JP2016008844A - Nuclear power plant exhaust gas monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear power plant exhaust gas monitoring system capable of acquiring a fluctuation distribution of a neutron multiplication factor corresponding to a change in a water level within a reactor structure.SOLUTION: A nuclear power plant exhaust gas monitoring system for monitoring FP gas discharged from a reactor structure 1, comprises: a radioactivity measuring device 6 measuring the radioactivity of a first nuclide and the radioactivity of a second nuclide for FP gas discharged from the reactor structure 1 whenever a water level within the reactor structure 1 rises; and a neutron multiplication factor distribution estimation device 7 computing a ratio α of the radioactivity of the first nuclide measured by the radioactivity measuring device 6 to the radioactivity of the second nuclide measured by the radioactivity measuring device 6 per water level within the reactor structure 1, computing a neutron multiplication factor k on the basis of this ratio α, and creating a fluctuation distribution of the neutron multiplication factor k corresponding to a change in the water level within the reactor structure 1.

Description

  The present invention relates to an exhaust gas monitoring system for a nuclear power plant that monitors FP gas discharged from a nuclear reactor structure.

  In a nuclear power plant that has caused a severe accident, the nuclear fuel in the nuclear reactor may melt, the nuclear instrumentation system installed in the nuclear reactor may be damaged, and a situation in which the state inside the nuclear reactor cannot be monitored may occur. When measuring the reactivity of a sound core (specifically, when the fuel is loaded or when the reactor is in critical proximity), a neutron detector is mainly used. However, nuclear power plants that have caused severe accidents are in a situation where access to the reactor is limited and neutron detectors cannot be installed. Therefore, the FP gas (fission product gas) discharged from the reactor structure is a clue to know the state in the reactor structure.

Here, a method has been proposed in which the ratio R of the production amount of two nuclides (133Xe, 88Kr) in the FP gas discharged from the reactor structure is obtained from the measured value, and the neutron multiplication factor k is estimated based on this ratio R. (For example, refer to Patent Document 1). In Patent Document 1, the following formula 1 is used to estimate the neutron multiplication factor k from the ratio R of the production amounts of two nuclides. Γ _{88Kr, SF} in the formula is the fission yield of the nuclide (88Kr) by spontaneous fission (SF) of the nuclear fuel material (Cm), and γ _{88Kr, NF} is the induced fission (NF: Neutron Induced) of the nuclear fuel material (U). Fission) is the fission yield of the nuclide (88 Kr). Further, γ _{133Xe, SF} is the fission yield of the nuclide (133Xe) by spontaneous fission of the nuclear fuel material (Cm), and γ _{133Xe, NF} is the fission yield of the nuclide (133Xe) by the induced fission of the nuclear fuel material (U).

JP 2013-257209 A

  When extracting molten fuel (fuel debris) from a reactor structure, knowing the reactivity of the molten fuel and how the molten fuel is distributed is important for planning a molten fuel removal operation plan. It is.

  By the way, in the operation of taking out the molten fuel, it is necessary to fill the reactor structure with water for the purpose of shielding γ rays. In the water filling process, the water level in the nuclear reactor structure rises, and the molten fuel originally present in the air is covered with water. If the molten fuel is covered with water, the reaction with neutrons is promoted and the neutron multiplication factor is increased. Therefore, the inventors of the present application have found that if water filling is used, the fluctuation distribution of the neutron multiplication factor corresponding to the change in the water level can be obtained, and the reactivity and distribution of the molten fuel can be estimated.

  An object of the present invention is to provide an exhaust gas monitoring system for a nuclear power plant capable of acquiring a fluctuation distribution of a neutron multiplication factor corresponding to a change in a water level in a nuclear reactor structure.

  In order to achieve the above object, the present invention provides an exhaust gas monitoring system for a nuclear power plant that monitors FP gas discharged from a nuclear reactor structure, and the water level in the nuclear reactor structure is adjusted by intermittent water injection of a water injection device. A radioactivity measuring device that measures the radioactivity of the first nuclide and the radioactivity of the second nuclide with respect to the FP gas discharged from the reactor structure each time it rises, and for each water level in the reactor structure And calculating the ratio between the radioactivity of the first nuclide and the radioactivity of the second nuclide measured by the radioactivity measuring device, and calculating the neutron multiplication factor based on this ratio, A neutron multiplication factor distribution estimation device that creates a fluctuation distribution of neutron multiplication factors corresponding to changes in the water level.

