet plenum 18, may be installed inside the cooling water pool 13. The inlet plenum 17 is connected with a gas supply pipe 20 for supplying the gas in the dry well 4. One end of the gas supply pipe 20 is connected to the dry well 4. The outlet plenum 18 is connected with a condensate return pipe 21 and a gas vent pipe 22. One end of the condensate return pipe 21 is connected to inside the containment vessel 3. FIG. 11 shows an example in which the condensate return pipe 21 is led into a LOCA vent pipe 8. However, the configuration is not limited to this example. For example, the condensate return pipe 21 may be led into the dry well 4 or into the suppression pool 6. The installation into the LOCA vent pipe 8 has a problem of increasing the pressure loss of the LOCA vent pipe 8 at the time of LOCA. The installation into the dry well 4 needs a PCCS drain tank installed in the dry well 4 for the sake of water sealing, and is thus not able to be employed unless there is room in the dry well 4. The installation into the suppression pool 6 increases the length of the condensate return pipe 21 outside the PCV, and thus has a problem that the possibility of leakage of radioactive materials increases. One end of the gas vent pipe 22 is led into the wet well 5 and installed to be submerged in the suppression pool 6. The gas vent pipe 22 is installed so that the submerging depth in the suppression pool 6 is smaller than the submerging depth of the topmost ends of the openings of the LOCA vent pipes 8 in the suppression pool 6. FIG. 13 is a sectional elevational view showing an example of the heat exchanger of the conventional passive containment cooling system. Referring to FIG. 13, the structure of the heat exchanger 16 of the conventional passive containment cooling system 12 will be described by using a horizontal heat exchanger as an example. In FIG. 13, the outlet plenum 18 is arranged below the inlet plenum 17. A large number of U-shaped heat exchanger tubes 19 are connected to a tube plate 23. The straight portions of the heat exchanger tubes 19 are installed horizontally. FIG. 13 shows only two of the heat exchanger tubes 19 in a simplified manner. The outside of the heat exchanger tubes 19 is filled with the cooling water 14 (see FIG. 11). The inlets of the heat exchanger tubes 19 are opened to the inlet plenum 17. The outlets of the heat exchanger tubes 19 are opened to the outlet plenum 18. The gas supply pipe 20 is connected to the inlet plenum 17, and supplies a mixed gas of nitrogen, oxygen, steam and the like in the dry well 4 to the inlet plenum 17. The mixed gas is led into the heat exchanger tubes 19. The steam condenses into condensate, which flows out of the outlets of the heat exchanger tubes 19 into the outlet plenum 18 and accumulates in the lower part of the outlet plenum 18. The condensate return pipe 21 is connected to the lower part of the outlet plenum 18. The condensate return pipe 21 returns the condensate in the outlet plenum 18 into the containment vessel 3 by gravity. The gas vent pipe 22 is connected to the upper part of the outlet plenum 18. Noncondensable gases that do not condense in the heat exchanger tubes 19, such as nitrogen and hydrogen, are discharged from the heat exchanger tubes 19 and accumulate in the upper part of the outlet plenum 18. The end of the gas vent pipe 22 is led to the suppression pool 6. The noncondensable gases in the outlet plenum 18 pass through the gas vent pipe 22, push down the pool water in the suppression pool 6, are vented into the pool water and then move to the wet well gas phase 7. Note that the shape of the heat exchanger tubes 19 is not limited to the U shape. There is a structure installing upright heat exchanger tubes 19 with vertical straight tube portions. The inlet plenum 17 is always located above the outlet plenum 18. In such a manner, the condensate condensed in the heat exchanger tubes 19 is led into the outlet plenum 18 by gravity. The advantages of the horizontal type are good seismic performance and effective utilization of the cooling water 14. On the contrary the advantage of the vertical type is high drainability of the condensate. Next will be described functions of the conventional passive containment cooling system 12 configured as such. If a loss-of-coolant accident (LOCA) with a break of a piping in the dry well 4 occurs, steam is generated in the reactor pressure vessel 2, which sharply increases the pressure in the dry well 4. The gas (mostly nitrogen and steam) in the dry well 4 passes through the gas supply pipe 20 of the passive containment cooling system 12 and is supplied to the heat exchanger 16. The noncondensable gases having accumulated in the outlet plenum 18 of the heat exchanger 16 passes through the gas vent pipe 22 and is discharged into the suppression pool 6. The discharge of the noncondensable gases is let by a pressure difference between the dry well 4 and the wet well 5. At the time of the LOCA, the pressure in the dry well 4 is higher than that in the wet well 5. The discharge of the noncondensable gases is thus performed smoothly. Consequently, the gas in the dry well 4 becomes mostly steam in some time. In such a state, the heat exchanger 16 can efficiently condense the steam in the dry well 4 and return (or circulate) the condensate into the containment vessel 3. Immediately after the occurrence of the LOCA, a large amount of steam generates from the coolant, and rapid venting of the gas in the dry well 4 to the wet well 5 is mostly performed through the LOCA vent pipes 8. The steam condenses in the suppression pool 6 while noncondensable nitrogen does not condense in the suppression pool 6 and moves to the wet well gas phase 7. By the rapid venting through the LOCA vent pipes 8, most of the nitrogen in the dry well 4 moves to the wet well 5, for example, in about one minute after the LOCA. Subsequently, the vent flowrate decreases. Since the submerging depth of the gas vent pipe 22 in the suppression pool 6 is set to be smaller than that of the LOCA vent pipes 8, the gas in the thy well 4 starts to be vented to the wet well 5 through the gas vent pipe 22 in some time after the LOCA. In such a manner, the vent flowrate subsides and the steam generated in accordance with the decay heat of the core fuel is released from the LOCA break into the dry well 4. It is designed that the steam is led through the gas supply pipe 20 into the heat exchanger 16 for cooling, but not through the LOCA vent pipes. As a result, because the decay heat of the core fuel is transferred to the outside cooling water 14, the increase of pressure in the containment vessel 3 due to heat up of the water in the suppression pool 6 can be prevented. The passive containment cooling system 12 is thus designed to be able to passively cool the containment vessel 3 without using external power at all. Next, in the case of a transient event such as a station blackout (hereinafter, may be referred to as “SBO”), the decay heat generated in the core is transferred to the suppression pool 6 by the reactor steam passing through the safety relief valve 72. As the reactor steam condenses in the suppression pool 6, the decay heat is transferred to the pool water and the temperature of the pool water increases gradually. After a lapse of certain time, the pool water is saturated and steam equivalent to the decay heat flows continuously into the wet well, gas phase 7 to pressurize the wet well gas phase 7. This activates the vacuum breakers 9, and the nitrogen and steam in the wet well gas phase 7 flow into the dry well 4. The dry well 4 is thereby pressurized, and the nitrogen and steam in the dry well 4 are led to the heat exchanger 16 of the passive containment cooling system 12 through the gas supply pipe 20, whereby the steam is condensed. Since the nitrogen, which is a noncondensable gas, simply remains in the heat exchanger 16, the passive containment cooling system 12 stops functioning. The reason is that although the gas vent pipe 22 is led from the heat exchanger 16 to the suppression pool 6, the pressure of the wet well gas phase 7 increases under the SW and so the noncondensable gas in the heat exchanger 16 is not able to be vented to the wet well gas phase region 7. To solve such a problem, Patent Document 1 discloses a method of providing an outer well 32 outside the dry well 4 and the wet well 5, and leading the gas vent pipe 22 into a water seal pool retained therein to release the noncondensable gas accumulated in the heat exchanger 16 into the outer well 32 (see FIG. 2 of Patent Document 1). The interior of the outer well 32 is inerted by nitrogen in consideration of the prevention of detonation even when hydrogen is vented. Patent Document 2 discloses a method of connecting the gas supply pipe 20 to the wet well gas phase 7 to directly lead the steam and nitrogen in the wet well gas phase 7 to the heat exchanger 16, and discharging noncondensable gases such as nitrogen accumulated in the heat exchanger into the dry well 4 by using an exhaust fan 24 arranged on the gas vent pipe 22 (see FIG. 2 of Patent Document 2). In either case, the gas supply pipe 20, the condensate return pipe 21, and the gas vent pipe 22 are installed outside the containment vessel 3. In preparation for a core meltdown in the event of a transient event such as a station blackout (SBO), ABWRs to be built in Europe and the U.S.A. have fusible valves 64 and lower dry well flooder pipes 65 inside the pedestal cavity 61a. The lower dry well flooder pipes 65 are extended from the LOCA vent pipes 8 through the wall of the pedestal 61 and connected to the fusible valves 64. The fusible valves 64 and the lower dry well flooder pipes 65 are installed on all the LOCA vent pipes 8. If the temperature of the lower dry well 61a reaches approximately 260 degrees Celsius, low melting point plug portions of the fusible valves 64 melt to open. At the time of a core meltdown accident, the corium melts the bottom of the reactor pressure vessel 2 through and falls into the pedestal cavity 61a. This increases the temperature in the pedestal cavity 61a abruptly, and the fusible valves 64 open and the cooling water in the LOCA vent pipes 8 flows into the pedestal cavity 61a through the lower dry well. flooder pipes 65 to flood and cool the corium. Other examples of the valves for pouring water on the fallen high-temperature corium with the same purpose as that of the fusible valves 64 include squib valves and spring valves. ESBWRs (Economic Simplified Boiling Water Reactors) use squib valves. EPRs (European Pressurized Reactors) use spring valves. A large amount of steam generated at that time flows into an upper dry well from openings 66 in the LOCA vent pipes 8, passes through the gas supply pipe 20, and is led to the heat exchanger 16 of the passive containment cooling system 12 for condensation. Meanwhile, the noncondensable gases accumulated in the heat exchanger 16 are vented into the wet well 5 through the gas vent pipe 22. In such a state, the pressure in the dry well 4 is higher than that in the wet well 5, so that the noncondensable gases are efficiently vented to the wet well gas phase 7. The condensate returns to a LOCA vent pipe 8 through the condensate return pipe 21, passes through the lower dry well flooder pipe 65, and is used to cool the corium again. In addition, the pool water in the LOCA vent pipes 8 is also supplied from the suppression pool 6 through the horizontal vent pipes 8a. The fusible valves 64 and the lower dry well flooder pipes 65 described above have had a problem; that is, if the pressure in the dry well 4 increases after the fusible valves 64 are opened, the high-temperature water pooled in the lower dry well 61a flows back into the suppression pool 6 to increase the temperature of the suppression pool water. Backflow prevention measures have been difficult to be implemented because the temperature of the portions of the lower dry well flooder pipes 65 in the lower dry well 61a become so high at the time of an accident that it is difficult to expect devices to function. The installation of devices inside the LOCA vent pipes 8 is also difficult since they interfere with the safety function of the vent pipes. Hence, the prevention measures were difficult. FIG. 4 of Patent Document 2 discloses a method for leading the condensate condensed in the heat exchanger 16 to a PCCS drain tank 76 by the condensate return pipe 21. It is further disclosed to provide an overflow pipe 77 on the gas phase region of the PCCS drain tank 76 to return overflow water into the containment vessel 3. However, the condensate return pipe 21, the PCCS drain tank 6, and the overflow pipe 77 are all installed outside the containment, vessel 3, and radioactive materials may possibly leak from such devices to the outside environment. Patent Document 3 discloses a method for providing a PCCS drain tank in the dry well and injecting cooling water in the PCCS drain tank into the containment vessel by gravity by using an injection pipe. However, according to such a method, the PCCS drain tank is installed in the dry well. In the case of the RCCV used for the ABWR, there no room to spare and the method has been impossible to be implemented. Next, a conventional filtered venting system will be described with reference to FIG. 14. A filtered venting system 50 has been employed in European nuclear power plants after the accident at the Chernobyl nuclear power plant. FIG. 14 is a sectional elevational view showing a design example of the conventional filtered venting system. The filtered venting system 50 includes a filtered venting tank 51 storing decontamination water 52, an inlet pipe 53 for leading gas in the containment vessel 3 to the decontamination water 3, and an outlet pipe 54 for releasing gas in the gas phase region of the filtered venting tank 51 to the environment. The upper portion of the outlet pipe 54 passes through a stack 75. The installation location of the filtered venting tank 51 and the like is not limited to inside the building. If the filtered venting tank 51 and the like are installed in an existing reactor as a backlit, the filtered venting tank 51 and the like are often installed outside the nuclear reactor building. If installed from the beginning of construction, the filtered venting tank 51 and the like may be installed inside the nuclear reactor building and the like. A Venturi scrubber 55 may be installed in the decontamination water 52 so that the gas led from the inlet pipe 53 passes through the Venturi scrubber 55. However, the Venturi scrubber 55 is not indispensable. A metal fiber filter 56 may be installed in the gas phase region of the filtered venting tank 51, although the metal fiber filter 56 is not indispensable. FIG. 14 shows a case in which both the Venturi scrubber 55 and the metal fiber filter 56 are installed. For example, one isolation valve 57 is installed on the inlet pipe 53. A rupture disc 58 is arranged in parallel with the isolation valve 57, and normally-opened isolation valves 59a and 59b are arranged in front of and behind the rupture disc 58. Two isolation valves 57 may be connected in series. An outlet valve 60 is installed, though not indispensable, on the outlet pipe 54. A rupture disc is often used instead of a motor-driven valve, in the conventional filtered venting system, one end of the inlet pipe 53 is directly connected to the containment vessel 3 to take in the gas inside the containment vessel 3. The filtered venting system can efficiently remove particulate radioactive materials, such as CsI, with a DF (Decontamination Factor) of approximately 1,000 to 10,000. However, because the conventional filtered venting system cannot remove radioactive noble gases or organic iodine, those radioactive materials are released to the environment through the outlet pipe 54 when it is activated. The filtered venting tank 51 of the conventional filtered venting system has a limited size, often with a decontamination water (scrubbing water) capacity of no more than 100 m3. If radioactive materials are removed, the decontamination water 52 thus evaporates and decreases due to the heat generated by the radioactive materials. In the event of an actual severe accident, the decontamination water has therefore needed to be replenished from outside. For powder separators, a cyclone separator by M. O. Morse (1886) has been widely used in sawmills, oil refining facilities, etc. A cyclone separator is an application of the principle of a centrifugal separator. A solid-containing liquid or gas is made to flow circumferentially into a funnel-like or cylindrical cyclone to trace a spiral by the flow of the gas or liquid. The gas or liquid is discharged upward from the center of the circle of the cyclone. The solid is centrifugally separated, collides with the wall surface, then falls by gravity, and accumulates below. With such a mechanism, the gas or liquid are discharged from the center of the circle after most of the solid components are removed. To collect the separated solid components, a collection container is often arranged under the cyclone. As the speed of the fluid flowing in from the inlet increases, the centrifugal force increases and the removal, efficiency of the cyclone separator improves. Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2014-10080 Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2014-81219 Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2004-333357 In the conventional passive containment cooling system, the heat exchanger is installed to be submersed in the cooling water pool, and the other pipes and devices are installed outside the containment vessel. If all the pipes and devices are installed inside the containment vessel, the containment vessel would become large in size. It has been difficult to install the pipes and devices inside a small-sized RCCV of an ABWR. Since the pipes and devices are installed outside the containment vessel to cool the containment vessel, there has been a possibility of leakage of radioactive materials from the pipes and the devices. In particular, since radioactive cesium iodide (CsI) concentrates in the condensate, there has been a possibility of a leakage of a large amount of radioactive materials if the condensate leaks from the condensate return pipe and the PCCS drain tank containing the condensate. The gas vent pipe contains a large amount of radioactive noble gases, organic iodine, and hydrogen. As a result, there has been a possibility of a leakage of a larger amount of radioactive materials and hydrogen if the gas vent pipe is installed outside the containment vessel. This has caused a risk of hydrogen detonation. Furthermore, since the gas vent pipe also contains CsI, CsI needs to be reliably removed if the exit of the gas vent pipe is outside the dry well or the wet well. As described above, though the conventional passive containment cooling system has the function of cooling the containment vessel, it has had a problem of inadequate function of controlling the leakage of radioactive materials and hydrogen. Moreover, the conventional passive containment cooling system has the following problem; that is, in the event of pressure increase in the wet well during a station blackout (SBO) and the like, the method for directly sucking in the gas front the wet well gas phase needs an exhaust fan using a power source to vent the noncondensable gases. This decreases the advantage of the passive safety system that the system can function even in an SBO. Furthermore, in the conventional passive containment cooling system, the gas supply pipe 20 is always open to the interior of the dry well 4. As a result, there has been a possibility that loose parts such as fragments of heat insulation material scattered into the dry well 4 at the time of an abrupt blowdown under a LOCA can be sucked into the heat exchanger 16 and clog the heat exchanger tubes 19. The conventional filtered venting system has a characteristic of removing particulate radioactive materials such as CsI efficiently but releasing a large amount of radioactive noble gases and organic iodine to the environment. Therefore, it has been a problem that although land contamination by CsI can be prevented, the venting cannot be performed until the resident have completely evacuated. The conventional containment vessel of a pressure suppression type is downsized and efficiently designed. On the other hand, if a large amount of hydrogen is generated by the oxidation of fuel cladding tubes at the time of a severe accident, the pressure of the containment vessel can increase beyond the designed pressure. The reason is that, unlike steam, hydrogen is noncondensable and thus cannot be removed by the suppression pool or by the passive containment cooling system. In such a case, there has been a possibility that part of the hydrogen leaks from the containment vessel and detonates outside. If the filtered venting system 50 is activated, the gas in the containment vessel 3 is discharged to the filtered venting tank 51. As a result, the gas supply pipe 20 of the passive containment cooling system 12 cannot supply the gas in the containment vessel 3 to the heat exchanger 16. The condensate is therefore unable to flow back into the containment vessel 3, and water injection into the containment vessel 3 needs to be continued from an outside water source. For example, if a residual heat removal system becomes unrecoverable because of a giant tsunami, the water injection from an outside water source needs to be continued for a long period. On the other hand, if the passive containment cooling system is operated alone without the activation of the filtered venting system, there has been a problem that radioactive materials in the containment vessel 3 are not removed and leak out of the containment vessel 3 to the environment at a design leakage rate. The passive containment cooling system has the excellent advantage of being able to cool the containment vessel 3 even if a core meltdown occurs due to a station blackout (SBO), while an active containment spray system cannot. However, there has been a problem of lacking the function of the active containment spray system of removing radioactive materials in the containment vessel 3. Consequently, it is an important challenge to enable the cooling of the containment vessel 3 by the passive containment cooling system 12 to eliminate the need for the water injection from an outside water source even if the filtered venting system 50 is activated to remove the radioactive materials. It is thus an object of an embodiment of the present invention to provide a passive containment cooling and filtered venting system and a nuclear power plant which can suppress leakage of radioactive materials and cool the containment vessel even if a severe accident accompanied by a core meltdown occurs due to a station blackout (SBO) and the like. According to an embodiment of the present invention, there is provided a passive containment cooling and filtered venting system of a nuclear power plant, the plant including: a core, a reactor pressure vessel that accommodates the core, a containment vessel including: a dry well that contains the reactor pressure vessel, a wet well that contains in its lower portion a suppression pool connected to the dry well via a LOCA vent pipe and includes in its upper portion a wet well gas phase, and a vacuum breaker that circulates gas in the wet well gas phase to the dry well, and a pedestal that supports the reactor pressure vessel in the containment vessel via an RPV skirt and forms a pedestal cavity inside, the passive containment cooling and filtered venting system comprising: an outer well that is arranged outside the dry well and the wet well, adjoins the dry well via a dry well common part wall, adjoins the wet well via a wet well common part wall, and has pressure resistance and gastightness equivalent to pressure resistance and gastightness of the dry well and the wet well; a scrubbing pool that is arranged in the outer well and stores water inside; a cooling water pool that is installed above the dry well and the outer well and reserves cooling water; a heat exchanger that includes an inlet plenum, an outlet plenum, and a heat exchanger tube, and is submerged at least in part in the cooling water; a gas supply pipe that is connected to the inlet plenum of the heat exchanger at one end and connected to a gas phase of the containment vessel at other end to lead gas in the containment vessel to the heat exchanger; a condensate return pipe that is connected to the outlet plenum of the heat exchanger at one end, passes through the outer well, and is connected to inside the containment vessel at other end to lead condensate in the heat exchanger into the containment vessel; and a gas vent pipe that is connected to the outlet plenum of the heat exchanger at one end, passes through the outer well, has other end installed as submerged in the scrubbing pool in the outer well, and releases noncondensable gas in the heat exchanger to the outer well. According to another embodiment of the present invention, there is provided a nuclear power plant comprising: a containment vessel that contains a reactor pressure vessel; an outer well that is arranged outside the containment vessel and has pressure resistance and gastightness; a scrubbing pool that is arranged in the outer well and stores water inside; a cooling water pool that is installed above the dry well and the outer well and reserves cooling water, a heat exchanger that includes an inlet plenum, an outlet plenum, and a heat exchanger tube, and is submerged at least in part in the cooling water; a gas supply pipe that is connected to the inlet plenum of the heat exchanger at one end and connected to a gas phase of the containment vessel at other end to lead gas in the containment vessel to the heat exchanger; a condensate return pipe that is connected to the outlet plenum of the heat exchanger at one end, passes through the outer wall, and is connected to inside the containment vessel at other end to lead condensate in the heat exchanger into the containment vessel; and a gas vent pipe that is connected to the outlet plenum of the heat exchanger at one end, passes through the outer well, has other end installed as submerged in the scrubbing pool in the outer well, and releases noncondensable gas in the heat exchanger to the outer well. According to an embodiment of the present invention, even if a severe accident accompanied by a core meltdown occurs due to a station blackout (SBO) and the like, leakage of radioactive materials can be suppressed and the containment vessel can be cooled. A passive containment cooling and filtered venting system and a nuclear power plant using the same according to embodiments of the present invention will be described below with reference to FIGS. 1 to 10. The same or similar parts as/to those of the foregoing conventional techniques, and the same or similar parts between the following embodiments, will be designated by the same reference numerals. Redundant descriptions will be omitted, and only essential parts will be described. FIG. 1 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a first embodiment of the present invention. FIG. 2 is a plan view showing the configuration around the containment vessel of a nuclear power plant according to the first embodiment of the present invention. The embodiment shown in FIGS. 1 and 2 uses a containment vessel called RCCV, whereas the type of the containment vessel is not limited to an RCCV. The embodiment is universally applied to all containment vessels of pressure suppression type having a pressure suppression function using a suppression pool. Other materials such as an SC composite and steel may also be used. In FIG. 1, a core 1 is contained in a reactor pressure vessel 2. The reactor pressure vessel 2 is contained in a containment vessel 3. The containment vessel 3 has a cylindrical shape (see FIG. 2). The interior of the containment vessel 3 is partitioned into a dry well 4, which contains the reactor pressure vessel 2, and a wet well 5. The dry well 4 and the wet well 5 each constitutes a part of the containment vessel 3. The wet well 5 forms a suppression pool 6 inside. A wet well gas phase 7 is formed above the suppression pool 6. The outer wall parts of the dry well 4 and the wet well 5 are integrated to constitute a cylindrical outer wall part of the containment vessel 3. The ceiling part of the dry well 4 is a flat plate, which will be referred to as a top slab 4a of the dry well 4. The atmosphere in the containment vessel 3 is inerted by nitrogen. In the present embodiment, an outer well 32 is provided outside the dry well 4 and the wet well 5. The outer well 32 adjoins the dry well 4 via a dry well common part wall 4b, and adjoins the wet well 5 via a wet well common part wall 5a. The ceiling part of the outer well 32 is a flat plate, which will be referred to as a top slab 32a of the outer well 32. The atmosphere in the outer well 32 is inerted by nitrogen. The outer well 32 has pressure resistance and gastightness equivalent to those of the dry well 4 and the wet well 5. The same materials as those of the containment vessel 3 may all be used for the outer well 32, such as reinforced concrete (RC), an SC composite, and steel. In the case of reinforced concrete, liners are laid on the inner surfaces as with the containment vessel 3. As shown in FIG. 2, the outer well 32 according to the present embodiment has a rectangular shape in a top plan view and is configured to surround a part of the outer walls of the dry well 4 and the wet well 5. However, the plane shape of the outer well 32 is not limited thereto. The outer well 32 may have any shape as long as the outer well 32 adjoins and surrounds at least a part of the outer walls of the dry well 4 and the wet well 5. Examples may include a trapezoidal shape, a polygonal shape, a crescent shape, a partial annular shape, and a full annular shape. A scrubbing pool 33 storing water inside is arranged in the outer well 32. A lid 33a covers the top of the scrubbing pool 33 (see FIG. 3). A space 33b is formed between the lid 33a and the pool water. A first outlet pipe 33c opening to the space 33b is arranged on the top of the lid 33a. A metal fiber filter (filter) 34 is connected to and arranged on one end of the first outlet pipe 33c. The metal fiber filter 34 is further connected with a second outlet pipe 34a which opens to the interior of the outer well 32 at the other end. FIG. 3 shows a detailed configuration around the scrubbing pool 33 and the metal fiber filter 34. The space 33b is needed if the water level rises as the gas in the dry well 4 is vented from the gas vent pipe 22. The lid 33a is needed to prevent the water from flowing out due to sloshing at the time of an earthquake. While only one metal fiber filter 34 is shown in the drawings, a plurality of metal fiber filters 34 may be installed. For example, four PCCS heat exchangers 16, four gas vent pipes 22, and four metal fiber filters 34 may be installed. Alternatively, four PCCS heat exchangers 16 may be installed with two integrated gas vent pipes 22 and two metal fiber filters 34. The scrubbing pool 33, the lid 33a, and the space 33b may be configured as an integral tank. As shown in FIG. 1, a cooling water pool 13 is arranged above the containment vessel 3 and the outer well 32. The cooling water pool 13 stores cooling water 14 inside. The cooling water pool 13 may be of either a pool type or a tank type. FIG. 1 shows one of a pool type. In the case of the pool type, the top of the cooling water pool 13 is covered with a lid. An exhaust port 15 for releasing steam to the environment is arranged on the gas phase in the upper part of the cooling water pool 13. A heat exchanger 16 is installed in the cooling water pool 13. The heat exchanger 16 is installed to be submerged at least in part in the cooling water 14. The present embodiment describes an example where the heat exchanger 16 is completely submerged in the cooling water 14. A gas supply pipe 20 is connected to the inlet plenum 17 of the heat exchanger 16. In the present embodiment, the gas supply pipe 20 passes through the top slab 32a of the containment vessel 3, and the other end of the gas supply pipe 20 opens in the dry well 4. A condensate return pipe 21 is connected to the lower part of the outlet plenum 18 of the heat exchanger 16. The condensate return pipe 21 is installed to pass through the top slab 32a of the outer well 32 and the interior of the outer well 32 so that its tip is submerged in the suppression pool 6 in the wet well 5. In such a structure, the condensate return pipe 21 is installed to pass through the interior of the outer well 32, and the condensate is prevented from leaking out to directly release radioactive materials such as CsI to the environment. If a core meltdown accident occurs, the atmosphere in the dry well 4 contains a large amount of particulate radioactive materials such as CsI. Most of the particulate radioactive materials such as CsI transfer to the condensate when the steam condenses in the heat exchanger 16. The condensate containing a large amount of CsI is circulated to and retained in the pool water of the suppression pool 6 via the condensate return pipe 21. The passive containment cooling and filtered venting system according to the present embodiment is thus configured to passively remove the particulate radioactive materials floating in the containment vessel 3. Consequently, according to the present embodiment, even if a core meltdown accident occurs due to a station blackout (SBO), an effect equivalent to as if the particulate radioactive materials are removed by an active containment vessel spray and circulated to the pool water of the suppression pool 6 is obtained. The structure that the condensate return pipe 21 is not installed in a LOCA vent pipe 8 will not increase the pressure loss of the LOCA vent pipe at the time of a LOCA. Moreover, the gas vent pipe 22 is connected to the upper part of the outlet plenum 18 of the heat exchanger 10. The gas vent pipe 22 is installed to pass through the top slab 32a of the outer well 32 and the interior of the outer well 32, with its tip submerged into the pool water of the scrubbing pool 33. In such a structure, since the gas vent pipe 22 is thus installed to pass through the interior of the outer well 32, the gas is prevented from leaking out to directly release radioactive materials such as radioactive noble gases, organic iodine, and CsI to the environment. Of these, particulate radioactive materials such as CsI are removed by the pool water of the scrubbing pool 33. The metal fiber filter 34 is configured to further remove particulate radioactive materials carried over to water droplets and the like. This can eliminate the need to have surrounding habitants move to other places for a long period of time because of the contamination of the land by particulate radioactive materials such as CsI released to the environment. The radioactive noble gases and organic iodine are released from the second outlet pipe 34a into the outer well 32 and retained in the outer well 32. This can eliminate the need to have surrounding habitants evacuate in advance or take iodine tablets due to direct release of radioactive noble gases and organic iodine to the environment when a conventional filtered venting system is in operation. In the present embodiment, a large amount of hydrogen generated at the time of a severe accident is also released into the outer well 32 through the gas vent pipe 22. The pressure of the dry well 4 and the wet well 5 at the time of the severe accident can thus be maintained to a sufficiently low level. Since the atmosphere in the outer well 32 is inerted by nitrogen, the confinement of the large amount of hydrogen will not cause detonation. In the present embodiment, a flooder pipe 68 for flooding the lower dry well is provided through the wall of the pedestal 61. The flooder pipe 68 is led into the lower dry well (pedestal cavity) 61a at one end, and opens in the suppression pool 6 at the other end. A flooder valve 67 is arranged on the portion of the flooder pipe 68 inside the lower dry well 61a. A check valve (flooder check valve) 69 is arranged on the portion of the flooder pipe 68 inside the suppression pool 6. The provision of the check valve 69 can prevent high-temperature water in the lower dry well 61a from flowing back to the suppression pool 6, even if the pressure in the dry well 4 increases. Since the check valve 89 is located in the suppression pool 6, the safety functions of the LOCA vent pipes 8 at the time of an accident will not be hampered. A total of ten flooder pipes 68 are installed to not overlap with the LOCA vent pipes 8, for example, in intermediate positions between the LOCA vent pipes (see FIG. 2). The flooder valves 67 may be the same type of fusible valves as in the conventional plants. Aside from fusible valves, any valves that do not need an operating power source at the time of an SBO can be used. For example, squib valves which use an, explosive for operation may be employed. Spring valves which use spring force for operation may also be employed. For improved reliability, five of the ten flooder valves may be squib valves and the other five may be spring valves. Otherwise, five may be fusible valves and the other five may be squib valves. At least two or more types among fusible, squib, and spring valves may be used in combination. FIG. 4 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a second embodiment of the present invention. In the present embodiment, the condensate return pipe 21 includes a U-bent portion (referred to as a “U-shaped water seal”) 35 and is led into the dry well 4 through the dry well common part wall 4b. The U-shaped water seal 35 stores water inside. A spray sparger 36 is arranged at the end of the condensate return pipe 21 inside the dry well 4. In FIG. 4, the spray sparger 36 is shown to be in contact with the side wall of the dry well 4. However, the spray sparer 36 is not limited to such a position. For example, the spray sparger 36 may be attached to the ceiling of the dry well 4. The spray sparger 36 may be attached to the top slab 4a of the dry well 4, since a flow occurs by gravity as long as the spray sparger 36 is located inside the dry well 4 in a position lower than the outlet plenum 18 of the heat exchanger 16. A check valve (condensate check valve) 37 is arranged on a portion of the condensate return pipe 21 between the heat exchanger 16 and the U-bent portion (U-shaped water seal) 35. The check valve 37 is installed in a direction of preventing a backflow from the U-bent portion (U-shaped water seal) 35 to the heat exchanger 16. The rest of the configuration is the same as that of the first embodiment. In the present embodiment having such a configuration, the condensate can be sprayed into the dry well 4. The dry well 4 can thus be maintained at low temperature. If a core meltdown accident occurs with a LOCA as an initiator, radioactive materials such as CsI released from the core fuel would be released from a break in the piping into the dry well 4 and deposit in the dry well 4. Decay heat occurring from the deposited radioactive materials increases the temperature in the dry well 4. If the situation is left without any countermeasures, the containment vessel 3 can be damaged from overheating. In the present embodiment, the condensate sprayed into the dry well 4 can limit the interior of the dry well 4 to low temperatures and passively prevent the containment vessel from overheating and damage. The provision of the spray sparger 36 can make the injected water into drops for a higher heat removal effect. The presence of the U-shaped water seal 35 can prevent the gas in the dry well 4 from flowing back through the condensate return pipe 21, bypassing the heat exchanger tubes 19, and being vented into the scrubbing pool 33 through the gas vent pipe 22. The check valve 37 can further ensure the prevention of the backflow. FIG. 5 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a third embodiment of the present invention. In the present embodiment, a PCCS drain tank 38 is arranged in the outer well 32. The PCCS drain tank 38 stores sealing water inside and has a gas phase above. An overflow pipe 39 is provided from the gas phase to the interior of the dry well 4. A spray sparger 36 is arranged at the end of the overflow pipe 39. One end of the condensate return pipe 21 is submerged in the water in the PCCS drain tank 38. A check valve (condensate check valve) 37 is arranged on the condensate return pipe 21 to prevent the water from flowing back from the PCCS drain tank 38 to the heat exchanger 16. A water level sensor (not shown) is provided for measuring the water level in the PCCS drain tank 38. The rest of the configuration is the same as that of the second embodiment. The present embodiment having such a configuration can provide a larger amount of sealing water compared to the U-shaped water seal 35 (FIG. 4). The large amount of sealing water can increase the water head against reverse pressure in the condensate return pipe 21 in the event of a backflow. Since the PCCS drain tank 38 is accommodated in the outer well 32, radioactive materials, such as CsI, contained in the condensate will not directly leak out to the environment. Consequently, even if the core fuel is damaged and radioactive materials and hydrogen are generated under a station blackout situation, the release to the environment and the detonation of the hydrogen can be prevented. In addition, a failure of the containment vessel by overheating can be prevented even if the state of a severe accident lasts long. FIG. 6 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a fourth embodiment of the present invention. In the present embodiment, a water injection pipe 40 is connected from the lower part of the PCCS drain tank 38 to inside the pedestal cavity 61a. A water injection valve 41 is arranged on the portion of the water injection pipe 40 inside the pedestal cavity 61a. A master valve 42 is arranged on the portion of the water injection pipe 40 inside the outer well 32. The master valve 42 is normally open. In the PCCS drain tank 38, a drain pit 43 is arranged storing water inside. One end of the condensate return pipe 21 is submerged in the water in this drain pit 43. The water injection valve 41 may be any one of a fusible valve, a squib valve, and a spring valve. A plurality of such valves may be used in combination in parallel. The rest of the configuration is the same as that of the third embodiment. According to the present embodiment, by opening the water injection valve 41 it is possible to inject the water stored in the PCCS drain tank 38 into the lower dry well 61a by gravity. As a backup for situations where the flooder valves 67 fail to open due to multiple failures, the water in the PCCS drain tank 38 can be used to cool the corium that has fallen into the lower dry well (pedestal cavity) 61a. Even if the water in the PCCS drain tank 38 is used for water injection and the water level drops, the water in the drain pit 43 remains. The function for water-sealing the condensate return pipe 21 is thus maintained. The condensate is constantly supplied from the condensate return pipe 21 to the drain pit 43 and overflows into the PCCS drain tank 38. This enables the PCCS drain tank 38 to continue cooling the corium via the water injection pipe 40. The steam to be supplied to the heat exchanger 16 of the PCCS 12 is generated by the water injected from the PCCS drain tank 38 being heated by the corium in the lower dry well 61a. In other words, according to the present embodiment, the generation of the steam and the supply of the condensate continue in circulation while the heat in the containment vessel is transferred from the heat exchanger 16 of the PCCS 12 to the cooling water 14 and further released into the air from the exhaust port 15. FIG. 7 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a fifth embodiment of the present invention. In the present embodiment, the gas supply pipe 20 is configured to be connected to the inlet plenum 17 of the heat exchanger 16 at one end, passes through the outer well 32, and is connected into the dry well 4 in the portion of the dry well common part wall 4b at the other end to lead the gas in the dry well 4 into the heat exchanger 16. A screen 20a is provided on the portion of the gas supply pipe 20 inside the dry well 4. The rest of the configuration is the same as those of the first to fourth embodiments. In the present embodiment having such a configuration, the gas supply pipe 20 passes through the outer well 32. If the radioactive gases and hydrogen in the gas supply pipe 20 leak from the pipe, the radioactive gases and hydrogen are contained in the outer well 32 and release into the environment is suppressed. Since the atmosphere in the outer well 32 is inerted by nitrogen, the detonation of the hydrogen can be prevented even if the leakage of the hydrogen occurs. The screen 20a can prevent loose parts such as fragments of thermal insulation material scattering into the dry well 4 at the time of an abrupt blowdown and the like under a LOCA from being sucked into the heat exchanger 16. FIG. 8 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a sixth embodiment of the present invention. In the present embodiment, a cyclone separator 45 is arranged in the outer well 32. One end of the gas supply pipe 20 is connected to an outlet of the cyclone separator 45. An inlet pipe 46 extending from an inlet of the cyclone separator 45 to inside the dry well 4 is also provided. A screen 47 is arranged at the end of the inlet pipe 46 inside the dry well 4. The rest of the configuration is the same as that of the fourth embodiment. In the present embodiment having such a configuration, loose parts such as fragments of thermal insulation material scattering into the dry well 4 at the time of an abrupt blowdown and the like under a LOCA can be prevented from being sucked into the heat exchanger 16. Most of the loose parts such as fragments are removed by the screen 47. Some fine solids may fail to be removed by the screen 47. The fine solids are led through the inlet pipe 46 into the cyclone separator 45 for removal. The removed fine solids are collected into a collection container installed under the cyclone separator 45. Since the gas flowrate inside the inlet pipe 46 at the time of a severe accident is as extremely high as approximately 25,000 m3/h even in terms of steam alone, the cyclone separator 46 can highly efficiently remove the fine solids. As a result, the heat exchanger tubes 19 can be prevented from being clogged with loose parts such as fragments in the dry well 4. FIG. 9 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to a seventh embodiment of the present invention. In the present embodiment, a new normally-closed isolation valve (gas supply isolation valve) 20b is arranged on the gas supply pipe 20. The isolation valve 20b may be any one of a motor-operated valve, a fusible valve, a squib valve, and a spring valve. A wet well gas supply pipe 48 for leading the gas in the wet well 5 to the heat exchanger 16 is further provided. One end of the wet well gas supply pipe 48 passes through the portion of the wet well common part wall 5 and opens in the wet well gas phase 7. The other end of the wet well gas supply pipe 48 is connected to a portion of the gas supply pipe 20 between the inlet plenum 17 and the isolation valve 20b. In another configuration example, the other end of the wet well gas supply pipe 48 may be connected to the inlet plenum 17 of the heat exchanger 16. The wet well gas supply pipe 48 passes through the outer well 32. A backflow prevention device 49 is further arranged on the wet well gas supply pipe 48 to prevent the gas in the inlet plenum 17 from flowing back into the wet well gas phase 7. The backflow prevention device 49 may be either of a check valve and a vacuum breaker. In FIG. 9, the isolation valve 20b on the gas supply pipe 20 is installed in a position inside the outer well 32. However, the isolation valve 20b may be installed inside the dry well 4 or above top of the top slab 32a of the outer well 32. Since the function of the isolation vale 20b is to isolate the gas supply pipe 20, the isolation valve 20b may thus be located in any position on the gas supply pipe 20. In the present embodiment having such a configuration, if an abrupt pressure increase occurs in the dry well 4 at the time of a blowdown and the like under a LOCA, the gas supply pipe 20 is being closed by the isolation valve 20b. Loose parts such as fragments of heat insulation material which can be produced in the dry well 4 are therefore completely prevented from flowing into the heat exchanger 16. The gas in the dry well 4 passes through the LOCA vent pipes 8 and reaches the wet well gas phase 7 via the suppression pool 6. In the process, the steam is condensed by the pool water, radioactive materials such as CsI are removed, and loose parts are removed as well. As a result, noncondensable gases such as nitrogen, hydrogen, radioactive noble gases, and organic iodine mainly reach the wet well, gas phase 7. These gases are further led to the heat exchanger 16 via the wet well gas supply pipe 48, further pass through the scrubbing pool 33 via the gas vent pipe 22, and are released into the outer well 32. In this process, since the gas in the wet well gas phase 7 does not contain a large count of steam, the heat up of the water in the scrubbing pool 33 due to steam heat can be prevented. The amount of water held in the scrubbing pool 33 can therefore be reduced. For example, no more than 100 m3 may be sufficient. If a core meltdown can be avoided at the time of a station blackout (SBO), the steam in the reactor pressure vessel 2 is transferred to the suppression pool 6 via a safety relief valve (SRV) 72 (see FIG. 11) and heats up the pool water. Once the pool water reaches saturation, steam is generated in the wet well gas phase 7. In such a case, the steam in the wet well gas phase 7 is supplied to the heat exchanger 16 through the wet well gas supply pipe 48 for condensation. The flowrate of the steam in this case is equivalent to the decay heat, and the entire amount of the steam is condensed by the heat exchanger 16. The steam therefore does not transfer to the scrubbing pool 33 via the gas vent pipe 22 and heat up the pool water. If a core meltdown occurs at the time of a station blackout (SBO) and corium melts the bottom of the reactor pressure vessel 2 through and falls into the lower dry well 61a, the feeder valves 67 are activated to flood and cool the corium. At that time, a large amount of steam is generated and through the openings 66 moves to the upper dry well. In this case also, the steam passes through the LOCA vent pipes 8 and is condensed in the suppression pool 6. The hydrogen generated here moves to the wet well gas phase 7, moves further to the heat exchanger 16 via the wet well gas supply pipe 48, passes through the scrubbing pool 83 via the gas vent pipe 22, and is released into the outer well 32. In that process, radioactive materials carried by the hydrogen are removed twice, once by the suppression pool 6 and once by the scrubbing pool 33. The water in the suppression pool 6 loses the steam condensation function after saturation. Thereafter the steam in the wet well gas phase 7 is condensed by the heat exchanger 16 of the passive containment cooling system 12 via the wet well gas supply pipe 48. As the gas vent pipe 22 is led into the outer well 32, the noncondensable gases accumulated in the heat exchanger 16 are efficiently discharged into the outer well 32. The reason is that the pressure in the wet well gas phase 7 is maintained higher than that in the outer well 32. Although the wet well gas supply pipe 48 is connected to the wet well gas phase 7, an active fan therefore does not need to be used to forcefully vent the noncondensable gases accumulated in the heat exchanger 16 into the dry well 4 as in Patent Document 2. The isolation valve 20b arranged on the gas supply pipe 20 therefore does not need to be opened. However, if the isolation valve 20b is opened, the steam generated by the cooling of the corium in the dry well 4 can be directly led to the heat exchanger 16 via the gas supply pipe 20 for condensation. This can provide the effect of maintaining the dry well 4 at lower pressure and temperature. In the case that the isolation valve 20b is used, it is opened after the flooder valve 67 is opened and the generation of the large amount of steam in the dry well 4 subsides. If the isolation valve 20b is opened, the gas supply pipe 20 and the wet well gas supply pipe 48 communicate with each other and the gas in the dry well 4 might flow back to the wet well gas phase 7. However, the occurrence of the backflow of the gas is prevented by the provision of the backflow prevention device 49 on the wet well gas supply pipe 48. FIG. 10 is a sectional elevational view showing a configuration around a containment vessel of a nuclear power plant according to an eighth embodiment of the present invention. In the present embodiment, a filtered venting tank 51 storing decontamination water 52 inside is arranged as the scrubbing pool 33 (FIGS. 1 to 9). The end of the gas vent pipe 22 is connected to an inlet pipe 53 of the filtered venting tank 51. The filtered venting tank 51 is configured to open in the cuter well 32 via an outlet pipe 54. A metal fiber filter 56 and a Venturi scrubber 55 are arranged inside the filtered venting tank 51. In the present embodiment having such a configuration, a filtered venting tank of an already-developed high-performance filtered venting system can be used. This provides the effect that radioactive materials can be removed with higher efficiency. While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 1: core; 2: reactor pressure vessel; 3: containment vessel; 4: dry well; 4a: top slab; 4b: dry well common part wall; 5: wet well; 5a: wet well common part wall; 6: suppression pool; 7: wet well gas phase; 8: LOCA vent pipe; 8a: horizontal vent pipe; 9: vacuum breaker; 10: containment vessel head; 11: water shield; 12: passive containment cooling system (PCCS); 13: cooling water pool; 14: cooling water; 15: exhaust port; 16: heat exchanger; 17: inlet plenum; 18: outlet plenum; 19: heat exchanger tube; 20: gas supply pipe; 20a: screen; 20b: isolation valve (gas supply isolation valve); 21: condensate return pipe; 22: gas vent pipe; 23: tube plate; 32: outer well; 32a: top slab; 33: scrubbing pool; 33a: lid; 33b: space; 33c: first outlet pipe; 34: metal fiber filter (filter); 34c: second outlet pipe; 35: U-shaped water sea; 36: sparger; 37: check valve (condensate check valve); 38: PCCS drain tank; 39: overflow pipe; 40: water injection pipe; 41: water injection valve; 42: master valve; 43: drain pit; 45: cyclone separator; 46: inlet pipe; 47: screen; 48: wet well gas supply pipe; 49: backflow prevention device; 50; filtered venting system; 51: filtered venting tank; 52: decontamination water; 53: inlet pipe; 54: outlet pipe; 55: Venturi scrubber; 56: metal fiber filter (filter); 57: isolation valve; 58: rupture disc; 59a, 59b: isolation valve; 60: outlet valve; 61: pedestal; 61a: pedestal cavity (lower dry well); 62: RPV skirt (vessel skirt); 63: RPV support (vessel support); 64: fusible valve; 65: lower dry well flooder pipe; 66: opening; 67: flooder valve; 68: flooder pipe; 69: check valve (flooder check valve); 71: main steam pipe; 72: safety relief valve; 73: discharge pipe; 75: stack; 100: nuclear reactor building |
|
claims | 1. An electromagnetic coil assembly for a control rod driving mechanism, comprising one or more coils and a yoke for embedding the one or more coils, wherein one or more damascene holes are disposed on the yoke, the one or more coils are installed in the one or more damascene holes, the yoke comprises at least one first yokes and at least one second yokes, and the one or more damascene holes are disposed on the at least one first yokes;the at least one first yokes are connected with the at least one second yokes, and a through hole for cooperating with a sealing shell assembly is disposed on the at least one second yokes;among the at least one first yokes and the at least one second yokes, the materials of the first yokes and the second yokes are different, a thermal conductivity of the at least one first yokes is stronger than a thermal conductivity of the at least one second yokes;either the one or more damascene holes or the through hole is a round hole, and an axis of the one or more damascene holes is collinear with an axis of the through hole;each of the one or more coil comprises an inner frame and a coil winding wound around the inner frame, the inner frame has a cylindrical shape, an axis of the inner frame is collinear with the axis of the one or more damascene holes, and a diameter of a center hole of the inner frame is larger than a diameter of the through hole; andprojection of the one or more coils toward an end surface of each of the second yokes falls outside the through hole. 2. The electromagnetic coil assembly for the control rod driving mechanism according to claim 1, wherein an amount of the at least one first yokes exceeds an amount of the at least one second yokes by one, two adjacent first yokes of the at least one first yokes are connected by one of the at least one second yokes, the one or more damascene holes are disposed on each of the at least one first yokes, and the one or more coils are installed in each of the one or more damascene holes. 3. The electromagnetic coil assembly for the control rod driving mechanism according to claim 1, wherein the at least one first yokes and the at least one second yokes are connected by a bolt, and a sealing ring is disposed on a connecting surface of the at least one first yokes and the at least one second yokes. 4. The electromagnetic coil assembly for the control rod driving mechanism according to claim 1, wherein a depth of each of the one or more damascene holes is equal to or greater than a length of each of the one or more coils, and a space between a hole wall of each of the one or more damascene holes and each of the one or more coils is filled with a potting layer; andtwo end faces of each of the one or more coils are both located between two end faces of each of the one or more damascene holes, or the two end faces of each of the one or more coils are respectively coincident with the two end faces of each of the one or more damascene holes. 5. The electromagnetic coil assembly for the control rod driving mechanism according to claim 1, wherein a wire hole is disposed on the at least one first yokes and the at least one second yokes, the wire hole disposed on the at least one first yokes and the one or more damascene holes are holes relatively independent from each other, and the wire hole disposed on the at least one second yokes and the through hole are holes relatively independent from each other. 6. The electromagnetic coil assembly for the control rod driving mechanism according to claim 4, wherein an end portion of each of the one or more coils is also covered with the potting layer. 7. The electromagnetic coil assembly for the control rod driving mechanism according to claim 4, wherein the potting layer is further embedded with thermally conductive insulating particles. |
|
047524324 | description | |
abstract | A radiation attenuation corridor couples a radiation therapy room and a control room. The radiation attenuation corridor is made of a material that substantially absorbs ionizing radiation and substantially blocks the transmission of the ionizing radiation. Specific wall portions at the entrance of the corridor are covered with borated polyethylene (BPE). Specific wall portions diverge from an axis defined by the corridor by from about 10 degrees to about 45 degrees. The corridor thus leads out of the room and angles laterally across the wall of the therapy room, before angling again and opening to a safe room. The added angles in the radiation corridor increase the distance of radiation travel, and make the path more indirect, thereby increasing the contact of the radiation emissions with the radiation shielding and further attenuating the radiation. |
|
043022871 | description | DETAILED DESCRIPTION OF THE DRAWINGS A fuel rod 1 is, as shown in FIG. 1, assembled such that a plurality of fuel pellets 3 are packed in a clad tube 2 with both end portions of the clad tube 2 being sealed by an end plug 4. Further, a spring 5 is disposed in the clad tube 2 to press the fuel pellets 3 downwardly. A rapid increase of nuclear reactor power such as in accordance with the pattern shown in FIG. 2(a) causes the PCI between the fuel pellets 3 and the clad tube 2. In order to avoid the failure of the fuel rod 1, it has been proposed to restrain the rate of increase of the linear heat generating rate when the linear heat generating rate is increased above the linear heat generating rate at which the PCI begins, as shown in FIG. 2(b). This invention has been accomplished through a following study. The failure of the fuel rod 1 due to the PCI takes place under the presence of the nuclear fission products such as iodine or cesium accumulated within the fuel rod and there is a large probability of failure when excessive strain appears in the clad tube 2. With the increase of power per a unit length along the fuel rod 1 (indicated as a linear heat generating rate), the temperature of fuel pellets 3 rises. When the value of thermal stress in the fuel pellets is over the breakage stress of fuel pellets 3, the fuel pellets 3 break and simultaneously expand outwardly due to thermal expansion. The fuel pellets 3 and the inner surface of the clad tube 2 contact each other to cause the PCI between the clad tube 2 and the fuel pellets 3, which results in strain taking place in the clad tube 2. Under this situation with the further increase of the linear heat generating rate of the fuel rod, the strain due to the PCI increases and especially local excessive strain appears in a local portion of the clad tube 2 opposite broken parts of the fuel pellets or opposite interfacing parts of the broken fuel pellets. The deformation of the fuel rod due to the PCI will be explained in detail with reference to FIG. 3. A fuel rod elongates along a curve 6 in FIG. 3 as the linear heat generating rate increases. After an operation of a nuclear reactor begins and until the fuel pellets contact the inner surface of the clad tube, the fuel rod elongates due to only thermal expansion. That is, up to a point F on the curve 6, the fuel pellets are deformed and come in contact with the inner surface of the clad tube due to only thermal expansion. At the point F at which the fuel pellets are deformed and contact the inner surface of the clad tube, the elongation of the fuel rod becomes larger. Under this situation, the elongation of the fuel rod increases greatly as compared with the elongation due solely to thermal expansion and the linear heat generating rate at the point F is the linear heat generating rate at which the PCI begins. The failure of the fuel rod under the pressure of nuclear fission products such as iodine or cesium is known as stress corrosion crack (indicated as SCC). Nuclear fission products sufficient to cause the SCC are accumulated in an amount within the fuel rods which have been used more than about one month in a nuclear reactor. The SCC is predicted in that the probability of occurrence is determined in accordance with the magnitude of strain which appears in the clad tube. The probability of occurrence of the SCC is discussed in the following description. FIG. 4 illustrates the relationship between strain .epsilon. of a fuel rod and the probability of the failure, under the condition that the fuel rod 1 is formed of fuel pellets of uranium dioxide and a clad tube 2 of zirconium alloy and was used over 2,000 MWD/T of the rate of combustion and, after that, the nuclear reactor power was rapidly raised up to a high linear heat generating rate, namely, generally 18.about.22 KW/ft. The probability of failure was treated by Weibull statistics. As is well known in Weibull statistics, when a probability variable of a phenomenon is expressed by a functional formula of independence variable, the phenomenon is expressed by a probability distribution of the variable. In FIG. 4, the failure of the fuel rod 1 is described by a probability variable of strain in the clad tube. According to the experimental data in FIG. 4, a failure probability of the fuel rod is expressed by the following formula (1). EQU FP(.epsilon.)=1.0-exp(-exp(Y)) (1) EQU Y=aX+b-exp(-c(X+d)) EQU X=1n.epsilon. wherein FP is the failure probability; PA1 .epsilon. is strain in a clad tube; PA1 X is ln .epsilon.; PA1 Y is aX+b-exp(-c(X+d)); and PA1 a, b, c and d are constants. PA1 P.sub.I is a linear heat generating rate at which the PCI begins; PA1 P is the rate of increase of the linear heat generating rate; PA1 Tp, T.sub.I and To are temperatures at the center of a fuel pellet, respectively, when P=P, P.sub.I, 0; PA1 Q.sub.1 and Q.sub.2 are activation energies; PA1 A.sub.1 and A.sub.2 are constants determined by coefficient .alpha. of thermal expansion and smear density Sd; PA1 B.sub.1 and B.sub.2 are constants determined by Young's modulus of the pellet and smear density Sd; and PA1 C.sub.1 is a constant determined by rate of creep .epsilon. c of the pellet. PA1 Fuel: about 90.about.98% T.multidot.D.multidot.UO.sub.2 pellets and about 90.about.98 Y.multidot.T.multidot.DUO.sub.2 +PuO.sub.2 pellet PA1 Clad tube: zirconium alloy PA1 Outside diameter: about 11-20 mm PA1 Thickness of clad tube: about 0.4-0.9 mm PA1 Diameter of fuel pellet: about 10.5-18.8 mm ##EQU3## PA1 A.sub.1 and A.sub.2 are constants which are determined by a factor similar to A in the above; and PA1 D.sub.1 and D.sub.2 are constants which are determined by a factor similar to D in the above. Next, the amount of strain in the clad tube 2 is determined in the following manner. FIG. 5 is a graph of experimental data obtained from a measurement of an amount of strain in clad tube 2 while a fuel rod 1, which was formed of fuel pellets of uranium dioxide in a clad tube 2 of ZIRCALOY-2.RTM., was irradiated in a reactor. This figure shows a predicted view of strain appearing in the clad tube 2. As apparent from FIG. 5, the strain .epsilon. in the clad tube 2 is determined in accordance with the formula (2) concerning a function of linear heat generating rate (P) and an increase rate of a linear heat generating rate (P). ##EQU1## wherein P is a linear heat generating rate; A "no failure" operation of fuel rods is defined such that no failure of any fuel rod resulting from cracks in the fuel rod occurs in the fuel rods located in a core of a nuclear reactor operated in power cycles in which all fuel rods have been used for a couple of years. The determination of no failure operation of fuel rods is indicated by the failure probability as follows. Assume that a number of fuel rods located in a core of a nuclear reactor is M, a number of power operation cycles in a fuel use duration is N, and when the failure probability FP of the fuel rods upon power increase satisfies the following formula (3), no failure operation of fuel rods is accomplished. EQU M.multidot.N.multidot.FP(.epsilon.)<1 (3) In conventional commercial nuclear reactors, generally M=3.times.10.sup.4 and N=3.times.10.sup.2. When these numeric values are substitutes in the formula (3), the formula (3) is changed as follows: EQU FP(.epsilon.)<10.sup.-7 (3A) If the formula (3A) is satisfied, no failure operation of fuel rods is ensured. From the function of the formula (1) as shown in FIG. 4 regarding the strain in a clad tube, when .epsilon..ltoreq.0.06(%), FP(.epsilon.)<<10.sup.-7 is satisfied such that the formula (2) is changed as follows in the conventional commercial nuclear reactors: EQU .epsilon.(P,P,P.sub.I)=0.06 (4) If a relationship between the linear heat generating rate (P) and the rate of increase of the linear heat generating rate (P) which satisfies the formula (4) is obtained, the relationship indicates a condition of no failure operation of fuel rods. The parameter P.sub.I in the formula (4), which is the linear heat generating rate at which the pellet-clad-mechanical-interaction begins between the fuel pellets and the clad tube, is a value determined by a fuel rod specification and an operation condition of power operation cycles before the power increase. Now assume that a gap between the fuel pellets and the clad tube 2 is small or the linear heat generating rate of operation cycles before the power increase is maintained at a substantially constant level for a short time, this situation is expressed by P.sub.I =0 KW/ft. As apparent from the formula (2), the above-noted situation represents the worst condition present for occurrence of the failure of fuel rods, which means that the strain in the clad tube is determined to be excessive. Under the condition when the formula (4) is solved, P is indicated as follows: ##EQU2## wherein A, B, C and D are constants determined by a fuel rod system and a value representing a property of the fuel rod. A is determined by a coefficient .alpha. of thermal expansion of a pellet and smear density Sd; B is determined by Young's modulus E of a pellet and smear density Sd; C is determined by a rate of creep .epsilon.c of a pellet; and D is determined by a coefficient .alpha. of thermal expansion of a pellet, Young's modulus E and smear density Sd. The value of P determined by the formula (5) is the critical rate of increase of the linear heat generating rate for no failure operation of fuel rods. If a nuclear reactor power is increased at the increase rate of a linear heat generating rate below P determined by the formula (5), there is no failure of fuel rods. When the below-described fuel rod is employed as an example of the fuel rod 1, each constant of the formula (5) is specified so that the formula (6) is obtained. This relationship is illustrated in FIG. 6. It will be understood that when the rate of increase of a linear heat generating rate is maintained below the critical increase rate of the linear heat generating rate given by the formula (6), a no failure operation of the fuel rods is provided. While the linear heat generating rate has been discussed above with regard to the worst condition in which P.sub.I =0 KW/ft., P.sub.I may take other values. For example, it is possible to increase P.sub.I to 2.about.10 KW/ft. by increasing the gap between the fuel pellets and the clad tube 2 or by increasing the linear heat generating rate before the power increase and by increasing the holding term. At this time, the formula (5) showing the increase rate of the critical linear heat generating rate is changed to the following formula (7): ##EQU4## wherein B and C are constants explained above; When the numerical values of the same fuel rod discussed above in connection with formula (6) are again employed, the formula (7) is changed to the following formula (8): ##EQU5## The critical increase rate P of the linear heat generating rate is indicated in FIG. 7 under a parameter P.sub.I. It will be understood that, if P.sub.I is increased, the increase rate P of the linear heat generating rate is increased. P.sub.I is a constant which is mainly determined by the form of the fuel rod and the value representing a property of the fuel rod. When the reactor power is increased at the increase rate of the linear heat generating rate below P determined by the formula (8), the predetermined power level is reached without the failure of the fuel rods. When the increase rate of an extremely small linear heat generating rate is employed, the fuel pellets and the clad tube come conditioned or fit properly with respect to one another so that the failure of the fuel rods due to the PCI is avoided. The proper fitting corresponds to the decrease of contact pressure acting between the fuel pellets and the clad tube. The decrease of the contact pressure causes an increase of the heat resistance, namely, the decrease of a gap conductance, between the fuel pellets and the clad tube. In a nuclear reactor, it is important to prevent the occurrence of the failure of the fuel rods during a normal operation, as well as to remove heat from the fuel rods upon a coolant loss accident in absence of a coolant in a core of the nuclear reactor. In consideration of the removal of heat upon a loss of coolant accident, it is necessary to keep the gap conductance above a constant value. Thus, in order to avoid the occurrence of fitting more than necessary, the increase rate of the linear heat generating rate must be limited in a suitable extent. FIG. 8 illustrates the relationship between the highest temperature of a clad tube upon the coolant loss accident and the gap conductance in the fuel rod constructed as discussed above. FIG. 9 illustrates the relationship between the gap conductance and an amount of interaction, and FIG. 10 illustrates the relationship between the amount of interaction and the increase rate of the linear heat generating rate. When the temperature of the clad tube exceeds about 1,200.degree. C., the clad tube and the cooling water chemically react so that the strength of the clad tube decreases extremely. Upon a loss of coolant accident, the highest temperature of the clad tube must be restricted at all times under about 1,200.degree. C. The gap conductance corresponding to about 1,200.degree. C. of the highest temperature of the clad tube is about 0.5 W/cm.sup.2 .degree.C., as apparent from FIG. 8. It is apparent that an amount of interaction corresponding to the above gap conductance is about 0.001% from FIG. 9. Furthermore, the increase rate of the linear heat generating rate is about 0.15 KW/ft/hr. from FIG. 10, corresponding to the above amount of interaction. Accordingly, in order to satisfy the restricted value of the highest temperature of the clad tube upon the loss of coolant accident, as well as to prevent the failure of the fuel rods upon the loss of coolant accident, it is necessary to hold the increase rate of the linear heat generating rate above 0.15 KW/ft/hr. Referring to FIG. 11, a preferred embodiment of the invention will be described. Fuel assemblies formed from fuel rods as shown in FIG. 1 are disposed in pressure tubes 11 passing through a calandria tank 10 which contains the D.sub.2 O, heavy water moderator. A first coolant conduit 14 connects the pressure tubes 11, a steam generator 12 and a circulation pump 13. The D.sub.2 O coolant flows in the conduit 14 and serves for cooling the fuel assemblies. Light water is supplied to the stream generator 12 through the coolant conduit 14'. The light water vaporizes in the steam generator 12 and the resultant steam is sent to a turbine 16 through a steam conduit 15. The steam exhausted from the turbine 16 is condensed in a condenser 17 and the condensed water is again supplied to the steam generator 12 through the conduit 14. A pump 18 is disposed in the coolant conduit 14'. Liquid poison is intermixed with the D.sub.2 O in the calandria tank 10. The D.sub.2 O is circulated in a heavy water circulating conduit 19 of which both ends are connected to the calandria tank 10. Both ends of a conduit 20 coupled with a poison remover 21 are connected to the heavy water circulating conduit 19. A poison solution reservoir 22 is connected to the heavy water circulating conduit 19 through a valve 23. Valves 24 and 25 are disposed in the conduit 20 with the poison remover 21 being disposed therebetween. When the valves 24 and 25 are open, the D.sub.2 O is sent to the poison remover 21 and the liquid poison in the D.sub.2 O is removed. The removing of the liquid poison in the D.sub.2 O serves for increasing the reactor power and, when the valve 23 is open, the liquid poison is supplied from the poison reservoir 22 to the D.sub.2 O such that the reactor power decreases. Further, at least one neutron flux detector 26 is provided for measuring neutron flux in the core and the flux magnitude is transmitted to control equipment 27 for control purposes. The following description provides an example of the operation of the nuclear reactor shown in FIG. 11 for increasing the power of the reactor. The valve 23 is closed and the valves 24 and 25 are open to supply the D.sub.2 O to the poison remover 21. The liquid poison in the D.sub.2 O is removed and the reactor power increases. The neutron flux in the core of the nuclear reactor is detected by the neutron flux detector 26 and the measured values are transmitted to the control equipment 27 for calculating a linear heat generating rate P according to the measured values with the increase rate of the linear heat generating rate P being obtained based on momentary changes of the linear heat generating rate P. To the extent that the linear heat generating rate P is lower than P=8.0+0.5 P.sub.I, when the obtained increase rate P of the linear heat generating rate is over 0.15 KW/ft/hr., the condition is held. However, when the rate of increase is below 0.15 KW/ft/hr., the valve 24 is opened and an amount of D.sub.2 O flowing to the poison remover 21 increases with the removal of poison increasing so that the increase rate of the linear heat generating rate P is adjusted to be no less than 0.15 KW/ft/hr. In the extent of P.gtoreq.8.0+0.5 P.sub.I, the amount of D.sub.2 O flowing to the poison remover 21 is adjusted by the operation of the valve 24 so that the increase rate of the linear heat generating rate is maintained to be no less than 0.15 KW/ft/hr. and satisfies the formula: ##EQU6## The valve 24 is adjusted by the control equipment 27 such that, in a case of P.sub.I =0 and P<8.0, the increase rate of the linear heat generating rate is at least 0.15 KW/ft/hr. and, when P.gtoreq.8.0, the increase rate of the linear heat generating rate is at least 0.15 KW/ft/hr. and below P determined by the formula (6). According to the present invention, the failure of the fuel rods due to the PCI and a loss of coolant accident is prevented while the time required for increasing the reactor power to the predetermined power level can be shortened. Moreover, the present invention is applicable to a boiling water reactor (BWR), as well as a pressured water reactor (PWR). In a BWR, the increase rate of the linear heat generating rate can be adjusted in the predetermined extent by the control of an amount of coolant flowing to a core of the reactor, whereas in a PWR, the increase rate is adjusted in the predetermined extent by the control of the consistency of liquid poison included in the coolant. |
054085080 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Referring now to the drawings, and particularly to FIG. 1, there is shown a typical nuclear power reactor vessel, generally referred to as 10, for producing heat by a controlled fission of a fissionable material (not shown). The reactor vessel 10 is disposed in a reactor cavity 12 defined by a containment building 14. The reactor vessel 10 includes a cylindrical shaped bottom 20 open at its top end and having a plurality of inlet nozzles 30 and outlet nozzles 40 attached to the upper portion thereof (only one of each nozzle is shown). A flanged, hemispherical shaped reactor vessel closure head 50, which may be carbon steel, is mounted atop the bottom 20 and is sealingly attached to the open top end of the bottom 20 so that the closure head 50 sealingly caps the bottom 20. Capping the bottom 20 in this manner allows for suitable pressurization of the coolant (not shown) circulating through the bottom 20 as the reactor vessel 10 operates. The coolant may be borated demineralized water maintained at a relatively high pressure of approximately 2500 psia and a temperature of approximately 650 degrees Fahrenheit. A reactor core 55 is disposed in the interior of the reactor vessel 10. The reactor core 55 comprises a plurality of nuclear fuel assemblies 57 containing the fissionable material. The fuel assemblies 57 include a plurality of vertically extending fuel rods (not shown) structurally bound together. A plurality of vertically extending thimble tubes (not shown) are selectively positioned within each fuel assembly 57 for receiving a control rod which functions to control the fissionable process. The thimble tubes are structurally bound together by a spider assembly forming a movable control rod cluster (not shown in FIG. 1). A plurality of closure head openings 60 are formed through the top of closure head 50 for respectively receiving a plurality of generally tubular shaped control rod drive mechanism (CRDM) penetration tubes 70. Each penetration tube 70 is affixed to the closure head 50 by weldments 77. Each CRDM penetration tube 70 houses a control rod drive shaft (not shown) extending therethrough; the drive shaft engaging at least one movable control rod cluster. A control rod drive mechanism (CRDM) 90 is connected to the penetration tube 70 for axially moving a drive rod 80 and thus the control rod cluster connected thereto. The CRDM comprises a generally tubular pressure housing 100, which may be type 304 stainless steel. An electromagnetic coil stack assembly 110 is attached to the pressure housing 100 for electromagnetically and axially moving the drive rod 80 as the coil stack assembly 110 is electrically energized. When the coil stack assemblies 110 are energized, the control rods are fully withdrawn from the core 55. When the coil stack assemblies 110 are deenergized, the control rods are fully inserted into the core 55. A rod position indicator (RPI) 120 is attached to the coil stack assembly 110 for monitoring the position of the control rods, as is well known in the art. As the reactor vessel 10 operates, the coolant enters the bottom 20 and circulates therethrough generally in the direction of the arrows. As the coolant circulates through the bottom 20, it also circulates over the fuel assemblies 57 for assisting in the fission process and for removing the heat produced by fission of the fissionable material contained in the fuel assemblies 57. The coil stack assemblies 110 axially move the control rod clusters in and out of fuel assemblies 57 to suitably control the fission process therein. The heat generated by the fuel assemblies 57 is ultimately transferred to a turbine-generator set for producing electricity in a manner well known in the art. Referring to FIG. 2, there is illustrated a system for testing the control rod clusters 125 in an analog rod position indication system. The coil stack assemblies 110 which drive the control rod clusters 125 are each connected to a power cabinet 130 via cables 140. The power cabinet 130 is located outside the containment building 14 and is the control device which selectively energizes predetermined coil stack assemblies 110 which, in turn, causes the associated control rod cluster to either be withdrawn or inserted into the reactor core 55. A switchgear panel 150 is connected via a bus 155 to the power cabinet 130 and contains a breaker (not shown) which interrupts the electrical power to the coil stack assemblies 110. The switch-gear panel 150 is connected to a power source (not shown) and supplies power to the power cabinet 130 and, eventually, the coil stack assemblies 110 when required. The electrical power to the coil stack assemblies 110 is typically energized or de-energized by respectively closing or opening the breaker by an operator, who may physically manipulate the breaker or remotely manipulate the breaker from a control room 175 as is well known in the art. To monitor the position of the control rod clusters 125, the RPI 120 is connected via signal cables 165 to an analog rod position indication system 160 (ARPI system) which functions with the RPI 120 for monitoring the position of the control rod clusters 125, as is well known in the art. Typical plant specifications require that all control rod clusters 125 be tested by fully withdrawing all the control rod clusters and then fully inserting them, by gravity, into the reactor vessel 55 prior to returning to power after a nuclear plant refueling. This requirement ensures that the refueling process has not affected their freedom of movement. To test the control rod clusters 125, a personal computer (PC) 170 is connected to both the ARPI system 160, via cables 180, and to the switchgear panel 150, via a cable 190. The PC 170 provides the operator interface and displays the results of the test on a display screen (not shown). The PC 170 contains input/output cards 175 for receiving signals from the ARPI system 160 and for performing functions such as filtering, analog to digital conversion, and memory storage of signals sent by the ARPI system 160. The memory storage of the PC 170 includes dedicated memory for each control rod cluster 125; the dedicated memory stores the entire drop time of each control rod cluster 125, typically less than 4 seconds. The input/output cards 175 are those such as model number PR-ADC1 which are commercially available from Elexor Associates, Inc. in Morris Plains, N.J. The PC 170 is attached to an electrical (normally closed) contact 195, although a normally open contact could also be used, which changes state (to the open position) when the reactor trip breaker inside the switchgear panel 150 is tripped or opened. To start the test, the coil stack assemblies 110 are sequentially energized in a predetermined fashion by the plant operator as previously described, which causes all the control rod clusters 125 to be fully withdrawn. Although all the control rod clusters 125 are tested in this embodiment, the present invention can test one or any combination of the control rod clusters 125 by selectively energizing the predetermined control rod cluster or clusters 125. The reactor trip breaker is then tripped by the operator located in control room 185 which, in turn, causes all the control rod clusters 125 to fall by gravity into the core 55. Simultaneously with the breaker tripping, the contact 195 opens which signals the PC 170 to start data collection. The ARPI system 160 transmits an analog signal representing the drop time of each control rod cluster over the cables 180 to the input/output cards 175 which condition and digitize the received signal. The PC 170 then generates the elapsed time profile of all the control rods 125 falling from the fully withdrawn position to the bottom of the core 55, hereinafter referred to as the elapsed time profile. Each control rod cluster profile may then be individually displayed on the screen for visual inspection. It is instructive to understand that the elapsed time profile is typically divided into two parts for analysis by test personnel for problems with the control rod clusters. This two part analysis is well known in the art, but was previously accomplished by visual approximations of a visicorder graph. The first part is a dashpot entry time which is the time between a control rod falling from the fully withdrawn position to time of entry of the control rod into the coolant. The second part is a turn-around time which is the time between the initial dropping of the control rod to the time the control rod hits the bottom of the core 55 (i.e., total drop time). The PC 170 includes software, which is obtainable from Westinghouse Electric Corp. in O'Hara Township, PA, that generates both the dashpot entry time and turnaround time. A flowchart of the software is shown in FIG. 3, which is better understood when taken in conjunction with the graph it generates, FIG. 4. The abscissa of FIG. 4 is the time it takes for a control rod cluster to fall into the core, and the ordinate of FIG. 4 is the voltage taken from ARPI system 160. The elapsed time profile is displayed in one millisecond intervals for enabling operators to better determine the cause of obstructions, if any. To calculate the dashpot entry time, the PC 170 starts at one half of the maximum amplitude value (A) of the profile (block 177) and scans the generated plot, going in a direction towards a maximum amplitude value (B) by looking at each adjacent point, for a first slope of negative 45 degrees, blocks 178 and 179. If that point is within 5 percent of the maximum amplitude value, block 181, the dashpot entry time is determined from the ordinate at this point, block 183. If it is not within 5 percent, the program continues to scan the generated plot from that point, going in a direction along the generated plot towards the maximum amplitude value (B) by looking at each adjacent point, for a slope of negative 26 degrees, blocks 178 and 179. If it is within 5 percent, block 181, the dashpot entry time is determined from the ordinate at this point, block 183. If it is not within 5 percent, the program then repeats this same process for the negative 14 degree point, blocks 178 and 179, and negative 7 degree point, blocks 178 and 179, so as to reach a point within 5 percent of the maximum value point. On each reiteration, the program checks for its next predetermined slope between the previous checked slope and the maximum amplitude value (B). After the dashpot entry time is determined, the turnaround time is determined by taking the time between the dashpot entry time, as determined above, and the time the control rods hit the bottom of the core, which is represented by the point where the graph crosses the ordinate (C). Referring to FIG. 5, to test the control rod clusters 125 in a digital rod position indicator system, additional components are added to the system. A conditioning chassis 210 is added to a digital rod position indication system 200 (DRPI system) and is connected internally to the appropriate control rod data collection points within the DRPI system 200. The signal conditioning chassis 210 includes the input/output cards 175 which perform filtering, analog to digital conversion and memory storage for the DRPI system 200 signals. The input/output cards 175 are the same input/output cards 175 as used in the analog system. The signal conditioning chassis 210 also includes a network card 215 to allow the input/output cards 175 and the PC 170, located remotely outside of the reactor containment building 14, to communicate with each other as is well known in the art. To test the control rod clusters 125, the system is initiated as stated above and repeated here for clarity. The coil stack assemblies 120 are sequentially energized by the plant operator which causes all the control rod clusters 125 to be fully withdrawn. The reactor trip breaker is then tripped by the operator located in control room 185, which causes all the control rod clusters 125 to fall, by gravity, into the core 55. Simultaneously with the breaker tripping, the contact 195 opens which signals the signal conditioning chassis 210 to start data collection. The elapsed time profile for each control rod cluster 125 is stored in memory on the input/output cards 175. At the completion of the control rod cluster 125 drops, the signal conditioning chassis 210 transmits the digitized data to the PC 170 where they are displayed one cluster at a time on the PC 170 screen. The elapsed time profile is printed and the data is written to the hard disk drive of the PC 170 as a file. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described merely a preferred or exemplary embodiment thereof. |
047284897 | claims | 1. In a fuel element support grid for supporting a plurality of nuclear fuel elements intermediate their ends in spaced relation for fluid flow therebetween, said grid including a polygonal perimeter and a plurality of fuel element compartments defined by pairs of first and second intersecting and slottedly interlocked grid-forming strips attached to said perimeter and to each other, the improvement comprising: at least some of said compartments defined by two pairs of intersecting and slottedly interlocked strips and said compartments each including two pairs of intersecting and welded together integral fluid flow directing vanes along adjacent edges of each of the strips of the two pairs with each of the adjacent integral fluid flow directing vanes curved from the planes of their respective strips and intersecting with the adjacent vane of an intersecting strip to form a substantially continuous smooth surface. 2. The fuel element support grid of claim 1 in which all of the integral fluid flow directing vanes are on the downstream edges of the strips relative to the direction of fluid flow between the fuel elements and in which the edges of a plurality of pairs of the integral fluid flow directing vanes remote from the areas of integral attachment of the vanes to their respective strips define a substantially sinusoidal curve. 3. The fuel element support grid of claim 1 in which the strips and integral fluid flow directing vanes are of stamped zircaloy. 4. The fuel element support grid of claim 1 in which the welds are at the points of intersections of the edges of a plurality of pairs of the integral fluid flow directing vanes most remote from the areas of integral attachment of the vanes to their respective strips. 5. The fuel element support grid of claim 1 in which the welds are at the intersections of the edges of a plurality of pairs of the integral fluid flow directing vanes adjacent to the areas of integral attachment of the vanes to their respective strips. 6. The fuel element support grid of claim 1 in which the welds are at the intersections of the edges of a plurality of pairs of the integral fluid flow directing vanes both remote from and adjacent to the areas of integral attachment of the vanes to their respective strips. |
claims | 1. A grid for a nuclear fuel rod assembly, the grid comprising:a plurality of perpendicularly flat plates, the flat plates forming substantially square cells;a plurality of deflectors formed integrally with the flat plates, wherein each deflector is oriented at an angle to a longitudinal axis of the grid, and wherein each cell has at least two opposing deflectors;each cell having an insertable spacer having a substantially octagonal shape that is [s]ymmetric about a center axis of the cell, the insertable spacer having a constant height along its perimeter, and a uniform cross-section along its height, the insertable spacer having a closed contour in a cross-sectional view, the insertable spacer formed of four convex surfaces and four concave surfaces, the four concave surfaces being in contact with the corresponding flat plates, and the four convex surfaces each having a flat portion for fixing a corresponding fuel rod and which is flat prior to insertion of the fuel rods,wherein opposite longitudinal surfaces of the insertable spacer are parallel to each other. 2. The spacing grid of claim 1, wherein a length of each cell is between 28 and 34 mm. 3. The spacing grid of claim 1, wherein a length of the spacer is between 0.3 and 0.9 of a length of each cell. 4. The spacing grid of claim 1, wherein the spacer is formed as a unitary element. 5. The spacing grid of claim 1, wherein the spacer has no openings along its body. 6. The grid of claim 1, wherein each concave surface has a flat portion in contact with a corresponding flat plate. 7. The grid of claim 1, wherein the insertable spacers are formed as tubular elements with a substantially octagonal cross-section. |
|
