JPS6122265B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device for managing the exposure dose of workers working in areas affected by radiation. Generally, workers working in areas affected by radiation, such as radiation controlled areas of nuclear power plants, carry film badges and dosimeters to monitor their exposure doses. When working in such an area, it is necessary to calculate the exposure dose of the workers performing the work before starting the work, and to formulate an exposure dose management plan. If this exposure dose management plan is inappropriate, the exposure dose will exceed the schedule, causing problems with the next work, and in some cases, the exposure dose will exceed the permissible value during the work, causing the worker to suffer. This may lead to inconveniences such as substitutions or work interruptions. Conventionally, such exposure dose management was performed as follows. That is, for example, when disassembling the waste liquid pump 1 that transfers radioactive waste liquid shown in FIGS. A dose rate distribution in this pump chamber 2 is prepared in advance. In addition, the curve in FIG. 1 shows an iso-dose rate line, and the number written in the middle of this iso-dose rate line shows a dose rate (mR/h). Next, as shown in Fig. 2, representative points 3 corresponding to the main work positions are determined from the movement path of the worker in the pump room 2, and these representative points 3 are determined from the dose rate distribution diagram in Fig. 1. Find the dose rate (mR/h). Then, the work content is analyzed to determine the worker's stay time at each representative point 3, and the worker's exposure dose is determined. Then, from this result, the amount of time the worker can stay in the pump room 2 in order to reduce the exposure dose to the planned value or less is calculated. and the man hours necessary for the work.
Calculate the number of people required for the work, taking into account the
Also determines the work plan. In the past, all such planning was done by radiation managers.
For this reason, managing such exposure doses requires a high degree of skill and experience, and it is necessary to secure a large number of skilled radiation managers. The present invention has been made based on the above circumstances, and its purpose is to provide an exposure dose management device that can automatically and accurately manage exposure doses. The present invention will be explained below with reference to an embodiment shown in FIGS. 3 to 11. This embodiment is for disassembling a waste liquid pump that transfers radioactive waste liquid from a nuclear power plant. That is,
1 in the figure is a waste liquid pump, and this waste liquid pump 1
is installed in a pump room 2 surrounded by a wall having radiation shielding ability. In this embodiment, the entire interior of the pump chamber 2 is defined as a unit work area. This unit work area generally includes the movement range of workers performing controlled work, and all of the radiation sources (internal or external) are distributed throughout the unit work area. In other words, the determination is made so as to satisfy that there is no shadow area within this unit work area, such as a wall or the like that has radiation shielding ability for the radiation source. Note that the shadow of pillars, piping, etc. that have radiation shielding ability but have a small projected area may be within this unit work area. Also,
It is preferable that this unit work area does not span multiple floors, that the path for workers to enter and leave the unit work area is clear, and that the path for movement of workers within this unit work area is clear. Further, this unit work area may include a plurality of unit work areas that overlap each other, or another unit work area may be defined within a large unit work area. In addition, the pump room 2 is surrounded by a wall having radiation shielding ability,
The entire inside of this room is affected by radiation from the waste liquid pump 1, which is a radiation source, and there are no areas that are shadowed by radiation, and workers must work only within this pump room 2, with clear entrances and exits. All of the above-mentioned conditions are satisfied, and in this embodiment, the entire interior of the pump chamber 2 is used as a unit work area. In the pump chamber 2, that is, in the unit work area, there are a plurality of radiation detectors 4a, for example, three radiation detectors.
4b and 4c are provided. These radiation detectors 4a, 4b, and 4c are arranged as follows. First, the dose rate at multiple locations within the pump chamber 2 is measured, and a dose rate distribution as shown in FIG. 1 is determined. Note that such measurements have already been performed with existing equipment, so the data can be used. Then, the geometric mean value and standard deviation of this dose rate distribution are determined. Then, a first radiation detector 4 is installed at a location in the pump chamber 2 that shows the above average value.
Install a. Note that if there are multiple locations showing this average value, the first radiation detector 4a is placed at the location closest to the radiation source, that is, the waste liquid pump 1.
