JPH06160587A - Criticality control method for solution nuclear fuel - Google Patents

Abstract

PURPOSE:To directly control the criticality of solution nuclear fuel based on the layout of a neutron detector and the counting rate of the neutron detector. CONSTITUTION:The water phase of a stock solution containing nuclear fuel is fed into a column 1 from a water phase inlet pipe 6, and the organic phase of an extracting solvent is fed from an organic phase inlet pipe 8. In a pulse column extracting a solution while a pulsation is applied from a pulse generator 11, the layout of a neutron detector capable of determining the concentration distribution and the plutonium accumulation is determined in consideration of the plutonium concentration distribution from the analyzed result of the solution extraction simulation code of the pulse column. The counting rate of a neutron detector is used and the reverse multiplication method and the distribution pattern method are applied to control the criticality of solution nuclear fuel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a criticality control method for a solution-type nuclear fuel in a solution extractor or a storage tank handled in a fuel reprocessing plant or the like.

[0002]

2. Description of the Related Art For example, nuclear fuel reprocessing methods include a wet method in which spent fuel is dissolved in an acid and treated in a solution state, and a dry method in which spent fuel is directly treated at a high temperature. The Purex method is widely used for the wet method. The purex method is a method in which spent fuel is dissolved in nitric acid, and then plutonium and uranium, which are nuclear fuel substances, are extracted, separated, and purified with TBP (butyl triphosphate).

In this extraction step, a pulsating solution countercurrent extraction tower (hereinafter referred to as a pulse column) as a solution extraction device and a stirring / separation type solution countercurrent extractor (hereinafter referred to as a mixer-settler) are used.
However, a cylindrical storage tank is also used as the liquid reservoir.

For the monitoring of the extraction process and the criticality monitoring, a neutron detector for detecting neutrons generated by the nuclear fuel material is appropriately used, for example, in the axial direction outside the column in the pulse column and in the radial direction below the settra portion in the mixer-settler. In addition, the storage tanks are arranged in the axial direction, and the concentration and distribution of nuclear fuel materials are monitored by measuring the count rate.

Further, in recent years, an in-line neutron monitor for criticality control, which monitors the absolute value of the concentration of the nuclear fuel material from the count rate and performs concentration criticality control, has been considered and is being developed.

[0006]

However, as described above, the neutron detector is equidistant in the axial direction of the column in the pulse column, in the radial direction below the setter portion in the mixer-settler, and in the axial direction in the storage tank. However, it is not arranged in consideration of the solvent extraction chemical process relating to the mass transfer between the two phases of the pulse column and the mixer settler in the normal time or the abnormal time.

Further, the counting rate of each neutron detector including the storage tank for containing the nuclear fuel material uses a pre-evaluated coefficient in monitoring only the concentration and distribution tendency of the nuclear fuel material and in the in-line neutron monitor for criticality control. It is only considered that the concentration is converted from the counting rate, and the concentration is not directly used for criticality control, so that there is a problem that appropriate criticality control cannot be performed.

The present invention has been made to solve the above-mentioned problems, and is suitable for performing process monitoring and criticality monitoring in a pulse column, a mixer-settler, and a storage tank that process a solution-type nuclear fuel in a chemical process. Another object of the present invention is to provide a criticality control method for a solution-type nuclear fuel that can perform criticality control directly from the arrangement of various neutron detectors and the count rate of those neutron detectors.

[0009]

A first invention is a pulsating solution countercurrent extraction column (pulse column) in which two kinds of solutions consisting of an aqueous phase and an organic phase containing nuclear fuel are countercurrently flowed to extract elements by mass transfer. Based on the axial concentration distributions of the nuclear fuel material and the associated fission products obtained at normal and abnormal times obtained by the analysis of the solvent extraction simulation code of the pulse column, the distribution of nuclear fuel material and the nuclear fuel material at abnormal time Neutron detectors for detecting neutrons generated by the nuclear fuel material are arranged at a plurality of axial positions suitable for detecting the accumulation of neutrons.

