JP4795879B2 - Identification method of plutonium generating element and computer program for identification - Google Patents

Description

  The present invention relates to management of plutonium (Pu) contained in MOX fuel.

  MOX (Mixed Oxide: mixed oxide) fuel, which is a kind of nuclear fuel, is a fuel in which uranium (U) is mixed with plutonium (Pu). Plutonium is produced by neutron absorption of uranium fuel. In addition, the generated plutonium disappears by causing fission in the core of the nuclear reactor. The burned MOX fuel contains plutonium produced from uranium contained in the MOX fuel and plutonium originally contained in the MOX fuel, and there is a demand for distinguishing these. That is, there is a demand for identifying and grasping plutonium generation elements contained in the burned MOX fuel. For example, Patent Document 1 discloses a technique for solving a combustion equation for each origin of heavy element nuclides from the amount of heavy element nuclides by source and the neutron flux of the fuel of interest from time to time, and calculating the amount of heavy element nuclides by time from time to time. Is disclosed. The identification can also be used for plutonium nationality management.

JP-A-7-181283

  Since the technique disclosed in Patent Document 1 can calculate the amount of heavy element nuclides by origin, for example, in identifying a plutonium production source element, U-235 of Pu-239 present in the burned MOX fuel. Can be obtained up to the original amount. However, for this reason, there is a problem that it takes time to identify the plutonium generating element contained in the burned MOX fuel.

  Therefore, the present invention has been made in view of the above, and a method for identifying a plutonium generating element and a plutonium generating element capable of shortening the time required to identify the plutonium generating element contained in the burned nuclear fuel An object of the present invention is to provide a computer program for identification.

  In order to achieve the above-mentioned object, the method for identifying a plutonium production element according to the present invention relates to the nuclear transmutation in a nuclear reactor in identifying the plutonium (Pu) production element contained in the burned nuclear fuel. A first combustion calculation procedure for calculating a combustion equation as a chain of the transmutation, and at least a chain in a process of converting uranium (U) to plutonium (Pu) for nuclear transmutation in a nuclear reactor. A second combustion calculation procedure for calculating a combustion equation using a reaction cross-sectional area and a neutron flux in the first combustion calculation procedure under a condition in which one place is divided, and the first combustion calculation procedure. Further, based on the amount of elements contained in the nuclear fuel and the amount of elements contained in the nuclear fuel calculated in the second combustion calculation procedure, Characterized in that it comprises a step of identifying the origin of the element plutonium (Pu) contained in the fuel, the.

  With this configuration, this plutonium production element identification method can identify plutonium originally contained in nuclear fuel (MOX fuel) and plutonium produced from uranium contained in nuclear fuel. . As a result, since it is not necessary to determine the amount of plutonium contained in the burned nuclear fuel for each origin, it is possible to shorten the time required to identify the plutonium generating element contained in the burned nuclear fuel. In addition to the mass of the nuclide, the amount of the element includes the mass of the nuclide per unit fuel mass, the number of the nuclide, and the number density of the nuclide.

  In identifying the plutonium production element according to the present invention, in the plutonium production element identification method, in identifying the plutonium (Pu) production element contained in the burned nuclear fuel, The plutonium (Pu) obtained in the second combustion calculation procedure is defined as plutonium (Pu) contained in the original nuclear fuel, and the plutonium (Pu) obtained in the first combustion calculation procedure and the second The difference from the plutonium (Pu) obtained in the combustion calculation procedure is preferably plutonium generated from uranium (U) contained in the original nuclear fuel.

  As in the method for identifying a plutonium producing element according to the present invention, in the method for identifying a plutonium producing element, in the second combustion calculation procedure, in the conversion process from U-236 to Pu-238, nuclear conversion It is preferable to calculate the combustion equation under a condition in which at least one part of the chain is divided and at least one part of the transmutation chain in the process of conversion from U-238 to Pu-239.

