JPS60165570A - Device for predicting distribution of space dose rate of radiation - Google Patents

Abstract

PURPOSE:To enable drafting of an effective radiation protection plan and reduction of exposure dose by enabling prediction and evaluation of the space dose rate distribution of the case in which a shielding body is placed in nuclear facilities simply by inputting the data relating to the shielding body to a titled device. CONSTITUTION:Respective radiation dose meters 1 are disposed in the respective working places in the control area of nuclear facilities. the output signals from the meters 1 are inputted via a process input device 2 to an arithmetic processing unit 4. A storage device 3 connected to the unit 4 keeps the necessary data and stores the result thereof. The device is so arranged that the operator can apply data to the unit 4 by an operation console 5. The space dose rate distribution evaluation by the unit 4 is displayed by a display device 6. The relating data in this stage are the intensity S of a radiation source, the correction term R by the shielding effect or the dose rate D at certain evaluation point and a specified correlative relation C and since D=SCR, the distribution of the case when the shielding body is placed is predicted without placing said body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an apparatus for predicting the rate distribution of radiation in the air, particularly to an apparatus for predicting the air dose rate distribution of radiation in a nuclear facility, which is used for radiation management in a nuclear facility.

[Technical background of the invention and its problems]

At nuclear power facilities such as nuclear power plants, measuring and monitoring the radiation air dose rate within the radiation control area is used to evaluate the exposure dose of workers in the facility in advance and to take measures to protect workers from radiation. is very important to take
Various laws and regulations also require these measurements. In particular, nuclear power plants are required by law to undergo periodic inspections at least once a year, and it is important to reduce the exposure dose of workers as much as possible during these periodic inspections. For this reason, radiation managers should measure the air dose rate distribution at the current work location, and compare the air dose rate distribution measured at the same work location in the past (for example, during a morning routine inspection) and the exposure associated with the work at that time. Based on the radiation dose, we are predicting and evaluating the exposure dose for this work and planning radiation protection measures.

Radiation protection measures generally include "moving away from radioactive sources";
There are three basic methods: ``shorten the exposure time'' and ``shield the radiation source with a sheltered body.'' However, in regular inspection work at nuclear power plants, etc., the work content itself is formulated. Of the three methods mentioned above, the latter method of ``shielding the radiation source with a sheltered body'' is more often used than the first two methods. In this method using a shield, it is necessary to evaluate the effect of the shield in advance and predict the air dose rate distribution after the shield is installed.

However, conventionally, this prediction has often been left to the experience of radiation managers. In other words, in order to determine the installation location of the support body, it is necessary to actually place the support body in various positions,
It was common practice to rely on a trial-and-error method of determining the optimal position by measuring the dose rate in each case and examining the effect of the shiitake body. In such a method,
Even before periodic inspection work begins, the radiation exposure during the preliminary shielding work becomes impossible to ignore, and the original meaning of the shielding work may be lost. Also, is it possible to consider a method of installing excessive shielding bodies from the beginning without performing trial-and-error work to determine the optimal position? As the number increases, the exposure dose will also increase accordingly.

Inside a nuclear facility such as a nuclear power plant, piping, tanks, etc. that serve as radiation sources are arranged in a complicated manner, so evaluating the air dose rate inside the facility based on all these radiation sources becomes extremely complicated. Generally, this evaluation is performed using various shielding calculation codes, but such shielding calculations usually require a large-sized computer. However, it is difficult to directly introduce such large-sized computers into radiation control work at the site, especially in situations where necessary equipment is introduced for each work such as during periodic inspections. For this reason, until now, it has not been possible to evaluate the air dose rate within a facility with a certain degree of accuracy by calculation alone.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an apparatus for predicting the spatial radiation dose rate distribution that can perform evaluations with a certain degree of accuracy and is useful for formulating radiation protection plans for work performed within nuclear facilities. purpose.

[Summary of the invention]

The feature of the present invention is that if the radiation source intensity is S and the correction term due to the shielding effect when a shield is placed is R1, then the dose rate at a certain evaluation point uses a constant correlation, C. By using the fact that D = SCR, the correlation C is determined theoretically in advance using the Shiyahei calculation code, and the radiation source intensity S is calculated without using a Shiyahei body. The latest value is determined periodically by back calculation using the correlation C from the periodic actual measured value of the dose rate (R = 1), and the correction term R is based on the data entered for the poppy and hemolytic bodies. Based on the theoretical considerations, we finally decided to calculate the line f[rate, so we could predict the spatial dose rate distribution of radiation when a shield body was placed, without actually placing the shield body. There is a point pressure like a vine.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on an illustrative embodiment.