description | The present invention relates to a nuclear reactor including a core. More specifically, the present invention relates to a cooling structure of a core. In pressurized water reactors (PWRs), light water is used as nuclear reactor coolant and neutron moderator, serves as high-temperature and high-pressure water that does not boil in the entire primary system. The high-temperature and high-pressure water is sent to a steam generator by which steam is generated by heat exchange, and the steam is then sent to a turbine generator to produce electricity. In such pressurized water reactors, the core is cooled by introducing coolant into the nuclear reactor from outside, and circulating the coolant. In other words, the coolant flows in through a plurality of coolant inlet nozzles formed on a reactor vessel, flows down a downcomer portion provided between the reactor vessel and a core barrel, and reaches a lower plenum. The coolant then flows upward by being guided by the inner spherical surface of the lower plenum in the upper direction, passes through a lower core plate and the like, and flows into the core. The coolant flowing into the core absorbs thermal energy generated by fuel assemblies that form the core, thereby cooling the fuel assemblies. The temperature of the coolant becomes high, then the coolant flows upward to an upper plenum, and is discharged through a coolant outlet nozzle formed on the reactor vessel. In such pressurized water reactors, the lower plenum includes structures such as a radial key that supports the core barrel and an in-core instrumentation guide tube for inserting test equipment into the fuel assemblies. Accordingly, the coolant supplied to the lower plenum through the downcomer portion collides with the structures and is dispersed. Consequently, the flow rate distribution of the coolant in the radial direction and the circumferential direction of the core is not uniform. Therefore, for example, Patent Document 1 discloses a method of providing a connection plate to straighten the flow of coolant in the lower plenum. In the core structure of a nuclear reactor disclosed in Patent Document 1, the lower plenum includes a connection plate whose outer peripheral shape is asymmetric to the main flowing direction of the coolant. Accordingly, it is possible to prevent the generation and formation of separation vortices. Because the coolant uniformly flows into the core, the pressure drop of the coolant flow can be reduced, thereby stabilizing the coolant flow. [Patent Document 1] Japanese Patent Application Laid-open No. 2005-009999 The streams of coolant flowing in through the coolant inlet nozzles flow downward while merging in the downcomer portion. When the coolant flow is changed upward in the lower plenum by the inner shape thereof, the connection plate prevents the generation of large vortices. However, vortices are often formed after passing through the connection plate and by the connection plate. Accordingly, it is difficult to produce uniform coolant flow in the radial direction and the circumferential direction of the core. The present invention has been made to solve the problems above and intended to provide a nuclear reactor that can enhance heat exchange efficiency, by uniformly supplying coolant introduced into the pressure vessel to the core from the lower plenum in the radial direction and the circumferential direction. According to an aspect of the present invention, a nuclear reactor includes: a pressure vessel that includes a coolant inlet nozzle and a coolant outlet nozzle at an upper portion thereof; a core barrel being disposed in the pressure vessel; a core being disposed in the core barrel; a lower plenum being partitioned by the pressure vessel and a bottom portion of the core barrel; and a downcomer portion being partitioned by the pressure vessel and a side wall of the core barrel, and being connected to the coolant inlet nozzle and the lower plenum. The lower plenum includes a straightener member including a straightening ring in a ring shape and a plurality of straightening spokes radially arranged inside the straightening ring. Advantageously, in the nuclear reactor, the straightening ring includes an upper ring and a lower ring, and is supported by a plurality of columns suspended from a lower core plate. Advantageously, in the nuclear reactor, the straightening ring includes an outer ring and an inner ring, and is supported by a plurality of columns suspended from a lower core plate, and the plurality of straightening spokes is disposed between the outer ring and the inner ring. Advantageously, in the nuclear reactor, an intermediate ring intersecting with the straightening spokes is provided between the outer ring and the inner ring. Advantageously, in the nuclear reactor, an outer diameter of the upper ring is set larger than an outer diameter of the lower ring. Advantageously, in the nuclear reactor, the straightening spokes arranged in the upper ring and the straightening spokes arranged in the lower ring are disposed to be misalign in a circumferential direction. Advantageously, the nuclear reactor further includes a straightening auxiliary member arranged towards an inner surface of a reactor vessel from an outer peripheral portion of the straightening ring. Advantageously, in the nuclear reactor, the straightening auxiliary member is in a ring shape and supported by the outer peripheral portion of the straightening ring with a plurality of connection members. Advantageously, in the nuclear reactor, an upper surface of the straightening ring is placed higher than an upper surface of the straightening auxiliary member. Advantageously, the nuclear reactor further includes a wall member on an upper surface of the outer peripheral portion of the straightening ring. Advantageously, in the nuclear reactor further includes a vortex elimination member having a larger outer diameter than that of the straightening ring or a width of the straightening spokes, on the straightening ring or the straightening spokes in a vertical direction. Advantageously, in the nuclear reactor, the straightening ring or the straightening spokes is (are) supported by a plurality of columns suspended from a lower core plate, and a vortex elimination member in a ring shape is provided on an outer peripheral portion of the columns. Advantageously, the nuclear reactor further includes a vortex elimination member on a side of each of the straightening spokes in a lengthwise direction of the straightening spokes. Advantageously, the nuclear reactor further includes an upper core plate in an upper portion of the core barrel in the pressure vessel, and an instrumentation guide tube penetrated through the upper core plate from the upper portion of the pressure vessel. In a nuclear reactor according to claim 1, a core barrel is disposed in a pressure vessel that includes a coolant inlet nozzle and a coolant outlet nozzle, a core is disposed in the core barrel, a lower plenum is partitioned by the pressure vessel and a bottom portion of the core barrel, and a downcomer portion is partitioned by the pressure vessel and a side wall of the core barrel. The lower plenum includes a straightener member formed of a straightening ring in a ring shape and a plurality of straightening spokes radially arranged inside the straightening ring. When coolant introduced into the pressure vessel flows down the downcomer portion, reaches the lower plenum, reversed in the lower plenum, and flows upward, the flow of coolant is dispersed by the straightening ring and the straightening spokes, thereby preventing the generation of large vortices. Because the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core, it is possible to enhance heat exchange efficiency. In a nuclear reactor according to claim 2, the straightening ring includes an upper ring and a lower ring, and is supported by a plurality of columns suspended from a lower core plate. The coolant that flows down the downcomer portion, reversed in the lower plenum, and flows upward, is dispersed by the columns in addition to the upper ring, the lower ring, and the straightening spokes, thereby preventing the generation of large vortices. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 3, the straightening ring includes an outer ring and an inner ring, and is supported by a plurality of columns suspended from a lower core plate, and a plurality of straightening spokes is provided between the outer ring and the inner ring. The coolant that flows down the downcomer portion, reversed in the lower plenum, and flows upward, is dispersed by the columns in addition to the outer ring, the inner ring, and the straightening spokes, thereby preventing the generation of large vortices. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 4, an intermediate ring is arranged between the outer ring and the inner ring, and the intermediate ring intersects with the straightening spokes. The coolant that flows down the downcomer portion, reversed in the lower plenum, and flows upward, is dispersed by the intermediate ring in addition to the outer ring, the inner ring, and the straightening spokes, thereby preventing the generation of large vortices. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 5, the outer diameter of the upper ring is set larger than the outer diameter of the lower ring. Because the flow area of the coolant flowing in the core is reduced, the coolant that flows down the downcomer portion, reversed in the lower plenum, and flows upward, is dispersed without fail, thereby preventing the generation of large vortices. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 6, the straightening spokes arranged in the upper ring and the straightening spokes arranged in the lower ring are disposed shifted in a circumferential direction. The coolant that flows down the downcomer portion, reversed in the lower plenum, and flows upward, is dispersed without fail, thereby preventing the generation of large vortices. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 7, a straightening auxiliary member is arranged towards an inner surface of a reactor vessel from an outer peripheral portion of the straightening ring. The coolant that flows down the downcomer portion and flows into the lower plenum is dispersed by the straightening auxiliary member, thereby preventing the generation of large vortices in the lower plenum. In a nuclear reactor according to claim 8, the straightening auxiliary member is in a ring shape and supported by the outer peripheral portion of the straightening ring with a plurality of connection members. By properly arranging the straightening auxiliary member between the outer peripheral portion of the straightening ring and the inner surface of the reactor vessel, the coolant that flows down the downcomer portion and flows into the lower plenum is dispersed by the straightening auxiliary member, using a simple structure, thereby preventing the generation of large vortices in the lower plenum. In a nuclear reactor according to claim 9, an upper surface of the straightening ring is placed higher than an upper surface of the straightening auxiliary member. The coolant that flows down the downcomer portion and flows into the lower plenum is dispersed by the straightening auxiliary member, guided by an outer peripheral surface of the straightening auxiliary member, and straightened as the flow in the circumferential direction, thereby preventing the generation of large vortices in the lower plenum. In a nuclear reactor according to claim 10, a wall member is arranged on an upper surface of the outer peripheral portion of the straightening ring. The coolant that flows down the downcomer portion and flows into the lower plenum is dispersed by the straightening auxiliary member, guided by the wall member, and straightened as the flow in the circumferential direction, thereby preventing the generation of large vortices in the lower plenum. In a nuclear reactor according to claim 11, a vortex elimination member having the outer diameter larger than that of the straightening ring or the width of the straightening spokes, is arranged on the straightening ring or the straightening spokes in a vertical direction. The vortices that have not been straightened by the straightening ring or the straightening spokes are straightened by the vortex elimination member. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 12, the straightening ring or the straightening spokes is (are) supported by a plurality of columns suspended from a lower core plate, and a vortex elimination member in a ring shape is provided on an outer peripheral portion of the columns. Accordingly, the vortices that have not been straightened by the straightening ring or the straightening spokes are straightened by the vortex elimination member. Consequently, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according claim 13, a vortex elimination member is arranged on a side of each of the straightening spokes in a lengthwise direction of the straightening spokes. The vortices that have not been straightened by the straightening ring or the straightening spokes are straightened by the vortex elimination member. Accordingly, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. In a nuclear reactor according to claim 14, an upper core plate is arranged in an upper portion of the core barrel in the pressure vessel, and an instrumentation guide tube is penetrated through the upper core plate from the upper portion of the pressure vessel. Accordingly, the lower plenum does not require columns and the like that support the instrumentation guide tube, and by optimizing the shape of the straightening ring and the straightening spokes, the generation of large vortices is appropriately prevented. Consequently, the flow rate of the coolant supplied to the core is uniformly straightened in the radial direction and the circumferential direction of the core. 12 pressurized water reactor 41 reactor vessel (pressure vessel) 44 inlet nozzle (coolant inlet nozzle) 45 outlet nozzle (coolant outlet nozzle) 46 core barrel 53 core 56 in-core instrumentation guide tube 57 upper plenum 58 lower plenum 59 downcomer portion 61, 71, 81, 91, 111, 121, 131, 141 straightener member 62, 92, 142 upper outer ring 63, 93 upper inner ring 64, 94, 144 upper spoke (straightening spoke) 65, 95, 145 upper ring (straightening ring) 66, 96 lower outer ring 67, 97 lower inner ring 68, 98 lower spoke (straightening spoke) 69, 99 lower ring (straightening ring) 70, 72, 73, 84, 101, 102, 103, 104, 148, 148 column 82, 83, 100 intermediate ring 112 auxiliary ring (straightening auxiliary member) 115 wall member 122 column (vortex elimination member) 132 vortex elimination ring (vortex elimination member) 146 vortex elimination pipe (vortex elimination member) Exemplary embodiments of a nuclear reactor according to the present embodiment will be described in detail with reference to the accompanying drawings. However, the present invention is not limited by the embodiments. [First Embodiment] FIG. 1 is a schematic of an internal configuration of a pressurized water reactor according to a first embodiment of the present invention. FIG. 2 is a sectional view taken along the line II-II in FIG. 1. FIG. 3 is a sectional view taken along the line III-III in FIG. 1. FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1. FIG. 5 is a schematic of a nuclear power plant that includes the pressurized water reactor according to the first embodiment. A nuclear reactor according to the first embodiment is a pressurized water reactor (PWR) that uses light water as nuclear reactor coolant and neutron moderator, as high-temperature and high-pressure water that does not boil in the entire core. The nuclear reactor sends the high-temperature and high-pressure water to a steam generator by which steam is generated by heat exchange, and sends the steam to a turbine generator to produce electricity. In a nuclear power plant that includes the pressurized water reactor according to the present embodiment, as shown in FIG. 5, a reactor containment vessel 11 includes a pressurized water reactor 12 and a steam generator 13. The pressurized water reactor 12 and the steam generator 13 are connected by coolant tubes 14 and 15. The coolant tube 14 has a pressurizer 16 and the coolant tube 15 has a coolant pump 15a. In this case, light water is used as moderator and primary coolant, and to prevent the primary coolant from boiling in a core portion, the primary coolant system is controlled so that the high-pressure state from about 150 atmospheres to about 160 atmospheres is maintained by the pressurizer 16. Consequently, in the pressurized water reactor 12, the light water as primary coolant is heated by using fuel such as low-enriched uranium or mixed oxide fuel (MOX), and the high-temperature primary coolant is sent to the steam generator 13 through the coolant tube 14, in a state in which the pressure is maintained at a certain high level by the pressurizer 16. In the steam generator 13, heat is exchanged between the high-pressure and high-temperature primary coolant and secondary coolant, and the cooled primary coolant is returned to the pressurized water reactor 12 through the coolant tube 15. The steam generator 13 is connected to a steam turbine 17 through a coolant tube 18. The steam turbine 17 includes a high-pressure turbine 19 and a low-pressure turbine 20, and to which a generator 21 is connected. A moisture separation heater 22 is provided between the high-pressure turbine 19 and the low-pressure turbine 20, and a coolant branch tube 23 branched from the coolant tube 18 is connected to the moisture separation heater 22. The high-pressure turbine 19 and the moisture separation heater 22 are connected by a low-temperature reheat tube 24, and the moisture separation heater 22 and the low-pressure turbine 20 are connected by a high-temperature reheat tube 25. The low-pressure turbine 20 of the steam turbine 17 includes a condenser 26, and a water intake tube 27 and a water drain tube 28 that supply and drain coolant (such as sea water) are connected to the condenser 26. A deaerator 30 is connected to the condenser 26 through a coolant tube 29, and the coolant tube 29 has a condenser pump 31 and a low-pressure feed water heater 32. The deaerator 30 is connected to the steam generator 13 through a coolant tube 33, and the coolant tube 33 has a feed water pump 34 and a high-pressure feed water heater 35. Accordingly, the steam generated by exchanging heat with the high-pressure and high-temperature primary coolant in the steam generator 13 is sent to the steam turbine 17 through the coolant tube 18 (from the high-pressure turbine 19 to the low-pressure turbine 20). The steam is used to drive the steam turbine 17, and the generator 21 generates electricity. At this time, the steam from the steam generator 13 drives the high-pressure turbine 19, and then drives the low-pressure turbine 20, after the moisture included in the steam is removed and being heated by the moisture separation heater 22. The steam that drives the steam turbine 17 is cooled by the condenser 26, and becomes condensate. In the low-pressure feed water heater 32, for example, the condensate is heated by low-pressure steam bled from the low-pressure turbine 20. After impurities such as dissolved oxygen and non-condensable gas (ammonia gas) are removed by the deaerator 30, in the high-pressure feed water heater 35, for example, the condensate is heated by high-pressure steam bled from the high-pressure turbine 19, and is returned to the steam generator 13. In the pressurized water reactor 12, as shown in FIGS. 1 to 4, a reactor vessel (pressure vessel) 41 includes a reactor vessel main body 42 and a reactor vessel cover 43 mounted on the upper portion of the reactor vessel main body 42, so that core internals can be inserted inside the reactor vessel 41. The reactor vessel cover 43 can be opened and closed relative to the reactor vessel main body 42. The reactor vessel main body 42 has a cylindrical shape, in which an upper portion is opened and a lower portion is closed in a spherical shape, and an inlet nozzle 44 and an outlet nozzle 45 for supplying and draining light water (coolant) as primary coolant are formed on the upper portion. As shown in detail in FIG. 2, four inlet nozzles 44 are formed on the upper portion of the reactor vessel main body 42. The four inlet nozzles 44 are arranged at a predetermined angle A relative to the 90-270 degree center line, and symmetrically arranged relative to the 0-180 degree center line. Four outlet nozzles 45 are formed thereon, and arranged at a predetermined angle B relative to the 0-180 degree center line, and symmetrically arranged relative to the 90-270 degree center line. In the reactor vessel main body 42, a core barrel 46 having a cylindrical shape is arranged below the inlet nozzles 44 and the outlet nozzles 45, with a predetermined space from an inner surface of the reactor vessel main body 42. At the upper portion of the core barrel 46, an upper core plate 47 in a disk shape to which a plurality of communication holes, which is not shown, is formed is connected. Similarly, at the lower portion of the core barrel 46, a lower core plate 48 in a disk shape to which a plurality of communication holes, which is not shown, is formed is connected. In the reactor vessel main body 42, an upper core support plate 49 in a disk shape is fixed above the core barrel 46. The upper core plate 47, in other words, the core barrel 46, is supportedly suspended from the upper core support plate 49 by a plurality of core support rods 50. A lower core support plate 51 in a disk shape is also fixed to the lower portion of the core barrel 46. The position of the lower core support plate 51, in other words, the core barrel 46, is determined and maintained by a plurality of radial keys 52 relative to the inner surface of the reactor vessel main body 42. A plurality of communication holes, which is not shown, is also formed on the lower core support plate 51. As shown in detail in FIG. 3, six radial keys 52 are formed and arranged every 60 degrees relative to the 0 degree center line. A core 53 is formed by the core barrel 46, the upper core plate 47, and the lower core plate 48. A large number of fuel assemblies 54 is arranged in the core 53. Each of the fuel assemblies 54, although not shown, includes a large number of fuel rods bundled in grid pattern by a support grid, and an upper nozzle is fixed to the upper end, and a lower nozzle is fixed to the lower end. In addition to the fuel rods, the fuel assembly 54 includes a control rod guide tube through which a control rod is inserted, and an in-core instrumentation guide tube through which an in-core instrumentation detector is inserted. A large number of control rod cluster guide tubes 55 is supported by the upper core support plate 49 by penetrating therethrough. A control rod cluster drive shaft extended from a control rod drive device, which is not shown, mounted on the reactor vessel cover 43 is extended to the fuel assembly 54 through each of the control rod cluster guide tubes 55, and a control rod is fixed to the lower end. A large number of in-core instrumentation guide tubes 56 is supported by the upper core support plate 49 by penetrating therethrough, and the lower end is extended to the fuel assemblies 54. Accordingly, because the control rod drive device moves the control rod cluster drive shaft and inserts the control rod into the fuel assembly 54, it is possible to control nuclear fission in the core 53. The light water filled inside the reactor vessel 41 is heated by the generated thermal energy, the hot light water is drained through the outlet nozzles 45, and as described above, sent to the steam generator 13. In other words, neutrons are released by nuclear fission of uranium or plutonium used as a fuel of the fuel assemblies 54, and the light water as moderator and primary coolant reduces the kinetic energy of the released fast neutrons, and turns them into thermal neutrons. Accordingly, new fissions are likely to occur, and the light water is cooled by absorbing the generated heat. The number of neutrons generated in the core 53 is adjusted by inserting the control rod into the fuel assembly 54, and the control rod is quickly inserted into the core 53 to stop the nuclear reactor urgently. In the reactor vessel 41, an upper plenum 57 connected to the outlet nozzle 45 is formed above the core 53, and a lower plenum 58 is formed below the core 53. A downcomer portion 59 that connects the inlet nozzle 44 and the lower plenum 58 is formed between the reactor vessel 41 and the core barrel 46. In other words, the upper plenum 57 is partitioned and formed by the core barrel 46, the upper core support plate 49, and the upper core plate 47. The upper plenum 57 is also connected to the outlet nozzle 45, and connected to the core 53 through a large number of communication holes formed on the upper core plate 47. The lower plenum 58 is partitioned and formed by the lower core support plate 51 that is a bottom portion of the core barrel 46 and the reactor vessel main body 42. The lower plenum 58 is also connected to the core 53 through a large number of communication holes formed on the lower core support plate 51 and the lower core plate 48. The downcomer portion 59 is partitioned and formed by the reactor vessel main body 42 and the side wall of the core barrel 46. The upper portion of the downcomer portion 59 is connected to the inlet nozzle 44 and the lower portion of the downcomer portion 59 is connected to the lower plenum 57. Accordingly, the light water flows into the reactor vessel main body 42 through the four inlet nozzles 44, flows down the downcomer portion 59, and reaches the lower plenum 58. The light water then flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, passes through the lower core support plate 51 and the lower core plate 48, and flows into the core 53. The light water flowing into the core 53 cools the fuel assemblies 54, by absorbing thermal energy generated by the fuel assemblies 54 that form the core 53. The temperature of the light water becomes high, then the coolant passes through the upper core plate 47, flows upward to the upper plenum 57, and discharged through the outlet nozzles 45. In the present embodiment, as shown in detail in FIGS. 1 and 4, the lower plenum 58 includes a straightener member 61 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59, and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 61 includes an upper ring (straightening ring) 65 in which an upper outer ring 62 and an upper inner ring 63 in a ring shape are connected by a plurality (six in the present embodiment) of upper spokes (straightening spokes) 64 radially arranged therebetween. The straightener member 61 also includes a lower ring (straightening ring) 69 in which a lower outer ring 66 and a lower inner ring 67 in a ring shape are connected by a plurality (six in the present embodiment) of lower spokes (straightening spokes) 68 radially arranged therebetween. The lower portions of a plurality (six in the present embodiment) of columns 70 suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring 66. Accordingly, the upper ring 65 and the lower ring 69 are arranged in a predetermined position in the lower plenum 58. In this case, the spokes 64 and 68 are arranged in the circumference direction of the rings 65 and 69, respectively, at regular intervals. One spoke is arranged between the adjacent two inlet nozzles 44, and two spokes are arranged between the separated two inlet nozzles 44. The columns 70 are arranged at the same positions as those of the spokes 64 and 68, in the circumferential direction of the outer rings 62 and 66. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 61, and flows into the core 53. At this time, the light water flowing into the reactor vessel main body 42 through the inlet nozzles 44, collides with the core barrel 46, and is dispersed in the circumferential direction. The light water then merges with the light water flowing in through the adjacent inlet nozzles 44, flows down the downcomer portion 59, and reaches the lower plenum 58. In other words, most of light water that flows down the downcomer portion 59 and flows into the lower plenum 58, flows down along the 0-90-180-270 degree center lines. Consequently, when the light water flows upward by the inner spherical surface of the lower plenum 58, the light water collides with the straightener member 61, in other words, the rings 62, 63, 66, and 67, the spokes 64 and 68, and the columns 70, and is dispersed, thereby preventing the generation of large vortices. Accordingly, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. Particularly, the light water that flows down along the 90-270 degree center line in the downcomer portion 59, collides with the spokes 64 and 68, and the columns 70 of the straightener member 61, and is dispersed in the circumferential direction. The flow of light water that flows down along the 0-180 degree center line in the downcomer portion 59 is widened in the circumferential direction. Because the light water is likely to collide with the spokes 64 and 68, and the columns 70 of the straightener member 61, and is dispersed in the circumferential direction, the generation of large vortices is appropriately prevented. In this manner, in the nuclear reactor according to the first embodiment, the core barrel 46 is arranged in the reactor vessel 41 including the inlet nozzles 44 and the outlet nozzles 45, and the core 53 is arranged in the core barrel 46. The lower plenum 58 is partitioned by the reactor vessel 41 and the bottom portion of the core barrel 46, and the downcomer portion 59 is partitioned by the reactor vessel 41 and the side wall of the core barrel 46. The lower plenum 58 includes the straightener member 61 formed of the upper ring 65 and the lower ring 69 in a ring shape and the spokes 64 and 68 radially arranged in the rings 65 and 69, respectively. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the rings 62, 63, 66, and 67, the spokes 64 and 68, and the columns 70, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. In the nuclear reactor according to the first embodiment, the straightener member 61 includes the upper ring 65 and the lower ring 69, and the rings 65 and 69 include the outer rings 62 and 66, and the inner rings 63 and 67, respectively. The spokes 64 and 68 are arranged between the outer rings 62 and 66, and the inner rings 63 and 67, respectively. The straightener member 61 is supported by the columns 70 suspended from the lower core support plate 51. Accordingly, the light water that flows down the downcomer portion 59, reversed in the lower plenum 58, and flows upward, is dispersed, by the rings 62, 63, 66, and 67, the spokes 64 and 68, and the columns 70. As a result, it is possible to prevent the generation of large vortices without fail. [Second Embodiment] FIG. 6 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a second embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the second embodiment, as shown in FIGS. 1 and 6, the lower plenum 58 includes a straightener member 71 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59, and flows upward to the core 53 in the circumferential direction and the radial direction of the core 53. The straightener member 71 includes the upper ring 65 in which the upper outer ring 62 and the upper inner ring 63 are connected by the six upper spokes 64, and the lower ring 69 in which the lower outer ring 66 and the lower inner ring 67 are connected by the six lower spokes 68. The lower portions of a plurality of columns 72 (12 in the present embodiment) suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring 66, and the lower portions of a plurality of columns 73 (six in the present embodiment) suspended from the lower core support plate 51 are connected to the upper spokes 64 and the lower spokes 68. Accordingly, the upper ring 65 and the lower ring 69 are arranged in a predetermined position in the lower plenum 58. In this case, the spokes 64 and 68 are arranged in the circumferential direction of the rings 65 and 69, respectively, at regular intervals. One spoke is arranged between the adjacent two inlet nozzles 44, and two spokes are arranged between the separated two inlet nozzles 44. The columns 72 are arranged at both sides of each of the spokes 64 and 68, in the circumferential direction of the outer rings 62 and 66. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 71, and flows into the core 53. At this time, the light water flowing into the reactor vessel main body 42 through the inlet nozzles 44, collides with the core barrel 46, and is dispersed in the circumferential direction. The light water then merges with the light water flowing in through the adjacent inlet nozzles 44, flows down the downcomer portion 59, and reaches the lower plenum 58. In other words, most of light water flowing into the lower plenum 58 through the downcomer portion 59 flows down along the 0-90-180-270 degree center lines. Consequently, when the light water flows upward by the inner spherical surface of the lower plenum 58, the light water collides with the straightener member 71, in other words, the rings 62, 63, 66, and 67, the spokes 64 and 68, and the columns 72 and 73, and is dispersed, thereby preventing the generation of large vortices. As a result, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. Particularly, the light water that flows down along the 90-270 degree center line in the downcomer portion 59 collides with the spokes 64 and 68, and the columns 72 and 73 of the straightener member 71, and dispersed in the circumferential direction. The flow of light water that flows down along the 0-180 degree center line in the downcomer portion 59 is widened in the circumferential direction. Accordingly, the light water is likely to collide with the spokes 64 and 68, and the columns 72 and 73 of the straightener member 71, and is dispersed in the circumferential direction. Accordingly, it is possible to appropriately prevent the generation of large vortices. In this manner, in the nuclear reactor according to the second embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 71 formed of the upper ring 65 and the lower ring 69 in a ring shape, and the spokes 64 and 68 radially arranged in the rings 65 and 69, respectively. The lower portions of the columns 72 and 73 suspended from the lower core support plate 51 are connected to the outer rings 62 and 66, and the spokes 64 and 68. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the rings 62, 63, 66, and 67, the spokes 64 and 68, and the columns 72 and 73, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. [Third Embodiment] FIG. 7 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a third embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the third embodiment, as shown in FIGS. 1 and 7, the lower plenum 58 includes a straightener member 81 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59 and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 81 includes the upper ring 65 in which the upper outer ring 62 and the upper inner ring 63 are connected by the six upper spokes 64, and the lower ring 69 in which the lower outer ring 66 and the lower inner ring 67 are connected by the six lower spokes 68. An upper intermediate ring 82 is provided between the upper outer ring 62 and the upper inner ring 63, and a lower intermediate ring 83 is provided between the lower outer ring 66 and the lower inner ring 67. The intermediate rings 82 and 83 are in a hexagonal shape and intersected and connected with the spokes 64 and 68. The lower portions of the 12 pieces of columns 72 suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring 66. The lower portions of the six pieces of columns 73 suspended from the lower core support plate 51 are connected to the upper spokes 64 and the lower spokes 68. The lower portions of six pieces of columns 84 suspended from the lower core support plate 51 are connected to the upper intermediate ring 82 and the lower intermediate ring 83. Accordingly, the upper ring 65 and the lower ring 69 are arranged in a predetermined position in the lower plenum 58. In this case, the spokes 64 and 68 are arranged in the circumferential direction of the rings 65 and 69, respectively, at regular intervals. One spoke is arranged between the adjacent two inlet nozzles 44, and two spokes are arranged between the separated two inlet nozzles 44. The columns 72 are arranged at both sides of each of the spokes 64 and 68, in the circumferential direction of the outer rings 62 and 66. The columns 84 are arranged between the columns 73 in the circumferential direction of the intermediate rings 82 and 83. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 81, and flows into the core 53. At this time, the light water flowing into the reactor vessel main body 42 through the inlet nozzles 44, collides with the core barrel 46, and is dispersed in the circumferential direction. The light water then merges with the light water flowing in through the adjacent inlet nozzles 44, flows down the downcomer portion 59, and reaches the lower plenum 58. In other words, most of light water flowing into the lower plenum 58 through the downcomer portion 59, flows down along the 0-90-180-270 degree center lines. Consequently, when the light water flows upward by the inner spherical surface of the lower plenum 58, the light water collides with the straightener member 81, in other words, the rings 62, 63, 66, 67, 82, and 83, the spokes 64 and 68, and the columns 72, 73, and 84, and is dispersed, thereby preventing the generation of large vortices. As a result, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the third embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 81 formed of the upper ring 65, the lower ring 69, the intermediate rings 82 and 83 in a ring shape, and the spokes 64 and 68 radially arranged in the rings 65, 69, 82, and 83. The lower portions of the columns 72, 73, and 84 suspended from the lower core support plate 51 are connected to the rings 62, 66, 82, and 83 and the spokes 64 and 68. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the rings 62, 63, 66, 67, 82, and 83, the spokes 64 and 68, and the columns 72, 73, and 84, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. [Fourth Embodiment] FIG. 8 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a fourth embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the fourth embodiment, as shown in FIGS. 1 and 8, the lower plenum 58 includes a straightener member 91 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59 and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 91 includes an upper ring 95 in which an upper outer ring 92 and an upper inner ring 93 are connected by six upper spokes 94, and a lower ring 99 in which a lower outer ring 96 and a lower inner ring 97 are connected by six lower spokes 98. A lower intermediate ring 100 is provided between the lower outer ring 96 and the lower inner ring 97. The lower intermediate ring 100 is in a hexagonal shape and intersected and connected with the lower spokes 98. The lower portions of 12 pieces of columns 101 suspended from the lower core support plate 51 are connected to the upper outer ring 92, and the lower portions of 12 pieces of columns 102 are connected to the lower outer ring 96. The lower portions of six pieces of columns 103 are connected to the upper spokes 94, and the lower portions of six pieces of columns 104 are connected to the lower spokes 98. In this case, because the outer diameter of the upper outer ring 92 is set larger than the outer diameter of the lower outer ring 96, the upper outer ring 92 is arranged outside in the radial direction than the lower outer ring 96. The spokes 94 and 98 are arranged in the circumferential direction of the rings 95 and 99 at regular intervals, but are shifted in the circumferential direction. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 91, and flows into the core 53. At this time, the light water that flows upward by the inner spherical surface of the lower plenum 58, collides with the straightener member 81, in other words, the rings 92, 93, 96, 97, 99, and 100, the spokes 94 and 98, and the columns 101, 102, 103, and 104, and is dispersed, thereby preventing the generation of large vortices. As a result, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the fourth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 91 formed of the upper ring 95, the lower ring 99, and the intermediate ring 100 in a ring shape, and the spokes 94 and 98 radially arranged in the rings 95, 99, and 100. The upper outer ring 92 and the lower outer ring 96 are shifted in the radial direction, and the upper spokes 94 and the lower spokes 98 are shifted in the circumferential direction. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44, flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the rings 92, 93, 96, 97, 99, and 100, the spokes 94 and 98, and the columns 101, 102, 103, and 104, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. [Fifth Embodiment] FIG. 9 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a fifth embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the fifth embodiment, as shown in FIGS. 1 and 9, the lower plenum 58 includes a straightener member 111 that uniformly disperses and straightens the light water supplied into the lower plenum 58 from the downcomer portion 59 and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 111 includes the upper ring 65 in which the upper outer ring 62 and the upper inner ring 63 are connected by the six upper spokes 64, and a lower ring similar to that in the first embodiment, which is not shown. The lower portions of 12 pieces of columns 72 suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring, and the lower portions of six pieces of columns 73 are connected to the upper spokes 64 and the lower spokes. An auxiliary ring (straightening auxiliary member) 112 is provided towards the inner surface of the nuclear reactor main body 42 from the outer peripheral portion of the upper outer ring 62. The auxiliary ring 112 has a ring shape having a diameter larger than that of the upper outer ring 62, and has a cylindrical or a round cross-section, and supported by the outer peripheral surface of the upper outer ring 62 with a plurality (eight in the present embodiment) of connection bars (connection member) 113. In this case, a predetermined space is provided between the auxiliary ring 112 and the outer peripheral surface of the upper outer ring 62. A predetermined space is also provided between the auxiliary ring 112 and the inner surface of the nuclear reactor main body 42. Accordingly, when the light water flowing into the nuclear reactor main body 42 through the inlet nozzles 44, flows down the downcomer portion 59 and reaches the lower plenum 58, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 111, and flows into the core 53. At this time, the light water that flows down the downcomer portion 59 collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58. The light water that flows upward by the inner spherical surface of the lower plenum 58 then collides with the straightener member 111, and is dispersed, thereby preventing the generation of large vortices. As a result, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the fifth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 111 formed of the upper ring 65 and the lower ring in a ring shape, and in which the auxiliary ring 112 projecting towards the inner surface of the reactor vessel main body 42 from the outer peripheral portion of the upper ring 65 is fixed. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59 and reaches the lower plenum 58, the light water collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58. When the light water is then reversed in the lower plenum 58 and flows upward, the light water further collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. The auxiliary ring 112 is in a ring shape and has a cylindrical or a round cross-section. When the light water from the downcomer portion 59 collides with the auxiliary ring 112 and is dispersed, the pressure loss due to the auxiliary ring 112 is reduced, thereby preventing the generation of vortices in the horizontal direction. [Sixth Embodiment] FIG. 10 is a longitudinal sectional view of a straightener member provided in a pressurized water reactor according to a sixth embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the fifth embodiment, it will be described with reference to FIGS. 1 and 9. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the sixth embodiment, as shown in FIGS. 1, 9, and 10, in the upper ring 65 that forms the straightener member 111, the auxiliary ring 112 is fixed to the outer peripheral surface of the upper outer ring 62, by the connection bars 113. In this case, the upper surface of the upper outer ring 62 is placed higher than the upper surface of the auxiliary ring 112. In other words, a level difference H1 is created between the upper surface of the upper outer ring 62 and the upper surface of the auxiliary ring 112. Accordingly, when the light water flowing into the reactor vessel main body 42 through the inlet nozzles 44 flows down the downcomer portion 59 and reaches the lower plenum 58, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 71, and flows into the core 53. The light water that flows down the downcomer portion 59 collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58, through a space between the upper outer ring 62 and the auxiliary ring 112, and a space between the auxiliary ring 112 and the reactor vessel main body 42. A part of the light water collided with the auxiliary ring 112 and is dispersed, flows the center of the reactor vessel main body 42. But because the level difference H1 is created between the upper surface of the upper outer ring 62 and the upper surface of the auxiliary ring 112, a part of the light water collides with the outer peripheral surface of the upper outer ring 62, and reaches the lower plenum 58 by flowing downward in the circumferential direction. The light water flowing into the lower plenum 58 flows upward by the inner spherical surface, further collides with the straightener member 111, and is dispersed, thereby preventing the generation of large vortices. Accordingly, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the sixth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 111 formed of the upper ring 65 and the lower ring in a ring shape and in which the auxiliary ring 112 projecting towards the inner surface of the reactor vessel main body 42 from the outer peripheral portion of the upper ring 65 is fixed, and the upper surface of the upper outer ring 62 is placed higher than the upper surface of the auxiliary ring 112. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down into the lower plenum 58 through the downcomer portion 59, the light water collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58. The light water also collides with the outer peripheral surface of the upper outer ring 62, reaches the lower plenum 58 by flowing downward in the circumferential direction, reversed in the lower plenum 58, and flows upward. The light water further collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. [Seventh Embodiment] FIG. 11 is a longitudinal sectional view of a straightener member provided in a pressurized water reactor according to a seventh embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the fifth embodiment, it will be described with reference to FIGS. 1 and 9. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the seventh embodiment, as shown in FIGS. 1, 9, and 11, in the upper ring 65 that forms the straightener member 111, the auxiliary ring 112 is fixed to the outer peripheral surface of the upper outer ring 62, by the connection bars 113. A wall member 115 is provided on the upper surface of the outer peripheral portion of the upper outer ring 62. The wall member 115 is in a ring shape along the outer periphery of the upper outer ring 62, has a rectangular cross-section, and fixed to the upper surface of the upper outer ring 62. In this case, the upper surface of the wall member 115 is placed higher than the upper surface of the auxiliary ring 112. In other words, a level difference H2 is created between the upper surface of the wall member 115 and the upper surface of the auxiliary ring 112. Accordingly, when the light water flowing into the reactor vessel main body 42 through the inlet nozzles 44 flows down the downcomer portion 59 and reaches the lower plenum 58, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 111, and flows into the core 53. At this time, the light water that flows down the downcomer portion 59, collides with the auxiliary ring 112, and is dispersed. The light water then reaches the lower plenum 58, through a space between the upper outer ring 62 and the auxiliary ring 112, and a space between the auxiliary ring 112 and the reactor vessel main body 42. A part of the light water collided with the auxiliary ring 112 and is dispersed flows the center of the reactor vessel main body 42, but also collides with the outer peripheral surface of the wall member 115, and reaches the lower plenum 58 by flowing downward in the circumferential direction. The light water flowing into the lower plenum 58 flows upward by the inner spherical surface, further collides with the straightener member 111, and is dispersed, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the seventh embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 111 formed of the upper ring 65 and the lower ring in a ring shape and in which the auxiliary ring 112 projecting towards the inner surface of the reactor vessel main body 42 from the outer peripheral portion of the upper ring 65 is fixed, and the wall member 115 in a ring shape mounted on the upper surface of the upper outer ring 62. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down into the lower plenum 58 through the downcomer portion 59, the light water collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58. The light water also collides with the outer peripheral surface of the wall member 115 and reaches the lower plenum 58 by flowing downward in the circumferential direction. When the light water is reversed in the lower plenum 58 and flows upward, the light water further collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. In the fifth, the sixth, and the seventh embodiments described above, the auxiliary ring 112 is provided over the entire circumference of the upper outer ring 62 in a ring shape. However, the auxiliary ring 112 may be partially provided in a curve shape or in a straight line shape. The auxiliary ring 112 has a cylindrical or a round cross-section. However, any shape that can reduce the resistance of the light water flowing downward such as an oval shape or a triangular shape may be used. In the seventh embodiment described above, the wall member 115 is arranged over the entire circumference of the upper surface of the upper outer ring 62 in a ring shape. However, the wall member 115 may be partially provided in a curve shape. [Eighth Embodiment] FIG. 12 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to an eighth embodiment of the present invention. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the eighth embodiment, as shown in FIGS. 1 and 12, the lower plenum 58 includes a straightener member 121 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59, and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 121 includes the upper ring 65 in which the upper outer ring 62 and the upper inner ring 63 are connected by the six upper spokes 64, and the lower ring similar to that of the first embodiment, which is not shown. The lower portions of the 12 pieces of columns 72 suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring, and the lower portions of the six pieces of columns 122 are connected to the upper spokes 64 and the lower spokes. In this case, the six pieces of columns 122 connected to the upper spokes 64 and the lower spokes are formed so as to function as a vortex elimination member having a larger outer diameter than the widths of the upper spokes 64 and the lower spokes. In other words, the upper ends of the columns 122 are fixed to the lower core support plate 51, and the lower ends of the columns 122 penetrate through the upper spokes 64 and the lower spokes, and extended around the bottom surface of the reactor vessel main body 42. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 121, and flows into the core 53. At this time, the light water that flows upward by the inner spherical surface of the lower plenum 58 in the upper direction, collides with the straightener member 121, and is dispersed, thereby preventing the generation of large vortices. The generated vortices are eliminated by flowing in the upper direction around the columns 122 having larger diameters that function as a vortex elimination member. The flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the eighth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 121 formed of the upper ring 65 and the lower ring in a ring shape and the columns 122 that function as a vortex elimination member. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. The generated vortices are eliminated by flowing in the upper direction around the columns 122. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. [Ninth Embodiment] FIG. 13 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a ninth embodiment of the present invention. FIG. 14 is a perspective view of a vortex elimination ring provided in the straightener member of the ninth embodiment. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In the nuclear reactor according to the ninth embodiment, as shown in FIGS. 1, 13, and 14, the lower plenum 58 includes a straightener member 131 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59 and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 131 includes the upper ring 65 in which the upper outer ring 62 and the upper inner ring 63 are connected by the six upper spokes 64, and the lower ring similar to that in the first embodiment, which is not shown. The lower portions of the 12 pieces of columns 72 suspended from the lower core support plate 51 are connected to the upper outer ring 62 and the lower outer ring, and the lower portions of the six pieces of columns 73 are connected to the upper spokes 64 and the lower spokes. In this case, the upper ends of the six pieces of columns 73 connected to the upper spokes 64 and the lower spokes are fixed to the lower core support plate 51, and the lower ends of the columns 73 penetrate through the upper outer ring 62 and the lower outer ring, and extended around the bottom surface of the reactor vessel main body 42. A vortex elimination ring (vortex elimination member) 132 in a ring shape is provided at the outer peripheral portion of the columns 73, and fixed by a plurality of support bars 133. The vortex elimination ring 132 is provided in plurality in the axial direction of the columns 73 at regular intervals. Accordingly, upon reaching the lower plenum 58 by flowing down the downcomer portion 59, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 131, and flows into the core 53. At this time, the light water that flows upward by the inner spherical surface of the lower plenum 58, collides with the straightener member 131, and is dispersed, thereby preventing the generation of large vortices. The generated vortices are eliminated by flowing in the upper direction around the columns 73 and colliding with the vortex elimination ring 132. The flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the ninth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 131 having the upper ring 65 and the lower ring in a ring shape and the vortex elimination ring 132 in a ring shape supported by the columns 72 and 73 suspended from the lower core support plate 51 and provided at the outer peripheral portion of the columns 73. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. The generated vortices are eliminated by flowing in the upper direction around the columns 73 and colliding with the vortex elimination ring 132. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. In the eighth and the ninth embodiments described above, the columns 122 that function as a vortex elimination member are provided on the upper spokes 64, and the vortex elimination ring 132 is provided at the outer peripheral portion of the columns 73. However, thick columns that function as a vortex elimination member may be provided on the upper outer ring 62, or a vortex elimination ring may be provided at the outer peripheral portion of the columns 72. [Tenth Embodiment] FIG. 15 is a horizontal sectional view of a straightener member provided in a pressurized water reactor according to a tenth embodiment of the present invention. FIG. 16 is a sectional view taken along the line XVI-XVI in FIG. 15. Because the overall configuration of a nuclear reactor according to the present embodiment is similar to that in the first embodiment, it will be described with reference to FIG. 1. The same reference numerals are denoted to portions having the same functions as those of the embodiment, and detailed descriptions thereof will be omitted. In a nuclear reactor according to the tenth embodiment, as shown in FIGS. 1, 15, and 16, the lower plenum 58 includes a straightener member 141 that uniformly disperses and straightens the light water supplied to the lower plenum 58 from the downcomer portion 59, and flows upward to the core 53, in the circumferential direction and the radial direction of the core 53. The straightener member 141 includes an upper ring 145 in which an upper outer ring 142 and a support shaft 143 are connected by six upper spokes 144, and the lower ring, similarly, in which the lower outer ring and the support shaft 143 are connected by six lower spokes, which is not shown. Vortex elimination pipes (vortex elimination member) 146 are provided at both sides of each of the upper spokes 144 in the lengthwise direction of the upper spoke 144, and is fixed by a plurality of connection bars 147. The lower portions of 12 pieces of columns 148 suspended from the lower core support plate 51 are connected to the upper outer ring 142 and the lower outer ring, and the lower portions of six pieces of columns 149 are connected to the upper spokes 144 and the lower spokes. The auxiliary ring 112 is provided towards the inner surface of the nuclear reactor main body 42 from the outer peripheral portion of the upper outer ring 142. The auxiliary ring 112 is in a ring shape having a diameter larger than that of the upper outer ring 142, and has a cylindrical or a round cross-section. The auxiliary ring 112 is supported by the outer peripheral surface of the upper outer ring 142 with the eight connection bars 113. Accordingly, when the light water flowing into the nuclear reactor main body 42 through the inlet nozzles 44 flows down the downcomer portion 59 to the lower plenum 58, the light water flows upward by being guided by the inner spherical surface of the lower plenum 58 in the upper direction, straightened by the straightener member 141, and flows into the core 53. At this time, the light water that flows down the downcomer portion 59, collides with the auxiliary ring 112, is dispersed, and reaches the lower plenum 58. The light water that flows upward by the inner spherical surface of the lower plenum 58 further collides with the straightener member 141, and is dispersed, thereby preventing the generation of large vortices. The generated vortices are eliminated by colliding with the vortex elimination pipes 146. Accordingly, the flow rate of the light water supplied to the core 53 from the lower plenum 58 is uniformly straightened in the radial direction and the circumferential direction of the core 53. In this manner, in the nuclear reactor according to the tenth embodiment, the lower plenum 58 in the reactor vessel 41 includes the straightener member 141 having the upper ring 145 and the lower ring in a ring shape, and in which the vortex elimination pipes 146 are fixed to both sides of each of the upper spokes 144. Accordingly, when the light water introduced into the reactor vessel 41 through the inlet nozzles 44 flows down the downcomer portion 59, reaches the lower plenum 58, reversed in the lower plenum 58, and flows upward, the light water collides with the upper ring 65 and the lower ring, and disperses the flow, thereby preventing the generation of large vortices. The generated vortices are eliminated by colliding with the vortex elimination pipes 146. Consequently, the flow rate of the light water supplied to the core 53 is uniformly straightened in the radial direction and the circumferential direction of the core 53. As a result, it is possible to enhance heat exchange efficiency. In the embodiments described above, the straightener member is formed by arranging two rings in the vertical direction. However, one ring or equal to or more than three rings may be formed. In the embodiments, the straightener member is formed by arranging one or two rings in the radial direction. However, equal to or more than three rings may be formed. The cross-section of the ring is rectangular, but it may also be circular or ellipse. The six straightening spokes are provided in the circumferential direction. However, equal to or less than five spokes may be provided, or equal to or more than seven spokes may be provided. The straightening spokes are provided in the circumferential direction at regular intervals. However, corresponding to the inner surface shape of the reactor vessel main body 42, the straightening spokes may be disposed at irregular intervals. In other words, the numbers of the straightening rings, the straightening spokes, and the columns may be appropriately set corresponding to the state of the vortex generated in the lower plenum 58. Depending on the state, the heights and the widths of the straightening rings, the straightening spokes, and the columns may be changed, and the resultant flow area of the light water flowing to the core 53, and the opening ratio may be set. In the embodiments described above, the straightening ring is supported by the columns suspended from the lower core support plate. However, if the lower core support plate and the lower core plate are commonly used, the straightening ring may be supported by the columns suspended from the lower core plate. In other words, the lower core plate according to the present invention includes the lower core support plate and the lower core plate. The nuclear reactor according to the present invention uniformly supplies the coolant towards the core from the lower plenum in the radial direction and the circumferential direction, by providing the straightener member in the lower plenum, and can be applied to any type of nuclear reactors. |
|
summary | ||
045004889 | summary | BACKGROUND OF THE INVENTION Uranium of different isotopic ratios has long been used in research throughout the world to support the nuclear reactor development program. The uranium may be natural, containing the normal ratio of .sup.235 U and .sup.238 U; enriched, where the .sup.235 U content has been raised; or depleted, where the .sup.235 U content has been reduced. In any case, bare uranium as a solid metal will oxidize when exposed to air. The rate of oxidation depends on several factors, including the degree of humidity in the atmosphere; and the oxide builds up on the surface of the parent metal and is radioactive. The oxide is easily brushed or scraped off the parent metal, so much so that anything coming in contact with the uranium becomes contaminated. This then requires an expensive decontamination process. Finding a suitable protective coating has been a serious and ongoing problem. Many research programs limit the extraneous material that can be introduced into the reactor with the uranium. Hydrogeneous materials are particularly undesirable due to their strong interaction with the neutron flux in the reactor. This precludes the use of most plastics as a coating. Some nonhydrogeneous coatings are available, notably some of the chloro-, fluoro-, bromoethylene polymers. However, this type of coating has a limited useful life (two years or so) whereupon the uranium must be cleaned and recoated. Use and handling can also shorten this life and risk contamination of the area. Often, the uranium fuel is only between 1/64" and 1/8" thick, and otherwise is shaped as rectangular plates from between 1" and 2" wide and 2" and 4" long. Attempts to encapsulate or clad the uranium plate(s) with stainless steel have not been totally successful either, because even when such encapsulating or cladding structures are formed of thin 15-20 mil (0.015-0.020") sheets, they generally introduce excessive extraneous material to adversely affect the sensitivity of the research. Moreover, manufacture of such structures with the narrow thickness-to-width ratios and with thin sheets of stainless steel has been difficult and unreliable, due to thermal warpage and dimensional instability. The problem of uranium contamination is even more burdensome in tests involving both uranium and plutonium. Plutonium is almost always cladded or enclosed in a sealed container. Both uranium and plutonium are radioactive, releasing alpha radiation; however, plutonium is also biologically toxic. Thus, preliminary radiation tests are made to detect "leakers" (where the cladding or enclosing container of the plutonium is imperfect), but such tests cannot distinguish between a plutonium container having exterior contamination induced by rubbing against an oxidized uranium fuel plate and a "leaker" container. It then becomes necessary to double check the suspect plutonium container with more costly and sophisticated tests, and it yet further necessitates the decontamination of the container. SUMMARY OF THE INVENTION This invention relates to an improved stainless steel structure for holding uranium fuel formed as plates as small as 1/64" thick, to an improved method of forming such a structure, and to the combination of the structure having fuel plate(s) encapsulated therein. This encapsulated unit is formed initially as a tube-like housing of very thin (5 mils-0.005") stainless steel sheet material, having an open/through dimension only slightly larger than the uranium fuel plate(s) that will fit inside the housing. End caps are designed to be welded to the housing to close the open ends thereof; one end cap being welded in place after the fuel plate(s) have been loaded into the housing so as to physically confine the fuel plate(s) therein. The end caps are preferably formed of a slightly porous metal having micron size pores, allowing the confined uranium to breath slightly while yet precluding the release of contaminating oxide from the uranium. The technique for fabricating the encapsulating structures involves beam welding two C-shaped channels together along opposite side seams where the channel legs butt against one another. For uniform fixturing of the channels and for proper heat distribution during welding, interior and exterior chill blocks of ground and hardened tool steel are used to sandwich and hold the channels therebetween. The interior chill block is composed of two wedges (1) that fit exactly thicknesswise between the two channel pieces when the ends of the channel legs just butt together, and (2) that can be expanded widthwise to snug up flush against the insides of the channel legs before welding and contracted widthwise to be easily removed from the tube-like housing after welding. A positioning pin is used to lock the widthwise expanded wedges quickly and accurately and with little operator effort. The channel pieces must butt exactly along the opposite side legs or they cannot be welded together. The electron beam weld is actually made in an evacuated chamber or in an inert atmosphere. The parameters such as the feed speed along the seam, beam power, beam focusing, etc., are initially set by trial and error but thereafter are regulated automatically. As practiced now, several complete sets of interior and exterior chill blocks are fixtured as a stack on a table in the welder and the table is automatically moved and indexed to make the seam welds successively on one side only of each tube-like housing. Thereafter, the chill blocks are flipped over as a stack and refixtured, etc., to make seam welds on the opposite side of the housing. |
045171521 | abstract | The invention relates to a method for testing fuel element tubes by ultrasonic energy. For testing, each tube becomes disposed in the space between a transmit transducer and a receive transducer. The echo signals falling within a predetermined time interval are evaluated. Since the distance between the transducers may vary as the transducers move through the space between fuel element tubes, the transmitted signal reaching the receive transducer without passing through the tube may be confused with the revolving echo signal. Therefore, this invention discloses an arrangement for cyclically controlling the setting of the time gate before each such tube is in position between the transducers. To this end, the ultrasonic transit time of signals between the transmit transducer and the receive transducer is measured in the gap between the last tested tube and the next to be tested tube. A constant value is subtracted from the measured transit time value and this constant value is selected so that the transmitted signal received during the transit time measurement falls just outside the gated time interval. |
051456397 | claims | 1. A reactor plant comprising: a containment structure defining a wet well, a dry well, and a condenser well, said wet well being in fluid communication with said dry well, said dry well containing a noncondensible gas, said wet well and said condenser well containing condenser coolant during normal operation, said condenser well being vented to an external environment, said wet well and said dry well being in fluid isolation relative to said external environment; a dual-phase reactor, said reactor having a reactor pressure vessel located within said dry well, said vessel containing a heat-transfer fluid during normal operation, said heat-transfer fluid including heat-transfer liquid and heat-transfer vapor, said vessel having a core for converting heat-transfer liquid to heat-transfer vapor, said reactor having a nominal liquid level; a turbine; turbine conduit means for conveying heat-transfer vapor to said turbine from said reactor; a condenser disposed within said condenser well, said condenser having pressure relief means for relieving excessive pressure within said reactor vessel by conveying heat-transfer fluid, primarily heat-transfer vapor, from said vessel to said collector plenum in the event of said excessive pressure, said pressure relief means being coupled to said reactor via a relief conduit mating with said reactor above said nominal liquid level and communicating with said distributor plenum through said base; and condensate return means for conveying heat-transfer liquid from said collector section to said reactor vessel through a condensate return conduit that mates with said reactor at a level below said nominal liquid level, said condensate return conduit communicating with said collector plenum through said base. 2. A reactor plant as recited in claim 1 further comprising a noncondensible gas conduit for transferring noncondensible gases from said collector plenum to said wet well, said noncondensible gas conduit extending through said base into said condenser volume to a level above a maximum level at which said tubes mate with said collector plenum. 3. A reactor plant as recited in claim 1 wherein the cross section of said sidewall has a perimeter and an area, said area being greater than the square of one-fourth of said perimeter. |
049873130 | claims | 1. A method of storing radioactive waste, comprising the steps of: (a) providing an upwardly open cast-iron vessel having a closed bottom, a solid wall unitary therewith and an upwardly open mouth; (b) closing said mouth by sealing engaging a cast-iron lid thereof, said lid being formed with separate vertically throughgoing intake and outlet passages and providing in said vessel at least one flow deflector aligned beneath said outlet passage; (c) surrounding said vessel with a heating jacket; (d) introducing into said vessel through said intake passage a radioactive liquid; (e) evacuating said vessel through said outlet passage and simultaneously heating said vessel with said jacket to evaporate liquid from said vessel and form vapors which are withdrawn past said deflector through said outlet passage; and (f) upon completion of filling of said vessel with a residue resulting from the evaporation of liquid from the contents of said vessel, hermetically engaging a cover over said passages. an upwardly open cast-iron vessel having a closed bottom, solid walls unitary with said bottom and an upwardly open mouth; a cast-iron lid sealingly engaged over and completely blocking said mouth, said walls being smooth along their exteriors, said lid being formed with said vertically throughgoing intake and outlet passages; means including screwthread formations for hermetically securing said lid over said mouth; a flow deflector aligned inside said vessel beneath said outlet passage; at least one cover sealingly engageable on said lid over said passages; means including screwthread formations for hermetically engaging said cover over said passages; and a heating jacket surrounding said vessel and in heat transferring contact with said walls. a metering vessel receiving radioactive liquid material from a nuclear power plant; at least one treating and storage container connectable to said vessel for receiving said material therefrom, said container being composed of cast iron and having a lid traversed by an inlet passage connectable to said vessel and an outlet passage, and a generally horizontal baffle disposed directly below said inlet passage; a condenser connected to said outlet passage for condensing condensate received therefrom; a suction pump connected to said condenser for evacuating said container through said condenser; and a heating jacket on said container for heating same simultaneously with evacuation of vapor therefrom. 2. The method defined in claim 1 wherein quantities of radioactive liquid are introduced into said vessel with intervening evacuation of vapors therefrom. 3. The method defined in claim 1 further comprising the step of condensing vapors withdrawn from said vessel. 4. An apparatus for the treatment of radioactive waste, comprising: 5. The apparatus defined in claim 4 wherein said vessel is formed with an internal lining of lead. 6. The apparatus as defined in claim 4 wherein said walls have a thickness less than about 20 centimeters. 7. An apparatus for treating and storing liquid radioactive waste, comprising: 8. The apparatus defined in claim 7 wherein a plurality of such containers are provided and all of said containers have respective inlet passages connected to said metering vessel, each of said containers having a respective outlet passage connected to a respective condenser and suction pump. 9. The apparatus defined in claim 8, further comprising an ultrafilter between each of said outlet passages and the respective condenser. 10. The apparatus defined in claim 8, further comprising a liquid separator between each condenser and the respective suction pump. 11. The apparatus defined in claim 8, further comprising a respective oil separator downstream of each suction pump. |
description | This application is based on and claims priority from Korean Patent Application No. 10-2018-0027313, filed on Mar. 8, 2018, the disclosure of which is incorporated herein in its entirety by reference for all purposes. The present disclosure relates to a pressurized water reactor; and, more particularly, to a fuel assembly for a long period operation of a pressurized water reactor and a mixed cycle length operation method, which can improve a nuclear reactor operation efficiency by providing an additional operation cycle of a nuclear reactor in consideration of an inactivation period that inevitably occurs at the time of exchanging a nuclear fuel and applying a nuclear fuel loading technique capable of employing the additional operation cycle. Generally, a pressurized water reactor refers to a nuclear reactor that uses pressurized water as a coolant and a neutron moderator. The fuel used in the pressurized water reactor, i.e., 3 to 5% U-235 enriched uranium dioxide (UO2) powder, is sintered to a cylindrical sintered body having a diameter of about 8 to 9 mm and a length of about 10 mm. The sintered body is stacked in a cladding tube having a diameter of about 9.5 to 10.2 mm at a height of about 3600 to 3800 mm. Then, a plenum having a length of about 200 to 200 mm is formed on the sintered body stack to collect fission gas. In order to promote heat transfer, helium is injected into a rod and both ends of the rod are sealed by welding. A fuel assembly is formed by loading the fuel rod to a nuclear fuel assembly frame including an upper fixing part, a lower fixing part, a guide pipe, a measuring pipe, a support grid, and the like. The fuel assembly thus formed is loaded to a reactor core. In the pressurized water reactor, once a nuclear fuel is loaded into the nuclear reactor, all the nuclear fuel is fixed and burned until the end of the operation cycle. The reactor has an operation cycle of about 18 months. At the end of the cycle at which all the loaded nuclear fuel is burned, the nuclear fuel that has combustion performance no more is taken out of the reactor and a new nuclear fuel is loaded. In general, it takes one month to replace the nuclear fuel and perform the maintenance of the nuclear reactor. During this period, the nuclear power plant stops and cannot produce electricity. In other words, in a conventional case, an operation cycle of 18 months is uniformly applied to one reactor core (replacing ⅓ of the fuel in the fuel rod with a new fuel every 18 months) and, thus, the improvement of the nuclear fuel operation efficiency is limited. In view of the above, the present disclosure provides a fuel assembly for a long period operation of a pressurized water reactor and a mixed cycle length operation method, which can additionally ensure an operation cycle of a nuclear reactor in consideration of an inactivation period that inevitably occurs at the time of exchanging a nuclear fuel and improve a nuclear reactor operation efficiency by applying a nuclear fuel loading technique capable of employing the additionally ensured operation cycle. In accordance with an aspect, there is provided a fuel assembly provided in a pressurized water reactor, comprising: first fuel rods that operate for a preset first operation time and second fuel rods that operate for a second operation time longer than the first operation time, wherein the pressurized water reactor operates by an operation schedule determined in consideration of the first operation time of the first fuel rods and the second operation time of the second fuel rods. Each of the first fuel rods and the second fuel rods may include fuel rods of a first group that are not used and fuel rods of a second group that are used once. After the pressurized water reactor operates for a first cycle of a preset period of time, the fuel rods of the second group are separated from the fuel assembly and discharged to the outside of the pressurized water reactor. After the first cycle operation is completed, a first number of fuel rods among the fuel rods of the first group are moved to a region where the fuel rods of the second group are to be arranged in the fuel assembly, and a second number of fuel rods that are the remaining fuel rods of the first group are separated from the fuel assembly and discharged to the outside of the pressurized water reactor. After new fuel rods that are not used are loaded in a region where the fuel rods of the first group are to be arranged and the pressurized water reactor operates for a second cycle of a preset period of time, a part of the second number of fuel rods and the new fuel rods arranged in the region of the first group are moved to the region where the fuel rods of the second group are to be arranged. New fuel rods that are not used are loaded in the region where the fuel rods of the first group are to be arranged and the pressurized water reactor operates for a third cycle of a preset period of time. The fuel rods of the first group and the fuel rods of the second group may be alternately arranged in an outward direction from a central position in the fuel assembly without being consecutively arranged horizontally. In the first cycle and the second cycle, the first group may include 101 fuel rods and the second group may include 76 fuel rods, and in the third cycle, the first group may include 57 fuel rods, the second group may include 104 fuel rods, and the first fuel rods may further include 16 fuel rods that are used twice. In accordance with another aspect, there is provided a method for operating a pressurized water reactor comprising: preparing a fuel assembly including first fuel rods that operate for a preset first operation time and second fuel rods that operate for a second operation time longer than the first operation time; creating an operation schedule of a pressurized water reactor by mixing the first operation time of the first fuel rods and the second operation time of the second fuel rods; and operating the pressurized water reactor by repeating the operation schedule. The operating the pressurized water reactor by repeating the operation schedule may include: operating the pressurized water reactor for a first cycle of a predetermined period of time by using a fuel assembly including fuel rods of a first group that are not used and fuel rods of a second group that are used once; separating, after the first cycle operation is completed, the fuel rods of the second group from the fuel assembly and discharging the fuel rods of the second group to the outside of the pressurized water reactor; moving, after the first cycle operation is completed, a first number of fuel rods among the fuel rods of the first group to a region where the fuel rods of the second group are to be arranged in the fuel assembly; separating a second number of fuel rods that are the remaining fuel rods of the first group from the fuel assembly and discharging the second number of fuel rods to the outside of the pressurized water reactor; loading new fuel rods that are not used in a region where the fuel rods of the first group are to be arranged and operating the pressurized water reactor for a second cycle of a preset period of time; moving, after the second cycle operation is completed, a part of the second number of fuel rods and the new fuel rods arranged in the region of the first group to a region where the fuel rods of the second group are to be arranged; and loading a preset number of new fuel rods that are not used in the region where the fuel rods of the first group are to be arranged and operating the pressurized water reactor for a third cycle of a preset period of time. The second fuel rods may have uranium enrichment that allows a long period of operation of 24 months. The uranium enrichment may range from 4.7 to 4.95 w/o. The first cycle and the second cycle may be 24 months, and the third cycle may be 18 months. The first cycle, the second cycle, and the third cycle may form one operation schedule, and the pressurized water reactor operates by repeating the one operation schedule. The remaining fuel rods among the second number of fuel rods may be loaded in the region where the fuel rods of the second group are to be arranged before the first cycle operation of a next operation schedule subsequent to the one operation schedule. In accordance with the present disclosure, in a fuel assembly for a long period operation of a pressurized water reactor and a mixed cycle length operation method, it is possible to improve a nuclear reactor operation efficiency by providing an additional operation cycle of a nuclear reactor in consideration of an inactivation period that inevitably occurs at the time of exchanging a nuclear fuel and applying a nuclear fuel loading technique capable of employing the additional operation cycle. Hereinafter, the operation of the present disclosure will be described in detail with reference to the accompanying drawings. In describing the embodiments of the present disclosure, if it is determined that detailed description of related known components or functions unnecessarily obscures the gist of the present disclosure, the detailed description thereof will be omitted. Further, the terminologies to be described below are defined in consideration of functions of the embodiments of the present disclosure and may vary depending on a user's or an operator's intention or practice. Accordingly, the definition thereof may be made on a basis of the content throughout the specification. FIG. 1 shows a cross sectional structure of a pressurized water reactor to which an embodiment of the present disclosure is applied. Hereinafter, the operations of the components of the pressurized water reactor to which the embodiment of the present disclosure is applied will be described in detail with reference to FIG. 1. First, the pressurized water reactor includes a vertical cylindrical pressure vessel 100. A fuel assembly 102 loaded with fuel rods is provided in the pressure vessel 100. The fuel assembly 102 includes a plurality of fuel rods in light water (H2O) and is disposed at a lower portion in the pressure vessel 100. The fuel rods can be enriched with uranium 235 at a preset ratio. In a conventional case, the fuel rods are enriched with uranium 235 at 2% to 3% and can operate for 18 months. However, in the case of operating the fuel rods for 18 months, the improvement of the efficiency of the fuel assembly 102 is limited as described above. Therefore, in the embodiment of the present disclosure, the fuel rods are enriched with 4.5% to 4.95% uranium to increase the operation period of the fuel assembly 102 to 24 months longer than the conventional operation period of 18 months. A cylindrical central riser 104 is concentrically disposed in the pressure vessel 100 and cooling water heated by the fuel assembly 102 can be moved through the cylindrical central riser 104 to the upper portion of the pressure vessel 100. A steam generator 106 surrounds the cylindrical central riser 104 between a lower space 110 and an upper space 112 in the pressure vessel 100. The steam generator 106 includes a plurality of tubes 108. The cooling water moves from the upper space 112 to the lower space 110 in the pressure vessel 100 through the tubes 108. Therefore, when the operation of the fuel assembly 102 is started, the cooling water heated by the fuel assembly 102 is moved to the upper portion of the pressure vessel 100 through the cylindrical central riser 104 and then moved to the lower portion of the pressure vessel 100 through the tubes 108 of the steam generator 106. The heated cooling water becomes steam while passing through the tubes 108 to be applied to a turbine (not shown) outside the pressurized water reactor, thereby generating power. FIG. 2 is a detailed block diagram of the fuel assembly shown in FIG. 1. Hereinafter, the operations of the components of the fuel assembly according to the embodiment of the present disclosure will be described in detail with reference to FIG. 2. First, the fuel assembly 102 includes a plurality of vertically arranged fuel rods 202. The fuel rods 202 in the fuel assembly 102 may be enriched with 4.5% to 4.95% uranium 235 for a long period operation of 18 months or more. Guide tubes 204 are provided between the fuel rods 202 and allow control rods 212 to be loaded into or unloaded from the fuel assembly 102. A plurality of spacer grids 206 fixes the fuel rods 202 in the fuel assembly 102. A control rod assembly 220 includes the control rods 212 connected to a connecting rod 216 by yokes or spiders 214. The control rods 212 are loaded or unloaded through the spaces between the fuel rods 202 in the fuel assembly 102 by predetermined control, thereby controlling the fission reaction rate of the fuel rods 202 in the fuel assembly 102. At this time, the connecting rod 216 is connected to a control rod drive mechanism (CRDM) (not shown) and vertically moved under the control of the CRDM. Accordingly, the control rods 212 are loaded or unloaded through the spaces between the fuel rods 202 in the fuel assembly 102. FIG. 2 shows a state in which the control rod assembly 220 is completely separated from the fuel assembly 102. When the control rod assembly 220 is completely separated from the fuel assembly 102, the fission reaction in the fuel rods 202 in the fuel assembly 102 is maximized. If it is required to slow down the reaction rate in the fuel rods 202, the CRDM moves the control rod assembly 220 downward so that the lower ends of the control rods 212 of the control rod assembly 220 can be loaded into the spaces between the fuel rods 202 in the fuel assembly 102 through the guide tubes 204 in the fuel assembly 102. At this time, the control rods 212 contain a neutron poison. Therefore, the control rods 212 loaded into the fuel assembly 102 absorb a part of neutrons generated from the fuel rods 202 due to the fission reaction. Accordingly, the fission reaction rate of the fuel assembly 102 can be slowed down. FIG. 3 shows a mixed cycle length operation method using a fuel assembly highly enriched with uranium in a pressurized water reactor according to an embodiment of the present disclosure. Hereinafter, a mixed cycle length operation method according to an embodiment of the present disclosure will be described in detail with reference to FIGS. 1 to 3. Conventionally, the core is divided into a group A, a group B, and a group C, and ⅓ of the core is loaded at one time. In the present disclosure, the core is divided into a group A and a group B. ⅔ of the fuel assembly is used and, then, ⅓ of the fuel assembly is used. At this time, if the group C is not used, the efficiency deteriorates. In order to effectively use the fuel in the fuel rods, a 18-month operation is mixed with a 24-month operation. Accordingly, the fuel efficiency can be further improved by using the fuel rods with shorter cycles. In other words, as shown in FIG. 3, in the embodiment of the present disclosure, the pressurized water reactor repeats a first set of mixed cycle length operation 300 and a second set of mixed cycle length operation 350, each including a first cycle S1 of 24 months, a second cycle S2 of 24 months, and a third cycle S3 of 18 months. In that case, the fuel rods 202 may include fuel rods (fresh) 310 of a first group that are not used and fuel rods (once) 312 of a second group that are used once. In the arrangement of the fuel rods (fresh) 310 of the first group and the fuel rods (once) 312 of the second group, as shown in FIG. 4 illustrating a loading pattern of the fuel assembly according to the embodiment of the present disclosure, the fuel rods (fresh) 310 of the first group and the fuel rods (once) 312 of the second group may be alternately arranged in an outward direction from the central position 400 in the entire region of the fuel assembly 100. Further, the fuel rods (fresh) 310 of the first group and the fuel rods (once) 312 of the second group may be concentrically arranged about the central position 400 without being consecutively arranged horizontally. Hereinafter, the arrangement of the fuel rods will be described in detail with reference to FIG. 4. In FIG. 4, only ¼ of the fuel assembly in which the fuel rods (fresh) 310 of the first group and the fuel rods (once) 312 of the second group are concentrically arranged about the central position 400 is illustrated as an example. In the conventional 18-month operation, fresh fuels, once-burned fuels, twice-burned fuels are arranged in the fuel assembly. However, in the 24-month operation according to the embodiment of the present disclosure, fresh fuels, i.e., the fuel rods (fresh) 310 of the first group and, and once-burned fuels, i.e., the fuel rods (once) 312 of the second group are used. Two types of fuel rods are used for the 24-month operation of which nuclear fuel efficiency is similar to that of the 18-month operation. In the case of using two types of fuels, it is preferable to set the uranium enrichment of the nuclear fuel to 4.7 to 4.95 w/o that is relatively higher than 4.65 w/o (enrichment in the 18-month operation). Hereinafter, the mixed cycle length operation method will be described more. In the first cycle S1 of the first set of mixed cycle length operation 300, the pressurized water reactor operates for the first cycle S1 of a preset period of time by using the fuel assembly 100 including the fuel rods 310 of the first group that are not used and the fuel rods 312 of the second group that are used once. At this time, the first cycle may be a cycle of operating the pressurized water reactor for 24 months. After 101 new fuel rods are loaded as the fuel rods 310 of the first group and 76 nuclear fuel rods that are used once in the previous cycle are loaded as the fuel rods 312 of the second cycle, the pressurized water reactor operates for the first cycle. Upon completion of the first cycle operation, the fuel rods 312 of the second group are separated from the fuel assembly 102 and discharged to the outside of the pressurized water reactor. Further, upon completion of the first cycle operation, a first number of fuel rods among the fuel rods 310 of the first group are moved to a region where the fuel rods 312 of the second group in the fuel assembly 102 are to be arranged. A second number of fuel rods that are the remaining fuel rods 310 of the first group are separated from the fuel assembly 102 and discharged to the outside of the pressurized water reactor, and new fuel rods that are not used are loaded in a region where the fuel rods 310 of the first group are to be arranged. In that state, the pressurized water reactor operates for the second cycle S2 of a preset period of time. For example, 101 new fuel rods loaded as the fuel rods 310 of the first group are used once in the first cycle. Among the 101 fuel rods that are used once, 76 fuel rods are selected and loaded as the fuel rods 312 of the second group. The remaining 25 fuel rods are separated from the fuel assembly 102 in the third cycle S3 and stored separately. Among the 25 fuel rods, four fuel rods are loaded as the fuel rods 312 of the second group in the third cycle operation, and twenty fuel rods are loaded as the fuel rods 312 of the second group in the first cycle operation of the second set of mixed cycle length operation 350. In other words, the first number of the fuel rods may be, e.g., 76, and the second number of the fuel rods may be 25. The 25 fuel rods that are used once are stored separately and used in a next cycle. At this time, one of the 25 fuel rods that are used once is discarded. This is because it is difficult to design a safety device since loading of one fuel rod that is used once during the operation of the nuclear reactor is improper when considering the ¼ symmetry operation of the nuclear reactor. The 76 fuel rods used as the fuel rods 312 of the second group in the first cycle are separated from the fuel assembly 102 and discharged to the outside the pressurized water reactor. At this time, the second cycle may be a cycle of operating the pressurized water reactors for 24 months. Upon completion of the second cycle operation, a part of the second number of fuel rods that are stored after the first cycle operation and the fuel rods 310 that are newly arranged in the region of the first group and used once in the second cycle operation are moved to the region where the fuel rods 312 of the second group are to be arranged. A preset number of new fuel rods that are not used are loaded in the region where the fuel rods 301 of the first group are to be arranged, and the pressurized water reactor operates for the third cycle of a preset period of time. For example, 101 new fuel rods loaded as the fuel rods 310 of the first group are used once in the second cycle operation. One of the 101 fuel rods that are used once is discarded and the remaining 100 fuel rods are loaded as the fuel rods 312 of the second group in the third cycle. Upon completion of the first cycle operation, among the fuel rods 310 of the first group, 25 fuel rods 310 that are used once are stored. Among the 25 fuel rods, four fuel rods are loaded as the fuel rods 312 of the second group in the third cycle. Therefore, 104 fuel loads in total are loaded as the fuel rods 312 of the second group in the third cycle. Further, 57 new fuel rods that are not used are loaded in the region where the fuel rods 310 of the first group are to be arranged. Among the 76 fuel rods used as the fuel rods of the second group in the second cycle, 16 fuel rods are loaded as fuel rods 314 of a third group in the third cycle. At this time, the third cycle may be a cycle of operating the pressurized water reactor for 18 months. After the third cycle operation of 18 months, in the first cycle of the second set of mixed cycle length operation 350, 20 fuel rods that are used once in the first cycle of the first set of mixed cycle length operation 300 and stored are loaded as the fuel rods of the second group, and 56 fuel rods that are used once in the third cycle are loaded as the fuel rods of the second group. Therefore, 76 fuel rods in total are loaded. 101 new fuel rods are loaded as the fuel rods of the first group, and the pressurized water reactor operates in the first cycle of the second set of mixed cycle length operation. Accordingly, the pressurized water reactor operates in the same manner as in the first set of mixed cycle length operation. In other words, the pressurized water reactor operates by repeating the first set of mixed cycle length operation 300 and the second set of mixed cycle length operation 350. In the case of improving the nuclear fuel efficiency by increasing the uranium enrichment of the fuel rods and increasing the operation cycle of the nuclear reactor, if the operation cycle is fixed to 24-24-24 months, the fuel rods used once in the first cycle cannot be used in the last 24-month cycle and thus are discarded after one cycle. Therefore, in the embodiment of the present disclosure, the efficiency of the fuel rods can be improved by setting the operation cycle of the nuclear reactor in the third cycle to 18 months and allowing the fuel rods that are used once can be reused in a next cycle. When the operation cycle of the nuclear reactor is 18 months, the fuel rods that are used once or twice are reused. Among the fuel rods that are used once or twice, the fuel rods that were relatively close to the central position of the nuclear reactor are reused in the 18-month operation, which makes it possible to improve the efficiency of the fuel rods. In other words, in the conventional case, one fuel assembly can be used for 54 months (18-18-18 months). However, when the operation cycle of the nuclear reactor is fixed to 24 months as in the present disclosure, only two cycles are used and, thus, the operation cycle of the fuel rods becomes 48 months (24 months+24 months), which is less effective compared to when one fuel rod is used for 54 months. By mixing the 18-month operation cycle with the 24-month operation as in the embodiment of the present disclosure, the cycle of 24-24-18 months is executed and one fuel rod can be used for 66 months. In other words, when the 24-month operation is continued, the amount of nuclear fuel that is not burned and discarded increases. Therefore, the 18-month operation is mixed with the 24 month-operation to provide a nuclear fuel that can be burned for about 18 months but cannot be burned for 24 months. Since the pressurized water reactor operates in a mixed cycle, the nuclear fuel can be used more efficiently. As described above, in accordance with the present disclosure, in a fuel assembly for a long period operation of a pressurized water reactor and a mixed cycle length operation method, it is possible to improve a nuclear reactor operation efficiency by providing an additional operation cycle of a nuclear reactor in consideration of an inactivation period that inevitably occurs at the time of exchanging a nuclear fuel and applying a nuclear fuel loading technique capable of employing the additional operation cycle. While the present disclosure has been shown and described with respect to the embodiments, various modifications may be made without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should be defined by the scope of the claim without being limited by the above-described embodiments. |
|