A second aspect of the present invention is a stirring / separating type solution countercurrent extraction column (mixer settler) in which two kinds of solutions containing a nuclear fuel, which are an aqueous phase and an organic phase, are countercurrently flowed to extract elements by mass transfer. Suitable for detecting the distribution of nuclear fuel material and the accumulation of nuclear fuel material at abnormal time based on the radial concentration distribution of nuclear fuel material and associated fission products obtained at normal time and abnormal time obtained by analysis of extraction simulation code A neutron detector for detecting neutrons generated by the nuclear fuel material is arranged at a plurality of radial positions.

According to a third aspect of the present invention, a plurality of neutron detectors for detecting neutrons generated by the nuclear fuel material are axially or radially arranged in a storage tank containing a solution-type nuclear fuel material. It is characterized in that a value obtained by dividing the count rate at the reference time in the normal time by the count rate at each time is monitored in time series, or the axial distribution of the count rate of the neutron detector is monitored.

[0012]

In the first aspect of the present invention, in the pulse column, the nuclear fuel material in the aqueous phase and the organic phase in normal time and abnormal time,
Axial concentration distributions of accompanying fission products and acids are analyzed by solvent extraction simulation code of pulse column.

As a result, the distribution of the nuclear fuel material and the accumulation of the nuclear fuel material at the time of the abnormality are determined based on the obtained axial concentration distributions of the nuclear fuel material of each phase at the normal time and the abnormal time, the associated fission products and the acid. Neutron detectors are placed at multiple axial positions outside the column suitable for detection.
This neutron detector controls the criticality of solution-type nuclear fuel in the pulse column.

In the second aspect of the present invention, in the mixer-settler, the radial concentration distributions of the nuclear fuel material in each phase, the associated fission products, the acid and the like at normal time and abnormal time are analyzed by the solvent extraction simulation code of the mixer-settler.

As a result, the distribution of the nuclear fuel material and the accumulation of the nuclear fuel material at the time of the abnormality are based on the obtained radial concentration distributions of the nuclear fuel material of each phase, the associated fission products, and the acid at the time of the abnormality. The neutrons generated by the nuclear fuel material are detected at a plurality of radial positions below the settler part of the mixer-settler suitable for detection, and the criticality control of the solution-type nuclear fuel in the mixer-settler is performed.

In the third invention, a plurality of neutron detectors are arranged axially or radially in the storage tank. The ratio of the count rate at each standard time of these neutron detectors to the count rate at each time, in particular the value obtained by dividing the former by the latter is monitored in time series, and the axis of the count rate of each neutron detector The directional distribution is monitored to control the criticality of the solution-type nuclear fuel in the storage tank.

[0017]

EXAMPLE A first example of the criticality control method for a solution-type nuclear fuel according to the present invention will be described with reference to FIGS. 1 and 3. 2 is fried as a conventional example for comparison with the present embodiment, and the first embodiment corresponds to the first invention.

A pulse column will be described with reference to FIG.
In the figure, reference numeral 1 is a cylindrical column in which a large number of sieve plates 2 called sheave plates are arranged at equal intervals via support rods 3. At the top of column 1 is an upper container 4
However, the lower containers 5 are welded to the lower ends, respectively. A water phase inlet pipe 6 for injecting a raw material solution such as a uranyl nitrate solution into the upper container 4, and a TB containing extracted uranium and the like.
It is connected to an organic phase outlet pipe 7 for flowing out an organic phase extract such as P.

On the other hand, in the lower container 5, an organic phase inlet pipe 8 for injecting a solvent for extraction such as TBP, an aqueous phase outlet pipe 9 for letting out a raffinate solution from which the raw material is extracted, and a raw material for extraction operation. A pulse leg 10 is connected to impart pulsation to the solution and the extraction solvent. Pulse generator for pulse leg 10
11 is connected. 2 shows a conventional example in which a plurality of neutron detectors 12 are attached to the column 1 in the axial direction.

