JPH04151590A - Neutron monitor apparatus - Google Patents

Abstract

PURPOSE:To prevent the critical state by emitting an alarm by measuring, calculating and evaluating the number of neutrons from plutonium (Pu) to compare the same with a preset Pu concn. upper limit control value to detect the abnormality of concn. CONSTITUTION:The neutron generated from a small amount of Pu contained in the waste extract (aqueous nitric acid solution or org. solvent solution) supplied to a mixer settler is measured by the neutron detection part 1 constituted of the counter surrounded by a neutron decelerating material. The signal from the detection part 1 is inputted to a Pu concn. calculator 3 as a count rate through a counter circuit 2. Pu isotope composition ratio analytical data also becomes the input data of the calculator 3. Further, a neutron effective multiplication constant memory apparatus 4 stores the data showing the relation between a neutron effective multiplication constant and Pu concn. on the basis of theoretical calculation and the calculator 3 refers to said data to correct neutron multiplication effect to calculate the concn. of Pu. The Pu concn. calculation value outputted from the calculator is sent to an alarm generator 5 to be compared with a Pu concn. upper limit value and, when the Pu concn. calculation value becomes said limit value or more, an alarm is emitted.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to the use of neutrons used in equipment that performs criticality control by plutonium concentration in the co-decontamination process and purification process of the reprocessing extraction process. The present invention relates to a monitoring device, and particularly to a neutron monitoring device equipped with a plutonium leakage detection function.

(Prior art) Conventionally, in the co-decontamination/distribution process and refining process of reprocessing plants, equipment that constantly handles nuclear fuel materials such as plutonium (Pu) and uranium (U) has an effective neutron multiplication factor of 1. Criticality safety design is carried out so that the temperature does not become less than 0, that is, criticality. In other words, in each of these devices, the acidity of the supplied liquid, the concentration of nuclear fuel materials such as Pu and U in it, and abnormalities in the concentration of Pu and U components in the nitric acid aqueous solution and organic solvent can be changed. The design limits the shape and volume so that it is subcritical to changes. On the other hand, equipment that performs criticality control using Pu concentration (Pullium content in nitric acid aqueous solution or organic solvent solution) attached to each of the above equipment has a low processing efficiency because the amount of Pu is small or hardly flows during normal operation. With this in mind, the design has relaxed restrictions on the shape, size, and volume of the equipment. However, there is a possibility that Pu may leak for some reason and become critical, so by installing neutron ray, gamma ray, etc. detectors in various places, it is possible to detect an increase in the radiation level and generate an alarm. Measures are taken, such as notifying staff and each required quality of the danger, and stopping the process based on human judgment.

(Problem to be Solved by the Invention) However, the level does not simply increase in proportion to the concentration of nuclear fuel material. For example, Pu is particularly important for criticality safety management, and it is known that the neutron generation rate from P'u varies greatly depending on the Pu isotope composition ratio.

This isotopic composition ratio varies greatly depending on the initial enrichment level and irradiation history of the reprocessed fuel, and therefore the level of neutron beam is not necessarily proportional to the amount of Pu. Therefore, the current situation is that it is not possible to quantify the Pu concentration simply by detecting the radiation level, and it is necessary to take an excessive margin for criticality safety management.

The present invention has been made in consideration of these points, and its purpose is to provide equipment for criticality control based on plutonium concentration attached to the co-decontamination/distribution process and purification process of the main reprocessing process. It is equipped with a signal generator that measures the number of neutrons from the Pu contained therein, takes in information on the Pu isotope composition ratio, etc., immediately evaluates the leaked Pu concentration, notifies the operator of the value, and issues an alarm. The aim is to provide a neutron monitoring device.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a device for measuring the number of neutrons from leaked plutonium in each device, and a device for measuring the number of neutrons from leaked plutonium in each device, and a device for measuring the number of neutrons from leaked plutonium in each device. A plutonium concentration calculation device calculates the plutonium concentration, and the plutonium concentration calculated by this calculation device is compared with the plutonium concentration upper limit value set on the safe side in advance, and an alarm is issued when the plutonium concentration exceeds the upper limit value. It is characterized by being equipped with a signal generator that emits a signal.

(Function) According to the present invention, the signal from the neutron number measuring device is input to the plutonium concentration calculation device, and the plutonium concentration is calculated. This calculated plutonium concentration is sent to a signal generator and compared with a preset plutonium concentration upper limit value, and if the plutonium concentration exceeds this upper limit value, an alarm is generated.

(Example) First, the theory underlying the present invention will be explained.

The neutron source is mainly the spontaneous nuclear fission of Pu and the (α, n) reaction with oxygen etc. due to alpha decay of Pu, but the neutron generation rate per unit weight of Pu is as shown in Table 1. It is known that it differs depending on the Pu isotope. On the other hand, the Pu isotope composition ratio in the reprocessed fuel varies greatly depending on the initial enrichment level, irradiation history, etc. of the reprocessed fuel.