description | The present invention relates to a high-temperature gas reactor control rod, which is used for high temperature gas reactors in nuclear electric power generation. The high-temperature gas reactor control rod, which is used for high temperature gas reactors in nuclear electric power generation, has a structure in which a plurality of control rod elements are joined to each other in a vertical direction (up/down direction). Each of the control rod elements accommodates a neutron absorber such as B4C. Conventionally, a metal-based high-temperature gas reactor control rod has been used for the control rod element serving as a means to accommodate a neutron absorber in a high temperature gas reactor. However, in the case of a large-scale high temperature gas reactor, in which the reactor core output power and the output power density are large and the temperature conditions are harsh, the control rod element made of a metallic material may cause the metal to melt, making it impossible to use the control rod repeatedly. This has been a technical problem. For this reason, in a large-scale high temperature gas reactor, a high-temperature gas reactor control rod made of C/C composite and a control rod element made of SiC/SiC composite, which can be used repeatedly, may be used as a control rod material that is an alternative to the metallic material. Here, a known elevating and lowering mechanism for the high-temperature gas reactor control rod that is driven by a control rod drive apparatus has the following mechanism. A wire fixed to and integral with the control rod element is inserted through the interior of the inner cylinder of each of the control rod elements. By moving the wire upward and downward, the high-temperature gas reactor control rod is elevated and lowered. In view of such circumstances, a mechanism has also been proposed, in which a screw thread or an engaging portion is provided at a lower portion of an outer cylinder and an inner cylinder of each of control rod elements to connect the control rod element to each other (see Patent Document 1 below). Such a mechanism can somewhat inhibit the high-temperature gas reactor control rod from swaying. However, with the screw thread joining, stress such as tensile, bending, and shearing stress concentrates on the screw thread. For this reason, hanging load cannot be made large (in other words, the number of control rod elements joined is limited). Moreover, the thread may break with, for example, small shaking. In view of this, a control rod having the following structure has also been proposed (see Patent Document 2 below). B4C powder is filled between the outer cylinder and the inner cylinder that use C/C composite and sintered. Connecting belts made of C/C are disposed in the outer cylinder of the control rod element, and the connecting belts are joined using a cruciform cross joint. The connecting belts adjacent to each other along the up/down direction are disposed so as to be twisted 90 degrees. [Patent Document 1] Japanese Unexamined Patent Publication No. H03 (1991)-134592 [Patent Document 2] Japanese Unexamined Patent Publication No. H06 (1994)-148372 However, the prior art invention has a configuration in which the cruciform cross joints provided for the control rod elements are joined by the connecting belts. Therefore, the entire weight of the control rod needs to be supported by the long connecting belts, so it is problematic in terms of strength. If the diameter of the cruciform cross joint is made larger to improve the strength of the cross joint, the width of the connecting belt needs to be made smaller correspondingly, so the strength of the connecting belt degrades. On the other hand, if the width of the connecting belt is made larger to improve the strength of the connecting belt, the diameter of the cruciform cross joint needs to be made smaller correspondingly, so the strength of the cross joint degrades. Therefore, it is difficult to improve the strength of the high-temperature gas reactor control rod as a whole. Accordingly, it is an object of the present invention to provide a high-temperature gas reactor control rod that does not degrade the joining state between the control rod elements even when stress such as tensile, bending, and shearing stress is applied thereto, by constructing a high strength support structure, and that can improve the safety of the high temperature gas reactor remarkably by improving the heat resistance thereof. In order to accomplish the foregoing object, the present invention provides a high-temperature gas reactor control rod comprising a plurality of control rod elements each having a neutron absorber between an outer cylinder and an inner cylinder that form a double cylindrical tubular shape, the control rod elements joined to each other in a vertical direction, the high-temperature gas reactor control rod characterized by comprising: a columnar support member for supporting at least the neutron absorber, the columnar support member disposed in the inner cylinder; and joining means for joining another control rod element, the joining means provided at least one of upper and lower ends of the support member. When the support member for supporting the neutron absorber is disposed in the inner cylinder as in the above-described structure, the weight of the neutron absorber is received by the support member; however, because the support member is in a columnar shape, the strength is higher than the joining belt. Therefore, even when stress such as tensile, bending, and shearing stress is applied, the joining state between the control rod elements is not impaired. As a result, the control rod main unit is not damaged at the time of emergency insertion to the nuclear reactor core and the output power adjustment, and the restart of the nuclear reactor thereafter can be done without any trouble. Moreover, since the joining means for joining another control rod element is provided at at least one of the upper and lower ends of the support member, joining of the control rod elements to each other can be accomplished smoothly. Thus, a high-temperature gas reactor control rod can be manufactured in a simple and easy manner while the safety is improved. It is desirable that, of the members that constitute the control rod element, the member/members other than the neutron absorber be made of a C/C composite material or a SiC/SiC composite material. When the member/members other than the neutron absorber is/are made of a C/C composite material or a SiC/SiC composite material, which has high shear strength and good heat resistance, the heat resistance can be increased and the mechanical strength can be improved. In particular, the SiC/SiC composite material has high strength, higher shear strength, and moreover excellent neutron damage resistance. For this reason, when this material is used, the above-described advantageous effects can be exhibited more significantly. Nevertheless, it is preferable that the SiC/SiC composite material be used only for the components that require strength and the like, as will be described later, because the SiC/SiC composite material is more costly than the C/C composite material. Moreover, when the member/members other than the neutron absorber is/are made of the above-mentioned material, it is possible to use the control rod repeatedly in an inert atmosphere at 2000° C., and there is no constraint on the operating conditions of the nuclear reactor because of the use temperature limit of the control rod. It is desirable that the support member have a side wall and a hollow portion surrounded by the side wall and extending in a vertical direction. When the support member has the hollow portion extending in a vertical direction, the weight of the support member can be reduced, so the weight received by the joining means can be accordingly reduced. This inhibits the high-temperature gas reactor control rod from damage. Therefore, the safety can be improved further. Moreover, the amount of the required raw material is less, so the cost of the high-temperature gas reactor control rod can be reduced. In addition, since the side wall exists around the hollow portion, the strength of the support member can be inhibited from degrading. It is desirable that the joining means have a shaft horizontally inserted through two holes formed in the side wall of the support member, and a ring-shaped joining belt through which the shaft passes. Thus, the control rod elements can be joined to each other merely by providing the shaft horizontally inserted through the two holes formed in the side wall of the support member and the ring-shaped joining belt through which the shaft passes. Therefore, it becomes possible to join the control rod elements to each other easily at low cost. It is desirable that the joining belt have a plate shape. Although the shape of the joining belt is not limited to a plate shape, it is possible to provide a joining belt that is lightweight and has improved strength when the joining belt has a plate shape. Moreover, the resistance to torsional stress can also be increased. It is desirable that a gap be provided between the control rod elements. When a gas is provided between the control rod elements, the shaft can move upward and downward within the joining belt. Therefore, even when stress is applied to the control rod element in an axial direction (in a vertical direction), the control rod elements can be prevented from damage. When the joining means are provided respectively at both upper and lower ends of the support member, it is desirable that the shaft provided at the upper end and the shaft provided at the lower end be disposed so as to be in a twisted state, and that the width of the joining belt be configured to be smaller than the axial length of the shaft in the hollow portion. When the width of the joining belt be configured to be smaller than the axial length of the shaft in the hollow portion, the joining belt can move along an extending direction of the shaft within the hollow portion. Moreover, when the shaft provided at the upper end and the shaft provided at the lower end are disposed in a twisted state, the joining belt provided at the upper end and the joining belt provided at the lower end can move in different directions. Therefore, the shaft and the joining belt can be prevented from damage even when stress is applied thereto from any direction as long as the direction is a direction perpendicular to the axis of the control rod element (i.e., a horizontal direction). It is desirable that the diameter of the shaft be smaller than the diameter of the two holes formed in the side wall. When the diameter of the shaft is smaller than the diameter of the two holes formed in the side wall (in other words, when the shaft is inserted through the holes with a slight clearance), stress can be alleviated in a similar manner to the above. It is desirable that an internal hollow portion width of the joining belt along a direction perpendicular to the axis of the shaft be larger than the diameter of the shaft. When the internal hollow portion width of the joining belt along a direction perpendicular to the axis of the shaft is larger than the diameter of the shaft, the shaft can slightly rotate in a horizontal direction within the joining belt. Therefore, the joining belt and the shaft can be prevented from damage even when stress is applied thereto in a bending direction (in a twist direction). It is desirable that the shaft be disposed at a position near the lower end of the side wall of the support member in a control rod element positioned upward of the adjacent control rod elements among the plurality of control rod elements, and the shaft be disposed at a position near the upper end of the side wall of the support member in a control rod element positioned downward thereof. The length of the joining belt can be kept small when the shaft is disposed at a position near the lower end of the side wall of the support member in the control rod element positioned upward while the shaft is disposed at a position near the upper end of the side wall of the support member in the control rod element positioned downward. As a result, the size of the joining belt can be reduced. Moreover, it is possible to prevent unnecessary swaying of the control rod. It is desirable that the shaft be kept in a condition such as to be inserted through the two holes even when one end of the shaft is in contact with an inner surface of the inner cylinder. As long as the shaft is kept in a condition such as to be inserted through the two holes even when one end of the shaft is in contact with an inner surface of the inner cylinder, the control rod elements can be prevented from falling, which results from disengagement of the shaft. It is desirable that a neutron absorber supporting flange extending toward the inner cylinder be formed at the lower end of the support member or in the vicinity thereof. When the neutron absorber supporting flange extending toward the inner cylinder is formed at the lower end of the support member or in the vicinity thereof, the neutron absorber can be supported from below. Thus, the neutron absorber can be supported easily. It is desirable that the support member have a polygonal cross-sectional shape, and that the polygon be an even number polygon. When the cross-sectional shape of the support member is in an even number polygonal shape, the shaft can be disposed between the side walls opposite to each other, so the support member can be manufactured easily. It is desirable that the support member in the polygonal cross-sectional shape be formed by combining flat plate-shaped parts made of a carbonaceous material with each other. When the support member in the polygonal cross-sectional shape is formed by combining flat plate-shaped parts made of a carbonaceous material with each other, the components that constitute the support member can be manufactured easily, and as a result, the manufacturing cost of the high-temperature gas reactor control rod is lowered. It is desirable that the neutron absorber supporting flange be integrally formed with the flat plate-shaped part made of a carbonaceous material. When the neutron absorber supporting flange is integrally formed with the flat plate-shaped part made of a carbonaceous material, the load of the neutron absorber is applied in a plane direction of the flat plate-shaped part made of a carbonaceous material, so the load of the neutron absorber is dispersed. As a result, the control rod elements can be prevented from damage, and the safety is improved further. The present invention achieves significant advantageous effects of not degrading the joining state between the control rod elements even when stress such as tensile, bending, and shearing stress is applied thereto, by constructing a high strength support structure, and of improving the safety of the high temperature gas reactor remarkably by improving the heat resistance thereof. A first embodiment of the present invention will be described hereinbelow with reference to FIGS. 1 through 15. As illustrated in FIG. 1, a high-temperature gas reactor control rod of the present invention has a structure in which a plurality of control rod elements 1 are joined to each other in a vertical direction (up/down direction). A slight gap is provided between the control rod elements 1. The gap is provided between the control rod elements 1 because, in that way, joining bolts 3a and 3b can move upward and downward within a later-described joining belt 6 when stress is applied to the control rod element 1 in an up/down direction, so that the control rod element 1 can be prevented from damage. As illustrated in FIGS. 2 to 4 (note that the neutron absorber 7 is not shown in FIG. 2), the control rod element 1 has an outer cylinder 9, an inner cylinder 8, neutron absorbers 7 disposed between the cylinders 8 and 9, a columnar support member 2 disposed in the inner cylinder 8, a lower lid 5, disposed at the lower ends of the cylinders 8 and 9, for supporting the neutron absorbers 7 at the bottom, and an upper lid 10 disposed at the upper ends of the cylinders 8 and 9. As illustrated in FIG. 5, the support member 2 has a substantially quadrangular cross-sectional shape, and it is constructed by combining two flat plate-shaped support plates 12a (side walls) made of a C/C composite material and two flat plate-shaped support plate 12b (side walls) made of a C/C composite material. When the support plates 12a and 12b are in a flat plate shape, it becomes easy to prepare the components constituting the support member 2, and when the support plates 12a and 12b are made of a C/C composite material, improvements in heat resistance and mechanical strength can be achieved. Furthermore, when the four support plates 12a and 12b are combined, a hollow portion 28 can be formed at the center of the support member 2 and the weight of the support member 2 can be reduced, so that the weight applied to a later-described joining means can be reduced. The detailed structure of the support plate 12a is as follows. As illustrated in FIGS. 6(a) and 6(b), flanges 13 to be fitted into the slits of the later-described support plate 12b are formed at side portions of a main portion 14 integrally with the main portion 14. In addition, at lower end positions of the support plate 12a, lower lid supporting flanges 15 extending toward the inner cylinder 8 are formed integrally with the flanges 13 (and also with the main portion 14), to form a structure in which the lower lid 5 is placed on the lower lid supporting flanges 15. The lower lid supporting flanges 15 extend toward the inner cylinder 8 and have the function of neutron absorbing material supporting flanges that bear the load of the neutron absorbing materials through the lower lid 5. With such a structure, the load of the neutron absorbers 7 applied through the lower lid 5 is applied in a plane direction of the support plate 12a, so the load of the neutron absorbers 7 can be dispersed. Therefore, the support member 2 can be prevented from damage. Moreover, since the load is applied in a plane direction of the support plate 12a, a structure utilizing the high shear strength of the C/C composite is formed. A hole 16 is formed near the lower end of the support plate 12a, to form a structure in which a bolt 3a (shaft), shown in FIG. 8, is inserted through the hole 16 and the ring-shaped joining belt 6 disposed in the support member 2 in a horizontal direction. The bolt 3a is secured to the support member 2 by a nut 4, shown in FIG. 9. For the same reason as described above (the reason that the strength and the like are taken into consideration), the joining belt 6, the bolt 3a, and the nut 4 are made of a C/C composite material. The joining belt 6 has a plate-like shape, whereby the low weight and high strength of the joining belt 6 are achieved. In addition, notches 17 for placing the upper lid 10 thereon are formed at upper end positions of the support plate 12a. On the other hand, the detailed structure of the support plate 12b is as follows. As illustrated in FIGS. 7(a) and 7(b), slits 18 in which the flanges 13 of the support plate 12a are fitted are formed in a main portion 20. Each of the slits 18 is a vertically long opening. Thereby, the contact area of the support plates is large, and the load is applied in a plane direction on both the support plates 12a and 12b, so that the high shear strength of the C/C composite can be utilized. In addition, at lower end positions of the support plate 12a, lower lid supporting flanges 19 extending toward the inner cylinder 8 are formed integrally with the main portion 20, to form a structure in which the lower lid 5 is placed on the lower lid supporting flanges 19. With such a structure, the load of the neutron absorbers 7 applied through the lower lid 5 is applied in a plane direction of the support plate 12b as in a similar manner to the above, so the load of the neutron absorbers 7 can be dispersed. Therefore, the support member 2 can be prevented from damage. Furthermore, since the load is applied in a plane direction of the support plate 12a, a structure utilizing the high shear strength of the C/C composite is formed. The support plates 12a and 12b may be merely combined with each other if it is possible to obtain a sufficient strength by merely combining them together. It is also possible to increase the joining strength using a carbonaceous adhesive agent. A hole 21 is formed near the upper end of the support plate 12b, to form a structure in which a bolt 3b (shaft), shown in FIG. 8, is inserted through the hole 21 and the ring-shaped joining belt 6 (shown in FIG. 10) disposed in the support member 2 in a horizontal direction. The bolt 3b is secured to the support member 2 by a nut 4, shown in FIG. 9. For the same reason as described above (the reason that the strength and the like are taken into consideration), the bolt 3b is made of a C/C composite material. In addition, notches 22 for fitting the upper lid 10 thereto are formed at upper end positions of the support plate 12a. The upper lid 10 may be bonded to the support plates 12a and 12b using a carbonaceous adhesive agent. The support plates 12a and 12b have a tensile strength of about 250 MPa. When the minimum cross-sectional area in which the bolt 3b passes through is 1.35 cm2, it is possible to hang a static load of 33.7 kN. The joining belt 6, the bolt 3a (or 3b), and the nuts 4 constitute the joining means. A low cost and highly reliable joining means can be provided because the strong joining means can be constructed with such a small number of components. In the case that the width of the joining belt 6 (L6 in FIG. 10(b)) is 28 mm and the thickness thereof (L7 in FIG. 10 (a)) is 3 mm, it is possible to hang a static load of 19.6 kN. Therefore, the tensile strength is improved remarkably. When the diameter of the bolt 3a (or 3b) (L1 in FIG. 8(b)) is 18 mm, the shear strength is 19.2 kN, so the shear strength is remarkably improved. In addition, the diameter of the holes 16 and 21 (L2 in FIG. 6 and L3 in FIG. 7) is configured to be slightly larger than the diameter of the bolts 3a and 3b (L1 in FIG. 8(b)). This allows the bolt 3a (or 3b) to pass through the holes easily. Moreover, the bolt 3a (or 3b) can slightly move within the holes 16 and 21 because the bolt 3a (or 3b) is inserted through the holes 16 and 21 with a slight clearance, and as a result, when external stress is applied thereto, the stress can be alleviated (in other words, the components that constitute the support member 2, such as the bolt 3a (or 3b) and the joining belt 6, can be prevented from breaking). Furthermore, the joining belt 6 is configured so that the internal hollow portion width (L4 in FIG. 10(a)) along a direction perpendicular to the axis of the bolt 3a (or 3b) is larger than the diameter of the bolt 3a (or 3b) (L1 in FIG. 8(b)). This configuration can also alleviate external stress for the same reason as described above. In addition, the width of the joining belt 6 (L6 in FIG. 10(b)) is configured to be smaller than the axial length of the bolt 3a (or 3b) (L5 in FIG. 8(b)) within the hollow portion 28. As a result, the joining belt 6 can move along an axial direction of the shaft, so that the external stress can be alleviated. Moreover, the bolt 3a and the bolt 3b are disposed in a twisted state (in a state in which their axes are at right angles to each other), and therefore, the two joining belts (i.e., referring to FIG. 5, the joining belt 6 disposed at an upper portion of the support member 2 and the joining belt 6 disposed at a lower portion of the support member 2) can move in different directions. As a result, stress can be alleviated even when stress is applied in a direction perpendicular to the axis of the control rod element 1 (e.g., in directions A or directions B in FIG. 5). In FIG. 5, a bolt 3c is disposed at a position near the lower end of the support plate 12a, while the bolt 3b is disposed at a position near the upper end of the support plate 12a. This structure allows the length of the joining belt 6 to be short, so the size of the joining belt can be made small. Furthermore, the bolts 3a, 3b, and 3c have such a length that, even when the nuts 4 come off from the bolts 3a, 3b, and 3c and the bolts are displaced toward one side within the inner cylinder 8 due to, for example, deterioration over time or shocks, the heads 30 of the bolts 3a, 3b, and 3c will not come into contact with the inner surface of the inner cylinder 8 so that the bolts can be prevented from coming off from the two holes 16 (or 21 or 23), which are in a inserted state. Thus, even when the nuts 4 come off, the bolt 3a, 3b, and 3c are prevented from coming off and consequently the control rod element 1 can be prevented from falling off. (Description of Other Components) As illustrated in FIGS. 11(a) and 11(b), the inner cylinder 8 has a cylindrical shape, and it is made of a C/C composite material. As illustrated in FIGS. 12(a) and 12(b), the outer cylinder 9 has a cylindrical shape having a larger diameter than the inner cylinder 8, and it is made of a C/C composite material. As illustrated in FIGS. 13(a) and 13(b), the upper lid 10 has a disk shape, and the outer diameter thereof (L8 in FIG. 13(b)) is configured to be the same as the outer diameter of the outer cylinder 9 (L9 in FIG. 12(b)). A notch 31 is formed in the outermost periphery of the upper lid 10, and the width of the notch 31 (L10 in FIG. 13(b)) is configured to be the same as the thickness of the outer cylinder 9 (L11 in FIG. 12(b)). In addition, a groove 32 is formed inward of the notch 31. The outer diameter of the groove 32 (L12 in FIG. 13(b)) is configured to be the same as the outer diameter of the inner cylinder 8 (L13 in FIG. 11(b)), and the width of the groove 32 (L15 in FIG. 13(b)) is configured to be the same as the thickness of the inner cylinder 8 (L14 in FIG. 11(b)). Furthermore, grooves 33 in which end portions of the support plates 12a and 12b are to be fitted are formed inward of the groove 32. With such a structure, the upper lid 10 can be fitted at a position above the inner cylinder 8, the outer cylinder 9, and the support member 10. As illustrated in FIGS. 14(a) and 14(b), the lower lid 5 has a disk shape. The lower lid 5 has substantially the same structure as that of the upper lid 10 (i.e., a notch 35, a groove 32, and a groove 33 are formed at the same locations). With such a structure, the lower lid 5 can be fitted at a position below the inner cylinder 8, the outer cylinder 9, and the support member 10. However, what is different is that an internal space shape 34 is slightly different, and that the thickness of the lower lid 5 (L17 in FIG. 14(b)) is slightly greater than the thickness of the upper lid 10 (L18 in FIG. 13(b)) in order to support the neutron absorbers 7 at a lower location. It should be noted that the safety of the nuclear reactor is improved by employing a structure in which the neutron absorbers 7 are supported by the disk-shaped lower lid 5 (i.e., not supported by a screw thread) in this way. The inner cylinder 8 and the outer cylinder 9 are the components only for accommodating the neutron absorbers 7, so the thicknesses of the cylinders 8 and 9 (L14 in FIG. 11(b) and L11 in FIG. 12(b)) may be made small. Also, the upper lid 10 is used only for sealing the control rod elements, and therefore, the thickness of the upper lid 10 (L18 in FIG. 13(b)) may be configured to be small. Furthermore, although the lower lid 5 has a slightly larger thickness than the upper lid 10, the thickness of the lower lid 5 (L17 in FIG. 14(b)) need not be made so great because only the regions sandwiched by the neutron absorbers 7 and the lower lid flanges 15 and 19 receive the load. By employing the structure as described above, the material cost of the high-temperature gas reactor control rod can be reduced. (Modified Examples of the First Embodiment) (1) Of the components that constitute the control rod element 1, the components other than the neutron absorbers 7 are made of a C/C composite material in the above-described example. However, it is possible that all the components other than the neutron absorbers 7 may be made of a SiC/SiC composite material. It is also possible that only the primary components (such as the bolts 3a, 3b, and 3c, and the joining belt) may be made of a SiC/SiC composite material. It is also possible that only the primary components (such as the bolts 3a, 3b, and 3c, and the joining belt) may be made of a SiC/SiC composite material and the other components may be made of an ordinary carbon material. (2) The shape of the support member is not limited to a quadrangular cross-sectional shape. It is of course possible to employ a regular hexagonal cross-sectional shape as shown in FIG. 15, or a regular octagonal cross-sectional shape, for example. It should be noted that when employing a regular hexagonal cross-sectional shape as shown in FIG. 15, the bolts 3 should be disposed so that the axes of the bolts 3 are at 60 degrees to each other. (3) The bolts 3a, 3b, and 3c and the joining belt 6 of the control rod element 1 disposed in an upper portion of the control rod are placed under a greater load than the bolts 3a, 3b, and 3c and the joining belt 6 the control rod element 1 disposed in a lower portion of the control rod. For this reason, it is possible that the bolts 3a, 3b, and 3c of the control rod element 1 disposed in an upper portion of the control rod may have a larger diameter than the bolts 3a, 3b, and 3c of the control rod element 1 that are disposed at a lower portion, or that the joining belt 6 of the control rod element 1 that is disposed at an upper portion may have a greater thickness than the joining belt 6 of the control rod element 1 disposed in a lower portion of the control rod. It is also possible that the bolts 3a, 3b, and 3c and the joining belt 6 of the control rod element 1 disposed in an upper portion of the control rod may be made of a SiC/SiC composite material while the bolts 3a, 3b, and 3c and the joining belt 6 of the control rod element 1 disposed in a lower portion of the control rod may be made of a C/C composite material. A second embodiment of the present invention will be described hereinbelow with reference to FIGS. 16 through 18. As illustrated in FIG. 16, a control rod element 1 according to the second embodiment has an outer cylinder 9, an inner cylinder 8, neutron absorbers 7 disposed between the cylinders 8 and 9, a cylindrical columnar support member 2 disposed in the inner cylinder 8, a lower lid 5, disposed at the lower ends of the cylinders 8 and 9, for supporting the neutron absorbers 7 at the bottom, and a support ring 50, and securing screws 51. The outer cylinder 9 has a bell-like shape tapered toward the top, and it has a structure in which the neutron absorbers 7 and the inner cylinder 8 are inserted from a lower opening 52. In the upper end of the outer cylinder 9, a through hole 53 is provided for passing the columnar support member 2 therethrough. In addition, at the center of the disk-shaped lower lid 5 disposed at the lower end of the inner cylinder 8, a through hole 55 is provided for passing the support member 2 therethrough. The outer diameter of the lower lid 5 (L21 in FIG. 18) is substantially the same as the inner diameter of the outer cylinder 9 (L20 in FIG. 18). In addition, the support ring 50 is disposed below the lower lid 5. The outer diameter of the support ring 50 (L22 in FIG. 18) is substantially the same as the inner diameter of the outer cylinder 9 (L20 in FIG. 18). In the outer cylinder 9 and the support ring 50, holes 56 and 57 are respectively formed at the positions that match each other when the support ring 50 is positioned in the outer cylinder 9. A plurality of (about 10 in the present embodiment) screws 51 made of, for example, a 2D-C/C composite are screw-fitted to the holes 56 and 57. Thereby, the support ring 50 is secured to the outer cylinder 9. The screws 51 are provided so as not to protrude from the outer surface of the outer cylinder 9. The length of the inner cylinder 8 is set at such a length that the upper end thereof is almost in contact with the upper inner surface of the outer cylinder 9, to form such a structure that a large number of neutron absorbers 7 can be disposed between the cylinders 8 and 9. In the above-described structure, the load of the inner cylinder 8 and the neutron absorbers 7 is received by the lower lid 5, and the lower lid 5 is supported from below by the support ring 50. The support ring 50 has a width along an up/down direction, and it is screw-fastened from horizontal directions. Thus, the load from the lower lid 5 is applied to the support ring 50 in a plane direction thereof and further to a plurality of screw-fastened portions, so that the load bearing performance is increased. The support member 2 is inserted in the inner cylinder 8. The support member 2 is provided with a bulging portion 62. The outer diameter of the bulging portion 62 (L25 in FIG. 16) is set larger than the hole diameter of the through hole 53 (L26 FIG. 16) provided at the upper end of the outer cylinder 9. Thus, the bulging portion 62 is caught by the through hole 53 so that the control rod element 1 can be supported by the support member 2 via the bulging portion 62. The upper end of the bulging portion 62 and the lower edge of the through hole 53 of the outer cylinder 9 are in a tapered shape, to form such a structure that, by bringing these portions into contact with each other, swaying of the outer cylinder 9 can be lessened. The detailed structure of the support member 2 is as follows. As illustrated in FIG. 17, it has an upper supporting member 60, the bulging portion 62, and a lower supporting member 64. The lower supporting member 64 has a thread portion 63, while the upper supporting member 60 has a threaded hole 61. At the lower end of the upper supporting member 60, a smaller diameter portion 66 having a smaller diameter than the other portion is provided. A step portion 68 is formed at the boundary between the smaller diameter portion 66 and a larger diameter portion 67 (the other portion). A fitting hole 69 is provided in the bulging portion 62. The diameter of the fitting hole 69 (L30 in FIG. 17) is set larger than the diameter of the smaller diameter portion 66 (L31 in FIG. 17) of the smaller diameter portion 66 but is set smaller than the diameter of the larger diameter portion 67 (L32 in FIG. 17). Thus, when the smaller diameter portion 66 of the upper supporting member 60 is inserted into the fitting hole 69 of the bulging portion 62 from below the upper supporting member 60, the upper end of the bulging portion 62 is caught by the step portion 68. When the thread portion 63 of the lower supporting member 64 is screw-fitted to the threaded hole 61 of the upper supporting member 60 under this condition, the bulging portion 62 is sandwiched and fixed between the upper supporting member 60 and the lower supporting member 64. Here, when a plurality of control rod elements 1 are joined to each other, a threaded hole (not shown) should be formed at the lower end of the lower supporting member 64 so that the support column of another control rod element (not shown), which is provided with the bulging portion and the thread portion, can be attached from below. In the case that a thread portion and a threaded hole are provided, it is also possible to employ a structure in which the upper supporting member 60 has the thread portion while the lower supporting member 64 has the threaded hole. This configuration achieves a structure in which the neutron absorbers 7 can be reliably accommodated in the outer cylinder 9 with a small parts count and with a simple configuration. In addition, the neutron absorbers 7 that have heavy weight can be supported stably by the support member 2. It should be noted that when all the parts and components, including the outer cylinder 9, of the present embodiment are formed of a C/C composite material, weight reduction can be achieved while ensuring high strength. It is also possible to use a SiC/SiC composite in place of the C/C composite, to achieve still higher strength. Nevertheless, because the SiC/SiC composite is expensive, it is possible to use the SiC/SiC composite only for the bulging portion 62, the lower lid 5, the support ring 50, and the screws 51, for example, which require particularly high strength. To integrally form the outer cylinder 9 with a shape tapered toward the top, it is preferable to use a filament winding method or a hand lay-up method. It is particularly preferable to use a filament winding method, with which even higher strength can be obtained. The filament winding method is as follows. Normally, a carbon fiber bundle, in which carbon fibers are bundled, is immersed in a low viscosity binder containing a thermosetting resin, a solvent, and the like, and thereafter, the carbon fiber bundle with the binder is wound around a mandrel in a crucible shape, to shape it into a required crucible shape. The winding of the carbon fiber bundle onto the mandrel may be conducted by any suitable method, for example, the method described in Japanese Unexamined Patent Publication No. 2003-201196, which is a patent application made by the present applicant. Thereafter, thermosetting is conducted at a temperature of from about 100° C. to about 300° C., for example, and the resultant molded product is carbonized in an inert gas such as a N2 gas at a temperature of about 1000° C., for example. After this carbonization, a phenolic resin, tar pitch, or the like is impregnated therein as needed, and the resulting article is further heated at a temperature of 1500° C. or higher to perform carbonization (graphitization). The crucible obtained through the above-described process is heated, for example, in a halogen gas atmosphere at a temperature of from about 1500° C. to about 2500° C., and a refining process is performed, to form a C/C material. The hand lay-up method is as follows. A carbon fiber cloth is adhered to a crucible mold to prepare a molded product, and thereafter, thermosetting, carbonization, graphitization, and refining process are performed in a similar manner to the FW method, to obtain a C/C material. A third embodiment will be described with reference to FIG. 19. The structures of the inner cylinder, the neutron absorbers, and the support member are the same as those in the second embodiment, and therefore, these components are not shown in FIG. 19. As illustrated in FIG. 19, through holes 70 are formed intermittently along the circumferential direction slightly above the lower end of the outer cylinder. Flat plate-shaped support plates 71 are inserted in the through holes 70. Both ends of each of the support plates 71 are supported from below by the outer cylinder 9 that is below the through holes 70, whereby the neutron absorbers and the inner cylinder are supported from below by the support plates 71. A through hole 55 for inserting the support member 2 therethrough is provided near the lengthwise center of each of the support plates 71. The number of the support plates 71 disposed using the through holes 70 is not limited to two, as described above, but may be one, or may be three or more, according to the strength required. The width of the through holes 70 may be set as appropriate. Moreover, the thickness of the support plate 71 may be set as appropriate according to the strength required. This configuration makes it possible to support neutron absorbers with an extremely simple configuration, in which the through holes 70 are formed and the support plates 71 are inserted in the through holes 70. Moreover, the thickness, width, and the like of the support plates may be set according to the weight of the subject to be supported, such as the neutron absorber and the inner cylinder, so the strength setting can be made easily. The neutron absorbers may be directly placed on the support plates 71, or may be placed on the lower lid 5 as shown in FIG. 18, which may be disposed above the support plates 71. It is also possible to use, in combination, the configuration that uses the lower lid 5 and the support ring 50 as shown in FIGS. 16 and 18, to increase the support strength. Furthermore, in the second embodiment and the third embodiment described above, it is also possible that, depending on the circumstances, a bolt or the like may be fitted to the location corresponding to the through hole 55, in the lower lid 5 or the support plate 71, for passing the support member, so that the control rod element can be connected to another control rod element using the bolt. The present invention is applicable to a high temperature gas reactor for nuclear electric power generation. |
|
abstract | A system is provided for use with a nuclear reactor which is mounted on a barge and which floats in a water tank. The system includes at least one water pipe which extends from a source of water to the interior of the tank. The system also includes a pipe which permits the drainage of water from the water tank. Valves are imposed in the piping so that the water in the tank will have a desired level and temperature. The system also enables fresh water to be supplied to the containment interior of the reactor. Further, the system includes piping and valves to supply water to the condenser and to drain water from the condenser. The system also includes flexible and slack tubular sections positioned in the piping between the barge and the water tank which allows the barge to move while maintaining the integrity of the tubing. |
|
039403114 | abstract | A system is provided for determining during operation of a nuclear reactor having fluid pressure operated control rod mechanisms the exact location of a fuel assembly with a defective fuel rod. The construction of the reactor internals is simplified in a manner to facilitate the testing for defective fuel rods and to reduce the cost of producing the upper internals of the reactor. |
047298707 | description | DETAILED DESCRIPTION OF THE INVENTION As is shown by FIG. 1, the plug 10 according to the invention is a solid metal cylindrical part having a small diameter cylindrical portion 12 fitting into the end of the tubular can 14 and a large diameter cylindrical portion 16, separated from portion 12 by a shoulder 18, which abuts against the end of can 14. As illustrated in FIG. 1, the external diameter of plug portion 16 is substantially equal to the external diameter of can 14. According to the invention, cylindrical portion 12 is designed in such a way that it can be fitted into can 14 by using a minimum force of approximately 15 daN, tightening being obtained by the elastic deformation of the can, which makes it possible to ensure the securing of the plug under optimum conditions prior to the carrying out of a good quality weld without filling metal. To this end, fig shows that the external diameter D of the cylindrical portion 12 is slightly smaller than the internal diameter d of the can. Three serrations 20 at 120.degree. from one another are formed on said cylindrical portion 12 according to the generatrixes thereof. As is more particularly illustrated by FIG. 2, each of the serrations 20 forms two beads 22, whereof the thickness e overhanging with respect to the norminal diameter D of the cylindrical portion 12 slightly exceeds (by approximately 1/100 mm) ##EQU1## so that the fitting of portion 12 into can 14 leads to a local elastic deformation of the interior of the can and the beads 22 adequate for ensuring the desired tightening. In known manner, the fitting of plug 16 into can 14 is facilitated by the bevelled shape of end 24 of cylindrical portion 12. When fitting has been completed, plug 16 and can 14 are welded at 26, without filler metal, along their respective junction plane. As can 14 is produced in successive batches, its internal diameter d can vary by a few hundreths of a mm between a maximum diameter d.sub.max and a minimum diameter d.sub.min. The diameter D of the cylindrical plug portion 12 is preferably chosen equal to the minimum diameter d.sub.min and the thickness e of the beads 22 formed by the serrations 20 is equal to ##EQU2## In the case of mass production from cans having an internal diameter varying between certain known limits, it is possible to ensure an automated fitting of the plugs into the cans with substantially no wastage and under tightening conditions very close to the ideal tightening of approximately 1/100 mmm for which all the defects observed with the prior art are eliminated. It should be noted that the number of serrations 20 formed on the cylindrical portion 12 of the plug can exceed 3. However, the fitting force of the plug rapidly increases with the number of serrations. Thus, whereas this force is 15 daN when three serrations are formed on the cylindrical portion 12 of a given plug, it increases to 30 daN if the cylindrical portion 12 of said plug had four serrations. FIG. 3 shows in exemplified manner a tool making it possible to form the serrations on the surface of the cylindrical plug portion 10. This tool comprises a body 30 having a bore 32 in which is located the cylindrical plug portion. Three holes 34 are made radially at the same level in body 30 of the tool and issue into bore 32. These holes 34 are distributed at 120.degree. from one another about the axis of body 30 and each of which receives a machining point 36, which is immobilized in the corresponding hole by means of a screw 38. The position of the points 36 is regulated by a member 40 shown in mixed line form in FIG. 3. Member 40 is centered in bore 32 and is provided at its end placed facing points 36 with a portion 40a, whose diameter determines the depth of the serrations to be made in the plug. When regulation or setting is at an end, the points 36 are immobilized by tightening screws 38. The machining of serrations 20 on plug portion 12 is then carried out by driving the latter into the bore 32 of the tool parallel to the axis of said bore. This operation is followed by finishing on the lathe making it possible to level the ends of the beads 22, so as to eliminate rough edges and calibrate said beads to the desired thickness e. |
claims | 1. A process for preparing a pharmaceutically-acceptable formulation of a radioactive chelate composition comprising the steps of:a) irradiating Sm-152 in a lower flux portion of the nuclear reactor having less than 8.5×1013 neutron/cm2-sec to form low specific activity Sm-153, wherein the isotope composition after the irradiation contains mainly Sm-152 and Sm-153 with impurity of Eu-154 less than 0.093,μCi Eu-154/ mCi Sm-153 after 5 days of decay, thereby providing an extended Expiration Date greater than or equal to about 5 days;b) taking the prepared isotope mixture from step a) and either using it in step c) or allowing it to decay and then using it in step c) which decay further lowers the specific activity of the Sm-153 formed in step a) while maintaining less than 0.093 μCi of Eu-154 per mCi of Sm-153; andc) reacting DOTMP or a physiologically-acceptable salt thereof as the chelant with the Sm-153 isotope mixture from step b) in an, aqueous solvent to form the radioactive chelate composition wherein the Sm-153 dosage is at least 35 mCi that is pharmaceutically-acceptable and has a Clinically Relevant Dosage that is therapeutically effective. 2. The process of claim 1 wherein the Sm-153 isotope of step (b) and step (c) is used without further dilution with non-radioactive Sm. |
|
claims | 1. An apparatus to remove carbon-dioxide with carbon-14 from atmospheric gases comprising:a. a mixture of atmospheric gases with a measurable abundance of carbon dioxide and a measurable abundance of carbon dioxide with carbon-14;b. a blower to accelerate said atmospheric gases to a predetermined velocity;c. a wide vortex chamber for the centrifugal separation of said atmospheric gases;d. an upper narrow vortex chamber for the centrifugal separation of said atmospheric gases;e. a lower narrow vortex chamber for the centrifugal separation of said atmospheric gases;f. an upper lateral adapter connected to said wide vortex chamber and connected to said upper narrow vortex chamber;g. a lower lateral adapter connected to said wide vortex chamber and connected to said lower narrow vortex chamber;h. an airflow adapter connected to said blower and connected to said wide vortex chamber, the airflow adapter comprising a blower input connector, a tangential airflow adapter, and a tangential airflow stabilizer, wherein the tangential airflow stabilizer further comprises inner reinforcements evenly spaced vertically and centered around the blower input connector, and wherein the interior cross-section of the airflow stream of the tangential airflow stabilizer is tapered or shaped at the top and bottom of the interior cross-section, excluding two wedge-shaped cross-sections from the tangential airflow;i. a cone having a tip and a foundation to shape airflow of said atmospheric gases during centrifugal separation inside said lower narrow vortex chamber, the foundation has axial alignment extrusions aligned with the central axis of the cone;j. a base having a top and bottom, the base being connected to said cone, the bottom of the base being perpendicular to the central axis of the lower narrow vortex chamber, the base has vertical vent fins symmetrically distributed around its central axis, connecting from the bottom of the base to the lower narrow vortex chamber, and the cone foundation has a diameter less than the diameter of the base to allow the cone foundation to be subsumed by the base, the bottom of the base has structural reinforcements to hold the cone foundation in alignment with the central axis of the lower narrow vortex chamber, the structural reinforcements including a central reinforcement, circular reinforcements, and symmetrically distributed radial reinforcements;k. a vent connected to said upper narrow vortex chamber to allow output of low-density gases from said atmospheric gases after centrifugal separation. 2. The apparatus of claim 1, wherein the upper and lower narrow vortex chambers have an interior radius and combined height, where the height of the upper narrow vortex chamber is less than or equal to half the lower narrow vortex chamber. 3. The apparatus of claim 1, wherein the radial to tangential airflow adapter changes the radial airflow at the blower input connector to a vertical stream at the tangential airflow stabilizer. 4. The apparatus of claim 1, wherein the position of the cone can be adjusted while remaining in alignment with the lower narrow vortex chamber. 5. The apparatus of claim 1, wherein the tangential airflow stabilizer further comprises outer reinforcements evenly spaced vertically and centered around the blower input connector. 6. An apparatus to remove carbon-dioxide with carbon-14 from atmospheric gases comprising:a. a mixture of atmospheric gases with a measurable abundance of carbon dioxide and a measurable abundance of carbon dioxide with carbon-14;b. a blower to accelerate said atmospheric gases to a predetermined velocity;c. a wide vortex chamber for the centrifugal separation of said atmospheric gases;d. a lower narrow vortex chamber for the centrifugal separation of said atmospheric gases;e. a lateral adapter connected to said wide vortex chamber and connected to said lower narrow vortex chamber;f. an airflow adapter connected to said blower and connected to said wide vortex chamber, the airflow adapter comprising a blower input connector, a radial to tangential airflow adapter, and a tangential airflow stabilizer, wherein the tangential airflow stabilizer further comprises inner reinforcements evenly spaced vertically and centered around the blower input connector, and wherein the interior cross-section of the airflow stream of the tangential airflow stabilizer is tapered or shaped at bottom of the interior cross-section, excluding a wedge-shaped cross-section from the tangential airflow;g. a cone of having a tip and a foundation to shape airflow of said atmospheric gases during centrifugal separation inside said lower narrow vortex chamber, the foundation has axial alignment extrusions aligned with the central axis of the cone;h. a base having a top and bottom, the base being connected to said cone, the bottom of the base being perpendicular to the central axis of the lower narrow vortex chamber, the base has vertical vent fins symmetrically distributed around its central axis, connecting from the bottom of the base to the lower narrow vortex chamber, and the cone foundation has a diameter less than the diameter of the base to allow the cone foundation to be subsumed by the base, the bottom of the base has structural reinforcements to hold the cone foundation in alignment with the central axis of the lower narrow vortex chamber, the structural reinforcements including a central reinforcement, circular reinforcements, and symmetrically distributed radial reinforcements; andi. a vent connected to said wide vortex chamber to allow output of low-density gases from said atmospheric gases after centrifugal separation. 7. The apparatus of claim 6, wherein the radial to tangential airflow adapter changes the radial airflow at the blower input connector to a vertical stream at the tangential airflow stabilizer. 8. The apparatus of claim 6, wherein the position of the cone can be adjusted while remaining in alignment with the lower narrow vortex chamber. 9. The apparatus of claim 6, wherein the tangential airflow stabilizer further comprises outer reinforcements evenly spaced vertically and centered around the blower input connector. |
|
048271390 | summary | BACKGROUND OF THE INVENTION In a nuclear reactor, the fissionable nuclear fuel is, most frequently, in the form of a plurality of individual rods assembled into a bundle of substantially square cross-sections, in such a manner that the rods are held in fixed, spaced relationship. Over a prolonged period of operation of the reactor, the fissionable fuel becomes depleted to the point where it no longer is capable of maintaining or fueling a fission reaction. When this state is reached, it is necessary to remove the rod assembly and replace it with a fresh one. The depleted rod assembly is still of potential value, however, since the rods are still highly radioactive and can be reprocessed in a suitable facility to become capable of sustaining or fueling a fission reaction. Inasmuch as reprocessing facilities are, more often than not, far removed from the nuclear reactor, it is necessary to ship the spent fuel over long distances, in as safe a manner as possible, both to the outside world and to the rod assembly itself. In order to insure the extreme degree of safety required, the rod assemble is generally loaded into a fuel basket which, in turn, is contained in a shipping cask. It is imperative that the basket and cask assembly be so constructed that harmful radiation does not escape, that the heat generated by the radioactive decay of the spent fuel is adequately dissipated, and that radioactive interaction between the fuel cells is kept below a critical level. To achieve these ends, numerous types of fuel cells shipping containers have been designed and used, examples of which are disclosed in U.S. Pat. Nos. 4,292,528 of Shaffer et al, 4,543,488 of Diem, 3,962,587 of Dufrance et al, and 4,399,366 of Bucholz. The Schaffer et al patent discloses a cask for radioactive material in which a plurality of internal fuel containing compartments are formed by a modular construction of surrounding heat conducting members and joined together as by welding, brazing, cementing, or mechanical interfitting. Neutron absorbing material is incorporated into the structure to suppress interaction between the fuel in adjacent compartments. Thus, Shaffer et al achieve the ends of heat dissipation and interaction suppression, as well as radiation suppression through the use of, for example lead shielding. Diem discloses a basket in which the individual fuel containing tubes are embedded, along with neutron absorbing plates, in a casting of high heat conductivity material, thereby creating an essentially solid, unitary structure having fuel containing tubes extending longitudinally therethrough. Dufrance et al disclose a basket and cask arrangement in which the basket is suspended within the surrounding cask by a plurality of metallic septa which are for coolant containing chambers. The septa are bonded to the basket and the outer shell to hold the basket firmly in its central orientation. Bucholz discloses a honeycomb-type structure for the fuel basket which defines a plurality of parallel tubes or cavities for holding the fuel cells. Neutron absorbing material is embedded within the walls of the honeycomb structure in the form of tubes, which may be filled with water to trap neutrons. The walls themselves function as heat conductors to the outer or cask wall. In all of the foregoing, the aims of suppressed interaction, heat dissipation, and radiation suppression are achieved. However, in these structures, as well as in much of the prior art, the problem of sudden dynamic shock and load in the event of an accident during handling or transportation is not addressed. The dynamic stresses imposed on the fuel basket in the event of an accident, such as, for example, a thirty foot fall by the cask onto an unyielding surface, can be and often are, catastrophic. Structural analysis of state-of-the-art type baskets under impact loading has shown that such baskets tend to suffer greatest stresses at points removed from the point of impact, and that multiple failures of the fuel containing tubes can occur. Further, such analysis has shown that in a substantialy unitary structure as shown in the Diem and Bucholz patents, there can be a failure or rupture of a plurality of fuel containing tubes or cells. A modular structure such as the Shaffer et al arrangement is also susceptible to catastrophic failure, since the tubes are actually formed of a plurality of pieces attached to each other, the points of attachment representing low stress resistance. In like manner, the septa of Dufrance et al are susceptible to detachment from the inner wall of the cask and from the wall of the basket under sudden heavy stress. SUMMARY OF THE INVENTION The present invention through its unique basket structure, achieves the desiderata of radiation and interaction suppression and heat dissipation, and, in addition, is less susceptible to catastrophic or widespread dynamic stress damage than prior art baskets. In one preferred embodiment of the invention, the fuel rod assembly containers, i.e., tubes, are seamless metallic members formed by casting, swaging, or other suitable means whose inside dimensions and shape are such that the rod assembly is essentially slip-fitted into the tube. The tubes are arranged into a pattern within the circular cask, with neutron poisoning spacers between adjacent tubes. The empty spaces resulting from an assemblage of substantially square tubes within a circular cavity are filled by filler blocks of suitable heat absorbing material which may also contain neutron poisoning material, if necessary. The entire assembly, rigid tubes, spacers, and filler blocks within a rigid wall cavity is itself rigid, with each element of the assembly held firmly in place by adjacent elements so that there is no relative motion between the elements under normal conditions, despite the fact that none of the elements of the assembly is attached or affixed to any other element. Because the various elements are not attached or connected to each other, in the event of a dynamic stress producing accident, such as the aforementioned thirty foot fall of the cask to impact upon an unyielding surface, the stresses produced are not transferred as readily to adjacent elements, and while elements along the axis of impact may be damaged, the stresses do not spread throughout the structure and damage substantially all of the element, especially the rigid, seamless tubes. Thus damage is not widespread or catastrophic, and a substantial margin of safety is, unlike in the prior art, maintained. Not only does the structure of the invention limit impact damage, it also limits stresses due to differential thermal expansion, as where some warping or bending of the walls of one of the tubes is not transferred as deformation stress to other adjacent tubes. In other embodiments of the invention, the spacers may be attached to the walls of the tubes principally to facilitate handling, and assembly of the basket, or alternatively, the tubes may be so formed that any pair of adjacent tubes forms a pocket between the tubes into which the neutron poisoning spacer is slipped and held in position. These and other features of the present invention will be more readily apparent from the following detailed description and the accompanying drawings. |
abstract | Perovskite single crystal X-ray radiation detector devices including an X-ray wavelength-responsive active layer including an organolead trihalide perovskite single crystal, a substrate layer comprising an oxide, and a binding layer disposed between the active layer and the substrate layer. The binding layer including a binding molecule having a first functional group that bonds to the organolead trihalide perovskite single crystal and a second functional group that bonds with the oxide. Inclusion of the binding layer advantageously reduces device noise while retaining signal intensity. |
|
052522580 | abstract | The invention provides a method of recovering and storing radioactive iodine by a freeze vacuum drying process, in which off-gas generated when spent fuel is subjected to shearing and dissolving treatments is scrubbed and, when necessary, is subjected to a precipitation treatment by addition of additives, after which waste liquid containing radioactive iodine is freeze-dried by a freeze vacuum drying process to recover radioactive iodine as iodine compounds. As a result, since the radioactive iodine does not vaporize, release of the radioactive iodine into the environment can be eliminated. In addition, consumption of a collecting agent such as silver zeolite for collecting vaporized radioactive iodine can be reduced. The iodine compounds containing the recovered radioactive iodine is given the same composition as a stable, naturally occurring mineral and is solidified and mineralized as by a high-pressure press. This makes it possible to store long half-life .sup.129 I radioactive iodine safely for an extended period by sealing recovered radioactive iodine in stable minerals for a long period of time. |
040100707 | description | DETAILED DESCRIPTION OF THE INVENTION As indicated above, FIG. 1 shows only the lowermost portion of an absorber element 1 having its leading tip 2, which must directly penetrate the pebble bed, having a substantially hemispherical shape, although other known tip shapes could be used. As shown, behind the tip 2, the element 1 has the shape of a substantially helically coiled rod, forming a single thread as contrasted to a multi-threaded or double-helical shape which would result in a considerably larger angle of pebble-bed penetration and, therefore, would require a considerably greater force of penetration P. The rod is preferably made of a suitable metal and is hollow or tubular, and is filled with the absorber material. Assuming that the pebbles or fuel spheres of the pebble bed have a characteristic cross-sectional size or diameter of 60 mm, the outside diameter of the element's rod or tube should likewise be about 60 mm. The element has an inside diameter and an axially directed coil convolution separation distance which are both greater than the cross-sectional dimension or diameter of the rod or tube used, and of the pebbles or fuel spheres. The tip 2 is formed by the leading end of the rod or tube, possibly as a integral part of the balance. In FIG. 2, the reactor container 3 is shown, containing the pebble bed 4 made up of a large number of pebbles or fuel spheres of which only a few are indicated at 4a. Only one of the new absorber elements 1 is shown, but of course, a larger number would ordinarily be provided. These would be distributed over the circumference of the bed 4 which has a generally cylindrical contour excepting for the conical run-out 3a of the container 3. The element 1 is shown substantially completely inserted in the bed 4. The upper end of the element 5 is provided with a tubular shank 6 provided with a rotative drive 7 which may also provide for vertical movement to the extent required for the initial insertion of the element 1, after which rotation of the element 1 effects its complete penetration into the bed 4. As previously indicated, the active portion of the rod 1 is itself hollow or tubular as shown by the broken-away segment in FIG. 1, the absorber material 1a then being on the inside of the rod or tube 1. It can be seen that the tip 2 is directed to penetrate the bed 4 in a non-vertical direction, and that this direction varies angularly during penetration of the tip in the bed. Behind the tip 2 the element 1 has the shape of the substantially helically coiled rod or tube. The interior of the helical shape and the spaces between the helical convolutions are open and permit the passage of the fuel sphere or pebbles. The new absorber element in its form of a helical spiral coil with its hollow or empty spaces both within the convolutions and from one convolution to another, has additional advantages over the described easier penetration. From the viewpoint of nuclear physics, the absorber effect of an absorber element depends essentially on the size of its surface, so the new element, for the same absorber volume, has a considerably greater absorber effect than would a conventional solid cylindrical rod, of the same diameter as the outside diameter of the new helical element, because the ratio of the surface to the volume is greater for the helical form. Therefore, the number of absorber element required for the reactor, can be reduced substantially, which is important with respect to the space requirement and the costs for the absorber drives, such as the drive illustrated schematically at 7. |
summary | ||
052215156 | abstract | A method and a device for manufacturing a grid for use in a nuclear reactor fuel assembly. A grid whose component parts are to be mutually welded is placed in a holding frame having passages for access to points to be welded on two major faces and on the sides. The frame containing the grid is gripped with a device in a chamber where an inert gas atmosphere is generated. Welding is carried out on one face of the grid at a time using a laser beam penetrating from outside the chamber and the welding operations are repeated on the other faces. During welding on one face, the laser beam is moved in two mutually orthogonal directions while the frame is held stationary. The apparatus may include two chambers each with a gripping device, one for welding the two major faces and the other for welding the sides. |
claims | 1. A longitudinally divided emergency core cooling (ECC) duct for emergency core cooling water injection to a nuclear reactor, the longitudinally divided ECC duct configured to be provided on a periphery of a core barrel of the nuclear reactor, the longitudinally divided ECC duct including an emergency core cooling water inlet configured to face a direct vessel injection nozzle, and configured to extend in a longitudinal direction of the core barrel, wherein the longitudinally divided ECC duct is formed of a plurality of longitudinally-divided ducts divided in the longitudinal direction;wherein the longitudinally divided ECC duct includes an upper surface with side slopes configured to form a flow passage for the emergency core cooling water injected from the direct vessel injection nozzle; andwherein a plurality of side supports extend outward from the side slopes of the longitudinally divided ECC duct to affix the longitudinally divided ECC duct to the periphery of the core barrel. 2. The longitudinally divided ECC duct according to claim 1, wherein a gap is formed between adjacent longitudinally-divided ducts of the longitudinally divided ECC duct. 3. The longitudinally divided ECC duct according to claim 2, wherein the longitudinally-divided ducts of the longitudinally divided ECC duct move and slide relative to one another in the longitudinal direction due to thermal expansion and/or shrinkage. 4. The longitudinally divided ECC duct according to claim 1, wherein the plurality of side supports are provided at intervals in the longitudinal direction of ECC duct. 5. The longitudinally divided ECC duct according to claim 4, wherein the inlet, through which emergency core cooling water is injected into the longitudinally divided ECC duct, is formed on the upper surface of the longitudinally divided ECC duct, and the upper surface is gently curved and convex with respect to a surface of the core barrel. 6. The longitudinally divided ECC duct according to claim 4, wherein an upper end of the longitudinally divided ECC duct is closed and a lower end of the longitudinally divided ECC duct is opened, the longitudinally divided ECC duct is provided with an outlet guide, which is configured to be positioned near below the lower end of the longitudinally divided ECC duct and the outlet guide is configured to change a direction of backflow when sudden backflow is generated from a core of the nuclear reactor toward the lower end of the longitudinally divided ECC duct, and the outlet guide protrudes from the surface of the core barrel and reduces reversal flow resistance, which is generated when a high-speed backward flow generated before the emergency core cooling water is injected into the nuclear reactor through the longitudinally divided ECC duct. 7. The longitudinally divided ECC duct according to claim 1, wherein the emergency core cooling water inlet and the direct vessel injection nozzle are not mechanically connected to each other. 8. The longitudinally divided ECC duct according to claim 7, wherein a cross sectional area of the inlet of the longitudinally divided ECC duct is larger than a cross sectional area of the direct vessel injection nozzle. |
|
claims | 1. A fuel element for a pressurized water reactor, comprising:a laterally open skeleton having control-rod guide tubes each with a first end and a second end, spacers fastened to said control-rod guide tubes, a fuel element head disposed at said first end of said control-rod guide tubes, and a fuel element foot disposed at said second end of said control-rod guide tubes; andgastight cladding tubes inserted into said skeleton, each of said gastight cladding tubes being filled with a column of fuel pellets, at least some of said gastight cladding tubes each having a multilayer wall, said multilayer including:a mechanically stable matrix formed of a first zirconium alloy of a given thickness, alloyed to a given extent, and disposed in a middle of said multilayer wall, said first zirconium alloy being formed of 0.8 to 2.8% niobium and zirconium of industrial purity and at most 2.7% of further additives; anda protective layer of a second zirconium alloy thinner than said given thickness and alloyed to a lesser extent than said given extent of said first zirconium alloy, said protective layer bound metallurgically to said matrix and disposed on an inside of said matrix facing said fuel pellets, said second zirconium alloy containing from 0.2% to 0.8% by weight of iron, a remainder being zirconium of industrial purity, said second zirconium alloy having precipitations of secondary phases, a size of said precipitations corresponding to a standardized annealing duration of about 0.1 to 3×10−18 h. 2. The fuel element according to claim 1, wherein in said first zirconium alloy, a quantity of said further additives is smaller than a quantity of the niobium. 3. The fuel element according to claim 1, wherein said first zirconium alloy contains 1.0±0.2% niobium, 0.14±0.02% oxygen, a remainder being the zirconium of industrial purity. 4. The fuel element according to claim 1, wherein said first zirconium alloy has precipitations of secondary phases, and a size of said precipitations of secondary phases corresponds to a standardized annealing duration of lower than 0.5×10−18 h. |
|
summary | ||
abstract | A radioactive waste container, for storing and transporting a radioactive waste, includes a container body, a cover and a water drain unit. The cover is fastened to the container body. The water drain unit is provided at the container body without protruding to an outside of the container body and configured to selectively drain water in the container body. |
|
summary | ||
summary | ||
abstract | A nuclear fission reactor fuel assembly and system configured for controlled removal of a volatile fission product and heat released by a burn wave in a traveling wave nuclear fission reactor and method for same. The fuel assembly comprises an enclosure adapted to enclose a porous nuclear fuel body having the volatile fission product therein. A fluid control subassembly is coupled to the enclosure and adapted to control removal of at least a portion of the volatile fission product from the porous nuclear fuel body. In addition, the fluid control subassembly is capable of circulating a heat removal fluid through the porous nuclear fuel body in order to remove heat generated by the nuclear fuel body. |
|
041750004 | abstract | An illustrative embodiment of the invention discloses a technique for disassembling a nuclear reactor fuel element without destroying the individual fuel pins and other structural components from which the element is assembled. A traveling bridge and trolley that span a water-filled spent fuel storage pool support a strongback. The strongback is under water and provides a working surface on which the spent fuel element is placed for inspection and for the manipulation that is associated with disassembly and assembly. To remove, in a non-destructive manner, the grids that hold the fuel pins in the proper relative positions within the element, bars are inserted through apertures in the grids with the aid of special tools. These bars are rotated to flex the adjacent grid walls and, in this way relax the physical engagement between protruding portions of the grid walls and the associated fuel pins. With the grid structure so flexed to relax the physical grip on the individual fuel pins, these pins can be withdrawn for inspection or replacement as necessary without imposing a need to destroy fuel element components. |
abstract | A thin, light-weight, flexible sheet product useful for the manufacture of radiation attenuation garments. The sheet product is a polymeric material and includes a heavy loading of high molecular weight metal particles. The sheet product is formed from a polymer latex dispersion into which a high molecular weight metal particles are dispersed, where the latex retains a sufficiently low viscosity to be pourable and allow casting of the sheet product. |
|
description | The rod 10 shown in FIG. 1 has cladding 12 closed by a connection plug 14 and by a top plug 16, and it contains a column of absorber material held pressed against the bottom connection plug 14 by a spring 20 which is compressed between the column and the top plug 16. The top plug 16 enables the rod to be secured to a finger of a spider 22. The top plug 16 and the means enabling it to be fixed to the spider 22 can be of the structure described in particular in French patent application No. 95/15488 (which issued as French Patent No. 2,742,912 and which issued as U.S. Pat. No. 5,889,832), to which reference can be made. The rod is of conventional shape, having a diameter that is constant except that its bottom end is bullet-shaped to make it easier to insert rods into the guide tubes of an assembly when an absorber cluster is lowered. The cladding 12, the connection plug 14, and the top plug 16 are advantageously made of austenitic stainless steel of a grade that enables them to be welded electrically with a tungsten electrode (TIG welding). The outside surface of the cladding, of the top plug, and of the connection plug is advantageously subjected to nitriding treatment prior to assembly so as to increase resistance to wear. An austenitic steel makes it possible to perform ionic nitriding treatment of good quality with low sensitivity to corrosion. The nitriding can be performed by the method described in document FR-A-2 604 188, to which reference can be made. In general, the pellets 24 occupying the cladding are made of boron carbide. Their diameter is slightly smaller than the inside diameter of the cladding 12, so as to allow them to be insetted and so as to accommodate swelling. The cladding can have an outside diameter of 9.68 millimeters (mm) and it can be about 1 mm thick, as is common in pressurized water reactors. In conventional manner, the spring 20 can be made of an xe2x80x9cInconelxe2x80x9d type alloy. The connection plug 14 is fixed to a bar 26 of hafnium, which is solid in the example shown in FIG. 1. The total length L0 of the bar 26 generally lies in the range 25% to 35% of the length L1 of the column of pellets 24. The hafnium bar 26 is fixed to the connection plug 14 by a connection that is purely mechanical. In the example shown in FIGS. 1 and 2, this connection is performed by crimping in the zone outlined by box 28. For this purpose, the connection plug 14 has a top portion which is engaged inside the cladding and a flange 30 which bears against the bottom edge of the cladding and which is welded to the cladding. The plug has an extension with circumferential grooves or channels machined therein, there being two such grooves in FIG. 2. The bar 26 is terminated by a thin tubular zone 31 constituting a skirt, which zone is deformed into the grooves of the connection plug 14 once they have been assembled together. It can be seen that the absorber column thus presents only very little discontinuity, because of the presence of the skirt. An axial bore is formed at the end of the skirt and opens out into a hole which is used for suspending the bars during oxidation treatment; this hole allows water to flow inside the connection and regenerate the oxide layer constantly. The crimping is advantageously performed by cold isostatic compression, for example using apparatus of the kind shown in FIGS. 3 and 4. This method and apparatus can be used to assemble together parts made of two different materials that are unsuitable for conventional thermal welding, which materials can be other than hafnium and stainless steel. The components to be crimped together (the hafnium bar and the cladding provided with plugs as shown in FIG. 2) are placed in such a manner that the zone to be crimped is in register with a ring 32 of a material which is deformable but incompressible or only very slightly compressible, such as certain elastomers. At rest, the inside diameter of the ring 32 is slightly greater than the outside diameter of the cladding to be deformed. The length of the ring 32 matches the length of the crimping that is to be performed. When crimping cladding to a hafnium bar as shown in FIG. 1, the length of the ring lies in the range a few millimeters to about 15 mm. Its outside diameter is about 10 mm greater than its inside diameter. It is radial deformation of the ring under the effect of axial compression that performs the crimping. In FIG. 4, it can be seen that the ring 32 is enclosed in a chamber defined by a high strength steel sleeve 34 and an annular piston 36 which slides in a bore of the sleeve. The sleeve is pierced by a hole for inserting the bar 26. The inside diameter of the piston is designed to allow the cladding 12 to pass through it. The apparatus includes a mechanism for urging the piston 36 into the sleeve. This mechanism is carried by a frame 40 to which there is secured a housing 42 for receiving the sleeve. The frame carriers a hydraulic actuator 44 whose plunger 46 bears against a rocker arm 47. The rocker arm bears against the piston 36 via an adjustment module constituted by two washers 48 that are screwed one in the other. These washers are pierced by a central hole and the arm 47 has a slot so as to allow the components for crimping together to pass through them freely. When the actuator is powered via pipe 50, it compresses the ring 32 which swells inwards so as to deform the tubular zone 31 of the bar and convert it from the shape shown in FIG. 4 to the shape shown in FIG. 2. The apparatus described above can be varied in numerous ways. Crimping can be performed in a single groove, thus enabling the length of the ring 32 to be shortened. Two rings separated by a spacer (or more than that) can be provided so that each ring acts over a groove. Crimping can be performed from the inside, in which case the ring 32 is placed inside the two tubular portions that are to be assembled together so as to give rise to expansion. The mechanical connection can also be provided by a screw connection, as shown in FIGS. 5 to 7 where members corresponding to those of FIGS. 1 and 2 are referenced by the same reference numerals. In this case, the connection plug 14 comprises in succession a portion which engages in the end portion of the cladding and which is terminated by a bearing shoulder, a tapped portion, and a thin deformable skirt 52. This connection plug 14 is welded to the cladding. The bar 26 is terminated by three zones of decreasing diameters. The first zone 54a has longitudinal notches (two such notches in the example shown) for receiving deformed zones of the skirt in register therewith so as to prevent the bar from turning. It also has centering zones so as to facilitate assembly. The second zone 54b is threaded and enables the bar to be assembled to the connection plug. It is designed to be screwed into the tapped portion of the plug and to be tightened with determined torque. The thread is dimensioned in such a manner as to provide sufficient mechanical resistance to the fatigue stresses to which it will be subjected in a reactor. Finally, the third zone 54c is constituted by an extension which engages inside the plug so as to ensure axial continuity of neutron absorption. After the bar has been fixed, it is locked against rotation by deforming the skirt 52 using a punch of suitable shape to press the skirt into the notches. Water can penetrate into this connection and can serve continuously to regenerate the protective oxide layer on the hafnium. Finally, the mechanical connection shown in FIG. 8, where members corresponding to those of FIG. 6 are referenced by the same references, has a connection plug 14 with a chamber for receiving a reduced-diameter terminal portion of the bar 26. A pin 60 is engaged in two aligned transverse bores in the connection plug 14 and the terminal portion of the bar. |
|
054855004 | summary | BACKGROUND OF THE INVENTION The present invention relates to a digital X-ray imaging system and method, and more particularly to a digital X-ray imaging system and method suitable for imaging a large field of view such as a chest. Conventional methods of taking an image of a subject by transmitting therethrough an X-ray are grouped into a method using an X-ray film and a digital radiography (hereinafter abbreviated as "DR") method of taking a digital X-ray image. The DR method is expected to improve a diagnosis performance by using image processing, and can electronically record, store, and search X-ray images. There are known various chest DR methods, including a film digitizing method in which an image taken on an X-ray film is digitized, a storage phosphor digital method in which storage phosphor is used in place of an X-ray film and a latent image is scanned by a laser beam to read it and form a visualized image, a scanography method in which a combination of a one-dimensional X,ray beam and a one-dimensional detector array is used, and an X-ray image intensifier-television camera-method (herein after abbreviated as "X-ray II-TV method) in which uses a combination of an X-ray image intensifier (hereinafter abbreviated as "X-ray II") for converting an X-ray image into an optical image and amplifying it and a television camera for converting the amplified optical image into electric signals. Of these DR methods, the X-ray II-TV method is also called a real time DR method, has the function of immediately displaying and storing a taken image, and has the shortest time required for taking and processing one image. Therefore, a success or failure of imaging can be judged at once, and this method is suitable for mass screening because of a short time required for one test. It is also suitable for urgent check, and routine as well as accurate diagnosis at hospitals because it takes a short time to obtain the results of imaging and it is possible to provide the functions of sequential imaging, dynamic imaging, fluoroscopy, and the like as well as quick diagnosis. The methods other than the X-ray II-TV method require 30 seconds or longer for imaging and reading image data. A technique disclosed, for example, in Electromedica Vol. 60(1992), No. 1, pp. 2-5 is known in which the X-ray II-TV method is used to obtain an X-ray image at an imaging target region wider than the field of view of the X-ray detector, by divisionally imaging the region a plurality of times while changing a relative position of the X-ray detector and the subject. According to this technique, a subject lies on a bed in a dorsal position, and the X-ray source and X-ray detector are moved in unison in one direction, for example, in parallel with the longitudinal direction of the subject. An angiogram of lower extremities, for example, is divisionally imaged a plurality of times, and a plurality of obtained images are joined together to display them as a one complete image. Although the X-ray II-TV method has the above-described superior advantages, conventional DR methods have been accompanied with the problem that one of a field of view and a spatial resolution is inferior to the other methods. It is technically difficult to manufacture an X-ray II which can take an image of a large view field at a ultra high resolution. As an X-ray II having a filed of view as large as about 40 cm * 40 cm necessary for imaging a chest, there is known an X-ray II having a field of view of 47 cm described in Radiology Vol. 171, No. 2 (May, 1989), pp. 297-307). This X-ray II however has a spatial resolution inferior to other methods. Another problem associated with an X-ray II is that the more the position goes apart from the center of the field of view, the more the spatial resolution at the position lowers. Therefore, when lungs are imaged, the central area of the X-ray II having a high resolution images the central region of the mediastinum, whereas the peripheral area of the X-ray II having a lower resolution images the lung field. With the technique disclosed in Electromedica Vol. 60 (1992), No. 1, pp. 2-5, images (photographs) of a target region divisionally taken a plurality of times are cut and pasted to join them together, and they are not image-processed by a computer. Therefore, image densities at areas around joining lines are discontinuous so that the image quality of a vascular system near the areas around joining lines is poor. In addition, this technique does not take into consideration imaging a plurality of regions of interest at the central area of the X-ray II having a higher resolution. With the above described divisional imaging method, X-ray beams transmitting through a subject are not parallel beams but diverging beams. Since the X-ray source and X-ray detector are moved relative to the subject, diverging X-ray beams passing through the same position of a subject have different incident angles when imaging the subject a plurality of times. This different incident angle of an X-ray beam generates a positioning error of the subject image in its depth direction, being unable to correctly join a plurality of images. This problem will be detailed with reference to FIG. 12. An X-ray source 3 and an X-ray detector 16 are moved in unison in parallel to a subject 17 at a dorsal position. As described previously, X-ray beams passing through the subject 17 are diverging beams. Therefore, when the X-ray source 3 is at point A, an X-ray beam 21 incident to the position at point P on the ventral side passes through the position at point Q on the dorsal side, whereas when the X-ray source 3 is at point B, an X-ray beam 22 incident to the position at point P on the ventral side passes through the position at point R on the dorsal side. Since an X-ray image is obtained as an X-ray transmitted image, if the X-ray images taken at positions A and B of the X-ray source 3 are joined by superposing two points P on the ventral side, the joined image is not correct because on the dorsal side, the points Q and R are joined. SUMMARY OF THE INVENTION It is an object of the present invention to provide a real time DR digital X-ray imaging system capable of solving the above problems associated with conventional techniques, and obtaining an X-ray image of a target region having a field of view wider than that of an X-ray detector by correctly joining a plurality of images divisionally taken a plurality of times while changing a relative position between the X-ray detector and an X-ray source. The above object of the present invention can be achieved by a digital X-ray imaging system including an X-ray source, an X-ray slit for limiting the area of an emitted X-ray from the X-ray source, an X-ray grid for shielding a scattered X-ray, an X-ray detection unit for detecting an X-ray transmitted through a subject, a signal processor for acquiring a signal from the X-ray detection unit and processing the signal to obtain an image of the subject, a display unit for displaying the image of the subject obtained through signal processing by the signal processor, and means for controlling to set an imaging view field by changing a relative position between the X-ray detection unit and the subject, the imaging view field setting means setting each of a plurality of regions of interest of the subject to generally a central area of a view field or an X-ray detecting plane of the X-ray detection unit, and setting at least one imaging view field to contain an intermediate region between a plurality of target imaging regions. According to the digital X-ray imaging system of this invention, each of a plurality of imaging target regions is imaged generally at a central area of the view field of the X-ray detection unit. It is therefore possible to obtain the image quality of each target region under the optimum condition. If the subject is a human chest, the right and left lung fields are imaged generally at a central area of the view field of the X-ray detection unit. It is therefore possible to obtain a more correct image of the lung field, improving the diagnosis performance of the lung field. Since the intermediate region between a plurality of target imaging regions is contained in at least one imaging view field, there is no missing part of the view field, allowing to image all necessary regions. By using a high resolution X-ray II-TV system, immediate display and diagnosis are possible, improving a throughput. It is possible to obtain an image having a wider view field than that of the X-ray detection unit and covering both the lungs, by a plurality of radiographic exposures. By joining together a plurality of images, diagnosis is possible by one display unit. By correcting the sensitivity of the X-ray detection unit and the geometric distortion and density of an image, it is possible to realize a digital X-ray imaging system capable of reducing the discontinuity at image joining regions and performing a more precise diagnosis. While the X-ray source and a subject are fixed, the X-ray detection unit has construction in which relative position between the X-ray detection unit and the subject is changed to set the X-ray grid generally perpendicular to a center line passing through the center of an X-ray input plane of the X-ray grid and the. X-ray source during the exposures. Therefore, the incident angle of an X-ray beam at the same position on the subject will not change at each of a plurality of radiographic exposures, generating no image distortion in the subject depth direction. It is therefore possible to correctly join a plurality of X-ray images by correcting the sensitivity non-uniformity of the X-ray detection unit and the geometric distortion in the image regions commonly contained in a plurality of X-ray images. An X-ray grid is mounted at the front of the X-ray detection unit. The X-ray grid covering the imaging view field effective transmits an X-ray and shields the scattered X-ray. As a result, even if the X-ray detection unit is moved, the scattered X-ray can be effectively shielded by the X-ray grid. By using a high resolution X-ray II-TV system, immediate image display and diagnosis become possible, improving a diagnosis throughput. By moving the position of the X-ray slit, unnecessary X-ray exposure to the subject can be avoided. According to the present invention, a wide region such as a lung field can be imaged in real time at a high spatial resolution, providing immediate display and diagnosis. It is therefore possible to easily perform re-imaging and easily change the imaging conditions, permitting precise diagnosis. In the chest DR or the like, an X-ray can be effectively and directly transmitted and the scattered X-ray can be shielded, while shielding the X-ray outside of the imaging view field. Therefore, unnecessary X-ray exposure to the subject can be avoided. |