  In the plutonium production element identification method, as in the plutonium production element identification method of the present invention, the second combustion calculation procedure divides the decay of U-237 and the decay of Np-239. It is preferable to calculate the combustion equation under conditions or conditions that divide the generation of U-237 and the generation of Np-239.

  A computer program for identifying a plutonium generator element according to the present invention is characterized by causing a computer to execute the plutonium generator element identification method.

  Thereby, the identification method of the plutonium production | generation element can be implement | achieved by a computer.

  With the method for identifying a plutonium producing element and the computer program for identifying a plutonium producing element according to the present invention, the time required to identify the plutonium producing element contained in the burned nuclear fuel can be shortened.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the best mode for carrying out the invention (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, or those that are substantially the same, so-called equivalent ranges.

  In this embodiment, in order to identify the element that produces plutonium remaining in the burned nuclear fuel (especially the MOX fuel), the combustion equation is calculated assuming that the transmutation chain is continuous for the transmutation in the nuclear reactor. A first combustion calculation procedure for calculating the combustion equation under a condition in which at least one part of the chain in the process of conversion from uranium (U) to plutonium (Pu) is divided for nuclear conversion in the nuclear reactor It is characterized in that it includes a combustion calculation procedure.

  FIG. 1 is a conceptual diagram showing a transmutation chain. 2 and 3 are explanatory diagrams showing an example of an isotope table created by using the plutonium production element identification method according to this embodiment. The isotope table (first isotope table) 1 shown in FIG. 2 and the isotope table (second isotope table) 2 shown in FIG. 3 are provided for each fuel assembly arranged in the nuclear reactor or for each same fuel type. Alternatively, it is created for each fuel assembly of the same fuel type and loaded in the core at the same time. The 1st isotope table 1 and the 2nd isotope table 2 describe the mass of the nuclide contained in the nuclear fuel with respect to the burnup.

  Combustion of nuclides in a nuclear reactor involves not only fission reaction due to neutron absorption but also conversion to other nuclides due to neutron capture reaction and decay of nuclides. Of particular importance is the production and consumption of plutonium. In MOX fuel, each of plutonium originally present in MOX fuel and plutonium produced from uranium undergoes fission, so it was originally included in MOX fuel, which occupies the final remaining plutonium in MOX fuel. It is difficult to identify the proportion of plutonium and plutonium produced from uranium in the reactor.

  Here, in managing the nationality of plutonium, it is not necessary to identify the nuclide of the element that is the source of plutonium, as in the method of Patent Document 1, and if the element that is the source of plutonium can be identified. Good. That is, it is not necessary to identify whether the element that has generated plutonium is U235 or U238.

The chain of each conversion shown in FIG. 1 is expressed by a simultaneous equation of a first-order differential with respect to time, as shown in Expression (1).
dN _i (t) / dt = g _i−1 N _i−1 (t) −l _i N _i (t) (1)
N is the number density of each nuclide, g is a time constant related to generation, and l is a time constant related to annihilation. Here, the time constant includes a decay constant, a capture reaction rate, and an (n, 2n) reaction rate. The capture reaction rate, (n, 2n) reaction rate, is represented by the product of the microscopic reaction cross section σ and the neutron flux φ. Note that i is a subscript for distinguishing each nuclide and is an integer.

  Plutonium is produced from U-238 neutron capture reaction, U-236 neutron capture reaction, and U-238 (n, 2n) reaction. Therefore, by dividing these transmutation chains and solving equation (1), and comparing with the results of solving equation (1) without breaking the transmutation chain, it is originally included in the MOX fuel. It is possible to identify the ratio of plutonium that has been produced to plutonium produced from uranium in the reactor.

  However, when the transmutation chain is broken and equation (1) is solved, the reaction rate in equation (1) changes, resulting in a change in time constant. Therefore, once the neutron micro cross section (capture, absorption, fission), number density N, and neutron flux φ of each nuclide are calculated by normal combustion calculation, and after storing these, the transmutation chain is broken and the equation is calculated. The number density N and neutron flux φ of each nuclide stored when solving (1) are applied.