  According to the present invention, the fluctuation distribution of the neutron multiplication factor corresponding to the change of the water level in the nuclear reactor structure can be acquired.

It is a block diagram showing the structure of the exhaust gas monitoring system of the nuclear power plant in the 1st Embodiment of this invention with a nuclear reactor structure and a water injection apparatus. It is a figure for demonstrating the linear function which is a relational expression of the radioactivity ratio of two nuclides and the neutron multiplication factor in the 1st Embodiment of this invention. It is a figure showing the specific example of the display of the neutron multiplication factor distribution in the 1st Embodiment of this invention. It is a block diagram showing the structure of the exhaust gas monitoring system of the nuclear power plant in the 2nd Embodiment of this invention with a nuclear reactor structure and a water injection apparatus.

  A first embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a block diagram illustrating the configuration of an exhaust gas monitoring system for a nuclear power plant according to the present embodiment, together with a nuclear reactor structure and a water injection device. In addition, in this FIG. 1, the state which water filling in the nuclear reactor structure was completed is shown.

  In the present embodiment, it is assumed that, for example, molten fuel (fuel debris) 2A, 2B exists in the reactor structure 1 (specifically, a reactor pressure vessel or a reactor containment vessel). . And in order to perform the water filling in the nuclear reactor structure 1, the water injection apparatus 3 is provided. The water injection device 3 includes a water injection unit 4 and a water level calculation unit 5.

  Although not shown in detail, the water injection unit 4 includes, for example, a pump that injects water into the nuclear reactor structure 1 via a pipe and the like, and a pump control unit that controls the pump. First, the pump controller drives the pump for a predetermined time to raise the water level in the reactor structure 1 by a predetermined interval ΔH. Thereafter, assuming that the molten fuel is covered with water as the water level in the reactor structure 1 rises and the reaction with neutrons is promoted, considering the waiting time for the reaction to reach a steady state, Stop the pump for a predetermined time. Such pump drive and stop are alternately repeated to intermittently inject water into the reactor structure 1.

  The water level calculation part 5 is based on the pump ON / OFF information from the water injection part 4 (in other words, the water injection ON / OFF information), based on the water injection amount of the pump and the shape of the reactor structure 1. The water level inside is calculated.

  Moreover, in this embodiment, the radioactivity measuring apparatus 6 and the neutron multiplication factor distribution estimation apparatus 7 are provided as what constitutes an exhaust gas monitoring system for monitoring the FP gas discharged from the nuclear reactor structure 1.

  The radioactivity measurement device 6 includes a γ-ray detector 8, a radioactivity calculation unit 9, and a radioactivity display unit 10. The γ-ray detector 8 is provided, for example, in a gas chamber that temporarily retains the FP gas discharged from the reactor structure 1 through a pipe, and γ of the FP gas discharged from the reactor structure 1 is provided. The line energy spectrum is detected at any time.

  The radioactivity calculator 9 is based on the γ-ray energy spectrum detected by the γ-ray detector 8, and the radioactivity of the first nuclide (88 Kr in this embodiment) in the FP gas discharged from the reactor structure 1 and the first The radioactivity of the two nuclides (135Xe in this embodiment) is calculated as needed, and these are output to the radioactivity display unit 10 and the neutron multiplication factor distribution estimation device 7. The radioactivity display unit 10 displays, for example, changes over time (time chart) of radioactivity of the first nuclide and radioactivity of the second nuclide.

  The neutron multiplication factor distribution measuring device 7 includes a data recording unit 11, a radioactivity ratio calculation unit 12, a linear function storage unit 13, a neutron multiplication factor calculation unit 14, a neutron multiplication factor distribution creation unit 15, and a neutron multiplication factor display unit 16 ( Display).

  The data recording unit 11 inputs water injection ON / OFF information from the water injection unit 4 of the water injection device 3, inputs water level information of the nuclear reactor structure 1 from the water level calculation unit 5 of the water injection device 3, and The radioactivity calculation unit 9 inputs the radioactivity of the first nuclide and the radioactivity of the second nuclide. First, temporal changes in the radioactivity of the first nuclide and the radioactivity of the second nuclide in the FP gas discharged from the reactor structure 1 before the change of the water level in the reactor structure 1 are temporarily stored. The allowable range is set based on the amount of change per unit time. Thereafter, the radioactivity of the first nuclide and the radioactivity of the second nuclide in the FP gas discharged from the reactor structure 1 after the change of the water level in the reactor structure 1 (in other words, from water injection ON to OFF) The time-dependent changes in the radioactivity of the first nuclide and the radioactivity of the second nuclide measured after a predetermined time has passed since the switch information was input, and the amount of change per unit time is It is determined whether it is within the allowable range. When it is determined that it is within the allowable range (in other words, when it is determined that it is in a steady state), the average value per unit time is calculated and associated with the water level in the corresponding reactor structure 1 Record.