description | This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2016/070148, filed Aug. 26, 2016, published as WO 2017/032864 on Mar. 2, 2017 on, which claims the benefit of European Patent Application Number 15182578.3 filed Aug. 26, 2015. These applications are hereby incorporated by reference herein. The invention relates to an X-ray imaging apparatus, a method of operating an X-ray imaging apparatus, a computer program element, and a computer readable medium. Grating-based interferometric differential-phase contrast and dark-field imaging is a promising technology that adds diagnostic value in particular in the area of chest imaging since the dark-field signal channel is highly sensitive to changes of the micro-structure of lung tissue. However, adapting grating based interferometric imaging equipment to different imaging tasks is remarkably cumbersome at times. For instance, the adaptation may involve difficult and time consuming adjustments of an interferometer used in the imaging. There may be a need for alternative X-ray imaging apparatuses. The object of the present invention is solved by the subject matter of the independent claims where further embodiments are incorporated in the dependent claims. It should be noted that the following described aspect of the invention equally apply to the method of operating an X-ray imaging apparatus, to the computer program element, and to the computer readable medium. According to a first aspect of the invention there is provided an X-ray imaging apparatus comprising: an X-ray source configured to emit X-radiation; an X-ray detector configured to detect said X-radiation; an interferometer arranged between said X-ray source and said detector, said interferometer comprising at least one (first) interferometric grating structure; wherein said at least one interferometric grating structure is tiltable around an axis perpendicular to an optical axis of said imaging apparatus, the at least one grating thereby capable of being oriented at different tilt angles relative to said axis. Tilting of the interferometric grating structure allows adjusting the imaging apparatus, in particular its interferometer, to different design energies as the tilting leads to an inclined illumination of the gratings structure and thus to a change of an effective Talbot distance through the interferometer. According to one embodiment, the imaging apparatus includes at least one further grating, referred to herein as a source grating, arranged between said interferometric grating and said X-ray source, said source grating structure configured to convert said emitted X-radiation into X-radiation with increased coherence, and said source grating structure likewise tiltably arranged around a second axis parallel to the first axis, so as to maintain or to re-establish a spatial relationship (in particular parallelism) between said source grating and the at least one interferometric grating. In particular the two gratings are to remain substantially parallel or their parallelism should be restored after the rotation if the gratings are independently rotatable. When tilted, the normal of the plane of the interferometer grating(s) and/or source grating is not parallel to the optical axis. Yet more specifically, the gratings are rotatable about respective axes that run parallel to the course of the direction of the gratings rulings (trenches and ridges). According to one embodiment, the said tilt angle is any one of approximately +/−30°, +/−45° and +/−60°. “+” and “−” indicate orientation (clockwise/counterclockwise) of the tilting or rotation and 0° indicates the configuration of perpendicular illumination, in other words, a configuration where the normal of the plane of the gratings is parallel to the optical axis. As mentioned above, the tilting of the source grating and/or of the at least one interferometric grating changes the design energy of said interferometer. In other words, the different tilt angels allow adjusting the imaging system to range of different design energies. In particular, in the configuration where the gratings are not tilted (normal irradiation), the system is configured to a certain ground design energy E0 and the tilting angle allows scaling up this ground design energy by a scale factor. For instance, +/−60° allows for a two-fold scale up. According to one embodiment, the imaging system comprises a grating adapter mechanism to adapt for an effective grating pitch in relation to the source grating (G0) and/or in relation to the at least one interferometer. In either words, the adapter may operate on or relation to the source grating or in relation to the one or two gratings (G1,G2) of the interferometer. The mechanism allows building a new or effective pitch. This may be achieved by exchanging one of the gratings for another or by combining gratings together to build an effective pitch from existing pitches. The new or effective pitch is configured to fit to the tilted grating geometry and is to ensure that certain grating design rules for Talbot or Lau-Talbot interferometers are observed. In particular, these rules impose certain functional relationships between the gratings pitches and the length of distances or “paths” between source grating and interferometer and the path length across the interferometer. More specifically, and according to a preferred embodiment, the grating adapter mechanism is a source grating adapter mechanism. It is configured to i) exchange the source grating structure for a new source grating structure having a pitch different from a pitch of the source grating or ii) to at least combine said source grating structure with another source grating structure having a pitch different from a pitch of the source grating, so as to compensate for a change in effective path length through a space between said source grating and said interferometer, said change in effective path length being caused by either one of said tilt angles. In other words, the grating adapter mechanism operates only on the source grating and not on the interferometric gratings G1,G2. This allows a simple implementation. According to one embodiment, the combiner operation performed by the source grating adapter mechanism is achieved by superimposing the two source gratings or by sliding the two source gratings relative to each other when the two source gratings are at least partly superimposed onto each other, so as to form a double decker grating structure having an effective pitch that compensates for said change in effective path length caused by either one of said tilt angles. According to one embodiment, the X-ray imaging system comprises a translator stage configured to translate, relative to the optical axis, the at least one interferometric grating and/or the source grating According to one embodiment, the interferometer further comprises a further grating structure (G2), wherein the further grating structure (G2) is likewise tiltably arranged around a third axis parallel to said first axis, so as to maintain or to re-establish a spatial relationship between said at least one interferometric grating (G1) and/or the source grating (G0). According to one embodiment, the interferometric grating and said further grating structure are arranged on mutually opposite sides of an examination region of the X-ray imaging apparatus. Alternatively, and according to one embodiment, the further interferometric grating structure and the interferometric grating are arranged on the same side of an examination region of the X-ray imaging apparatus. The term “further grating structure” is either a separate, discrete or standalone interferometric grating in addition to the first interferometric grating. The further interferometric structure may be part of the interferometer, so the interferometer comprises two gratings. But the further interferometric structure may also be part of other imaging equipment of the system such as the detector. In some embodiments, it is the detector itself that forms the further interferometric structure. The proposed system allows for a convenient way to adapt the system for different design energies. In particular this can be achieved without changing the distance between the source grating and the interferometer. Also, there is no need to change aspect ratios of the interferometric gratings as rotation around an axis parallel to direction of the grating rulings has been found to automatically yield a corresponding scale up of grating heights thanks to the inclined illumination. According to one embodiment, the system further comprises an X-radiation filter configured to broaden a spectral window around a design energy for a given tilt angle to facilitate collection of spectral information. The spectral (energy) window defines the range of design energies for any given grating (s) inclination. The configuration and arrangement of the filter allows achieving this spectral window broadening by harnessing the fact that, for non-parallel beam geometries, there is a design-energy versus fan-angle dependency. In other words, design energies different from the one that corresponds to the chosen inclination can be achieved because the respective changes of the effective Talbot distances through the interferometer vary with fan angle. More specifically, and according to one embodiment, the X-radiation filter has a plurality of filter elements configured for different K-edge energies. The filter elements are arranged across the optical axis in an ascending or descending order in sequence according to their respective K-edge energies. The respective thickness and or material of the respective filter elements are configured to that the respective transmission functions of the different filter elements are configurable in a “balanced” fashion so as to achieve better separation of the spectral information. The X-ray imaging apparatus according to the present invention allows for useful application in a clinical environment such as a hospital. More specifically, the present invention is very suitable for application in imaging modalities such as mammography, diagnostic radiology and interventional radiology for the medical examination of patients. In addition, the present invention allows for useful application in an industrial environment. More specifically, the present invention is very suitable for application in non-destructive testing (e.g. analysis as to composition, structure and/or qualities of biological as well non-biological samples) as well as security scanning (e.g. scanning of luggage on airports). According to another aspect, there is provided a method for operating an X-ray imaging apparatus having an interferometer arranged between an X-ray source and a detector, said interferometer comprising at least one interferometric grating structure: receiving a specification of a design energy for the X-ray imaging apparatus; and in response to the specified design energy, tilting said grating relative to an optical axis of the X-ray imaging apparatus. FIG. 1 affords two different side elevation views of an X-ray imaging apparatus at two different states shown in pane A and pane B respectively. The X-ray imaging apparatus comprises an X-ray source XR, a radiation sensitive detector D arranged across an examination region ER opposite said source XR. The examination region ER is configured to receive at least a part of an object OB to be imaged. Preferably, the X-ray source is operable at different voltages to produce X-radiation at different energies. The X-ray imaging apparatus further comprises an interferometer IF arranged between the X-ray source and the detector. In the following it will be convenient to introduce a reference frame of axis X, Y, and Z to better explain operation of the X-ray imaging apparatus as proposed herein. Axis X, Y define the image plane or plane of the field of view of the detector D. For instance, axis X, Y may be taken to extend, respectively, along two adjoining edges of the detector D. Perpendicular to the image plane X, Y is axis Z. This axis corresponds in general to the propagation direction of the X-ray beam which emanates a focal spot FS of the X-ray source XR. Also, axis Z is parallel to the optical axis of the X-ray imaging apparatus. The optical axis runs form the focal spot FS of the source XR to the center of the image plane of the detector D. In one embodiment there is also a pre-collimator PC as shown in the FIG. 1 arranged between the object OB and the X-ray source XR. According to one embodiment, instead of or in addition to the pre-collimator PC, there is a post-collimator (not shown) between the object OB and the detector D. Referring now in more detail to FIG. 1 in particular to pane A of FIG. 1, the imager IM has a multi-channel imaging capability that is at least partly afforded by the interferometer IF built into the X-ray imaging apparatus. “Multi-channel imaging”, as used herein, means in particular the capability of imaging for i) a spatial distribution of refraction (phase contrast imaging) activity caused by the object OB and/or ii) spatial distribution of small angle scattering (dark field imaging) activity as caused by the imaged object. In addition thereto, the more traditional way of imaging for spatial distribution of absorption in the object OB may also be possible. This type of multi-imaging capability is sometimes referred to as DPCI (differential phase contrast imaging), but, this does not exclude imaging for the other image signals, dark-field and/or absorption. In one embodiment, the interferometer IF comprises two grating structures G1 and G2 although single grating interferometers (having only a single grating G1) are not excluded herein and will be described later below. The grating G1 is either an absorption grating or phase shift grating whereas G2 is an absorption gating. The gratings are manufactured by photo lithographically processing suitable substrates such as a silicon wafer (rectangular or even square shaped but other shapes may also be called for in other contexts). A pattern of periodic rulings is formed in those substrates as a sequence of parallel trenches, with any two neighboring trenches separated by bars or ridges. In FIG. 1, the rulings (that is, trenches and ridges) run along the Y-direction, that is, extend into the drawing plane in FIG. 1. The trenches may be filled with suitable filling material such as gold or other to cause a desired phase shifting behavior. The ruling patterns are preferably one dimensional but may also be two dimensional such as to confer a checker board pattern in which there are two sets of trenches: one set runs in the Y-direction, the other runs across the first in the X-direction. In the 1D example the rulings extend only in one direction across the surface of the substrate. Preferably the X-ray detector D is a 2D full view X-ray detector either planar or curved. A plurality of detector pixels are arranged in rows and columns as an array to form a pixelated 2D X-ray radiation sensitive surface capable of registering X-ray radiation emitted by the X-ray source. Alternatively the X-ray detector D may also be arranged as a plurality of discreetly spaced individual lines of detector elements. Such X-ray detector is sometimes referred to as a “line detector” arrangement. The detector D is either of the energy integrating type or is, alternatively, of the energy resolving type (such as a photon counting detector). The X-ray detector D and the X-ray source are spaced apart to form an examination region ER. The examination region is suitably spaced to receive the object OB to be imaged. The object OB may be inanimate or animate. For instance the object may be a piece of luggage or other sample to be imaged such as in non-distractive material testing etc. Preferably, however, a medical context is envisaged where the (animate) “object” is a human or animal patient or is at least an anatomic part thereof as it not always the case that the whole of the object is to be imaged but only a certain anatomic region of interest. In one embodiment, the interferometric grating structures G1 and G2 are arranged in between the X-ray source XR and the X-ray detector D so that the examination region ER is defined between the X-ray source and the interferometer IF. More specifically, the X-ray source XR has a focal spot FS from which the X-ray radiation beam emerges. It is the space between the focal spot FS and the X-ray detector's radiation sensitive surface where the two grating structures G1 and G2 are arranged with the examination region then being formed by the space between the focal spot and the grating D1. It will be convenient in the following to refer to the grating G1 as the phase grating and to grating G2 as the analyzer grating. Functionally, the grating G1 is either an absorber grating or preferably a phase shift grating, whereas G2 is an absorber grating. However other functional combinations are not excluded herein. In some embodiments, there is, in addition to the interferometric gratings G1, G2 of the interferometer IF, a further grating G0 which will be referred to herein as the source grating. The source grating G0 is arranged in proximity at distance f0 from the focal spot FS of the X-ray source. For instance, the source grating G0 may be arranged at the egress window of a housing of the X-ray tube unit XR. If there is a source grating, the examination region is between the source grating G0 and the interferometer IF, in particular between G0 and G1. The function of the source grating G0 is to make the emitted radiation at least partly coherent. In other words, the source grating G0 can be dispensed with if an X-ray source is used which is capable of producing native coherent radiation. During an imaging operation, the at least partly coherent radiation emerges downstream the source grating G0 (if any), passes then through the examination region ER and interacts with the object OB therein. The object then modulates attenuation, refraction, and small angle scattering information onto the radiation which can then be extracted by operation of the interferometer IF gratings G1 and G2. More particularly the gratings G1, G2 induce an interference pattern which can be detected at the X-ray detector D as fringes of a Moiré pattern. Yet more particularly, if there was no object in the examination region there is still an interference pattern detectable at the X-ray detector D, called the reference pattern which is normally captured during a calibration imaging procedure. The Moiré pattern comes about by especially adjusting or “de-tuning” the mutual spatial relationship between the two gratings G1 and G2 by inducing a slight flexure for instance so that the two gratings are not perfectly parallel. Now, if the object is resident in the examination region and interacts with the radiation as mentioned, the Moiré pattern, which is now more appropriately called the object pattern, can be understood as a disturbed version of the reference pattern. This deviation from the reference pattern can then be used to compute a desired one, or two or all of the three images (attenuation, phase contrast, dark field). For good imaging results, the detuning of the gratings G1, G2 is such that a period of the Moiré pattern should extend for a few of its cycles (two or three) across the field of view of the detector. The Moiré pattern can be Fourier-processed for instance to extract the at least one (in particular all) of the three images. Other types of signal processing such as phase-stepping techniques are also envisaged herein. The interferometer IF as described above is what is commonly referred to as a Talbot-Lau interferometer. Much of the accuracy of the imaging capability of the interferometric X-ray apparatus rests with the distinctness with which the Moiré pattern or interference pattern is detected at the detector D. Said distinctness can be quantified by the interferometric concept of “visibility”. Visibility is an experimentally verifiable quantity defined for instance as the ratio (Imax−Imin)/(Imax+Imin). Said differently, the visibility can be understood as the “modulation depth” of the interference pattern, that is, the ratio of fringe amplitude and the average of fringe oscillation. The visibility of the interference pattern is in turn a function of “design energy” at which the x-radiation (as produced by the X-ray source) illuminates the interferometer and the source grating G0 (if any). The design energy is the energy at which the interference pattern has the maximum visibility. Each interferometric set up is in general adjusted to a certain design energy or at least to certain design energy bandwidth around a design energy value. Examples for suitable design energies are for instance 25 keV or 50 keV but these numbers are purely exemplary. Operating the X-tube at energies different from the design energy or at least at energies outside the bandwidth will result in Moiré patterns of lower visibility and hence an overall degradation of image quality. It is also inefficient in terms of energy consumption and dose incurred to operate for instance at an energy higher than the design energy. The chosen design energy for the X-ray imaging apparatus is usually a function of the nature of the object one wishes to image. Higher design energies are called for thicker or denser objects. Chest X-rays for instance usually require higher design energy than do thinner anatomical parts such as arms or legs because of the longer in-tissue path lengths involved. This is because, for achieving good imagery, it must be ensured that a sufficient fraction of the X-ray beam actually passes through the object to be detectable at all at the detector. Furthermore, the choice of a certain design energy imposes restrictions on the interferometric and source grating set up. The interferometric set up includes one or more (in particular all) of the following design parameters: there is the intra-grating distance d0, or Talbot distance, which is the distance of a path along the optical axis of the imaging system between grating G1 and grating G2. There is also the distance l0 between the source grating G0 (if any) and the interferometer IF, that is, the distance along the optical axis from the G0 and analyzer grating G1. This distance l0 will be referred to herein as the “source grating distance”. The interferometric or source grating set up further includes structural properties of the gratings themselves. Said structural properties include pitches p0, p1 and p2 of the three gratings, respectively and the aspect ratios of the source grating G0 and of G1 and/or G2. “Pitch” is the spatial period of the grating rulings. The aspect ratio describes the ratio between the height of the respective trenches formed in the grating's substrate and the distance between two neighboring trenches. Aspect ratios in the order of 30-50 for instance are not unheard of, which means that the respective height of the trenches is 30-50 times the distance between two neighboring trenches. For example, aspect ratios in the order of 30-40 having a trench height of 30-40 micrometers call for inter-trench distances of about 1 micrometer. Such micro structures are difficult to produce and in the past they had to be adapted to different design energy requirements. For instance, as the source grating G0 acts as an absorber grating, this imposes certain requirements on the trench height required in order to perform this function properly. Increasing the energy with which the energy source operates to achieve the desired energy will in general mean for a given fixed grating height that the absorption characteristic of the source grating decreases. This will then lead to incoherent radiation emerging downstream the source grating G0 which in turn will compromise the function of the interferometer. Similar demands are required for the analyzer grating G2 (also configured in general as an absorber grating) which operates essentially to scale up the interference pattern as produced by the G1 source in order to make the interference pattern detectable at the detector for a given resolution. Also, grating G1 is adapted to produce the interference pattern down-stream at the desired Talbot distance (where the absorber grating G2 is positioned) with a precisely defined phase shift (usually π or π/2). Again, to ensure that the interference pattern is precisely replicated at the desired Talbot distance at the required phase shift, a suitable aspect ratio is required for the specific design energy that is desired for a given imaging task. In one embodiment, the proposed X-ray imaging apparatus is capable of operating at different design energies whilst maintaining the dimension (in Z direction) of the X-ray imaging apparatus without necessarily changing the aspect ratios of the interferometer gratings G1 and G2. More particularly, the distance between the focal spot and the detector can remain the same for any of the chosen design energies. In particular, in one embodiment the X-ray imaging operating is operable at the double of a certain given design energy E0. This adaptability to different design energies is achieved by inclined or oblique lamination of the interferometric gratings (illustrated in view B of FIG. 1), as compared to normal incident illumination as shown in view A of FIG. 1. More specifically, it is proposed herein to arrange the interferometer IF to be tiltable relative to the optical axis of the system. That is, the normal of the plane of the interferometer grating(s) G1 can be adjusted to be no longer parallel to the optical axis. Yet more specifically, the grating G1 is rotatable about the Y-axis, that is, around an axis that runs parallel to the course of the trenches of the grating. The rotation angle can be measured clockwise +θ or anti-clockwise −θ. The rotation angle θ corresponds to the tilt angle between the normal of the plane of the grating and the optical axis. In 2D gratings, one may rotate around Y axis or the X axis. Being able to operate at different design energies affords dual energy imaging capability which allows producing images for material decomposition. More specifically, dark field or phase contrast images or absorption images for different material types can be produced. Also, the absorption signal can be decomposed into contributions from Compton scattering and photoelectric absorption, etc. An arrangement where the interferometer IF is rotated by an exemplary rotation angle θ=60°, is shown in pane B of FIG. 1. If the interferometer comprises two gratings, G1, G2, as shown in FIG. 1, both are rotatable around respective rotation axes by the required angle so as to remain parallel at all times or at least to maintain the previously adjusted de-tuning to achieve the Moiré reference pattern. The two gratings G1 and G2 are rotatable simultaneously or independently. The respective rotation axes of G1 and G2 are parallel to each other and to the Y-axis. If the apparatus also comprises a source grating G0 this too is rotatable around another rotation axis parallel to the respective rotation axes of G1 and G2, so as to remain parallel to the interferometer gratings G1, G2 of interferometer IF. The respective rotations of the interferometer IF and the source grating G can be effected by respective actuator mechanisms (also referred to herein as rotation stages) RS1 and RS2, respectively. More specifically, a rotation stage RS2 for the source grating G0 can be implemented by using a piezo-electric actuator or a stepper motor or similar. Yet more specifically, and according to one embodiment, the G0 substrate is framed in a framelet (not shown). The grating framelet is rotatably arranged via at least one, preferably two, pivot points PP in a mounting cage 202. The one or more pivot points define a rotation axis that runs through the center of the grating G0 parallel to the direction of the grating rulings. In one embodiment, a set of two pins at opposite sides of the framelet are formed. The pins are received in respective recess in the mounting cage 202 to so afford a rotatable mounting of the framelet and hence of the grating G0. In the view of FIG. 1B, the rotation axis extends perpendicularly into the drawing plane. More specifically, the rotation axis through the respective gratings is perpendicular to the normal of the plane defined by the respective gratings and passes through the center of gravity of the grating G0. The mounting cage 202 and the framelet should be made from material of sufficient stiffness such as aluminum, or hardened steel, etc. The, for instance piezo-electric, actuator may then be applied to the framelet to effect the rotation, relative to the optical axis, of the framelet, and hence of the grating G0 arranged therein. In the embodiment where the grating is a 2D grating, rotation is switchable either around the Y-axis parallel to one set of trenches or round the X-axis parallel to the other set of trenches. This rotatability around the two orthogonal axes can be implemented for instance by mounting two framelets in a nested fashion in two gimbals, each having a pair of pins, the pairs arranged orthogonal to each other on respective one of the two framelets. Each of the framelets in the gimbals can be locked to ensure that the grating rotates only around the X or Y axis, as desired for a given imaging task. The selection of the rotation around X- or Y can be done manually or automatically via catcher mechanism controllable by a suitable actuator mechanism, such as electro-magnetic or otherwise. A similar construction to effect the tilting with respect to the optical axis is also envisaged for the rotation stage RS for the interferometer IF. That is, in one embodiment, the two gratings G1 and G2 are together arranged in a double frame or “box” 206 to form the interferometer, with grating G1 on top of grating G2 when viewed along the negative Z direction toward the detector D. The interferometer box 206 is then rotatably arranged around a rotation axis at one or preferable two pivot points in mounting cradle 208. Again, as with grating G0, the rotation axis of the interferometer IF extends perpendicular into the drawing plane of FIG. 1. The rotation axis passes through the center of the grating G1 or G2 or is arranged halfway between the two gratings and passes through opposite sides of the interferometer box. As similar pin-in-recess mounting can be used as described above for RS1 to afford rotatability of the gratings G1, G2. To ensure a sufficient field of view even when the interferometer is rotated, the two gratings G1,G2 are slidable relative to each other as shown in FIG. 1. In one embodiment, the gratings slide away from each other in response to a request for a certain rotation angle θ≠0° (and hence a certain design energy) to cover a larger FOV and, for θ=0°, slide back towards each other, with G1 aligned atop G2. In a preferred embodiment, one or both of rotation stages RS1, RS2 are based on piezoelectric actuators but other options, such as stepper motors or others are also envisaged herein. In some embodiments, the source grating G0 and the interferometer IF are rotatable independently from each other. In one embodiment, even the gratings G1, G2 are independently rotatable. Alternatively, the respective actuator mechanisms RS1 and RS2 are mechanically coupled by a suitable gearing mechanism so as to achieve a simultaneous rotation of the source grating G0 and the interferometer IF. Also, in one embodiment, the gratings G1, G2 are mechanically coupled to be rotatable concurrently together so as to better maintain their mutual alignment. If the imaging apparatus is of the scanning type, there is a relative motion induced, during the image acquisition, between the object OB to be imaged and the X-ray source XR and/or the detector D. The scanning system can be implemented according to different embodiments. The scanning motion can be linear or curved, eg a pendulum motion around a pivot point which may or may not be situated at the focal spot FS of the X-ray source XR. In one embodiment there is a scan arm which is used to scan the object OB. This is the case for instance in some mammography imaging systems. The scan arm may be used to move both, detector D and the interferometer IF, relative to the object during the scan. In some (but not necessarily all) of these embodiments, the area of the detector D is essentially coextensive with the interferometer footprint (ie, the area of the grating(s)). Alternatively, the scan arm only includes the interferometer and only this is scanned relative to a stationary detector which is preferably but not necessarily a full field 2D detector having preferably, but not necessarily, a larger area than the interferometer footprint. In either one of these scanning system embodiments, at least the interferometric gratings and the source gratings can be rotatably arranged around their respective axes perpendicular to the optical axis on or within the scan arm as described above. In other embodiments, the scanning system is a slit scanning-system where the pre-collimator PC (or the post collimator) is configured to follow the scanning motion and is arranged as a slit collimator to divide the beam into one or more relatively narrow slit beams that each illuminate a respective part of the detector. If the detector is arranged as a series of one or more line detectors, each detector line is illuminated by respective ones of the slit beams at a time. Turning now back to the rationale for having the gratings rotatably arranged: assuming that the above mentioned design parameters have been set up for certain a “primary” design energy E0 for normal radiation at θ=0° (see FIG. 1A), geometric considerations carried out by the Applicant have shown that the respective rotation to achieve inclined illumination of the gratings, G0, G1 and G2, leads to a scale up of all the design parameters for design energy E0. The scale up is by the factor of 1/cos(θ), with θ being the rotation angle. This results in a corresponding scale up of the primary design energy E0 by the same factor of 1/cos(θ). For instance for a gratings rotation of θ=60°, envisaged herein in an advantageous embodiment, the design energy E0 (at θ=0°) is doubled into 2*E0. The interferometric and source grating setup is governed by certain “design rules” that must be respected. One such design rule is the requirement that:—d0/l0=p2/p0 (1) This is assumed to hold for the E0 at θ=0°. Fortunately, because d0, l0 scale together by the above mentioned common scale factor 1/cos(θ), eq (1) is preserved or is invariant under rotation. This invariance allows maintaining in particular the Talbot requirement underlying operation of the interferometer IF. In other words, denoting by deff, leff the scaled up effective Talbot distance (that is the intra-grating path length through the interferometer) and the scaled up effective source grating distance, respectively, the following holds:—d0/l0=deff/leff=p2/p0 (2) However, a scaling of the source distance l0 is also unfortunate in another sense as this would mean changing the dimensioning of the X-ray apparatus in Z direction which is undesirable because of space restrictions for instance or because of a need for complex mechanism to achieve the scaling of the source grating distance l0. To obviate this requirement to scale the source distance l0, Applicant has found that design rule as per eq (2) can still be respected by a suitable adaptation of pitch of p0, say into p0′. This pitch adaptation can be used to compensate for the otherwise required scaling of the source distance l0. It is therefore proposed herein to include in the interferometric X-ray imaging apparatus, a pitch adaption mechanism SGC (not shown in FIG. 1 but see FIGS. 2, 3) combined with rotation stage RS2. The pitch adaption mechanism SGC is configured to adapt the pitch p0 of G0 to compensate for the changed intra-grating path length and to thereby maintain the source grating distance as per the design energy EO for normal illumination at the reference inclination θ=0°. In other words, using an adapted source pitch p0′, equality in eq (2) can be maintained for the same l0:—deff/l0=p2/p0′ (3) As an illustration, suppose we use instead of d0 the effective distance d′=d0/cos 60°=2*d0, for θ=60°. Then we have from (3) deff/l0=2*d0/l0=2*p2/p0=p2/(½*p0). Introducing the adapted pitch p′0 for a “pseudo” grating G′0 (p′0=½*p0), equation (3) is fulfilled as per deff/l0=p2/p′0. Thus, an increase of Talbot distance by a factor of 2 is compensated by a G′0-grating having half of its primary pitch while the source grating distance l0 is maintained. In other words, by a gratings rotation of θ=60°, envisaged herein in an advantageous embodiment, the design energy E0 for θ=0° is doubled whilst the source grating distance l0 as per the θ=0° setup is maintained. In return for keeping the source grating distance constant when the gratings are rotated, the pitch of the source grating p0 is halved. Of course the same reckoning will hold true for any θ but now the scaling is as per factor 1/cos(θ). For instance, a rotation by θ=45° allows to increase primary design energy E0 by roughly 40% whereas a rotation by θ=30° affords an increase by about 15%. It is of note, that previously mentioned aspect ratios also scale accordingly, which affords an enormous simplification, as there is no longer the need to use dedicated grating with specific aspect ratios for different design energies. Because of the inclined illumination effected by the rotations it is also the path through the gratings that is scaled up by the right amount. This then results in correct effective aspect ratios Referring now to FIG. 2, there are shown embodiments of the source grating adapter mechanism SGC introduced above. In the embodiments of FIG. 2, the source grating adapter mechanism exchanges, in dependence on the desired design energy, one source grating for another one having a different pitch that corresponds to the desired design energy. In other words a set of plurality of source grating is exchanged, each having a dedicated pitch that fits a respective one of design energies in a predefined set of design energies as per eq (3) above. FIG. 2 shows two different embodiments of how such an exchanger mechanism SGC can be implemented. FIGS. 2A and 2B show two different views of one embodiment with FIGS. 2C, 2D showing two different views of another embodiment. View A, C are side elevations along Y whereas views B, D are plan views along Z. Broadly, the embodiment as per views 2A, 2B is a “revolver” structure for exchanging the source gratings whereas FIGS. 2C and 2D show a linear exchanger structure. The different gratings have each a dedicated pitch adapted for different design energies and are designated in view A as G01-G04. That is, the exchanger SGC is capable of exchanging for four different gratings but this is for illustration only and any other plurality (other than four), e.g. two, or three, or five etc. is also envisaged herein. The individual rotatability of each of the gratings may be implemented as previously explained for rotation stage RS2, the exchanger essentially implementing a plurality such rotation stages, one for each grating in the set of gratings. In other words, each source grating G01-G04 is framed in their respective framelet (not shown), each rotatably arranged in their mounting cradle 202 similar to what has been explained above at FIG. 1. The cradles 202 are inter-connected by connective elements 204 to form an essentially ring or cylindrical structure which as a whole is rotatably arranged to orbit around a center point, for instance around the focal spot FS. Preferably, the revolver structure SCG is rotatable clockwise and counterclockwise to increase responsiveness of the exchanging operation. The rotation of the revolver structure SGC allows placing a desired one of the source gratings G01-G04 under the focal spot FS for exposure by the X-ray beam. Once the desired source grating has been rotated under the focal spot (when viewed along the negative z direction) and onto the optical axis, it is then the respective grating itself that is rotated by θ to adjust for the new design energy scaled up by 1/cos(0). The system is then ready for exposure. In the view of Figure A, it is currently source grating G01 that resides under the focal spot FS and rotated around θ, ready for exposure. An actuator AC effects rotation by θ of the respective framelet (with the grating therein) and around a rotation axis though the center of the respective grating as described above for rotation stage RS2. There is either a single actuator AC or each grating G01-G04 has its own actuator to effect the rotation of the gratings G01-G02 once they have been placed under the focal spot. FIGS. 2C, 2D show a different embodiment of an exchanger mechanism where the exchange operation is effected not by revolution as in FIGS. 2A, 2B but by linear translation. Framelets with the grating structures G01-G03 therein are rotatably arranged in linear sequence in a mounting cradle 202. One or more actuators AC effect the respective rotation of the gratings as described above for rotation stage RS2. The whole structure SGC can be advanced forwards or backwards past the focal spot FS so as to place a desired one of the gratings under the focal spot FS. Either one of the two exchanger structures as shown in FIG. 2 can be arranged for instance inside the housing of the X-ray unit or outside the housing. It should be understood that implementations as per FIG. 2 are exemplary embodiments and other suitable mechanical implementations or variants of the above are also envisaged herein. In one embodiment, the exchanger structure SGC includes exactly two source gratings G01, G02 one being adapted in pitch to one design energy E0, the other to double the design energy 2*E0. Rotation of the source grating adapted to 2*E0 is then by θ=60°. Rotation is reset to θ=0° when exchanger SGC exchanges back for the grating whose pitch is adapted to the (“primary”) design energy E0. However, other such “dual” combinations are also envisaged. For instance, a rotation by θ=45° allows to increase primary design energy E0 by roughly 40% whereas a rotation by θ=30° affords an increase by about 15%. Turning now to FIG. 3, this shows another embodiment of the source grating adapter mechanism SGC. In this embodiment, there is no exchange operation but a first source grating is combined with a second source grating to achieve the pitch adaptation. More particularly, and in one embodiment, two gratings G01 and G02, having respective pitches p0′ and p0′/2, are arranged one on top of the other in at least a partial superposition. The superposition of the gratings is such that the rulings of the two gratings are parallel, in other words the bars and trenches of the two gratings run parallel. When viewed along the optical axis, a double-decker grating structure is then formed where the two gratings are combined to overlap. When the respective bars of the two gratings are aligned in registry with each other, the pitch of the double decker grating structure at the overlap is p0′. But if a lateral displacement across the ruling directions Δx=½*p0′ of one of the gratings is effected in a direction perpendicular to the rulings so that the respective gratings are brought into anti-registry (that is, the bars of one grating block the trenches of the other grating when viewed along the optical axis), the pitch of the double decker grating structure at the overlap is now p0′/2. Therefore, the pitch of the double decker grating structure can be selectively doubled or halved by laterally moving one of the two gratings by Δx or −Δx to convert from first order energy E0 to second order energy 2*E0. In other words, in this embodiment a new grating structure (the overlapping region or double decker) is combined from the two gratings, and this new grating structure has an effective pitch of p0′/2 p0′ depending on whether the two sets of bars are in registry or anti-registry. With continued reference to FIG. 3, a non-limiting embodiment of lateral displacement for pitch adaptation is shown. A cage or frame structure 302 formed from material of sufficient rigidity (aluminum or hardened steel, etc.) is shown in FIG. 3, with A, B affording different views along different directions. View A shows a side elevation on the source grating adaptation mechanism SGC along Y direction (that is, along the orientation of the grating rulings), with view B being a side elevation at 900 along X direction across the directions of the rulings. Two sets of tracks 306, an upper and lower (relative to the −Z direction) are formed in side walls of the frame structure 302. The two gratings G01 and G02 are slidable relative to each other in said tracks 302. In this way, the lateral displacement of the two gratings can be facilitated. It is sufficient for only one of the gratings to be slidable relative the other (stationary one) although an embodiment where both gratings are slidable is not excluded herein. The lateral displacement is effected by an actuator AC. It is understood that the source grating adapter structure SGC is built into the rotation stage RS2 of FIG. 1. In other words, the whole of the source grating adaptation mechanism SGC is rotatable with respect to the optical axis by θ=60°, in dependence at which of the (in this case two) design energies, E0 or 2*E0, one wishes to operate. As before, this rotation is effected by the actuator of stage RS2 (not shown in FIG. 3). Alternatively one single actuator may be configured to effect both, the lateral displacement and the rotation, by a suitable gearing mechanism. In accordance with eq (3), one (or both) of the source gratings G0, G02 are displaced by Δx to achieve half the pitch p0′/2 if a scale up by 100% of the design energy is called for. If the displacement is reversed by −Δx, and the double decker grating is rotated back to θ=00, the system returns to primary energy E0 configuration. The relative displacement Δx or −Δx of the gratings G01, G02 for the purpose of pitch adaptation can occur concurrently whilst the double decker is rotated by +/−θ or the rotation and displacement are carried out in sequence. The rotation +/−θ is about a rotation axis along the grating rulings and extends into the y direction, that is, into the plane of the drawing as per side elevation view FIG. 3A). The rotation axis passes through the center or the interspace between the superimposed gratings G01 and G02. FIGS. 4 and 5 are schematic illustrations of the principle underlying operation of the source grating adapter as per FIG. 3. In FIG. 4 a p0-pitch grating in the upper part and a p′0-grating (p′0=½*p0) in the lower part are compared. In the lower right, every other trench of the G′0 grating is blocked out and the resulting grating is a “second order” G′0-grating, that is, a grating whose pitch is now adapted to double the design energy. Comparing this second order G′0-grating to the upper right one, which is a (first order) G0-grating, it is recognized that at least with respect to the pitches both gratings are identical. As consequence, equality in design rule equation (3) can be maintained (d′/lo=p2/p′0) with the same l0 and essentially the same G0-grating (safe for the blocked out trenches). This mutual blocking out is sound, because all trenches of a G0-grating act as a separate coherent X-ray sources, which produce their own intensity distributions (Talbot-carpets) in the space between the gratings G1 and G2 having all their minima and maxima at the same positions. Blocking out of some of these independent X-ray sources will then only reduce the total X-ray flux at the G2-grating. A regular blocking pattern of trenches, as in the lower right of FIG. 4, will then cause a homogenous reduction of X-ray flux by half compared to when there is no blocking. FIG. 5 is a practical implementation (as per FIG. 3) of the concept in FIG. 4. That is, the block-out of the trenches mentioned in relation to FIG. 4 is achieved by aligning the bars between the gratings in anti-registry. That is, the first order high energy grating with pitch p′0 is converted to a second order grating by the superposition of two gratings, combined with the small linear displacement relative to one another. This principle is similar to the one described in Applicant's WO2012/063169A1. As shown in FIG. 5, the two gratings are superimposed: one (G01) having a pitch p0′, the other one (G02) having double the pitch 2*p0′ but provided with absorbing bars, which have the same widths as the bars of the first grating G01. The gratings are so aligned that their rulings are parallel. In FIG. 5, the Y-axis runs from top to bottom and view on the gratings is in Z direction. According to FIG. 5, left hand side, if the gratings are superimposed whilst their respective bars are in registry, the overlapping area formed by the superimposed gratings will reproduce the p0′-pitch grating. But performing a slight displacement relative to one another of the superimposed grating results in a grating of double the pitch 2*p′0=p0, having the same trench width as the p0′ grating and the bars now being aligned in anti-registry in the overlapping area. Thus a new source grating G0 is formed as a result of this gratings combination operation. In other words, by arranging the two gratings in at least partial superposition and by ensuring that the so formed overlapping area is within the optical axis, the pitch in the overlapping area can be changed by a relative translation of the two gratings in a direction X across the rulings. It will be appreciated that the solution as per FIG. 3 will demand a smaller footprint as the solutions proposed in FIG. 2, in particular FIGS. 2C, 2D, because in FIG. 3 the two gratings remain essentially superimposed at all times and under the focal spot FS with only a rather minute lateral displacement Δx required for design energy conversion between the two energy orders E0 and 2*E0. In contrast, in the exchanger mechanism as per FIGS. 2C, 2D, there is only one of the gratings under the focal spot FS at any one time, thus the footprint requirement is at least double that of the footprint in FIG. 3. As an alternative to the embodiment in FIG. 3, a solution without lateral displacement across the ruling directions is also envisaged although this comes at the expense of a larger footprint requirement. In this embodiment, there is only a motion along the direction of the grating rulings to effect the superposition and to build up the overlapping area. The two gratings are moved so as to build up the double decker structure. In this embodiment, the gratings are already held in alignment with the two sets of bars in anti-registry as in the right side of FIG. 5. If the gratings are not yet superimposed, (left, lower side of FIG. 5) it is only the grating with the higher pitch (G02) that intersects the optical axis. If the changeover to the other (double design energy) is called for, the other grating (which is not yet intersecting the optical axis) is moved along the rulings direction to form the overlapping area of the double decker grating structure, having the lower pitch, and so as to intersect with the optical axis. The situation where the two gratings are partially overlapping is shown on the right in FIG. 5, with the bars of grating G01 shown hatched and the bars of G2 in black to better illustrate that they are in anti-registry with each other. Although the embodiments in FIGS. 3-5 have been explained for θ=60°, that is for a doubling or halving of the design energy, it will be understood that it can be applied also to other scaling factors 1/cos(θ). According to one embodiment and as mentioned earlier, operation of the interferometer as proposed relies on the Moiré fringe pattern having a suitably adjusted period across the effective local field of view of the interferometer. The adjustment of the Moiré period of the fringe pattern can be effected herein by using an additional translating stage in combination with the above mentioned rotation stages. The adjustment of the Moiré fringe pattern is done by mutually detuning the G1/G2 unit, combined with a translation stage that slightly adjusts d0 or, preferably, l0. In one embodiment, the X-ray imaging apparatus comprises an X-, Z-translation stage TS. This embodiment with the additional translation stage can be combined with any of the above described embodiments in FIGS. 1-2. Combination with FIG. 3 embodiment is also possible, however in this case care must be taken to adjust for both, pitch in the overlapping area and the fringe pattern. The translation stage affords via a suitably configured actuator, a translation along the Z-axis and along the X axis across the direction of the grating rulings. The actuator for the translation stage TS is either in addition to the RS stage actuator or a single actuator may be configured to effect both, the X, Z translations and the rotations, by a suitable gearing mechanism. In one embodiment, the translation stage TS is coupled with the rotatable interferometer G1/G2. Alternatively and preferably, the X-, Z-translation stage is combined with the rotatable G0-unit as shown in FIG. 1. In a first step of fringe adjustment, the system is set to θ=0° and by using the z-stage component of the translation stage TS, the appropriate Moiré fringe direction is adjusted. In a second step, after rotation of the grating G0 or G1/G2 by θ, the X-translation component of stage TS is used for the fringe direction adjustment at the second order design energy of the system. This is due to the fact that in the case of the rotated state (e.g., θ=60°) any change Δx along the X axis of the G0-grating will cause an effective change Δleff of the l0 distance according to Δleff=Δl/cos θ. It is noted here, that the X-adjustment does not affect the Δ=0° state because of the translational invariance of the grating system with respect to the x-direction across the trenches (grating trenches run parallel to the Y axis). But in order to ensure that an appropriate dynamic range of Δleff can be achieved in order to maintain the Talbot distance versus source grating distance ratio in eq (3), it might be necessary to increase the dynamic range for the Δx displacement. When the rotation axis runs through the center of the grating as in FIG. 1, the Δx displacement range is restricted to slightly smaller than ½ the G0-grating edge length along the X axis. Therefore, in FIG. 6 a variant to the embodiment in FIG. 1 is proposed, where now the rotation axis of G0 is set off-center, preferably close to one of the edges of the G0-grating. Thus by asymmetric rotation, the available dynamic range Δleff is nearly doubled compared to the symmetric embodiment of FIG. 1 where rotation of G0 is around a central axis through the G0 grating. A similar off center rotation for gratings G1 or G2 can be arranged if the translation stage TS is coupled instead to the interferometer IF. In the following, a number of variants or additions to the above embodiments will be described. For instance, it should be noted herein, that the above proposed design energy switching functionality by rotating the gratings, is not restricted to scanning DPCI systems but is also applicable to static DPCI systems. In the latter system, phase stepping is performed by a relative motion of the G1 and G2 grating perpendicular to the trench direction (here denoted as Y direction) or by a preferred motion of the G0-unit relative to the G1/G2-interferometer unit. In this case of a static phase stepping system, the above described x-, z-translation stage TS further includes an X-stage translation component for translation along the X axis across the direction of the rulings. The Y-translation component can then be used for the phase stepping whereas the others are used for the fringe adjustment or pitch adaptation (FIG. 3), as described above. Although in the above embodiment, the rotation of the gratings is effected automatically by suitable actuators, manual embodiments are not excluded herein. For instance, by suitable gearing mechanism the rotation and or translation of the gratings can be affected by operation of a suitable manual actuator for instance thumb wheel etc. In one embodiment the X-ray imaging apparatus includes a user input device (e.g., GUI or otherwise) to select a desired design energy of the X-ray imaging apparatus. The desired energy can be expressed on term of a current design energy time the scale factor 1/cos θ. The specified design energy is then received in a step S10 at a control module CC. In response to such a selection, a suitable signal is forwarded in step S20 by control module CC to the actuators of the gratings to effect a corresponding rotation θ and/or translation of the interferometer and the source gratings (if any). The control module CC may be arranged as a software module on a general purpose computing unit such as a work station. The rotation so effected corresponds to the desired design energy selected by the user. In the manual embodiment, selection of a desired design energy will indicate to the user the angle θ by which the gratings need to be tilted. The user can then use the manual actuator, such as the thumb wheel, to effect the corresponding rotation. To increase accuracy, visual guiding tools may be used to help the user when manually setting the rotation angle θ to the desired value. For instance, sensors at the gratings can pick up a current rotation angle and a visual indication thereof can be rendered on a display unit against a visual indication of the target rotation. As a further variant to any of the above embodiments, and referring back to eqs (1-3), it may also be possible to adjust the pitch p2 of the analyzer grating instead of the pitch p0 of the source grating to ensure equality in the design equations. However, adjusting source grating pitch p0 as described above is preferable because this has been found by Applicant to be easier to implement. If a pitch adaptation mechanism for G2 is used similar to the one explained above for G0, the pitch of G1 will need to be adjusted accordingly. These alternatives are also envisaged herein. In particular, any of the above described adapter mechanisms as per FIGS. 2,3 can be applied for G2 and/or G1 instead. The linear translation solutions may be particularly suitable in this respect. Although in the above embodiments a separate or discrete, dedicated absorber grating structure G2 was used in the interferometer IF, this may not necessarily be so in all embodiments. For instance, the analyzer grating G2 functionality can also be integrated into the X-ray detector D itself. What is more, the grating function can be entirely taken over by the X-ray detector by a careful arrangement of the pixel geometry, in particular the inter-spacing between the pixels to replicate the G2 functionality. This “hybrid” or “no-G2 grating” interferometer arrangement with a single grating G1 can be used in any one of the embodiments. In particular then, in this embodiment, it is the detector D that is tilted by θ relative to the optical axis in concert with the tiltings by the same angle of G0 and G1. In this single grating interferometer IF embodiment, the X-ray detector D preferably has a pitch sufficiently small, hence a spatial resolution sufficiently large, for detecting, i.e., adequately resolving, the interference pattern generated by the grating G1 for the purpose of differential phase contrast imaging and/or dark field imaging. For that purpose the X-ray detector may be a high resolution X-ray detector, with spatial resolution in the micrometer range or sub-micrometer range, such as 50 micrometers or more. As a yet further variant, an interferometer IF geometry inverse to the one shown in FIGS. 1-6 may be used. In this inverse geometry interferometer, the examination region is sandwiched between the interferometer IF, that is, the Examination region ER is between grating G1 and G2 or the examination region is between G1 and the detector for the single grating interferometer embodiment. This is different to the embodiment shown in FIGS. 1, 6, where the examination region is between the source grating and the grating G1 of the interferometer IF. In the inverse geometry case, one may then arrange source grating G0 and grating G1 rotatably and together in a frame structure as described above for the rotation stage RS1. Although all of the above embodiments work well in sufficient approximation for most practical purposes, it will be noted that the design energy at the chosen inclination θ0 will hold true strictly speaking only for that part of X-ray beam that propagates along the optical axis OA as shown in FIG. 7. For rays propagating along different angles relative to the optical axis, as is the case in a fan-beam geometry rather than a parallel beam geometry, these are optimized for different design energies. More specifically, for individual X-ray beams that are not propagating along the optical axis but at a fan angle ϕ relative to the optical axis (−Δϕ<ϕ<Δϕ), the effective inclination angle θeff is θeff=θ0+ϕ. For the effective design energy Eeff(ϕ) there is then a fan-angle dependence as per:Eeff(ϕ)=E0/cos(θeff)=E0/cos(θ0+ϕ)=Eeff(ϕ=0)*cos(θ0)/cos(θ0+ϕ) (4)with E0 being the ground design energy at ϕ=θ0 and θ0 denoting the given tilt angle or given inclination currently assumed by the gratings. This fan angle versus design energy dependency (4) can be used to refine the proposed dual- or multi energy imaging scheme by broadening the spectral design energy window around the mean design energy for the chose inclination. For instance, in some DCPI systems, for a grating inclination of θ0=60°, a broadening of about +/−7.5% is achievable for the design energy associated with θ0. For instance, compared to a given spectral width or “full width at half maximum” (FWHM) of a grating system of about 12 keV and a choice of the design energy at the optical axis of 33 keV, an additional variation of about 5 keV in design energy can be achieved by using the above noted fan angle versus design energy dependency. For this numerical example, an effective total energy window width of about 17 keV can be realized, ranging from about 25 to 41 keV. It has been found that the so broadened energy window excellently matches the energy dependence of the dark field signal over a large set of structural parameters. The spectral information can be collected either by using an energy resolving detector D such as a photon counting detector, with suitable number of bins (two or more, preferably three) set up for the different design energies in the broadened range. However, a conventional energy integrating detector may also be used instead when combined with a balanced X-radiation filter FL as shown in FIG. 7. The filter FL comprises a series of filter elements FEi, each configured by material choice and/or thickness for different K-edge energies. Because of the above noted fact that the design energy varies steadily with the fan-angle, the filter elements FEi are arranged linearly across the optical axis in increasing or decreasing order of their respective K-edge energies. Whether the filter elements FEi are ordered along the x-axis in decreasing or increasing order depends on the direction of the rotation of the grating system. In the embodiment of FIG. 7, the K-edge energies EKn associated with the respective filter elements FEi increase along the X-axis whilst the interferometer IF rotates clockwise. In one embodiment, there is an uneven number of filter elements such as three or five (as in the FIG. 7 embodiment), with the element at the center arranged at the optical axis and having a K-edge energy that approximately equals to the scaled up design energy associated with the given inclination θ0. An even number of filter elements (two or more) can also be used where the K-edge energies of the two central elements straddle the design energy corresponding to the inclination θ0. For reasons of radiation dose savings, the filter FL can be arranged anywhere in between the x-ray source XR and the object OB. In one embodiment, the filter FL is mounted above (relative to the propagating direction of the X-ray beam) or below the pre-collimator PC. Alternatively, the filter FL is mounted on top or below the G0-source grating. Alternatively, the filter FL can be arranged at the interferometer IF, either on top thereof or within the interferometer IF (ie, between the G1 and G2 gratings). Alternatively, the filter FL is mounted between the interferometer IF and the detector. As mentioned, to achieve better spectral separation, the materials and/or thicknesses of the filter elements FEi are configured so that the transmission functions of the respective filter elements are “balanced”. In other words, the filter elements are chosen such that the respective low energy branches to the left of the K-edges are essentially coincident as shown in the diagram of FIG. 8 at the example of three transmission curves T for a filter FL whose three filter elements are formed from three different materials, namely Ag (Z=47; K-edge=25.5 keV), In (Z=49; K-edge=27.9 keV) and Sb (Z=51; K-edge=30.5 keV), having respective thicknesses. The vertical axis is the proportion (in %) of the transmitted radiation and the horizontal axis is the radiation energy in keV. Alternatively, the respective high energy branches (to the right of the K-edges) are made to essentially coincide. By forming respective difference images from the filtered signals, a sharp spectral separation can be realized for dual or multi-energy imaging having almost no flux-contributions outside the energy windows which are defined by the K-edge energies of the K-edge filter elements. This spectral separation is exemplary shown in FIG. 9 where two respective difference signals, Sb—In and In—Ag, are shown based on the transmission functions in FIG. 8. In FIG. 9, the vertical axis represents the photon flux and the horizontal axis represents the photon energy in keV. Suitable other material combinations and thicknesses for mammography applications include: Sn (Z=50, K-edge=29.2 keV), and Te (Z=52; K-edge=31.8 keV). Filter thicknesses of around 40 to 50 μm are suitable in this context. For other than medical applications, Cd (Z=48) may also be used. In a different photon energy region around 50 to 60 keV, suitable elements include Gd (Z=64; K-edge=50.2 keV), Tb (Z=65; K-edge=52.0 keV), Dy (Z=66; K-edge=53.8 keV), Ho (Z=76; K-edge=55.6 keV), Er (Z=68; K-edge=57.5 keV) and Yb (Z=70; K-edge=61.3 keV). Using as an example the three-element filter formed from Ag (Gold), Sb (Antimony) and In (Indium), the equation for balancing the filter FL is given by:μAg(E0=25 keV)*dAg(=40 μm)=μIn(E0)*dIn=μSb(E0)*dSb (5)with E0 being a reference x-ray photon energy, e.g. 25 keV, and pAg(E), μIn(E0) and μSb(E0) being the attenuation coefficients of the appropriate filters at energy E0 and dAg, dIn and dSb being the balanced filter thicknesses. It should be clear that eqs (6) are applicable to any number of filter elements in any material combination. What the system (6) of balancing equations ask for is that respective ratios of the material attenuation coefficients are constant and equal to the inverse ratios of the respective thicknesses. In this example, relative to a 40 μm thickness of the Ag element, the balanced thicknesses of the In and Sb filters are 53 μm and 51 μm, respectively. In general, there is a slight mismatch in the high energy region above the K-edge thresholds. As mentioned earlier, alternatively, one could attempt matching the thicknesses of the balanced filter set the other way around by trying to make the high energy parts of the transmission curves coincide. Due to the fact that the design energy varies with fan angle, the system IM is preferably of the scanning type because any part of the object OB one wishes to image should be exposed by the whole effective spectral width of the DPCI set up. In other words, thanks to the scanning motion in scanning type systems IM, each part of the object can be imaged by using respective rays filtered by each of the respective filter elements FEi. The filter FL is moved in concert with the scanning motion. This can be implemented for instance by coupling the filter FL to the pre-collimator or to the G0-grating unit. The broadening of the spectral window achievable by the X-ray filter FL is particularly useful for chronic obstructive pulmonary disease (COPD) detection in lung or chest dark-field imaging. By increasing the available energy window in DPCI in the described manner, more accurate information on local micro structure properties of the imaged lung tissue can be provided. In an alternative, simpler embodiment, the X-ray filter FN comprises only a single (solid material) filter element that is arranged within the imager IM so that this single filter element FE1 affects only a part of the X-ray beam. Specifically, in one embodiment, the single filter element FE1 is arranged to only extend up to the optical axis OA, thus only half way across the beam at the given cross-section. The single filter element thus affects only half the X-ray beam whilst the other part passes essentially unfiltered through “air”. Thus the filter comprises the single, solid part filter element part FE1 and an “air part” on the other side of the optical axis OA. Lastly, all of what has been explained in the above embodiments is of equal application for imaging system where the optical axis is movable, in particular rotatable or translatable, relative to the imaging region. Examples are CT scanners or tomosynthesis imaging apparatuses as used in mammography scanners. In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system. The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above-described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention. This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention. Further on, the computer program element might be able to provide all necessary steps to fulfill the procedure of an exemplary embodiment of the method as described above. According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it which computer program element is described by the preceding section. A computer program may be stored and/or distributed on a suitable medium (in particular, but necessarily, a non-transitory medium), such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems. However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention. It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. |
|
summary | ||
claims | 1. A Radioactive Isotope (RI) manufacturing apparatus comprising:an accelerator which accelerates charged particles;a target which is irradiated with the charged particle accelerated by the accelerator,thereby manufacturing a radioactive isotope;a built-in shield that is a wall body which is configured to be provided inside a building and surrounds the accelerator and the target to shield radiation; anda target shield that is a wall body which is disposed in an internal space formed so as to be surrounded by the built-in shield and surrounds the target to shield the radiation; wherein, said target shield is connected to the lead-out tube at the bottom of the shield in order to further attenuate radiation. 2. The RI manufacturing apparatus according to claim 1, wherein the target shield includesa gamma ray shielding plate which shields gamma rays, anda neutron radiation shielding plate which is disposed on the target side of the gamma ray shielding plate and shields neutron radiation. 3. The RI manufacturing apparatus according to claim 1, wherein the built-in shield is composed of a plurality of parts and at least one of the plural parts is movable,the target shield includes an openable and closable door, anda joint between the door and another member adjacent to the door is formed at a position deviated from a joint between the plural parts of the built-in shield. 4. The RI manufacturing apparatus according to claim 1, wherein a cutout portion which makes a lead-out tube that leads out the radioactive isotopes in the target pass therethrough is provided on the lower surface side of the target shield. |
|
summary | ||
summary | ||
claims | 1. An imaging system comprising:a radiation source configured to project radiation from a focal spot onto an object;a plurality of radiation detectors disposed around at least a portion of the object, wherein the plurality of radiation detectors detect received radiation along a path projected from the focal spot to the plurality of detectors; anda plurality of collimators positioned between the object and the plurality of detectors, wherein the collimators have a tapered configuration, the plurality of collimators comprising laminated collimator plates extending along a height of the plurality of collimators, each laminated collimator plate arranged with a tallest plate interposed between shorter plates across a width of the laminated collimator plate. 2. The imaging system of claim 1, wherein the collimators have a base proximate to the plurality of radiation detectors and a top proximate the object, wherein the base is wider than the top. 3. The imaging system of claim 1, wherein the plurality of collimators are formed from single tapered plates having a constant slope. 4. The imaging system of claim 1, wherein the laminated collimator plates are arranged with one plate laminated between a pair of shorter plates that are laminated between a pair of shorter plates. 5. The imaging system of claim 1, wherein the radiation source projects electromagnetic waves. 6. The imaging system of claim 1, wherein the plurality of collimators comprise x-ray absorbing material and adjacent collimators form a channel therein for restricting scatter radiation from reaching the plurality of radiation detectors, the channel having an inlet aperture and an outlet aperture, wherein the inlet aperture is wider than the outlet aperture. 7. The imaging system of claim 6, wherein the channel inlet aperture and the channel output aperture are defined as a function of a focal spot size and motion of the radiation source. 8. The imaging system of claim 1, wherein the plurality of collimators have a first slope on a first side and a second slope on a second side, the first slope having a first inclination angle, the second slope having a second inclination angle, with the first inclination angle and the second inclination angle being equal. 9. The imaging system of claim 1, wherein the plurality of collimators have a first slope on a first side and a second slope on a second side, the first slope having a first inclination angle, the second slope having a second inclination angle, with the first inclination angle and the second inclination angle being unequal. 10. A method for collimating a radiation detector, the method comprising:disposing a plurality of radiation detectors to surround at least a portion of an object;providing a plurality of tapered edge collimators between the object and the plurality of detectors, wherein the plurality of tapered edge collimators are configured to increase exposure of the plurality of radiation detectors to a range of focal spot positions, the plurality of tapered edge collimators comprising laminated collimator plates extending along a height of the plurality of tapered edge collimators, each laminated collimator plate arranged with a tallest plate interposed between shorter plates across a width of the laminated collimator plate; andconfiguring the plurality of radiation detectors to measure a transmitted radiation along a path projected from a focal spot to the plurality of radiation detectors through the object. 11. The method of claim 10, wherein the plurality of tapered edge collimators have a base proximate to the plurality of radiation detectors and a top proximate the object, wherein the base is wider than the top. 12. The method of claim 10, wherein the plurality of tapered edge collimators comprise x-ray absorbing material and adjacent collimators form a channel therein for restricting scatter radiation from reaching the plurality of radiation detectors, the channel having an inlet aperture and an outlet aperture, wherein the inlet aperture is wider than the outlet aperture. 13. The method of claim 12, wherein the channel inlet aperture and the channel output aperture are defined as a function of a focal spot size and motion range of the x-ray source. 14. A method for manufacturing a collimator for an imaging system, the method comprising:forming a plurality of collimator elements that define walls for a plurality of channels for the collimator; andproviding a tapered slope on a first side of the plurality of collimator elements and a tapered slope on a second side of the plurality of collimator elements, the plurality of collimator elements comprising laminated collimator plates extending along a height of the plurality of collimator elements, each laminated collimator plate arranged with a tallest plate interposed between shorter plates across a width of the laminated collimator plate. 15. The method of claim 14, wherein the slope of the first side and the slope of the second side are equal. 16. The method of claim 14, wherein the slope of the first side and the slope of the second side are unequal. |
|
claims | 1. An x-ray apparatus, comprising:a first rotatable disk comprising a first plurality of angled slots;a first shutter comprising a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots, and wherein at least one of the first plurality of protruding members is positioned within a second angled slot of the first plurality of angled slots,wherein the first shutter at least partially defines an x-ray collimation aperture, and wherein the apparatus is configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the x-ray collimation aperture;a second rotatable disk comprising a second plurality of angled slots; anda second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a first angled slot of the second plurality of angled slots, and wherein at least one of the second plurality of protruding members is positioned within a second angled slot of the second plurality of angled slots,wherein the first shutter and the second shutter at least partially define the x-ray collimation aperture, and wherein the apparatus is configured such that rotation of the second rotatable disk results in movement of the second shutter to alter the size of the x-ray collimation aperture. 2. The x-ray apparatus of claim 1, wherein the apparatus is configured such that the first rotatable disk can be rotated independently of the second rotatable disk. 3. The x-ray apparatus of claim 2, wherein the apparatus is configured such that rotation of the first rotatable disk through a first angle results in movement of the first shutter of a first distance, wherein rotation of the second rotatable disk through the first angle results in movement of the second shutter of a second distance, and wherein the first distance differs from the second distance. 4. An x-ray apparatus, comprising:a first rotatable disk comprising a first plurality of angled slots; anda first shutter comprising a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots, and wherein at least one of the first plurality of protruding members is positioned within a second angled slot of the first plurality of angled slots,wherein the first shutter at least partially defines an x-ray collimation aperture, and wherein the apparatus is configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the x-ray collimation aperture, wherein the first angled slot extends towards a center of the first rotatable disk at a first angle, wherein the second angled slot extends towards the center of the first rotatable disk at a second angle, and wherein the first angle is greater than the second angle. 5. The x-ray apparatus of claim 4, wherein the first angled slot has a first radius of curvature, wherein the second angled slot has a second radius of curvature, and wherein the first radius of curvature is greater than the second radius of curvature. 6. The x-ray apparatus of claim 4, further comprising:a second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a third angled slot of the first plurality of angled slots, and wherein at least one of the second plurality of protruding members is positioned within a fourth angled slot of the first plurality of angled slots. 7. The x-ray apparatus of claim 6, wherein the third angled slot extends towards the center of the first rotatable disk at a third angle, wherein the third angle is at least substantially identical to the first angle, wherein the fourth angled slot extends towards the center of the first rotatable disk at a fourth angle, and wherein the fourth angle is at least substantially identical to the second angle. 8. An x-ray apparatus, comprising:a first rotatable disk comprising a first plurality of angled slots; anda first shutter comprising a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots, and wherein at least one of the first plurality of protruding members is positioned within a second angled slot of the first plurality of angled slots,wherein the first shutter at least partially defines an x-ray collimation aperture, wherein the apparatus is configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the x-ray collimation aperture, and wherein the first rotatable disk further comprises:a plurality of protrusions positioned along at least a portion of a perimeter of the first rotatable disk, wherein the protrusions protrude beyond the perimeter adjacent to the protrusions, and wherein the protrusions are configured to allow a user to rotate the first rotatable disk in order to alter a size of the x-ray collimation aperture. 9. The x-ray apparatus of claim 8, further comprising:a second rotatable disk comprising a second plurality of angled slots and a second plurality of protrusions positioned along at least a portion of a perimeter of the second rotatable disk, wherein the second plurality of protrusions protrude beyond the perimeter of the second rotatable disk adjacent to the protrusions, and wherein the second plurality of protrusions are configured to allow a user to rotate the second rotatable disk in order to alter a size of the x-ray collimation aperture; anda second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a first angled slot of the second plurality of angled slots, and wherein at least one of the second plurality of protruding members is positioned within a second angled slot of the second plurality of angled slots,wherein the first shutter and the second shutter at least partially define the x-ray collimation aperture, and wherein the apparatus is configured such that rotation of the second rotatable disk results in movement of the second shutter to alter the size of the x-ray collimation aperture. 10. The x-ray apparatus of claim 9, wherein the first plurality of protrusions have at least one of a different shape and a different size relative to the second plurality of protrusions. 11. An x-ray apparatus, comprising:an x-ray generator configured to generate x-ray electromagnetic radiation;a visible light generator configured to generate visible electromagnetic radiation, wherein the visible light generator is configured to deliver the visible electromagnetic radiation such that the visible electromagnetic radiation at least partially overlaps the x-ray electromagnetic radiation;a collimation aperture configured to deliver overlapping radiation comprising x-ray electromagnetic radiation from the x-ray generator and visible electromagnetic radiation from the visible light generator, wherein the collimation aperture is configured to deliver the visible electromagnetic radiation in a visible target shape and to deliver the x-ray electromagnetic radiation in an x-ray target shape, wherein the size of the visible target shape varies according to the size of the collimation aperture, and wherein size of the x-ray target shape also varies according to the size of the collimation aperture;a first rotatable disk; anda first shutter operably coupled with the first rotatable disk such that rotation of the first rotatable disk results in movement of the first shutter to alter the size of the collimation aperture. 12. The x-ray apparatus of claim 11, wherein the visible light generator comprises a light-emitting diode. 13. The x-ray apparatus of claim 11, further comprising a mirror, wherein the mirror is positioned and configured to reflect light from the visible light generator through the collimation aperture, wherein the mirror is transparent to x-ray electromagnetic radiation, and wherein the mirror is positioned in between the x-ray generator and the collimation aperture and configured such that x-ray electromagnetic radiation from the x-ray generator passes through the mirror before being delivered through the collimation aperture. 14. The x-ray apparatus of claim 13, wherein the mirror comprises a silver coating. 15. The x-ray apparatus of claim 14, wherein the silver coating comprises a silver oxide coating. 16. The x-ray apparatus of claim 13, wherein the x-ray generator is positioned away from a center of the mirror by a first distance, wherein the visible light generator is positioned away from the center of the mirror by a second distance, and wherein the first distance is at least substantially identical to the second distance. 17. The x-ray apparatus of claim 13, wherein the first rotatable disk comprises a first plurality of angled slots, wherein the first shutter comprises a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots, and wherein at least one of the first plurality of protruding members is positioned within a second angled slot of the first plurality of angled slots. 18. The x-ray apparatus of claim 17, further comprising:a second rotatable disk comprising a second plurality of angled slots; anda second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a first angled slot of the second plurality of angled slots, wherein at least one of the second plurality of protruding members is positioned within a second angled slot of the second plurality of angled slots, and wherein the second shutter is operably coupled with the second rotatable disk such that rotation of the second rotatable disk results in movement of the second shutter to alter the size of the collimation aperture. 19. An x-ray apparatus, comprising:an x-ray generator configured to generate x-ray electromagnetic radiation;a visible light generator configured to generate visible electromagnetic radiation, wherein the visible light generator is configured to deliver the visible electromagnetic radiation such that the visible electromagnetic radiation at least partially overlaps the x-ray electromagnetic radiation;a first rotatable disk comprising a first plurality of angled slots;a first shutter comprising a first plurality of protruding members, wherein at least one of the first plurality of protruding members is positioned within a first angled slot of the first plurality of angled slots, and wherein at least one of the first plurality of protruding members is positioned within a second angled slot of the first plurality of angled slots;a second rotatable disk comprising a second plurality of angled slots; anda second shutter comprising a second plurality of protruding members, wherein at least one of the second plurality of protruding members is positioned within a first angled slot of the second plurality of angled slots, and wherein at least one of the second plurality of protruding members is positioned within a second angled slot of the second plurality of angled slots,wherein the first shutter and second shutters at least partially define a collimation aperture, wherein the apparatus is configured such that rotation of the first rotatable disk results in movement of the first shutter to alter a size of the collimation aperture, wherein the apparatus is configured such that rotation of the second rotatable disk results in movement of the second shutter to alter a size of the collimation aperture,wherein the apparatus is configured to deliver overlapping radiation comprising x-ray electromagnetic radiation from the x-ray generator and visible electromagnetic radiation from the visible light generator, wherein the collimation aperture is configured to deliver the visible electromagnetic radiation in a visible target shape and to deliver the x-ray electromagnetic radiation in an x-ray target shape, wherein the size of the visible target shape varies according to the size of the collimation aperture, and wherein size of the x-ray target shape also varies according to the size of the collimation aperture. |
|
description | The present invention relates to a miniature electron column including an electron emission source and lenses, and, more particularly, to a miniature electron column having a structure that can facilitate the alignment and assembly of an electron emission source and lenses. A microcolumn as a miniature electron column, which operates under the basic principle of a Scanning Tunneling Microscope (STM) and is based on an electron emission source and electro-optical parts having micro-structures, was first introduced in the 1980s. The microcolumn is fabricated by assembling micro-parts precisely, thereby minimizing optical numerical values and, therefore, constructing an improved electron column. A plurality of micro-structures is arranged and can be used for a multi-microcolumn having a parallel or series structure. The microcolumn is a mechanical micro-structure that includes a micro-electronic lens and a deflector and has a high aspect ratio. In general, the microcolumn includes an electron emission source, a source lens, a deflector, and an Einzel lens. For a microcolumn, the alignment and fastening of an electron emission source, a source lens and an Einzel lens are very important in the light of the performance of the microcolumn. With respect to such alignment and fastening of a microcolumn, a conventional microcolumn is disclosed in Journal of Vacuum & Science Technology B14 6, pp. 3792-3796, “Experimental evacuation of a 2020 mm footprint microcolumn”, which was published in 1996. FIG. 1 is a perspective view of a conventional microcolumn, which shows the conventional microcolumn in which an electron emission source, a source lens, deflectors and an Einzel lens are aligned and fastened. An upper plate 2, along with a micro-positioner (not shown) located on the top of the upper plate 2, forms a member for supporting the electron emission source, and a through hole is formed at the center of the member to position the electron emission source 1 therein. A lower plate 5 used as a support member for accommodating the upper plate 2 and the lenses, as shown in FIG. 1, is fastened using upper bolts via four support bars 6. The source lens 3 is aligned with the electron emission source 1 and is attached to the top of the lower plate 5 through epoxy bonding or the like. The deflectors 4 are arranged to the right and left of the lower plate 5. Furthermore, the Einzel lens (not shown) is assigned and fastened to the bottom of the lower plate 5 to be opposite the source lens 3 in the same manner as the source lens. The upper and lower plate 2 and 5 are respectively provided with through holes at the central axes thereof so that an electron beam emitted from the electron emission source 1 can pass through the lenses and the deflector. FIG. 2 is a conceptual view showing the operation of conventional electron columns, which illustrates the concept of the operation of the conventional electron column. In FIG. 2-A, an electron beam B emitted from the electron emission source 1 passes through the holes of a source lens 3, is deflected by a deflector 4, and is focused on a sample by a focus lens 6. The above-described conventional microcolumn is inconvenient in that the assembly and use thereof are inconvenient due to the wiring of the deflector 4 and the wiring of the focus lens 6. Furthermore, the associated procedure is complicated. FIG. 2-B shows an embodiment in which a deflector is eliminated by performing both focusing and deflecting using a deflector-type lens layer. This technology is disclosed in Journal of Vacuum & Science Technology B13(6), pp. 2445-2449, “Lens and deflector design for microcolumn”, and pp. 3802-3807, “The electrostatic moving objective lens and optimized deflection systems for Microcolumn”, which was published in 1995. In the electron column of FIG. 2-B, a focus lens 6′ includes a deflector-type lens layer 6b, which will be described later (refer to the description of FIG. 4), in the central layer thereof, and performs focusing and deflector functions, instead of the deflector 4 of FIG. 2-A. Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an electron column having a simple structure that is formed by combining a deflector and a focus lens together. In addition, the electron column of the present invention reduces the complexity of wiring, thereby simplifying processes. In addition, the electron column of the present invention aims to simplify the wiring and control processes of a multiple electron column. An electron column having a simple structure according to the present invention basically includes an electron emission source, a source lens, and a deflector. Furthermore, the present invention provides an electron column having an electron emission source and a lens unit, wherein the lens unit comprises two or more lens layers and performs both a source lens function and a focus lens function. Furthermore, compared with the conventional microcolumn, the microcolumn according to the present invention source lens can additionally perform the function of a focus lens. Moreover, the source lens can perform both focusing and deflecting functions. The structure of the microcolumn of the present invention uses microcolumn technology, which has already been developed (refer to [1] H. S. Kim, D. W. Kim, S. J. Ahn, Y. C. Kim, S. S. Park, S. K. Choi, D. Y. Kim, J. Korean Phys. Soc., 43 (5), 831, (2003), [2] E. Kratschmer, H. S. Kim, M. G. R. Thomson, K. Y. Lee, S. A. Rishton, M. L. Yu, S. Zolgharnain, B. W. Hussey, and T. H. P. Chang, J. Vac. Sci. Techno. B 14 (6), 3792 (1996), [3] T. H. P. Chang, M. G. R. Thomson, E. Kratschmer, H. S. Kim, M. L. Yu, K. Y. Lee, S. A. Rishton, and B. W. Hussey, J. Vac. Sci. Techno. B 14 (6), 3774 (1996)). An electron column generally includes an electron emission source configured to emit electrons, a source lens unit composed of three electrode lens layers and configured to control an electron beam and filter out part of the beam, two pairs of 8-pole deflectors for scanning the electron beam, and an Einzel lens or focus lens for condensing the electron beam. This structure is a basic structure for electron microscopes or lithography. Electron columns are not always fabricated to have such a structure. The overall length of an electron column is equal to or shorter than 3.5 mm, which is the overall length from an electron emission source to the last electrode of a focus lens. The electron column, which is significantly decreased in size compared to a conventional electron column, can maximize beam current and minimize various lens aberrations, thereby increasing resolution. Furthermore, since an electron beam is emitted using a low voltage of 1˜2 kV, problems of space charging and electron-electron scattering, which occur when a voltage higher than 10 kV is used in the conventional art, can be solved. Such electron columns can be fabricated using silicon or metallic membranes when a previously developed semiconductor micro-fabrication technology is utilized. Since an electron column according to the present invention has no inherent focus lens, the structure thereof is simplified compared to that of the conventional electron column, so that wiring and control are facilitated and, for a multiple electron column, the fabrication of the electron column and the control of a lens are further simplified and facilitated. With reference to the accompanying drawings, the microcolumn of the present invention is described in detail below. FIG. 3 is a conceptual view showing embodiments of the operation of an electron column according to the present invention, which corresponds to the operation of the conventional electron column of FIG. 2. FIG. 4 is a plan view showing the lens layer of the source lens of the present invention, which additionally performs a deflector function. In FIG. 3-A, an electron beam B′ emitted from an electron emission source 11 passes through the holes of a source lens 13. The source lens 13 includes an upper lens layer 13a, a central lens layer 13b and a lower lens layer 13c. In this case, the upper lens layer 13a functions as an extractor and induces the emission of electrons from the electron emission source 11, while the central lens layer 13b performs both an accelerator function of accelerating electrons emitted from the electron emission source 11 and a focusing function. The lower lens layer 13c performs a focusing function, causes the electron beam B′ to be focused on a sample as desired, and limits electrons emitted from the electron emission source 11 to form an effective electron beam. Furthermore, the electron beam focused as described above is deflected toward the sample by a deflector 14. In FIG. 3-B, an electron beam B′ emitted from an electron emission source 11 passes through the holes of a source lens 13′. Furthermore, the electron beam B′ having passed through the source lens 13′ is focused on a sample and deflected. The source lens 13′ of FIG. 3-B includes an upper lens layer 13a, a central lens layer 13b′ and a lower lens layer 13c. The electron column of FIG. 3-B is characterized in that a lens unit is composed only of a source lens and, particularly, the central lens layer 13b′ is of a deflector type, therefore a simple electron column can be constructed using only three lens layers (electrodes). That is, using the deflector-type lens layer, an electron column including the lens unit having a simple structure can be fabricated. Furthermore, in the construction of FIG. 3-B, the entire source lens may be constructed using deflector-type lens layers, but it is preferred that only the necessary number of deflector-type layers be used because a deflective-type lens layer is complicated with respect to the wiring and control of the lens, compared to a general lens. In the electron column having the construction of FIG. 3-B, the upper lens layer 13a functions as an extractor and, therefore, induces the emission of electrons from the electron emission source 11, while the central lens layer 13b′ performs both an accelerator function of accelerating electrons emitted from the electron emission source 11, and focusing and deflector functions. The lower lens layer 13c performs a focusing function, causes the electron beam B′ to be well focused on a sample, and limits electrons emitted from the electron emission source 11 to form an effective electron beam. The operation of the electron column according to the present invention, which is illustrated in FIG. 3, is configured such that a voltage difference is created between the lens layers (electrodes) of the source lens, and focusing can be additionally performed on the electron beam passing through the source lens. The lens layer 40 of FIG. 4 is a lens layer that corresponds to a central one 13b, 13b′ and 6b of 3 lens layers constituting the source lens 13 or focus lens 16, and additionally performs a deflecting function. In the lens layer 40 of FIG. 4, a single lens layer is divided into 4 regions, or electrodes 41, 42, 43 and 44. The 4 regions are insulated from each other by 4 insulating portions 49, therefore separate voltages can be respectively applied to the 4 regions 41, 42, 43 and 44. In this case, the insulating portions 49 are made of insulation material, or the lens layer is divided and fastened using Pyrex, with narrow space gaps being disposed therebetween, thus forming insulating portions only through the division. In the above-described FIG. 3, only the central layer 13b′ of the source lens 13′ is formed of a deflector-type lens layer for deflection, however, all of the 3 layers may be formed of deflector-type lens layers. That is, the source lens can be constructed by selecting one or more deflector-type lens layers as one or more layers among the respective layers of the source lens. In general, the source lens or focus lens is formed of one or more lens layers, but the source lens unit according to the present invention requires two or more layers. By forming one or more of the layers using deflector-type lens layers, the operation of FIG. 3-B can be implemented. Separate voltages are applied to the lens unit for respective lens layers. However, a number of different voltages equal to the number of deflecting regions is applied to the deflector-type lens, unlike voltages applied to general lens layers. Accordingly, the voltage that must be applied to a corresponding layer, plus or minus a deflection voltage for the deflection of a corresponding region, is applied to the deflector-type lens layer. Although, in the present embodiment, the deflector-type lens layer is divided into 4 regions and functions as a deflector, the deflector-type lens layer may be divided into 8 regions and used. The number of regions to be obtained through division may be determined according to need. Furthermore, although, in FIG. 3, the deflector is formed of a single layer, it may be formed of 2 or more layers and perform deflection. FIGS. 5 and 6 are diagrams showing lens layers, respectively, that are used to construct source lenses using deflector-type lens layers of the present invention in a multiple electron column. FIG. 5 shows a lens layer 50 for a general multi-ple electron column, not a deflector-type lens layer, and FIG. 6 shows a deflector-type lens layer 60. Like the source lens for the above single-type electron column, the source lens for the multiple electron column may be fabricated by combining the general multiple electron column lens layer of FIG. 5 with the multiple electron column lens layer of FIG. 6, or the source lens for a multiple electron column may be fabricated using only the lens layers 50 for a multiple electron column. That is, the lens may be constructed to have a construction identical or similar to the construction of the lens of the single-type electron column illustrated in FIG. 3. In FIG. 5, reference numerals 52 designate holes through which an electron beam can pass, and reference numerals 53 designate a single unit lens electrode. That is, reference numerals 53 correspond to each lens layer of a single-type electron column and the single unit lens electrode 53 encircles the hole 52. FIG. 6 shows a deflector-type lens layer 60 for a multiple electron column, in which the deflector-type lens is fabricated as a multi-type using a method identical to that of FIG. 5. In FIG. 6, reference numerals 62 designate holes through which an electron beam can pass, and electrodes 63a, 63b, 63c and 63d correspond to each lens layer of a single-type electron column of a multi-type lens layer. Insulating portions 69 are identical to those of the lens layer of FIG. 4. The operation of respective layers is performed in such a way that separate voltages for deflection, in addition to basically necessary voltages, are applied to respective regions, like the operation of the deflector-type lens of the single-type electron column of FIG. 4. However, in order to operate respective deflectors in the multiple electron column, respective regions are separately wired based on the directions of the deflector-type lens, thus performing both a deflection function and the function of a corresponding lens layer. In the multiple electron column, wiring and voltage control can be further facilitated by applying the same voltage in each direction, according to the situation. In this case, the voltage that is obtained by adding a deflection voltage to the voltage necessary for the function of a corresponding lens layer, in consideration of the characteristics of an electron beam, is applied to each region in the same direction. For example, it is preferable to use data about the application of voltages for focusing and deflecting, or to use a voltage that is obtained by adding a deflection voltage to the corresponding voltage of the source lens for a corresponding region in each direction. In FIGS. 5 to 7, each of the multiple electron columns is formed in a 2×2 arrangement composed of 4 single-type electron columns. However, the multiple electron column may be formed in various n×m arrangements in the same manner as described above. The operation method thereof may be the same as that of the above-described single-type electron column. For the method of operating the multiple electron column, refer to Korean Patent Application No. 10-2004-0052102, entitled “Method for Controlling Electron Beam in Multi-microcolumn and Multi-microcolumn”, which was filed on Jul. 5, 2004. FIG. 7-A is a cutaway perspective view showing an embodiment of the multiple electron column according to the present invention, which illustrates the construction of the multiple electron column 70 according to the present invention. In FIG. 7-A, the multiple electron column according to the present invention includes a multi-type electron emission source 71, a source lens 73, and a deflector 76 including two deflector-type lens layers 76b. That is, the source lens 73 is formed of the lens of FIG. 5, and the deflector 76 and the electron emission source layer 71 are constructed using the lens layers of FIGS. 5 and 6, as shown in the drawing. Of the layers of the deflector 76, layers designated by reference numeral 76b are deflector-type lens layers 76b. The layer between the deflector-type lens layers 76b is intended to space the deflectors apart from each other, and is formed of an insulation layer having a shape identical to that of the lens layer of FIG. 5. FIG. 7-B is a cutaway perspective view showing another embodiment of the multiple electron column according to the present invention, which shows the multiple electron column having a simple construction identical to the above-described construction of FIG. 3-B, in which there is no separate deflector and the central layer 73b of the source lens 73 is formed of a deflector-type lens layer. In this drawing, the source lens and the deflector are formed of combinations of lens layers. Although not described in detail, insulation layers may be interposed between respective lens layers and the coupling between the lenses is achieved using a conventional method. The above-described source lens, in the present invention, functions as a conventional source lens and, at the same time, performs focusing. Although the term source lens is used to follow the conventional jargon, the source lens of the present invention must be distinguished from the conventional source lens. The construction of the electron column according to the present invention is simplified, and a multiple electron column having a simple structure can be fabricated and used. |
|
