Method for calculating and evaluating activation radioactivity and method for accumulating weight for each radioactivity level category

Abstract

To provide a method for simply calculating and evaluating activated radioactivity, and a method for simply integrating a weight for each radioactivity section.SOLUTION: A calculation evaluation method for activated radioactivity is a method for calculating and evaluating activation radioactivity of objects arranged within a calculation target range around a nuclear reactor, the method comprising: dividing the calculation target range into a plurality of regions; and classifying the regions into calculation evaluation sections based on a material of the objects arranged in the regions.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for calculating and evaluating activated radioactivity and a method for integrating weights for each radioactivity level classification.

Background Art

[0002] In nuclear power plants and the like, methods for obtaining the radioactivity concentration distribution due to activation contamination have been proposed. For example, Patent Document 1 proposes a radioactivity concentration display device that calculates the radioactivity concentration for each activated nuclide based on the material information of the site for a structure having a plurality of sites with different materials.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conventional method for evaluating activated radioactivity has problems that a large amount of information is required for the evaluation and the calculation for the evaluation is complicated.

[0005] Therefore, an object of the present invention is to provide a method for easily calculating and evaluating activated radioactivity and a method for easily integrating weights for each radioactivity level classification.

Means for Solving the Problems

[0006] (1) The present invention is a method for calculating and evaluating the activated radioactivity of an object arranged in a calculation target range around a nuclear reactor, a step of dividing the calculation target range into a plurality of regions, and a step of further classifying the regions into calculation evaluation classifications according to the material of the object arranged in the regions. This is a method for calculating and evaluating the radioactivity of activation.

[0007] (2) Furthermore, the division of the calculation target range into the aforementioned region is performed based on the distance from the reactor, and is the calculation and evaluation method of activation radioactivity described in (1).

[0008] (3) Furthermore, the division of the calculation target range into the aforementioned region is performed based on the value of the neutron flux, which is the calculation and evaluation method of activation radioactivity described in (1).

[0009] (4) Furthermore, the classification of the region into the calculation evaluation category is a calculation evaluation method of activation radioactivity described in any one of (1) to (3), based on the ease with which the material is activated.

[0010] (5) A calculation and evaluation method for activation radioactivity according to any one of (1) to (4), further comprising the step of determining the radioactivity level category to which the calculation evaluation category belongs based on the calculated and evaluated activation radioactivity.

[0011] (6) In addition, in the calculation and evaluation method of activation radioactivity described in (5), Furthermore, for each of the radioactivity level categories, the step includes accumulating the weights of the objects included in the calculation evaluation category to which it belongs. This is a method for calculating the sum of weights for each radiation level category. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for easily calculating and evaluating the activation radioactivity, and a method for easily accumulating the weight for each radioactivity level category. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram illustrating the overview of a nuclear power plant. [Figure 2] This diagram shows the flowchart for calculating and evaluating the activation radioactivity and accumulating the weight for each radioactivity level category. [Figure 3] This figure shows examples of methods for calculating and evaluating activation radioactivity and accumulating weights for each radioactivity level category, such as dividing the area into regions. [Figure 4] This figure shows examples of methods for calculating and evaluating activation radioactivity and accumulating weights for each radioactivity level category, such as dividing the area into regions. [Figure 5] This figure shows examples of methods for calculating and evaluating activation radioactivity and accumulating weights for each radioactivity level category, such as dividing the area into regions. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described below, primarily based on Figures 1 and 2. Figure 1 is a diagram showing an overview of nuclear power plant 1. Figure 2 is a diagram showing the flow chart of the method for calculating and evaluating the activation radioactivity and accumulating the weight for each radioactivity level category. In this embodiment, a method for calculating and evaluating activation radioactivity and a method for accumulating weights for each radioactivity level category are described using the decommissioning work of a nuclear power plant as an example. However, these methods are not limited to the decommissioning work of nuclear power plants. These methods can be broadly used to evaluate the level of activation radioactivity.