For example, consider U-236. The transmutation from the left side to the right side in FIG. 1 (for example, conversion from U-235 to U-236) is based on the neutron capture reaction, and the transmutation from the upper side to the lower side in FIG. The conversion to Np-237 is due to decay. When the neutron capture cross section is σc and the neutron flux is φ, the neutron capture reaction rate per nuclide is σc × φ. For example, the capture reaction of U-235 per unit time and unit volume can be expressed as N ^U235 × σc ^U235 × φ. Since this is the generation rate of U-236, equation (2) for U-236 is
dN ^U236 (t) / dt = N ^U235 (t) × σc ^U235 × φ−N ^U236 (t) × σc ^U236 × φ (2)
It becomes. Here, σc and φ depend on the nuclide concentration (density), respectively.

  The production rate of U-236 is expressed by equation (2). Similar to U-236, a combustion equation is created for each necessary nuclide from which the production rate is obtained from the equation (1). Then, by solving the combustion equation for each created nuclide and arranging it in relation to the burnup, the first isotope table 1 shown in FIG. 2 is obtained. The burnup can be calculated based on the neutron flux during the reactor operation. As can be seen from the first isotope table 1, the mass of U-235 decreases with increasing burnup due to fission. Moreover, since U-238 absorbs neutrons and is converted to plutonium, the mass of U-238 decreases as the burnup increases. And the mass of Pu-239 and Pu-240 increases with the increase in burnup.

  When managing the nationality of Pu, it is necessary to identify the source element of Pu. As described above, since σc and φ depend on the nuclide concentration (density), the initial value in the combustion calculation (mass such as U when the burnup = 0) is used to identify the generation source element of Pu. Even if it is changed, a result consistent with the first isotope table 1 cannot be obtained. Therefore, σc and φ used when calculating the isotope table 1 are stored. This is stored for each nuclide.

  Next, for example, a combustion equation in which a chain for transmutation from U to Np is divided is solved to create a second isotope table 2 (FIG. 3). The nuclear transmutation chain may be divided at least at one point of the chain in the process of conversion from U to Pu.

  In order to create the second isotope table 2, when calculating the combustion equation, the chain for transmutation from U to Np was divided by using σc and φ used when the first isotope table 1 was calculated. Solve the combustion equation. Thereby, Pu converted from U can be obtained as a difference between the first isotope table 1 and the second isotope table 2.

  Since the mass of uranium (U-235, U-238) in the first isotope table 1 and the second isotope table 2 does not change, these become the mass of uranium after combustion. The mass of plutonium (Pu-239, Pu-240) in the first isotope table 1 and the mass of plutonium in the second isotope table 2 are different. In this example, the mass of plutonium in the first isotope table 1 is larger than the mass of plutonium in the second isotope table 2.

  Here, since the second isotope table 2 is obtained by solving a combustion equation in which a chain for transmutation from U to Np is divided, the plutonium in the second isotope table 2 is not converted from uranium. Absent. Therefore, the plutonium in the second isotope table 2 can be identified as plutonium contained in the original fuel, or converted from this plutonium. The mass of plutonium in the second isotope table 2 corresponds to the mass of plutonium contained in the original fuel or plutonium converted from this plutonium.

  Further, the difference between the mass of plutonium in the first isotope table 1 and the mass of plutonium in the second isotope table 2 corresponds to the mass of plutonium converted from uranium contained in the original fuel. Next, a procedure example of a plutonium production element identification method and a plutonium production element identification apparatus according to this embodiment will be described. First, a plutonium production element identification apparatus will be described.

  FIG. 4 is an explanatory diagram showing the configuration of the plutonium production element identification device according to this embodiment. As shown in FIG. 4, the plutonium generating element identification device 50 includes a processing unit 52 and a storage unit 54. Further, an input / output device 51 is connected to the plutonium generating element identifying device 50, and the heavy element nuclide belonging to the actinide element contained in the nuclear fuel (MOX fuel) is input by the input means 53 provided therein. Are input to the processing unit 52 and the storage unit 54. Here, an input device such as a keyboard and a mouse can be used for the input means 53.