048658049 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 4 thereof, there is shown the new and improved nuclear reactor fuel rod end plug constructed in accordance with the present invention and generally designated by the reference character 100. It is to be initially noted at this juncture that the new and improved end plug 100 of the present invention is similar to the conventional prior art end plug 10 shown in FIG. 1, except of course for the particularly new improvements thereof which in fact constitute the present invention, and consequently, all component parts or structural features which are similar or common to both the conventional end plug 10 and the new and improved end plug 100 of the present invention have been designated with corresponding reference characters except that all structural components of the new and improved end plug 100 of the present invention have been designated with reference characters within a 100 series. In particular, then, in accordance with the teachings of the present invention, it is seen that in lieu of the sharply defined interior corner characteristic of the conventional nuclear reactor fuel rod end plug 10 as formed by the circumferentially extending, axially oriented, land surface 18 and the annularly extending, radially oriented shoulder portion 20, which surfaces are fabricated in accordance with critically toleranced dimensional values, as are the corresponding mating surfaces of the fuel rod cladding tubing, not shown, in order to eliminate the conventional internal structural defects or deficiencies which had previously manifested themselves in connection with the employment of TIG welding techniques for performance of the end plug-fuel rod cladding tubing girth welds, the new and improved nuclear reactor fuel rod end plug 100 of the present has eliminated such precisely fabricated corner structure and has replaced the same with a machined notch or groove 126 which extends annularly about the end plug 100. It is seen that the notch or groove 126 is formed in part by means of the radially oriented, annularly extending shoulder portion 120 as well as by means of a conical surface 128 which extends radially outwardly from the radially innermost portion of shoulder 120 to circumferentially extending, axially oriented land surface 118, surface 128 being disposed at an angle .beta. of 45.degree. with respect to shoulder portion or surface 120 and extending toward the tapered forward end 116 of the plug 100. As has been noted hereinabove, while the conventional nuclear reactor fuel rod end plug 10, with its particular, critically toleranced interior corner structure as defined by annular shoulder surface 20 and land surface 18, has facilitated the production of girth welds defined at the fuel rod end plug-cladding tubing which have been free of internal defects or deficiencies when the girth welds were formed utilizing TIG welding techniques and apparatus, porosity defects in fact manifested themselves within the girth welds at the fuel rod end plug-cladding tubing juncture when the conventional end plugs 10 were employed, and when laser beam welding techniques and apparatus were being utilized, such defects or deficiencies being shown in FIGS. 2 and 3. However, when the new and improved nuclear reactor fuel rod end plug 100 of the present invention was employed within the end plug-cladding tubing assemblies, and the same were welded together by means of laser beam welding techniques and apparatus, the resulting weldments defined between the end plugs and the cladding tubing were free of the aforenoted porosity defects or deficiencies, as best seen with reference being made to FIGS. 5 and 6A-6B. As may be particularly seen from these photographic figures, desirable fillets have formed between the cladding tube walls and the annular shoulder wall 120 of the end plugs, and the entire weldments disclose as absence of porosity defects. A similar appreciation of the defect-free weldment produced as a result of employment of the end plug 100 of the present invention under laser beam welding conditions may also be attained from reference to the photographic figure of FIG. 7. The aforenoted production of the nuclear reactor fuel rod end plug-cladding tubing assembly was in fact produced, for example, by means of welding operations wherein a RAYTHEON 550 YAG laser was employed. The groove or notch 126 was machined within the sidewall of the end plug 100 to a radially inwardly depth or extent of 0.100 inches as measured from the outer surface of the land area 118, however, it later became apparent after production review of, for example, FIG. 5, that a full penetration weld had in fact been adequately achieved, and that a similarly adequate heat affected zone could have been achieved with an annular groove 126 machined to a depth of, for example, only 0.05-0.07 inches. It is also to be noted at this juncture in connection with the actual production of the satisfactory weldment between the fuel rod end plug of the present invention and the fuel rod cladding tubing, that an additional benefit derived from the usage of the end plug 100 of the present invention resides in the fact that as a result of the provision of the groove or notch 126 within the end plug 100, approximately one-half of the end plug's effective heat sink has been removed. Consequently, it was also observed during production of the end plug-cladding tubing weldment utilizing laser beam technology, that in lieu of normally being required to operate the laser equipment at a power rating of, for example, 400 watts with the attendant standardized parameters in order to achieve a satisfactory weld of this type, in accordance with the welding process employing the end plug 100 of the present invention, the aforenoted satisfactory full penetration weld was in fact able to be accomplished utilizing the laser equipment at a power rating of only 340 watts. This is a significantly positive result achieved in connection with the fabrication of the end plug-cladding tubing assemblies in view of the fact that if the laser equipment need not necessarily be operated at its maximum power rating, extending service life will be able to be achieved. It is lastly to be noted that while the present invention has in fact been developed in order to overcome the various drawbacks of accomplishing nuclear reactor fuel rod end plug-cladding tubing welded assemblies utilizing laser beam welding technology, whereby production defects or structural deficiencies have been able to be eliminated, the particular end plug structure of the present invention is likewise applicable to TIG welding technology. It is to be remembered that TIG welding techniques have been heretofore successfully employed in connection with the weld production of nuclear reactor fuel rod end plug-cladding tubing assemblies only because high quality-control criticalities were enforced in connection with the production of the end plugs and their mating cladding tubes. However, as a result of the present invention, such criticalities or production tolerances are no longer mandatory. Consequently, the machining costs involved in connection with the production of end plugs and cladding tubing for the end plug-cladding tubing assemblies may be significantly reduced. It is to be noted that in view of the higher energy input requirements characteristic of TIG welding operations as compared to those of laser beam welding operations, the groove or notch 126 of the end plug 100 of the present invention may have to be larger both in radial depth and axial extent, and in fact may have to be altered so as to comprise a different geometrical configuration, such as, for example, that of a square viewed in cross-section, as opposed to the triangularly configured groove or notch 126 which has effectively been employed in connection with laser beam welding techniques as illustrated in FIG. 4. Thus, it may be seen that the present invention has significant advantages over known prior art nuclear reactor fuel rod end plugs in that by means of the provision of the notch or groove 126 within the end plugs 100 of the present invention, porosity defects or structural deficiencies within the weldment may in fact be eliminated regardless of whether TIG or laser beam welding technology is being employed. It is to be emphasized that while the present invention was initially developed to especially overcome defects or deficiencies manifesting themselves in connection with laser beam welding operations in connection with the fabrication of nuclear fuel rod end plug-cladding tubing assemblies, it is in fact equally applicable to TIG welding operations as noted hereinabove and for the reasons set forth hereinbefore. It is to be especially emphasized at this point, however, and in light of the development of TIG welding operations in connection with the fabrication of nuclear reactor fuel rod end plug-cladding tubing assemblies, that the present invention must be considered to be, in effect, a dramatic teaching away from the prior art. In particular, porosity defects or deficiencies had in fact manifested themselves in connection with the fabrication of nuclear reactor fuel rod end plug-cladding tubing assemblies employing TIG welding technology, however, such defects or deficiencies were able to be subsequently controlled and effectively eliminated by the adherence to strict quality control manufacturing tolerances. Consequently, when such similar defects or structural deficiencies manifested themselves within the end plug-cladding tubing assemblies fabricated in accordance with laser beam welding technology, it would have followed that continued adherence to such manufacturing tolerances, or adherence to increasingly critical manufacturing tolerances would have rectified the problem of the occurrence of the porosity defects within the laser beam welded regions. However, this proved not to be the case. Subsequently, the present invention was developed wherein it is appreciated that the present invention has developed the technology in an effectively diametrically opposite mode or teaching away from such prior art or known processes. In lieu of increasing manufacturing tolerance criticalities, and the requirement of strictly adhering thereto, the present invention has in fact effectively relaxed such requirements. As can be appreciated by those skilled in the art, references in the specification and claims to particular angles and dimensions in describing the end plug of the present invention are to be construed as indicating preferable and general such angles and dimensions. Also, as is known to those skilled in the art and shown in FIG. 8, a typical nuclear reactor fuel rod 200 (which contains fuel pellets 204) employing the present invention would include one end plug 100 as shown in FIG. 4 welded to one end of the cladding tube 202 and a second end plug 100' as shown in FIG. 4 but without the bore 122 and without the bore 124 (i.e. a solid such end plug) welded to the other end of the cladding tube 202. Additionally, the bore 122 is closed by a seal weld at its outside opening 206. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. |
description | FIG. 1 shows an example of a previously known fuel assembly 10 which has already been described above. FIG. 2 shows examples of spacers 14 according to the prior art. FIG. 2a shows here an example of sleeve-formed cells 16 which are welded together. FIG. 2b shows another kind of spacer 14 where the cells 16 are shaped as relatively open elements with support points and opposite resilient members which hold the fuel rods and other parallelly extending elongated elements in position. Although the present invention here below is described primarily in connection with the second kind of cells 16, i.e. similar to those which may be seen in FIG. 2b, it should be noted that the invention in no way is limited to such a kind of cells 16. The invention may thus also be applied to the kind of cells 16 which is shown in FIG. 2a. Also other kinds of cells 16 for spacers 14 may be formed according to the invention. For example, there are spacer cells 14 which consist of completely round tubes which are welded together. FIG. 3 shows a side view of an example of a part which may be formed to a deflecting member 22. The shown part may be produced from a thin metal sheet in some now commonly used material, such as a nickel-based alloy (Inconel), stainless steel or a zirconium alloy. A deflecting member 22 may be formed in that the shown part is folded along the line 30 in such a manner that the right part in the figure is folded away from the plane of the drawing and forms an angle of about 75xc2x0-120xc2x0 with the left part in the figure. The right part thereby forms a vane 24 with a first edge 34 and a second edge 36, which edges meet in a corner portion 38. The left part forms a base portion 28. The base portion 28 may now be arranged vertically next to a flow channel 18 in a spacer 14 or in another part of the fuel assembly 10. The base portion 28 may for example be point-welded to a spacer cell 16, such that the vane 24 extends from the cell 16 into the neighbouring flow channel 18. With a suitable inclination of the vane 24 relative to a vertical plane 26 (see FIG. 5) a controlled vortex formation is formed in a cooling medium flowing in the flow channel 18, which vortex formation is relieved from the vane 24 at the upper part of the vane, primarily at the corner portion 38. FIG. 4 shows an example of one kind of spacer cell 16 for an elongated element. A number of such cells 16 are combined in a manner known by the person skilled in the art to a spacer 14 of similar kind to that shown in FIG. 2b. As has been mentioned above, a fuel assembly 10 is usually positioned such that the fuel rods 12 extend in a vertical direction. Thereby also the cells 16 in the spacer 14 are directed in a vertical direction. In connection with such a vertically positioned fuel assembly 10 it is thus clear what is ment by upwards, downwards, vertical and horizontal. These concepts will therefore be used in this description and in the following claims. It should however be pointed out that the fuel assembly 10 or the fuel rods 12 not necessarily must be positioned completely vertically. This description and the following claims are therefore not limited to such a vertically arranged fuel assembly 10. FIGS. 4 and 5 thus show a cell 16 for a spacer 14. In a usual vertically arranged fuel assembly 10, the cells 16 thus extend in a vertical direction. The upper parts in FIGS. 4 and 5 thus correspond to the upper parts when the cells 16 are positioned in a spacer 14 for a fuel assembly 10 which has en extension in the vertical direction. FIG. 6 shows such a cell 16 seen from above and FIG. 7 shows a flow channel 18 which is formed by four neighbouring cells 16. With reference to the figures, the invention will now be more closely described. A cell 16 of this kind usually has a number of support points 20. Some of these support points have a resilient function for holding the elongated elements, for example the fuel rods 12, in predetermined positions in the fuel assembly 10. The deflecting member 22 which forms part of a spacer 14 according to the invention may form a part which separate from the cell 16 or may form one integrated unit with the cell 16. In the now described embodiment, the deflecting member 22 forms an integrated unit with the cell 16. The deflecting member 22 comprises a vane 24. The vane is inclined relative to a vertical plane 26 (see FIG. 5). A suitable angle of inclination depends, inter alia, on which kind of cooling medium is used in the reactor and on the speed of flow of the cooling medium. A suitable angle of inclination is normally between 5xc2x0 and 30xc2x0. It has been found that a particularly suitable angel of inclination is between 10xc2x0 and 25xc2x0. In the here described embodiment, the deflecting member 22 also includes a base portion 28. The base portion 28 may, but need not, form a unit with the cell 16. The vane 24 may hereby, as is shown in the figures, be formed as a folded-out continuation of the base portion 28. According to such an embodiment, the vane 24 thus meets the base portion 28 along a line 30. As can be seen in the figures, the vane 24 is wider in its upper part than in its lower part. The vane 24 extends in a direction from a cell 16 into the neighbouring flow channel 18 (this can clearly be seen in FIG. 7). Suitably, the vane 24 is folded-out from the base portion 28 such that an angle 32 of about 75xc2x0-120xc2x0, for example 90xc2x0-100xc2x0, is formed therebetween. According to the shown embodiment, the vane 24 has a first edge 34 and a second edge 36. The first edge 34 and the second edge 36 meet in a corner portion 38. The second edge 36 is preferably formed to extend horizontally, but also an inclination relative to a horizontal plane is possible. In the shown embodiment, the first 34 and the second 36 edges are straight. Since the vane 24 is inclined relative to a vertical plane 26, an overpressure is formed on the lower side of the vane 24 by the flowing cooling medium (which normally flows upwards in the figures). In FIG. 5, the vane is directed out towards the viewer. The first edge 34 is thus shown here. In this figure, the lower side of the vane 24 is indicated by 40 and the upper side of the vane 24 is indicated by 42. In the flowing cooling medium, a higher pressure is thus formed on the lower side 40 of the vane 24 than on the upper side 42 of the vane 24. This has as a consequence that the cooling medium, in order to equalize the pressure difference, flows from the lower side 40 of the vane 24 around the first edge 34 to the upper side 42 of the vane 24. A vortex is thus formed at the first edge 34 of the vane 24. Since the cooling medium flows upwards, the so formed vortex or, vortices are relieved from the vane 24 at the upper part of the vane, i.e. close to the corner portion 38. If the vane extends in towards and reaches about the middle of the flow channel (see FIG. 7), then the vortex is thus relieved from the vane approximately in the middle of the flow channel. It should be noted that when here the middle of the flow channel 18 is mentioned, then this does not necessarily mean also in the middle as seen in a vertical direction, i.e. the vane 24, may also be formed to project up from the spacer 14 and to still reach into the middle of the axial extension of the flow channel 18. Since a controlled vortex formation in this manner is produced by the deflecting member in the axial centre of the flow channel 18, a controlled distribution of the cooling medium out towards the neighbouring parallelly extending elongated elements, for example the fuel rods 12, is achieved. Suitably, the vane 24 or the vanes are positioned asymmetrically in the flow channels 18. In the described embodiment, there is only one vane 24 in the flow channel 18 (see FIG. 7). Such an asymmetrical positioning of the vane 24 in the flow channel 18 has several advantages. The vortex which is formed by the vane in the flowing cooling medium is not disturbed by vortices from any other closely positioned vanes. By only using one vane 24 in the flow channel 18, the vane 24 does not cause any high pressure drop in the flowing cooling medium even if the vane 24 is comparatively large. Similarly, since the vane 24 has a relatively small angle of inclination against the vertical plane 26, the vane 24 does not cause any higher pressure drop in the flow channel 18 even if the vane 24 is relatively long. Since the vane 24 is formed as a folded-out portion directly in the metal sheet of the spacer cell 16, a mechanically very stable construction is achieved. Furthermore, the base portion 28 of the vane 24 may thereby consist of a vertical part of the cell 16 which has the advantage that unwanted vortex or turbulence formation at the base portion 28 is avoided. Thereby a controlled vortex may be formed by the vane 24, which vortex is not essentially disturbed by other turbulence. The base portion 28 of the deflecting member 22 may also be formed to be slightly bent in order to correspond to the bent surface of the elongated element which is held in place by the cell 16. The spacer according to the invention may for example be made in a zirconium alloy or in other presently common materials such as Inconel or stainless steel. With a spacer 14 with a deflecting member 22 according to the invention, several advantages are thus achieved. Since the vane 24 may be made to be relatively long with a relatively small angle between the vane 24 and a vertical plane 26, an orderly vortex formation may thus be achieved, which vortex formation has a clear net rotational movement. The relatively random turbulence which has been created by previously known constructions of deflecting members 22 may thereby be avoided. The orderly vortex formation leads to the effect that the cooling medium is moved out towards the elongated elements, and the steam which is formed in the fuel assembly next to the fuel rods 12 will thus be concentrated close to the middle of the flow channels 18. By the invention, an efficient cooling of the fuel rods 12 is thus achieved. The fuel assembly 10 and thereby the nuclear boiling water reactor thus achieve an improved dryout performance. It should be noted that the deflecting member 22 does not need to be positioned at or formed in a cell 16 which holds the elongated elements in position. The deflecting member 22 may also be positioned close to or formed in the metal sheet of the frame of the spacer 14; i.e. the metal sheet which constitutes the outer limitation of the spacer 14. As has been previously explained it is also possible to arrange the vanes in a separate structure (as so-called intermediate spacer) which does not support the rods but which has the purpose to hold all the vanes in accurate positions between the rods. The supporting function and the vortex formation function are thereby separated, which, hopefully, results in a lower total pressure drop. A deflecting member 22 according to the invention may also be positioned in another position in the fuel assembly 10 than at the spacer 14 or at a so-called intermediate spacer. In a fuel assembly 10, there are other kinds of flow channels. For example, there are types of fuel assemblies 10 which have so-called part length rods, i.e. fuel rods which do not extend along the whole fuel assembly 10 but which end at a lower level. Above such part length rods 12A (FIG. 1) a larger flow channel may thus be formed. Also in such a flow channel, deflecting members 22 according to the invention may be arranged. The principle is thereby the same as that which has been described above. That is, in order to achieve a controlled vortex formation, a long vane 24 with a relatively small inclination is used, which vane is positioned such that the vortex is relieved from the vane 24 close to the corner portion 38 of the vane 24, and, suitably, the vane 24 is arranged such that the vane 24 extends in towards the middle of the flow channel such that a controlled vortex is relieved from the vane 24 approximately in the middle of the flow channel. Such a deflecting member 22 may of course be constructed in accordance with the different embodiments which have been described above in connection with the spacer. As an example of such an application of the invention, the vane may be arranged in a spacer positioned at a level which is above the level where the part length rod ends. Above such a part length rod, a larger flow channel is formed. This flow channel, in this case thus consists of the cell in the spacer which is positioned above the part length rod and of the four neighbouring flow channels corresponding to the flow channels which are formed between the fuel rods when these reach up through the spacer. In such a larger flow channel, a vane may be arranged in the manner which has been described in the previous embodiments above. Since this flow channel is larger than the flow channels which have been described above, the vane which has been arranged in such a channel is suitably larger to a corresponding degree. The flow channel may comprise more than one vane. Suitably, the vanes are thereby asymmetrically arranged in the flow channel. Preferably, also this kind of flow channel comprises only one vane. The present invention is not limited to the described embodiments but may be varied and modified within the scope of the following claims. |
|
summary | ||
048141372 | claims | 1. A fuel pellet for a nuclear reactor fuel rod comprising: a substantially cylindrical central section; a convex first end section smoothly joined to one axial end of said central section at a first junction, said first junction approximating a smooth and continuous curved surface; a concave second end section joined to said central section at a second junction, said second junction approximating a smooth and continuous curved surface, wherein the curvature of said concave second end section is conformed to the curvature of said convex first end section. a tubular cladding jacket means for accommodating a plurality of fuel pellets; a plurality of interior fuel pellets disposed in said cladding jacket, said fuel pellets each comprising: an end plug means, disposed at a first end of said cladding jacket means, for retaining said interior fuel pellets within said cladding jacket means; a spring means, disposed at a second end of said cladding jacket means, for positioning said interior fuel pellets; and a second end plug means, disposed at said second end of said cladding jacket means, for retaining said interior fuel pellets within said cladding jacket means. a substantially cylindrical first terminal pellet central section; a first terminal pellet bearing section joined to said first terminal pellet central section at a first junction, said first junction approximating a smooth and continuous curved surface, wherein the curvature of said first terminal pellet bearing section conforms to the curvature of said end plug means bearing surface; and a first terminal pellet concave end section joined to said first terminal pellet central section at a second junction, said second junction approximating a smooth and continuous curved surface, wherein the curvature of said first terminal pellet concave end section conforms to the curvature of said interior pellet convex end section. wherein the curvature of said first terminal pellet bearing section conforms to the curvature of said first end plug means bearing surface such that said first terminal pellet bearing section is securely accommodated in said first end plug means. a substantially cylindrical second terminal pellet central section; a second terminal pellet bearing section joined to said second terminal pellet central section at a first junction, said first junction approximating a smooth and continuous curved surface, and wherein said second terminal pellet bearing section has a substantially planar surface adapted to accommodate an end portion of said spring means; and a second terminal pellet convex end section joined to said second terminal pellet central section at a second junction, said second junction approximating a smooth and continuous curved surface, wherein the curvature of said second terminal pellet convex section conforms to the curvature of said interior pellet concave end section. a substantially cylindrical terminal pellet central section; a terminal pellet bearing section joined to said terminal pellet central section at a first junction, said first junction approximating a smooth and continuous curved surface, and wherein said terminal pellet bearing section has a substantially planar surface adapted to accommodate an end portion of said spring means; and a terminal pellet convex end section joined to said terminal pellet central section at a second junction, said second junction approximating a smooth and continuous curved surface, wherein the curvature of said terminal pellet convex end section conforms to the curvature of said interior pellet concave end section. a bundle comprising a plurality of generally cylindrical fuel rods each comprising a cladding and a plurality of control rods; a plurality of spacer grid means for retaining said bundle, said spacer grid means each being axially displaced from one another along a longitudinal extent of said bundle; a plurality of interior fuel pellets stacked end-to-end within each of said fuel rods, each of said interior fuel pellets comprising: an end plug means, having a bearing surface, for retaining said interior fuel pellets in said fuel rod; a spring means for positioning said interior fuel pellets in said fuel rod; and a first terminal fuel pellet disposed contiguously to said end plug including: a substantially cylindrical second terminal pellet central section; a second terminal pellet bearing section joined to said second terminal pellet central section at a first junction, said second terminal pellet bearing section having a substantially planar surface adapted to accommodate an end portion of said spring means; and a second terminal pellet convex end section joined to said second terminal pellet central section at a second junction; wherein the curvature of said second terminal pellet convex section is formed so as to securely accommodate an interior pellet concave end section. 2. The fuel pellet according to claim 1, further comprising first and second depression means disposed in said first and second end sections for absorbing expansion of said fuel pellet. 3. The fuel pellet according to claim 1, further comprising a plurality of fission gas venting paths disposed radially along each of said first and second end sections. 4. The fuel pellet according to claim 3, wherein said fission gas venting paths comprise shallow fillet-shaped grooves integrally formed in said first and second end sections. 5. A fuel rod for a nuclear reactor comprising: 6. A fuel rod according to claim 5, wherein said first end plug means includes a bearing surface and wherein the fuel rod further comprises a first terminal fuel pellet disposed immediately adjacent said first end plug means bearing surface, said first terminal fuel pellet comprising: 7. The fuel rod according to claim 6, wherein said first end plug means bearing surface and said first terminal pellet bearing section are substantially planar. 8. The fuel rod according to claim 6, wherein said first end plug means bearing surface is concave and said first terminal pellet bearing section is convex; and 9. A fuel rod according to claim 6, further comprising a second terminal fuel pellet disposed immediately adjacent said spring means, said second terminal fuel pellet comprising: 10. A fuel rod according to claim 9, wherein said first terminal pellet concave end section and said second terminal pellet convex end section each further comprise a depression means for absorbing thermal expansion of said first and second terminal pellets, respectively. 11. A fuel rod according to claim 5, further comprising a terminal fuel pellet disposed immediately adjacent said spring means, said terminal fuel pellet comprising: 12. A fuel rod according to claim 5, wherein each of said interior pellets further comprise first and second depression means, disposed in said first and second interior pellet end sections, for absorbing thermal expansion of said interior fuel pellets. 13. The fuel rod according to claim 5, wherein each of said interior fuel pellet further comprise a plurality of fission gas venting paths disposed radially along each of said first and second interior fuel pellet end sections. 14. The fuel pellet according to claim 13, wherein said fission gas venting paths comprise shallow fillet-shaped grooves integrally formed in said interior fuel pellet first and second end sections. 15. A fuel assembly for a nuclear reactor comprising: 16. A fuel assembly for a nuclear reactor according to claim 15, wherein each of said fuel rods further comprise: 17. A fuel assembly for a nuclear reactor according to claim 16, wherein each of said fuel rods further comprise a second terminal pellet disposed contiguously to said spring means and comprising: 18. A fuel assembly for a nuclear reactor according to claim 17, wherein said first and second terminal pellet bearing sections are joined to said first and second terminal pellet central sections, respectively, at junctions which approximate a smooth and continuous curved surface. 19. A fuel assembly for a nuclear reactor according to claim 17, wherein each of said interior pellets further comprise depression means for absorbing expansion of said interior pellets. 20. A fuel assembly for a nuclear reactor according to claim 15, wherein each of said interior pellets further comprise depression means for absorbing expansion of said interior pellets. 21. A fuel assembly for a nuclear reactor according to claim 15, wherein each of said interior pellets further comprise a plurality of fission gas venting paths disposed radially along each of said first and second interior pellet end sections. 22. The fuel assembly according to claim 21, wherein said fission gas venting paths comprise shallow fillet-shaped grooves integrally formed in said first and second interior pellet end sections. 23. A fuel pellet for a nuclear reactor fuel rod assembly, the pellet having a substantially cylindrical longitudinal outer surface terminating at one end in an axially symmetric convex end surface and at the other end in an axially symmetric concave end surface, the end surfaces joining smoothly with the longitudinal surface, and at least a peripheral section of the convex end surface being congruent to a peripheral section of the concave end surface. 24. The fuel pellet according to claim 23, further comprising depression means disposed in each of said convex and concave end surfaces. 25. The fuel pellet according to claim 23, further comprising a plurality of fission gas venting paths disposed radially along each of said convex and concave end surfaces. 26. The fuel pellet according to claim 25, wherein said fission gas venting paths comprise shallow fillet-shaped grooves integrally formed in said convex and concave end surfaces. |
claims | 1. An X-ray imaging spectrometer with a well-defined spectral resolution for each wavelength in a spectral range of interest, said X-ray imaging spectrometer comprising:an X-ray detector;an X-ray source;a glass substrate machined to a multi-cone form;a crystal slab attached to the glass substrate, wherein said multi-cone form is generated by superimposing a plurality of cones with different aperture angles on a common nodal line,wherein said multi-cone form provides a rotational symmetry of a ray pattern,wherein said crystal slab reflects X-rays onto said X-ray detector,wherein said reflected X-rays intersects a corresponding cone axis. 2. The X-ray imaging spectrometer of claim 1, wherein the X-ray detector comprises a streak camera. 3. The X-ray imaging spectrometer of claim 1, wherein the X-ray detector comprises a gated strip detector. 4. The X-ray imaging spectrometer of claim 1, wherein said substrate comprises a 3D printed material having a multi-cone form. 5. A method for imaging each wavelength in a spectral range of interest of small X-ray sources employing an X-ray imaging spectrometer;the X-ray imaging spectrometer comprising:a glass substrate machined to a multi-cone form;a thin crystal slab attached to the glass substrate; anda point-like X-ray source,the method comprising:calculating a multi-cone geometry, wherein said multi-cone geometry is determined by superimposing a plurality of cones with different aperture angles on a common nodal line, wherein said plurality of cones includes a cone for each Bragg angle;machining said glass substrate to have said multi-cone geometry;providing a rotational symmetry of a ray pattern; andimaging each wavelength in a spectral range of interest. 6. The method of claim 5, wherein the thin crystal slab provides a well-defined and very large spectral resolution. 7. The method of claim 5, further comprising assessing large Bragg angles >50°. 8. The method of claim 5, further comprising using a crystal that increases ray throughput. 9. A method for an X-ray imaging spectrometer employing multi-cone focusing crystal geometry, said method comprising:attaching a thin crystal slab to a substrate;machining at least said substrate to have a multi-cone geometry, wherein said multi-cone geometry is determined by superimposing a plurality of cones with different aperture angles on a common nodal line, wherein said plurality of cones includes a cone for each Bragg angle;providing an X-ray imaging spectrometer, wherein said X-ray imaging spectrometer includes said thin crystal slab having multi-cone geometry and an X-ray detector;exposing said X-ray imaging spectrometer to an X-ray source, wherein said X-ray source comprises a point-like X-ray source;thereby providing a rotational symmetry of a ray pattern and imaging each wavelength in a spectral range of interest at a high resolution. |
|
abstract | A fixed cluster for the core of pressurized-water nuclear reactor including rods and a holder for rods. The holder includes: an upper head; fins extending radially towards the outside from the upper head; systems for mounting the rods and distributed on the fins; and at least two abutment elements on the upper plate of the core, each of the abutment elements protruding longitudinally from a respective fin beyond the mounting systems so as to be vertically oriented towards the top when the fixed cluster is provided on a nuclear fuel assembly. |
|
053902190 | description | DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION FIG. 2 shows the intermediate part of the steam generator of FIG. 1. The upper part 10 of the tube bundle envelope 8 surrounds the upper part 9 of the bundle of tube 3. It can be seen that at this level the pressure envelope 7 widens, i.e., it has a conical shape, leaving a space 14, known as the water return, between the pressure envelope 6 and the outside of the envelope 8. It is in this space that the water distributed by the supply ring mixed with the recirculated water is piped into the lower part of the steam generator and that the device according to the invention can be located. FIG. 2 shows circular sectors of grids 16 placed on the outer surface 17 of the upper part 10 of the nest bundle envelope 8 and extending through the water return 14 in order to be flush with the inner surface 18 of the pressure envelope 7. The grids 16 are shown in the horizontal position, but this is only an example. The functional aspect of the position of the grids 16 is that they must extend over virtually the entire cross-section of the water return 14 in order to have an optimum efficiency. The grids 16 are preferably positioned in the water return 14 by means of brackets 19, which are preferably fixed to the outer surface 17 of the upper part 10 of the tube bundle envelope 8. The width of the grids 16 is very slightly less than the width of the water return 14 at this location leaving, a space or clearance 20 between the grids 16 and the inner surface 18 of the pressure envelope 7. The function of this clearance 20 is to permit expansions due to temperature differences between the pressure envelope 7, the tube bundle envelope 8, the grids 16 and the brackets 19. FIG. 2 also shows the outer strips 21 fixed to the outer periphery of the grids 16 to prevent the reintroduction by the secondary water of objects trapped on the grids 16, between the latter and the pressure envelope 7. Inner strips 22 are positioned horizontally between the grids 16 and the outer surface 17 of the upper part 10 of the tube bundle envelope 8. Thus, the clearance left between grids 16 and the envelope 8, which can be conical, cylindrical or the like, is filled. In the same way, outer strips 30 fixed to the inner surface of the pressure envelope 7 fill the clearance left between the grids 16 and the pressure envelope 7. Assuming that the tubes of the bundle 3 (FIG. 1) are spaced by a distance, the meshes of the grids 16 are dimensioned in such a way as not to permit the passage of migrating bodies or objects liable to jam or become wedged between two tubes of the bundle 3. In other words, the meshes of the grids 16 must not permit the passage of objects whose size exceeds the distance separating the tubes. Thus, the maximum width of the meshes of the grids 16 is less than the said distance. The grids 16 are shown with a certain thickness E, i.e., height. Bearing in mind that these grids 16 can be made of metal, they can therefore have a sufficient mechanical strength to withstand the various stresses, in particular top to bottom vertical stresses. Thus, the grids 16 must firstly withstand the hydraulic stresses imposed by the mixture of the water from the supply ring and the recirculated water descending between the pressure envelope 7 and the tube bundle envelope 8, during both normal and emergency operation. Moreover, during the installation of the steam generator, the grids 16 can carry one or more operators, thus facilitating the installation of the various steam generator components, together with inspection and maintenance operations. In this case, the grids 16 form a type of all-round path around the upper part 10 of the tube bundle envelope 8. Without damage, i.e., breaking or deformation, grids 16 must also be able to withstand the impacts of migrating bodies. As shown in FIG. 3, the mesh for the grids 16 may be square. Without taking into account the scale in which these meshes are shown, the diagonal of the square of each of the meshes must be smaller than the distance separating the tubes of the bundle. This is an order of magnitude for indicating that the size of the grid meshes of the device according to the invention must be such that they do not permit the passage of objects liable to jam or become wedged between the tubes of the bundle. This square mesh grid can be constituted by a first series of parallel metal sheets 23, defining two opposite sides of the meshes of the same column or line, and a second series of metal sheets 24 perpendicular to sheet 23 and fitted in the latter in order to define the two other opposite sides of the meshes. The fitting can be achieved by providing slots 29 on half the height in each of the metal sheets of each series at the point of intersection of the sheets 23 and 24. FIG. 4 shows grids having triangular meshes. It is thus possible to construct a thick grid formed by a series of bent or undulated metal sheets welded on either side of two planar sheets. The largest side of the triangle must be smaller than the distance separating the tubes of the bundle. FIG. 5 shows a third embodiment of the grids constructed in a rigid plate 26, in which holes 27 are made, e.g., in a staggered manner. The diameter of the holes 27 must obviously be smaller than the distance separating the tubes of the bundle. The embodiments of the meshes described in FIGS. 3, 4 and 5 are in no way limitative with respect to the construction and shape of the meshes forming the grids 16. FIG. 6 shows in detail a way of attaching the grids 16 to their brackets 19, which have a T-shaped profile. The bracket 19 extends radially with respect to the steam generator tube bundle envelope and can be welded to the latter. The grids 16 can be fixed to the brackets 19 by screwing, e.g., using bolts 28, which makes it possible to dismantle them. They can also be welded to the brackets 19. Thus, it is possible to fix to each bracket 19 two adjacent grids 16, with or without leaving a space between them. The T-shape of the brackets and in particular the upper part of the T makes it possible to close any radial clearances left between the grids 16. Therefore the grids 16 make it possible to form a type of trapping or filtering grating for migrating bodies from the upper inner circuits of the steam generator, the feed water system of the secondary circuit or which are simply circulating within the steam generator. The invention is not limited to the embodiments described hereinbefore. Any system equivalent to a grid and fulfilling the same function can be used. The supporting procedure can also differ and can involve welding to other parts or using other means (e.g., screwing). The height position of the device within the steam generator can be at a random level between the secondary water supply ring and the tube plate. |
description | It shall first be shown theoretically on the basis of FIGS. 1-20 how a system can be provided, which satisfies the requirements with respect to uniformity and telecentricity for any desired illumination distribution A in a plane with an illumination device according to the invention. The system shown is a system with field-raster element and pupil raster element plates. A principal diagram of the beam path of a refractive system with two raster element plates is illustrated in FIG. 1. The light from source 1 is collected by a collector lens 3 and transformed into a parallel or convergent light beam. Field raster elements 5 of the first raster element plate 7 decompose the light pencil and produce secondary light sources at the site of pupil raster elements 9. The field lens 12 images these secondary light sources in the exit pupil of the illumination system or the entrance pupil of the subsequent objective. Such an arrangement is characterized by an interlinked beam path of the field and pupil planes from the source up to the entrance pupil of the objective. For this the designation xe2x80x9cKohler illuminationxe2x80x9d is often selected, as defined, for example, in U.S. Pat. No. 5,677,939, whose disclosure is incorporated to the full extent in the present application by reference. The illumination system according to FIG. 1 will be considered segmentally below. Since the intersection of the light intensity and aperture distribution lies in the plane of the field raster elements, the system can be evaluated independently of the type of source and the collector mirror. The field and pupil projection for the central pair of raster elements 20, 22 is shown in FIGS. 2A and 2B. The field raster element 20 is imaged on reticle 14 or the mask to be imaged by means of pupil raster element 22 and field lens 12. The geometric extension of field raster element 20 determines the shape of the illuminated field in reticle plane 14. The image scale is approximately given by the ratio of the distance between pupil raster element 22 and reticle 14 and the distance between field raster element 20 and pupil raster element 22. The optical effect of field raster element 20 is to form an image of light source 1, a secondary light source, at the site of pupil raster element 22. If the extension of the light source is small, for example, approximately point-like, then all light rays run through the centers of the pupil raster elements 22. In such a case, an illumination device can be produced, in which the pupil raster elements are dispensed with. As shown in FIG. 2B, the task of the field lens 12 consists of imaging the secondary I light sources in the entrance pupil 26 of an objective 24. If a field lens is introduced into the beam path, then the field imaging can be influenced in such a way that the image of the field raster elements is deformed by the control of the distortion. It is possible to deform a rectangle into a ring segment. The image scale of the field raster element projection is thus not changed. The beam path of the light rays is shown in FIG. 3 for a special geometric form of a field raster element and a pupil raster element. The shape of field raster element 20 is a rectangle in the embodiment shown in FIG. 3. The aspect ratio of field raster element 20 thus corresponds to the ratio of the arc length to the annular width of the required annular field in the reticle plane. As shown in FIG. 4, the annular field is shaped by the field lens. As shown in FIG. 3, without the field lens, a rectangular field results in the reticle plane. In order to form annular field 30, as shown in FIG. 4, a grazing-incidence field mirror 32 is used. Under the constraint that the beam reflected by the reticle should not be directed back to the illumination system, one or two field mirrors 32 is (are) required, depending on the position of the entrance pupil of the objective. If the principal rays run divergently into the objective that is not shown, then one field mirror 32 is sufficient, as shown in FIG. 4. In the case of principal rays entering the projection objective convergently, two field mirrors are required. The second field mirror must rotate the orientation of the ring. Such a configuration is shown in FIG. 5. In the case of an illumination system in the EUV wavelength region, all components must be reflective ones. Due to the high reflection losses for xcex=10 nm-14 nm, it is advantageous that the number of reflections will be kept as small as possible. In the construction of the reflective system, the mutual vignetting of the beams must be taken into consideration. This can occur due to construction of the system in a zigzag beam path or by operation with obscuration. The process according to the invention for preparation of a design for an EUV illumination system with any illumination in a plane A will be described below as an example. The definitions necessary for the process according to the invention are shown in FIG. 6. First the beam path for the central pair of raster elements will be calculated. In a first step, the size of the field raster elements 5 of the field raster element plate 7 will be determined. As indicated previously, the aspect ratio (x/y) results for rectangular raster elements from the form of the arc-shaped field in the reticle plane. The size of the field is determined by the illuminated area A of the intensity distribution of the arbitrary light source in the plane of the field raster elements and the number N of field raster elements on the raster element plate, which in turn is given by the number of secondary light sources. The number of secondary light sources in turn results from the uniformity of the pupil illumination as well as the intermixing. The raster element surface AFRE of a field raster element can be expressed as follows with xFRE, yFRE: AFRE=xFRExc2x7yFRE=(xfield/yfield)xc2x7y2FRE whereby xfield, yfield describe the magnitude of the rectangle, which establishes the annular field. Further, the following is valid for the number N of field raster elements: N=A/AFRE=A/[y2FRExc2x7(xfield/yfield)]. From this, there results for the size of the individual field raster element: yFRE={square root over (A/N[Nxc2x7(xfield+L yfield+L )])} and xFRE/yFRE=xfield/yfield The raster element size and the size of the rectangular field establish the imaging scale xcex2FRE of the raster element imaging and thus the ratio of the distances d1 and d2. xcex2FRE=xfield/yfield=z2/d1 The pre-given structural length L for the illumination system and the raster element imaging scale xcex2FRE determine the absolute size of d1 and d2 and thus the position of the pupil raster element plate. The following is valid: d1=L/(1+xcex2FRE) d2=d1xc2x7xcex2FRE Then, d1 and d2 determine in turn the radius of the pupil raster elements. The following is valid: R FRE = 2 · z 1 · z 2 z 1 + z 2 In order to image the pupil raster elements in the entrance pupil of the objective and to remodel the rectangular field into an arc-shaped field, one or more field lenses, preferably in toroidal form, are introduced between pupil raster element and reticle. By introducing the field mirrors the previously given structural length is increased, since, among other things, the mirrors must maintain minimum distances in order to avoid vignetting. The positioning of the field raster elements depends on the intensity distribution in the plane of the field raster elements. The number N of field raster elements pre-given by the number of secondary light sources. The field raster elements are preferably arranged on the field raster element plate in such a way, that they cover the illuminated surface, without mutually vignetting. In order to position the pupil raster elements, the raster pattern of the secondary light sources in the entrance pupil of the objective is given in advance. The secondary light sources are imaged counter to the light direction by the field lens. The aperture stop plane of this projection is in the reticle plane. The images of the secondary light sources give the (x, y, z) position of the pupil raster elements. The tilt and rotation angles remain as degrees of freedom for producing the light path between field and pupil raster elements. If a pupil raster element is assigned to each field raster element in one configuration of the invention, then a light path is produced by tilting and rotating field and pupil raster elements. Thereby the light beams are deviated in such a way that the center rays all intersect the optical axis and reticle plane. The assignment of field and pupil raster elements can be made freely. One possibility for arrangement would be to assign spatially adjacent raster elements to one another. Thereby the deflection angles will be minimal. Another possibility consists of homogenizing the intensity distribution in the pupil plane. This is made, for example, if the intensity distribution in the plane of the field raster elements is non-homogeneous. If field and pupil raster elements have similar positions, the pattern is transferred to the pupil illumination. The intensity can be homogenized by intermixing. Advantageously the individual components of field raster element plate, pupil raster element plate, and field mirror of the illumination system are arranged in the beam path such that the beam course is as free of vignetting as possible. If such an arrangement has effects on the imaging, then the individual light channels and the field lenses must be re-optimized. Illumination systems for EUV lithography can be obtained with the previously described design process for any desired illumination A with two normal-incidence and one to two grazing-incidence reflections. These systems have the following properties: a homogeneous illumination, for example, of an arc-shaped field a homogeneous and field-independent pupil illumination the combining of exit pupil of the illumination system and entrance pupil of the objective the adjustment of a pre-given structural length the collection of the maximal possible waveguide value. Arrangements of field raster elements and pupil raster elements will be described below for one form of embodiment of the invention with field and pupil raster element plates. First, different arrangements of the field raster elements on the field raster element plate will be considered. The intensity distribution can be selected as desired. The depicted examples are limited to simple geometric shapes, such as circle, rectangle, and the coupling of several circles or rectangles. The intensity distribution will be homogeneous within the illuminated region or slowly varying. The aperture distribution will be independent of the field. In the case of circular illumination A of field raster element plate 100, field raster elements 102 may be arranged, for example, in columns and rows, as is shown in FIG. 7. Alternatively, the center points of the raster elements can be distributed uniformly by shifting the rows over the surface, as is shown in FIG. 8. The latter distribution is better adapted to a uniform distribution of the secondary light sources. A rectangular illumination A is shown in FIG. 9. A shifting of the rows, as shown in FIG. 10, leads to a more uniform distribution of the secondary light sources. These are arranged, however, according to the extension of the field raster element plate within a rectangle. In order to be able to distribute the secondary light sources in the circular diaphragm plane, a double facetting is provided. The pupil raster elements sit at the site of the secondary light sources. In the case of rectangular illumination, it is necessary to tilt the field raster elements in order to produce a light path between field and pupil raster elements, such that the beams impinge on the pupil raster elements, which are arranged, for example within a circle, and which also must be tilted. If the illumination A of field raster element plate 100 comprises several circles A1, A2, A3, A4, for example, by coupling of different beam paths of one or more sources, then with the same raster element size the intermixing is insufficient in the case of an arrangement of the raster elements in rows and columns according to FIG. 11. A more uniform illumination is obtained by shifting the raster element rows, as shown in FIG. 12. FIGS. 13 and 14 show the distribution of field raster elements 102 in case of combined illumination from individual rectangles A1, A2, A3, A4. Now, for example, arrangements of the pupil raster elements on the pupil raster element plate will be described. Two points of view are to be considered in arranging the pupil raster elements: 1. For minimizing the tilt angle of field and pupil raster elements for production the light path, it is advantageous to maintain the arrangement of the field raster elements. This is particularly advantageous with an approximately circular illumination of the field raster element plate. 2. For homogenous filling of the pupil, the secondary light sources should be uniformly distributed in the entrance pupil of the objective. This can be achieved by providing a uniform raster pattern of secondary light sources in the entrance pupil of the objective. These are imaged counter to the direction of light with the field lens in the plane of the pupil raster elements, and determine in this way will the ideal site of the pupil raster elements. If the field lens is free of distortion, then the distribution of the pupil raster elements corresponds to the distribution of the secondary light sources. However, since the field lens forms the arc-shaped field, distortion is purposely introduced. This does not involve rotation-symmetric cushion or semicircular distortion, but the bending of horizontal lines into arcs. The y-distance of the arcs remains constant in the ideal case. Real grazing-incidence field mirrors, however, also show an additional distortion in the y-direction. A raster 110 of secondary light sources 112 in the entrance pupil of the objective, which is also the exit pupil of the illumination system, is shown in FIG. 15, as it had been produced for distortion-free imaging. The arrangement of secondary light sources 112 corresponds precisely to the pre-given arrangement of the pupil raster elements. If the field lenses are utilized for arc-shaped field-formation as in FIG. 16, then secondary light sources 112 lie on arc 114. If the pupil raster elements of individual rows are placed on an arc, which compensate for the distortion, then one can place the secondary light sources again on a regular raster. If the field lens also produces distortion in the y-direction, the pupil is distorted in the y-direction, as shown in FIG. 17. The extent of the illuminated area onto field raster element plate is determined by the input illumination. The illumination of the pupil raster element plate is determined by the structural length and the aperture in the reticle plane. As described above in detail, the two surfaces must be fine-tuned to one another by rotation and tilting of the field and pupil raster elements. For illustration, the problems of this principle will be explained for refractive designs. The examples can be transferred directly, however, to reflective systems. Various configurations can be distinguished for a circular illumination of the field raster element plate, as shown below. If a converging effect is introduced by tilting the field raster elements, and a divergent effect is introduced by tilting the pupil raster elements, then the beam cross section can be reduced. The tilt angles of the individual raster elements are determined by tracing the center rays for each pair of raster elements. The system acts like a telescope-system for the central rays, as shown in FIG. 18. How far the field raster elements must be tilted depends on the convergence of the impinging beam. If the convergence is adapted to the reduction of the beam cross section, the field raster elements can be introduced on a planar substrate without a tilting angle. A special case results if the convergence between field and pupil raster element plate corresponds to the aperture at the reticle, as shown in FIG. 19. No divergent effect must be introduced by the pupil raster elements, so they can be utilized without tilting. If the light source also possesses a very small waveguide value and the secondary light sources are nearly point-like, the pupil raster elements can be completely dispensed with. A magnification of the beam cross section is possible, if a diverging effect is introduced by tilting the field raster elements, and a collecting effect is introduced by tilting the pupil raster elements. For the central rays, the system operates as a retro-focus system, as shown in FIG. 20. If the divergence of the impinging radiation corresponds to the beam divergence between field and pupil raster elements, then the field raster elements can be used without tilting. Instead of the circular shape that has been described, rectangular or other shapes of illumination A of the field raster element plate are possible. The arrangements shown in FIGS. 21A-56 described below show an embodiment of the invention for which undulators are used as synchrotron radiation light sources, without the invention being limited thereto. The radiation of the undulator light source can be described as a point light source with strongly directed radiation, for example, the divergence both in the horizontal as well as the vertical direction is less than 10 mrads. Therefore, all illuminating systems described below as examples have only one mirror or one lens with raster elements, without the invention being limited thereto. Undulator sources have in a predetermined plane in which a predetermined wavelength spectrum is irradiated, a beam divergence of less than 100 mrads, preferably less than 50 mrads. Therefore, collectors along the electron path for collecting the synchrotron radiation and bundling it, as described, for example, in U.S. Pat. No. 5,439,781 or U.S. Pat. No. 5,512,759 are not necessary for such sources. Three possible configurations of an illumination system with an undulator source 200 and a mirror with raster elements will be described below. Here: Type A describes an embodiment, in which the individual raster elements of the first mirror are individual tilted planar facets. Type B describes an embodiment, in which the individual raster elements are designed as facets in the convergence beam path. Type C describes an embodiment, in which the raster elements of the first mirror form one structural unit with the means for beam broadening. An illumination system according to type A in a refractive form is shown for the definition of the parameters in FIGS. 21A and 21B. In an embodiment according to type A, the means for beam broadening comprise a diverging lens 206 or diverging mirror, without being limited thereto. The collecting effect for producing the secondary light sources is introduced by the collective mirror or collective lens 208 situated behind the diverging lens or diverging mirror 206. The means for beam broadening and the mirror or the lens with collecting effect form a so-called collector unit or a collecting system 210. If a mirror with raster elements is not present, the collective mirror would image source 200 in the diaphragm plane 212 of the illumination system. The secondary light source 216 is decomposed into a plurality of secondary light sources 218 by the mirror with raster elements 214 or the facetted mirror. The raster elements 214 can be formed as planar facets, since the secondary light sources or light sources in this form of embodiment are imaged in the diaphragm plane by means of the collector unit. The tilting angles of the planar facets are such that the center rays of each facet in the focal plane 220 coincidence on the optical axis 222. For the center rays, the facetted mirror or lens acts as a divergent mirror or lens. For illustration purposes, FIGS. 21A and 21B show the schematic structure based on a refractive, linearly constructed system. The facetted lens was removed in FIG. 21A. The secondary light source 216 lies in the diaphragm plane. The facetted lens 214 is inserted in FIG. 21B. The arrangement of individual prisms in the refractive presentation corresponds to the tilt of the facets. An arrangement of the facetted mirror or lens in the convergent beam path according to type B as shown in FIGS. 22A and 22B is also possible. The collective mirror 208 is designed in such a way that the source 200 is imaged in the focal plane 220 of the illumination system, as shown in FIG. 22A. The collecting effect of facets 214 is then designed such that secondary light sources 218 are produced in the diaphragm plane 212, as shown in FIG. 22B. In the embodiment of the invention according to type C, as shown in FIGS. 23A and 23B, the collective mirror or collective lens and the facetted mirror or lens are combined. In such a configuration, the collecting effect of the collector mirror is superimposes the facets as a tilt. The raster elements are shown as a superimposition of a prism and a collective lens in the schematic presentation in FIGS. 23A and 23B. In the reflective embodiment this is a tilted collective mirror 224. The following formulas describe the imaging by the raster elements for the illumination arrangement according to types A-C: NA Ret = DU BL 2 d 5 ⇒ DU BL = 2 · d 5 · NA Ret DU BL x Wabe · d 4 + d 5 d 5 = 4.0 ⇒ x Wabe = DU BL 4.0 · d 5 d 4 + d 5 β Wabe = x Feld x Wabe = d 5 d 4 ⇒ β Wabe = x Feld x Wabe ⇒ d 4 = d 5 β Wabe Wabe=raster element=FRE DU=diameter Feld=field BL=diaphragm The notations are: d5: measurement for the structural length NAret: aperture in the reticle plane. Number of raster elements in a raster element row=4 in the present form of embodiment. This is a measure for the number of secondary light sources, the uniformity of the field, and the uniform illumination of the pupil. xfield: x-extension of the field. DUBL: diameter of the diaphragm xraster element: x-extension, raster element yraster element: y-extension, raster element If the illumination systems shown in FIGS. 21A to 23B being examples for refractive systems are designed for 13-nm EUV radiation, then these systems must be reflective systems for 13-nm radiation with as few reflections as possible due to the high reflection losses. Beam-broadening means, which can be combined with a collective mirror into one collector unit are necessary for illuminating the mirror with raster elements when an undulator source is used as light source. For an undulator source, the collector unit for 13-nm radiation can comprise a first grazing-incidence mirror or a scanning mirror, which broadens the radiation, and a second normal-incidence mirror, which collects the radiation. In order to achieve an advantageous design in the case of 13-nm wavelength, due to the higher reflectivity, grazing-incidence mirrors (R≈80%) are preferred over normal-incidence mirrors (R≈65%). Advantageously, the distance d1 from the source to the first mirror should be at least d1=3000 mm. In the case of such an embodiment, a free space of 2000 mm should be maintained between the first mirror and the remaining optics for the radiation-protection wall. Alternatively to the arrangement with a first mirror in front of the radiation-protection wall and second mirror behind this wall, the first mirror can also be placed behind the radiation-protection wall with d1 greater than 5000 mm. It can be designed as a grazing-incidence or normal-incidence mirror. Advantageously the source irradiates in the horizontal direction. The horizontally-situated reticle is illuminated at a principal beam angle of at most 20xc2x0, preferably 10xc2x0, and most preferably 5.43xc2x0. A horizontal arrangement of reticle and wafer is necessary to avoid a bending of the optics in the gravitational field. Advantageously, two grazing-incidence field mirrors are used for forming the field, in order to illuminate the reticle with correct annular orientation and to deflect the light separated from the illumination system into the objective. Illumination systems according to types A and B are shown in FIG. 24 in schematic representation. The system according to types A and B comprises a collector mirror 300, which is formed as a grazing-incidence toroidal mirror, which broadens the beam rays, and a normal-incidence collector mirror 302, which illuminates the mirror with raster elements 304 in a round manner and projects the light source either in the diaphragm plane (type A) or in the reticle plane (type B). The reference number 304 designates the normal-incidence facetted mirror or mirror with raster elements. The field mirrors 306, 308 are formed as grazing-incidence field mirrors and form the field in the reticle plane. The system parameters can be designed such that the optical axis is tilted only around the x-axis (xcex1-tilt). The meridional plane remains the same. The distances between the mirrors are adapted to the boundary conditions of the source. Such a type A system is described in detail below. Individually tilted planar facets are used as raster elements. The undulator source was assumed to be a homogeneous surface radiator with a diameter of 1.0 mm and NAundulator=0.001. The facet rows 310 were arranged in a displaced manner relative to one another for the uniform distribution of the secondary light sources in the diaphragm plane, as shown in FIG. 25. The circle 312 in FIG. 25 shows the illumination of the mirror with raster elements, which are planar facets 314 by the broadened undulator source 200. The arrangement of the mirrors relative to the global coordinate system of the source, of the type A illumination system shown in FIGS. 26 to 33 is compiled in the following Table 1. The z-axis of the reticle plane is at 90xc2x0 relative to the z-axis of the source coordinate system. The z-distance between source 200 and collector mirror 300 is 5000 mm in the system described below. For radiation-protection wall 316, a z-distance of 1900 mm is provided between collector mirror 300 and facetted mirror 304. The reticle plane 318 lies 2287.9 mm above the source. The design will now be described on the basis of FIGS. 26 to 33: FIG. 26 shows the entire system up to the entrance pupil 320 of the objective in the yz-section including source 200 and divergent mirror 300, collective mirror 302, planar facetted mirror 304, field mirrors 306, 308, reticle plane 318 and entrance pupil 320 of the objective. The center beams are indicated for the central field raster elements (0,0) and the two outermost field raster elements. The beams intersect in reticle plane 318 and illuminate the entrance pupil 320 of the objective. FIG. 27 shows an excerpt beginning with the collector mirror. The beam deflection of the edge beams with the tilted facets can be clearly seen. FIG. 28 shows a fan of beams, which strikes the central raster element (0, 0) 322. The collector mirror produces the secondary light source 212 in the diaphragm plane. The field mirrors form the arc-shaped field and images the secondary light sources in the entrance pupil of the objective. FIG. 29 shows the entire system with objective in yz-section, comprising: divergent mirror 300, collective mirror 302, planar mirror 304 with facets, field mirrors 306, 308, reticle plane 318 and 4-mirror projection objective 330. The beam bundle runs separated from the illumination system into the objective. Of course, other projection objectives are also possible, for example, 5-or 6-mirror objectives. The illumination of the reticle with a 30xc2x0 annular field (r=211 mm; xe2x88x923.0 mm less than xcex94r less than +3.0 mm) in an contour-line representation of a system according to FIGS. 27 to 29 is shown in FIG. 30. Here, r is the ring radius, wherein a 30xc2x0 segment from the ring is used. An intensity section parallel to the y-axis at x=0.0, 15 mm, 30 mm, and 45 mm is shown in FIG. 31. Since the secondary light sources have only minimal extension, an ideal xe2x80x9chutxe2x80x9d profile results. The width of the intensity profile increases at the edge of the field, due to the ring curvature and the non-optimal superimposition of the partial images. In order to keep the scanning energy constant, the maximal intensity decreases to the same extent. The integral scanning energy, i.e., the integration of the intensity along the scanning path is a decisive factor in the lithography process. As shown in FIG. 32, the integral scanning energy is nearly homogeneous in the present embodiment. It may be controlled by the design of the optical elements, such as field mirrors or field lenses. FIG. 33 finally shows the pupil illumination in the center of the field. Intensity peaks 332 in the pupil illumination result corresponding to the raster element distribution. The maximal aperture amounts to NAret=0.025. The aperture of a partial pupil is negligibly small (NApartial pupil=2E-6) corresponding to the small waveguide value of the undulator source. However, a filling of the pupil results, when seen as an integral, due to the uniform distribution of the secondary light sources. A form of embodiment of the invention according to type B with a facetted mirror in the convergent beam path is shown in FIGS. 34 to 41. The light source is assumed to be similar to the light source described in the embodiment according to FIGS. 26 to 33. The facets or raster elements are arranged as in FIG. 25 and are formed as collecting hollow facets, which are mounted on a planar support surface. The arrangement of the mirrors relative to the overall coordinate system of the source is compiled in Table 2. The z-axis of the reticle plane is at 90xc2x0 relative to the z-axis of the source coordinate system. The z-distance between source 200 and collective mirror 302 is 5000 mm. For the radiation-protection wall (not shown), a z-distance between divergent mirror 300 and facetted mirror 304 of 2100 mm is provided. The reticle plane 318 lies 2298.9 mm above the source. FIG. 34 shows the entire system up to entrance pupil 320 of the objective in the yz-section, comprising: source 200, divergent mirror 300, convergent mirror 302, facetted mirror 304, field mirrors 306, 308, reticle plane 318, entrance pupil of objective 320. The center beams, which intersect in the reticle plane and illuminate the entrance pupil of the objective are indicated for the central field raster element (0,0) and the two outer field raster elements. A section beginning at the divergent mirror 300 is shown in FIG. 35. The indicated rim rays are not influenced by facetted mirror 304, since this involves center beams and the facets are mounted on a planar support plate. A fan of beams, which impinges the central raster element (0,0) is depicted in FIG. 36. The convergent effect of the raster element produces the secondary light source in the diaphragm plane. The field mirrors 306, 308 form the arc-shaped field and image the secondary light sources in the entrance pupil of the objective. FIG. 37 shows the entire system with objective in the yz-section, comprising: divergent mirror 300, collective mirror 302, facetted mirror 304 in the convergent beam path, field mirrors 306, 308, reticle plane 318 and 4-mirror objective 330. The beams bundle run into the objective separated from the illumination system. The illumination of the reticle with the 30xc2x0 annular field (r=211 mm; xe2x88x923.0 mm less than xcex94r less than +3.0 mm) is shown in FIG. 38 as a contour-line representation. Here, r is the ring radius, wherein a 30xc2x0 segment from the ring is used. FIG. 39 shows an intensity section parallel to the y-axis at x=0.0, 15 mm, 30 mm, and 45 mm. Since the secondary light sources have only minimal extension, an ideal xe2x80x9chutxe2x80x9d profile is formed at least in the center of the field. The width of the intensity profile increases at the edge of the field, due to the ring curvature and the non-optimal superimposition of the partial images. The maximum intensity decreases with the broadening of the edges and the increased value of the half-width, so that the scanning energy remains constant. As FIG. 40 shows, the integral scanning energy of the presently described embodiment is nearly homogeneous. The pupil illumination in the center of the field is shown in FIG. 41. Illumination systems of type C will be described below. The undulator light source is taken as before as the point-like light source. The system according to type C comprises in a first embodiment according to type C1 a first grazing-incidence collector mirror 400, which deflects radiation downward. Mirror 400 broadens the beam and illuminates the facetted mirror 402, which reverses the radiation direction again towards the undulator source 200. In order to provide a solution that is free of vignetting, facetted mirror 402 also introduces a tilt of the optical axis around the y-axis, the so-called g tilt. Therefore the system axis runs beside the radiation-protection wall. FIG. 42 shows the lateral view in the y-z-plane of such a system and FIG. 43 shows the top view in the x-z-plane. The second embodiment, type C2, of a system according to type C is shown in FIG. 44. In the system according to type C2, the grazing-incidence mirror 402 is replaced by a normal-incidence mirror. This has the consequence that the system axis again runs away from the undulator source after two reflections at mirror 402 and facetted mirror 404. The mirrors must then be tilted only around the x-axis, the so-called xcex1-tilt. A tilt of the optical axis around the y-axis as in the case of type C1 is not necessary. Mirror 402 for beam broadening is found outside the source chamber in the case of type C2. Since the source radiation is polarized nearly linearly in the horizontal direction, the optical axis can also be deflected by larger angles without increased losses at the site of the beam-broadening mirror 402. A system according to type C1 is shown once more in more detail in FIGS. 45 to 54. The arrangement of the mirrors of this system shown in FIGS. 45 to 54 is compiled in Table 3. The z-axis of the reticle plane is at 90xc2x0 relative to the z-axis of the source coordinate system. The z-distance between source and divergent mirror amounts to 5000 mm. The back-running optical axis is rotated by the tilt of the facetted mirror around the x and y axes such that the objective does not cross the path of the illumination beam and the radiation-protection wall. The facetted mirror lies xe2x88x921026.1 mm beneath the source, and the reticle plane lies 345.79 mm above the source. The design of type C1 given as an example will now be described in more detail on the basis of the figures. FIG. 45 shows the entire system up to the entrance pupil of the objective in the y-z section, comprising: source 200, divergent mirror 402, facetted mirror 404 with convergent effect, field mirrors 406, 408, reticle plane 408, entrance pupil 410 of the objective. The center beams are shown for the central raster element (0,0) and the two outermost field raster elements. They intersect in the reticle plane and illuminate the entrance pupil of the objective. FIG. 46 shows a section from the divergent mirror 400 in the x-z section. The depicted rim rays are deflected by the facetted mirror, such that they intersect in the reticle plane. The segment from the divergent mirror 400 in the x-z section is shown in FIG. 47. The facetted mirror 402 with convergent effect tilts the optical axis away from the incoming beam bundle. Therefore, space is created for the objective and the radiation-protection wall. A fan of beams, which impinges on central raster element (0,0) is depicted in FIG. 48. The convergent effect of the raster element produces the secondary light source in the diaphragm plane. Field mirrors 404, 406 form the annular field and image the secondary light source 412 in the entrance pupil 410. FIG. 49 shows the entire system with objective in the y-z section, comprising: divergent mirror 400, facetted mirror 402 with convergent effect, field mirrors 404, 406, reticle plane 410, 4-mirror objective 430. The beams run into the objective separated from the illumination system. The entire system with objective is shown in the x-y section in FIG. 50. In this view, the separation of the objective and the illumination beam path between divergent mirror 400 and facetted mirror 402 is clearly seen. FIG. 51 shows the illumination of the reticle with the 30xc2x0 annular field (r=211 mm; xe2x88x923.0 mm less than xcex94r less than +3.0 mm) in contour-line representation. An intensity section parallel to the y-axis for x=0.0, 15 mm, 30 mm, and 45 mm is shown in FIG. 52. As can be seen from FIG. 53, the integral scanning energy of the presently described embodiment is homogeneous. The pupil illumination in the center of the field of a type C1 system is shown in FIG. 54. It is not necessary that the diaphragm plane is accessible, so one may also operate with a virtual diaphragm plane. The light would then leave the mirror facets divergently. According to type B and type C, the facets would not be formed convergent, but rather divergent. For type C the following is possible: The first collector mirror produces a virtual secondary light source 1000, as shown in FIG. 55A. The divergent beams are deflected by planar mirrors such that their center beams intersect the reticle plane at the optical axis. The tilted planar mirrors are shown as prisms in FIG. 55B. By this, a plurality of secondary light sources 1002 are produced in the virtual diaphragm plane. The following formulas describe relationship of the system parameters according to FIGS. 55A and B: NA Ret = DU BL 2 d 4 ⇒ DU BL = 2 · d 4 · NA Ret DU BL x Wabe · d 4 - "LeftBracketingBar" d 3 "RightBracketingBar" d 4 = 4.0 ⇒ x Wabe = DU BL 4.0 · d 4 d 4 - "LeftBracketingBar" d 3 "RightBracketingBar" β Wabe = x Feld x Wabe = d 4 "LeftBracketingBar" d 3 "RightBracketingBar" ⇒ β Wabe = x Feld x Wabe ⇒ "LeftBracketingBar" d 3 "RightBracketingBar" = d 4 β Wabe DU=diameter BL=diaphragm Wabe=raster element Feld=field wherein: d4: measurement for the structural length NAret: aperture in the reticle plane. Number of raster elements in a raster element cell=4. This provides for the number of secondary light sources, the uniformity the field, and the uniform illumination of the pupil. xfield: x-extension of the field It is clear from the schematic representation according to FIGS. 55 A-B that the distances d2 and d3 are approximately of equal magnitude for the undulator source with NAsource=0.001. Together with a structural length that can realized, this will require in practical terms a normal-incidence collector mirror. In order to smear the sharp intensity peaks as shown, for example, in FIG. 54 in the pupil and to effectively increase the waveguide value, the last field mirror can be designed as a moving mirror, a so-called wobbling field mirror, in all forms of embodiment of the invention. The movement of a wobbling field mirror primarily changes the aperture angle and has little influence on the field position. In addition to a movement of the entire mirror, a periodic surface change of the last mirror is also conceivable in order to achieve this smearing of the sharp intensity peaks in the pupil. In order to reduce the raster element aspect ratio, the use of astigmatic facets is possible. By this, the diaphragm plane is split into sagittal and tangential diaphragm planes. The aspherical field mirrors image these two planes in the entrance pupil of the objective. The illumination distribution in the reticle plane can be influenced by the design of the field lens. For example, a uniform scanning energy can be achieved in this way. For the control of the scanning uniformity, in another configuration of the invention, one of the two field mirrors can be configured as an active mirror. The azimuthal distortion can be controlled by several actuator rows, which run in the y-direction. |
|
039754715 | claims | 1. In a process for the production of fuel compacts consisting of an isotropic, radiation resistant graphite matrix of good heat conductivity and having embedded therein coated particles of the group consisting of (1) coated fuel particles, (2) coated fertile particles and (3) a mixture of coated fuel particles and coated fertile particles for insertion in high temperature fuel elements of the coated particles (1), (2) or (3) being overcoated with a molding composition consisting essentially of graphite powder and a binder of a thermoplastic resin capable of being hardened the improvement comprising providing only the outer surface of the overcoat with a hardener for the resin and a lubricant and subsequently compressing in a mold at a constant temperature of about 150.degree.C. and removing the hardened and finished compacts therefrom. 2. The process of claim 1 wherein the thermoplastic resin is a phenol-aldehyde resin. 3. The process of claim 2 wherein the resin is a phenol-formaldehyde novolak. 4. The process of claim 3 wherein the hardener is hexamethylenetetramine. 5. A process according to claim 1 wherein a portion of the particles are replaced by similar granulates three dimensionally precompressed and of about the same particle size as said coated particles (1), (2) or (3), said granulates are also provided only on the outer surface of the overcoat with a hardener for the resin and a lubricant and the mixture of particles and precompressed granulates are compressed at said constant temperature of about 150.degree.C. to harden the resin and form the finished compacts. 6. A process according to claim 1, comprising applying the hardener and lubricant simultaneously to said overcoat surface. 7. A process according to claim 1 comprising adding the hardener and lubricant dissolved in a solvent to the overcoat surface, said solvent being one which does not dissolve the resin binder. 8. A process according to claim 7 wherein the solvent is trichloroethylene. 9. A process according to claim 1 comprising completing the hardening during the molding after the conclusion of the densification. 10. A process according to claim 1 wherein the thermoplastic resin is a phenol-formaldehyde novolak, cresol-formaldehyde resin, furfuryl alcohol resin or phenolhexamethylene tetramine resin. |
summary | ||
abstract | A method of assaying potentially radioactive material comprises selecting a plurality of samples from a material mass on a site (200). In a sequence of steps (104, 106, 108, 110, 112), an activity measurement based on a gross count of each of the samples (212) in the plurality of samples is performed on the site (200), and the activity measurement is compared with one or more activity thresholds in order to categorize the radioactive material for disposal purposes. The threshold(s) and/or activity measurement are based on an assumed parameter set. In a further step (114), sample x from every y of the plurality of samples is selected, where x<y, and a spectroscopic measurement of the emitted radiation from the sample x is performed on the same site (200). In a further step (116), it is automatically determined whether the spectroscopic measurement corroborates the assumed parameter set before the y samples leave the site (200) for disposal purposes. |
|
description | This application claims the benefit of Taiwan Patent Application No. 105140122, filed on Dec. 5, 2016, in the Taiwan Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. The present invention is related to a fixture for use in test of shake table to fasten a device, and more particularly to a self-rotating universal fixture for fastening a device under test. To ensure the safe operation of nuclear power plants, relevant equipments used in nuclear power plants are designed to sustain structural integrity and maintain its safety function during and after earthquake. In order to achieve this goal, quality of the equipment is granted through seismic qualification test, and a shake table is used for performing seismic qualification test. Generally speaking, during the seismic qualification test, the device under test (the structure of equipment) has to be mounted on a fixture, then the fixture is fastened to the test platform of the shake table to perform the test. In order to make the test results accurate, the fixture must possess considerable stiffness and rigidness without introducing unwanted amplification effect. Also the fixture must avoid producing resonance within the test frequency range. Generally speaking, the fixture used in seismic test has to be designed according to the size, weight, and mounting measure in the field of the device. Therefore, each device under test is collocated with a dedicated fixture, and this is the necessary cost of the test. If there is a universal fixture that can be reused with most kinds of device, the cost of test can be reduced. Moreover, when a tri-axial shake table is not available, and a bi-axial or single-axial shake table is to be used in order to comply the test standard/specification, the fixture has to dismantled from the test platform first and rotates together with the device under test by 90 degree, and then fasten the fixture and the device to the test platform again so as to perform test for other axes. This process is very time-consuming and toilsome. As a result, there is a motive to develop a universal and versatile self-rotating fixture for reducing the time consumed and cost incurred in the seismic test. An object of the present invention is to provide a rotatable fixture for substantially tackling with the drawbacks encountered by the prior art. The rotatable fixture of the present invention can be applied to a small-sized device under test (especially a device weighs less than 10 kilograms). Also, the rotatable fixture of the present invention does not resonate within the frequency band of the seismic test and can rotate by itself with a simple mechanism. Thus, the rotatable fixture of the present invention can significantly reduce the time and cost incurred by the seismic test, and can eliminate the safety issues arising from the hoist, dismantlement, and rotation of the fixture. For the object mentioned above, the present invention provides a rotatable fixture, which includes a base, a rotating disc, a fastening frame, and at least one fixing plate. The base is set to be securely mounted on the test platform of a shake table. The rotating disc is pivotally connected to the base through a central axle and is able to rotate with respect to the base by at least four rolling steel ball assembly. The fastening frame is uprightly fastened to the rotating disc, and the fixing plate is used to allow a device under test to be secured thereto. By way of at least one fastening member that can movably pass through the rotating disc and the fastening holes of the base, the rotating disc is fastened and the rotation of the rotating disc with respect to the base is limited. When the fastening member is removed, the rotating disc, the fastening frame, and the device under test mounted thereon can be rotated together to a certain angle (e.g. 90 degree) for the next test procedure. In this way, the test procedure that requires the fixture to be hoisted and dismantled from the test platform of the shake table and rotate by a certain degree can be eliminated. Furthermore, the fastening frame is formed of a H-shaped steel plate that is configured as a hollow rectangle. The overall structural design of the fixture of the present invention makes its basic natural frequency to be larger than 33 Hz. Thus, resonance will not occur during the seismic test. Moreover, the fastening frame is configured to secure the device under test by the fixing plates and thus is applicable to all kinds of small-sized device. Now the foregoing and other features and advantages of the present invention will be best understood through the following descriptions with reference to the accompanying drawings, in which: Referring to FIG. 1, a perspective exploded view of a rotatable fixture according to a preferred embodiment of the present invention is shown. The rotatable fixture includes a base 10, a rotating disc 20, a fastening frame 30, and a pair of fixing plates 31, 32. The base 10 is shaped as a plate having a plurality of perforations thereon. The perforation 11 located in the center of the base 10 is set to allow a central axle 50 to be installed therein and past therethrough. Referring to FIG. 3A and FIG. 4A, the central axle 50 includes a central cone 51, a spring 52, and a headless screw bolt 53, all of which are sequentially mounted in the perforation 11 of the base 10. The front end of the central cone 51 is exposed through the perforation 11 of the base 10 for allowing the rotating disc 20 to be mounted thereon, and the flange located in the rear end of the central cone 51 contacted with the spring 52. The spring 52 provides the lift force to pop up the base 10 therethrough the central cone when it is released from compressed state. The headless screw bolt 53 beneath spring 52 is used to prop up spring 52 at this position. FIG. 2 shows an assembly side view of a rotatable fixture according to a preferred embodiment of the present invention. Referring to FIG. 1 and FIG. 2, at least four perforations 12 are disposed at locations away from the central axle 50 by an appropriate equal distance for embedding a rolling steel ball assembly 60 therein the base 10. As shown in FIG. 3B and FIG. 4B, the rolling steel ball assembly 60 includes a rolling steel ball 61, a rolling steel ball cushion 62, a spring 63, a spring cushion 64, and a headless screw bolt 65, all of which are sequentially disposed in the perforation 12. The spring 63 is clamped by the rolling steel ball cushion 62 and the spring cushion 64. The front end of the rolling steel ball cushion 62 with a cone surface props up the rolling steel ball 61 and the rear end of the spring cushion 64 is propped up by the headless screw bolt 65, the headless screw bolt 65 is used to plug the perforation 12 and as a foundation to prop up the spring cushion 64 at its position. In this manner, the rolling steel ball 61 is slightly exposed from the base 10. in this embodiment, four sets of rolling steel ball assembly are depicted to illustrate the possible configuration of the rolling steel ball assembly 60. However, the amount of the rolling steel ball assembly is not limited to the precise number disclosed herein. The rotating disc 20 is also shaped as a plate and has a perforation 21 at its center. The perforation 21 corresponds to the central axle 50 for allowing the central axle 50 to pass therethrough and pivotally connect to the base 10. Thus, the rotating disc 20 can rotate with respect to the base 10. In order to make the rotation of the rotating disc 20 smooth, the elastic force of the spring 63 will be applied to the rolling steel ball 61 of the rolling steel ball assembly 60 during the rotation process, and thus the rotating disc 20 is slightly lifted and propped up by the rolling steel ball 61, such that the rotating disc 20 can be easily rotated by hand pushing with the relative rolling motion of the rolling steel ball 61. A fastening-member 40 is set to movably pass through the fastening hole 24 of the rotating disc 20 and the fastening hole 14 of the base 10, as shown in FIG. 5. The fastening member 40 is used to secure the rotating disc 20 and limit the rotation of the rotating disc 20 with respect to the base 10. When the fastening member 40 loosens the fastening of the rotating disc 20 with the base 10, as shown in FIG. 6A, the rotating disc 20 and the fastening frame 30 as well as the device 91 can be rotated together to an angle for the next test step (the angle for the next step may be, for example, 90 degree, as shown in FIG. 6B). Thus, the present invention can avoid the drawbacks that the conventional fixture has to be dismantled first and then rotate to a certain angle and secure to the test platform. As shown in the drawings, the fastening member 40 may be formed of a screw bolt. In addition, the fastening holes 14 and 24 may be used to mount lugs therein for allowing the rotatable fixture to be hanged thereby. On the other hand, the base 10 has a plurality of mounting holes 13, and the rotating disc 20 correspondingly has a plurality of mounting holes 23. The mounting holes 13 and 23 are untapped so as to secure the rotatable fixture to the test platform. The fastening frame 30 is formed of a H-shaped steel plate, as shown in FIG. 1. Preferably, the H-shaped steel plate of the fastening frame 30 is configured as a hollow rectangle. The fastening frame 30 is set to be secured to the rotating disc 20 by way of, for example, welding, such that the basic natural frequency of the fixture is larger than 33 Hz. Taking a seismic test as an example, the major frequency band of a seismic wave is ranged between 1 to 33 Hz. Hence, resonance of fixture will not occur within the test frequency band, so as to ensure that the test result is free from distortion and not over tested. The fastening frame 30 has a pair of fixing plates 31, 32 located at both sides of the fastening frame 30. The fixing plates 31 and 32 may be secured to the fastening frame 30 by screws. Also, the fixing plates 31 and 32 both include several lock holes 301 that are used for fixing the device under test. Hence, the rotatable fixture of the present invention is available to fasten with most kinds of device 91, regardless of its size. Typically, the device 91 under seismic test is a small-sized article weights less than 10 kilograms. Thus, the fixture of the present invention serves as a universal fixture and avoids the disadvantages encountered by the prior art that each device 91 requires a dedicated fixture for testing. During the practical use, the device 91 is fastened to the fixing plate 31 or 32 of the fastening frame 30, as shown in FIG. 5. Afterwards, the device 91, the rotating disc 20, and the base 10 as well as the rest of the fixture are secured to test platform (not shown) of shake table through mounting holes 13 and 23 for testing. When it is desired to rotate the fixture during a test, the fastening member 40 can be removed to loosen the fastening between the base 10 and the rotating disc 20, as shown in FIG. 6A. Meanwhile, the rotating disc 20 is pivotally connected to the base 10 through the central axle 50, and the rotating disc 20 is propped up by the springs 52 and 63 on the base 10. In this way, the rotating disc 20 is slighted separated from the base 10, and the rolling steel ball 61 functions to provide bearing effect, so the rotating disc 20 can easily rotate to a desired agree (e.g. 90 degree), as shown in FIG. 6B. Afterwards, the fastening member 40 is secured to continue with the following test procedures. Therefore, the rotatable fixture of the present invention is advantageous in terms of a simple structure, an easy assembling process, and excellent universalness. The present invention is particularly suitable for small-sized device under test with the weight being less than 10 kilograms. In addition, the natural frequency of the fixture is distant from the test frequency band by way of its special structural configuration. Also, the rotation of the rotating disc with respect to the base allows the fixture to rotate directly, without the need of being dismantled and re-installed. Thus, the rotatable fixture of the present invention can effectively shortened the time and cost for performing the test. While the present invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention need not be restricted to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present invention which is defined by the appended claims. |
|
claims | 1. A radiation shielding lid for a radiation shielding container, the lid comprising:a body having an upper surface and an opposing lower surface;a vial opening defined in the body, the vial opening having a lower end at the lower surface of the body and an upper end intermediate the upper and lower surfaces of the body;a finger recess in the upper surface of the body, the finger recess sized and shaped to allow at least distal portions of at least two digits to enter the finger recess, wherein the finger recess has an upper edge adjacent the upper surface of the body and a lower edge adjacent the upper end of the vial opening;first and second wings extending upward from adjacent the upper end of the vial opening, each of the first and second wings having opposite sides, a top portion, and an inner surface extending partially around a circumference of the upper end of the vial opening;wherein the inner surfaces of the first and second wings and the vial opening together define a vial passageway extending from the top portions of the first and second wings through the lower surface of the body, the vial passageway being sized and shaped for receiving a vial therein;wherein respective adjacent sides of the first and second wings are spaced apart from one another around the vial opening to partially define first and second finger channels leading from the finger recess to the vial passageway, each of the first and second finger channels being sized and shaped to allow at least the distal portion of one of the two digits to enter the corresponding finger channel from the finger recess to facilitate gripping of the vial during at least one of insertion of the vial in the vial passageway and removal of the vial from the vial passageway. 2. The lid set forth in claim 1, wherein the inner surface of each of the first and second wings extends at least 45 degrees and less than 180 degrees around the circumference of the upper end of the vial opening. 3. The lid set forth in claim 2, wherein the top portions of the first and second wings extend above the upper surface of the body. 4. The lid set forth in claim 2, wherein the inner surface of each of the first and second wings extends at least 60 degrees around the circumference of the upper end of the vial opening. 5. The lid set forth in claim 4, wherein the inner surface of each of the first and second wings extends at least 90 degrees around the circumference of the upper end of the vial opening. 6. The lid set forth in claim 1, wherein the inner surfaces of the first and second wings are diametrically opposed to one another with respect the vial opening. 7. The lid set forth in claim 1, wherein the sides of the respective first and second wings extend into the finger recess. 8. The lid set forth in claim 1, wherein the finger recess comprises first and second finger recesses, wherein the first and second finger recesses are diametrically opposed to one another with respect to the vial opening. 9. The lid set forth in claim 8, wherein the lower edge of the first finger recess extends between the corresponding adjacent sides of the first and second wings to partially define the first finger channel, and wherein the lower edge of the second finger recess extends between the corresponding adjacent sides of the first and second wings to partially define the second finger channel. 10. The lid set forth in claim 1, wherein the top portions of the first and second wings extend above the upper surface of the body. 11. The lid set forth in claim 10, wherein at least one of the first and second wings has a notch in the corresponding top portion. 12. The lid set forth in claim 1, wherein the upper end of the vial opening is substantially circular, and wherein the inner surfaces of the first and second wings are generally arcuate. 13. The lid set forth in claim 1, wherein a portion of the vial passageway defined by the inner surfaces of the wings tapers from the top portions of the wings toward the vial opening. 14. The lid set forth in claim 1, wherein each of the first and second wings includes a plurality of ribs on the inner surface of each wing projecting inward into the vial passageway, the ribs on each wing being spaced apart from one another between the opposite sides of each wing. 15. The lid set forth in claim 14, wherein the ribs project generally toward a centerline of the passageway from the inner surface of the corresponding wing, such that each rib has a terminal, guiding surface generally facing a centerline of the vial passageway, wherein each guiding surface is uniformly spaced from the centerline of the vial passageway along its length. 16. The lid set forth in claim 1, wherein the body is substantially disk-shaped and is formed, at least in part, from a radiation shielding material comprising at least one of depleted uranium, tungsten, tungsten impregnated plastic, or lead. 17. The lid set forth in claim 1, further comprising an elution tool opening defined in the body, wherein the elution tool opening is spaced apart and separate from the vial opening. 18. A lid for a radiation shielding container comprising:a body having upper and lower surfaces;a vial opening in the body having a centerline extending through the upper and lower surfaces of the body, the vial opening being sized and shaped to allow insertion of a vial therein;first and second alignment wings extending upward from the vial opening, each of the first and second alignment wings having opposite sides, a top portion, and an inner surface extending partially around a circumference of the vial opening;wherein the first and second alignment wings enable alignment of a longitudinal axis of a vial with the centerline of the vial opening as the vial is inserted in the vial opening;wherein respective adjacent sides of the first and second alignment wings partially define at least one finger channel, the at least one finger channel being sized and shaped to allow at least the distal portion of at least one digit to enter the finger channel to facilitate at least one of insertion of the vial in the vial opening and removal of the vial from the vial opening. 19. The lid set forth in claim 18, wherein the inner surface of each alignment wing extends at least 45 degrees and less than 180 degrees around the circumference of the vial opening, wherein said at least one finger channel comprises at least a first finger channel and a second finger channel. 20. The lid set forth in claim 19, further comprising first and second finger recesses in the upper surface of the body, each of the first and second finger recesses having an upper edge adjacent the upper surface of the body and a lower edge leading to the vial opening, wherein the first and second finger recesses are diametrically opposed to one another with respect to the vial opening. 21. The lid set forth in claim 18, further comprising an elution tool opening defined in the body, wherein the elution tool opening is spaced apart and separate from the vial opening. |