  The radioactivity ratio calculation unit 12 calculates the ratio α between the radioactivity of the first nuclide and the radioactivity of the second nuclide for each water level in the nuclear reactor structure 1 recorded by the data recording unit 11. The linear function storage unit 13 stores a linear approximate expression (linear function) that is a relational expression between the radioactivity ratio α and the neutron multiplication factor k, and the neutron multiplication factor calculation unit 14 uses the linear function, The neutron multiplication factor k is calculated from the radioactivity ratio α calculated by the radioactivity ratio calculation unit 12.

Here, the linear function described above will be described. First, assuming that the neutron source intensity is S ₀ , the neutron number S when the neutron multiplication factor k <1 can be expressed by the following Equation 2.

In the case of a molten fuel (fuel debris) system, the neutron sources are neutrons from spontaneous fission of nuclear fuel material (Cm) and neutrons from induced fission of nuclear fuel material (U). The neutron number S _SF due to the spontaneous fission of the nuclear fuel material (Cm) can be expressed by the following Equation 3, and the neutron number S _NF due to the induced fission of the nuclear fuel material (U) can be expressed by the following Equation 4.

Further, the spontaneous fission number F _SF of the nuclear fuel material (Cm) can be expressed by the following formula 5, and the induced fission number F _NF of the nuclear fuel material (U) can be expressed by the following formula 6. In the equation, ν _SF is the number of neutrons generated per spontaneous fission, and ν _NF is the number of neutrons generated per induced fission.

Consider the first and second nuclides described above. Nuclide density N _A of the first species, the use of Equation 5 and Equation 6 above can be expressed by Equation 7 below. Similarly, the nuclide density of the second nuclide can be expressed by the following equation 8 using the above equations 5 and 6. V in the equation is the volume of the gas phase in the reactor structure. Λ _A is the decay constant of the first nuclide, γ _{A and SF} are the fission yield of the first nuclide by spontaneous fission, and γ _{A and NF} are the fission yield of the first nuclide by induced fission. Λ _B is the decay constant of the second nuclide, γ _{B and SF} are the fission yield of the second nuclide by spontaneous fission, and γ _{B and NF} are the fission yield of the second nuclide by induced fission.

The radioactivity Q _A of the first species _(i.e., a product decay constant lambda _A and nuclide density N _A of the first species) radioactivity Q _B and the second species _(i.e., the decay constant lambda _B of the second species Taking the α ratio of the nuclide product of density N _B), using equation 7 and equation 8 above, it is possible to derive the equation 9 below.

  Then, using Equation 9 above, for example, as shown in FIG. 2, the neutron multiplication factor k and the radioactivity ratio α (in this embodiment, the ratio between 88 Kr radioactivity and 135 Xe radioactivity) are plotted in a coordinate system. For example, a linear approximate expression (Expression 10 below) which is a relational expression between the radioactivity ratio α and the neutron multiplication factor k can be obtained. In the case of FIG. 2, the slope c = 2.555 and the intercept d = −0.111.

  The first order approximate expression (linear function) obtained in this way is stored in advance in the storage unit 13 and is used for the calculation of the neutron multiplication factor k.

  The neutron multiplication factor distribution creating unit 15 inputs the neutron multiplication factor k calculated for each water level in the nuclear reactor structure 1, and the fluctuation distribution of the neutron multiplication factor k corresponding to the change in the water level in the nuclear reactor structure 1. (Hereinafter referred to as neutron multiplication factor distribution) is created and output to the neutron multiplication factor distribution display unit 16. The neutron multiplication factor distribution display unit 16 displays a neutron multiplication factor distribution as shown in FIG. 3, for example.

  As described above, in the present embodiment, the neutron multiplication factor distribution can be acquired and displayed. Therefore, the reactivity and distribution of the molten fuels 2A and 2B can be estimated.

  A second embodiment of the present invention will be described with reference to FIG.

  FIG. 4 is a block diagram showing the configuration of the exhaust gas monitoring system for the nuclear power plant in this embodiment, together with the reactor structure and the water injection device. In addition, in this embodiment, the part equivalent to the said 1st Embodiment attaches | subjects the same code | symbol, and abbreviate | omits description suitably.