  The storage unit 54 stores a computer program including a plutonium generation element identification method and a plutonium generation element identification computer program according to this embodiment. Here, the storage unit 54 is a hard disk device, a magneto-optical disk device, a non-volatile memory such as a flash memory (a storage medium that can be read only such as a CD-ROM), or a RAM (Random Access Memory). Such a volatile memory or a combination thereof can be used.

  Further, the computer program may be capable of realizing the plutonium generating element identification method according to this embodiment in combination with a computer program already recorded in the computer system. Also, a computer program for realizing the plutonium generating element identification method according to this embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read by a computer system and executed. Accordingly, the method for identifying a plutonium generating element according to this embodiment may be executed. The “computer system” here includes an OS and hardware such as peripheral devices.

  The processing unit 52 includes a memory and a CPU. When identifying a plutonium production element by the plutonium production element identification method according to this embodiment, the processing unit 52 reads the computer program into a memory incorporated in the processing unit 52 and performs an operation. At that time, the processing unit 52 appropriately stores the numerical value in the middle of the calculation in the storage unit 54, and advances the calculation by taking out the stored numerical value. The processing unit 52 may realize the function of the processing unit 52 by using dedicated hardware instead of the computer program. The identification result obtained based on the plutonium production element identification method and the operation management data (isotope table) according to this embodiment are displayed on the display means 55 connected to the input / output device 51.

  Here, a CRT (Cathode Ray Tube), a liquid crystal display device or the like can be used for the display means 55. The identification result and the operation management data (isotope table) can be output to a printer provided as necessary. The storage unit 54 may be built in the processing unit 52 or may be in another device (for example, a database server). As described above, the plutonium generating element identification device 50 may be a device that accesses the processing unit 52 and the storage unit 54 by communication from a terminal device including the input / output device 51. Next, a method for identifying a plutonium production element according to this embodiment will be described. In the following description, please refer to FIGS. 1 and 2 as appropriate.

  FIG. 5 is a flowchart showing a procedure of a method for identifying a plutonium production element according to this embodiment. 6-8 is explanatory drawing which shows the isotope table created by the identification method of the plutonium production | generation element which concerns on this embodiment. In the isotope table shown in FIGS. 6 to 8, the mass of the nuclide per ton of nuclear fuel is described for each burnup. Only a part of the mass of the nuclide is described.

  In identifying the plutonium generation element contained in the burned nuclear fuel (MOX fuel), the initial concentration of the heavy element nuclide belonging to the actinoid element contained in the nuclear fuel is determined via the input means 53 of the input / output device 51. , And input to the plutonium production element identification device 50 (step S101).

  Next, the processing unit 52 of the plutonium production element identification device 50 executes the first combustion calculation procedure (step S102). In the first combustion calculation procedure, the initial concentration of the heavy element nuclide input in step S101 is given to the combustion equation, and this combustion equation is solved under the condition that the chain of transmutation is continuous. When the range indicated by A in the chain of transmutation shown in FIG.

In the range indicated by A, Np238 is not handled explicitly, and the neutron capture amount of Np237 is the generation term of Pu238 in the matrix of Equation (3). On the other hand, U237 is handled explicitly in the matrix of Equation (3), and of the decrease due to neutron absorption (σ _a ) of U236, neutron capture (σ _C ) is the generation of U237. Further, as the nuclear reaction, the (n, 2n) reaction of U238 is handled, and the generation contribution of U237 is considered in the equation (3). Note that σ _a = σ _f + σ _c −σ _(n , 2 _n) . Here, σ _a is the absorption cross section, σ _c is the capture cross section, σ _f is the fission, and σ _(n , 2 _n) is the (n, 2n) reaction cross section.