|
description | 1. Field Example embodiments generally relate to fuel structures and radioisotopes produced therein in nuclear power plants and other nuclear reactors. 2. Description of Related Art Radioisotopes have a variety of medical applications stemming from their ability to emit discreet amounts and types of ionizing radiation. This ability makes radioisotopes useful in cancer-related therapy, medical imaging and labeling technology, cancer and other disease diagnosis, medical sterilization, and a variety of other industrial applications. Radioisotopes, having specific activities are of particular importance in cancer and other medical therapy for their ability to produce a unique and predictable radiation profile. Knowledge of the exact amount of radiation that will be produced by a given radioisotope permits more precise and effective use thereof, such as more timely and effective medial treatments and improved imaging based on the emitted radiation spectrum. Radioisotopes are conventionally produced by bombarding stable parent isotopes in accelerators or low-power reactors with neutrons on-site at medical facilities or at nearby production facilities. The produced radioisotopes may be assayed with radiological equipment and separated by relative activity into groups having approximately equal activity in conventional methods. Example embodiments and methods are directed to irradiation target positioning devices and systems that are configurable to permit accurate irradiation of irradiation targets and accurate production of daughter products, including isotopes and radioisotopes, therefrom. Example embodiments include irradiation target plates having precise loading positions for irradiation targets, where the targets may be maintained in a radiation field, such as a neutron flux. Example embodiment target plates may further include holes and target spacing elements to further refine the positioning of irradiation targets of very small or large size within the field. Example embodiments may further include a target plate holder for retaining and positioning the target plates and irradiation targets therein in the radiation field. Example embodiment target plate holders may further include spacer plates to further refine the positioning of irradiation target plates within example embodiment target plate holders. Example embodiments may be fabricated of materials with known absorption cross-sections for the radiation field to further permit precise, desired levels of exposure in the irradiation targets. Example methods configure irradiation target retention systems to provide for desired amounts of irradiation and daughter product production. Example methods may include determining a desired daughter product, determining characteristics of an available radiation field, configuring the irradiation targets within example embodiment target plates and target plate holders, and/or irradiating the configured system in the radiation field. Detailed illustrative embodiments of example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the language explicitly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. FIG. 1 is an illustration of an example embodiment target plate 100. As shown in FIG. 1, example embodiment target plate 100 may be a circular disk, or, alternatively, any shape, including square, elliptical, toroidial, etc., depending on the application. Target plate 100 includes one or more loading positions 101 where irradiation targets may be placed and retained. Loading positions 101 are positioned in target plate 100 at positions of known radiation levels when target plate 100 is subject to a neutron flux or other radiation field. As used herein “radiation level” or “radiation field” includes any type of ionizing radiation exposure capable of transmuting targets placed in the radiation field, including, for example, high-energy ions from a particle accelerator or a flux of neutrons of various energies in a commercial nuclear reactor. For example, if target plate 100 is placed in neutron flux at a particular position in an operating commercial nuclear reactor, exact levels and types of neutron flux at loading positions 101 are known, such that each position may correspond to a particular level of exposure given an exposure time. In this way, loading positions 101 may be arranged in example embodiment target plate 100 so as to ensure irradiation targets at those positions are exposed to an exact and desired level of radiation exposure. As an example, it may be desirable to place loading positions 101 so that each position is exposed to an equal amount of neutron flux in a light-water reactor. Knowing the flux profile to which target plate 100 will be exposed and the relevant cross-sections, including absorption and scattering/reflection cross-sections, of target plate 100, loading positions 101 can be arranged such that each loading position 101 receives equal irradiation, including, for example, having loading positions 101 be more frequent at an outer perimeter of target plate 100 where more flux is encountered, as shown in FIG. 1. FIG. 2 is another view of example embodiment target plate 100 showing various example arrangements at loading positions 101 and irradiation targets 150 therein, wherein detailed views are provided in FIGS. 2A-2F. One or more holes 102 that extend partially or completely through target plate 100 may be at a loading position 101 to hold one or more irradiation target 150. Holes 102 may be any shape. For example, as shown in the details of FIG. 2A and 2C, holes 102 may be shaped to match a shape of irradiation targets 150 therein, including, for example, cylindrical holes 102 to hold cylindrical irradiation targets 150. As a further example, as shown in the details of FIG. 2D and 2F, holes 102 may be shaped as slits to hold disk or flat irradiation targets 150. A number of irradiation targets 150 may be loaded into any hole 102 based on the estimated neutron flux profile at a loading position 101 of the hole. For example, loading positions 101 expected to be exposed to higher levels of radiation may include holes 102 having more irradiation targets 150 loaded therein. While example embodiments illustrate holes 102 at loading positions 101, it is understood that other irradiation target retention mechanisms, such as an adhesive or containment compartment, for example, are useable to retain irradiation targets 150 at loading positions 101. A single hole 102 may be at a loading position 101, as shown in the details of FIG. 2A, for example, or multiple holes may be at a loading position 101, as shown in the details of FIG. 2C, for example. Example embodiment target plates 100 may include a variety of holes 102 of different shapes and numbers at different loading positions 101. For example, in order to accommodate different shapes of irradiation targets 150 and based on the known flux profile to which target plate 100 is exposed, multiple square holes 102 may be placed at edge loading positions 101 while a single, cylindrical hole 102 may be at interior loading positions 101. Irradiation targets 150 may take on a number of shapes, sizes, and configurations and may be placed, sealed, and/or retained in holes 102 or other retaining mechanisms at loading positions 101 in a variety of ways. The size of the irradiation targets 150 may be adjusted as appropriate for their intended use (e.g., radiography targets, brachytherapy seeds, elution matrix, etc.). For instance, an irradiation target 150 may have a length of about 3 mm and a diameter of about 0.5 mm. Irradiation targets 150 may also be spherical-, disk-, wafer-, and/or BB-shaped, or any other size and shape, within different types of holes 102 in the same target plate 100, as shown in FIG. 2. It should be understood that the size of the holes 102 and/or the thickness of the example embodiment target plates 100 may be adjusted as needed to accommodate the targets 150. Irradiation targets 150 are strategically loaded at the appropriate loading positions 101 based on various factors (including the characteristics of each target material, known flux conditions of a reactor core, the desired activity of the resulting targets, etc.) discussed in greater detail below, so as to attain daughter products from irradiation targets 150 having a desired concentration or activity level, such as a relatively uniform activity. Irradiation targets 150 may be formed of the same material or different materials. Irradiation targets 150 may also be formed of natural isotopes or enriched isotopes. As used herein it is understood that irradiation targets 150 include those materials having a substantial absorption cross-section for the type of irradiation to which example embodiments may be exposed, such that irradiation targets 150 include materials that will absorb and transmute in the presence of a radiation field. For example, suitable targets 150 may be formed of cobalt (Co), chromium (Cr), copper (Cu), erbium (Er), germanium (Ge), gold (Au), holmium (Ho), iridium (Ir), lutetium (Lu), molybdenum (Mo), palladium (Pd), samarium (Sm), thulium (Tm), ytterbium (Yb), and/or yttrium (Y), although other suitable materials may also be used. Similarly, targets may be liquid, solid, or gaseous within appropriate containment at loading positions 101, such as in holes 102. In order to preserve spacing among irradiation targets 150 and orientation of irradiation targets 150 within a known radiation field to which they are exposed, one or more spacing elements 105 may space and/or retain irradiation targets 150 within holes 102. For example, as shown in the details of FIG. 2B, a single target spacing element 105A may be placed in a hole 102 to retain and space irradiation targets 150 at proper positions at loading positions 101. Alternatively, as shown in the details of FIG. 2E, one or more target spacing elements 105B may be shaped like a dummy target and inserted into hole 102 to retain and space irradiation targets 150 at proper positions within a hole 102 at irradiation target loading position 101. FIG. 3 is an illustration of an example embodiment target plate 100 using target spacing elements 105B, like those shown in the details of FIG. 2E, at each loading position 101 having a hole 102. As shown in FIG. 3, each hole 102 may be equally filled with a combination of target spacing elements 105B and/or irradiation targets 150. In accordance with example methods, discussed below, loading positions 101 at a periphery may contain an increased ratio of irradiation targets 150 to target spacing elements 105B, whereas loading positions 101 may have a lower ratio, in order to produce daughter products of a desired activity. Still alternatively, as shown in FIG. 2D, target spacing elements 105C may be shaped like wafers having a thickness sufficient to separate irradiation targets 150 in a slit-type hole 102. The separation may space irradiation targets 150 at desired positions for irradiation. Other types of spacing and retaining elements, including caps, adhesives, elastic members, etc. may be useable as target spacing elements 105. Example embodiment target plate 100 and any spacing elements 105 therein may be fabricated from materials having a desired cross-section, in view of the type of radiation field to which example embodiments may be exposed. For example, example embodiment target plate 100 being exposed to a thermal neutron flux field may be fabricated of a material having a low thermal neutron absorption and scattering cross-section, such as zirconium or aluminum, in order to maximize neutron exposure to irradiation targets 150 therein. For example, if example embodiment target plate 100 is exposed to an aggregate neutron flux with a wide energy distribution, spacing elements 105 may be fabricated of a material, such as paraffin, having a high absorption cross-section for particular energy neutrons to ensure that irradiation targets 150 are not exposed to a neutron flux of the particular energy. The above-described features of example embodiment target plate 100 and the known radiation profile to which target plate 100 is to be exposed may uniquely enable accurate irradiation of irradiation targets 150 used therein. For example, knowing an irradiation flux type and profile; a shape, size, and absorption cross-section of irradiation targets 150; and size, shape, position, and absorption cross-section of example embodiment target plate 100, loading positions 101 on the same, and target spacing elements 105 therein, one may very accurately position and irradiate targets 150 to produce desired isotopes and/or radioisotopes. Similarly, one skilled in the art can vary any of these parameters, including irradiation target type, shape, size, position, absorption cross-section etc., in example embodiments in order to produce desired isotopes and/or radioisotopes. FIG. 3 illustrates an example arrangement for target plate 100 where outer loading positions 101 will be directly exposed to higher levels of radiation when the target plate 100 is placed in a neutron flux, such as found in an operating nuclear reactor core. A greater number of irradiation targets 150 may be placed at each of the outer positions 101, thereby resulting in more equal activity amongst the irradiation targets 150 in the outer loading positions 101. Fewer irradiation targets 150 may be placed in each of the inner loading positions 101 to offset the fact that these irradiation targets 150 will be farther from the flux, thereby allowing irradiation targets 150 in the inner loading positions 101 to attain activity levels comparable to targets 150 in the outer loading positions 101. It is understood, however, in light of the above discussion, that the example arrangement of FIG. 3 may be altered in several ways so as to increase/decrease the resulting activity of each irradiation target 150 following irradiation. For instance, irradiation targets 150 formed of materials having lower capture cross-sections for a particular radiation field may be arranged at loading positions 101 that will be in closer proximity to the field, whereas irradiation targets 150 of materials with higher cross-sections may be positioned in example embodiment target plates 101 farther away from the field. FIG. 4 is an illustration of an example embodiment target plate holder 200 that is useable with example embodiment target plates 100 described above. As shown in FIG. 4, example embodiment target plate holder 200 may include a body 201 that is insertable in a radiation field. Body 201 may be rigid or flexible. Body 201 may be shaped and/or sized to fit in areas where radiation fields may exist, including, for example, an instrumentation tube of a light-water reactor, a nuclear fuel rod, an access tube for a particle accelerator, etc. Similarly, multiple example embodiment target plates holders 200 may be inserted and/or placed together and body 201 may be sized and shaped to permit multiple insertions, for example, in a 4″ hole commonly found in nuclear reactors. Body 201 may further include one or more connectors 202 that may permit holder 200 to be attached to extensions or insertion devices, such as a snaking cable. Body 201 holds at least one example embodiment target plate 100. For example body 201 may include a shaft upon which target plates 100 may fit and be retained. Body 201 and parts thereof may be sized and shaped to match any of the various possible shapes of target plate 100, including a square, circular, triangular, etc. cross-section. As shown in FIG. 5, one or more spacer plates 203 may be placed with target plates 100 in or adjacent to body 201. Spacer plates 203 may separate and position target plates 100 at precise locations within example embodiment target plate holder 200 in order to achieve accurate exposure for irradiation targets 150 therein. Spacer plates 203 may have thicknesses that result in a desired degree of separation among target plates 100. For example, if example embodiment target plates 100 are fabricated and configured to substantially absorb neutron flux passing therethrough, a thicker spacer plate 203 may separate target plates 100 in target plate holder 200 to ensure that plates have a minimal effect on each other's irradiation, so as to achieve more even irradiation of irradiation targets 150 therein. Alternatively, more spacer plates 203 may be placed at greater frequency to achieve the same spacing and/or exposure as thicker spacer plates 203. Spacer plates 203 may be shaped and sized in any manner to achieve desired positions of target plates. Spacer plates 203 may be any shape, such as rectangular, triangular, annular, etc., based on positioning of target plates 100 in example embodiment target plate holder 200. Spacer plates 203 may further provide for securing irradiation targets 150 within example embodiment target plates 100 stacked consecutively with spacer plates 203 on body 201. Spacer plates 203 may also be colored, textured, and/or bear other indicia that indicates their physical properties and/or the identities of irradiation targets 150 within target plates 100 placed adjacently. Spacer plates 203 and body 201 may be fabricated of a material having a desirable radiation absorption profile. For example, spacer plates 203 and body 201 may have a low cross-section (e.g., approximately 5 barns or less) for thermal energy neutrons by being fabricated of a material such as aluminum, stainless steel, a titanium alloy, etc. Similarly, some spacer plates 203 and/or body 201 may be fabricated of materials having higher cross-sections for particular radiation fields, such as silver, gold, a boron-doped material, a barium alloy, etc. in thermal neutron fluxes. Spacer plates 203 may be strategically placed on body 201 based on its effect on the radiation field. For example, high cross-section (e.g., over 5 barns) spacer plates 203 placed on either side of target plates 100 may reduce or eliminate irradiation of irradiation targets 150 therein from the side, permitting a desired activity level of isotopes produced therefrom. Similarly, annular spacer plates 203 may provide for maximum irradiation of target plates 100 from a side. The above-described features of example embodiment target plate holder 200 and spacer plates 203 and target plates 100 therein, and the known radiation profile to which target plate holder 200 is to be exposed may uniquely enable accurate irradiation of irradiation targets 150 used therein. For example, knowing an irradiation flux type and profile; a shape, size, and absorption cross-section of irradiation targets 150; precise positioning of irradiation targets 150 within radiation flux; size, shape, position, and absorption cross-section of example embodiment target plate 100 and spacing elements 105 therein; position of target plate 100 and spacer plate 203 within target plate holder 200; size, shape, and absorption cross-section of plate holder 200 and spacer plate 203, one may very accurately irradiate targets 150 to produce desired isotopes and/or radioisotopes. Similarly, one skilled in the art can vary any of these parameters in example embodiments in order to produce desired isotopes and/or radioisotopes. FIG. 5 is a flow chart of an example method of using example embodiment target plates 100 and/or target plate holders 200. As shown in FIG. 5, the user determines a desired isotope/radioisotope to be produced, and amount to be produced, in example methods in S110. The desired isotope and amount thereof may be chosen based on any number of factors, including, for example, an available irradiation target, desired industrial application, and or an available radiation field. By virtue of correspondence between daughter product and parent nuclide, the user will also select the material and amount for irradiation targets 150 in S110. In S120, the user will determine the characteristics of an available radiation field. The relevant characteristics may include type of radiation, energy of radiation, and/or variations of type and energy in a particular space. For example, the user may determine the level and variation of a neutron flux at a particular access point to a research reactor in S120. Alternatively, the user may determine the energy and type of ions encountered at a target stand in a particle accelerator in S120. Based on the physical properties of the selected irradiation target 150 and the properties of the radiation field, both determined above, the user then configures target plate(s) 100, irradiation target(s) 150, target spacing element(s) 105, target plate holder(s) 200, and/or spacing plate(s) 203 in order to achieve an amount of irradiation necessary to produce a desired amount and/or activity of produced isotopes, in S130. Such configuration may include determining locations of loading positions 101 in target plate 100, placing and positioning irradiation targets 150 in target plates 100 at loading positions 101 with target spacing elements 105, and positioning target plates 100 in target plate holder 200 with spacing plates 203 to achieve a precise position of each irradiation target 150 within a radiation field. Additionally, such configuration may include selecting materials with known absorption cross-sections for a radiation spectrum relevant to the radiation field in order to achieve desired amounts of irradiation for irradiation targets 150 placed within that field. For example, a desired activity may be a substantially equal activity among several produced isotopes from several irradiation targets 150. In S130, the user may also calculate an exposure time based on the configuration, radiation field properties, and irradiation target 150 properties to achieve a desired magnitude of irradiation for irradiation targets 150 placed in example embodiment devices in that field. In S140, the user may then place the configured irradiation targets 150 in example embodiment devices configured in S130 and place them into the determined radiation field so as to produce the desired isotopes and/or radioisotopes of a desired amount and/or activity. Alternatively, the user may deliver or otherwise provide the configured example embodiment devices for another to insert the irradiation targets 150 and irradiate them in the determined radiation field in S140. Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. For example, although various example embodiment plates, holders, and spacers are used together with example methods of producing desired isotopes, each example embodiment may be used separately. Similarly, for example, although cylindrical example embodiments are shown, other device types, shapes, and configurations may be used in example embodiments and methods. Variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
|
claims | 1. A method for designing a phase shift mask, having a substrate (200) with a transparent property, and an opaque layer (100) formed on said substrate and having an opaque property, wherein a plurality of rectangular apertures are formed in said opaque layer, a two-dimensional layout pattern is formed by opaque parts (120) comprising regions at which said opaque layer is formed, and transparent parts (110) comprising regions at which said apertures are formed, and for a pair of adjacently disposed apertures, so that a phase of light transmitted through one of said pair of adjacent apertures will be shifted by 180 degrees with respect to a phase of light transmitted through other of said pair of adjacent apertures, a trench (220), having a predetermined depth and an outline greater than an outline of said one aperture, is formed on a portion of said substrate at which said one aperture is formed,said phase shift mask designing method comprising the steps of:a two-dimensional layout designing step (S1) of defining an XY plane on a surface of said substrate, determining a width Wx in an X-axis direction and a width Wy in a Y-axis direction of an aperture and a width Ws of an opaque part, and positioning a plurality of apertures of a same size at least along the X-axis to thereby design a two-dimensional layout on said XY plane;a three-dimensional structure determination step (S2) of determining, for each of said plurality of apertures, whether or not phase shifting is to be performed and determining, for the apertures with which phase shifting is to be performed, a trench depth d and an undercut amount Uc, which indicates a distance between a position of an outline of the trench and a position of the outline of the aperture, to thereby determine a three-dimensional structure;a three-dimensional analysis step (S3) of using a three-dimensional structural body, which is defined by said two-dimensional layout designing step and said three-dimensional structure determination step, to determine a light intensity deviation D, which indicates, for a case where light is transmitted under same exposure conditions through a pair of adjacent apertures that have been designed to realize a phase shift of 180 degrees with respect to each other, a deviation in intensities of light transmitted through the respective apertures;a two-dimensional analysis step (S4) of using a two-dimensional structural body, which is defined by said two-dimensional layout, to determine, in a case where, for said pair of adjacent apertures, a light transmittance of one aperture is set to 100% and a light transmittance of the other aperture is set to T %, a transmittance T such that a deviation in intensities of light transmitted through each of said pair of adjacent apertures will be equal to said light intensity deviation D; anda layout correction step (S5) of correcting said two-dimensional layout based on said transmittance T. 2. The phase shift mask designing method as set forth in claim 1, whereinin the two-dimensional analysis step, a light intensity deviation D is determined for each of a plurality of transmittances and a transmittance, which provides a result matching the light intensity deviation D determined in the three-dimensional analysis step, is determined as the transmittance T. 3. The phase shift mask designing method as set forth in claim 2, whereinin the two-dimensional analysis step, a database, with which a value of the light intensity deviation D is determined for each of various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T, is prepared in advance, and in determining a light intensity deviation D for a specific two-dimensional structural body, said database is searched to determine the light intensity deviation D. 4. The phase shift mask designing method as set forth in claim 3, whereina database, having the width Wy in the Y-axis direction of an aperture in addition as a parameter value, is prepared. 5. The phase shift mask designing method as set forth in claim 3, whereinin a case where a combination of parameter values that matches search conditions does not exist among combinations of parameters prepared inside the database, an interpolation operation using parameter values that are close is performed. 6. The phase shift mask designing method as set forth in claim 3, whereinin the two-dimensional layout designing step, a plurality of apertures are positioned in two-dimensional matrix form in the X-axis direction and the Y-axis direction, and as the width Ws of the opaque parts, two parameters of a width Wsx in the X-axis direction of an opaque part existing between apertures that are adjacent in the X-axis direction and a width Wsy in the Y-axis direction of an opaque part existing between apertures that are adjacent in the Y-axis direction are used. 7. The phase shift mask designing method as set forth in claim 1, whereinin the three-dimensional analysis step, a database, with which a value of the light intensity deviation D is determined for each of various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the undercut amount Uc, is prepared in advance, and in determining a light intensity deviation D for a specific three-dimensional structural body, said database is searched to determine the light intensity deviation D. 8. The phase shift mask designing method as set forth in claim 1, whereinin the layout correction step, a database, with which an optimal correction amount δ is determined for each of various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T, is prepared in advance, and in performing a correction of a specific two-dimensional layout, with which a specific transmittance is defined, said database is searched to determine the optimal correction amount δ. 9. The phase shift mask designing method as set forth in claim 1, whereinin the three-dimensional structure determination step, apertures with which phase shifting is to be performed are determined so that every other aperture of the plurality of apertures that are positioned along the X-axis direction or the Y-axis direction are selected. 10. The phase shift mask designing method as set forth in claim 1, whereina part or all of the process of determining the light intensity deviation D in the three-dimensional analysis step, the process of determining the transmittance T in the two-dimensional analysis step, and the correction process in the layout correction step are executed using computer simulation. 11. The phase shift mask designing method as set forth in claim 1, whereina part or all of the process of determining the light intensity deviation D in the three-dimensional analysis step, the process of determining the transmittance T in the two-dimensional analysis step, and the correction process in the layout correction step are executed by experimentation using an actually manufactured phase shift mask. 12. A device for designing a phase shift mask, having a substrate (200) with a transparent property, and an opaque layer (100) formed on said substrate and having an opaque property, wherein a plurality of rectangular apertures are formed in said opaque layer, a two-dimensional layout pattern is formed by opaque parts (120) comprising regions at which said opaque layer is formed, and transparent parts (110) comprising regions at which said apertures are formed, and for a pair of adjacently disposed apertures, so that a phase of light transmitted through one of said pair of adjacent apertures will be shifted by 180 degrees with respect to a phase of light transmitted through another of said pair of adjacent apertures, a trench (220), having a predetermined depth and an outline greater than an outline of said one aperture, is formed on a portion of said substrate at which said one aperture is formed,said phase shift mask designing device comprising:a two-dimensional layout determination tool (10), which, based on instructions from an operator, determines a width Wx in an X-axis direction and a width Wy in a Y-axis direction of an aperture and a width Ws of an opaque part on an XY plane defined on a surface of said substrate and positions a plurality of apertures of a same size at least along the X-axis to determine a two-dimensional layout on said XY plane;a three-dimensional structure determination tool (20), which, based on instructions from an operator, determines whether or not phase shifting is to be performed for each of the plurality of apertures and determines, for apertures with which phase shifting is to be performed, a trench depth d and an undercut amount Uc, which indicates a distance between a position of an outline of the trench and a position of an outline of the aperture, to thereby determine a three-dimensional structure;a three-dimensional simulator (30), which performs a three-dimensional analysis process of executing a three-dimensional simulation using a three-dimensional structural body, which is defined by said two-dimensional layout determination tool and said three-dimensional structure determination tool, as a model to determine a light intensity deviation D that indicates a deviation of intensities of light transmitted through each of a pair of adjacent apertures, designed to realize a phase shift of 180 degrees with respect to each other, when light is transmitted through the apertures under same exposure conditions; anda two-dimensional simulator (40), which performs a two-dimensional analysis process of executing two-dimensional simulations using a two-dimensional structural body, which is defined by said two-dimensional layout, as a model to determine a transmittance T, such that, when for a pair of adjacent apertures, a light transmittance of one aperture is set to 100% and a light transmittance of another aperture is set to T %, a deviation in intensities of light transmitted through each of said pair of adjacent apertures becomes equal to said light intensity deviation D, and performs a layout correction process of executing two-dimensional simulations using a model, with which said transmittance T is applied to the two-dimensional structural body defined by said two-dimensional layout, to correct said two-dimensional layout. 13. The phase shift mask designing device as set forth in claim 12 whereinwhen the two-dimensional simulator performs the two-dimensional analysis process, a light intensity deviation D is determined for each of a plurality of transmittances, and a transmittance, which provides a result matching the light intensity deviation D determined by the three-dimensional analysis process performed by the three-dimensional simulator, is determined as the transmittance T. 14. The phase shift mask designing device as set forth in claim 12, wherein:a database (55), in which light intensity deviations D, each defined as a value that indicates a deviation of intensities of light transmitted through each of a pair of adjacent apertures, which are of a predetermined three-dimensional structural body and are designed to realize a phase shift of 180 degrees with respect to each other, when light is transmitted through the apertures under the same conditions, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the undercut amount Uc; anda light intensity deviation determination tool (50), which determines a specific light intensity deviation D by searching said database using specific parameter values determined by the two-dimensional layout determination tool and the three-dimensional structure determination tool;are provided as an alternative means to the three-dimensional simulator. 15. The phase shift mask designing device as set forth in claim 14, whereina database, having the width Wy in the Y-axis direction of an aperture in addition as a parameter value, is prepared. 16. The phase shift mask designing device as set forth in claim 14, whereinin order to accommodate for a two-dimensional layout, with which a plurality of apertures are positioned in two-dimensional matrix form in the X-axis direction and the Y-axis direction, two parameters of a width Wsx in the X-axis direction of an opaque part existing between apertures that are adjacent in the X-axis direction and a width Wsy in the Y-axis direction of an opaque part existing between apertures that are adjacent in the Y-axis direction are used as parameter values in the database as the width Ws of the opaque parts. 17. The phase shift mask designing device as set forth in claim 14, whereinin a case where a combination of parameter values that matches search conditions does not exist among combinations of parameters prepared inside the database, the light intensity deviation determination tool, transmittance determination tool, or correction amount determination tool performs an interpolation operation using parameter values that are close to determine the light intensity deviation D, transmittance T, or correction amount δ. 18. The phase shift mask designing device as set forth in claim 12, wherein:a database (65), in which light intensity deviations D, each defined as a value that indicates a deviation of intensities of light transmitted through each of a pair of adjacent apertures, which are of a predetermined two-dimensional structural body and with which a transmittance of one has been set to 100% and a transmittance of the other has been set to T %, when light is transmitted through the apertures under the same conditions, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T; anda transmittance determination tool (60), which searches said database using specific parameter values determined by the two-dimensional layout determination tool and a specific light intensity deviation D determined by the three-dimensional simulator to determine a transmittance T, by which a light intensity deviation equal to said specific light intensity deviation D is obtained;are provided as an alternative means to the two-dimensional simulator for executing the two-dimensional analysis process. 19. The phase shift mask designing device as set forth in claim 12, wherein:a database (75), in which correction amounts δ, each of which concerns widths of the respective apertures and is required to make equal the intensities of light transmitted under the same conditions through each of a pair of adjacent apertures, which are of a predetermined two-dimensional structural body, are of the same size, and with which a transmittance of one has been set to 100% and a transmittance of the other has been set to T %, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T; anda correction amount determination tool (70), which searches said database using specific parameter values determined by the two-dimensional layout determination tool and a specific transmittance T determined by the two-dimensional analysis process performed by the two-dimensional simulator to determine a correction amount δ for said two-dimensional layout;are provided as an alternative means to the two-dimensional simulator for executing the layout correction process. 20. A device for designing a phase shift mask, having a substrate (200) with a transparent property, and an opaque layer (100) formed on said substrate and having an opaque property, wherein a plurality of rectangular apertures are formed in said opaque layer, a two-dimensional layout pattern is formed by opaque parts (120) comprising regions at which said opaque layer is formed, and transparent parts (110) comprising regions at which said apertures are formed, and for a pair of adjacently disposed apertures, so that a phase of light transmitted through one of said pair of adjacent apertures will be shifted by 180 degrees with respect to a phase of light transmitted through another of said pair of adjacent apertures, a trench (220), having a predetermined depth and an outline greater than an outline of said one aperture, is formed on a portion of said substrate at which said one aperture is formed,said phase shift mask designing device comprising:a two-dimensional layout determination tool (10), which, based on instructions from an operator, determines a width Wx in an X-axis direction and the width Wy in a Y-axis direction of an aperture and a width Ws of an opaque part on an XY plane defined on a surface of said substrate and positions a plurality of apertures of a same size at least along the X-axis to determine a two-dimensional layout on said XY plane;a three-dimensional structure determination tool (20), which, based on instructions from an operator, determines whether or not phase shifting is to be performed for each of the plurality of apertures and determines, for apertures with which phase shifting is to be performed, a trench depth d and an undercut amount Uc, which indicates a distance between a position of an outline of the trench and a position of an outline of the aperture, to thereby determine a three-dimensional structure;a first database (55), in which light intensity deviations D, each defined as a value that indicates a deviation of intensities of light transmitted through each of a pair of adjacent apertures, which are of a predetermined three-dimensional structural body and are designed to realize a phase shift of 180 degrees with respect to each other, when light is transmitted through the apertures under same conditions, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the undercut amount Uc;a light intensity deviation determination tool (50), which determines a specific light intensity deviation D by searching said first database using specific parameter values determined by said two-dimensional layout determination tool and said three-dimensional structure determination tool;a second database (65), in which light intensity deviations D, each defined as a value that indicates a deviation of intensities of light transmitted through each of a pair of adjacent apertures, which are of a predetermined two-dimensional structural body and with which a transmittance of one has been set to 100% and a transmittance of the other has been set to T %, when light is transmitted through the apertures under the same conditions, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T;a transmittance determination tool (60), which searches said second database using specific parameter values determined by said two-dimensional layout determination tool and a specific light intensity deviation D determined by said light intensity deviation determination tool to determine a transmittance T, by which a light intensity deviation equal to said specific light intensity deviation D is obtained;a third database (75), in which correction amounts δ, each of which concerns widths of the respective apertures and is required to make equal the intensities of light transmitted under the same conditions through each of a pair of adjacent apertures, which are of a predetermined two-dimensional structural body, are of the same size, and with which a transmittance of one has been set to 100% and a transmittance of the other has been set to T %, are stored according to various different combinations of parameter values of the width Wx in the X-direction of an aperture, the width Ws of an opaque part, and the transmittance T; anda correction amount determination tool (70), which searches said third database using specific parameter values determined by said two-dimensional layout determination tool and a specific transmittance T determined by said transmittance determination tool to determine a correction amount S for said two-dimensional layout. |
|
description | The present invention relates to a focused ion beam apparatus. For an application of a focused ion beam (FIB) apparatus, a thin film sample having a thickness of 1 μm or less is widely prepared by using a sputtering function and this thin film sample is observed and evaluated by a transmission electron microscope (TEM). JP-A-04-062748 (Patent Literature 1) discloses that when a sample is tilted by a few degrees to perform thin film processing, a thin film sample having a uniform film thickness is prepared. When this technology is used for preparation finish of a thin film sample, TEM observation can be performed over a wide range with high accuracy. Further, internal structure analysis in which sample cross section processing using a focused ion beam and scanning electron microscope (SEM) observation are combined is widely performed. JP-A-2008-286652 (Patent Literature 2) proposes a method for using as an image a secondary electron signal from a cross section using a focused ion beam or processing beam and observing a processed surface in real time without interrupting FIB processing and sequentially observing a cross section. JP-A-2004-127930 (Patent Literature 3) discloses that a aperture position on an objective lens is staggered from an optical axis and a beam out of the optical axis is selectively taken in, and further, when a beam is made incident out of the optical axis of the objective lens to cancel an aberration, a chromatic aberration and a coma aberration are cancelled, respectively, and a beam is irradiated on a sample at a tilt angle of 10° or more. This technology is applicable also to a focused ion beam apparatus. Patent Literature 1: JP-A-04-062748 Patent Literature 2: JP-A-2008-286652 Patent Literature 3: JP-A-2004-127930 As a result of extensive investigations about an application of focused ion beam processing, the present inventors have the following knowledge. The present inventors have considered that in a focused ion beam application such as thin film sample preparation and cross section observation during cross section processing, since a sample stage is not required to be tilted at a large angle, when a focused ion beam is tilted without tilting the sample stage, sufficient processing can be practically performed. To solve the above-described problem, although there is concern that beam convergence is reduced through the tilt of a focused ion beam, the present inventors have experimentally studied a method for performing thin film sample preparation or cross section processing by using a tilted focused ion beam. As a result, the present inventors have found that also in the case where a beam passes through out of an optical axis and it is tilted on a sample, when a tilt angle is small at nearly 1°, the nearly same processing shape as that at the time of tilting a sample stage is obtained only by adjusting an objective lens voltage. However, when a beam tilt function is actually mounted on the focused ion beam device, the control is required to be performed so as to set or adjust a tilt direction or tilt angle of a beam through an operator as well as so as to reproducibly set a beam tilt condition. Further, in the case where the focused ion beam device is used for thin film processing, an adjustment fails to be performed for each processing. Unless the tilted beam is set to be automatically selected, processing efficiency is not improved. An object of the present invention is to achieve a focused ion beam processing observation through an operation of an optical system in the same manner as in the case of mechanically tilting a sample stage. The present invention relates to control over an aperture in a focused ion beam optical system, a tilting deflector, a beam scanner, and an objective lens, and further irradiation of an ion beam tilted to an optical axis of the optical system. According to the present invention, thin film processing or cross section processing can be achieved without an adjustment or operation for a sample stage. In an embodiment, disclosed is a focused ion beam device including a sample stage which mounts a sample, an ion source which discharges an ion beam, a aperture which narrows down the ion beam discharged from the ion source, a tilting deflector which deflects the ion beam passing through the aperture, a beam scanner which scans the ion beam passing through the tilting deflector, an objective lens which irradiates the ion beam passing through the beam scanner on a sample, and a control device which controls the aperture, the tilting deflector, the beam scanner, and the objective lens. Further, disclosed is the focused ion beam device including the control device which allows the aperture to be moved out of an optical axis, the tilting deflector to deflect an ion beam in the same direction as the aperture is moved, the ion beam to pass through out of the optical axis of the objective lens, and the ion beam tilted to the optical axis to be irradiated on a sample. In the present embodiment, disclosed is the focused ion beam device including the control device which stores a combination of an aperture position, a tilting deflector voltage, an objective lens voltage, and a beam scanner voltage. In the present embodiment, disclosed is the focused ion beam device including a display device which displays a direction or/and incidence angle of a tilted beam. In the present embodiment, disclosed is the focused ion beam device in which a convergent point of a lens located upstream of the aperture is set within the tilting deflector. In the present embodiment, disclosed is the focused ion beam device including the control device which irradiates an ion beam tilted to the optical axis on a sample and prepares a thin film having a nearly uniform film thickness. In the present embodiment, disclosed is the focused ion beam device including the control device which irradiates an ion beam tilted to the optical axis on a sample and forms a cross section image from a secondary particle signal generated along with cross section processing of the sample. In the present embodiment, disclosed is the focused ion beam device including the control device which finishes cross section processing in the case where the formed cross section image satisfies a predetermined condition. In the present embodiment, disclosed is the focused ion beam device including the control device which changes a processing condition in the case where the formed cross section image satisfies a predetermined condition. In the present embodiment, disclosed is the focused ion beam device including the control device which irradiates an ion beam tilted to the optical axis on a sample and prepares a pillar sample having the nearly same tilt as that of a side surface of the sample. In the present embodiment, disclosed is the focused ion beam device including the control device which irradiates an ion beam tilted to the optical axis on a micro-sample and fixes the micro-sample and a fixed object by using a deposition film. In the present embodiment, disclosed is the focused ion beam device including the control device which irradiates an ion beam on a sample and prepares a cross section on the sample while changing a tilt angle of the ion beam to the optical axis. In the present embodiment, a processing observation method of a sample for use in the focused ion beam device including a sample stage which mounts a sample, an ion source which discharges an ion beam, a aperture which narrows down the ion beam discharged from the ion source, a tilting deflector which deflects the ion beam passed through the aperture, a beam scanner which scans the ion beam passed through the tilting deflector, an objective lens which irradiates the ion beam passed through the beam scanner on a sample, and a control device which controls the aperture, the tilting deflector, the beam scanner, and the objective lens, includes allowing the aperture to be moved out of an optical axis, the tilting deflector to deflect an ion beam in the same direction as the aperture is moved, the ion beam to pass through out of the optical axis of the objective lens, and the ion beam tilted to the optical axis to be irradiated on a sample. In the present embodiment, disclosed is a processing observation method of a sample for changing a tilt of an ion beam to an optical axis when a combination of an aperture position, a tilting deflector voltage, an objective lens voltage, and a beam scanner voltage is changed. In the present embodiment, disclosed is the processing observation method of a sample for displaying a direction or/and incidence angle of a tilted beam on a display device of the focused ion beam device. In the present embodiment, disclosed is the processing observation method of a sample for setting a convergent point of a lens located upstream of the aperture within the tilting deflector. In the present embodiment, disclosed is the processing observation method of a sample for irradiating an ion beam tilted to the optical axis on a sample and preparing a thin film having a nearly uniform film thickness. In the present embodiment, disclosed is the processing observation method of a sample for irradiating an ion beam tilted to the optical axis on a sample and forming a cross section image from a secondary particle signal generated along with cross section processing of the sample. In the present embodiment, disclosed is the processing observation method of a sample for finishing cross section processing in the case where the formed cross section image satisfies a predetermined condition. In the present embodiment, disclosed is the processing observation method of a sample for changing a processing condition in the case where the formed cross section image satisfies a predetermined condition. In the present embodiment, disclosed is the processing observation method of a sample for irradiating an ion beam tilted to the optical axis on a sample and preparing a pillar sample having the nearly same tilt as that of a side surface of the sample. In the present embodiment, disclosed is the processing observation method of a sample for irradiating an ion beam tilted to the optical axis on a micro-sample and fixing the micro-sample and a fixed object by using a deposition film. In the present embodiment, disclosed is the processing observation method of a sample for irradiating an ion beam on a sample and preparing a cross section on the sample while changing a tilt angle of the ion beam to the optical axis. The above-described and other new features and effects will be described later with reference to the drawings. Each embodiment can be arbitrarily combined and the combination form is also disclosed in the present specification. In the present embodiment, thin-film processing using a tilted beam will be described. FIG. 1 is a configuration diagram illustrating a focused ion beam optical system according to the present embodiment. The focused ion beam optical system mainly includes an ion source 1, a condenser lens 2, an aligner 3, a movable aperture 4, a tilting deflector 5, a blanker 6, a beam scanner 7, an objective lens 8, and a sample stage 9. In this focused ion beam optical system, the tilting deflector 5 is the same deflector of eight-pole structure as the aligner, and can deflect an ion beam in an arbitrary direction. FIG. 2 is a control system diagram illustrating the focused ion beam optical system. While observing a sample by using an image display device 11 using as an input signal a secondary electron detector 19, an operator performs a device operation through a control computer 12. During the normal observation or processing, a beam fails to have an intermediate convergence point 10 between a condenser lens and an objective lens. However, when selecting a tilted beam, the operator elevates a condenser lens voltage more than a voltage at normal times, and subjects a beam to an intermediate convergence within the tilting deflector 5. The operator allows a movable aperture drive mechanism to be operated, staggers an aperture hole of the movable aperture 4 in the direction in which a beam is tilted from the optical axis, and changes an incidence angle to the objective lens by using the tilting deflector 5. A moving amount of an aperture and setting of tilting deflector voltage in the tilted beam depend on a tilt angle. In the present embodiment, fundamentally, an adjusted value is stored in the control computer 12 and its registration value is reproduced, based on an adjustment procedure described later. A first step of adjusting the tilted beam is to adjust a condenser lens voltage and match an intermediate convergence point of the beam with an interior portion of the tilting deflector. For that purpose, the following matters are performed. While operating the tilting deflector in a level of ±10 V and 1 Hz, the objective lens voltage is adjusted so that a secondary electron image fails to move. Thereafter, the condenser lens voltage is adjusted and a focus is matched with the sample. Through this operation, a beam locking condition in which even if a voltage is imposed on the tilting deflector, an irradiation position on the sample fails to move can be achieved. Under this state, a sample stage is operated and a feature object or mark in which an irradiation position can be identified is set. A second step is to stagger the aperture hole of the movable aperture from the optical axis. An optimal distance for staggering the aperture hole is determined by a tilt angle for cancelling an aberration. Since an optimal distance with respect to a tilt angle (to 1°) for practical use is larger than a radius of a beam irradiation range on the movable aperture, it may be set in nearly 50% of the radius in the beam irradiation range. FIG. 4 illustrates a positional relationship between the beam irradiation range 21 on the aperture plate 20 and the aperture opening 22. As compared with a position of the aperture plate in normal use illustrated in FIG. 3, the aperture opening 22 of FIG. 4 is shifted from a position of the optical axis indicated by a cross-shape. In the case where a plurality of tilted beams having different tilt directions and angles are defined, a shift distance or direction of the aperture needs to be determined, respectively. After determining a position of the aperture opening of the tiled beam, while changing the objective lens voltage by nearly several volts, a secondary electron image is observed and a moving direction of the image is confirmed to be matched with a direction desired to tilt a beam (FIGS. 6 and 7). In the case where the moving direction of the image is not matched with a direction (here, a down direction of the image) desired to tilt a beam, a direction in which the feature object 26 of the image moves is not parallel to a direction to tilt a beam as illustrated in FIG. 6. In this case, the aperture position is mechanically adjusted and the moving direction of the image is allowed to be matched with the direction desired to tilt a beam as illustrated in FIG. 7. An aperture moving mechanism mounted on this device is two-axis driving and has a location accuracy of 1 μm or less in each axis. The aperture moving mechanism preferably has a location accuracy in a level of a diameter in the aperture opening to be used. As illustrated in FIG. 5, when a aperture plate in which an aperture is provided in a previously staggered position is used, a drive mechanism of two axes need not be used. Since a beam blurring in the tilt direction becomes large at the time of the tilt, the aperture may have not a perfect circle but an elliptical shape being flat in the tilt direction. A third step is to measure a tilt angle of a beam and set a deflection voltage of the tilting deflector. To the tilting deflector, a deflection voltage is applied in the range of passing through an electrode hole of the objective lens, and an objective lens voltage is changed by several volts. Through the process, a focusing position changes, and at the same time, the secondary electron image moves. As typically illustrated in FIG. 8, when a value of a change 33 in a focusing height due to a change in the lens voltage is set as ΔZ and a value of a shift 34 of the image is set as ΔY, a tilt angle θ of a beam is represented by tan θ=ΔY/ΔZ. A voltage of the tilting deflector is adjusted so as to acquire a value of necessary θ. When a changing rate (dZ/dV) of a focusing distance to the objective lens voltage is previously measured and a focus variation rate is previously calculated at the time of changing the objective lens voltage by a steady value, the deflector voltage can be determined based on a length measurement of a shaped width in the secondary electron image. Even when a voltage of the tilting deflector is set just as a position of the aperture opening is finely adjusted, a tilt direction is confirmed while changing the objective lens voltage. For the purpose of cancelling an aberration, a deflection direction of the tilting deflector and a shift direction of the aperture opening are the same as each other, and further an adjustment may be required due to an error of the aperture mechanism or alignment. When the aperture position is present on the optical axis, a tilt angle T increases proportionally to a voltage Vt of the tilting deflector. In the case where the aperture position is displaced from the optical axis, since failing to originally pass through a center of the objective lens, the beam is tilted. For this purpose, when the beam is deflected by using the tilting deflector as illustrated in FIG. 9 and it passes through near the center of the lens, the tilt angle becomes equal to nearly zero. At the final step, the objective lens voltage is adjusted so as to bring a beam into focus most in a tilted state, and a correction voltage for shifting an image is calculated so as to return the mark set on the sample at a first step to an original position on the screen. Since the objective lens voltage to be adjusted is necessarily lower than that at the time of vertical incidence, a value of ΔVo is negative. As illustrated in FIG. 9, an absolute value is nearly proportional to a square of the tilt angle. This fact is set as a function of the tilt angle, or registered in a control system as a table for control. Much the same is true on a position correction shift voltage. Since an incident point on the lens is not changed in this shift, it is performed not by the tilting deflector but by the beam scanner 7 (FIG. 1). The focus voltage in the case where the tilt angle is small is not nearly changed with that at non-tilting time, and therefore the focus voltage need not be changed. Or alternatively, in the case where a beam cannot be skillfully brought into focus only by the adjustment of the objective lens voltage, an astigmatism corrector may be used. With that, the tilted beam can be adjusted. A condenser lens voltage, coordinates of a aperture drive mechanism, a tilting deflector voltage, an objective lens voltage, a correction shift voltage, and an astigmatism correction voltage are one combination of registration values, and stored in a control computer. Here, the adjustment of an aligner axis is supposed to be performed at the time of normal beam adjustment before registration of the tilted beam. For the purpose of performing finish processing of a thin film prepared in the screen horizontal direction, the tilt of ±2° is performed in the vertical direction (Y direction) of the image. Therefore, two beams of +2° and −2° are adjusted by using an acceleration voltage 30 kV and registered. The aperture diameter is 30 μm, a shift distance from the optical axis is ±150 μm, and the tilting deflector voltage is +10.20V and −10.35V in the Y direction, respectively. With regard to the objective lens voltage, any of the tilted beams of ±2° are set lower by 30V than that of the non-tilted beam. It is oddly considered that absolute values of the deflection voltages of the same tilt angle are different from each other. However, it is considered that an error of an optical system alignment is included. In the focused ion beam device according to the present embodiment, beam conditions of different incidence angles can be registered by using the same acceleration voltage or aperture. To avoid a mixed use, registration conditions are clearly discriminated on the software by using GUI (FIG. 10). A displayed selection menu 40 of the beam conditions includes an acceleration voltage, an X direction tilt angle, a Y direction tilt angle, and a aperture opening diameter. T represents a tilted beam. For example, 30 kV−T(0°, +1°)−30φ represents that a tilted beam of an acceleration voltage 30 kV is tilted by +1° in the Y direction and a variable aperture of diameter 30 μm is selected. As compared with a normal beam having no intermediate convergence point, the tilted beam has a high current density on the variable aperture, and therefore the tilted beam is several times as large as the normal beam in a beam current and a processing speed is fast even in the same aperture diameter. Accordingly, this discrimination is preferably cleared. In even the tilted beam, the tilt angle can be set to 0°, and FIG. 11 illustrates a screen in which the beam is selected, a secondary electron image is taken in, and setting of thin film processing is performed. When the tilted beam is selected so as not to mixedly use the tilted beam and the vertical beam, the registered beam direction and absolute value of the tilt angle are screen-displayed on a captured screen of the secondary electron image by an arrow 44 and a value 45. Note that since an observation may be interrupted, these displays can be set to nondisplay as an optional extra. In the case where processing is performed by using the normal beam, the setting of combining it with a slant shift of a stage is required. In this case, since the beam is tilted, a stage tilt is not required. In a processing registration through the tilted beam, an image is actually captured by using the tilted beam and a shape of a processing area designation graphic 41 is determined on the image. Since a side surface part of a thin wall to be processed can be aimed and a processing area can be disposed, a failure in which an upper part of the thin film is sputtered and broken is small. In addition, the tilted beam with a large beam current has a large merit in terms of a throughput. Since an image recognition fails to receive an influence due to a tilt angle of 2°, automatic processing can be performed by using a position correction mark 42. Since the stage is not moved, a previous adjustment of eucentric tilt is not required. An influence such as a displacement and beam blurring is exerted due to a displacement of a sample height. However, there is no problem in the range of ±2 μm and the tilted beam can be used in the same manner as in the normal vertical beam. FIG. 14 typically illustrates a cross section shape 51 of a thin film through the tilted beam 50. A thin film having a uniform film thickness can be prepared in the same manner as in the time of tilting the sample stage. A reference numeral 53 of FIG. 15 denotes a cross section shape at the time of performing processing by a non-tilted beam 52, and since a lower part is thick, it fails to transmit an electron at the time of TEM observation. According to the present embodiment, provided is the focused ion beam device in which since an optical condition of beam tilt can be reproduced in a necessary case and a tilt direction and angle can be displayed, a processing condition is easily confirmed, a formation condition of a tilted beam is simply adjusted, and working efficiency is high. According to the present embodiment, when a beam is tilted and thin film processing is performed, a taper shape due to beam flare is eliminated, thin film processing of a nearly vertical shape is performed without tilting a sample, and a sample having preferable transmissivity of an electron beam and a uniform film thickness is easily prepared. In the present embodiment, cross section processing in which an analysis through a cross section SEM image is automatically started from a desired cross section is performed by using a tilted beam. Hereinafter, the second embodiment will be described with a focus on a difference from the first embodiment. A cross section image during processing using an ion beam is conventionally acquired from an image stretch. As illustrated in FIG. 16 by an arrow, however, since an incidence angle θ (an angle to an observation sample surface) is small in the vertical beam, an irradiation range of beams is stretched to 1/sin θ times on the cross section and resolution in the tilt direction is largely reduced. In the case where the cross section image is pattern-recognized, reliability is low. However, when a processing beam 60 is slightly tilted, the resolution of a decompression cross section image is largely improved (b). The reason is that θ with respect to the tilted beam 61 is several times as large as θ (≈0) with respect to the vertical beam. Using the above, a process in which an end point of cross section processing is automatically detected by using pattern recognition and a cross section SEM observation is performed will be described with reference to FIG. 18. Images (a), (b), . . . , (f) illustrate structures in which a cross section is viewed from a vertical direction, and images (a′), (b′), . . . , (f′) illustrate cross section images obtained by stretching secondary electron signals obtained by the tilted beam. In the case where a cross section analysis of a defective plug 63 illustrated in FIG. 18A is performed, a plug 64 having similar shapes is manually subjected to cross section processing and a reference image (FIG. 18B′) is acquired through the tilted beam. Thereafter, while slice processing in which a cross section is gradually trimmed automatically is advanced, the cross section image is periodically captured by using the tilted beam, matched with the reference image, and a score is calculated. As a result, the score indicates a behavior illustrated in FIG. 19. When advancing the processing, the score increases at the time when a similar cross section shape (e′) appears, and as a result it can be determined that the processing reaches a desired cross section. When a plug unit appears at the cross section, the score gradually decreases and, when an upper wiring part 65 is eliminated, it is drastically reduced. Here, the control is performed through a flow in which a threshold Sth is set, when a cross section image larger than Sth is detected in the score (here, from matching of NO-th cross section image), the processing is finished, and capturing of the cross section SEM image is started (FIG. 21). The setting of processing termination conditions of this device is performed through an interface of FIG. 20. The capturing of the reference image through the tilted beam, the setting of the threshold, and an interval of a cross section image capturing through the tilted beam can be set on this screen. Processing in which a comparison range is limited to a part of the cross section images can be performed. In this device, this setting screen belongs to a cross section processing step and the setting of capturing analysis of the cross section SEM is performed on another setting screen. Further, when the process is continuously performed, information such as a cross section processing position is transferred. As a result, a capturing process of the SEM image can be limited only to the vicinity of an analysis point. As a trigger for starting the capturing of the cross section SEM image, since a score value has large variation, a method for counting a local maximal point or local minimal point in which a moving average of the score is taken is also effective. Further, also in the case where a plurality of similar structures of semiconductor devices are used, any one of them can be specified to start an analysis. Since processing is advanced also during the capturing of images through the tilted beam, control switching of the focused ion beam and the SEM, and processing interruption during the capturing of images can be avoided and a processing time can be shortened. Since unnecessary data is not captured, the accumulated amount of image data is also reduced. Using as a trigger a matching score, an adjustment for changing a current value of an ion beam or processing conditions and a pretreatment for manually performing an analysis can be also automated. According to the present embodiment, when a beam is tilted and an image is scanned on a cross section, resolution on the cross section can be improved, pattern recognition whether a necessary shape appears can be made, and processing control can be easily automated. In the present embodiment, described is an example in which a beam tilt function is applied to a step of sequentially repeating FIB processing and cross section SEM observation and measuring a structure within a semiconductor in the FIB-SEM. Hereinafter, the third embodiment will be described with a focus on a difference from the first and second embodiments. The measurement according to the present embodiment is performed to a wafer sample of 300 mm. A warpage is easy to be generated in a wafer of large diameter and a normal direction on a sample surface is not matched with a processing cross section through the FIB in many cases. Accordingly, a correction is required at the time of reconstructing a three-dimensional structure from a cross section image. FIG. 22 illustrates a cross section SEM image at the time of performing preliminary cross section processing. It is seen from FIG. 22 that a junction between a lower wiring layer 72 and an interlayer wiring layer 71 is already processed and eliminated and the cross section is not correctly matched with the laminate direction of the device as compared with a case where a portion near an upper wiring layer 70 of the interlayer wiring layer 71 is left. Therefore, a processing beam is tilted from a vertical direction by 0.5° to perform processing, and as a result, the above phenomenon is not viewed as illustrated in FIG. 23. The reason is considered that as illustrated in a schematic diagram of FIG. 24, a cross section 76 is tilted through processing using the tilted beam 77 and matched with the device laminate direction. In this case, when the three-dimensional structure is reconstructed from a cross section observation image of the SEM, this 0.5° is added. In the present embodiment, a sample is supposed to be tilted. It is considered that a beam is actually tilted and made incident due to an alignment error of the FIB optical system or an assembling axis deviation error of an electrostatic lens electrode. Also in such a case, the correction can be similarly performed by setting the tilt angle. When a taper angle becomes large on only one surface of thin film samples as a defective case, the correction is effective. In the present embodiment, described is an example in which a beam tilt function is applied to preparation of a pillar sample used at the time of three-dimensionally measuring a device structure by using a transmission electron microscope. Hereinafter, the fourth embodiment will be described with a focus on a difference from the first to third embodiments. FIG. 25 illustrates an example in which when a aperture is two-dimensionally moved around the optical axis, a pillar sample is prepared. The pillar sample 80 is used at the time of three-dimensionally measuring a device structure by using a transmission electron microscope. In order that a vision may be made the same as each other at the time of rotating the sample on a fixed sample surface at the center of the vertical axis, a finishing angle of each surface of the column is required to be kept the same as much as possible. When the processing is performed while going to and from the transmission electron microscope and the focused ion beam device, the sample is preferably placed on a side entry stage holder capable of rotating the sample. However, a rotary sample holder 81 has angle accuracy of only nearly ±3° in a rotational transfer. In terms of precision, it is extremely difficult to perfect four surfaces through the rotation to the tilt. Accordingly, while tilting the rotary sample holder, the processing is performed only in the vertical direction (Y direction), and the surfaces in the horizontal direction are perfected changing the tilt direction of the beam. Here, the beam of ±1° in the X direction is previously registered and a processing area designation graphic 84 of finish processing of each surface is set on the image of the tilted beam as illustrated in FIGS. 26 and 27. As a result, a taper is not present also on a surface in the horizontal direction in which the stage fails to be tilted, and therefore a nearly vertical surface can be formed. A tilted beam can be used for other processing in addition to sputtering. In the present embodiment, an example in which a focused ion beam deposition is used will be described with a focus on a difference from the first to fourth embodiments. Referring to FIGS. 28 and 29, described is an example in which a micro-sample 90 picked out from a substrate is stuck and fixed on an electron microscope sample holder 91 by using focused ion beam deposition. A bottom part is separated from the substrate by using the tilt of the sample stage, and the micro-sample 90 is fixed on the probe 95 by using the deposition. Thereafter, a junction between the micro-sample 90 and the substrate is cut off through sputtering and the micro-sample 90 is moved onto the sample holder after taking up the probe. As illustrated in the drawing, an upper part of the above-described prepared micro-sample is thick and wedge-shaped. A thin edge part being a lower part of this micro-sample is stuck and fixed on a top surface or side surface of the electron microscope sample holder 91 by using the focused ion beam deposition. Since a bottom end of the micro-sample has no simple shape, whether the bottom end is contacted with the holder is not clearly seen in many cases through a scanning ion microscope image (SIM image) obtained by scanning a non-tilted focused ion beam. When the sample is stuck and fixed by using the deposition, the deposition film 92 may fail to be continued and stuck as illustrated in FIG. 28. However, when a tilted beam 96 is used at this sticking step, a beam is irradiated on the bottom end of the micro-sample with high accuracy. As a result, wrap-around of the deposition film 92 can be more effectively performed and yield can be improved. In the present embodiment, an incidence angle of a focused ion beam at the time of cross section finish processing is changed for each frame in a direction parallel to a surface. The surface is finished so as to make an observation cross section flat, and a cross section measurement is easy to be performed. Hereinafter, the sixth embodiment will be described with a focus on a difference from the first to fifth embodiments. FIG. 30 illustrates a processing area designation graphic 100 of the secondary electron image observed from the upper part. A beam is raster-scanned for a finish cross section 101 with a main deflection being set as a long side direction of the processing area designation graphic 100. The tilt angle of beams is alternately changed to +2° and −2° in the horizontal direction for each frame. This is performed for each frame by switching a voltage of the tilting deflector on the objective lens to only an objective lens voltage. Since the tilt direction of beams changes, convergence of the beam can be improved in the case where a position of the aperture opening is also shifted in the horizontal direction as described in the optical system according to the first embodiment. In the finish processing, the scan is fast with a frame time being about 0.5 sec, and when a waiting time in which a aperture position is mechanically changed is added to a processing time, the processing time is several times as long as the frame time. Therefore, only the deflection voltage and objective lens voltage to be switched over a short amount of time are switched. A beam largely becomes blurry in the tilt direction, namely, in the direction parallel to the finish cross section 101, and has a flat shape; however, an influence is small because of the finish processing. As illustrated in FIG. 31, since the incident direction is alternately changed, linear processing traces (steps 104) are formed through the reflection of the structure 105 in the upper part of the cross section in the case where processing is performed by using a non-tilted beam. As illustrated in FIG. 32, the processing traces are averaged and become blurry as in a reference numeral 107, and as a result the cross section observation is easy to be performed. As in a holography thin film sample necessary for extremely high flatness, this method can be applied also to a case where there is a problem that noise of D/A conversion is overlapped and input. According to the present embodiment, thin film processing and cross section processing using a focused ion beam can be automated, and yield can be improved. For example, when the present invention is applied to a cross section monitor to detect an end point, the cross section processing can be easily automated. 1 Ion source 2 Condenser lens 3 Aligner 4 Movable aperture 5 Tilting deflector 6 Blanker 7 Beam scanner 8 Objective lens 9 Sample stage 10 beam crossover 11 Image display device 12 Control computer 13 Condenser lens power supply 14 Two-axis aperture drive mechanism 15 Tilting deflector power supply 16 Blanker power supply 17 Beam scanner power supply 18 Objective lens power supply 19 Secondary electron detector 20 Aperture plate 21 Beam irradiation area 22 Aperture opening 23 Optical axis position 24 Beam tilt special aperture plate 25 Elliptical aperture opening 26 (on a sample) Feature object 30 Beam incident direction 31 Sample surface 32 Over-focus height 33 Change in focus height 34 Shift of image 40 Selection menu of beam conditions 41 Processing area designation graphic 42 Position correction mark 43 Thin film processing area 50, 61, 77, 96, 103 Tilted beam 51 Cross section shape of thin film 52, 94, 102 Non-tilted beam 53 Thin film through non-tilted beam processing 60 (non-tilted) Beam 62 Processing cross section 63 Defective plug 64 (nondefective) Plug 65 Upper conductive layer portion 66 Cavity within defective plug 70 Upper conductive layer 71 Interlayer conductive layer 72 Lower conductive layer 73 Surface protection film 74 Insulation film 75 Window open processing 76 Angle-corrected cross section 80 Pillar sample 81 Rotary sample holder 82 Tilt direction 83 Rotation direction 84 Processing area designation graphic 90 Micro-sample 91 Electron microscope sample holder 92 Deposition film 93 Gas nozzle 95 Probe 100 Processing area designation graphic 101 Finish cross section 104 Step 105 Upper structure 106 Lower structure 107 Averaged processing trace |
|
summary | ||
description | The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/415,680 filed on Oct. 3, 2002, which is assigned to the assignee of the present application and incorporated herein by reference. The present disclosure relates to a Potter-Bucky device for use in a radiation image recording apparatus, and more particularly to a Potter-Bucky device having a movable counter-weight arranged to reduce vibrations produced by a moving grid of the Potter-Bucky device. One of the most effective ways to reduce scattered radiation from an object being radiographed is through the use of a Potter-Bucky device. The Potter-Bucky device is used with most diagnostic x-ray equipment. More commonly known as a ‘bucky’, this is an assembly which is normally located under the table of a diagnostic x-ray set and holds the x-ray film cassette and a secondary radiation grid. The grid is used to prevent secondary x-ray emission from the patient from reaching the x-ray film, and is formed from a large number of thin strips of lead separated by a radiolucent material. To prevent the outline of the grid from appearing on the film, a mechanism is provided for rapidly moving the grid in a reciprocating manner during exposure. However there is a problem in that, though rapidly moving the grid prevents the outline of the grid from appearing on the film, rapidly moving the grid is also apt to transmit vibrations to other parts of the x-ray system. What is still desired, therefore, is a new and improved Potter-Bucky device for use with medical diagnostic imaging and scanner systems. In particular, what is desired is a new and improved Potter-Bucky device that prevents grid outlines from appearing on x-ray film, but transmits less vibrations to other parts of the x-ray system. The present disclosure provides a new and improved Potter-Bucky device for use with medical diagnostic imaging and scanner systems. The Potter-Bucky device is for a radiation image recording apparatus in which an image recording medium is exposed to radiation which has passed through an object in order to record a radiation image of the object on the recording medium includes a grid which is movably supported between the object and the recording medium and is reciprocated parallel to the recording medium. A counter-weight is connected to the grid and is reciprocated in synchronization with the grid but in an opposite direction. Among other features and advantages, a new and improved Potter-Bucky device constructed in accordance with the present disclosure reduces or eliminates the vibrations created by the moving grid of the device. The present disclosure also provides a method for moving a grid in a Potter-Bucky device. The method includes movably supporting the grid for reciprocating motion in a plane, positioning at least one movable cam adjacent the grid, moving the cam to cause reciprocating movement of the grid in the plane, and attaching a counter-weight to the grid for reciprocating motion in the plane in directions opposite the grid. Another Potter-Bucky device according to the present disclosure includes a frame, tracks secured to the frame, a first set of brackets slidably received in the tracks for supporting a grid, a second set of brackets slidably received in the tracks, a counter-weight secured to the second set of brackets, a drive pulley and an idler pulley secured to the frame, and a continuous belt extending around the drive pulley and the idler pulley such that the belt include first and second portions which move in opposite directions between the pulleys upon rotation of the drive pulley. The first set of brackets is secured to the first portion of the continuous belt and the second set of brackets is secured to the second portion of the continuous belt. The counter-weight reduces or eliminates vibrations created by reciprocating movement of a grid secured to the frame. The foregoing and other features and advantages of the present disclosure will become more readily apparent from the following detailed description of the disclosure, as illustrated in the accompanying drawing. Like reference characters designate identical or corresponding components and units throughout the several views. Referring first to FIG. 1, an exemplary embodiment of a Potter-Bucky device 10 constructed in accordance with the present disclosure is shown. The Potter-Bucky device 10 is for being positioned in a radiation image recording apparatus (not shown, but for example a computer tomography scanner) for exposing an image recording medium to radiation which has passed in a first plane through an object (not shown, but for example a patient lying over the Potter-Bucky device) to the recording medium in order to record a radiation image of the object on the recording medium. Among other features and advantages, the new and improved Potter-Bucky device 10 constructed in accordance with the present disclosure reduces or eliminates the vibrations created by a moving grid 12 of the device. The Potter-Bucky device 10 generally includes the grid 12, which is movably supported for reciprocating motion in a second plane extending parallel to the recording medium between the object and the recording medium, and a counter-weight 414 movably supported and operatively connected to the grid for reciprocating motion in the second plane in directions opposite the grid. A mass of the grid 12 is substantially equal to a mass of the counter-weight 14, and an inertia of the grid is equal to an inertia of the counter-weight during reciprocating motion. With this arrangement, the vibration caused by the displacement of the center of gravity of the Potter-Bucky device 10 due to the movement of the grid 12 is compensated for by the movement of the counter-weight 14, and accordingly, no vibration is transmitted to parts of the radiation image recording apparatus using the Potter-Bucky device. Although not shown in FIG. 1, the Potter-Bucky device 10 preferably includes at least one movable cam positioned adjacent the grid 12 for causing reciprocating movement of the grid in the second plane upon movement of the cam. Even more preferably, the cam is also arranged so as to also cause reciprocating motion of the counter-weight 14 in the second plane in directions opposite the grid 12. Although not shown in FIG. 1, the Potter-Bucky device 10 also includes at least one spring biasing the grid 12 against the cam and biasing the counter-weight 14 against the cam. FIG. 2 is a top plan view of another exemplary embodiment of a grid 22 and a counter-weight 24 of a Potter-Bucky device 20 constructed in accordance with the present disclosure. In the embodiment of FIG. 2, the cam comprises a single, rotatable, elliptical cam 26 positioned between the grid 22 and the counter-weight 24, so that rotation of the cam 26 causes opposing reciprocating motion of both the grid and the counterweight. Although not shown, the Potter-Bucky device 20 also includes a motor, such as an electric rotary motor, operatively connected to the cam 26 for causing rotary movement of the cam adjacent the grid 22. In the exemplary embodiment of FIG. 2, the spring of the Potter-Bucky device 20 comprises first and second helical compression springs 28, 30, and the grid 22 is positioned between the first spring 28 and the cam 26, and the counter-weight 24 is positioned between the second spring 30 and the cam 24. In effect then, the grid 22 and the counter-weight 24 are pushed together by the springs, 28, 30 and against the cam 26. FIG. 3 is a top plan view of a further exemplary embodiment of a grid 42 and a counter-weight 44 of a Potter-Bucky device 40 constructed in accordance with the present disclosure. In the embodiment of FIG. 3, the cam comprises two, rotatable, elliptical cams 46 positioned between the grid 42 and the counter-weight 44, so that rotation of the cams 46 causes opposing reciprocating motion of both the grid and the counterweight. Although not shown, the Potter-Bucky device also includes motors, such as electric rotary motors, operatively connected to the cams 46 for causing rotary movement of the cams adjacent the grid 42 and the counter-weight 44. In the exemplary embodiment of FIG. 3, the spring of the Potter-Bucky device 40 comprises a single helical tension spring 48 connected between the grid 42 and the counter-weight 44. In effect then, the grid 42 and the counter-weight 44 are pulled together by the spring 48 and against the cam 46. In the exemplary embodiment of FIG. 3, the grid 42 is shown movably supported by linear bearings 50. It should be understood, however, that a Potter-Bucky device constructed in accordance with the present disclosure can be provided with other types of supports for movably supporting the grid and the counter-weight for reciprocating motion. FIGS. 4 through 6 shown an exemplary embodiment of a portion of a Potter-Bucky device constructed in accordance with the present disclosure and including a frame assembly 100 for supporting a grid (not shown), wherein the frame assembly includes a counter-weight 102 for reducing or eliminating vibrations created by a grid mounted to the frame assembly 100 and moving in a reciprocating manner on the frame assembly 100. The frame assembly 100 includes a frame 104, tracks 106a, 106b secured to the frame, a first set of brackets 108a, 108b slidably received in the tracks 106a, 106b for supporting a grid, and a second set of brackets 110a, 110b, 110c slidably received in the tracks 106a, 106b. The counter-weight 102 is secured to the second set of brackets 110a, 110b, 110c, as shown best in FIG. 4. The frame assembly 100 also includes a drive pulley 112 and an idler pulley 114 secured to the frame 104, and a continuous belt 116 extending around the drive pulley 112 and the idler pulley 114 such that the belt 116 is divided into first and second portions 116a, 116b which move in opposite directions between the pulleys 112, 114 upon rotation of the drive pulley 112. The one of the first set of brackets 108b is secured to the first portion 116a of the continuous belt 116 and the counter-weight 102 is secured to the second portion 116b of the continuous belt 116 (through clamp 118), such that the counter-weight 102 will move in reciprocating directions opposite a grid secured to the first set of brackets 108a, 108b. The counter-weight 102 reduces or eliminates vibrations created by reciprocating movement of a grid secured to the frame assembly 100. As shown, best in FIG. 6, the frame assembly 100 also includes a reversible motor 120 connected to the drive pulley 112 for causing reciprocating movement of the belt 116. It should be further understood that the embodiments of the present disclosure described herein are merely exemplary and that a person skilled in the art may make variations and modifications to the embodiments described without departing from the spirit and scope of the present disclosure. For example, other types of cams and springs can be used with a Potter-Bucky device constructed in accordance with the present disclosure. All such equivalent variations and modifications are intended to be included within the scope of this disclosure as defined by the appended claims. |
|