In the pulse column having the above structure, two kinds of solutions consisting of an aqueous solution (aqueous phase) containing a nuclear fuel and an organic solvent (organic phase) are counter-currently flowed, and elements are extracted by mass transfer. That is, the water phase flows in from the upper water phase inlet pipe 6,
The organic phase is introduced from the lower organic phase inlet pipe 8 and pulsed by the pulse generator 11. As a result, one phase is dispersed through the packing such as the perforated plate 2 in the column 1 and mass transfer is performed by AC contact.

By the way, for example, 1986 No. 10 pp.883-895 of "Journal of the Atomic Energy Society of Japan" and "Phytokinetic Technical Report" 1
December 76, 990, simulation calculation code of solvent extraction process for pulse column in Purex method is described. That is, there is a model that describes the solvent extraction chemical process and a simulation calculation code that is a computer program of the model, and evaluates the axial position dependence of the concentrations of nuclear fuel materials, fission products, acids, etc. in each phase. You can The solvent extraction simulation code has been developed in each country with the United States as a pioneer (refer to Table 5-1 of "kinetic combustion technique" above).

FIG. 3 shows an analysis result of the concentration in the pulse column for washing uranium in the aqueous phase where plutonium is present after the distribution of plutonium and uranium in the distribution process of spent fuel reprocessing based on the Purex method, for example. An example of an axial plutonium concentration of 13 is shown. In the figure, the vertical axis represents the concentration of plutonium, and the horizontal axis represents the position of the pulse column in the column axis direction.

In this example, plutonium, which has a nuclide that generates a large amount of neutrons generated by the reaction of spontaneous α-fission or emitted α-particles with oxygen in its atomic composition, is distributed in the axial direction of the pulse column. In the embodiment shown in FIG. 3, for example, the axial position (3) to the axial positions (1), (3),
By disposing the neutron detector 12 in (6) and (8), it is possible to detect the maximum concentration of plutonium or to know the entire concentration distribution.

In the conventional example, the neutron detector 12 is perpendicular to the direction of the external axis of the column 1 as shown in FIG. 2, but the neutron detector 12 may be arranged parallel to or inclined with respect to the axis. Further, the neutron detector 12 is surrounded by a neutron moderator such as polyethylene and arranged at equal intervals in order to improve neutron detection efficiency and sensitivity.

Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment corresponds to the second invention, and a conventional mixer-settler will be described with reference to FIGS. 4 and 5 as a reference example for explaining the present embodiment.

4 and 5 show a stirring / separating solution countercurrent extractor for countercurrently flowing two kinds of solutions consisting of an aqueous solution (aqueous phase) containing a nuclear fuel and a solvent (organic phase) and extracting elements by mass transfer. It is an example of a certain mixer settler 14.

That is, the mixer-settler 14 is composed of a mixer section 15 for stirring / mixing an aqueous solution and a solvent, and a settler section 16 for allowing the mixed solution to stand / separate. Mass transfer is performed by mixing and contacting at 15.

The spent nuclear fuel reprocessing facility uses a large amount of mixer-settler 14, and the processing is carried out by the so-called Purex method based on the solvent extraction method.

Conventionally, as shown in FIGS. 4 and 5, a neutron detector 12 for detecting neutrons generated by a nuclear fuel material is used in the radial direction of the mixer-settler 14 to improve the neutron detection efficiency, increase the sensitivity, and reduce Holes 18 are formed in a neutron moderator 17 such as polyethylene that suppresses the ground, and the holes are surrounded by the neutron moderator 17 and arranged at equal intervals directly below the radial center of each stage.

Regarding the solvent extraction chemical process in the mixer-settler 14, as described in, for example, "Kineki Giho" December 76, 1990, a model describing the process and a computer program for the model are described. There is a calculated calculation code, and it is possible to evaluate the radial position dependence of the concentration of the nuclear fuel material, the fission product, the acid, etc. in each phase.