  When the first combustion calculation procedure is executed (step S102), the processing unit 52 creates the first isotope table 1 and stores it in the storage unit 54 of the plutonium generating element identification device 50 (step S103). . The processing unit 52 stores σ and φ when the first isotope table 1 is created in the storage unit 54 (step S104).

Next, the processing unit 52 executes a second combustion calculation procedure (step S105). For example, the second combustion calculation procedure is executed under the condition (part indicated by C in FIG. 1 is divided) where the decay of U-237 is disrupted and the decay of Np239 is disrupted. The combustion equation under the condition where the decay of U-237 is disrupted and the decay of Np239 is disrupted is expressed by equation (4) when the range indicated by A in the transmutation chain shown in FIG. 1 is described.

Further, the second combustion calculation procedure may be executed under the condition that the generation of U-237 is divided and the generation of Np239 is divided (the portion indicated by B in FIG. 1 is divided). The combustion equation under the condition that the generation of U-237 is divided and the generation of Np239 is divided is expressed by equation (5) when the range indicated by A in the transmutation chain shown in FIG. 1 is described.

  The processing unit 52 reads out σ and φ from the storage unit 54 when the first isotope table 1 stored in the storage unit 54 in step S105 is created, and gives it to the equation (4) or the equation (5) to obtain the second Run the combustion calculation procedure. When the second combustion calculation procedure is executed (step S105), the processing unit 52 creates the second isotope table 2 and stores it in the storage unit 54 of the plutonium generating element identification device 50 (step S106).

  Next, the processing unit 52 reads the created first isotope table 1 and the second isotope table 2 from the storage unit 54, and creates isotope tables used for reactor operation management (step S107). The isotope table includes a U-U isotope table 3 for uranium, a Pu-Pu isotope table 4 for plutonium contained in the original MOX fuel, and a U-Pu isotope table 5 for plutonium generated from uranium. A seed is created. These isotope tables are used for nationality management of plutonium, nuclear reactor operation management, and the like.

  The U-U isotope table 3 is obtained by extracting only uranium from the first isotope table 1 (see FIG. 2). The Pu-Pu isotope table 4 is obtained by removing uranium from the second isotope table 2 (see FIG. 3). The U-Pu isotope table 5 describes the difference between the mass of the nuclide described in the first isotope table 1 and the mass of the nuclide described in the second isotope table 2 for each burnup. It is a thing.

  The Pu-Pu isotope table 4 describes the mass of plutonium originally contained in the MOX fuel, and the U-Pu isotope table 5 contains plutonium produced from uranium contained in the MOX fuel. Mass is described. That is, plutonium originally contained in the MOX fuel can be identified by the Pu-Pu isotope table 4, and plutonium generated from uranium contained in the MOX fuel can be identified by the U-Pu isotope table 5. . Thereby, the plutonium generation element contained in the burned MOX fuel is identified (step S108).

  There are various approximations to the combustion chain. In the above example, α decay from U-238 to U-234 is omitted. Strictly speaking, U-234 generated by the nuclear transmutation from Pu-238 to U-234 can be considered to be uranium generated from plutonium. For this reason, in the plutonium production | generation element identification method which concerns on this embodiment, you may handle U-234 as what was produced | generated from Pu-238, assuming that the production | generation path | route of U-234 is derived from Pu-238. .

  Further, since the amount of U-234 produced is extremely small, as described above, the α-decay from Pu-238 to U-234 is considered to have a very small effect on the identification of the plutonium producing element according to this embodiment. May be ignored. Also, the generation of U-234 is not ignored, the generation of U-234 is treated as positive, and the combustion equation is calculated by dividing the chain from Pu-238 to U-234 in the second combustion calculation procedure. May be. There are other nuclides that are generated in a very small amount in the nuclear reactor, such as U-234 generated by the nuclear transmutation of Pu-238 to U-234. To U-234 nuclear transmutation.