059094753 | description | DETAILED DESCRIPTION The basic technology for spent fuel containers in use today can be described using a convenient schematic drawing, i.e. FIG. 1. With the goal of storing spent fuel in the form of elongated rods the basic unit of the container is an elongated tube. Tubes are typically grouped in tubular assemblies, collectively the spent fuel basket, such as the assembly 11 shown in FIG. 1, and the basket is placed within a container 12. The container 12 is cylindrical in cross section for maximum strength. The tubes in the basket 11 may be circular in cross section, or may have a square or rectangular cross section and are packed to maximize storage efficiency. In the prior art the basket 11 has been made in a variety of configurations to optimize the space within the cylindrical container. The structure and composition of these tubes and tube assemblies is known in the art and is described, for example, in U.S. Pat. No. 4,827,139 issued May 2,1989. It is also known that such prior art tube assemblies are expensive to construct. The basket assembly of the invention eliminates the elongated tubes, reduces costs and is constructed in a novel and efficient way as will be described in conjunction with FIGS. 2-7. As will be appreciated as this description proceeds there is an important distinction between the tubes typical of the prior art, and what we believe are more aptly described as compartments in the structure to be described. In the usual multi-tube array, there are two tube walls separating the individual storage sites, and there typically is a gap or void between at least portions of these walls. By contrast it will be seen that the individual storage sites in the structure of this invention are separated by one wall thus eliminating the potential for gaps or voids between storage sites. Because of the significance of this difference, as will become more apparent below, the individual storage sites will be referred to as compartments rather than tubes, and the storage array that is formed as the result of the new structure will be termed a compartmented array rather than a tubular array. With reference to FIG. 2 the container, designated generally 20, is shown in an end view similar to the view seen in schematic FIG. 1, with the compartmented assembly shown generally at 21, the compartments shown at 22, and the outer casing shown at 23. The lateral extensions of the compartmented assembly are shown at 42. The construction of the compartmented assembly may be more fully appreciated with reference to FIGS. 3 and 4. The structure is modeled after what we term the egg crate principle. The interlocking design is in the form of an x-y grid and is shown in perspective in FIG. 3. Three comb members 32 in the x-dimension and three comb members 33 in the y-dimension form the interlocking unit as shown. While three comb members, forming four compartments 34, are shown in this schematic diagram an actual compartmented assembly could have more comb members in each dimension, or even a different number in each dimension. Since the container is typically cylindrical an equal number of comb members in each dimension is most efficient, and at least four such members in each dimension gives a reasonably useful number of compartments. The comb members may be similar in overall shape, or may have different shapes and dimensions to accommodate different compartmented assembly designs. For cost considerations, the comb members are similar in design. A front view of one of the comb members 32 is shown in FIG. 4 and consists of comb portion 41 and radial tab portions 42. The radial tab portions correspond to the lateral extensions shown at 42 in FIG. 2. The interlocking units 31 of FIG. 3 are stacked to form continuous elongated storage compartments in the manner shown in FIG. 5. FIG. 5 is a sectional view through A--A of FIG. 2. FIG. 5 shows five interlocking units (shown cutaway from a larger stack for simplicity) stacked in a vertical, i.e. z-dimension. The bottom of the stack is sealed with end plate 51. It will be evident that the use of x-,y-, and z-dimensions is for convenience in providing a clear description of the invention and that the container can be oriented in any dimension during manufacture and use. The intermediate metal shell is formed with the shell end plates 62 shown in FIG. 6, and the shell corner plates 71 shown in FIG. 7. The compartmented array is assembled by inserting the radial tab portions 42 of the interlocking units 31 through the slots 61 of four shell end plates 62, then completing the intermediate shell by fastening, e.g. welding, the corner plates 71 to the end plates 62. The completed compartmented assembly appears in the x-y plane as in FIG. 2. A notable feature of the container of this invention includes the absence of thermal barriers to heat flow from the center of the container to the exterior wall of the container. The result of the absence of gaps or voids between the compartments, as mentioned earlier, is a continuous thermal path from any given compartment to the exterior of the container. In fact there are multiple thermal paths to the exterior from any point in the compartmented array. This is due to the combination of interlocking plates, i.e. an integral compartmented array, and the thermal connection between the plates and the exterior container wall that is afforded by the lateral extensions of the plates. This principle can be implemented in a variety of structures as will be discussed in more detail below. Typical details for the design and construction of a spent fuel container according to the invention will be given in the context of the embodiment shown in FIGS. 2-7. It will be understood that this embodiment, while preferred, is exemplary of many possible structures incorporating the principles on which the invention is based. The individual comb plates shown in FIG. 4 may be manufactured by milling the slots 43 in a sheet of steel of the desired thickness, e.g. a 3/4 inch ferritic steel plate. Alternatively the plate may be of stainless steel or other appropriate material. Stainless steel is considerably more expensive and is a less efficient heat conductor so we prefer to use a coated ferritic steel. An aluminum flame-spray can be applied to the comb plates during their production, with any weld areas masked off to prevent weld contamination. Flame-spray techniques and appropriate masking procedures are well known in the art. The plate is in the shape of a slat, having in this embodiment a thickness of 3/4 inch as just mentioned, a nominal width of 12" and a length of 84". The length of the tab extensions, or radial heat sinks, 42 is 18", and the slots are 3/4".times.6" slots spaced at 9". As will be evident from FIG. 2, the length of the tab extensions varies somewhat due to the curvature of the surface of the outer casing 23. The slats used in the other dimension, that interlock with those shown in FIG. 4, may be identical except that the slots 43 extend from the top edge of the slat. The slat structures in this embodiment look somewhat like a comb, hence the terminology "comb plate". With reference again to FIGS. 3 and 4, the plates 32 and 33 are similar as just described except that the slots extend from the bottom of comb plates 32 and from the top of comb plates 33. If desired the plates 32 and 33 can be identical, i.e. symmetrical, if the tabs extend from the middle of the comb section of the plate. The individual comb plates are assembled similarly to an egg carton and may be spot welded, or full welded, where the plates join. However, a significant advantage to the construction technique of this invention is that the interlocking of the comb units gives sufficient structural integrity, and provides sufficient heat flow, that welded joints are not necessary. This results in a significant cost saving. The resulting interlocking grid units are then stacked as shown in FIG. 5, in this embodiment to a height of 160". The four end plates 62 in FIG. 6 are milled with slots 61 to receive the tab extensions 42 of the comb plates. The slots 61 are spaced so the interlocking grids 31 (FIG. 3) are just touching. It will be appreciated that while the tab extensions 42 are shown in this embodiment with approximately half the plate width the tabs can have any desired width, but preferably less than the plate width. As an alternative, a continuous slot could be used, extending nearly the full length of end plate 61, in place of the multiple slots 61, and thus accommodate grids with tabs having the full width of the plates. The welding of the ends of the radial tab extensions to the end plates can be performed from the exterior of the assembled basket. This facilitates access with a welding torch. The weld between the extensions of the comb plates and the exterior container must be structural but need not be full penetration. A partial penetration weld, combined with a fillet weld will give adequate strength and facilitate welding and dye penetrant weld inspection of the root and final weld passes. The bottom plate 51, shown in FIG. 5, is welded onto the bottom end of the finished container to close off the containment structure. The bottom end plate may be welded only at the outer periphery of the structure; there is no need to weld the interlocking grid assemblies to the bottom plate. After assembly of the interlocking grid units and the end plates, the corner plates 71 (FIG. 2) are added. The purpose of the corner plates is twofold: they act to stabilize the structure by connecting adjacent end plates, and they displace concrete from the final cask as will be evident after the next step. Alternatively, corner plates 71 can be omitted and the width of the end plates extended so they meet together to form an essentially square cross section as viewed in FIG. 2. The finished basket is prepared for concrete pour by installing reinforcing bars (rebar) in the circumferential and longitudinal directions. The rebar size is chosen to provide adequate structural strength for the finished cask, while maintaining a small enough diameter and sufficient spacing to allow the concrete aggregate material to pass between the pouring form and the basket wall. Superplasticizer may be added to the concrete mix to reduce the tendency to form voids in the concrete. Types of concrete, and mixing and curing methods, are well known in the art. Again, as known in the art, some aggregates, e.g. aggregates high in iron content, are preferred over others due to higher gamma radiation cross section. Insulating material may also be applied to the basket exterior and to the comb plate tabs to prevent excessive temperatures in the concrete when the cask is placed in service. Insulation should be restrained to prevent dislocation during the pour. After concrete pour, the concrete is allowed to cure. The concrete pouring forms are removed after the concrete has set up, and up to several weeks are allowed for a complete concrete cure. The thickness of the concrete layer of the cask, which corresponds generally to the length of the tab extensions on the interlocking grid assemblies (31, FIG. 3), is determined by the dose rate requirements for handling of the spent fuel cask during fuel loading and movement to the cask storage site. In the embodiment described above the concrete thickness is approximately 18". The outer casing 23 of the container is applied by plug-welding curved sections of steel to the comb plate tabs 42. The bottom plate is welded to these steel sections. These outer casing plates may have a thickness of typically 1/8 to 1/2 inch and may consist of stainless steel or other appropriate thermally conductive material. This outer casing represents a second containment vessel so that there are two air tight seals. In use, the spent nuclear fuel rod is loaded into each of the compartments, an inert gas such as helium or nitrogen is pumped into the container, and the container is sealed with a cover. The cover may be a thick, e.g. 7", steelcover that is gravity sealed, or sealed by other appropriate methods, onto the top of the container. In the structure of FIG. 2 the heat transfer members 42 are generally sufficient in number to be effective for the purposes described. However, if desired, additional radial heat transfer members can be provided. For example, additional radial members can be affixed between the corner plates 71 and the outer casing 23. Another cooling expedient is to extend radial members 42 through the outer casing and attach cooling fins to the outer ends of the radial members. If this expedient is properly implemented a wider choice for the material of the outer casing may be available, i.e. the thermal conductivity requirements of the outer casing are less important. For example, high strength, lightweight and non-corroding polymer materials may be used. In the preferred embodiment of FIGS. 2-7 the basket structure is described as an interlocking "egg crate" grid. However, still within the spirit of one important aspect of the invention, other types of grids can be used. According to this aspect of the invention a grid assembly similar to that appearing in FIG. 2, i.e. a grid assembly with radial thermal heat sink members, can be made by other techniques. For example, the compartmented geometry shown in FIG. 2 can be cast from an appropriate material such as steel, or a high strength, thermally conductive alloy. The use of casting as a method for making the basket assembly allows flexibility in the design of the basket. For example, a grid cross section like that shown in U.S. Pat. No. 4,827,139 can be easily cast. Other arrangements for space efficiency, like hexagonal close packed arrays, can also conveniently be implemented using casting techniques. The spent fuel cask may provide the entirety of the required radiation shielding itself, or it may be placed within a simple concrete structure that provides additional shielding. Such an additional structure, or overpack, may be ventilated to allow cooling air to remove heat from the cask. The spent fuel cask of the invention may also be inserted into a steel overpack for shipment to a central storage facility. The steel overpack provides additional puncture resistance and impact absorbing ability in transport. Various additional modifications of the invention as described here will occur to those skilled in the art. All such variations and deviations which basically rely on the teachings through which this invention has advanced the art are properly considered within the scope of this invention and equivalents thereof, as described herein and claimed in the appended claims. |
description | 1. Field This invention relates in general to light water nuclear reactors and in particular to an instrumentation system for monitoring in real time the temperature of the reactor coolant within the reactor coolant system piping. 2. Related Art The primary side of nuclear reactor power generating systems, which are cooled with water under pressure, comprises a closed circuit which is isolated and in heat exchange relationship with the secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel 10 having a closure head 12 (also shown in FIG. 2), enclosing a nuclear core 14. A liquid reactor coolant, such as water, is pumped into the vessel 10 by pump 16 through a cold leg 23 of the reactor coolant loop piping 20 to the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator, in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. At least one of those loops normally includes a pressurizer 19 connected to the hot leg 25 of the reactor coolant loop piping 20 through a charging line 21. An exemplary reactor design is shown in more detail in FIG. 2. In addition to the core 14, comprised of a plurality of parallel, vertical, co-extending fuel assemblies 22, for purposes of this description, the other vessel internal structure can be divided into the lower internals 24 and the upper internals 26. In conventional designs, the lower internals' function is to support, align and guide core components and instrumentation as well as direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies 22 (only two of which are shown for simplicity in this figure), and support and guide instrumentation and components, such as control rods 28. In the exemplary reactor shown in FIG. 2, coolant enters the reactor vessel 10 through one or more inlet nozzles 30, flows down through an annulus between the vessel and the core barrel 32, is turned 180 degrees in a lower plenum 34, passes upwardly through a lower support plate 37 and a lower core plate 36 upon which the fuel assemblies 22 are seated and through and about the assemblies. In some designs, the lower support plate 37 and the lower core plate 36 are replaced by a single structure, the lower core support plate, at the same elevation as the lower support plate 37. The coolant flowing through the core 14 and surrounding area 38 is typically large on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tend to cause the fuel assemblies to rise, which movement is restrained by the upper internals 26, including a circular upper core plate 40. Coolant exiting core 14 flows along the underside of the upper core plate 40 and upwardly through a plurality of perforations 42. The coolant then flows upwardly and radially to one or more outlet nozzles 44. The upper internals 26 can be supported from the vessel 10 or the vessel head 12 and include an upper support assembly 46. Loads are transmitted between the upper support assembly 46 and the upper core plate 40, primarily by a plurality of support columns 48. A support column is aligned above a selected fuel assembly 22 and perforations 42 in the upper core plates 40. The rectilinearly movable control rods 28 typically include a drive rod 50 and a spider assembly 52 of neutron poison rods 28 that are guided through the upper internals 26 and into aligned fuel assemblies 22 by control rod guide tubes 54. The guide tubes are fixedly joined to the upper support assembly 46 and connected to the top of the upper core plate 40. By inserting and withdrawing the neutron poison rods into and out of guide thimbles within the fuel assemblies within the core the control rods regulate the extent of the nuclear reactions within the core. Boron, dissolved within the reactor coolant water, also functions to control the nuclear reactions and manages more gradual changes in reactivity than the control rods. By varying the reactivity, the reactor operators can vary the temperature of the coolant within the core. In nuclear reactor instrumentation systems that are used to track the state of the nuclear reaction within the core, calculation of operating parameters, such as Over Pressure Delta Temperature and Over Temperature Delta Temperature (OPΔT/OTΔT) requires high accuracy temperature measurements. Reactor Coolant System (RCS) temperature measurements of fluid in hot leg 25 and cold leg 23 piping are typically accomplished by placing three resistance temperature detectors (RTD) 74 approximately 120 degrees apart around the pipe circumference 66, as shown in FIG. 3. (In other cases six RTDs are placed approximately 60 degrees apart.) The RTD elements 74 are placed in thermowells 76, which enable the RTDs to make physical contact with the coolant water through the thermowell metal interface, and protect the RTD from the impact of the flowing water. The RTD-thermowell interface basically acts as a thermo hydraulic filter. Conventionally, system temperature values are derived from sampling the three RTDs 74. The RTD signal is initially filtered in order to reduce process and electrical noise. After the initial filtering, streaming corrections based on the mixed mean temperature are performed. After initial filtering and adjustments for streaming, the three resulting signals are compared and, depending on the results, one of the signals can be discarded from downstream processing. Response time and accuracy of the mixed mean temperature determination are the two main challenges faced by the current RTD-based temperature measurement instrumentation. Typical response time is approximately 2 to 4 seconds. This response time is due to the thermodynamic properties of the RTD-thermowell interface. The response time from the RTD instrumentation is added to the overall system response time. The mixed mean temperature is a challenging parameter to measure with the current RTD instrumentation and, thus, accuracy in its measurement is difficult to achieve. The fluid in the reactor coolant system hot leg 25 and cold leg 23 is turbulent and not well-mixed, which causes large variations in coolant temperature. Instantaneous temperature differences in excess of 25 degrees F. exist within the hot leg as depicted in FIG. 4. This rapid temperature fluctuation is another source of error allowance needed. The RTDs 74 only measure temperature at discrete points within the turbulent flow which, as described before, can result in inaccurate, abrupt changes in measured temperature. The foregoing issues are overcome by a nuclear reactor system that provides a real-time measure of the mixed mean temperature of the reactor coolant at the sensor locations, comprising: a reactor vessel; a nuclear core including a plurality of nuclear fuel assemblies housed within the reactor vessel and immersed within a reactor coolant, the fuel assemblies structured to heat the reactor coolant; a primary coolant loop piping system in fluid communication with a heat utilization mechanism and the reactor vessel, for conveying the reactor coolant between the reactor vessel and the heat utilization mechanism and back to the reactor vessel; and an auxiliary piping system in fluid communication with the primary coolant piping for adding or extracting reactor coolant to or from the primary coolant loop piping system. An acoustic transmitter is acoustically coupled to a first location on an outer surface of either the primary coolant loop piping system or the auxiliary piping system and configured to transmit an acoustic pulse through the reactor coolant. Preferably, the acoustic pulse is a continuous signal of pulses. An acoustic receiver is acoustically coupled to a second location on an outer surface of the either of the primary coolant piping system or the auxiliary piping system that is substantially diametrically opposed to the first location, with the acoustic receiver configured to receive the acoustic pulse. An acoustic control system is connected to the acoustic transmitter and the acoustic receiver and configured to determine the time lag between the transmission of the acoustic pulse at the acoustic transmitter and the receipt of the acoustic pulse at the acoustic receiver and correlate the time lag to a temperature of the reactor coolant. In one embodiment the nuclear reactor system further includes a second acoustic transmitter acoustically coupled to a third location on the outer surface of the either of the primary coolant loop piping system or the auxiliary piping system and configured to transmit a second acoustic pulse through the reactor coolant; and a second acoustic receiver acoustically coupled to a fourth location on the outer surface of the either of the primary coolant piping system or the auxiliary piping system that is substantially diametrically opposed to the third location, with the acoustic receiver configured to receive the second acoustic pulse. In this latter embodiment, the acoustic control system is also connected to the second acoustic transmitter and the second acoustic receiver and is configured to determine a second time lag between the transmission of the second acoustic pulse at the second acoustic transmitter and the receipt of the second acoustic pulse at the second acoustic receiver and correlate the second time lag to a temperature of the reactor coolant. Preferably, the acoustic pulse is an ultrasonic pulse and the system includes a flow meter configured to measure the speed of the reactor coolant within the either of the primary coolant piping system or the auxiliary piping system and provide an output indicative thereof that is communicated to the acoustic control system, wherein the acoustic control system uses the output of the flow meter to compensate the temperature for changes in the speed of the reactor coolant. In another embodiment, the system includes a boron concentration meter configured to determine and provide an output indicative of the real-time concentration of boron within the reactor coolant, wherein the acoustic control system has an input from the output of the boron concentration meter to compensate the temperature for changes in a boron concentration within the reactor coolant. In one such arrangement, the either of the primary coolant piping system or the auxiliary piping system is a hot leg of the primary coolant piping system. In another such arrangement, the either of the primary coolant piping system or the auxiliary piping system is a cold leg of the primary coolant piping system. Preferably, the acoustic transmitter and the acoustic receiver comprise solid state vacuum micro-electronic devices and the acoustic transmitter and the acoustic receiver are powered by a thermoelectric generator having a hot junction in thermal communication with a wall of the either of the primary coolant piping system or the auxiliary piping system. Desirably, the thermal communication is through a heat pipe that extends through thermal insulation surrounding the piping and the thermoelectric generator is positioned outside of the insulation. Desirably, the transmitted pulse of the acoustic transmitter and the output of the acoustic receiver are connected to a wireless transmitter and the transmitted pulse from the acoustic transmitter and the output of the acoustic receiver are wirelessly transmitted to the acoustic control system. Preferably, the wireless transmitter comprises solid state vacuum micro-electronic devices. One preferred embodiment of this invention comprises employing several ultrasonic transmitters 56 and receivers 58 positioned 180 degrees apart around the circumference of the RCS hot or cold leg piping 25, 23, as shown in FIG. 5. A solid state vacuum microelectronic device signal driver 78 powered by thermo-electric generator (TEG) 68 sends a continuous ultrasonic signal through the pipe 23, 25, 21 and the water flowing through it. The thermoelectric generator 68 is in thermal communication with the pipe surface 66, with the hot junction of the thermoelectric generator supported outside of the pipe insulation 64 and in thermal contact with one end of the heat pipe 70. The other end of the heat pipe 70 extends through the insulation and is supported in thermal contact with the pipe surface 66. The signal received on the other side of the pipe by the ultrasonic receiver 58 is wirelessly transmitted by the wireless transmitter 60 to an acoustic control system 80 by way of a wireless receiver 62, at a base station elsewhere for post-processing. The speed of the signal traveling through the reactor coolant system pipe varies as the temperature of the water flowing through it changes; therefore, the temperature of the coolant flowing through the pipe is correlated to the speed of the signal. The preferred embodiment of the sensors, signal processing, and wireless transmission electronics devices utilize vacuum micro-electronic device based electronics and materials. The characteristics of these device based electronics and materials allow the critical features of these devices to be replaced by micro-scale vacuum tube technology having performance characteristics shown to be essentially impervious to radiation damage and very high temperatures. An application of the vacuum micro-electronic devices wireless transmitter technology is disclosed in U.S. Pat. No. 8,767,903, entitled “Wireless In-Core Neutron Monitor.” Such devices, known as SSVDs, are commercially available from Innosys Inc., Salt Lake City, Utah. An example of such a device can be found in U.S. Pat. No. 7,005,783. It must be noted that the speed of the ultrasonic signal might vary also due to the speed of the water flow in the pipe, therefore, the system will compensate accordingly for this variable. The average velocity of the coolant is determined from the average flow rate derived from the elbow tap ΔP measurements. Since the plants operate the pumps at a constant speed during power operations, this parameter will not influence the total measurements significantly. Nevertheless, in the interest of improving the accuracy of the temperature measurement, the outputs from existing coolant flow meters within conventional reactor systems can be used to compensate for this affect. Such a flow meter output can be wirelessly transmitted to the acoustic control system 80, as schematically represented by block 82 in FIG. 5. Similarly, changes in the boron concentration within the reactor coolant can affect the speed of sound through the coolant. A boron concentration meter, schematically represented by block 84 in FIG. 5, can be employed to wirelessly provide an output indicative of the boron concentration of the coolant, to the acoustic control system 80 to compensate the mixed mean temperature determination for changes in boron concentration. Any boron concentration meter cable of detecting the concentration of the boron in the coolant at the monitored location and transmit an output indicative thereof can be used for this purpose, though an example of such a meter can be found in U.S. patent Ser. No. 15/066607, entitled “Real-Time Reactor Coolant System Boron Concentration Monitor Utilizing An Ultrasonic Spectroscopy System,” filed concurrently herewith. Prior to the installation of the hardware, an Electro-Magnetic Interference (EMI) site survey is performed in order to identify potential sources of noise or interference. The transmission frequency for the wireless data transfer is chosen to occupy an unused frequency band at the RCS pipe location. The received measured signal is also filtered as needed in order to minimize electrical interference and other related issues impacting the accuracy of the transmitted signal. The DC power 72 required by the ultrasonic signal driver 78, ultrasonic signal receiver 58 and the wireless data transmitter 60 is generated via one or more thermoelectric generators 68 that have the heated junction connected to the heat pipe and the cold junction located on the opposite side of the pipe. It should be noted that the vacuum micro-electronic device ultrasonic signal hardware and wireless data transmitter can be powered by a conventional cable, if necessary. In the same way, measurement data could also be transmitted through conventional cabling. Typical Pressurized Water Reactors (PWRs) operate at 2,220 psig and 626° F. According to the N. Bilaniuk and G. S. K. Wong model from N. Bilaniuk and G. S. K. Wong (1993), Speed of Sound in Pure Water as a Function of Temperature, J. Acoust. Soc. Am. 93(3) pp 1609-1612, as amended by N. Bilaniuk and G. S. K. Wong (1996), Erratum: Speed of Sound in Pure Water as a Function of Temperature, [J. Acoust. Soc. Am. 93, 1609-1612 (1993)], J. Acoust. Soc. Am. 99(5), p 3257, the speed of sound in water is c=5,062.664 ft/s at 212.00° F. and 5,062.336 ft/s at 212.18° F. Using equation 1, the travel time of the signal can be calculated. t = d c equation 1 where d is the diameter of the pipe and c is the speed of sound in water at a specific temperature. A temperature change between 212.00° F. and 212.18° F. (temperature delta of 0.1° C.) in a typical 31 inch RCS pipe results in a speed of sound change of 0.328 ft/s, which results in a travel time change of 33 nsec. The base station receiving the signal employs an ultra-stable commercial off the shelf crystal oscillator clock at 1,000 MHz in order to distinguish a 33 nsec change in the time of receipt of the signal. By using the above described instrumentation and methodology, two important characteristics are improved compared to conventional systems. The first involves the mixed mean temperature accuracy. The fact that the flow is not well mixed in the RCS piping will not affect the type of instrumentation and methodology being proposed in this disclosure because this system is not taking discrete measurements. Instead, by measuring the time delay of the ultrasonic pulse from one side of the pipe to the other, a mean measurement is acquired by default. The final temperature measurement acquired, reflects the mean temperature of the ellipsoid-shaped volume 86 in the acoustic signal. The second concerns response time. The thermodynamic slow response time from the thermowell-RTD interface is eliminated by this system and significantly improved from approximately 3 seconds to only hundreds of milliseconds because the ultrasonic signal travel time, the standard response time of the SSVD and the response time of the base station electronics are in the range of hundreds of milliseconds. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
|
abstract | An event-based system and process for recording and playback of collaborative electronic presentations is presented. The present system and process includes a technique for recording collaborative electronic presentations by capturing and storing the interactions between each participant and presentation data where each interaction event is timestamped and linked to a data file comprising the presentation data. The present system and process also includes a technique for playing back the recorded collaborative electronic presentation, which involves displaying the presentation data in an order it was originally presented and reproducing the recorded interactions between each participant and the displayed presentation data at the same point in the presentation that they were originally performed, based on the aforementioned timestamps. |
|
summary | ||
abstract | A Faraday cup structure for use with a processing tool. The cup structure has a conductive strike plate coupled to a circuit for monitoring ions striking the strike plate to obtain an indication of the ion beam current. The electrically conductive strike plate is fronted by a mask for dividing an ion beam intercepting cross section into regions or segments. The mask including walls extending to the strike plate for impeding ions reaching the sensor and particles dislodged from the sensor from entering into the evacuated region of the processing tool. |
|
abstract | A removable rail assembly for use with a spent fuel handling machine, including a support rail, a rail guide carried by the support rail, a rail joint connector supported by the rail guide for coupling the rail guide to adjacent rails, and at least one jacking screw supported by the support rail for lifting the support rail assembly. Another embodiment of the invention includes a second jacking screw received in the top surface of the rail guide. The joint connector is tongue and groove joint with a tapered parting line that permits a tight fit between the removable rail and adjacent fixed rails. During removal of the removable rail, the jacking screw distributes a uniform lifting force along the length of the rail, loosening the joint connector. Once the joint connector is loosened, the rail is coupled to a lifting crane and transported to a storage area. |
|
description | Not Applicable Not Applicable 1. Field of Invention This invention relates to the field of target assemblies for use with accelerators for the production of radioisotopes. More particularly, this invention pertains to target assemblies, which have less than ideal thermal conductivity, having internal cooling channels and thermally optimized target chambers. 2. Description of the Related Art Positron Emission Tomography (PET) is a powerful tool for diagnosing and treatment planning of many diseases wherein radioisotopes are injected into a patient to diagnose and assess the disease. Accelerators are used to produce the radioisotopes used in PET. Generally, an accelerator produces radioisotopes by accelerating a particle beam and bombarding a target material, housed in a target system, with the particle beam. Several factors must be considered when developing a target system for the production of radioisotopes. In the case of gas or liquid targets, the target material must be maintained at an elevated pressure during bombardment to compensate for the effects of density reduction of the target material due to heating/expansion/phase change (boiling). Further, it is desirable to operate at higher beam currents to increase production of the radioisotopes. Because of the amount of heat generated during bombardment, cooling the target material and other components of the target system is of significant importance. Enriched water targets are used for the commercial production of the short lived (t1/2=109.8 minutes) positron emitter fluorine-18 (18F) for use as a tracer for Positron Emission Tomography (PET). The desired isotope is produced by proton bombardment of 18O enriched water (enrichment typically above 95%), using the 18O(p,n)18F reaction. The 18F isotope is used to produce fluorodexyglucose (FDG), which, when introduced within a patient, is used to map metabolic rates in the patient. The cost of the enriched water and the short half-life of 18F drive competing constraints on the target design. In order to overcome decay losses the target production must be maximized. This requires the target assemblies be designed for maximum operating current, which also increases ionization heating of the bombarded water. In order to minimize cost of reagents (specifically the expensive enriched water), the target assemblies necessarily have a small volume (<2 ml). Typical volume averaged power density in such targets is 400 W/cc. However peak power densities can be as much as two orders of magnitude greater. FIGS. 1 and 2 illustrate perspective views of a prior art target assembly 110 showing the front surface 112 and rear surface 212, respectively. FIG. 3 is a cross-sectional view of the target assembly 110. The target assembly 110 has a front face 112, which is adapted to connect to an accelerator or cyclotron. The target assembly 110 has a cylindrical body which fits into a cylindrical slot which supplies cooling water to the target assembly 110. The target assembly 110 also has a rear face 212, which has connections 220, 222 for the enriched water and openings for securing 214, 216 the target assembly 110. The prior art target assembly 110 includes a target chamber 104 encased in silver and having cooling channels 102, 102′, 202, 204, 302, 304 along the outside surface of the target assembly 110. Typically, cooling water flows into the channel 102′ on the bottom of the target assembly 110, through the channels 302, 304 along the circumference of the target assembly 110 and the channels 202, 204 along the rear surface 212 of the target assembly 110, and collecting in the channel 102 on the top of the target assembly 110, where it is removed and run through a heat exchanger to remove the collected heat. The channels 302, 304 are formed between the fins 306, 308 positioned around the circumference of the target assembly 110. In the illustrated prior art target assembly 110, the first fin 306 is separated from the other fins 308 by a larger gap, or channel, 302 in order to allow the target assembly 110 to receive a fastener. The prior art target assembly 110 includes a target chamber 104, which is filled with enriched water via an inlet port 220 on the back side 212. The target chamber 104 is sealed with a window 310 adjacent the front face 112. The inlet port 220 feeds an inlet channel 106, through which the enriched water enters and fills the target chamber 104. The air pushed out of the target chamber 104 exhausts through the outlet port 222. Before being irradiated, the enriched water completely fills the target chamber 104. The prior art target assembly 110 is fabricated from a silver ingot and operates at approximately 600 watts (10 MeV protons at 60 μA) on the target water. Irradiation of 18O-water in silver target bodies with proton beam currents higher than 30 μA generally leads to formation of gray or black colloids which frequently clogs the 18F ion delivery lines. More importantly, the reactivity of the 18F ion thus obtained is severely diminished. A model of the prior art target assembly 110 has been generated. This model of the external coolant cycle exposed inefficient cooling mechanisms, opportunities for coolant dryout, and likelihood of flow instabilities. Silver target assemblies 110 oxidize under the conditions seen in a high pressure water target, and eventually this oxidation leads to failure of the system, both through increased temperature drops through the oxide, sequestering of the fluoride product on the oxide surface, and oxide particles fouling the product capillary tubing and subsequent synthesis into the desired tracer. At high currents, such as 40-60 μA, the silver target holders are typically only usable for 20 to 30 runs to create radioisotopes such as Flourine-18 before being too contaminated for further use to maintain sufficiently pure radiochemicals. At that point the target assembly must be removed from the accelerator and cleaned to recover functionality. Various factors effect the production of radioisotopes from liquid targets with low energy accelerators. One such factor includes the configuration of the holding assemblies that retain the liquid target during the irradiation process. The holding assemblies must withstand severe environments created during the irradiation process and also enable the production of contaminant-free radiochemicals. When the liquid target is irradiated, the proton beam quickly heats the liquid target and creates high pressure within the target holder. The target holder must be capable of withstanding the elevated pressures without rupturing and without removing too much energy from the proton beam. Conventional liquid target holders have a thin front window through which the proton beams must pass before hitting the liquid target. Thicker windows are desirable to withstand the pressures generated from heating the liquid, but the thicker windows provide more mass through which the proton beam must pass before reaching the target. Accordingly, the thicker windows absorb more beam energy, thereby decreasing the effectiveness of the proton beam. When a low energy beam is used, it is highly desirable to ensure that as much energy remains in the proton beam as possible by the time it reaches its liquid target to maximize the beam's efficiency for irradiating the liquid target. So, while the strength of the thick window is desired, the resulting energy decrease in the beam is not. Another factor includes providing a liquid target that will fully absorb the remaining energy of the proton beam. As the proton beam is passed into the target holder and the target liquid, the target liquid must have a sufficient depth or thickness so as to fully absorb the particles from the beam. If the proton beam passed completely through the liquid target and the target holder, the particle beam could create a radioactive environment external to the holding assembly. Another significant factor in forming the radioisotopes or radiochemicals is controlling the target liquid's temperature during the irradiation process. When the proton beam bombards the target liquid, the temperature of the target liquid quickly increases. Heat must be efficiently drawn from the target liquid to maximize the effective density of the target liquid. The quantity of radioisotopes produced in a liquid target is very small (e.g., an isotope concentration in the target may be in the order of 10−12), so it is important that the target body not introduce contaminants into the target material. Such contaminants would reduce the quantity of the available useful radioisotopes, and hinder the subsequent chemical processes in incorporating the radioisotope into the desired radiochemical. Removal of the heat generated in the target is a significant problem that limits the magnitude of the incoming beam's current and hence, the production rate. Higher production rates are achieved if beams with higher currents can be used. Prior art target holders have been made of silver, which has a high thermal conductivity that allows heat to be quickly drawn from the liquid target. The silver target holders, however, often introduce impurities such as silver oxides that can react with or impede the reaction of the radiochemical formed in the target holder. A description of water targets is provided in an article titled “Tantalum [18O] Water Target for the Production of [18F] Fluoride with High Reactivity for the Preparation of 2-Deoxy-2-[18F]Fluoro-D-Glucose,” by N. Satyamurthy, Bernard Amarasekera, C. William Alvord, Jorge R. Barrio, Michael E. Phelps, in Molecular Imaging and Biology, Vol. 4, No. 1, at 65-70 (2002). This article describes the use of tantalum for the body of the water target and discloses some of the disadvantages and problems of the prior art silver target assemblies. The article further discloses the lower heat conductivity of tantalum, along with its chemical inertness, radiochemical reactivity, and low induced activation. FIG. 1 of the article illustrates that the target assembly is cooled by heat transfer into a cooling water plenum located inside the assembly. Test results using tantalum show an average actual yield of 112.7 mCi/μA for the nine runs over 60 minutes in duration. This yield is 68.3% of the theoretical yield. None of the documented tests had a beam current above 40 μA and the beam energy was at 10.8 MeV. An example of target cooling is disclosed in U.S. Pat. No. 5,917,874, titled “Accelerator Target,” issued to Schlyer, et al. on Jun. 29, 1999, which discloses a target 14 with radial cooling fins 28. The Target 14 contains a sample 12 in the front side and a cooling system on the back side. The cooling system includes an integral solid cone 42 with a grouping of radial fins 28 disposed on the outer surface of the cone 42 to increase the surface area for cooling. A water jet 40a is directed at the apex 42a of the cone 42 from a single center inlet 40d. The coolant 40a flows along the cone 42 and radial fins 28, through a plenum 40c, and out a pair of outlets 40e. U.S. Pat. No. 6,586,747, titled “Particle Accelerator Assembly With Liquid-Target Holder,” issued to Erdman on Jul. 1, 2003, discloses a target assembly 12 with two windows 62, 64. The target cavity 60 has a front window 62, formed of Havar, through which the particle beam 17 passes. The target cavity 60 has a thin rear window 64, formed of a thin section of the holder body 56, formed of niobium, which separates the target cavity 60 from the cooling channel 74. Transfer of the heat from the target cavity 60 is through the rear window 64 and by passing cooling fluid through the cooling block 68 and over the rear window 64. The cooling block 68 is mounted to the holder body 56 and has support ribs 72 that form parallel cooling channels 74 through which the cooling fluid flows. The target cavity 60 is at an angle to the particle beam 17, thereby allowing the particle beam 17 to pass through a greater thickness of the target fluid 54, which allows for using higher energy particle beams 17. According to one embodiment of the present invention, a target assembly is provided. The target assembly includes channels in which developed flow of a coolant removes the heat from the target liquid. In one embodiment, a pair of parallel channels provide cooling. In another embodiment, the target assembly is fabricated out of tantalum, which allows for higher current proton beams to be applied to the target liquid without reducing the life of the target assembly or introducing contaminants in the target liquid. In still another embodiment, the target chamber is shaped to promote natural circulation of the target liquid as it undergoes bombardment. An apparatus for containing and cooling a liquid target is disclosed. The apparatus, a target assembly 10, has a chamber in which enriched water is irradiated with a proton stream. FIGS. 4 and 5 illustrate one embodiment of the present invention. The target assembly 10 has a target body with a relatively solid outside surface with an upper flow channel 404 and a lower flow channel 406 through which cooling water can be provided. The target chamber 104′ has a front window 310 approximating a one-quarter circle, and the target chamber 104′ extends into the target assembly 10 with a sloping, or canted, rear wall 512 to allow for expansion of a vapor jet adjacent to the beam strike area 312 of the entrance window 310. The target liquid is introduced into the target assembly 10 through port 106, located at the lower portion of the target chamber 104′ and extending into the front face 112 of the target assembly 10. The target assembly 10 contains the same inlet and outlet ports 220 and 222 as shown in FIGS. 2 and 3. In one embodiment, the target assembly 10 is fabricated of tantalum, which has superior oxidation resistance compared to silver, but poorer thermal conductivity. Silver has high thermal conductivity of 415 W/m-K, whereas tantalum has a lower thermal conductivity of 57 W/m-K. Target assemblies fabricated of silver encounter oxidation problems with beam currents above 60 μA. Target assemblies 10 of tantalum have been tested up to 100 μA (1000 W at 10 MeV) and have provided excellent longevity and increased output at heretofore unattainably high production levels. FIG. 5 illustrates a section of the target 10 through one of two parallel channels 502, 504, 506, 508, each off center relative to the vertical midplane of the target 10. Each of the two channels are defined by 4 blind holes 502, 504, 506, 508, which, in one embodiment, are drilled into the target assembly 10. In one embodiment, the 4 blind holes 502, 504, 506, 508 are each 0.067″ diameter and are approximately 0.180″ off the vertical midplane of the target 10. In operation, the target liquid is introduced into the target chamber 104′ through the port 106. Cooling water is pumped from the lower channel 406, through the two parallel channels 502, 504, 506, 508, and into the upper channel 404. The target liquid is irradiated and the heat is removed by the cooling water flowing through the channels 502, 504, 506, 508. In particular, a high Reynolds number flow path through the two parallel channels 504, 506 cool the horizontal upper condenser plate surface 514 and the canted back wall 512 inside the beam strike, thereby compensating for the low thermal conductivity of the tantalum target assembly 10. The target assembly 10 includes a target chamber 104′, which is filled with enriched water via an inlet port 220 on the back side 212, as shown in FIG. 3. The target chamber 104′ is sealed with a window 310 adjacent the front face 112. The inlet port 220 feeds an inlet channel 106, through which the enriched water enters and fills the target chamber 104′. The air pushed out of the target chamber 104′ exhausts through the outlet port 222. Before being irradiated, the enriched water completely fills the target chamber 104′. The accelerator beam strikes the target chamber 104′ at a circular region 312 (the beam strike) in the lower portion of the chamber 104′. The beam heats the window 310 and the enriched water in the immediate vicinity of the window 310. The window 310 is typically Havar and is elevated to a high temperature by the beam. The window 310 transfers some of its heat to the water, which is also being heated by the beam. The enriched water experiences localized boiling adjacent to the window 310 at the beam strike area 312, which causes a jet of superheated steam to form. The jet moves upward, into a stable steam bubble in the top portion 514 of the target chamber 104′. The enriched water circulates in the target chamber 104′ from the target strike area 312, to the top portion 514 of the target chamber 104′, where it is condensed, down the back wall 512 and the side walls of the chamber 104′ and toward the front window 310, where the enriched water re-enters the beam strike area 312 and is reheated, continuing the cycle. The cooling water enters the lower channel 502 and passes through the channel 504 adjacent the rear wall 512 of the target chamber 104′. The cooling water, which is warmer after passing by the rear wall 512, then passes through the channel 506 adjacent the upper wall 514 of the target chamber 104′ and then out of the target assembly 10 through the upper channel 508. The cooling water progressively heats as it moves through the channels 502, 504, 506, 508, thereby presenting the enriched water at the back wall 512 with the coolest water possible. The differential temperature between the enriched water and the cooling water is maximized by having the cooling water enter at the bottom. Further, the developed flow of the cooling water allows for greater heat transfer from the target assembly 10. The embodiment of the target chamber 104′ illustrated in FIG. 5 has a configuration that aids the cooling of the enriched water by allowing for natural circulation of the enriched water. In one embodiment, the function of containing the target liquid for irradiation is performed by the target chamber 104′ within the target body. In another embodiment, the function of containing the target liquid for irradiation is performed by the target chamber 104′, which includes the arcuate upper wall 514 and the back wall 512. In one embodiment, the function of cooling the target assembly 10 is performed by at least one cooling channel 506 adjacent to and parallel to the upper wall 514, with the cooling channel 506 having developed flow. In another embodiment, the function of cooling the target assembly 10 is performed by at least one set of cooling channels 504, 506 adjacent to and parallel to the back wall 512 and the upper wall 514, respectively, with the cooling channels 504, 506 having developed flow. In one embodiment, the function of inducing fluid flow within the target chamber 104′ is accomplished by the shape of the target chamber 104′. In another embodiment, the function of inducing fluid flow within the target chamber 104′ is accomplished with the front window 310 having a larger area than the beam strike area 312, the curved upper wall 514, and the canted back wall 512. In one embodiment, the flow is adjusted to 0.25 gpm through each of the two parallel channels 502, 504, 506, 508 and for a 5 psi drop. The Reynolds number calculated for this configuration is 11799, indicating a truly turbulent regime. The flow is fully developed in the slanted channel 504, and nearly fully developed in the top horizontal channel 506. The pressure available in the target assembly 10 is being used more efficiently than in the prior art. The pressure drop along the two channels 504, 506 sums to 4.73 psi. These numbers also compare favorably with an inlet dynamic head of 0.04 psi, indicating that flow instabilities from entrance conditions are less likely. The target assembly 10 has heat transfer coefficients of 32,019 W/m2-K, owing to the turbulent diffusion of thermal energy. This gives much lower and more realistic temperature drops in the boundary layer, and a reasonable 3.81 degrees Celsius increase in water temperature over the course of the flow. FIG. 6 is a cross-sectional view illustrating one of the parallel upper channels 506 and the top surface 512 of the target chamber 104′. The enriched water in the target chamber 104′, in one embodiment, is pressurized to 600 psi. The circular cross-section of the channels 504, 506 allows the channels 504, 506 to be close to the surface of the target chamber to maximize heat transfer while still allowing the target chamber 104′ to contain an elevated pressure without rupturing. With the low heat transfer rate of tantalum, cooling efficiency is increased by locating the channels 504, 506 as close as possible to the back and upper walls 512, 514 of the target chamber 104′. The shorter conduction paths 504, 506 and more optimal cooling enables operation of target assemblies 10 with materials such as tantalum, which are less desirable from the standpoint of thermal conductivity, but have superior chemical properties. The complexity of the target assembly 10 has also been reduced, compared to the prior art target assembly 110. Extensive testing of the illustrated embodiment of the target assembly 10 has been conducted. The tested target assembly 10 was constructed of tantalum. With 48 runs of over 60 minutes duration, the average actual yield of 130.7 mCi/μA. This yield is 84.5% of the theoretical yield, which is much greater than the yield achieved from the target assembly described in the Satyamurthy article. The Satyamurthy article used an RDS-112 accelerator, which has a beam energy, after passing through all of the entrance foils, of approximately 10.8 MeV. At that energy, the theoretical yield of the 18F production in 18O enriched water is 165 mCi/μA at saturation. In the bombardments over 60 minutes in duration (n=9), the average saturation yield obtained with the configuration of the target assembly disclosed in the Satyamurthy article was 112.7 mCi/μA at saturation, or 68.3% of theoretical. The tested target assembly 10 was operated with a gridded window support which intercepts beam current, so an additional correction factor of 0.91 was applied to the beam current. With this correction, the average saturation yield of the bombardments over 60 minutes in duration (n=48) was 130.7 mCi/μA at saturation. The tested embodiment had currents of 60 to 100 μA. The accelerator these bombardments were performed with, the RDS Eclipse, has a beam energy of about 10.3 MeV after passing through all foils. At that lower energy than the accelerator used for the Satyamurthy experiments, the theoretical yield is 154.7 mCi/μA at saturation. Therefore tested target assembly 10 achieves 84.5% of theoretical yield, even though the beam current is much higher than the target assembly used in the Satyamurthy article. This high yield with tantalum is an unexpected benefit. Although known in the art, the use of tantalum, in combination with the cooling system described herein, provides unexpected results considering the low heat coefficient of tantalum and the use of higher beam currents. From the foregoing description, it will be recognized by those skilled in the art that a novel target assembly has been provided. The target assembly is fabricated of tantalum, which has superior oxidation resistance, and has cooling channels utilizing minimal conduction paths and high Reynolds number flows, which permits the target assembly to operate at high beam currents. The higher beam currents, along with the oxidation resistance, increases the performance and production capabilities over the prior art target assemblies. While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept. |
|
abstract | A nail lamp for curing UV-curable nail gel uses light emitting diodes (LEDs) that emit ultraviolet light and are relatively lower power. The nail lamp is powered from an exterior power source, such as a wall socket, or by a rechargeable battery pack. A battery compartment of the nail lamp holds the battery pack, which is removable without disassembling the nail lamp. The nail lamp is easily transportable to different locations and can be used even when a wall socket is unavailable. A curing time of the nail lamp is user-selectable. The nail lamp can also include detection sensors to detect a person's hand or foot in a treatment chamber and automatically turn on or off the LEDs. |
|
059638869 | summary | BACKGROUND OF INVENTION This invention relates to the monitoring of a system. More particularly, it relates to a method of and an arragement for monitoring a system. The system may be any type and may, for example, be an electric utility, a ship or craft, a chemical plant, or an amusement park. SUMMARY OF INVENTION Such systems have supervisory control and data acquisition arrangements which monitor the amplitude, state or condition of various parameters of equipment and components thereof and display alarm conditions on a display, to be acted on by control staff. In this specification, the amplitude, condition or state of a parameter will be referred to as the "value" of the parameter. A parameter is regarded as "abnormal" if its value attains an amplitude greater than or less than a predetermined amount or if its condition or state changes in an undesired way. Correspondingly, a parameter is regarded as "normal" if it has an amplitude less than or greater than the said predetermined amount (as the case may be) or if its condition or state is acceptable. According to the invention there is provided a method of monitoring a system, which includes choosing a part of the system; PA1 determining the values of a number of parameters of components forming part of equipment included in the chosen part of the system; PA1 deciding from the values if the selected parameters are abnormal; PA1 grouping the parameters in a plurality of different categories; PA1 selecting certain types of the components and certain of the categories; and PA1 displaying all of the components of the chosen part of the system and all of the categories having abnormal parameters in a graphical manner, with the selected types of components and categories being displayed in a differentiated manner to those that have not been selected. PA1 a choosing means for choosing a part of the system; PA1 a value determining means for determining the values of a number of parameters of components forming part of equipment included in the chosen part of the system; PA1 an abnormal value deciding means, for deciding from the values if the selected parameters are abnormal; PA1 a grouping means for grouping the parameters in a plurality of different categories; PA1 a selecting means for selecting certain types of the components and certain of the categories, and PA1 a display means for displaying all of the components of the chosen part of the system and all of the categories having abnormal parameters in a graphical manner, with the selected types of components and categories being displayed in a differentiated manner to those that have not been selected. The selected types of components and categories may be displayed in a normal way, with the non-selected component types and categories being "greyed-out". The method may also include summarising the number of abnormal parameters in each category for a predetermined time interval and also diplaying this number in a graphical manner with the appropriate category of abnormal parameters being displayed. The method may also include selecting certain operating characteristics which are associated with the selected types of components. The method may also include identifying in a display, which types of components and which operating characteristics are present in the part of the system that has been chosen. The types of components, the categories and the operating characteristics may be selected by means of a pointing device by picking and acting on appropriate symbols from the display. The component types, the operating characteristics and the parameter categories may be selected and implemented in terms of a desired paradigm. Further according to the invention there is provided an arrangement for monitoring a system, which includes Conveniently, the selected types of components and categories may be displayed in a normal way, with the non-selected component types and categories being "greyed-out". The categories of parameters may be represented by icons. The arrangement may also include a summarising means for summarising the number of abnormal parameters in each category for a predetermined time interval, and displaying this number in the appropriate icon. The various categories may be represented by icons of different colours. The system may have operating characteristics which are associated with certain types of components, with the selecting means also including the option to select certain operating characteristics. The system may form part of an electric utility and the operating characteristics may be the different voltage levels of the system. The arrangement may include an identifying means for identifying which types of components and which operating characteristics are present in the part of the system that has been chosen, with the component types and operating characteristics that are present in the chosen part being indicated in a predetermined manner, thereby assisting a user to make a selection. The component types and operating characteristics that are present in the part of the system that has been chosen may be displayed in a normal way and other types of components and operating characteristics which are not present in the chosen part of the system being "greyed-out". Thus, a particular voltage level may be selected and the components which operate at that voltage level will be displayed in a normal way and the components that operate at a different level are "greyed-out". The arrangement may include one or more central processing units for implementing the choosing means, the abnormal value deciding means, the grouping means and the selecting means in a software manner. The arrangement may be interactive. Th selecting means may include a pointing device which is used for picking and acting on appropriate symbols representing the component types, the operating characteristics and the categories. The selecting means may include a selection procedure whereby the component types, the operating characteristics and the categories are selected and implemented in terms of a desired paradigm. Thus, the selection procedure may include a "select to include" paradigm or a "select to exclude" paradigm. In terms of the "select to include" paradigm, initially nothing is selected and when an appropriate control button is activated everything is "greyed-out" and the component types, the operating characteristics and the categories are only displayed after being selected. In terms of the "select to exclude" paradigm, initially all of the components types, operating characteristics and categories are displayed in a normal way and only when an appropriate control button is activated and the desired component types, the operating characteristics and the categories are selected, are the unwanted portions of the display "greyed-out". The arrangement may also operate in a progressive or triggered mode. In the progressive mode, the selected component types, the operating characteristics and the categories may be selected and varied at any time. In the triggered mode, the component types, the operating characteristics and the categories may only be selected and varied together by means of the control button. It will be appreciated that, if a particular component type is selected, only that component type will be displayed in a normal way, with all other component types being displayed "greyed-out". If an operating characteristic is selected, all the components which operate with that characteristic will be displayed in a normal way with all those components that operate with a different characteristic being "greyed-out". If both a component type and an operating characteristic are selected, an AND operation is performed and only those components of the selected type and with the selected operating characteristic will be displayed in a normal way. If multiple component types and operating characteristics are selected, each component type will be ANDed with each operating characteristic and all combinations will be ORed together to form a complete inclusive set. Further, if certain parameter categories are selected, then only the icons for the selected categories for those components in the set will be displayed in a normal manner. Those skilled in the art will appreciate that data values of the abnormal parameters may also be displayed. The invention is now described, by way of an example, with reference to the accompanying drawings, in which: |
055747590 | claims | 1. A method for dismantling bulky parts of pressure-vessel fittings of a nuclear plant and for storing the dismantled parts, which comprises: setting down a dismantling container for pressure-vessel fittings in a water tank; inserting the pressure-vessel fittings into the dismantling container; introducing a receiving container for the dismantled parts into the dismantling container; fixing a dismantling manipulator relative to the dismantling container; separating the pressure-vessel fittings into predeterminable smaller-size parts; introducing the smaller-size parts into the receiving container; removing the receiving container from the dismantling container; and transferring the parts disposed within the receiving container, within the nuclear plant, into a transport container. setting down a bottom part of the dismantling container in the water tank; inserting the pressure-vessel fittings to be dismantled into the bottom part; and pushing a casing part of the dismantling container over the pressure-vessel fittings like a sleeve, and releasably connecting the casing part to the bottom part. 2. The method according to claim 1, which comprises: 3. The method according to claim 1, which comprises introducing the receiving container into a shielding container within the water tank and transferring the receiving container from the shielding container into the transport container outside the water tank. 4. The method according to claim 1, which comprises inserting a shielding container together with the receiving container disposed in it, into the transport container. 5. The method according to claim 3, which comprises bringing the shielding container and the transport container into position axially-parallel one above the other, removing at least one of a bottom and a cover of the mutually adjacent containers, and passing the receiving container from the shielding container into the transport container with a lifting appliance. |
061480622 | claims | 1. A beam-shaping filter of variable area, which comprises a main frame in the form of a flat ring provided with a central circular opening for passage of a beam of radiation, at least one sliding rail fixed to one of the main surfaces of the main frame and at least one compensating plate made of a radiation-absorbent material, which can be moved along the rail between a retracted position in which the compensating plate lies outside a maximum field of view of the beam and active positions in which the compensating plate lies at least partly within the maximum field of view of the beam wherein the compensating plate comprises a first and second plate element which can be moved one relative to the other in such a way that, when the plate is in an active position, the thickness of absorbent material through which the beam passes is constant. 2. Filter according to claim 1 wherein the plate elements can be moved rotationally. 3. Filter according to claim 2 wherein the first plate element is joined by a first of its ends to the sliding rail and the second plate element is joined, so as to pivot by a first of its ends, to a second of the ends of the first plate element opposite the first end. 4. Filter according to claim 3 wherein the second plate element rotates with respect to the first plate element by the second plate element pivoting with respect to a pivot pin connected to the second end of the first plate element and to a first end of the second plate element. 5. Filter according to claim 4 wherein a second end of the second plate element has a curved elongate slot into which a stud engages, this stud being fixed to the first plate element and sliding in the slot in order to guide the second plate element during its rotation. 6. Filter according to claim 5 wherein the plate comprises a stressed spring joined respectively by one of its ends to the first and second plate elements so that the second plate element rotates with respect to the first plate element automatically under the action of the spring during the movement of the plate from its retracted position to an active position. 7. Filter according to claim 6 wherein a stop is fixed to the main frame so that, when the plate is in its retracted position, the second plate element is held in place against the force exerted by the spring. 8. Filter according to claim 4 wherein the plate comprises a stressed spring joined respectively by one of its ends to the first and second plate elements so that the second plate element rotates with respect to the first plate element automatically under the action of the spring during the movement of the plate from its retracted position to an active position. 9. Filter according to claim 8 wherein a stop is fixed to the main frame so that, when the plate is in its retracted position, the second plate element is held in place against the force exerted by the spring. 10. Filter according to claim 9 wherein the second plate element is a curved plate of constant width. 11. Filter according to claim 10 wherein the relative translation between the first plate element and the second plate element is provided by a pairs of studs fixed to the first plate element engaging in parallel straight slots provided in the second plate element. 12. Filter according to claim 1 wherein the plate elements can be moved in relative translation. 13. Filter according to claim 12 wherein the relative translation between the first plate element and the second plate element is provided by a pairs of studs fixed to the first plate element engaging in parallel straight slots provided in the second plate element. 14. Filter according to claim 1 wherein the plate elements have a minimum overlap area in the maximum field of view of the beam and in that they are bevelled in their parts corresponding to the minimum overlap area in such a way that the thickness of absorbent material through which the beam passes is constant. 15. Filter according to claim 1 comprising two diametrically opposed parallel straight rails and two compensating plates each of which can be moved respectively on one of the rails. 16. An imaging machine comprising a source of beam radiation, a shaping filter disposed in the beam and means for collecting the radiation and forming an image wherein the shaping filter comprises a main frame in the form of a flat ring provided with a central circular opening for passage of a beam of radiation, at least one sliding rail fixed to one of the main surfaces of the main frame and at least one compensating plate made of a radiation-absorbent material, which can be moved along the rail between a retracted position in which the compensating plate lies outside a maximum field of view of the beam and active positions in which the compensating plate lies at least partly within the maximum field of view of the beam wherein the compensating plate comprises a first and second plate element which can be moved one relative to the other in such a way that, when the plate is in an active position, the thickness of absorbent material through which the beam passes is constant. |
abstract | A system for forming a thick flowing liquid metal, in this case lithium, layer on the inside wall of a toroid containing the plasma of a deuterium-tritium fusion reactor. The presence of the liquid metal layer or first wall serves to prevent neutron damage to the walls of the toroid. A poloidal current in the liquid metal layer is oriented so that it flows in the same direction as the current in a series of external magnets used to confine the plasma. This current alignment results in the liquid metal being forced against the wall of the toroid. After the liquid metal exits the toroid it is pumped to a heat extraction and power conversion device prior to being reentering the toroid. |
|
abstract | A radiation attenuation system is disclosed. The system includes a polymeric resin comprising a web. The system also includes a radiation attenuation material dispersed at least partially in the web. The system has a radiation transmission attenuation factor of at least about 10% of a primary 100 kVp x-ray beam. A method of making a radiation attenuation system including a radiation attenuation material dispersed at least partially in a polymeric resin is also disclosed. The method includes extruding the radiation attenuation material and the polymeric resin thereby forming an extrusion. The method also includes forming the extrusion into a web. The web has a radiation transmission attenuation factor of at least about 10% of a primary 100 kVp x-ray beam. A shield for the attenuation of radiation is also disclosed. |
|
043022847 | description | As illustrated in FIGS. 1 and 2, a toroidal plasma device 10 includes a primary confinement vessel in the form of a toroidal liner 12 which confines and defines a primary toroidal chamber 14 containing appropriate gas at a suitable low pressure. In the design illustrated, the liner 12 is made of thin wall stainless steel which permits rapid penetration of toroidal electric field to start up and drive plasma current in the primary toroidal chamber 14. The toroidal liner 12 is disposed within and supported from a secondary confinement vessel in the form of a toroidal shell 16. The shell 16 as shown is formed of a relatively thick copper wall forming a secondary toroidal chamber 18. The secondary chamber 18 is evacuated through conduits 20 and a header 22 by a vacuum pump means not shown. The primary chamber 14 is evacuated through conduits 24 and a header 26 by vacuum pump means also not shown. As shown in FIGS. 4 and 5, the shell 16 includes a ceramic break 28 which serves to interrupt the toroidal conductive path around the shell 16 which would otherwise short circuit the toroidal conductive path through the plasma. The conductance of the liner 12 is sufficiently low in respect to the conductance of the plasma as not to be wasteful of energy. That is, a magnetic field may readily penetrate the conductive shell 16 because of the ceramic break 28 and penetrate the liner 12 because it is relatively thin and of lower conductivity than the material forming the shell 16. At the same time, the liner 12 provides an electrical bridge across the ceramic break 28 and isolates the ionized plasma from the electrical break thereby formed in the conductive shell 16. At the same time, the conducting shell 16 aids in stabilization of the plasma by repelling plasma current trying to move toward the wall of the shell 16. As with tokamak devices, the plasma current is produced by a toroidal electric field induced by a solenoid coil 30 disposed axially of the major axis of the toroidal liner 12 and inside the torus. The toroidal electric field is created by operation of the solenoid coil 30 and additional turns 32 disposed to channel the poloidal flux outside the liner 12. The solenoid coil 30 and additional turns 32 are energized in a conventional manner by a power supply not shown, whereby the change in electrical current in the coil causes a change in magnetic flux linking the single turn secondary formed by the liner 12 and its contents. The change in flux, in turn, generates plasma current within the primary chamber 14. A plurality of first windings 34 are wound substantially helically upon a coil form 36 which surrounds the shell 16. As shown best in cross section, FIG. 2, the first windings are substantially equally spaced about the minor circumference of the coil form 36, which may be in the form of two halves bolted together as illustrated. A plurality of second windings 38 are wound substantially helically upon the coils form substantially midway between respective successive first windings. Each of the windings 34 and 38 may be formed of a plurality of turns of conductors 40 which may be square in cross section and insulated from one another. The conductors 40 may include central passages 42 for the circulation of coolant for cooling the conductors. The first and second windings 34 and 38 are regarded as helical even though they do not form true helices in the sense of being wound upon circular cylinders. The windings 34 and 38 are wound uniformly as they progress around the torus so that the first windings upon making a complete circuit of the torus register with first windings so as to form continuous first windings all the way around the major axis of the torus. That is, where there are two first windings, the number of turns must be integral or half way between. In the latter case, what was one first winding the first time around is the other first winding the second time around. The same thing is true for the second windings 38. The first windings 34 are energized by a direct current source 44, and the second windings 38 are energized by a direct current source 46. The direct current sources 44 and 46 are oppositely poled so as to pass current through the respective first and second windings in opposite directions. Such currents provide a steady state helical magnetic field within the primary chamber 14 for combining with the poloidal magnetic flux produced by the plasma current for the purpose of containing the plasma current away from the conductive walls of the liner 12. The helical windings 34 and 38 are preferably wound at such pitch as to produce relatively small interwinding forces and good plasma stability. An angle of about 45.degree. to the minor axis of the torus is suitable. As shown in FIGS. 1, 2, and 3, there may be two first windings and two second windings disposed about the minor circumference of the torus. Three of each such windings can also be used, filling the primary chamber more fully with plasma but possibly with less stability. A greater number is possible under some conditions. The power supplies are connected so that the current through the first windings can be equal to or slightly greater than the current through the second windings, whereby a zero or a net toroidal magnetic field is produced by the helical windings 34 and 38. In general, the total current in the second windings 38 is comparable in magnitude to one half the plasma current. The additional turns 32 can be operated to apply a vertical magnetic field to the plasma as to balance the effect of hoop force which tends to expand the plasma in major radius, or to adjust the equilibrium plasma for best stability. The device may include observation ports 48. In typical operation of a device as shown in FIGS. 1 through 5, the plasma current generated by operation of the solenoid coil 30 and additional turns 32 is about 40 kA maximum, which requires a magnetic flux swing of about 0.3 V-sec. with a rise time of about 10 msec. To achieve a ratio .beta. of plasma pressure to magnetic field pressure of about 0.1 while maintaining good stability, typically the temperature T of the plasma will be about 100 eV, with a density n of 10.sup.13 particles per cc., a magnetic flux density B of 1 kilogauss, an energy containment time .tau..sub.E of 0.3 msec. and a pulse duration .tau..sub.pulse of 30 msec. The total current in the first windings is about 20 kA and in the second windings is also about 20 kA. The ratio of the mean radius of the plasma current r.sub.p to the mean radius of the windings r.sub.w is about 0.75. Under such conditions, the equilibrium profiles of certain parameters have been calculated to be qualitatively as shown in FIG. 6. The relationships among the various parameters of the system and their relationships to the operation of the system are complicated and depend upon many different factors. For the sake of explanation, the curves of FIG. 6 have been prepared based upon certain parameters which have been selected somewhat arbitrarily. For the curves illustrated, the aspect ratio of the primary chamber 14, that is, the ratio of major to minor radii of the torus, is high. More particularly, the parameters there illustrated are: j.sub.z, the current density in the direction of the minor axis of the torus; j.sub..theta., the current density in the direction around the minor axis; B.sub.z, the net magnetic flux density in the direction of the minor axis; B.sub..theta., the magnetic flux density around the minor axis, and q, the safety factor related to B.sub.z and the pitch of the magnetic field lines as defined previously. The parameter r/r.sub.s is the ratio of the minor radius coordinate to the minor radius of the separatrix, this ratio evaluated along an angle of 45.degree. to the X/r.sub.s axis of FIG. 7. FIG. 7 illustrates the magnetic flux surfaces generated under these conditions at points A and B of FIG. 6. A condition for stability is that q pass through zero. The manner of operation of this invention with the resultant stable plasma can be described mathematically. The mathematics, however, becomes very complex for certain configurations. If certain practical approximations are made, the explanation can be much simplified. For example, as a practical matter it is desirable to operate with a high aspect ratio; that is, the ratio of the major radius to the minor radius of the torus can be very large, somewhat like a bicycle tire. In such cases the toroidal effects can be neglected in favor of a cylindrical approximation. The main field is B.sub..theta.,o (r) produced by the plasma current. A helical winding produces a magnetic field given by a static potential .PHI., EQU .PHI.=(b/k)I.sub.l (kr) cos (l.theta.+kz) (3) where I.sub.l is the modified Bessel function of order l. The components of the magnetic field are given by ##EQU5## Here I.sub.l ' (kr) is the derivative of I.sub.l (kr) with respect to its argument. The entire field may be expressed in terms of the flux function .psi.* given by EQU .psi.*=.psi..sub.o *-(br/l)I.sub.l '(kr) sin (l.theta.+kz) (7) where .psi..sub.o *=-.intg.B.sub..theta.,o dr. Surfaces defined by .psi.*=const. are the flux surfaces. The shapes of the flux surfaces may be calculated approximately by setting ##EQU6## By expansion, ##EQU7## It follows EQU .xi..about.-{(ba/l)I .sub.l '(ka)/(B.sub..theta.,o)} sin (l.theta.+kz). (11) The translational transform may be calculated by the flux line equations ##EQU8## By using expansion (8) ##EQU9## The average value is then given by ##EQU10## The safety factor q is as defined above ##EQU11## The volume .DELTA.V between two flux surfaces .psi.* and .psi.*+.DELTA..psi.* may be calculated from ##EQU12## By using r=a+.xi., ##EQU13## The longitudinal flux .psi. is calculated from EQU .psi.=.intg.B.sub.z rdrd.theta. (17) By using Eqs. (6), (8), and (10), ##EQU14## The combination of Eqs. (16) and (18) yields ##EQU15## It is a decreasing function of a and indicates d.sup.2 V/d.psi..sup.2 <0. This characteristic has been called a magnetic well; C. Mercier, "Lectures in Plasma Physics", Fontenay-aux-Roses (1974). In the limit of .beta..fwdarw.0, this assures stability. More intuitively, the magnetic well means that the average longitudinal magnetic field increases as one moves away from the plasma, where "average" means flux-surface average. The maximum well depth occurs for r=0. Using Mercier's notation, the magnetohydrodynamic equilibria in the cylindrical approximation may be calculated using the equation given by ##EQU16## The helical variable u=l.theta.-hz in the cylindrical coordinates (r,.theta.,z) and the vector u=(le.sub.z +hre.sub..theta.) (l.sup.2 +h.sup.2 r.sup.2).sup.-1 define the helix. The magnetic field B is written as EQU B=fu+ux grad F (21) The operation L is defined by ##EQU17## It is convenient to use the variable G defined by ##EQU18## Then ##EQU19## It is instructive to calculate a simple example equilibrium, where f=const. and p'=const. Then Eq. (20) becomes ##EQU20## By integrating ##EQU21## where C is a constant. Putting G=G.sub.o (r)+g(r,u) (27) ##EQU22## This is a special case where the vacuum field g is separated out. In order to avoid the singularity on the axis in the absence of the internal conductor, ##EQU23## By integration of Eq. (28), ##EQU24## The external vacuum field g is given by EQU g=(b/h)I.sub.l (hr) sin (l.theta.-hz) (32) The function F is then given by ##EQU25## The magnetic fields are ##EQU26## If there is no solenoidal field applied, then the axial field vanishes at the plasma edge r=r.sub.o. Then EQU f/l=-(hr.sub.o.sup.2 /2)p' (36) This indicates that the plasma produces a paramagnetic axial field of f/l on the axis. On the other hand, if f=0, an external field of -(hr.sub.o.sup.2 /2) p' is required. The plasma is diamagnetic to this field. The current density j is given by ##EQU27## The azimuthal component is ##EQU28## Obviously f=const. does not lead to small j.sub..theta.. The equilibria with small j.sub..theta. are the ones of interest. Consider a case where f=(2h/l)F and p'=const. The equilibrium equation is given by ##EQU29## Putting EQU F=-(l.sup.2 /4)p'r.sup.2 +H (40) Eq. (39) becomes ##EQU30## In this case, the pressure is supported by azimuthally symmetric j.sub.z B.sub..theta. force and the helical field H is a force-free field. The field and the current are given by ##EQU31## Note that only j.sub.z and B.sub..theta. have non-helical components. Equations 42-47 describe an equilibrium which has no non-helical contribution to B.sub.z on axis. On the other hand, the equilibrium described by equations 34-38 has a very large non-helical B.sub.z component. In between these two equilibria lie equilibria that have an intermediate B.sub.z component to give an appropriate q profile. Thus, by superposing the two example equilibria described, an equilibrium of a desired amount of the solenoidal axial field may be obtained. FIGS. 6 and 7 illustrate qualitatively the type of equilibrium which is desired. Such an equilibrium is expected to be stable according to Mercier's criterion for beta values in excess of 10%. Mercier's criterion, which must be satisfied for the plasma to be stable, is given by ##EQU32## The quantity .XI. as used by Mercier is proportional to the pressure gradient and the last term corresponds to the destabilizing effect of the pressure. The criterion reduces to the Suydam's criterion for a cylindrical pinch given by ##EQU33## It has been known that pinches can be made stable by profiling B.sub.z and q. The outer part of the plasma is stabilized by a large shear and a small .beta. with respect to the axial field. The inner part is made stable by having a hollow pressure distribution. In these configurations, the axial field is reversed, i.e., there is a null of the axial field in the plasma. The profile must be maintained for the stability throughout the duration of the discharge. This is one of the experimental difficulties of the reversed field pinch. If B.sub.z is taken to represent the axial transform in the criterion, the outer part of the plasma is stabilized because of the shear and a large transform. The inner part has to be stabilized by an axial field produced by the plasma current and/or by unbalancing the current in the helical windings to counter the axial transform, thus having a q profile similar to the reversed field pinch. At any rate, the q profile in this case is externally controlled. The amount of the axial field is controlled by unbalancing the current in the positive and the negative helical windings. A proper q profile can be maintained independent of the plasma skin time. Relating this physically to the structure illustrated in FIGS. 1-5 and to the curves of FIGS. 6 and 7, the twisted magnetic field produced by plasma current and the helical magnetic field produced by windings 34 and 38 result in magnetic flux surfaces wherein the safety factor q as a function of radial displacement from the minor axis of the toroid has a substantial slope and changes monotonically, reversing sign near the outer edge of the plasma. By adding or subtracting a small amount of toroidal magnetic flux relatively uniformly across the torus, the net toroidal flux as a function of radial displacement can be moved up or down to cross zero at an optimum radius for confining the plasma. Such additional toroidal magnetic flux is generated by the unbalance of the helical magnetic fields produced by the respective first and second windings 34 and 38. As defined above, a flux surface is a surface on which the magnetic flux density, evaluated at any point on the surface, has no component normal to the surface. In other words, a flux surface is a surface which no magnetic field lines penetrate. The field lines lie on the flux surfaces. The flux surfaces are nested. A criterion for stability is that the flux surfaces be nested and separated from the confinement wall. In a toroidal configuration, the flux surfaces must be closed. Thus, in accordance with the present invention, the combination of the poloidal magnetic field produced by the plasma current and the helical magnetic field produced by the helical windings provide a magnetic limiter separating the plasma current from the confinement wall of the plasma vessel. This creates the separatrix, which defines a closed surface which limits and encloses the region within which the closed and nested flux surfaces exist. As defined above in equation 1, ##EQU34## where q is the safety factor, R is the major radius of the torus, and dz/d.theta. is the average length traversed in the toroidal direction per unit poloidal angle of rotation of a magnetic field line on a magnetic flux surface. In accordance with this definition, an average magnetic field line in a flux surface makes q transits around the torus in the toroidal direction in making a single transit in the poloidal direction. (In the present case, q is a fraction which is less than 1.) Thus, the safety factor q on a particular flux surface is the ratio of the average pitch of magnetic field lines in that flux surface to the major circumference of the torus, where pitch is the displacement in the toroidal direction for a single transit, or cycle, in the poloidal direction. As stated by equation 12, dz/d.theta. is also given by ##EQU35## where r is the minor radius, B.sub.z is the longitudinal or toroidal magnetic field and B.sub..theta. is the poloidal magnetic field. ##EQU36## is the translational transform. Thus, ##EQU37## where the angular brackets indicate an average over a flux surface. For circular concentric flux surfaces in an axisymmetric system, the average is a simple average over the poloidal angle .theta.; that is, ##EQU38## but since neither B.sub.z nor B.sub..theta. depends strongly on .theta., ##EQU39## for such case. Equation 52 is appropriate for a tokamak or a reversed field pinch. For tokamaks, q is greater than 1 everywhere, and for the reversed field pinch, q vanishes only when B.sub.z vanishes. In such case, B.sub.z is a net toroidal field, meaning that it persists when averaged over poloidal angle .theta.. In the case of the present invention, in the embodiment where the currents in the helical windings are balanced, there is no net B.sub.z except that due to poloidal plasma currents. However, there can be an average B.sub.z on a flux surface. This may be understood by reference to FIG. 8, which is a simplified version of FIG. 2. The windings 34 and 38 are represented by single conductors and the rest of the apparatus is omitted for the sake of clarity in this explanation. Dashed lines 50 and 52 have been drawn to separate the space in the chamber 14 into quadrants. On these lines, the toroidal magnetic field is zero. In quadrants I and III, the toroidal field is caused by the first windings 34 and is directed up out of the plane of FIG. 8 for the twist as shown. In quadrants II and IV the toroidal field is opposite to this. The toroidal field averaged over a circular loop 54 is zero, because it passes equally through all four quadrants. If the circle is distorted into an ellipse 56, the toroidal field averaged over the loop is now non-zero. For the loop 56, the path is longer in quadrants I and III and shorter in quadrants II and IV. Also, the path is nearer to the first windings 34 in quadrants I and III, where the toroidal field is stronger, and farther from the second windings 38 in quadrants II and IV, in a reduced toroidal field. Both the extra path length and larger field weight the average to have quadrants I and III dominate. This makes an average toroidal field on the loop 56 which is directed up out of the plane of FIG. 8. Near the center of the plasma the net toroidal field is generated by poloidal plasma current. At a point near the edge of the plasma the effect of the remaining poloidal plasma current, that which remains between that point and the edge, is relatively much smaller and can be overcome by the flux-surface-average toroidal field due to the helical coils. This gives the q reversal with balanced coils when the appropriate currents and fields are applied with proper polarity. The device of the present invention as thus described differs fundamentally in both principle and structure from the prior art devices as exemplified by tokamaks, stellarators and reversed field pinch devices, although the present device has certain features in common with each. More particularly, like the tokamak, the present device requires plasma current to generate the appropriate magnetic flux configuration, and the configuration does not decay on the flux diffusion time scale. On the other hand, the tokamak requires toroidal field coils and not helical field coils; whereas the present device requires helical field coils but not toroidal field coils. The tokamak requires q greater than 1; whereas the present device does not. The present device requires q to cross zero as a function of radial displacement; whereas the tokamak does not. Like the stellarator, the present device requires helical field coils; but unlike the stellarator, it does not require toroidal field coils. As in the stellarator, the magnetic configuration does not decay on the flux diffusion time scale, but unlike the present device, the stellarator does not require plasma current to generate the magnetic configuration. The stellarator requires a large toroidal flux B.sub.z ; whereas the present device does not require any net applied toroidal flux, although a small applied B.sub.z may be desirable for optimization. The present device requires that q cross zero as a function of radial displacement, which the stellarator does not. In contrast, a stellarator with a substantial plasma current generally requires q>1 for stability. Like reversed field pinch devices, the present device requires plasma current to generate the magnetic configuration and for q to cross zero. Neither requires q greater than 1. On the other hand, the present device requires helical coils, which the reversed field pinch devices do not, and has a separatrix, which the reversed field pinch does not. The magnetic configuration decays on the flux diffusion time scale in reversed field devices but not in the present device. These differences and others provide substantial advantages for the present device. The fact that no large toroidal magnetic field is required permits great economy in manufacture and ease of operation as makes this a more practical device. The large toroidal magnetic fields required for tokamaks and stellarators apparently require superconducting magnetic coils and imply large interwinding forces that produce stresses difficult to contain. Prior devices have often involved neutral beam heating which has proven inefficient, bulky, and expensive, and has caused problems when the beam hit a wall. The present device in general is relatively smaller, being capable of high beta, high aspect ratio, and no applied net toroidal field, and permits adequate ohmic heating in conjunction with the induced plasma current. A problem, particularly with tokamaks, has been the relatively small space available for the plasma heating coils. The present device in its preferred form has a relatively large aspect ratio, permitting more space for such coils and other appurtenances such as a reactor blanket. This eases the design requirements of the heating coils. This also permits scaling to larger devices merely by increasing the major radius while keeping the minor radius the same. The present design provides a higher .beta., the ratio of plasma pressure to magnetic pressure, permitting more efficient operation at lower magnetic fields. The present design provides an inherent magnetic limiter whereby the separatrix moves radially outward as the plasma current increases, maintaining a stable configuration. This is because outside the confining flux surface there it no confinement and any plasma outside the separatrix is immediately lost to the confining wall without wastefully carrying any substantial current. The present design also facilitates the incorporation of a divertor, which is difficult to introduce in tokamaks. An advantage over the reversed field pinch devices is that such devices operate with a q profile that changes for the worse as the magnetic flux diffuses out of the system. The time is so short as to have severely limited the development of a practical reactor based on the reversed field concept. While the novel aspects of a fusion device in accordance with the present invention have been shown in a preferred embodiment, various modifications may be made therein within the scope of the invention, as in the size and shape and in driving currents. For example, the direct current in the windings 34 and 38 may take the form of relatively long unidirectional pulses. The device may also include various well-known appurtenances of fusion devices such as power supplies, vacuum pumps, instrumentation, blankets, supporting structures, and heat exchangers. Although the preferred embodiment of the invention is a toroidal system, the invention may also be utilized in a straight cylindrical system appropriately bounded. As the length L of a toroidal system is the major circumference 2.pi.R, the safety factor q may be defined in terms of L: ##EQU40## This safety factor as thus defined is applicable to a straight cylindrical system of length L. |
summary | ||
abstract | A perforated plate support supports dual-cooled fuel rods, each of which has concentric outer and inner tubes and is coupled with upper and lower end plugs at upper and lower ends thereof, and guide thimbles, each of which is used as a passage for a control rod. The perforated plate support is formed as a support plate having the shape of a flat plate, which includes internal channel holes, each of which has a diameter corresponding to an outer diameter of the inner tube, guide thimble holes, each of which has a diameter corresponding to an outer diameter of the guide thimble, and sub-channel holes around each internal channel hole. The upper or lower end of the dual-cooled fuel rod is coupled to the support plate such that the outer diameter of the inner tube is matched with the diameter of the internal channel hole. |
|
summary | ||