FIG. 6 is an example showing the radial direction plutonium concentration 19 of the concentration distribution analysis result of one plutonium refinement extractor in the plutonium refinement process of spent fuel reprocessing based on the Purex method, for example.

In this example, plutonium having a nuclide that generates a large amount of neutrons generated by the reaction of spontaneous α-fission or emitted α-particles with oxygen is distributed in the radial direction of the mixer-settler in the atomic composition.

In the criticality control method of the second embodiment, for example, the neutron detectors 12 are arranged at radial positions (9) to (15) shown in the horizontal axis of FIG. It is possible to detect the maximum concentration of or to know the entire concentration distribution.

Further, the presence or absence of plutonium can be detected by disposing neutron detectors at the radial positions (1) to (4).

The simulation calculation code of the solvent extraction process of the pulse column and the mixer-settler can evaluate transient changes related to changes in the flow rates of the aqueous solution (aqueous phase) and the solvent (organic phase).
In this embodiment, a detector is arranged at the axial or radial position where, for example, plutonium accumulates during transient changes, and the plutonium accumulation is detected.

The neutron count rate of the neutron detector 12 shown in FIGS. 2 to 4 and 5 is a constant value in normal times, and a coefficient rate in a normal time is stored as a value. As the count rate, only a value at a certain normal time may be used, but if the count rate is within a certain range in time series, an average value thereof may be adopted.

In this case, the ratio of the reference count rate to the count rate at each time, especially the value obtained by dividing the former by the latter, is monitored in time series, and if no abnormality occurs, the count rate ratio not shown is shown. Although the sequence is constant, if an abnormality occurs and, for example, nuclear fuel material such as plutonium accumulates at a certain axial position, FIG.
As shown in, the time series of the count rate ratio gradually approaches zero and predicts the approach to the criticality.

Such a characteristic is often used in the critical proximity of a nuclear reactor, but this embodiment is characterized in that the time is used on the horizontal axis. Further, as shown in FIG. 7, by monitoring the time series of the count rate ratios of the detectors A, B, and C, the count rate ratio of the detector C installed at the position where the reactivity is high has a moderate reactivity. It is also possible to monitor the place with the highest reactivity, which approaches zero faster than the count rate ratio of the detector B installed at a certain position and the count rate ratio of the detector A installed at a low reactivity position. , The tendency of the proximity to the criticality and the time can be evaluated as a whole of the time series of each detector.

When the neutron detector 12 is installed as described above, the effect is further enhanced as compared with the first and second embodiments.

The neutron count rate distribution of the neutron detector 12 has a constant shape in normal times, and stores a count rate distribution in normal times. This count rate distribution may use only a certain normal distribution, but if the count rate distribution is within a certain range in time series, the average value of those distributions may be adopted.

In this case, the reference count rate distribution is monitored in time series, and if no abnormality occurs, the time series of the count rate distribution is flat and almost does not change, but an abnormality occurs, for example, a nuclear fuel such as plutonium. When the substance accumulates, the distribution of the neutron flux in the system gradually changes according to the reactivity of the system, as shown in Fig. 8, and it is convex in the center from A to B, C, D. Distribution, predicting proximity to criticality (assuming uniform fuel distribution in the axial direction in this example).

In this case, the distribution form is represented by a value obtained by dividing the count rate near the distribution edge by the count rate near the center, and the value is arranged by the subcriticality obtained by subtracting the effective multiplication factor from 1 9
The criticality control can be performed by using FIG. 9, and the tendency and time of approaching the criticality can be evaluated by monitoring the time series.

Next, a third embodiment according to the present invention will be described with reference to FIG. This embodiment corresponds to the third invention. FIG. 10 is an example of a storage tank 20 for storing a solution-type nuclear fuel, in which a solution is supplied from a solution supply port (not shown), and a plurality of axial positions or radial positions (not shown) detect neutrons generated by fissile material. A neutron detector 21 is installed.