[0015] <Decommissioning work and radioactivity of nuclear power plants> During the decommissioning of nuclear power plants, it is necessary to understand the extent of radioactive contamination of objects placed around the reactor. This is because objects placed around the reactor may become radioactive due to exposure to neutrons produced by the nuclear fission reaction inside the reactor. Specifically, it is necessary to calculate the total weight of objects subject to radioactive contamination, such as structures and equipment located around the reactor, according to their respective radioactivity levels. This is because it will enable the decommissioning of nuclear power plants to be carried out safely and smoothly. In order to calculate the total weight for each classification of the radioactivity level, it is necessary to sum up the weights for each classification of the radioactivity level. For this purpose, it is necessary to know the weight of the objects belonging to each classification of the radioactivity level.

[0016] <Classification of Radioactivity Level> First, the classification of the radioactivity level will be described. The following classifications can be exemplified as the classification of the radioactivity level. That is, there are four classifications: those with a relatively high radioactivity level (L1), those with a relatively low radioactivity level (L2), those with an extremely low radioactivity level (L3), and those that do not need to be treated as radioactive waste (CL (Clearance Level)).

[0017] In order to sum up the weights for each classification of the radioactivity level, first, it is necessary to perform a calculation and evaluation of the activation radioactivity. The following specific procedures will be described. In the following description, the range to be calculated around the nuclear reactor is set as the periphery of the reactor pressure vessel.

[0018] <Nuclear Power Plant> First, the outline of Nuclear Power Plant 1, particularly the parts related to this embodiment, will be described based on FIG. 1. FIG. 1 is a diagram showing the outline of Nuclear Power Plant 1. As shown in FIG. 1, Nuclear Power Plant 1 can be roughly divided into a reactor building 10 and a turbine building 20.

[0019] <Reactor Building> The reactor building 10 is equipped with a reactor pressure vessel (RPV) 11. The reactor pressure vessel 11 is equipped with uranium fuel 11A and control rods 11B. Further, a reactor recirculation pump 14 is connected to the reactor pressure vessel 11. In the reactor recirculation pump 14, water is circulating as shown by arrow C. Also, two isolation valves 16 are provided in the reactor pressure vessel 11. The reactor pressure vessel 11 is connected to the turbine 21 via the isolation valve 16 and the first pipe 17. The reactor pressure vessel 11 is located inside the reactor containment vessel (PCV) 12. A pressure suppression chamber 15 is connected to the reactor containment vessel 12. The reactor containment vessel 12 is also covered by a shielding wall (BSW) 13.

[0020] <Turbine Building> Meanwhile, the turbine building 20 is equipped with a turbine 21, a generator 22, and a condenser 23. Steam flows into the turbine 21 from the reactor pressure vessel 11, as shown by arrow A. The generator 22 is connected to the turbine 21. The turbine 21 rotates using the steam from the reactor pressure vessel 11. This rotation is transmitted to the generator 22. As a result, electricity is generated. Furthermore, the turbine 21 is connected to the condenser 23. In the condenser 23, steam from the reactor pressure vessel 11 is cooled and returned to water. This water is returned to the reactor pressure vessel 11 via the first pump 23P, the first piping 17, and the isolation valve 16, as shown by arrow B. Furthermore, the reactor auxiliary cooling seawater system (RSW) 24 is connected to the condenser 23. Cooling of the steam in the condenser 23 is performed by the reactor auxiliary cooling seawater system 24. The reactor auxiliary cooling seawater system 24 includes an intake port 24E for taking in seawater, a discharge port 24D for discharging seawater, and a second pipe 27 connecting the intake port 24E and the discharge port 24D. A second pump 24P is also provided near the intake port 24E. In the reactor auxiliary cooling seawater system 24, as shown by arrow D, seawater flows from the intake port 24E into the second pipe 27. This inflow is due to the action of the second pump 24P. Then, heat exchange takes place between steam and seawater in the condenser 23. That is, in the condenser 23, the steam is cooled and turned into water, while in the second pipe 27, the temperature of the seawater rises. The seawater with the increased temperature is then discharged from the discharge port 24D via the second pipe 27, as shown by arrow E.