FIG. 2 is a diagram illustrating the range of Pu isotope composition ratios using Pu-240 as a representative composition. Based on this, in the present invention, we consider the range of Pu isotopic composition that includes all reprocessed fuel stipulated in the acceptance specifications, and calculate the Pu isotopic composition ratio (referred to as Pu vector) as shown in Figure 3. The relationship between Pu and the neutron generation rate s (Pu) per unit weight of Pu is determined. In addition, Figure 4 shows that the effective neutron multiplication factor of the auxiliary extractor for cleaning and removing trace amounts of Pu in the waste liquid is 84. The KefT of the system is a function of the Pu concentration, and is determined based on theoretical calculations.

Table 1 Pu neutron generation rate (n/sec ・gPu) Note 1) H2O: 100% Note 2) TBP: 30V%, Dodecane:
70 v% In the present invention, by determining the above relationship in advance, the Pu concentration is calculated based on the following principle, and the Pu concentration abnormality can be detected by comparing it with the Pu concentration alarm value (upper limit value). conduct.

First, a method for calculating the Pu concentration will be described. Neutron count rate C
is proportional to the neutron generation rate S per unit volume of Pu solution and also depends on the Kerr of the system. In addition, the strength S of the neutron source per unit volume is determined by the Pu concentration n and the acceptance P
It is the product of the neutron generation rate S per unit weight.

That is, C-α・S/(1-K) ・・・・・・・・・
... (1) o err S -n-s (Pu) ...
. . . (2) Here, α is a constant, which is determined by measurement using a system in which the specifications of the radiation source are known. In addition, Kef'r of the system is a function of n and individuals, and ...... From the formula, the relationship between C and n can be found as follows: C-a・n-s (Pu)/ (1-Ke, f(n,
Pu) ) - (4) That is, when the neutron count rate C is given, the Pu concentration can be calculated using equation (4).

Next, Figure 5 shows, as a typical example, a trace amount of Pu in the waste liquid.
This figure shows the relationship between the neutron count rate and the Pufi degree in the auxiliary extractor (mixer settler) that washes and removes neutrons. In the figure, the broken line represents the relationship when the neutron multiplication effect is not present, and the solid line represents the relationship when the neutron multiplication effect is present. From this figure, the Pu concentration is 1gPu#! If the Pu concentration is less than a certain amount, the neutron multiplication effect may be set to zero, but when the Pu concentration reaches about several grams of Pu#7, it is clear that it is necessary to take the neutron multiplication effect into consideration. In the figure, AA' is the change range of the counting rate corresponding to the maximum Pu concentration during normal operation when considering process quantity fluctuations such as acid concentration and flow rate of nitric acid aqueous solution and organic solution, -BB'
is the control concentration for process management (maximum allowable leakage Pu concentration)
, and the hatched range represents the range of count rate when the entire accepted Pu composition range is considered.

The alarm value for the Pu concentration is set to a value NA lower than the control concentration, but the corresponding counting rate range is CC'. By giving Pu composition information, n^ can be uniquely determined for one count rate data by the above equation (4).

Embodiments of the neutron monitor device according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the first embodiment of the neutron monitoring device of the present invention. , which shows the positional relationship between the Pu solution and the neutron detection section 1. The signal from the neutron detector is input to the Pu concentration calculation device 3 via the counting circuit 2 as a counting rate. In addition, the Pu isotope composition ratio analysis data is also input data to the device. The neutron effective multiplication factor storage device 4 has built-in data indicating the relationship between the neutron effective multiplication factor and the Pu concentration based on theoretical calculations, etc., and by referring to this, the device 3 can:
The Pu concentration is calculated by correcting the neutron multiplication effect. The calculated Pu concentration value output from the device 3 is sent to the alarm generating device 5.
is sent to and compared with the Pu concentration alarm value, and if the value exceeds the Pu concentration alarm value, the alarm generator 5 issues an alarm.

That is, in this neutron monitoring device, neutrons generated from a small amount of Pu contained in the extraction waste liquid (nitric acid aqueous solution or organic solvent solution) supplied to the mixer settler are collected using a He-3 counter surrounded by a neutron moderator (polyethylene, etc.). ,B-1
Measurement is performed by a neutron detector 1 consisting of a 0 counter and the like.

The counting circuit 2 includes a preamplifier, an amplifier, a pulse height discriminator, a counter, and the like.

The Pu concentration calculation device 3 is a device that calculates the Pu concentration, and inputs the analysis data of the neutron count rate and the Pu isotope composition ratio of the received fuel solution, and further calculates the neutron effective multiplication factor stored in the neutron effective multiplication factor storage device 4. A Pu concentration that satisfies the above equation (4) is calculated from data showing the relationship between the multiplication factor and the Pu concentration. The neutron effective multiplication factor storage device 4 stores data indicating the relationship between the Pu concentration and the neutron effective multiplication factor based on logical calculation results, criticality safety handbooks, etc. Considering that the shape of the Pu solution part changes with fluctuations, if the effective neutron multiplication factor is set to the minimum value within the fluctuation range,
In equation (4), the n value is evaluated to be relatively large and becomes on the safe side. In addition, the constant α value in formula (4) is calculated using neutron sources with various source strengths and shapes (Cf-252, Pu solution, etc.).
The response characteristics of the neutron detector are measured in a system simulating the equipment or in a real system using Note that even if the Pu concentration is the same, the shape of the Pu solution part changes as the process amount changes, and if the α value is set to the minimum value within the fluctuation range, the n value in equation (4) is evaluated as being on the safe side.