Place. Furthermore, a second radiation detector 4b is placed at a location where the value is one standard deviation higher than this average value, and a third radiation detector 4c is placed at a location where the value is one standard deviation lower than the average value. do. And these three radiation detectors 4a, 4b, 4c
are placed as far away from each other as possible. Signals from these radiation detectors 4a, 4b, and 4c are respectively input to an arithmetic circuit 5 installed in the central control room. The arithmetic circuit 5 is configured to perform the following arithmetic processing. First, data A obtained by measuring dose rates at multiple locations within the pump chamber 2 is input into the arithmetic circuit 5 in advance. Then, in response to such input data A, the arithmetic circuit 5 calculates a dose rate distribution and a distribution function from this data A, and determines the type of the distribution. In this case, since the unit work area is set as described above, the type of the distribution is a log-normal distribution or a log-double exponential distribution. This has been confirmed by the experimental results of the present inventors, and if the setting of the unit work area satisfies the above-mentioned conditions, it will necessarily have a lognormal distribution or a logarithm double exponential distribution. Since the lognormal distribution and the logarithm double exponential distribution have a certain relationship in the probability densities of given variables as shown in D and E in Figure 5, the number of workers within a unit work area is Assuming that the workers move randomly, the probability of the worker's exposure dose rate can be calculated. That is, first, for input data A, data of each measurement point is arranged in descending order of dose rate x _i and their rank i is determined. If the distribution type is lognormal distribution, the cumulative percentage Gi of each measurement point is Gi=i-0.375/N+0.25×100(%)...
... is given by (1). Note that N is the number of measurement points.
Also, if the distribution type is logarithmic double exponential distribution, Gi=i-0.44/N+0.12×100(%)...
...(2) is given. In addition, the pump chamber 2 of this embodiment
The table below shows the calculation results of the actual data for the 11 measurement points.

[Table] When the results of this table are plotted on a lognormal probability graph, it becomes as shown in Figure 6, and since it can be approximated by a nearly straight line, it is shown that the dose rate distribution in this pump chamber 2 is lognormal. There is. Figure 7 shows cumulative percentages calculated from dose rate data measured for other unit work areas and plotted on a log-normal probability graph, and Figure 8 shows data of measured dose rates for other unit work areas. The cumulative percentage was calculated from the dose rate data obtained and plotted on a logarithmic double exponential probability graph. The results in Figures 7 and 8 can also be approximated by a straight line, so as long as a unit work area is set under the conditions described above, the dose rate distribution within that unit work area will be a lognormal distribution or a logarithmic double exponential distribution. Something is clearly shown. Then, this arithmetic circuit 5 obtains a general probability density function from the processing results of the input data A as described above. When the dose rate distribution type is lognormal distribution, its standard lognormal density function g
(z)dz is , where z is a standard variable and z=nx-μ/σ (4). Note that x is a variable, μ is a population mean, and σ is a population standard deviation. Furthermore, if the dose rate distribution type is a logarithmic double exponential distribution, its standard logarithmic double exponential density function g(z)dz is g(z)dz=e ^-z・e ^-ez dz... ...(5) where z is a standard variate and z=nx-μ/σ ......(6). In addition to the above, the arithmetic circuit 5 also calculates the average value (geometric mean value), standard deviation, etc. from the input data A. The results of these calculations are then stored in the storage circuit 6. Next, the arithmetic circuit 5 verifies and corrects the above-mentioned arithmetic results based on the signals from the radiation detectors 4a, 4b, and 4c provided in the pump chamber 2. That is, since the data A of the dose rate in the pump chamber 2 described above is obtained in advance, if the intensity of the radiation source changes after that, it is necessary to make corrections to the calculation results based on the data A. . For example, in the case of the pump room 2, the relationship between the dose rate and the cumulative percentage calculated based on the data measured when there is no radioactive waste liquid in the radiation source, that is, in the waste liquid pump 1, is shown in F in Figure 9. However, if radioactive waste liquid exists in this waste liquid pump 1, the dose emitted from this waste liquid pump 1 increases, so the relationship of the distribution of the dose rate, that is, the distribution function changes, and it is difficult to measure this state. The relationship between the dose rate calculated based on the data and its cumulative percentage changes as shown in G in FIG. 9. The arithmetic circuit 5 first compares the signals from the radiation detectors 4a, 4b, and 4c with the already input data A, and if there is no change in the dose rate, calculates the result based on the already input data A. The decision is made that it can be used as is. In addition, when there is a change in the dose rate, it is determined based on the signals from the first radiation detector 4a and the other second or third radiation detectors 4b and 4c installed at the location showing the average value. The distribution function is corrected and the relationship between dose rate and cumulative percentage is newly calculated. That is, a distribution function such as a log-normal distribution or a log-double exponential distribution can be defined from the mean value and standard deviation. Therefore, the first radiation detector 4a installed at the location showing the average value