[0021] <Calculation and evaluation of activated radioactivity> The following explanation, based on Figures 2 to 5, describes the calculation and evaluation of activation radioactivity and the summation of weights for each radioactivity level category, assuming the calculation area is the vicinity of the reactor pressure vessel 11. Figure 2 shows a flowchart illustrating the method for calculating and evaluating activation radioactivity and accumulating the weight for each radioactivity level category. Figures 3 to 5 show examples of methods for calculating and evaluating activation radioactivity and accumulating weights for each radioactivity level category, such as dividing the area into regions. Figures 2 and 3 show examples of equipment inside a pressure vessel, Figure 4 shows an example of equipment inside a containment vessel, and Figure 5 shows an example of equipment inside the shielding wall 13. As shown in Figure 2, the calculation and evaluation of activation radioactivity is performed by determining the calculation range, dividing it into regions, calculating the neutron flux value, setting the temperature conditions, setting the material, and setting the neutron irradiation period. These steps are explained in order below. Please note that the following explanation is an example illustrating the evaluation calculation method. Therefore, it does not, for example, refer to all structures and devices within the scope of the calculation. References below are limited to those necessary to explain the evaluation calculation method.

[0022] <Calculation range> First, the calculation scope is set. In the examples shown in Figures 2 to 5, the calculation scope is set to include the equipment inside the pressure vessel, the equipment inside the containment vessel, and the shielding wall 13.

[0023] <Division into regions> Next, the defined calculation range is divided into multiple regions. This region division can be done based on the neutron flux value of the target area and the distance (horizontal distance and height) of the target area from the reactor.

[0024] <Temperature conditions> If the calculation range includes areas with different temperature conditions, it is preferable to divide the area into regions within areas with the same temperature conditions. Temperature conditions refer to the normal temperature of that region or the normal ambient temperature of that region. The reason why it is preferable to divide an area into regions within a region with the same temperature conditions is that temperature conditions must be used in the calculation and evaluation of activation radioactivity. When an area with the same temperature conditions is divided into regions, the temperature conditions within each divided region are fixed to one. This simplifies the calculation and evaluation of activation radioactivity.

[0025] For example, the equipment inside the pressure vessel includes areas with different temperature conditions, as shown in Figure 3. The temperature conditions differ between the lower and upper ends of the core. The temperature condition at the lower end of the core is the reactor water inlet temperature. In contrast, the temperature condition at the upper end of the core is the reactor water outlet temperature. In the equipment inside the pressure vessel, the division into regions is carried out within areas with the same temperature conditions. Specifically, the division into regions occurs at the lower end of the core where the temperature condition is the reactor water inlet temperature, and at the upper end of the core where the temperature condition is the reactor water outlet temperature.

[0026] As mentioned above, the criteria for dividing the region can be the neutron flux value or the distance from the reactor. In particular, it is preferable to divide the region based on the neutron flux value. This is because it allows for calculations that are closer to the actual radioactivity when performing calculation evaluations of the activated radioactivity. The calculation and evaluation of activation radioactivity requires the use of neutron flux values. Therefore, if the neutron flux values ​​are equivalent in each part of the region, the calculation and evaluation of activation radioactivity will yield a value close to the actual radioactivity. As described above, by dividing the region based on the neutron flux value, the calculation and evaluation results of the activation radioactivity become more accurate.

[0027] However, comprehensively determining the neutron flux value within the calculation range can be a cumbersome task. Therefore, it is preferable to use the distance from the reactor, more specifically the distance from the reactor core, as the criterion for dividing the region, rather than the neutron flux value. This is because the neutron flux value depends on the distance from the reactor, and determining the distance from the reactor is usually easier than determining the neutron flux value. By dividing the area into regions based on distance from the reactor (horizontal distance and height), the area can be divided simply and uniquely, making it easier to understand the objects within each region.