The alarm generating device 5 has a function of comparing the Pu concentration calculation value outputted from the device 3 with the Pu concentration alarm value and generating an alarm when the value exceeds the Pu concentration alarm value.

Note that information such as neutron count rate, Pu isotope composition, effective neutron multiplication factor, and Pu concentration, which are the input and output values of the device according to the present invention, can be outputted to a recorder or printer at the request of the operator, so that the operator can always know the information. It goes without saying that things can be done to encourage caution.

The second embodiment is as shown in FIG. 6, and is an example in which the system of the first embodiment is simplified.

Focusing on the fact that the neutron multiplication efficiency is small when the Pu concentration alarm value is about 1 gPu# or less, the effective neutron multiplication factor in the first embodiment is calculated by setting the neutron effective multiplication factor to zero in equation (4). The system is simplified by omitting the storage device 4.

The third embodiment is as shown in FIG. 7, and is an attempt to improve the calculation accuracy of the Pu concentration by further incorporating process amount information in the first embodiment. That is,
Considering that the shape of the Pu solution changes as the process amount changes, and the detector response characteristics and neutron multiplication effect of the system change, α and Kerr in equation (4) depend on the shape of the Pu solution. The amount is set to 1. For this reason, the Pu concentration calculation device 3 inputs the process amount in addition to the analysis data of the neutron count rate and the Pu composition of the received fuel solution. On the other hand, the effective neutron multiplication factor storage device 4 stores representative patterns of the shape of the Pu solution for various process amount fluctuations, and the effective neutron multiplication factor is evaluated for each based on theoretical calculation results, criticality safety handbooks, etc. Data indicating the relationship between magnification and Pu concentration is stored. The calibration constant storage device 4' also contains P
U Representative patterns of solution shapes are stored, and calibration constants α corresponding to each are stored. The calibration constant α is calculated based on neutron detection using a system that simulates equipment or a real system using neutron sources with various source intensities and shapes (Cf-252, Pu solution, etc.), assuming variations in various process quantities. The response characteristics of the device are measured in advance, and each representative pattern is determined based on those results. The Pu concentration calculation device 3 determines to which pattern the shape of the Pu solution belongs based on the input process amount information, and stores the information in the storage device 4.
Data indicating the relationship between the calibration constant α and the effective neutron multiplication factor and the Pu concentration are extracted from the equation (4) and the Pu concentration is calculated from the equation (4).

The target equipment of the present invention is not limited to mixer settlers, but is also applicable to other equipment containing Pu, such as pulse columns and storage tanks. In addition, in the present invention, a function is provided to calculate a calibration constant and an effective neutron multiplication factor using a neutron transport calculation code and a diffusion calculation code, and if necessary, a method of calculating or correcting the Pu concentration can be considered. .

〔Effect of the invention〕

As described above, the neutron monitoring device of the present invention measures the number of neutrons from leaked Pu in equipment that performs criticality control based on Pu concentration that is attached to the co-decontamination process and purification process of the reprocessing extraction process. , this is done manually to remove the Pu inside the device.
Not only the concentration but also the effective neutron multiplication factor can be calculated, and its criticality safety can be continuously monitored or evaluated at the request of the operator, and the upper limit value of the Pu concentration, which is set in advance on the safe side, can be calculated. Criticality can be prevented by comparing and detecting an abnormal Pu concentration and generating an alarm.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of a neutron monitoring device according to the first embodiment of the present invention, Figure 2 is a diagram showing the range of Pu isotopic composition ratios, and Figure 3 is a diagram showing the neutron generation rate per unit weight of Pu. Figure 4 shows the relationship between the Pu isotope composition ratio (represented by Pu-240), Figure 4 shows the relationship between the effective neutron multiplication factor and Pu concentration, and Figure 5 shows the alarm value in the relationship between the neutron count rate and Pu concentration. FIG. 6 is a block diagram showing a neutron monitor device according to a second embodiment of the present invention, and FIG. 7 is a block diagram showing a neutron monitor device according to a third embodiment of the present invention. 1... Neutron detection unit, 2... Counting circuit, 3... P
u concentration calculation device, 4... neutron effective multiplication factor storage device,
4'... Calibration constant storage device, 5... Alarm generating device.

Claims (1)

[Claims] a device for measuring the number of neutrons from leaked plutonium in each device; a plutonium concentration calculation device for calculating the plutonium concentration in each device by inputting the measured value of the number of neutrons; and a plutonium concentration calculated by the calculation device. A neutron monitor device comprising: a signal generating device that compares plutonium concentration with an upper limit value set on the safe side in advance and issues an alarm when the plutonium concentration exceeds the upper limit value.