  As described above, in this embodiment, it is possible to identify plutonium originally contained in nuclear fuel (MOX fuel) and plutonium generated from uranium contained in nuclear fuel (MOX fuel) by the above-described procedure. . Thus, in identifying the plutonium generation element contained in the burned nuclear fuel, it is only necessary to solve the combustion equation only twice, so there is no need to obtain the amount of plutonium contained in the burned nuclear fuel by origin. As a result, the calculation time can be greatly shortened, so that the time required to identify the plutonium generating element contained in the burned nuclear fuel can be shortened.

  As described above, the plutonium generating element identifying method and the plutonium generating element identifying computer program according to the present invention are useful for managing plutonium contained in burned nuclear fuel (especially MOX fuel). It is suitable for shortening the time required to identify the plutonium generating element contained in the burned nuclear fuel.

It is a conceptual diagram which shows the chain of transmutation. It is explanatory drawing which shows an example of the isotope table created using the identification method of the plutonium production | generation element which concerns on this embodiment. It is explanatory drawing which shows an example of the isotope table created using the identification method of the plutonium production | generation element which concerns on this embodiment. It is explanatory drawing which shows the structure of the identification apparatus of the plutonium production | generation element which concerns on this embodiment. It is a flowchart which shows the procedure of the identification method of the plutonium production | generation element which concerns on this embodiment. It is explanatory drawing which shows the isotope table created by the identification method of the plutonium production | generation element which concerns on this embodiment. It is explanatory drawing which shows the isotope table created by the identification method of the plutonium production | generation element which concerns on this embodiment. It is explanatory drawing which shows the isotope table created by the identification method of the plutonium production | generation element which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st isotope table 2 2nd isotope table 3 U-U isotope table 4 Pu-Pu isotope table 5 U-Pu isotope table 50 Plutonium production | generation element identification device 51 Input / output device 52 Processing part 53 Input means 54 Memory | storage Part 55 display means

Claims (5)

In identifying the element from which plutonium (Pu) is contained in the burned nuclear fuel,
A first combustion calculation procedure for calculating a combustion equation for a nuclear transmutation in a nuclear reactor, assuming that the transmutation chain is continuous;
Regarding the nuclear transmutation in the nuclear reactor, the reaction cross section and the neutron flux in the first combustion calculation procedure under the condition that at least one part of the chain in the process of conversion from uranium (U) to plutonium (Pu) is divided A second combustion calculation procedure for calculating a combustion equation using
From the difference between the amount of the element contained in the nuclear fuel calculated in the first combustion calculation procedure and the amount of the element contained in the nuclear fuel calculated in the second combustion calculation procedure, the burned atom A procedure for identifying the element from which plutonium (Pu) contained in the fuel is produced;
A method for identifying a plutonium-producing element, comprising:   The plutonium (Pu) obtained in the second combustion calculation procedure is defined as plutonium (Pu) contained in the original nuclear fuel, and the plutonium (Pu) obtained in the first combustion calculation procedure and the second Of plutonium (Pu) contained in the burned nuclear fuel by using the difference from the plutonium (Pu) obtained in the combustion calculation procedure of the above as plutonium produced from uranium (U) contained in the original nuclear fuel. The original element is identified, The plutonium production | generation element identification method of Claim 1 characterized by the above-mentioned.   In the second combustion calculation procedure, at least one part of the transmutation chain in the process of conversion from U-236 to Pu-238 and at least one of the transmutation chain in the process of conversion from U-238 to Pu-239. The method for identifying a plutonium-producing element according to claim 1 or 2, wherein the combustion equation is calculated under a condition in which one place is divided.   In the second combustion calculation procedure, the combustion equation is calculated under conditions that divide the decay of U-237 and Np-239, or the conditions that divide the generation of U-237 and the generation of Np-239. The method for identifying a plutonium producing element according to claim 3.   A computer program for identifying a plutonium producing element, which causes a computer to execute the method for identifying a plutonium producing element according to any one of claims 1 to 4.

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