  The neutron multiplication factor distribution estimation device 7 of this embodiment includes a data recording unit 11A, a radioactivity correction unit 17, a radioactivity ratio calculation unit 12, a linear function storage unit 13, a neutron multiplication factor calculation unit 14, and a neutron multiplication factor distribution creation unit. 15 and a neutron multiplication factor display unit 16.

  As with the data recording unit 11 of the first embodiment, the data recording unit 11A inputs water injection ON / OFF information from the water injection unit 4 of the water injection device 3 and the reactor structure from the water level calculation unit 5 of the water injection device 3. 1 is input, and the radioactivity of the first nuclide (88 Kr in this embodiment) and the radioactivity of the second nuclide (135 Xe in this embodiment) are input from the radioactivity calculation unit 9 of the radioactivity measuring device 6. It is like that. As in the data recording unit 11 of the first embodiment, the radioactivity of the first nuclide and the second nuclide in the FP gas discharged from the reactor structure 1 before the water level in the reactor structure 1 is changed. Is stored temporarily, and an allowable range is set based on the amount of change per unit time. Thereafter, the radioactivity of the first nuclide and the radioactivity of the second nuclide in the FP gas discharged from the reactor structure 1 after the change of the water level in the reactor structure 1 (in other words, from water injection ON to OFF) The time-dependent changes in the radioactivity of the first nuclide and the radioactivity of the second nuclide measured after a predetermined time has passed since the switch information was input, and the amount of change per unit time is It is determined whether it is within the allowable range. When it is determined that it is within the allowable range (in other words, when it is determined that it is in a steady state), the average value per unit time is calculated and associated with the water level in the corresponding reactor structure 1 Record.

  In the present embodiment, in order to correct the radioactivity of the second nuclide (135Xe), which will be described later, the radioactivity calculator 9A of the radioactivity measurement device 6 also calculates the radioactivity of the nuclide (135I) as needed, It outputs to the multiplication factor distribution estimation apparatus 7. Then, the data recording unit 11A calculates the average value per unit time of the nuclide (135I) and records it in association with the water level in the corresponding nuclear reactor structure 1 in the same manner as the first nuclide and the second nuclide described above. .

  The data recording unit 11A determines whether or not the radioactivity of the first nuclide or the second nuclide has fluctuated more than a predetermined fluctuation amount, so that the molten fuel becomes water as the water level in the reactor structure 1 rises. It is determined whether the reaction with neutrons has been promoted. When the radioactivity of the first nuclide or the second nuclide fluctuates more than a predetermined fluctuation amount, the switching timing from water injection OFF to ON (in other words, the fluctuation timing of the water level in the reactor structure 1) and the first The delay time (in other words, the time until the FP gas reaches the γ-ray detector from the nuclear reactor structure 1) is calculated from the difference from the radioactivity variation timing of the first nuclide or the second nuclide, and the corresponding reactor Recorded in association with the water level in structure 1. For the water level for which the delay time was not obtained, record the delay time obtained at a higher water level than that level, or if not, record the delay time obtained at a lower water level. To do.

  The radioactivity correction unit 17 corrects the radioactivity of the corresponding first nuclide and the radioactivity of the second nuclide based on the corresponding delay time for each water level in the reactor structure 1 recorded by the data recording unit 11. To do. That is, the radioactivity of the first nuclide and the radioactivity of the second nuclide (in other words, the radioactivity at the time of measurement) in the FP gas discharged from the reactor structure 1 are the same as those in the FP gas in the reactor structure 1. Correction is made so that the radioactivity of the first nuclide and the radioactivity of the second nuclide (in other words, the radioactivity at the time of generation) are obtained. This will be specifically described below.

The nuclide densities (88 Kr, 135 Xe, 135 I) in the FP gas discharged from the reactor structure 1 are defined as N _{Kr (t)} , N _{Xe (t)} , N _{I (t),} and the inside of the reactor structure 1 The nuclide density in the FP gas (88Kr, 135Xe, 135I) is N _{Kr (0)} , N _{Xe (0)} , N _{I (0),} and the decay constant of the nuclide (88Kr, 135Xe, 135I) is λ _Kr , λ _Xe, if λ _I, formula 11 to 13 of the following is established.

  Further, by integrating with the delay time t in the above mathematical expressions 11 to 13, the following mathematical expressions 14 to 16 can be derived.