The neutron count rate of the neutron detector 21 shown in FIG. 10 is a constant value in normal times, and a certain count rate in normal times is stored as a value. As the count rate, only a value at a certain normal time may be used, but if the count rate is within a certain range in time series, an average value thereof may be adopted.

In this embodiment, the ratio of the reference count rate to the count rate at each time, in particular, the value obtained by dividing the former by the latter is monitored in time series, and if no abnormality occurs, the count rate ratio not shown is shown. Although the series is constant, if an abnormality occurs and the concentration of fission material such as plutonium increases at a certain axial position or radial position, the time series of the counting rate ratio gradually becomes zero as shown in FIG. Approach and predict approach to criticality.

As shown in FIG. 7, by monitoring the time series of the counting rate ratio of each detector, it is possible to monitor at the place where the reactivity is highest, and also the tendency toward the criticality and the time as a whole. Can also be evaluated.

In this embodiment, the neutron count rate distribution of the neutron detector 21 arranged in the axial direction or in the radial direction (not shown) has a constant shape in normal time, and stores a certain count rate distribution in normal time. . This count rate distribution may use only a certain normal distribution, but if the count rate distribution is within a certain range in time series, the average value of those distributions may be adopted.

Further, the reference count rate distribution is monitored in time series, and if no abnormality occurs, the time series of the count rate distribution is flat and almost does not change, but an abnormality occurs, for example, fissile material such as plutonium. If the concentration increases at a certain axial position and / or radial position, the time series of the count rate distribution changes as shown in FIG. 8, and the distribution system is convex at a portion where the fuel concentration gradually increases or in the vicinity thereof. And predict the proximity to criticality.

In this example, the distribution form is represented by a value obtained by dividing the count rate near the distribution edge by the count rate near the center, and rearranging the value by the subcriticality obtained by subtracting the effective multiplication factor from 1 is shown in FIG. The criticality control can be performed by using FIG. 9, and the tendency and time of approaching the criticality can be evaluated by monitoring the time series.

Next, the embodiments of the present invention will be summarized as follows. (1) In the pulse column, based on the axial concentration distributions of the nuclear fuel material and associated fission products in normal and abnormal times obtained by analysis of solvent extraction simulation code, the distribution of nuclear fuel material and the nuclear fuel material in abnormal time Place neutron detectors at multiple axial positions suitable for detecting the accumulation of neutrons.

(2) In the mixer-settler, based on the radial concentration distributions of the nuclear fuel material and accompanying fission products obtained in the normal time and the abnormal time obtained by the analysis of the solvent extraction simulation code, the distribution of the nuclear fuel material and the abnormal time Place neutron detectors at multiple radial positions suitable for detecting the accumulation of nuclear fuel material.

(3) In (1), the ratio of the count rate at the normal reference time of each neutron detector arranged at the axial position of the pulse column to the count rate at each time is monitored in time series. Also, monitor the axial distribution of the counting rate of each neutron detector.

(4) In (2), the ratio of the count rate at the standard time of each neutron detector arranged at the radial position of the mixer settra to the count rate at each time is monitored in time series. Also, monitor the radial distribution of the counting rate of each neutron detector.

(5) A neutron detector is arranged along the axial direction or the radial direction of the storage tank containing the solution-type nuclear fuel, or both of them, and the counting rate at the normal time of each neutron detector is calculated at each time. Monitor the value divided by the counting rate in chronological order. Also, monitor the axial distribution of the count rate of each neutron detector.

[0055]

According to the present invention, it is possible to detect the concentration distribution and the accumulation or presence of plutonium at the time of abnormality in consideration of the analysis result of the concentration distribution of the nuclear fuel material by the analysis of the solvent extraction simulation code. In addition, criticality control can be performed directly in the mixer-settler, pulse column and storage tank by the inverse multiplication method and the distributed method using the count rates of these neutron detectors.