A second signal installed at a location where the signal from the
Alternatively, it is possible to calculate the distribution function and the relationship between the dose rate and its cumulative percentage when the intensity of the radiation source changes based on the signals from the third radiation detectors 4b and 4c. In addition, if a new radiation source occurs in a unit work area, or if there are multiple radiation sources in a unit work area and the intensity of some of the radiation sources changes, the radiation source and unit The relative relationship to the dose rate at each location within the work area, ie the quality of the distribution, changes. In such a case, the difference between the signal of the first radiation detector 4a located at the position showing the average value and the signal of the second radiation detector 4b located at the position showing the value higher than the average value by the standard deviation. The relationship between the difference between the signal of the first radiation detector 4a and the signal of the third radiation detector 4c located at a position showing a value lower than the average value by the standard deviation changes. Therefore, it is detected that the quality of the distribution has changed due to this change. Then, as described above, the input data A and the radiation detectors 4a, 4b, 4c
The calculation results, such as the type of distribution, average dose rate, standard deviation, presence or absence of change in the quality of distribution, etc., calculated by this calculation circuit 5 based on the signals from the It is printed out from the printer 8 in accordance with the above. Further, data B such as the conditions of work to be performed in the pump room 2, such as the number of people, work time, and planned radiation exposure dose, is input to the arithmetic circuit 5. Then, the calculation circuit 5 calculates the probability that the radiation exposure dose of the worker will exceed the planned radiation exposure dose when performing this work from such data B and the above-mentioned calculation results. In other words, the sixth
The relationship between the dose rate and the cumulative percentage as shown in the figure shows the dose rate and the probability that the worker will receive when the worker moves randomly within the pump room 2. Therefore, using the relationship shown in Figure 6 as an example, if the worker's exposure dose rate is 25 millirem/h (25 mR/h in terms of dose rate), the probability that this exposure dose rate will not be exceeded is 99%. So, the probability of exceeding is 1%
It is. Therefore, if the number of workers is 10, the number of workers who exceed the planned exposure dose rate is 0.1, and in reality there is no worker who exceeds the planned exposure dose rate. . The calculation circuit 5 performs such calculations to determine the probability that all workers will exceed the planned exposure dose at the end of all work, and displays this on the CRT 7 as shown in Figure 11.
It is also printed out from the printer 8. Furthermore, data C of the radiation exposure dose of the worker after actually performing the work is input to the arithmetic circuit 5. The arithmetic circuit 5 compares the result calculated before the work with the actual data C and displays it on the CRT 7 as a graph or the like as shown in FIG. The result is stored in the memory circuit 6 as necessary, and can be used as a reference when performing the same type of work later. In the above explanation, only the pump room 2 was illustrated, but in reality, a unit work area is set over the front area affected by the radiation source, and each unit work area is provided with a radiation detector. Of course, the configuration is such that the signal from the radiation detector is input to the arithmetic circuit 5. Furthermore, as shown in FIG. 13, inside the reactor containment vessel 9, there is a pedestal 10 of the reactor pressure vessel in the center, and around this pedestal 10 there is a radiation source 11.
...For example, there is a main steam pipe, etc. Therefore, within this reactor containment vessel 9, there are parts that are in the shadow of the pedestal 10 for each radiation source 11...
occurs. Therefore, when setting a unit work area in such a reactor containment vessel 9, it is necessary to set the unit work area so that it is included in each shaded portion. In one embodiment of the present invention configured as described above, first, the dose rate at multiple locations within each unit work area is measured, and the data A is input into the arithmetic circuit 5.
From this data, the arithmetic circuit 5 determines the type of distribution of the dose rate and the relationship between the dose rate and the cumulative percentage for each unit work area, and stores this in the storage circuit. When performing work, for example, disassembling the waste liquid pump 1, the radiation detector 4a in the unit work area, for example, the pump room 2,
The signals from 4b and 4c are input to the arithmetic circuit 5.