FIG. 1 is a block diagram showing a schematic configuration of the present invention.

A radiation dose rate meter 1 is placed at each work location in the controlled area of the nuclear facility, and the radiation dose rate meter 1 is input to the processing unit j14 via the process input device 2. Ru.

The storage device 3 connected to the arithmetic processing device 4 stores data necessary for processing performed by the arithmetic processing device 4 and also stores the processing results. An operator can provide data to the processing unit 4 through an operator console 5 connected to the processing unit 4 . Arithmetic processing unit 4
The air dose rate distribution evaluated by is displayed on the display 6.

FIG. 2 shows an example of the air dose rate distribution displayed by the display 6. The spatial dose rate distribution formed by the radiation from the radiation source 7 and the influence of the deflection body 8 is expressed in terms of the same level of dose rate.

Next, the functions of this device will be explained. In general, a certain point 7
A certain evaluation point due to the radiation source placed in 1?・The dose rate D(7) is expressed by equation (1).

DC')=S(7)C(7-"'?,) ・・"・(1
)''凰IJ Here, SC7,) is the intensity of the radiation source placed at point −+i, and C(η-box) is a constant correlation between p(7j) and S(sei). In a work area within a nuclear facility such as a nuclear power plant, multiple pieces of equipment that serve as radiation sources are usually arranged, and each piece of equipment usually has a certain spatial orientation. Therefore, in practice, each piece of equipment is divided into appropriate sections, and each section is treated as an independent radiation source. In other words, it is handled as if there were multiple devices with multiple radiation sources for each category. Therefore, in reality, the dose rate D (r J ) at a certain evaluation point 7 is given as multiple radiation sources,
It is given by equation (2).

Each represents the first source intensity and its corresponding correlation. If we determine the position 7·l of the radiation source and the position 7·l J of the evaluation point, and give the shape, geometrical arrangement, etc. of the radiation source, we get
The value of this correlation CBCri-rj) can be determined theoretically by an electronic computer using a Shiyahei calculation code.

With this device, the CIJ (
The values of r i' J ) are determined theoretically for all i, ie, all radiation sources, and for all j1, ie, all evaluation points, and are stored in the storage device 3. Note that the calculation to determine CI J (r t r J ) is performed by an external computer, etc.
Only the results are stored in the storage device 3 of this device.

In general, the radiation source intensity S i (rs) changes depending on the operational status of the nuclear facility, changes over time, and the like. Therefore, in order to improve the accuracy of the spatial dose distribution within the facility, the source strength J (
It is necessary to use the latest data on ri). Therefore, in this device, the value of each radiation source intensity is determined periodically based on the measured value by the radiation dose rate meter 1 installed at several locations in the facility, and the latest source intensity value is always stored in the storage device 3. Do it like this. Specifically, this is done as follows. FIG. 3 shows an example of the positional relationship between a plurality of radiation sources and a plurality of radiation dose rate meters. The first equipment 9 (for example, a tank) and the second equipment 10 (for example, piping) are each divided into appropriate divisions of radiation source blocks, and each radiation source block is treated as an independent radiation source. Radiation dose rate meters 1a to 1d provided at four locations measure the dose rate at each measurement point.

The dose rate measured by each radiation dose rate meter is due to each radiation source block of both the first device 9 and the second device 100. As explained in Figure 1, each radiation dose rate meter 1
The output signal is input to the arithmetic processing unit 4 via the process input device 2. This signal is D (r
J).

The arithmetic processing unit 4 uses data regarding cij (ri-rj) stored in advance in the storage device 3 to back-calculate the value of each radiation source intensity 84 (rH) based on equation (2). In addition, D (r
If the value of J) alone is insufficient, measure the dose rate at any measurement point using a portable dose rate meter such as the survey meter Ila or llb as shown in Figure 3, and send this value to the operator console. You can also input from 5. In general, there are various problems in accurately determining the source intensity of each divided source block from such a relatively small number of measured values, but the spatial attenuation characteristics of the gamma dose rate depend on the distance. It can be determined with a certain degree of accuracy by considering the physical property that it is inversely proportional to the square and by assuming that the radioactivity concentration in the fluid within the pipe is uniform. Furthermore, if the source intensity of a certain radiation source cannot be determined by the arithmetic processing unit 4 despite the above method, the operator can directly input the radiation source intensity from the operator console 5. In this way, in this apparatus, the arithmetic processing unit 4 calculates D (r J ) obtained by the radiation dose rate meter and C stored in the storage device 3.
i J (r 1 r J ), the value of the source intensity 5i(r, ) is always calculated at a constant period, and the latest value is stored in the storage device 3. This constant period is preferably about 1 hour.