The radioactivity of the nuclides (88Kr, 135Xe, 135I) in the FP gas discharged from the reactor structure 1 is defined as Q _{Kr (t)} , Q _{Xe (t)} , Q _{I (t)} , and the reactor structure 1 If the radioactivity of nuclides (88Kr, 135Xe, 135I) in the FP gas is Q _{Kr (0)} , Q _{Xe (0)} , Q _{I (0)} , Equations 17 to 19 are established.

The radioactivity calculator 17 corrects the radioactivity Q _{Kr (t)} of the first nuclide (88 _Kr) to Q _{Kr (0)} using the above equations 17 to 19, and the radioactivity of the second nuclide (135Xe) Q _{Xe (t)} is corrected to Q _{Xe (0)} . The radioactivity ratio calculator 12 calculates the ratio between the corrected radioactivity of the first nuclide and the corrected radioactivity of the second nuclide.

  Also in the present embodiment configured as described above, a neutron multiplication distribution can be acquired and displayed as in the first embodiment. Therefore, the reactivity and distribution of the molten fuels 2A and 2B can be estimated. Moreover, in this embodiment, the precision of a neutron multiplication factor can be improved compared with the said 1st Embodiment.

In the second embodiment, the radioactivity Q _{I (t)} of the nuclide (135I) in the FP gas discharged from the reactor structure 1 is measured, and the nuclide in the FP gas in the reactor structure 1 is measured. The radioactivity Q _{I (0)} of (135I ₎ is calculated, and the above formula 18 including the radioactivity Q _{I (0)} of this nuclide (135I) as a parameter is used to calculate the FP gas in the reactor structure 1 The case where the radioactivity Q _{Xe (0)} of the nuclide (135Xe) is calculated has been described as an example. However, the present invention is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. That is, considering that the nuclide (135I) is water-soluble and its decay constant is smaller than that of the nuclide (135Xe), the second term of Equation 18 may be approximated to zero. Therefore, the radioactivity Q _{I (t)} of the nuclide (135I) in the FP gas discharged from the nuclear reactor structure 1 need not be measured. Also in this case, the accuracy of the neutron multiplication factor can be improved as compared with the first embodiment.

  In the second embodiment, the case where the data recording unit 11 of the neutron multiplication factor distribution estimation device 7 calculates the delay time has been described as an example. However, the present invention is not limited to this, and the gist and technical idea of the present invention are described. Modifications can be made without departing from the scope. That is, for example, the radioactivity display unit 10 of the radiation measuring device 6 displays the timing of water injection ON / OFF together with the time-dependent changes in the radioactivity of the first nuclide and the radioactivity of the second nuclide, and the operator is delayed based on this. The time may be calculated and input to the neutron multiplication factor distribution estimation device 7. In this case, the same effect as described above can be obtained.

  Moreover, in the said 1st and 2nd embodiment, when the water injection apparatus 3 has the water level calculating part 5 (that is, the neutron multiplication factor distribution estimation apparatus 7 receives the water level information in the reactor structure 1 from the water injection apparatus 3). However, the present invention is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. That is, the neutron multiplication factor distribution estimation device 7 may have the water level calculation unit 5 (that is, the neutron multiplication factor distribution estimation device 7 inputs water injection ON / OFF information from the water injection device 3 and based on this information, the reactor The water level in the structure 1 may be calculated). In this case, the same effect as described above can be obtained.

  Moreover, in the said 1st and 2nd embodiment, although the case where the display part 16 which displays a neutron multiplication distribution on a screen was provided as an example as an output part which outputs a neutron multiplication distribution was demonstrated, it is not restricted to this. Modifications can be made without departing from the spirit and technical idea of the present invention. That is, for example, a printer that prints an image of the neutron multiplication factor distribution may be provided. In this case, the same effect as described above can be obtained.

In the first and second embodiments, the case where 88 Kr is selected as the first nuclide and 135 Xe is selected as the second nuclide has been described as an example. However, the present invention is not limited to this, and the gist and technology of the present invention Modifications can be made without departing from the concept. That is, in order to establish the above-described Equation 9, a nuclide near the mass number 90 may be selected as the first nuclide, and a nuclide near the mass number 135 may be selected as the second nuclide (specifically, the second nuclide) For example, 133Xe may be selected). However, the selection conditions are preferably those having a relatively simple decay chain that does not have a long-lived parent nuclide. Preferably, the yield of induced fission γ _{A, NF} of the first nuclide and the yield of induced fission γ _{B, NF} of the second nuclide are relatively large (for example, γ _{A, NF} , γ _{B, NF} > 0. 01), the ratio between the induced fission yield γ _{A, NF} of the first nuclide and the yield γ _{A, SF} of the spontaneous fission is relatively small (for example, γ _{A, SF} / γ _{A, NF} <0.2), The ratio between the induced fission yield γ _{A, NF} of the second nuclide and the yield γ _{A, SF} of the spontaneous fission is close to 1 (for example, 0.8 <γ _{A, SF} / γ _{A, NF} <1.2). The half-life of the first nuclide and the half-life of the second nuclide should be larger than the delay time. As shown in Table 1 below, 88Kr as the first nuclide and 135Xe or 133Xe as the second nuclide satisfy the selection conditions described above.