[0028] A specific example is shown in Figure 3. In this embodiment, as shown in Figure 3, the lower end of the reactor core is divided into two regions: lower end 1 and lower end 2 in the equipment inside the pressure vessel. The upper end of the reactor core is also divided into two regions: upper end 1 and upper end 2. The difference between core bottom 1 and core bottom 2 lies in the point within the region that is closest to the reactor, or more specifically, closest to the core center. Core bottom 1 is the region where the horizontal distance from the core center is 0 mm or more and less than 1720 mm, and the height from the core center is 24875 mm or more and less than 25432 mm. Core bottom 2 is the region where the horizontal distance from the core center is 1720 mm or more and less than 1880 mm, and the height from the core center is 24875 mm or more and less than 25432 mm. Similarly, the upper end of the reactor core is divided into two regions, upper end 1 and upper end 2, based on the horizontal distance from the core center and the height from the core center. Thus, the equipment inside the pressure vessel is divided into a total of four regions, 1-1, 1-2, 1-3, and 1-4, based on temperature conditions, horizontal distance from the core center, and height from the core center.

[0029] <Containment vessel equipment, shielding wall> The containment vessel equipment and shielding walls, like the pressure vessel equipment, can be divided into regions based on their horizontal distance from the core center and their height from the core center. As shown in Figure 4, the equipment inside the containment vessel is divided into three regions, 2-1, 2-2, and 2-3, based on the horizontal distance from the core center and the height from the core center. Furthermore, as shown in Figure 5, the shielding wall is divided into three regions, 3-1, 3-2, and 3-3, based on the horizontal distance from the core center and the height from the core center.

[0030] In Figure 3, the equipment inside the pressure vessel is divided into regions mainly by its distance from the core center, while in Figure 4, the equipment inside the containment vessel is divided into regions mainly by its height from the core center.

[0031] Unlike the equipment inside the pressure vessel, the equipment inside the containment vessel and the shielding wall are subject to only one temperature condition. Therefore, the same temperature-based classification used for the equipment inside the pressure vessel was not applied to the equipment inside the containment vessel and the shielding wall.

[0032] <Calculation of Neutron Flux Value> Next, we will explain how to calculate the neutron flux value. The neutron flux value is calculated for the entire calculation evaluation range. Furthermore, the neutron flux value is set for each divided region in the calculation evaluation of activation radioactivity. As mentioned above, the regions are divided based on their distance from the reactor core. Therefore, it is thought that the neutron flux values ​​do not vary significantly within the same region. The neutron flux value can be calculated using a two-dimensional DORT code, for example, based on the shape of the object or the source spectrum. Furthermore, it is preferable to set the neutron flux value in the calculation evaluation of activation radioactivity to the maximum value of the neutron flux within each region. This is because it allows for a calculation evaluation of activation radioactivity that is more likely to ensure safety.

[0033] <Setting temperature conditions> In the calculation evaluation flow shown in Figure 2, the item for setting temperature conditions is listed after the calculation of the neutron flux value. However, in this embodiment, as mentioned above, the temperature conditions are considered before the region is divided. Therefore, the temperature conditions for each divided region are determined. Consequently, no special consideration is required in the item for setting temperature conditions. On the other hand, unlike this embodiment, if temperature conditions are not considered during the division into regions, it is preferable to perform classification by temperature conditions in the section on setting temperature conditions. This is because it simplifies the subsequent calculation and evaluation of activation radioactivity.

[0034] <Material Settings> Next, we will explain the material settings. Calculation evaluations are performed separately for each material being evaluated. This is because the ease of activation differs depending on the material, or more specifically, the elemental composition of each material. Therefore, the materials used in the calculation evaluation must be selected from materials whose elemental composition as the starting material (the substance before activation) has been properly determined. Examples of materials with standardized elemental compositions of starting materials include SUS304, SUS304L, SUS316, SUS316L, concrete, and carbon steel.

[0035] This will be explained in detail based on Figure 4. Figure 4 is a diagram showing an example of the calculation and evaluation of the activation radioactivity of equipment inside the containment vessel.