Based on the data A that has already been input and the signals from the radiation detectors 4a, 4b, and 4c, the calculation circuit 5 makes corrections to the calculation results based on the data A as necessary, and also changes the distribution. If the quality has changed, that fact will be displayed on the CRT7. Note that if the quality of the distribution has changed, the dose rates at multiple locations within the pump chamber 2 are measured again, and the data is input to the calculation circuit 5. Next, data B regarding the work plan is input to this arithmetic circuit 5. Based on this data B, this calculation circuit calculates the probability that the planned exposure dose will be exceeded when the work is performed, and displays it on the CRT 7. If this probability is too large, the work plan is changed and inputted to the arithmetic circuit 5 again. and,
If the probability of exceeding the planned exposure dose is sufficiently small for practical purposes, work will be carried out based on that work plan.
After the work is completed, the actual radiation exposure dose of the worker is determined and this data C is input to the arithmetic circuit 5. The arithmetic circuit 5 then compares this data C with the result calculated before the work, displays the comparison result on the CRT 7, and stores it in the memory circuit 6. Therefore, when performing the same type of work later, this comparison result can be read out again and used as a reference for work planning. Note that the present invention is not limited to the above embodiment. For example, the number of radiation detectors may be two in a unit work area where the quality of the dose rate distribution is unlikely to change. Furthermore, there may be four or more radiation detectors in a unit work area. As described above, in the present invention, a unit work area is defined as an area that includes the range in which a worker moves and is affected by a radiation source over the entire area, and a plurality of radiation detectors are provided in this unit work area. Based on the input dose rate distribution in the unit work area, the type of dose rate distribution in this unit work area and the cumulative percentage of the dose rate are calculated to calculate the probability that the worker will exceed the predetermined exposure dose. It is equipped with an arithmetic circuit that makes corrections based on signals from the detector, and a display that displays the arithmetic results of this arithmetic circuit. Therefore, the probability that a worker will exceed a predetermined exposure dose is automatically calculated, making exposure dose management extremely easy, and corrections for changes in dose rate within a unit work area are also automatically made, ensuring accurate exposure. The effects are great, such as the ability to manage doses.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing the dose rate distribution inside the pump chamber. 3 to 13 show one embodiment of the present invention, FIG. 3 is a schematic block diagram, FIG. 4 is a block diagram explaining the function of the arithmetic circuit, and FIG. 5 is a log-normal distribution and a log-normal distribution. Figure 6 is a diagram showing the relationship between variables of heavy exponential distribution and probability density; Figure 6 is a diagram showing the relationship between dose rate and its cumulative percentage based on dose rate data in the pump room of one example; Figure 7 is a diagram showing the relationship between the dose rate and its cumulative percentage. and Figure 8 is a diagram showing the relationship between the dose rate and its cumulative percentage based on dose rate data in other unit work areas, and Figure 9 shows changes in the relationship between the dose rate and cumulative percentage in the pump room. The diagrams and FIGS. 10 to 12 are diagrams each showing an example of display on a CRT, and FIG. 13 is a cross-sectional view illustrating the setting of a unit work area within the reactor containment vessel. 1... Waste liquid pump, 2... Pump room (unit work area), 4a, 4b, 4c... Radiation detector, 5... Arithmetic circuit, 6... Memory circuit, 7... CRT (display).

Claims (1)

[Claims] 1. A unit work area is defined as an area that includes the area where workers move during work and is affected by one or more radiation sources over the entire area, and Based on the plurality of radiation detectors and the dose rate distribution in the unit work area entered in advance, the type of dose rate distribution and the cumulative percentage of the dose rate in this unit work area are determined based on this cumulative percentage. an arithmetic circuit that calculates the probability that a worker working in the unit work area will exceed a predetermined exposure dose and corrects the cumulative percentage of the dose rate based on the signal from the radiation detector; An exposure dose management device characterized by comprising a display device that displays calculation results. 2 One radiation detector is installed at a location where the average value of the dose rate distribution in the unit work area is shown, and one radiation detector is installed at a location where the value is one standard deviation higher than this average value.
2. The exposure dose management device according to claim 1, wherein three devices are provided, one at a location where the value is one standard deviation lower than the average value.