  Although not specifically described in the first and second embodiments, spontaneous fission is considered when induced fission is considered in a region where the neutron multiplication factor k is close to 1 or in a region where the neutron multiplication factor k is close to 0. When considering fission, the yield of nuclides may be weighted based on the composition of the fission system. Even in such a modification, the same effect as described above can be obtained.

DESCRIPTION OF SYMBOLS 1 Reactor structure 3 Water injection apparatus 6 Radioactivity measuring apparatus 7 Neutron multiplication factor distribution estimation apparatus 16 Neutron multiplication factor distribution display part

Claims (4)

In an exhaust gas monitoring system of a nuclear power plant that monitors FP gas discharged from a nuclear reactor structure,
Each time the water level in the reactor structure rises due to intermittent water injection by the water injection device, the radioactivity of the first nuclide and the radioactivity of the second nuclide are applied to the FP gas discharged from the reactor structure. A radioactivity measuring device to measure,
For each water level in the reactor structure, the ratio between the radioactivity of the first nuclide and the radioactivity of the second nuclide measured by the radioactivity measuring device is calculated, and the neutron multiplication factor is calculated based on this ratio. An exhaust gas monitoring system for a nuclear power plant, comprising: a neutron multiplication factor distribution estimation device that creates a fluctuation distribution of a neutron multiplication factor corresponding to a change in a water level in the nuclear reactor structure. The exhaust gas monitoring system for a nuclear power plant according to claim 1,
The neutron multiplication factor distribution estimation apparatus is
The amount of change per unit time of the radioactivity of the first nuclide in the FP gas discharged from the reactor structure after the change of the water level in the reactor structure is changed before the change of the water level in the reactor structure. When it is determined that the amount of change per unit time of the radioactivity of the first nuclide in the FP gas discharged from the reactor structure is within the allowable range set as a reference, the water level in the reactor structure Using the average value per unit time of the radioactivity of the first nuclide in the FP gas discharged from the reactor structure after the change of
The amount of change per unit time of the radioactivity of the second nuclide in the FP gas discharged from the reactor structure after the change of the water level in the reactor structure is changed before the change of the water level in the reactor structure. When it is determined that the change per unit time of the radioactivity of the second nuclide in the FP gas discharged from the reactor structure is within the allowable range set as a reference, the water level in the reactor structure Using the average value per unit time of the radioactivity of the second nuclide in the FP gas discharged from the reactor structure after the change of
An exhaust gas monitoring system for a nuclear power plant, wherein a ratio between the radioactivity of the first nuclide and the radioactivity of the second nuclide is calculated. The exhaust gas monitoring system for a nuclear power plant according to claim 1,
The neutron multiplication factor distribution estimation apparatus is
The delay time is calculated from the difference between the water level fluctuation timing in the reactor structure by the water injection device and the radioactivity fluctuation timing of the first nuclide or the second nuclide measured by the radioactivity measurement device. Based on the time, the radioactivity of the first nuclide and the radioactivity of the second nuclide in the FP gas exhausted from the reactor structure are calculated as the radioactivity of the first nuclide and the second radioactivity of the FP gas in the reactor structure. It has a function to correct for radioactivity of nuclides,
For each water level in the reactor structure, calculate the ratio between the corrected radioactivity of the first nuclide and the corrected radioactivity of the second nuclide, calculate the neutron multiplication factor based on this ratio, An exhaust gas monitoring system for a nuclear power plant that creates a fluctuation distribution of a neutron multiplication factor corresponding to a change in a water level in a nuclear reactor structure. The exhaust gas monitoring system for a nuclear power plant according to claim 1,
A nuclear power plant, comprising: a display unit that displays a fluctuation distribution of a neutron multiplication factor corresponding to a change in a water level in the nuclear reactor structure.

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