[Brief description of drawings]

FIG. 1 is an elevational view showing a pulse column for explaining a first embodiment of a criticality control method for a solution-type nuclear fuel according to the present invention.

FIG. 2 is a conceptual diagram showing a conventional example in which a neutron detector is attached to the column in FIG.

FIG. 3 is a curve diagram showing the analysis result of the axial concentration distribution in FIG.

FIG. 4 is a perspective view showing a mixer-settler for explaining a second embodiment of the criticality control method for solution-type nuclear fuel according to the present invention.

5 is an axial sectional view showing a conventional example of one stage of the mixer-settler shown in FIG.

FIG. 6 is a characteristic diagram showing a result of analyzing a radial concentration distribution of the mixer-settler in FIG.

FIG. 7 is a characteristic diagram showing a time series of a count rate ratio obtained by dividing the reference count rate by the count rate at each time in FIG.

FIG. 8 is a curve diagram showing the count rate distribution in the axial direction or the radial direction in FIG.

9 is a curve diagram showing the relationship between a value obtained by dividing the count rate near the end of the count rate distribution in FIG. 4 by the count rate near the center and the subcritical degree.

FIG. 10 is a perspective view showing an arrangement relationship between a storage tank and a neutron detector in a third embodiment of the solution-type nuclear fuel criticality control method according to the present invention.

[Explanation of symbols]

1 ... column, 2 ... perforated plate, 3 ... support rod, 4 ... upper container,
5 ... Lower container, 6 ... Water phase inlet pipe, 7 ... Organic phase outlet pipe, 8
… Organic phase inlet pipe, 9… Water phase outlet pipe, 10… Pulse leg, 11
... Pulse generator, 12 ... Neutron detector, 13 ... Axial plutonium concentration, 14 ... Mixer setra, 15 ... Mixer part, 16 ... Setra part, 17 ... Neutron moderator, 18 ... Hole, 19 ... Radial plutonium concentration, 20 … Storage tank, 21… Neutron detector.

Claims (3)

[Claims] 1. A solvent extraction of a pulse column to a column of a pulsating solution countercurrent extraction column (pulse column) for extracting elements by mass transfer by countercurrently flowing two kinds of solutions containing an aqueous phase and an organic phase containing nuclear fuel. Based on the axial concentration distribution of nuclear fuel material and associated fission products at normal and abnormal times obtained by analysis of simulation code,
Criticality of solution-type nuclear fuel characterized by arranging neutron detectors for detecting neutrons generated by the nuclear fuel material at a plurality of axial positions suitable for detecting the distribution of the nuclear fuel material and accumulation of the nuclear fuel material at abnormal times Management method. 2. A solvent extraction simulation code of mixer-settler for a stirring / separating solution countercurrent extraction tower (mixer-settler) that countercurrently flows two kinds of solutions containing an aqueous phase and an organic phase containing nuclear fuel and extracts elements by mass transfer. Based on the radial concentration distributions of nuclear fuel material and associated fission products obtained during normal and abnormal times obtained by the analysis of the above, multiple diameters suitable for detecting the distribution of nuclear fuel material and the accumulation of nuclear fuel material during abnormal times A criticality control method for a solution-type nuclear fuel, characterized in that a neutron detector for detecting neutrons generated by the nuclear fuel material is arranged in a direction position. 3. A plurality of neutron detectors for detecting neutrons generated by the nuclear fuel material are arranged in an axial direction or a radial direction in a storage tank containing a solution-type nuclear fuel material, and the neutron detectors for normal operation of each of the neutron detectors are arranged. A method for criticality control of a solution-type nuclear fuel, characterized in that a value obtained by dividing the count rate at a reference time by the count rate at each time is monitored in time series, or the axial distribution of the count rate of the neutron detector is monitored. .