[0036] The equipment inside the containment vessel is divided into three areas: area numbers 2-1, 2-2, and 2-3. We will explain the material settings using the containment vessel's 1st floor (area number 2-1) as an example. In the physical volume survey results shown in Figure 4, the representative material refers to the material of the main component among the materials that make up the object included in the calculation scope. Furthermore, the main component refers to the material that primarily constitutes the object in terms of weight. In the containment vessel's first floor, as shown by sub-section numbers 9 to 19 in Figure 4, 11 different materials are used as representative materials. Individually calculating and evaluating the activation radioactivity for all parts corresponding to these materials would be cumbersome.

[0037] The ease with which a material becomes activated varies depending on its material, or more specifically, its elemental composition. However, some materials have similar elemental compositions. Therefore, materials with similar elemental compositions are grouped together. In other words, materials are classified based on their ease of activation. This simplifies the calculation and evaluation of their activation radioactivity. The material to be selected at that time is chosen from the materials whose elemental composition of the starting material has been determined, as described above. This allows for the calculation and evaluation of the activation radioactivity, because the elemental composition of the selected material is known. However, as an exception, if there is a large difference in the ease of activation among the materials whose elemental composition is known, and especially if the ease of activation of the representative material is greater than that of the material to be selected, it is necessary to ensure that the weight of the object made of that representative material is negligibly small compared to the weight of the objects in the entire calculation and evaluation range before setting it.

[0038] Let's explain using the containment vessel level 1F shown in Figure 4 as an example. In containment vessel level 1F, 11 representative materials with sub-classification numbers 9 to 19 are grouped into four calculation evaluation classes with calculation evaluation class numbers 9 to 12. Here, a calculation evaluation class refers to a class that is calculated as a single unit in the subsequent calculation evaluation of activation radioactivity. Specifically, the four representative materials from sub-categories 10 to 13—SUS316, SUS32A, SUS32B, and SUS14—are grouped together into a single calculation evaluation category, calculation evaluation category number 10. This is because the ease with which SUS32A, SUS32B, and SUS14 become activated is similar to that of SUS316. Similarly, sub-classification numbers 14 and 15 are grouped into calculation evaluation category 11, and sub-classification numbers 16 and 17 are grouped into calculation evaluation category 12. In this way, by grouping representative materials with similar susceptibility to activation into a single calculation evaluation category based on their susceptibility to activation, the calculation evaluation of activation radioactivity can be simplified. For example, in the first floor of the containment vessel, the number of calculation evaluations has been reduced from 11 to 4.

[0039] Furthermore, as shown in Figure 4, in the containment vessel equipment, representative materials with similar susceptibility to activation are grouped together in one calculation evaluation category, even on the second floor of the containment vessel. Specifically, S25C and S28C, with sub-category numbers 23 and 24, are grouped together in one calculation evaluation category 16.

[0040] <Setting the Neutron Irradiation Period> Next, we will explain how to set the neutron irradiation period. The degree of activation depends not only on the neutron flux value but also on the duration of neutron irradiation. Therefore, for example, if there is a period when neutron irradiation is stopped, it is preferable to take this into account when calculating and evaluating the activation radioactivity. Furthermore, if a component is replaced during the neutron irradiation period, it is preferable to set the neutron irradiation period for that component in accordance with the actual situation. Figure 3 shows an example where different neutron irradiation periods are set for each representative material at the lower core end 1 of the pressure vessel equipment. Specifically, at the lower core end 1 of region number 1-1, SUS304, which is in calculation evaluation category 1, has a neutron irradiation period of the entire duration. On the other hand, SUS316L, which is in calculation evaluation category 2 at the lower core end 2, has a period set after the shroud replacement. In this way, by setting the neutron irradiation period according to the conditions of the object being evaluated, it is possible to perform a more accurate calculation and evaluation of the activated radioactivity.