The arithmetic processing device 4 executes C1j stored in the storage device 3.
Based on the data of (r, -rj) and S t (r J ), calculate the air dose rate distribution as shown in Figure 2,
It can be output to the display 6. However, the purpose of this device is to predict the dose rate distribution in order to help formulate radiation protection plans. Specifically, the main purpose is to predict and evaluate the spatial dose distribution when a jiyahei body is placed at an arbitrary position. Therefore, with reference to the flowchart shown in FIG. 4, the method of predictive evaluation by this apparatus will be explained below. In step S1, the operator inputs evaluation conditions such as the evaluation location, the size of the leprosy body, and the shape 9 position from the operator console 5. In accordance with this condition, the arithmetic processing unit 4 obtains the CI of each evaluation point necessary for evaluation from the storage device 3 in step S2.
J (rx r J ), followed by step S
3 to search for the latest 5i(ri).

Next, in step S4, it is determined whether there is a shielding body between the radiation source and the evaluation point, and if there is a shielding body, step S5 is performed.
Calculate the correction coefficient due to the dejahei effect. This correction coefficient R1jCry-rj) is calculated based on the data input in step s1.

Subsequently, in step S6, the value of D i (r j) is determined using equation (3).

Di(rj)=Si(r4)CHjCri-rj)R
lj(rj-rj)・<al where Di(rj) is i
This is the dose rate at the jth evaluation point caused by the radiation source. Therefore, the dose rate D(r-) at the j-th evaluation point is (4)
Determined by the formula.

D(rj)=10D4 (rj>-.-14) Therefore, a loop is formed by steps S7 and S8, and Di(rj) is determined for all i, and these are summed in step S9. Construct a loop through steps 810 and 811 to calculate the dose rate at all necessary evaluation points, and calculate D (r j) for all j.
Then, in step 812, an isodose rate curve is created to represent the spatial dose rate distribution.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to predict and evaluate the air dose rate distribution when a radioactive body is placed in a nuclear facility such as a nuclear power plant by simply inputting data regarding the radioactive body. By using the evaluation results for radiation management, it is possible to formulate an effective radiation protection plan and contribute to reducing exposure doses.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of the present invention, FIG. 2 is an example of an iso-dose rate curve diagram showing a multiple distribution of space lines created by the apparatus according to the present invention, and FIG. 3 is a block diagram showing a plurality of FIG. 4 is an explanatory diagram showing an example of the positional relationship between a radiation source and a plurality of radiation dose rate meters, and FIG. 4 is a flowchart showing a method for predicting and evaluating spatial dose distribution when a barrier is placed using the apparatus according to the present invention. 1... Radiation dose rate meter, 2... Process input device, 3
...Storage device, 4...Arithmetic processing unit, 5...Operator console, 6...Display device, 7...Radiation source, 8
. . . Shiyahei body, 9. . . . First equipment, 10. . . Second equipment, 11. . . Survey meter. Applicant's agent Kiyoyoshi Inomata 1 Figure 3 Oni 2 Senko 3 Figure

Claims (1)

[Claims] 1. A radiation dose rate meter that measures the radiation dose rate caused by a radiation source, and a process input device that receives an output signal from the radiation dose rate meter and outputs a signal according to the output signal. and a storage device in which the correlation between the radiation source and the radiation dose rate caused by the radiation source at evaluation points located at predetermined positions relative to the radiation source is stored in advance, and an operator directly inputs the data. an operator console for periodically calculating the intensity of the radiation source based on the output of the process input device and the correlation; and calculating the intensity of the radiation source based on the output of the process input device and the correlation; An apparatus for predicting the spatial dose rate distribution of radiation, comprising: an arithmetic processing device that calculates a spatial dose rate distribution diagram based on data regarding a shielding body; and a display device that displays the spatial dose rate distribution diagram.