description | The present invention relates to a multi-leaf collimator device for radiotherapy, and more particularly, to a multi-leaf collimator device for radiotherapy, which may be provided in a radiotherapy device for treating a cancer patient or an animal and may precisely apply radiation to a treatment target portion. The present invention is derived from a research project supported by the Atomic Energy Research & Development (R&D) Program of the Ministry of Education, Science, and Technology [Project No.: 20090062218, Project Name: Development of Internal Organ Motion Tracking Medical Physics Technology for Radiotherapy]. As nowadays many people have difficulties in maintaining good health due to stress and irregular meals in our complex society, it is very common for people to die from malignant tumors, i.e., cancer. Since the risk of cancer has constantly increased, effective counter measures are strongly needed. Therefore, recently, methods of treating cancer, and in particular, radiotherapy, have become important points of interest. Two core elements are necessary for successful radiotherapy on tumors. First, radiation is required to be precisely applied to a tumor, and second, a planned radiation dose should be identical to a radiation dose which is actually applied. A variety of displacement errors must be reduced in order to precisely apply radiation to a tumor. Displacement errors caused by a patient's body may be classified into three categories: a position related organ motion error, a gap fraction organ motion error, and an internal fraction organ motion error. The position related organ motion error occurs due to changes in positions of a patient's internal organs according to a patient's posture, such as standing or lying down, while the patient is being treated. The position related organ motion error may be reduced by considering in advance the patient's posture for treating the patient and planning a treatment position. The gap fraction organ motion error occurs due to changes in positions of a corresponding organ and its neighboring organs according to the filling degree of the bladder, rectum, or stomach. The gap fraction organ motion error may be removed by ensuring that the patient's condition during treatment planning and the actual treatment is the same. The internal fraction organ motion error occurs due to changes in positions of a corresponding organ and its neighboring organs according to breathing or heartbeat. The internal fraction organ motion error is of physiological nature and occurs frequently in any living body. In particular, breathing has a significant effect and thus the internal fraction organ motion error is a serious problem affecting organs influenced by diaphragmatic respiration. Thus, the internal fraction organ motion error may be removed by tracing an external anatomic motion according to the patient's breath and applying radiation only to a specific part of an internal organ according to a change in a position of the specific part. The inventors of the present invention have invented devices disclosed in Korean Patent Nos. 0706758 and 0740340. However, if the above devices are used to apply radiation to a patient's portion to be treated, a radiation opening and closing device is opened only when an organ is at a specific position, which increases a time taken to actually treat the patient. Meanwhile, in order to apply radiation to a patient's portion to be treated, a shield for protecting a normal tissue of the patient is manufactured and attached to a radiotherapy apparatus during an actual treatment. Examples of such shield include a generally used Lipowitz metal shield and a multi-leaf collimator (MLC). In the case of a Lipowitz metal shield, it takes one or two days to manufacture an alloy block, whereas in the case of an MLC, no shield is manufactured and the MLC may be more easily manufactured into various irradiation surfaces compared to the alloy block. However, conventional MLCs are expensive and do not operate in association with various radiation devices. The present invention provides a multi-leaf collimator device for radiotherapy, which may continuously and precisely apply radiation only to a patient's portion to be treated and may be cheaper and more efficient than a conventional multi-leaf collimator device. According to an aspect of the present invention, there is provided a multi-leaf collimator device for radiotherapy, including: a frame that has a box shape and through-holes formed in top and bottom surface thereof; a plurality of collimators that are received in the frame, wherein each of the collimators includes a rack gear formed on the top surface of the collimator, and the collimators are symmetrically arranged in a left-right direction with respect to a central portion of the frame, and are slidably provided on the frame; and a motion driving unit that includes a pinion gear that is formed to be detachable from the rack gear formed on the top surface of the collimator, and is provided on the frame to move the pinion gear in a front-back direction of the frame and an up-down direction of the frame. A multi-leaf collimator device for radiotherapy according to the present invention effectively controls a multi-leaf collimator set to specify a radiation treatment area of a patient's portion. The present invention reduce the manufacturing costs and improve device efficiency, thereby leading to a more efficient treatment by effectively controlling the multi-leaf collimator. The multi-leaf collimator is controlled by a first motor and a second motor. The first motor controls a linear motion of the multi-leaf collimator. The second motor controls a rotational motion of a pinion gear. The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. FIG. 1 is a perspective view illustrating a multi-leaf collimator device 10 for radiotherapy, according to an embodiment of the present invention. FIG. 2 is a front view illustrating the multi-leaf collimator device 10 of FIG. 1. FIG. 3 is a bottom view illustrating the multi-leaf collimator device of FIG. 1. FIG. 4 is a plan view illustrating the multi-leaf collimator device 10 of FIG. 1. FIG. 5 is a view for explaining a motion driving unit 30 of the multi-leaf collimator device 10 of FIG. 1. FIG. 6 is a view illustrating a case where collimators 23 are moved by the motion driving unit 30 of FIG. 5. FIG. 7 is a view illustrating a case where the collimators 23 are set to define a radiation treatment area in the multi-leaf collimator device 10 of FIG. 1. Referring to FIG. 1 through 7, the multi-leaf collimator device 10 is mounted on a radiotherapy apparatus for applying radiation to a patient's portion to be treated and is used to apply radiation only to the patient's portion to be treated. The collimator device 10 includes a frame 20, the collimators 23, and the motion driving unit 30. The frame 20 is fixed to the radiotherapy apparatus (not shown). The frame 20 is manufactured by combining a plurality of boards. The frame 20 is formed of a metal material such as carbon steel or an aluminum alloy. However, a material of the frame 20 is not limited to a metal material. The frame 20 has a box shape having an inner space. Through-holes 22 are formed in top and bottom surfaces of the frame 20. In the present embodiment, the through-holes 22 have rectangular shapes. Radiation applied by the radiotherapy apparatus passes through the through-holes 22. The collimators 23 are received in the inner space of the frame 20 by being slidably provided in the frame 20. In detail, the collimators 23 are symmetrically arranged in a left-right direction Y with respect to a central portion of the frame 20. A rack gear 24 is formed on a top surface of each of the collimators 23. The collimators 23 are formed of a material capable of shielding radiation such as carbon steel or a tungsten alloy. Since the collimators 23 have a plate shape, the collimators 23 are referred to as a shield leaf. The motion driving unit 30 moves the collimators 23 to form a desired shape and determines an area to which radiation is to be applied by the radiotherapy apparatus. The motion driving unit 30 is provided on the frame 20. Two motion driving units 30 are symmetrically arranged in the left-right direction Y about the frame 20. Each of the motion driving units 30 includes a pinion gear 42 that is detachably coupled to the each of rack gears 24 formed on the collimators 23. The pinion gear 42 moves the collimators 23 in the left-right direction Y of the frame 20 and sets a radiation treatment area having a specific shape. The pinion gear 42 may be moved by the motion driving unit 30 in a front-back direction X of the frame 20 and an up-down direction Z of the frame 20. The motion driving unit 30 includes a ball screw 32, a first motor 34, a ball nut 35, a moving member 36, a linear motion guide 38, an elevation member 40, the pinion gear 42, a pulley 44, a second motor 46, and a timing belt 48. The ball screw 32 extends in a direction perpendicular to a direction in which the collimators 23 slide. In detail, as shown in FIG. 1, the ball screw 32 extends in the front-back direction X of the frame 20. An end portion of the ball screw 32 is coupled to an output shaft of the first motor 34. The other end portion of the ball screw 32 is rotatably provided on the frame 20. Accordingly, when the first motor 34 rotates, the ball screw 32 rotates. The first motor 34 is fixed to the frame 20. The first motor 34 may be a stepping motor or a servo motor having high precision. The ball nut 35 is coupled to the ball screw 32. In general, the ball screw 32 and the ball nut 35 operate together to convert a rotational motion to a linear motion. The moving member 36 is coupled to the ball nut 35. The moving member 36 is fixed to the ball nut 35 and integrally moves with the ball nut 35. The linear motion guide 38 is disposed parallel to the ball screw 32. The moving member 36 is slidably coupled to the linear motion guide 38. The linear motion guide 38 enables the moving member 36 to linearly move more precisely. The elevation member 40 is slidably coupled to the moving member 36. In detail, the elevation member 40 is elevatably coupled to the moving member 36. The elevation member 40 is elevatable by using air pressure. The elevation member 40 may be elevated by using air pressure by using well-known technology, and thus, a detailed explanation thereof will not be given. The pinion gear 42 is provided on a lower end portion of the elevation member 40. The pinion gear 42 is rotatably provided on the elevation member 40. The pinion gear 42 protrudes from the lower end portion of the elevation member 40. The pulley 44 is coupled to a rotational shaft of the pinion gear 42. The pulley 44 is integrally coupled to the rotational shaft of the pinion gear 42 to smoothly connect to a driving source for rotating the pinion gear 42. The second motor 46 is fixed to an upper end portion of the elevation member 40. A rotational shaft of the second motor 46 and the pulley 44 are connected to each other through the timing belt 48. Accordingly, when the rotational shaft of the second motor 46 rotates, the pulley 44 rotates through the timing belt 48 and the pinion gear 42 integrally coupled to the pulley 44 rotates too. The second motor 46 may be a stepping motor or a servo motor having high precision. Motions of the first motor, the second motor 46, and the elevation member 40 may is be controlled by a computer (not shown). As such, the motion driving unit 30 may be controlled by the computer. Accordingly, the collimator device 10 may be efficiently controlled by inputting data necessary for a shape of a portion to be treated by using an input device such as a keyboard of the computer. A case where a shape of a radiation treatment area as shown in FIG. 7 is set by using the multi-leaf collimator device 10 constructed as described above will be explained. First, all of the collimators 23 of the multi-leaf collimator device 10 are gathered at the central portion of the frame 20. In an initial condition, since radiation is completely shielded by the collimators 23, no radiation is applied to the patient's portion to be treated. A process of setting a shape of the radiation treatment area as shown in FIG. 7 to precisely apply radiation to the patient's portion to be treated will be explained. A user of the collimator device 10 inputs an arrangement shape of the collimators 23 to be set by using the input device of the computer. A condition input to the computer may be a graphic shape or a numerical condition. Once the condition is input, a central processing unit (CPU) of the computer generates control data for controlling the motion driving unit 30 of the collimator device 10. A driving signal of the motion driving unit 30 is transmitted from the computer. The motion driving unit 30 determines a position by driving the first motor 34 to move the moving member 36 in the front-back direction X. The motion driving unit 30 elevates the elevation member 40 in the up-down direction Z of the frame 20 by using air pressure and couples the pinion gear 42 to the rack gear 24. The motion driving unit 30 drives the second motor 46 to rotate the pulley 44. Once the pulley 44 rotates, the pinion gear 42 rotates and one of the collimators 23 moves in the left-right direction Y of the frame 20 due to the rack gear 24 coupled to the pinion gear 42. When a motion of one of the collimators 23 is completed, the elevation member 40 rises and the pinion gear 42 is separated from the rack gear 24. The first motor 34 is driven to move the pinion gear 42 to another one of the collimators 23. The shape of the radiation treatment area as shown in FIG. 7 may be set by repeatedly performing the process. The two motion driving units 30 may sequentially move the collimators 23 such that the collimators 23 form the required shape. Since the collimators 23 received in the frame 20 are sequentially moved by the motion driving unit 30 by coupling the rack gear 24 and the pinion gear 42, the collimator device 10 may be effectively controlled. The collimator device 10 may reduce the risk of radiation exposure to users and may precisely arrange the collimators 23 compared to conventional collimator devices which manually control the collimator 23. Also, a conventional collimator device requires a driving unit for each of the collimators 23. However, since the collimator device 10 according to the present invention may be fabricated with reduced manufacturing costs compared to the conventional collimator device, the collimator device 10 may be used in applications where conventional collimator devices are not available because of high costs. In conclusion, the collimator device 10 may reduce the medical costs for patients. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. According to an aspect of the present invention, there is provided a multi-leaf collimator device for radiotherapy, including: a frame that has a box shape and through-holes formed in top and bottom surfaces thereof; a plurality of collimators that are received in the frame, wherein each of the collimators include a rack gear formed on a top surface of the collimator, the collimators are symmetrically arranged in a left-right direction about a central portion of the frame, and are slidably provided on the frame; and a motion driving unit that includes a pinion gear that is formed to be detachable from the rack gear formed on the top surface of the collimator, and is provided on the frame to move the pinion gear in a front-back direction of the frame and an up-down direction of the frame. Two motion driving units may be symmetrically arranged in the left-right direction of the frame. The motion driving unit may include: a ball screw that extends in a direction perpendicular to a direction in which the collimators slide; a first motor that is coupled to an end portion of the ball screw; a ball nut that is coupled to the ball screw; a moving member that is fixed to the ball nut; an elevation member that is elevatably coupled to the moving member; the pinion gear that is provided on a lower end portion of the elevation member to be rotatable relative to the elevation member; a pulley that is integrally coupled to a rotational shaft of the pinion gear; a second motor that is fixed to an upper end portion of the elevation member; and a timing belt that connects a rotational shaft of the second motor and the pulley. The multi-leaf collimator device may further include a linear motion guide that is disposed parallel to the ball screw such that the moving member is slidable. The elevation member may be elevatable by using air pressure. The motion driving unit may be controlled by a computer. |
|
claims | 1. A system for reducing tritium migration comprising:a spent nuclear fuel pool comprising a body of tritiated water having an exposed surface;a cover movable between an open state in which the cover does not obstruct access to the exposed surface of the body of tritiated water and a closed state in which the cover covers the exposed surface of the body of tritiated water;wherein the cover is a tent structure comprising a frame and a vapor impermeable membrane coupled to the frame, the frame comprising a base that surrounds the spent nuclear fuel pool in the closed state, the tent structure forming a cavity between the vapor impermeable membrane and the exposed surface of the body of tritiated water in the closed-state; andwherein the tent structure comprises an internal funnel that is configured to flow tritiated water vapor that condenses on an inner surface of the vapor impermeable membrane back into the body of tritiated water of the spent nuclear fuel pool. 2. The system of 1 further comprising a gasket forming a perimeter about the spent nuclear fuel pool, a hermetically sealed interface formed between the base of the frame of the tent structure and the gasket in the closed state. 3. The system of claim 2 wherein the gasket comprises an upper surface having a groove in which the base of the frame of the tent structure nests in the closed-state. 4. The system of claim 2 further comprising one or more adjustable clamps that clamp the base of the frame of the tent structure into contact with the gasket. 5. The system of claim 1 further comprising a condenser operably coupled to the cavity to condense tritiated water vapor present in the hermetically sealed cavity and return dried air to the hermetically sealed cavity. 6. The system of claim 1, wherein the vapor impermeable membrane comprises a vapor impermeable layer, a radiation shielding layer, and a thermal insulating layer. 7. The system of claim 1 wherein the cover hermetically seals the exposed surface of the body of tritiated water in the closed state. 8. A system for reducing tritium migration comprising:a spent nuclear fuel pool comprising a body of tritiated water having an exposed surface;a cover comprising a vapor impermeable membrane, wherein the cover is movable between an open state in which the cover does not obstruct access to the exposed surface of the body of tritiated water and a closed state in which the cover covers the exposed surface of the body of tritiated water;wherein the cover comprises an internal funnel configured to flow tritiated water vapor that condenses on an inner surface of the vapor impermeable membrane back into the body of tritiated water of the spent nuclear fuel pool; andwherein the vapor impermeable membrane comprises a vapor impermeable layer, a radiation shielding layer, and a thermal insulating layer. 9. The system of claim 8 comprising a gasket that forms a closed perimeter about the spent nuclear fuel pool. 10. The system of claim 9 wherein a groove is provided in the top surface of the gasket. 11. The system of claim 10 wherein the cover further comprising a frame, the frame comprising a base that nests in the groove. |
|
summary | ||
summary | ||
abstract | The invention relates to energy mechanical engineering and can be used in power installations involving a liquid-metal heat carrier. A mass transfer apparatus including a housing and, provided therein, a flow reaction chamber filled with a solid-phase granulated oxidation agent, and an electric heater positioned in the reaction chamber. The housing of the apparatus is equipped with a repository for reserves of the solid-state granulated oxidation agent, said repository being located below the reaction chamber and being made in the form of a cup having a bottom, said cup being connected to the re-action chamber. The technical result consists in extending the operational duration of the mass transfer apparatus. |
|
047028785 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, shown in FIGS. 1 and 2 is a portion of a conventional nuclear steam generator, generally indicated by the numeral 10, having an outer cylindrical shell 11 provided with an opening 12, generally referred to as a handhole, located approximately 18 inches from the tube sheet 13 adjacent the bottom of the shell. Generally the handhole is only six inches in diameter. As shown in FIG. 2, the steam generator further includes a plurality of closely spaced vertical tubes 14 supported by and extending upwardly from the tube sheet 13. The vertical tubes 14 are associated by pairs with a U-bend at the top (not shown) so as to straddle two sides of an aisle 15 extending centrally across the shell. The tubes 14 are surrounded by a wrapper barrel 16 spaced approximately two inches from the interior wall of the shell 11 to form an annulus 17, therewith. As shown in FIG. 1, the wrapper barrel 16, and consequently the annulus 17, extend downwardly to a point six inches above the tube sheet 13. As further shown in FIG. 1 an inspection hole 18 is provided below the handhole 12 in the shell and is located at a point just above the tube sheet 13. As shown in FIGS. 1 and 2, the search and retrieval device of the present invention includes a guide tube, generally indicated by the numeral 20, having a straight main segment 21 and an upper segment 22 bent at a right angle to the main segment. The guide tube further includes a lower segment 23 also bent at a right angle to the main segment and extending in a direction rotated 90.degree. from the direction of the upper segment 22. The lower segment 23 of the guide tube 20 rests on and is parallel to the surface of the tube sheet 13. The upper segment 22 and the lower segment 23 may be constructed as separate parts from the main segment 21 of the guide tube 20 to facilitate insertion of the guide tube into the steam generator. The guide tube is secured at its upper end to the shell 11 by means of a guide plate 24 fastened to the shell by suitable means such as bolts 25. Referring particularly to FIGS. 3 and 4, the search and retrieval device also includes a sled, generally indicated by the numeral 30, which comprises a flat front plate 31, an intermediate plate 32 angled upwardly at approximately a 30.degree. angle and a back plate 33 attached to the intermediate plate and positioned in a plane above but parallel to the plane of the front plate 31. Mounted on the back plate 33 is an upstanding bracket 34 for receiving and securely holding the end of a flexible steel tube 36 which extends from the back plate 33 of the sled 30 up through the guide tube 20 to the outside of the shell of the steam generator. Preferably, the flexible tube 36 has a diameter of one inch. While the flexible tube 36 preferably is constructed of steel, it also may be constructed of other suitable materials which are flexible enough to permit insertion through the guide tube 20 and the annulus 17 but yet is sufficiently rigid to permit pushing of the sled 30 around the periphery of the shell 11 on the tube sheet 13. An inspection probe 40 and a gripper 41 are associated with the sled 30 as most clearly shown in FIG. 2. The probe may be of any suitable type which permits inspection of the surface of the tube sheet 13. For example, the probe may comprise either a fiberscope or a miniature TV camera and preferably has a diameter of 3/8 inch. The gripper may be of any type suitable for picking up small objects from the surface of the tube sheet. The gripper shown in FIG. 2 has a plurality of prongs 42 which may closed and opened to grasp and release objects. The probe 40 is connected to a flexible probe cable 43 which extends from the probe back through the flexible tube 36 to the outside of the steam generator. The gripper 41 is connected to a flexible gripper shaft 44 which also extends back through the flexible tube 22 to the outside of the steam generator. The gripper shaft 44 preferably has a diameter of 1/4 inch. As shown in FIG. 5, the gripper shaft 44 consists of an inner shaft 45 slidably received within an outer shaft 46. The inner shaft 45 is connected to the end of gripper 41 whereby when the inner shaft is pushed forwardly the gripper prongs 42 are opened and when the inner shaft 45 is pulled backwardly the prongs 42 close to grasp an object. The probe cable 43 and the gripper shaft 44 constitute control means for the probe 40 and the gripper 41. Adjusting means, generally indicated by the numeral 50, are mounted on the sled 30 for changing the operating positions and direction of the probe and the gripper. The adjusting means 50 is comprised of a rotatable turret 51 having a circular passageway 52 extending through the upper portion thereof and a worm wheel 53 fixedly attached to the lower portion thereof by any suitable means such as bolts 54 as shown in FIG. 5. The turret 51 is rotatably attached to the front plate 31 of the sled by shaft 55. A worm gear 56 is rotatably mounted on shaft 57 secured by bracket 58 to the front plate 31 of the sled 30. Bracket 58 is mounted to front plate 31 by any suitable means such as bolts 59. The worm gear 56 meshes with worm wheel 53 whereby rotation of the worm gear causes the worm wheel 53 and consequently turret 51 to rotate. The probe cable 43 and the gripper shaft 44 freely pass through the circular passageway 52 of the turret 51 so that they may slide therethrough. Attached to the end of the shaft 57 on which worm gear 56 is mounted is a universal mechanism 60 which in turn is attached to the end of an actuator cable 61 rotatably received within an outer cable 62 which extends through a flexible tube 36 to the outside of the steam generator as shown in FIGS. 4 and 5. Actuator cable 61 rotates within outer cable 62 in a manner similar to a speedometer cable. Rotation of cable 61 causes the worm gear to also rotate or turn. An emergency pull wire 64 also extends through the flexible tube 36 and is welded to the flexible tube at each end thereof. The emergency pull wire 64 extends outwardly from the outer end of the flexible tube whereby if the flexible tube 36 becomes stuck, the emergency pull wire will prevent unraveling of the flexible tube 36 while the tube is being pulled out. In operation of the search and retrieval device of the present invention, the outer end of the flexible tube 36 is initially inserted through the guide tube 20 and out through the end of the upper segment 22 thereof. The sled 30 and the guide tube 20 having the flexible tube 36 passing therethrough are then inserted through the handhole 12 until the sled 30 is positioned on the surface of the tube sheet 13 and the lower segment 23 of the guide tube 20 is parallel to the surface of the tube sheet. An operator of the device may view the guide tube 20 through the inspection hole 18 to ensure that the guide tube is positioned correctly. Once the sled and the associated components mounted thereon are in position on the periphery of the tube sheet, the probe may be activated to search for any loose objects on the surface of the tube sheet. The sled is moved along the periphery of the tube sheet by pushing the flexible tube through the guide tube 20. Pushing or pulling on the flexible tube 36 causes the sled to slide over the surface of the tube sheet. The sled may be stopped at any point and the turret 51 rotated by turning or rotating actuator cable 61 in order to turn the probe and the gripper inwardly to face the rows of the tubes 14. Both the probe cable 40 and the gripper shaft 44 then may be pushed by any suitable means outside of the shell of the steam generator whereby the probe cable 43 and the gripper shaft 44 slide through the circular passageway 52 of the turret to extend the probe 40 and the gripper 41 to a position among the tubes. When an object to be removed is located by use of the probe, the gripper shaft is then pushed until the gripper comes in contact with the object whereupon the inner shaft 45 of the gripper shaft 44 is pulled to close the prongs 42 and grasp the object. The entire sled assembly is then removed from the steam generator and the object released from the gripper. The above-described operation is then continually repeated until the entire tube sheet has been inspected and cleaned. The flexible tube 36 may be pushed through the guide tube 20 either manually or by automatic means (not shown) located outside the shell of the generator. In addition, the rotation of the actuator cable 61 and the pushing and pulling of the probe cable 43 and the gripper shaft 44 may also be done either manually or by suitable automatic means (not shown) located outside the shell of the generator. It is apparent from the foregoing that many advantageous features are provided by the present invention over the prior art. A device for searching and retrieving objects in the small spaces between the tubes on a tube sheet of a nuclear steam generator is disclosed which is relatively simple and economical in construction and which may be readily maneuvered into and through the small spaces present in a steam generator to retrieve objects which have been dropped on the tube sheet and have to be removed. The present invention permits such removal without having to dismantle any part of the steam generator to provide access to the interior portions thereof. Numerous alterations and modifications of the structure herein disclosed will suggest themselves to those skilled in the art. It is to be understood, however, that the present disclosure relates to the preferred embodiments of the invention which is for purposes of illustration only and is not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims. |
050948008 | claims | 1. In a press for compressing elongated radioactive structural elements, including a horizontally disposed press line that comprises a press shaft provided with a cover, a press ram operated via a hydraulic cylinder, and a removable counterpunch in place of which, after a compression process has been completed, is inserted a transfer shaft into which is introduced the highly compressed pressed object via further advancement of said press ram, the improvement wherein: said press to a large extent comprises components that can be remotely handled, with said press ram being divided into several press ram sections and with said cover being divided into several cover portions; a displacement drive mechanism is provided for the longitudinal displacement of said press shaft between parallel tie rods that interconnect two crosspieces, one for supporting said hydraulic cylinder, which is a short press cylinder, and the other, oppositely disposed crosspiece supporting whichever of said counterpunch and said transfer shaft that is present; and said press shaft, at an end thereof that is disposed in the pressing direction, is provided with: a horizontal support surface for whichever of said counterpunch and said transfer shaft that is present, first vertical abutment surfaces for bracing a pressing force at said counterpunch, second vertical abutment surfaces of a stop of said press shaft to brace one of said cover portions in the pressing direction, and third vertical abutment surfaces for end face engagement against said transfer shaft. 2. A press according to claim 1, in which said press shaft has an interior that is provided with a replaceable, U-shaped, upwardly open wear insert means. 3. A press according to claim 2, in which said wear insert means of said press shaft comprises several wear insert sections that are disposed one after the other in the pressing direction, whereby the leading wear insert section, as viewed in the pressing direction, is positively connected with said press shaft via holding strip means, and whereby the trailing wear insert section, in the pressing direction, is disposed ahead of a remotely controllable displacement drive means that is adapted to bring all of said wear insert sections into engagement against one another in such a way that there are no gaps between them, and is also adapted to bring said leading wear insert section into engagement against said holding strip means on a base and inner walls of said press shaft. 4. A press according to claim 1, in which said cover portions have surfaces that face said press shaft and that are provided with wear plate means, whereby the leading cover portion as viewed in the pressing direction, is positively connected with pertaining wear plate means via holding strip means. 5. A press according to claim 4, in which the trailing cover portion, in the pressing direction, is disposed ahead of a remotely controllable displacement drive means that, prior to a tightening of said cover portions via cover bolts, is adapted to bring all of said cover portions into engagement against one another in such a way that there are no gaps between them, and is also adapted to bring said leading cover portion into engagement against said third abutment surface of said stop on said press shaft. 6. A press according to claim 1 in which said cover portions, independently of one another, are secured against an upper side of said press shaft via hook-like cover bolts that are pivotably mounted, in pairs, in crossbars, and that positively engage in recess means disposed on the outside of side walls of said press shaft; which includes central control means for remotely pivoting said cover bolts, in pairs, into an engagement position; and which includes nuts for tightening said cover bolts. 7. A press according to claim 1, in which said press cylinder is provided with a piston rod, and said press ram sections include, as viewed in the pressing direction, a trailing cylinder ram that is detachably secured to said piston rod, a leading guide ram for engagement against material that is to be compressed, and between said cylinder ram and said guide ram at least one extension ram, with said press ram sections being provided with recess means for receiving connector pieces for positively interconnecting same. 8. A press according to claim 7, in which each of said connector pieces has two ends, one of which is directed toward said press cylinder and is provided on two sides with pivot pin means that extends transverse to the pressing direction, and the other oppositely disposed end is directed in the pressing direction and has an underside that is provided with a hook-like projection that has an inclined leading surface; and in which said recess means for positively receiving said connector pieces are disposed in upper surfaces of said cylinder ram, said extension rams, and said guide ram. |
046876308 | summary | CROSS REFERENCE TO RELATED APPLICATION Reference is hereby made to the following copending applications dealing with related subject matter and assigned to the assignee of the present invention: 1. "Nuclear Reactor Fuel Assembly With Improved Top Nozzle And Hold-Down Means" by Robert K. Gjertsen et al, assigned U.S. Ser. No. 542,625 and filed Oct. 17, 1983, now U.S. Pat. No. 4,534,933, issued Aug. 13, 1985. 2. "Reconstitutable Nuclear Reactor Fuel Assembly With Unitary Removable Top Nozzle Subassembly" by John M. Shallenberger, assigned U.S. Ser. No. 673,681 and filed Nov. 20, 1984, a continuation-in-part of U.S. application Ser. No. 457,790, filed Jan. 13, 1983. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to fuel assemblies for nuclear reactors and, more particularly, is concerned with a top nozzle incorporating improvements which limit the handling loads that can be imposed on the fuel assembly especially when it is being loaded into or removed from the reactor core. 2. Description of the Prior Art Conventional designs of fuel assemblies include a multiplicity of fuel rods held in an organized array by grids spaced along the fuel assembly length. The grids are attached to a plurality of control rod guide thimbles. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the control rod guide thimbles which extend above and below the opposite ends of the fuel rods. At the top end of the fuel assembly, the guide thimbles are attached in openings provided in the top nozzle. Conventional fuel assemblies also have employed a fuel assembly hold-down device to prevent the force of the upward coolant flow from lifting a fuel assembly into damaging contact with the upper core support plate of the reactor, while allowing for changes in fuel assembly length due to core induced thermal expansion and the like. Such hold-down devices have included the use of springs surrounding the guide thimbles, such as seen in U.S. Pat. Nos. 3,770,583 (No. Re. 31,583) and 3,814,667 to Klumb et al and U.S. Pat. No. 4,269,661 to Kmonk et al. Due to occasional failure of some fuel rods during normal reactor operation and in view of the high costs associated with replacing fuel assemblies containing failed fuel rods, the trend is currently toward making fuel assemblies reconstitutable in order to minimize operating and maintenance expenses. Conventional reconstitutable fuel assemblies incorporate design features arranged to permit the removal and replacement of individual failed fuel rods. Reconstitution has been made possible by providing a fuel assembly with a removable top nozzle. The top nozzle is mechanically fastened usually by a threaded arrangement to the upper end of each control rod uide thimble, and the top nozzle can be removed remotely from an irradiated fuel assembly while it is still submerged in a neutron-absorbing liquid. Once removal and replacement of the failed fuel rods have been carried out on the irradiated fuel assembly submerged at a work station and after the top nozzle has been remounted on the guide thimbles of the fuel assembly, the reconstituted assembly can then be reinserted into the reactor core and used until the end of its useful life. One type of such reconstitutable fuel assembly can be seen in the aforementioned Klumb et al patents. The fuel assembly of Klumb et al includes a top nozzle which incorporates a hold-down plate and also coil springs coaxially disposed about upwardly extending alignment posts. The alignment posts extend through an upper end or adapter plate, spaced below the hold-down plate, and are joined thereto and to the upper ends of the guide thimbles with fastener nuts located on the underside of the adapter plate. The upper hold-down plate is slidably mounted on the alignment posts and the coil springs are interposed, in compression, between the hold-down plate and the adapter plate. A radially enlarged shoulder on the upper end of each of the alignment posts reacts with a shoulder on the hold-down plate to retain the hold-down plate on the posts. When the fuel assembly is free standing after being removed from the reactor core, the hold-down plate is held at its uppermost position along the alignment posts by the coil springs. Further upward sliding movement of the hold-down plate is prevented by contact of the plate with the enlarged shoulders on the upper ends of the alignment posts. On the other hand, when the fuel assembly is positioned in the reactor core, the hold-down plate is pressed downward by the upper core plate of the reactor core. Thus, during reactor service, the hold-down plate slidably moves downward away from its freestanding position. Transfer of the fuel assembly between its service position in the reactor core and a location outside of the core, such as a work station for reconstitution of the fuel assembly, is accomplished by use of a conventional fuel assembly handling machine. For handling the fuel assembly, a gripper of the machine is brought into engagement with the hold-down plate and then moved in an upward direction so as to lift the fuel assembly via its top nozzle. While the gripper so supports the fuel assembly, the load passes from the gripper to the hold-down plate and therefrom to the guide thimbles via the alignment posts in view that the connection between the hold-down plate and the guide thimbles is, in effect, substantially unyielding or rigid. The above-described type of connection of the hold-down plate with the guide thimble alignment posts in the reconstitutable fuel assembly of the Klumb et al patents imposes on the design of the fuel assembly structure the requirement that it be capable of withstanding large lifting loads, typically on the order of 6 g. These high loads are impulse type loads which are of very short duration. (The fuel assembly handling machine has a load limiting system to prevent sustained high loads on the fuel assembly.) The postulated 6 g axial load can occur when the fuel assembly is being lowered adjacent to another assembly, and it momentarily hangs up on the stationary assembly. For example, the grids interlock or the bottom nozzle of the fuel assembly being lowered catches on the top nozzle of the stationary assembly. The fuel assembly being lowered then breaks loose from its hangup and drops downwardly until it is stopped by the fuel assembly handling machine which has continued downward. The impact energy caused by this sudden drop is now absorbed by the fuel assembly structure. (The fuel handling machine is assumed to be rigid.) Although the above-described event occurs very infrequently, the fuel assembly structure must be designed to withstand these high loads. Unfortunately, the occurrence of these high loads, however infrequent, reduces the overall reliability of the fuel assembly structure and increases the complexity of the design of the top nozzle and guide thimble connections in the fuel assembly. Consequently, a need exists for a fresh approach to fuel assembly top nozzle design with the objective of reducing the loads on the top nozzle and guide thimble joints and thereby increasing fuel assembly reliability. SUMMARY OF THE INVENTIO The present invention provides an improved top nozzle and guide thimble joint structure designed to satisfy the aforementioned needs. Underlying the present invention is a recognition that the problem with the prior art fuel assembly is the rigid connection between the top nozzle hold-down plate and the fuel assembly guide thimble when the fuel assembly is in its freestanding position, such as when it is supported by the fuel assembly handling machine. If an energy absorbing means could be interposed between the fuel assembly handling machine gripper and the fuel assembly structure, the design loads for the fuel assembly could be reduced. The improved joint structure of the present invention provides a flexible connection of the hold-down plate to the guide thimble alignment posts which serves as an energy absorber. Provision of the flexible, or yieldable, joint structure reduces the loads on the top nozzle and guide thimble joints and, as a result, increases fuel assembly reliability. More importantly, it simplifies the design of the fuel assembly top nozzle and guide thimble connections. Accordingly, the present invention is provided in a nuclear fuel assembly having at least one control rod guide thimble and a top nozzle, wherein the guide thimble includes an upper extension member and the top nozzle includes an upper hold-down plate having a passageway slidably receiving an upper end portion of the extension member. The present invention is directed to an improved joint structure flexibly interconnecting the hold-down plate with the upper end portion of the guide thimble upper extension member. The improved joint structure basically comprises: (a) first overlapping means on the upper hold-down plate at the passageway thereof; and (b) second overlapping means on the upper end portion of the guide thimble extension member. The first and second overlapping means are respectively disposed to interfere with one another so as to limit upward movement of the hold-down plate along the guide thimble extension member. At least one of the first and second overlapping means is resiliently yieldable for absorbing the energy of an impulse load applied to the hold-down plate so as to thereby limit transfer of the load to the guide thimble extension member. More particularly, the first overlapping means is an internal ledge defined on the hold-down plate within its passageway, being preferably located in a lower portion of the passageway. The second overlapping means includes a recess defined on the upper end portion of the guide thimble extension member, and a spring member fitted on the upper end portions within the recess thereon and extending outwardly therefrom so as to overlie the internal ledge in the hold-down plate passageway. Still further, the recess is defined between a lower upwardly-facing shoulder on the upper end portion of the guide thimble extension member and an upper detachable member releasably applied to the upper end portion of the extension member. The spring member is at least one belleville spring which deflects axially upon application of a large impulse load thereto via the internal ledge of the hold-down plate. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. |
claims | 1. A mirror to totally reflect X-rays comprising:a silicon plate body subjected to plastic deformation, wherein the silicon plate body includes a reflecting surface, the reflecting surface of the silicon plate body having a degree of smoothness at an angstrom level for total X-ray reflection, wherein the reflecting surface of the silicon plate body is plastically deformed to have a given curved surface shape configured to totally reflect X-rays; anda large number of X-ray passage grooves formed on a reverse side of the reflecting surface of the silicon plate body to extend parallel to each other, wherein the large number of X-ray passage grooves are formed before the silicon plate body is subjected to the plastic deformation. 2. The mirror as defined in claim 1, wherein the curved surface shape of the reflecting surface of the silicon plate body includes a part of a paraboloid of revolution and a part of a hyperboloid of revolution. 3. The mirror as defined in claim 1, wherein the large number of X-ray passage grooves are formed by lithography. 4. A reflecting device to totally reflect X-rays comprising a plurality of mirrors, wherein each of the plurality of mirrors is a mirror that is comprised of:a silicon plate body subjected to plastic deformation, wherein the silicon plate body includes a reflecting surface, the reflecting surface of the silicon plate body having a degree of smoothness at an angstrom level for total X-ray reflection, wherein the reflecting surface of the silicon plate body is plastically deformed to have a given curved surface shape configured to totally reflect X-rays; anda large number of X-ray passage grooves formed on a reverse side of the reflecting surface of the silicon plate body to extend parallel to each other, wherein the large number of X-ray passage grooves are formed before the silicon plate body is subjected to the plastic deformation, wherein the curved surface shape of the reflecting surface of the silicon plate body includes a part of a paraboloid of revolution and a part of a hyperboloid of revolution;wherein the plurality of mirrors are arranged around a straight line so that the straight line becomes a rotation axis for the plurality of minors, and wherein an angle of each of the plurality of mirrors is set to allow X-rays entering parallel to the rotation axis to be reflected once at each of the paraboloid-of-revolution surface and the hyperboloid-of-revolution surface, and then converged. 5. A reflector to totally reflect X-rays comprising:a plurality of reflecting mirrors, wherein each of the plurality of reflecting minors is a minor that is comprised of:a silicon plate body subjected to plastic deformation, wherein the silicon plate body includes a reflecting surface, the reflecting surface of the silicon plate body having a degree of smoothness at an angstrom level for total X-ray reflection, wherein the reflecting surface of the silicon plate body is plastically deformed to have a given curved surface shape configured to totally reflect X-rays; anda large number of X-ray passage grooves formed on a reverse side of the reflecting surface of the silicon plate body to extend parallel to each other, wherein the large number of X-ray passage grooves are formed before the silicon plate body is subjected to the plastic deformation;wherein the plurality of reflecting mirrors are laminated such that the reflecting surface and the groove-formed reverse side are opposed to each other, and wherein the reflector is configured to allow X-rays entering one of the large number of X-ray passage grooves approximately parallel thereto to undergo total reflection at the reflecting surface of the silicon plate body opposed to the groove, and then exit from a distal end of the groove. 6. A reflecting device to totally reflect X-rays comprising:a plurality of reflectors, wherein each of the plurality of reflectors is a reflector that comprises:a plurality of reflecting minors, wherein each of the plurality of reflecting mirrors is a mirror that is comprised of:a silicon plate body subjected to plastic deformation, wherein the silicon plate body includes a reflecting surface, the reflecting surface of the silicon plate body having a degree of smoothness at an angstrom level for total X-ray reflection, wherein the reflecting surface of the silicon plate body is plastically deformed to have a given curved surface shape configured to totally reflect X-rays; anda large number of X-ray passage grooves formed on a reverse side of the reflecting surface of the silicon plate body to extend parallel to each other, wherein the large number of X-ray passage grooves are formed before the silicon plate body is subjected to the plastic deformation;wherein the plurality of reflecting minors are laminated such that the reflecting surface and the groove-formed reverse side are opposed to each other, and wherein the reflector is configured to allow X-rays entering one of the large number of X-ray passage grooves approximately parallel thereto to undergo total reflection at the reflecting surface of the silicon plate body opposed to the groove, and then exit from a distal end of the groove,wherein the plurality of reflectors are arranged around a straight line parallel to an entrance direction of X-rays so that the straight line becomes a rotation axis for the plurality of reflectors, in such a manner as to allow the X-rays exiting from the plurality of reflectors to be converged. 7. A method of producing a reflecting mirror to totally reflect X-rays, comprising:a smoothing operation of smoothing a surface of a silicon plate to a degree of smoothness at an angstrom level for total X-ray reflection;a groove forming operation of forming a large number of parallel grooves on a reverse surface of the silicon plate; anda plastically deforming operation of applying pressure and heat to the silicon plate by a master die having a given curved surface shape, to cause plastic deformation therein and thereby form the surface of the silicon plate to have the given curved surface shape configured to totally reflect X-rays, wherein the plastically deforming operation is performed after the groove forming operation. 8. The method as defined in claim 7, wherein the curved surface shape of the silicon plate includes a part of a paraboloid of revolution and a part of a hyperboloid of revolution. 9. The method as defined in claim 8, wherein the plastically deforming operation includes simultaneously performing annealing in hydrogen atmosphere. 10. The method as defined in claim 7, wherein the plastically deforming operation includes simultaneously performing annealing in hydrogen atmosphere. 11. The method as defined in claim 7, which comprises an operation of, after the plastically deforming operation, forming a single-layer or multilayer metal thin film on the smoothed silicon surface. 12. The method as defined in claim 7, wherein the groove forming operation includes lithography. |
|
summary | ||
description | The present invention relates to an electron beam irradiation device capable of finely processing a semiconductor device for use in a semiconductor device, in a manufacturing process of semiconductor devices such as LSIs. It is possible to say that the performance of a semiconductor device today largely depends on the accuracy of a fine processing (i.e., reducing the minimum feature size in semiconductor integrated system) through a semiconductor lithography technology (See FIG. 12). In a fine processing using a conventional lithography technology with light (electromagnetic wave) of a visible light band, the wavelength of light determines the resolution. Accordingly, as shown in FIG. 13, in order to achieve a finer processing, it is necessary to use light of a shorter wavelength band than a visible light region; e.g. EUV (Extreme Ultraviolet Rays) or X ray. However, it is not easy to design a device for generating light of such a short wavelength band, or an optical system for focusing the light beam which is patterned by reticle. For this reason, there has been a suggestion to use an electron beam (electron ray) in a fine processing by a semiconductor lithography technology, on the grounds that an electron beam is relatively easy to generate or control, though it is difficult to tailor diverging lens. However, a semiconductor manufacturing (lithography) device adopting an already-existing electron beam directly draws a circuit pattern of a semiconductor device with a use of a single electron beam. Accordingly, a large amount of irradiation time (several hours to several tens of hours) is required to draw an entire circuit pattern of a highly-integrated semiconductor device. In other words, a wavelength-dependent electron beam irradiation method for breaking through the limit of the fine processing is one dimensional exposure method for a practical. Therefore, a large amount of exposure time should be reduced and the development of two-dimensional irradiation is required. In recent years, in order to shorten the irradiation time of electron beam lithography, a two-dimensional irradiation method which collectively forms a two-dimensional electron beam pattern have been developed. Examples of such two-dimensional electron beam collective irradiation methods are called SCALPEL method developed by AT&T and PRIVAIL method developed by IBM. In the SCALPEL method as shown in FIG. 14(a), an electron beam 31 is projected on a reticule 32 having a dispersing section 32b which have device pattern on the surface of a membrane 32a. Through an optical system having an electronic lens 33 and a back focal plane filter 34, the emitted electron beam is projected on an electron ray resist. Thus, a circuit pattern is formed. This SCALPEL method is also described in Patent Citation 1. As shown in FIG. 15(a) and FIG. 15(b), in the PRIVAIL method, an Si substrate 44 on which a hole 44a is formed according to the pattern is used as a reticule. Toward this patterned Si substrate 44, an electron beam 41 is projected. Through an optical system, the electron beam 41 having passed the hole 44a is projected to an electron ray resist, thereby exposing the wafer to the beam. Examples of the optical system in PRIVAIL method are: an electronic lens 42; an illumination lens 43 having a yoke for polarizing an axis of the electron beam; a collimation lens 45; and a projection lens 46 having a contrast aperture 46. Note however that the PRIVAIL method is not able to manufacture an Si substrate 44 having a hollow portion as shown n FIG. 15(c). Patent Citation 2 describes the PRIVAIL method. (Patent Citation 1) U.S. Pat. No. 5,260,151 (Date of Patent: Nov. 9, 1993) (Patent Citation 2) U.S. Pat. No. 5,466,904 (Date of Patent: Nov. 14, 1995) As shown in FIG. 14(b), in the SCALPEL method, the electron beam 31 needs to pass the membrane 32a. Therefore, the resolution in that portion is significantly deteriorated. On the other hand, the PRIVAIL method has the following problem. When forming a complicated pattern (e.g. when forming a pattern as shown in FIG. 15(c) having a hollow part), we can not suspend the central Si substrate, and in order to fabricate the pattern shown in FIG. 15(c), we have to divide its pattern to two patterns without hollows which can not be suspended from anywhere. Moreover, we have to adjust the positions of two patterns with nanometer resolution. Due to the accuracy of the adjustment, the resolution is significantly limited at about 100 nm in the case of SCALPEL method. Both methods require troublesome operations such as manufacturing of reticule or adjusting the multiple masks positioning in vacuum. As above-described, the both methods have some fundamental problems. The present invention is aimed at providing an electron beam irradiation device capable of forming a highly accurate lithography pattern, using an electron beam. It is further an object of the present invention to provide an electron beam irradiation device capable of promptly forming a desirable two-dimensional lithography pattern at a low cost, by a two-dimensional collective irradiation. In order to achieve the foregoing object, an electron beam irradiation device of the present invention includes: a light pattern generating section for generating a two-dimensional light pattern; an electron amplification section for (i) generating an electron beam array based on the light pattern introduced, (ii) amplifying the electron beam array, and (iii) emitting the electron beam array as an amplified electron beam array; and an electron beam lens section for converging the amplified electron beam array toward an electron ray resist. In the electron beam irradiation device, above-mentioned electron beam lens section is preferably capable of performing at least one of (i) acceleration of the amplified electron beam array, (ii) alignment of the amplified electron beam array, and (iii) projection of the amplified electron beam array. In the above-mentioned system, the amplified electron beam array generated by the two-dimensional light pattern is projected toward the electron ray resist on the substrate having a metal thin film. Thus, it is possible to form a two-dimensional patterned electron beam array, and shorten the time of processing of electron beam irradiation. Furthermore, the system adopts the amplified electron beam array generated from a two-dimensional light pattern. Therefore, the intensity of the electron beam projected on the electron ray resist is enough increased. As a result, the time of electron beam irradiation is further reduced, and the lithography speed is improved. Accordingly, the system can improve the accuracy of the lithography pattern because of the use of short electron wave and the speed of forming the lithography pattern. Therefore, for example, fine processing of a semiconductor device with the minimum feature size of 5 nm or smaller is accurately and quickly performed. This allows manufacturing of a LSI having a highly integrated semiconductor device of 5 nm scale or smaller, at a low cost. Furthermore, when the electron beam lens section is capable of accelerating the amplified electron beam array, it is possible to shorten the wavelengths of the electron rays. In this case, it is possible to fabricate a more miniaturized lithography pattern, and improve the accuracy of the lithography pattern and the lithography speed. In addition, when the electron beam lens section is capable of aligning the amplified electron beam array, it is possible to further improve the accuracy of the lithography pattern. In the electron beam irradiation device, above-mentioned electron amplification section includes multiple cylindrical microchannels which are preferably arranged to be adjacent to one another in a direction perpendicularly crossing a direction of a light axis of the light pattern so that respective axes of the microchannels are parallel to the direction of the light axis. With the system having the microchannels, it is possible to more accurately form the amplified electron beam array which is a collection of micro electron beams obtained by dividing the light pattern having been projected. As a result, the system more surely yields the amplified electron beam array. Therefore, the speed of forming the lithography pattern can be improved. With this, for example, it is possible to more accurately, more finely, and promptly fabricate a semiconductor device, with the miniaturized feature size of 5 nm or smaller. This allows manufacturing of a LSI having a highly integrated semiconductor device of 5 nm scale or smaller, at a low cost. In the electron beam irradiation device, said electron amplification section preferably includes a photoelectric film for converting photons of a lithographic pattern into electrons and for emitting the electrons. In the system, the photoelectric section is provided on a light pattern entering side at the electron amplification section. Therefore, even if the light intensity of the light pattern from the light pattern generating section is low, an electron pattern according to the light pattern is amplified in the electron amplification section, and the amplified electron beam array is more surely obtained. In the electron beam irradiation device, said light pattern generating section preferably includes: a femto-second laser; and a micro-mirror array section for reflecting a laser beam from the femto-second laser, thereby forming the two-dimensional light pattern. In the system, the laser beam from the femto-second laser is turned into a two dimensional pattern by the micro-mirror array section. Then, when the light pattern is projected on the electron amplification section, the electron beam array according to the light pattern is generated in the electron amplification section. Therefore, the system allows formation of a semiconductor device through a highly accurate and prompt lithography, as in the case where the photoelectric film is used. Moreover, since the photoelectric film can be omitted in the system utilizing the femto-second laser, the vacuum state required for avoiding oxidation of a photoelectric film does not have to be maintained. Therefore, it is possible to restrain an increase in the size of the device and an increase in the cost. In the electron beam irradiation device, said light pattern generating section preferably includes a compensating section. The system is provided with the compensating section for compensating the distortion in the electron beam array. Therefore, by performing, on the light pattern side, the compensation of the projected pattern of the amplified electron beam array, it is possible to surely and promptly make the lithography pattern close to the desirable architected pattern. In the electron beam irradiation device, above-mentioned compensating section preferably includes a section generating reversely-distorted light pattern which in capable of controlling the light pattern in order to compensate distortion that occurs in the amplified electron beam array. The system is provided with the section generating reversely-distorted light pattern for generating the reverse-distortion light pattern in order to compensate distortion that occurs in the amplified electron beam array. Therefore, the accuracy of the lithography pattern is improved by the cancellation of the distortion. In the electron beam irradiation device, above-mentioned compensating section preferably includes a section generating divided light pattern which can generate multiple divided light patterns whose all patterns interpolate one another and form the desirable architected device pattern. Therefore, multiple divided and patterned electron beam arrays compensating one another are obtained from the divided light patterns. By projecting, on a specific area for an architected device on electron ray resist, the divided patterned electron beam arrays at different time along a time axis, it is possible to form the lithography pattern corresponding to the light pattern on the electron ray resist. At this point, it is possible to increase the distance between adjacent electron beams in each divided patterned electron beam array. Therefore, it is possible to reduce electrostatic interactions between adjacent electron beams in each divided patterned electron beam arrays, and between electrons dispersed inside the electron ray resist. As a result, with the system, an irradiated pattern with less distortion, corresponding to a desirable architected lithography pattern, can be obtained on the electron ray resist. It is possible to improve the accuracy of the irradiated pattern formed by the divided patterned electron beam array. It is preferable that the electron beam irradiation device includes: a grid electrostatic lens section 16 provided on an emitting side of the electron amplification section, for restraining divergence of emission angle of the amplified electron beam array from the electron amplification section. In the system, the amplified electron beam array passes the grid electrostatic lens section. Therefore, it is possible to restrain the divergence of the emission angle and make the beams of the amplified electron beam array parallel to one another, thereby reducing deterioration of the resolution due to the divergence. Furthermore, since the divergence of the emission angle is restrained, the projected pattern is made closely resemble to the desirable architected pattern. Thus, the accuracy in the lithography pattern is improved. In the electron beam irradiation device, each above-mentioned microchannels preferably have such a shape that its inner surface at an edge portion, on an emission side of the amplified electron beam array, is gradually spread outwardly towards an emission end of the microchannel, for a purpose of restraining divergence of emission angle of the amplified electron beam array from the electron amplification section. In the system adopting the outwardly-spread shape, each micro electron beam of the amplified electron beam array is directed in order to be substantially parallel to the central axis of the corresponding microchannel, as is the case of adopting the grid electrostatic lens section. Since the divergence of the emission angle is restrained, it is possible to reduce deterioration of the resolution caused by the divergence. Furthermore, it is possible to improve the resemblance of the formed pattern compensating to the desired pattern. Thus, the accuracy of the lithography pattern can be improved. As mentioned above, an electron beam irradiation device of the present invention includes: a light pattern generating section for generating a two-dimensional light pattern; an electron amplification section for (i) generating an electron beam array from the light pattern entered, (ii) amplifying the electron beam array, and (iii) emitting the electron beam array as an amplified electron beam array; and an electron beam lens section for converging the amplified electron beam array toward an electron ray resist. Accordingly, with the system, it is possible to perform highly-accurate, programmable, and high-resolutional lithography by projecting the patterned amplified electron beam array. As a result, as mentioned above, it is possible to, for example, perform finer processing with the more miniaturized feature size of about 5 nm or smaller. Thus, it is possible to manufacture a LSI having a semiconductor device of 5 nm scale or smaller. The following describes an embodiment of an electron beam irradiation device and a semiconductor manufacturing device, according to the present invention, with reference to FIG. 1 through FIG. 11. As shown in FIG. 1, the semiconductor manufacturing device having the electron beam irradiation device has a box-like vacuum chamber 1. The vacuum chamber 1 is capable of maintaining vacuum state therein, and is provided in such a manner that a degree of vacuum in the vacuum chamber 1 is not more than 10−6 Torr. In the present embodiment, the degree of vacuum is set at 10−8 Torr. In a bottom portion of the vacuum chamber 1, a stage 2 for placing thereon a substrate 5 to be subject to an irradiation is mounted in such a manner that the stage 5 is moveable in horizontal directions. Inside or outside the vacuum chamber 1, a mechanical drive 3 for driving and moving the stage 2 is provided in such a manner that a later-mentioned controller 17 is able to control the mechanical drive 3. Further, a stage position monitor 44 for monitoring the position of the stage 2 (i.e., to which position the stage 2 has moved) is provided. The stage position monitor 44 informs the controller 17 of a monitored position. On a surface of the substrate 5 placed on the stage 2, a thin film 6 (e.g. metal thin film, semiconductor film, insulation film) for forming a circuit of a semiconductor device is formed. Further, on a surface of the thin film 6, an electron ray resist 7 is applied. For example, the electron ray resist 7 can be a positive resist or a negative resist. As the positive resist, a macro molecule whose principal chain is quaternary carbon is preferable, on the ground that a ratio of the principal chain broken by an electron ray (in actinochemistry, G-value standing for the number of reactions for every 100 eV is used) is large. Examples of the macro molecule of the positive resist are: halogenated poly acrylate such as poly methyl methacrylate (PMMA), poly hexafluoro butyl methacrylate (FBM), poly (trifluoro-α-chloroacrylate) (EBR-9), or the like; and a copolymer of methyl acrylate. Other examples of macro molecule of the positive resist are: poly butene-1-sulfone which is highly sensitive (1 μC/cm2); and DNQ-novolac resin. For example, the DNQ-novolac resin is made of novolac resin and poly methyl pentene sulfone (PMPS). Alternatively, the positive resin may be a chemically amplified resist which utilizes an acid catalyst deprotection reaction. The negative resist may be: poly (glycidyl methacrylate) (PGMA); a copolymer (COP) of glycidyl methacrylate and ethyl acrylate; or a resist of polystyrene, each containing an epoxy group, which utilizes its characteristic that its macromolecule exhibits a high sensitivity in a cross-linking reaction with an electron ray. The resist of polystyrene is a copolymer of a monomer containing an epoxy group and a monomer containing an aromatic ring. To improve the sensitivity, each resist may contain, in its chemical structure, at least one of halogen, chlormethyl group, and allyl group. Nearby the top portion of the vacuum chamber 1, a projector (light pattern generating section) 8 for generating a two-dimensional light pattern 13 corresponding to a circuit pattern of the semiconductor device is provided so as to emit the light pattern 13 from a light-emission surface of the projector 8. Examples of the projector 8 are: a projector adopting a transmissive liquid crystal method; and a projector adopting a single plate DLP (Digital Light Processing) method. A slight amount of photons existing in the dark portion of the light pattern 13 is multiplied by 1000 or more by a later-mentioned MCP 11, and is eventually project on a targeted portion of the electron ray resist 7 which is subject to the irradiation. Therefore, the projector is preferably the one adopting a single plate DLP method whose contrast ratio is generally high. In case where an electron ray resist 7 is a resist material having a sufficient photosensitivity, and the contrast ratio of the projector 8 becomes a problem, a mask to block light may be arranged on a top surface (light entering surface) of the MCP 11 instead of using the projector 8. That is, by setting a photomask (including a liquid crystal shutter or the like) on a back surface of the MCP 11 (a light pattern 13 entering side), and by projecting light on the entire back surface of the MCP 11, it is not necessary to use the projector 8. In this case, however, it is necessary to set a photomask for every light pattern 13. The photomask does not require a high resolution, because a patterned amplified electron beam array 14 is eventually converged through a later-mentioned electron beam lens section 12. Further, the projector 8 and the later-mentioned lens 9 can be replaced with an organic electroluminescence light emission section (hereinafter, EL light emission section) on which organic electroluminescence devices are arranged in a matrix manner. In this case, the following is also possible. The EL light emission is integrated with a later-mentioned photoelectric film 10. From the EL light emission, a light pattern 13 is directly projected to the photoelectric film without changing the size, so that a patterned electron beam array corresponding to the light pattern is projected from the photoelectric film 10 into the later-mentioned MCP 11. In either cases, the accuracy of the light pattern only needs to be a micrometer level at the later-mentioned stage where the photoelectric film 10 is projected; i.e., at a position where the photoelectric film enters the later-mentioned MCP 11. On the light path of the light pattern 13, the microchannel plate (hereinafter, MCP (electronic amplification section)) 11 is provided. The MCP 11 generates a patterned electron beam array from the light pattern 13 having entered, amplifies the electron beam array to several thousands to several tens of thousand times, and then emits the amplified patterned electron beam array 14. This MCP 11 is provided so that the light path of the amplified electron beam array 14 extends substantially along the light path of the light pattern 13. On the light path between the projector 8 and the MCP 11, it is possible to provide as needed a convex or a concave lens 9 for allowing the light pattern 13 to efficiently enter the MCP 11. Further, on the light-entering side of the MCP 11, it is preferable to provide a photoelectric film 10 for converting the entered light into electrons, and emitting the electrons. Representative examples of a material for the photoelectric film 10 are: a multi alkali material (e.g. Na—K—Sb—Cs), a bi-alkali material (e.g. Sb—Rb—Ce, Sb—K—Cs), Ce—Te, Ag—O—Cs, GaAs, GaAsP or the like. CdS is widely used in the visible region. To increase the sensitivity, Cu, Ag, Sb or the like is added in general. The present embodiment deals with a case where CdS is adopted. Note that the photoelectric film 10 can be omitted if photons of the light pattern 13 have energy which is larger comparing to the work function of the semiconductor section on the inner surface of the microchannel of the MCP 11. Further, the photoelectric film 10 is not needed either, in cases where a light pattern 13 of a short-wavelength UV ray of 200 nm or shorter is projected on the inside of the MCP 11. This is because secondary electrons are generated in the semiconductor section on the inner surface, and the amplified beam array 14 corresponding to the light pattern 13 can be obtained. The light pattern 13 of a UV is produced by providing a UV photo mask on a top surface (on the light-entering side) of the MCP 11. Next, the following describes the MCP 11. As shown in FIG. 2 and FIG. 3, the MCP 11 includes multiple cylindrical microchannels 11a. The microchannels 11a are formed so that: (i) they are adjacent and in parallel to one another (in a direction which perpendicularly crosses a light axis of the light pattern 13); and (ii) each of the microchannels 11a is extended in the direction of the light axis. The cylindrical shape of the microchannels 11a may be: a circular-cylindrical shape; a rectangular-cylindrical shape; or a hexagonal-cylindrical shape. However, in the present embodiment, a circular-cylindrical shape is adopted. The following explanation regarding manufacturing of the MCP 11 deals with a single microchannel 11a of the MCP 1. First, in a main body 11b made of a lead glass plate for example, multiple cylindrical sections each extended in the thickness direction of the main body 11b are formed in parallel to one another. Each cylindrical section is 1 μm to 100 μm in diameter. A ratio (L/d) of the diameter versus the length of the cylindrical section is 20 to 2000, and is preferably 40 to 100. In the present embodiment, the diameter is set at 2μ to 10 μm, and the ratio (L/d) is set between 40 to 80. Further, the axis of the cylindrical section may be parallel to the normal direction of a surface of the lead glass, or tilted by approximately 8° with respect to the normal direction. In the present embodiment, the axis of the cylindrical section is parallel to the normal direction. On the inner surface of each cylindrical section, a semiconductor section 11c is formed. The semiconductor section 11c is such that, when a single electron hits, secondary electrons are emitted multiple. The semiconductor section 11c is formed as a resistive semiconductor section on a surface of the main body 11b, by subjecting the main body 11b to a reduction process under a hydrogen atmosphere, at a high temperature of 250° C. to 450° C. The resistance of the semiconductor section 11c in the thickness direction of the main body 11b is set within a range from 108Ω to 1010Ω. The semiconductor section 11c may be a diamond-like carbon film deposited by means of plasma CVD (Plasma Chemical Vapor Deposition). Subsequently, electrodes 11d and 11e are respectively formed on both sides of the main body 11 made of the lead-glass plate, the main body 11 having the cylindrical semiconductor sections 11c are formed in the thickness direction. The electrodes 11d and 11e are formed through vapor deposition of Nichrome or Inconel. Thus, microchannels 11a as shown in FIG. 4 are manufactured. Here, the electron-entering side of each of the microchannels 11a is negative, and the electron-emitting side of the same is positive. When a direct voltage of 600 to 1100V is applied between the electrodes 11d and 11e of the microchannel 11a, a single electron 25 enters from the side of the electrodes 11d on the electron-entering side. Then, the single electron 25 hits the semiconductor section 11c in the microchannel 11a, and multiple secondary electrons 27 are emitted in the hitting direction. The emitted electrons 27 hit the semiconductor section 11c, and emits more electrons. This process is repeated, and from a single electron, 5×102 to 3×105 electrons 25 are emitted in the form of electron beam 29. The curve “CHEVRON” in FIG. 5 shows a case where the MCP 11 includes two stages in series. The electrons in the electron beam 29 from each microchannel 11a are intermittently emitted due to the charge/discharge characteristic of the MCP 11. Therefore, respective electrons of the adjacent electron beams 29 hardly becomes adjacent to each other. In other words, the electrons of the beams 29 hardly come close to each other by a distance between the respective central axes of the electron beams 29. Thus, repulsion between the electron beams 29 is weak. Thus, the foregoing amplified electron beam array 14 is a collection of the multiple electron beams respectively from the microchannels 11a. The electron beams are apart from one another, and are emitted in the direction of the light path of the light pattern 13 (i.e., the lengthwise direction of the microchannels 11a). However, the multiple micro electron beams do not necessarily have to be in parallel to the lengthwise direction or the direction of the light path, and the beams may be slanted, as long as they are converged on the surface of the electron ray resist. Here, it is possible to replace the photoelectric film 10 and the MCP 11 with HARP (High-gain Avalanche Rushing amorphous Photoconductor) film, in which case the HARP is used as an avalanche type photoconductor film. HARP film is a film of an amorphous selenium to which a high voltage is applied. When light is incident on the surface of the HARP film, photoelectric conversion occurs in the HARP film, and avalanche amplification of charge occurs in the same. Thus, electrons are emitted. Accordingly, when the light pattern 13 is incident on one surface of the HARP film, a patterned amplified electron beam array 14 is emitted from a surface on another side of the HARP film. Further, in the present embodiment, the combination of the light pattern generating section 8, photoelectric film 10, and MCP 11 can be replaced with another device. The other device can be any device provided that the device is capable of generating a patterned amplified electron beam array 14 through a voltage control, and that a resist is exposed to the electron beam array 14. Such a device may be any one of the following electron emitting source: a surface-conduction electron-emitter (SED); a micro-dip array having a sharp end portion made of silicon or molybdenum, carbon nanotube array; and a field emission display (FED) such as a diamond thin film or the like As shown in FIG. 1, FIG. 6, and FIG. 7, the vacuum chamber 1 includes an electron beam lens section 12 for accelerating, converging, aligning, and projecting the amplified electron beam array 14 emitted from the MCP 11, along the light path of the patterned amplified electron beam array 14. The electron beam lens section 12 includes: an accelerating tube section 12a; a converging lens section 12b; a multipole polarization electrode section 12c for alignment; and a projection lens section 12d, each section being arranged along a direction in which the amplified electron beam array 14 travels. The electron beam lens section 12 at least includes the converging lens section 12b. However, the electron beam lens section 12 may further include as needed at least one of accelerating tube sections 12a, a multipole polarization electrode section 12c for alignment, and a projection lens section 12d. The accelerating tube section 12a is for accelerating the amplified electron beam array 14, shortening the wavelength of each electron ray, and improving the lithography resolution on the electron ray resist 7. The converging lens section 12b is for converging the patterned amplified electron beam array 14 in the in-plane direction which perpendicularly crosses the light path of the array 14. The multipole polarization electrode section 12c is for compensating distortion in the amplified electron beam array 14 having passed the converging lens section 12b. The projection lens section 12d is for projecting, on the electron ray resist 7, a desirably sized amplified electron beam array 14 having passed the multipole polarization electrode section 12c, thereby forming the lithography pattern 14a corresponding to the amplified electron beam array 14. With the accelerating tube section 12a such as an acceleration lens or an acceleration electrode, the wavelength of each electron ray in the amplified electron beam array 14 is shortened to approximately 0.01 nm, at 100 keV. Therefore, with the amplified electron beam array 14 whose wavelengths are shortened, it is possible to form finer lithography pattern 14a of 5 nm scale or smaller on the electron ray resist 7 exposed. After that, a highly integrated semiconductor device having a fine pattern is formed through an ordinary semiconductor manufacturing process. As shown in FIG. 1, a controller (compensating section) 17 is provided in a computer. The controller 17 is for generating a two-dimensional light pattern 13 in the projector 8, controlling an electron beam lens section 12, and controlling mechanical drive 3 for moving and driving the stage 2. To this controller 17, connected are (i) a display 18 serving as a display output section and (ii) an input section 19 such as a keyboard or a mouse. Then, the controller 17 is set so as to also serve as a compensation section for compensating the light pattern 13. That way, distortion in the lithography pattern 14a formed by accelerating, converging, aligning and projecting the amplified electron beam array 14 is reduced. A first exemplary compensation could be compensation of distortion in the electron beam lens section 12. An electric field generated by the electron beam lens section 12 spatially exhibits its intensity distribution. Therefore, the rate of reduction nearby the center of the patterned amplified electron beam array 14 converged differs from that nearby the periphery of the array 14. In order to solve this problem, the controller 17 controls the projector 8 so as to generate an entering light pattern (reverse distortion light pattern) which is a product of inverse function of distortion which occurs in the electron beam lens section 12 in relation to a desirable pattern. As such, the controller 17 includes a reverse distortion light pattern generating section. Accordingly, in the first example, distortion of the lithography pattern 14a formed by the amplified electron beam array 14, which distortion occurs in the electron beam lens section 12 is canceled by the entering light pattern. Further, it is possible to obtain, on the electron ray resist 7, a lithography pattern 14a formed by converging and projecting the two-dimensional amplified electron beam array 14, which pattern corresponds to a desirable circuit pattern, with an ordinary resolution of electron beams. As a result, in the first example, the lithography pattern 14a which is an irradiated pattern formed by the amplified electron beam array 14 can be formed highly accurately and programmably, by performing the compensation from the side of the light pattern 13. Therefore, for example, it is possible to perform finer processing with the more miniaturized feature size of 5 nm or smaller, and a LSI having a semiconductor device of an about 5 nm scale or smaller can be manufactured programmably at a low cost. Next, a second exemplary compensation is described below. The second exemplary compensation is for avoiding lowering of the resolution which occurs as follows. As the amplified electron beam array 14 is converged on the electron ray resist 7 through the electron beam lens section 12 and approaches the electron ray resist 7 (see FIG. 8(a) and FIG. 8(b)), a force of interaction between adjacent micro electron beams 14b increases as shown in FIG. 8(c). The force of interaction causes scattering of the beams, consequently deteriorating the resolution. In view of the problem, as shown in FIG. 9(a), the projector 8 is controlled by the controller 17 so as to generate in a time-sharing manner, multiple divided light patterns 11a-1 to 11a-3, which compensate one another, from the light pattern 13 entering the microchannels 11a arranged in a matrix manner in the MCP 11. Since each of the divided light patterns 11a-1 to 11a-3 are formed so as to compensate one another, overlapping of all the patterns will restore the light pattern 13 as shown in FIG. 9(b). Thus, the controller 17 includes a section generating divided light pattern. As described, in the second exemplary compensation, the micro electron beams 14b in each of the divided light patterns 11a-1 to 11a-3 to be projected on the electron ray resistor 7 are apart from one another. Therefore, the problem caused by the force of interaction is further restrained. Thus, the second exemplary compensation also prevents lowering of the resolution, and thereby allows highly accurate and programmable manufacturing of a super high-density LSI, at a low cost. Here, Embodiment 1 deals with a case of three divided light patterns 11a-1 to 11a-3; however, it is possible that the number of divided light patterns is 100 for example. Since each divided light pattern is controlled by light, it is possible to successively project the 100 divided light patterns in milli second order. Further, in the electron beam irradiation device or the semiconductor manufacturing device of the present invention, a grid electrostatic lens section 16 can be provided on the emission side of the MCP 11 as shown in FIG. 10(a) and FIG. 10(b), to prevent lowering of the resolution caused by uneven emission angle of the amplified electron beam array 14 from the MCP 11. The grid electrostatic lens section 16 has hollow sections 16a which are aligned in a grid manner so as to respectively correspond to microchannels 11a of the MCP 11. Each of the hollow sections 16a is formed so that a space is formed in the direction in which an amplified electron beam from the associated one of microchannels 11a travels. When a voltage is applied to the grid electrostatic lens section 16, a force that attracts the amplified electron beam array 14 from the MCP 11 is generated. By letting the amplified electron beam array 14 having been accelerated pass the hollow sections 16a arranged in the grid manner, the beams in the array 14 are made parallel to each other, and the divergence of the emission angle is restrained. Therefore, lowering of the resolution attributed to the divergence is restrained, and the lithography pattern 14a is mad more similar to the light pattern 13. Thus, a highly accurate lithography pattern 14a is obtained. As described, when: (I) using the MCP 11 having microchannels 11a each of which is 10 μm in diameter, and which are arranged so that a distance from the center of one microchannel 11a to that of an adjacent microchannel 11a is 12 μm; and (II) supposing that a total irradiation current is 20 mA when a rated electron voltage of 2 keV is applied to each of electrodes 11d and 11e of the MCP 11, a micro electron beam 14b of 0.5 μA is obtained from each microchannel 11a of the MCP 11, and the speed of irradiation is 40000 times faster than a lithography process using a conventional electron beam 14c obtained by using the same irradiation current (See FIG. 11(a)). This value of speed of irradiation corresponds to the number of microchannels 11a formed in the MCP 11. As such, it is believed that increasing the number of the microchannel 11a in the MCP will further accelerate the irradiation speed (lithography speed) proportionally. Further, from a calculation supposing that a total amount of overall electrons used in exposing the electron ray resist 7 and the wavelength are the same as the conventional case, it is believed that the resolution of lithography improves 40000 times better than that using a conventional electron beam. This is based on the supposition that the resolution (i.e., diffusion of electron beams) is proportional to the primary current. From the above result, it is apparent that the electron beam irradiation device and the semiconductor manufacturing device of the present invention have high potentials. Further, since the present invention adopts an electron beam which allows fine irradiation and processing beyond the limit of the wavelength of light, the present invention allows irradiation of resist and direct fine processing in a manufacturing process of a semiconductor device or a micro machine. Furthermore, in the present invention, a two dimensional pattern formed by electron beams is projected at once. Therefore, reticule is no longer needed, and high-speed and programmable irradiation and processing are possible. Since the wavelength of the electron beam is dependent on a acceleration voltage, accelerating an electron ray by applying a high voltage allows a fine processing according to the accelerated speed. The present invention provides drastic solutions to conventional problems which caused difficulties in practical application, and largely advances LSI manufacturing technologies. For example, conventionally, in manufacturing of 1G DRAM adopting rules of 180 nm to 150 nm scale, an excimer laser (wavelength: 193 nm) is used. Through the two-dimensional collective (one-time) irradiation of the present invention, fine processing at an irradiation wavelength of 1/10,000 or shorter is possible (10T DRAM is possible), ideally. Therefore, a significant improvement of LSI performance is expected, even after considering the diffusion of electron. The following describes an electron beam irradiation device of Embodiment 2 according to the present invention, with reference to FIG. 16 and FIG. 17. In Embodiment 2, the members having the same functions as those described in Embodiment 1 are given the same symbols, and explanation therefor are omitted here. First, Embodiment 1 deals with a case of adopting a photoelectric film 10. Since the photoelectric film 10 cannot be exposed to the air, it is necessary to maintain the vacuum state. Due to such a photoelectric film 10, the entire device such as the vacuum chamber 1 and vacuum pump is enlarged. In view of the problem, in the present embodiment, the projector 8 is replaced with a different light pattern generating section 21 so as to eliminate the photoelectric film 10 (See FIG. 16). The light pattern generating section 21 includes a femto-second laser 22, and a micro-mirror array section 23 for reflecting thereon a laser beam from the femto-second laser 22 in a form of two dimensional light pattern. An example of the femto-second laser 22 is a femto-second laser whose cyclic frequency is 50 MHz, pulse width is 90 fsec (femto second) to 180 fsec, wavelength is in the visible region (e.g. 780 nm). Specifically, for example, a titanium-sapphire laser or a Yb:YAG laser can be used. Further, the average output of the femto-second laser 22 is, for example, 10 mW to 60 mW. As shown in FIG. 17, the micro-mirror array section 23 includes: a substrate 23a; multiple drive sections 23b; and micro mirrors 23c respectively driven by the drive sections. An example of the micro-mirror array section 23 is Digital Mirror Device®. Each of the micro mirrors 23c is a mirror formed in the form of a square plate, which mirror reflects visible light. The micro mirrors 23c are arranged in a matrix manner. The number of micro mirrors ranges from 480 thousand to 1.31 million. Here, “arranged in a matrix manner” means that the micro mirrors 23 are aligned in a checker-board manner. That is, the micro mirrors are aligned in a raw direction and a column direction which cross each other (preferably cross each other perpendicularly), so as to form a two-dimensional light pattern 13. In Embodiment 2, the micro-mirror array section 23 adopted includes micro mirrors 23c which are divided into 16×64 blocks corresponding to 64×16 of data transmission unit blocks. Further, the drive sections 23b are provided for the micro mirrors 23c on a one-by-one basis. For example, each micro mirror 23c is able to rotate by approximately ±12 degrees, about its rotation axis which is the central axis extended in the raw direction. Further, the drive section 23b is capable of repetitively rotating the associated micro mirror 23c several thousand times in a single second. The control of the drive sections 23 is similar to image displaying control in a liquid crystal panel, and is as described below. First, two-dimensional pattern data for the light pattern 13 is latched (to retain data to synchronize the data) by a shift register. Then, data loading is performed for each of the blocks of the micro mirrors 23c forming a matrix. Subsequently, information of 0 or 1 (i.e., information of plus 12 deg. or negative 12 deg. for example) is transmitted to a row element designated by a row decoder for each micro mirror 23c. Based on the information, each drive section 23b slants the micro mirror 23c as in the case of micro mirror 23c1 or 23c2. Then, the laser beam 22a from the femto-second laser 22 is projected on each of the micro mirrors 22c. Then, light having reflected on the micro mirror 23c is projected on the microchannel 11a of the MCP 11, in the form of the light pattern 13. In the semiconductor section 11c on the inner surface of each microchannel 11a, the total energy of multiple photons in the light pattern 13 is larger than the energy of the work function of the semiconductor section 11c. As such, a multiphoton excitation state occurs, and electrons are mainly emitted in a direction corresponding to the direction in which the photons have entered. As mentioned above, secondary electrons are generated in the semiconductor section 11c from the electrons emitted. Then, lithography is performed by converging the patterned amplified electron beam array 14 on the electron ray resist 7, as is already mentioned. With Embodiment 2, it is possible to form a lithography pattern 14a of 5 nm or less in line width on the electron ray resist 7 by performing a programmable irradiation using the amplified electron beam array 14. Further, it is possible to omit the photoelectric film 10 which requires maintenance of the vacuum state. Therefore, it is possible to downsize the electron beam irradiation device and vacuum pomp, and to lower the costs. Further, in Embodiment 2, the micro-mirror array section 23 is used. Therefore, by individually controlling the micro mirrors 23c, it is possible to correct the light pattern 13 as is done in Embodiment 1. Note that both Embodiments 1 and 2 deal with a case where the shape of the inner surface of each microchannel 11a is in a straight cylindrical shape with its inner diameter kept constant from the light-entering side to the light-emitting side. However, as shown in FIG. 18, it is possible to adopt an electron beam reshaping section 11h whose end on the light-emitting side has an outwardly-spread shape. Here, by “outwardly-spread shape”, it means that the inner diameter is gradually increased towards the end on the light-emitting side. With the electron beam reshaping section 11h having the outwardly-spread shape, the electron beam emitted from the microchannel 11a can be collimated: i.e., the electron beam is directed to a direction corresponding to the direction of the central axis of the microchannel 11a. Accordingly, even without the grid electrostatic lens section 16, the alternative form yields an effect similar to that obtained when the grid electrostatic lens section 16 is provided. This allows, while allowing downsizing, formation of highly fine lithography pattern. Further, the electron beam irradiation device may be adapted so that the electron amplifying section is an avalanche photoconductor film. In the electron beam irradiation device, the light pattern generating section may include a light source, and a mask pattern for generating the light pattern with the light from the light source. With the system adopting the mask pattern, the light pattern generating section is simplified, and the overall cost can be reduced. Further, if distortion in the lithography pattern is predictable to a certain degree, the distortion can be restrained by using a mask pattern corrected according to the predicted distortion. That way, the accuracy of the lithography pattern can be improved. In order to solve the foregoing problems, a semiconductor device of the present invention includes: a vacuum chamber; any one of the above mentioned electron beam irradiation devices which is provided inside the vacuum chamber; an electron ray resist, provided inside the vacuum chamber, on a surface of which resist an amplified electron beam array is converged; and a stage for placing thereon a substrate having the electron ray resist on its surface, the irradiation device having a light pattern generating section for generating a two-dimensional light pattern according to a circuit pattern of a semiconductor device. With the system having the electron beam irradiation device of the present invention, the light pattern generating section generates a two-dimensional light pattern according to a circuit pattern of a semiconductor device. Based on the light pattern, a patterned electron beam array is generated. By accelerating the electron beam array, it is possible to achieve the shortest possible wavelength of electron rays in the electron beam array. Accordingly, for example, it is possible to perform a fine processing with feature size of 5 nm or smaller. Therefore, it is possible to manufacture a LSI having a semiconductor device of about 5 nm scale or smaller. The semiconductor manufacturing device preferably includes a substrate moving section for moving the substrate in a direction perpendicularly crossing a direction in which the amplified electron beam array to be converged on the substrate is projected. In the system, there is provided the substrate moving section for moving the substrate (e.g. a wafer of 100 mm or 500 mm in diameter) in the direction perpendicularly crosses the amplified electron beam array projecting direction (e.g. a horizontal direction). Therefore, it is possible to form a lithography pattern according to a circuit pattern, by moving the substrate. Thus, it is possible to form a lithography pattern corresponding to a circuit pattern, even on a substrate having a large surface area. Further, by performing compensation on the light pattern side by using a compensating section in the used irradiation device, distortion in the formed pattern is restrained. Thus, it is possible to manufacture a super-highly-integrated semiconductor device more accurately and promptly. As mentioned above, the semiconductor manufacturing device of the present invention includes the electron beam irradiation device of the present invention, and the light pattern generating section generates a two-dimensional light pattern according to a circuit pattern of a semiconductor device. Therefore, with the system, it is possible to highly accurately and programmably form a desirable circuit pattern at a high resolution, which pattern is formed by the amplified electron beam array. As a result, for example, it is possible to perform a fine processing with the minimum feature size of 5 nm or smaller, and manufacture a LSI having a semiconductor device of 5 nm scale or smaller. An electron beam irradiation device of the present invention allows speeding up of a pattern irradiation using an electron beam capable of finer processing. Therefore, it is possible to manufacture at a low cost a semiconductor device whose performance is improved through a finer processing. Since the electron beam irradiation device of the present invention is capable of simplifying and speeding up a manufacturing process of more highly accurate semiconductor device, the device is suitably applicable to a field of manufacturing semiconductors such as a lithography device and LSI, a field of communications devices such as mobile phones using LSIs, and a computer field in which semiconductor devices such as LSIs are used in many occasions. |
|
summary |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.