[0041] As described above, for objects placed within the calculation range, the neutron flux value, temperature conditions, material, neutron irradiation period, etc., can be determined for each divided region. Once these values ​​are determined, it becomes possible to calculate and evaluate the activation radioactivity.

[0042] <Calculation and evaluation of activated radioactivity> This section explains the calculation and evaluation of activation radioactivity. The calculation and evaluation of activation radioactivity, in other words, the calculation of the concentration of radioactive materials due to activation contamination, can be performed, for example, using the radioactive material production and decay calculation code ORIGEN-S (IC Gauld, et al.: "ORIGEN-S: SCALE SYSTEM MODULE TO CALCULATE FUEL DEPLETION, ACTINIDE TRANSMUTATION, FISSION PRODUCT BUILDUP AND DECAY, AND ASSOCIATEDRADIATION SOURCE TERMS", ORNL / TM-2005 / 39, Version 5.1 Vol. II, Book1, Sect.F7). Then, using the aforementioned neutron flux value, neutron irradiation period considering the neutron irradiation history, and the material of the target object, the estimated amount of activation was calculated and the activation radioactivity was evaluated.

[0043] <Calculation of weight for each radiation level category> Next, we will explain how to calculate the sum of weights for each category of radioactivity level. The procedure for calculating the sum of weights for each radioactivity level category is as follows: Based on the calculated and evaluated values ​​of activated radioactivity, the radioactivity level category to which each calculation evaluation category belongs is determined. Then, the weights of the objects within each calculation evaluation category belonging to that radioactivity level category are added together. This allows for the calculation of the total weight of objects belonging to each radioactivity level category.

[0044] The following will provide a detailed explanation with reference to Figures 3 through 5. For some of the calculation evaluation categories in Figures 3 to 5, explanatory symbols are entered in the columns for weight, calculation evaluation of activated radioactivity, and radioactivity level classification. Specifically, W1 to W11 are entered in the weight column, B1 to B11 are entered in the calculation evaluation of activated radioactivity column, and L1 to L3 and CL are entered in the radioactivity level classification column. W1 to W11 represent weight (kg), and B1 to B11 represent radioactivity intensity per unit weight (Bq / g). Furthermore, as mentioned above, the radioactivity level classifications L1, L2, L3, and CL represent the following categories: L1 indicates a relatively high level of radioactivity, L2 indicates a relatively low level of radioactivity, L3 indicates an extremely low level of radioactivity, and CL indicates a level that does not need to be handled as radioactive waste, i.e., a clearance level.

[0045] <Determination of Radioactivity Level Classification> Using the explanatory symbols mentioned above, we will now explain how to calculate the sum of weights for each category of radioactivity level. First, the radioactivity level category to which each calculated evaluation category belongs is determined based on the calculated and evaluated values ​​of the activated radioactivity. In the examples shown in Figures 3 to 5, B1 (Bq / g) of calculation evaluation category 1 and B6 (Bq / g) of calculation evaluation category 6 are assumed to be activation radioactivity values ​​belonging to radioactivity level category L1. Similarly, B2 (Bq / g) in calculation evaluation category 2, B4 (Bq / g) in calculation evaluation category 4, B8 (Bq / g) in calculation evaluation category 8, B21 (Bq / g) in calculation evaluation category 21, and B22 (Bq / g) in calculation evaluation category 22 are assumed to be activation radioactivity values ​​belonging to radioactivity level category L2. Furthermore, B18 (Bq / g) in calculation evaluation category 18 and B20 (Bq / g) in calculation evaluation category 20 are considered to be activation radioactivity belonging to radioactivity level category L3. Furthermore, B17 (Bq / g) in calculation evaluation category 17 and B19 (Bq / g) in calculation evaluation category 19 are considered to be activation radioactivity belonging to radioactivity level category CL.

[0046] Next, the weights of the calculated evaluation categories belonging to each radioactivity level category are added together. In the example above, radioactivity level L1 includes calculation evaluation categories 1 and 6. Therefore, the total weight of the objects belonging to radioactivity level L1 is the sum of the weight of calculation evaluation category 1, W1 (kg), and the weight of calculation evaluation category 6, W6 (kg). Similarly, the total weight of objects belonging to radioactivity level L2 is the sum of W2 (kg), W4 (kg), W8 (kg), W21 (kg), and W22 (kg). Furthermore, the total weight of objects belonging to radioactivity level L3 is the sum of W18 (kg) and W20 (kg). Furthermore, the total weight of objects belonging to radioactivity level CL is the sum of W17 (kg) and W19 (kg). In this way, the cumulative weight for each radioactivity level category can be determined. The cumulative weight calculations for each radioactivity level category shown in Figure 2 are intended as an illustrative representation of the concepts explained above.

[0047] As described above, in the method of calculating and evaluating the activation radioactivity and accumulating the weight for each radioactivity level category of this embodiment, a region in which the neutron flux values ​​are considered to be equivalent is set, and this region is further classified according to the material. This makes it possible to simplify the calculation conditions and the calculation itself in the calculation and evaluation of the activation radioactivity. Specifically, it simplifies the classification and organization of information such as equipment weight for organizing calculation conditions. It also reduces the man-hours required for inputting calculation conditions in calculation evaluation. Furthermore, it reduces the number of evaluation calculations. For example, the number of evaluation calculations can be reduced to (number of domain divisions) × (sum of the number of materials in each domain) × (sum of the number of neutron irradiation period settings for each domain and material). As described above, the method of this embodiment can shorten the time required for calculation and evaluation, thereby improving work efficiency.

[0048] Furthermore, the method of calculating and evaluating the activation radioactivity and accumulating the weight for each radioactivity level category in this embodiment has the effect of making calculations easier, as described above, and also of reducing the effort required for on-site investigations. In other words, it is usually difficult to position all objects around a nuclear reactor. Therefore, by defining a spatial area in the calculation evaluation, it is possible to determine whether or not each object is included in that area without having to position all of them. This makes it possible to reduce or eliminate the effort required for on-site surveys. [Explanation of symbols]

[0049] 1. Nuclear power plant 10. Reactor building 11. Reactor Pressure Vessel (RPV) 11A Uranium Fuel 11B control rod 12. Reactor Containment Vessel (PCV) 13. Shielding Wall (BSW) 14. Reactor recirculation pump 15 Pressure Control Room 16 Isolation valve 17. First piping 20 Turbine Building 21 Turbine 22 Generators 23 Condenser 23P First pump 24. Reactor Auxiliary Cooling Seawater System (RSW) 24P Second pump 24E Water intake 24D water outlet 27 Second piping

Claims

1. A method for calculating and evaluating the radioactive activity of objects placed within a calculation target area around a nuclear reactor, The steps include dividing the calculation range into multiple regions, The process includes the step of further classifying the region into calculation evaluation categories based on the material of the object placed in the region, The division of the calculation range into the aforementioned region is performed based on the value of the neutron flux. For each of the calculation evaluation categories, the process further includes the step of calculating the activation radioactivity by radioactive material production and decay calculation using the neutron flux value, neutron irradiation period, and the material of the object. A method for calculating and evaluating the radioactivity of activation.

2. The division of the calculation range into the aforementioned region is performed based on the distance from the reactor. The method for calculating and evaluating the activation radioactivity according to claim 1.

3. The classification of the aforementioned region into the calculation evaluation category is performed based on the ease with which the material is activated. The method for calculating and evaluating the activation radioactivity according to claim 1 or 2.

4. The process includes a step of determining the radioactivity level category to which the calculated evaluation category belongs, based on the calculated and evaluated activation radioactivity. The method for calculating and evaluating the activation radioactivity according to claim 1 or 2.

5. In the method for calculating and evaluating the activation radioactivity described in claim 4, further, For each of the aforementioned radioactivity level categories, the process includes a step of accumulating the weights of the objects included in the calculation evaluation category belonging to that category. Method for calculating the sum of weights for each radiation level category.

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