JPH0479430B2 - - Google Patents

Description

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

[Technical background of the invention and its problems] In nuclear facilities such as nuclear power plants, measuring and monitoring the ambient radiation dose rate within the radiation control area is necessary to evaluate in advance the exposure dose of workers inside the facility. It is very important to take measures to protect workers from radiation, and various laws and regulations 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 measure the air dose rate distribution of the current work place, and check the air dose rate distribution measured at the same work place in the past (for example, during a regular inspection one year ago) and the air dose rate distribution associated with the work at that time. Based on the exposure dose, we are predicting and evaluating the exposure dose for this work and planning radiation protection measures.

In general, there are three basic radiation protection measures: ``moving away from the radiation source,'' ``shortening the exposure time,'' and ``hiding the radiation source with a shield.'' In periodic inspection work at facilities, etc., the work content itself is formulated, so the first two methods are more effective than the first two of the above three methods.
The latter is ``shielding the radiation source with a thin body.''
It often depends on the method. 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. That is,
To decide where to install the shield, we actually place the shield in various positions, measure the dose rate in each case, examine the effect of the shield, and decide on the optimal position. It was common practice to rely on trial and error methods. In such a method,
Even before periodic inspection work begins, the radiation exposure during the preparatory work can already become too much to ignore, and the original meaning of the work may be lost. In addition, without the trial and error process of determining the optimal position,
It is possible to consider methods such as not having excess radiation or installing shields from the beginning, but in the end, the amount of radiation needed to be installed increases, which increases the amount of work required for installation, and the amount of radiation exposure increases 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 carried out using various calculation codes, but such 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, conventionally it has not been possible to evaluate the air dose rate within a facility with a certain degree of accuracy solely by calculation.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a radiation air dose rate distribution prediction device that can perform evaluations with a certain degree of accuracy that are 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 damping effect when a damping body is placed is R, then the dose rate D at a certain evaluation point has a certain correlation C. Taking advantage of the fact that D=SCR can be expressed by using the equation, the correlation C is calculated theoretically in advance using the Shiyahei calculation code, and the radiation source intensity S is not set. The latest value is periodically obtained by back calculation using the correlation C from the periodic actual measured value of the dose rate D for the case (R=1), and the correction term R is input for the shy body. Because the dose rate D is calculated theoretically based on the data obtained, the spatial dose rate distribution of radiation when a shiyahei body is placed can be predicted without actually placing the shiyahei body. The point is that we have made it possible to do so.

[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 within the controlled area of the nuclear facility, and the output signal of this radiation dose rate meter 1 is input to the arithmetic processing device 4 via the process input device 2. . The storage device 3 connected to the arithmetic processing device 4 is
It stores data necessary for processing performed by the arithmetic processing unit 4 and also stores the processing results. An operator can provide data to the arithmetic processing unit 4 through an operator console 5 connected to the arithmetic processing unit 4 . The air dose rate distribution evaluated by the arithmetic processing unit 4 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 being affected by the radiation shield 8 is expressed by dose rate contour lines.

Next, the functions of this device will be explained. in general,
The dose rate D(r→ _j ) at a certain evaluation point r→ _j caused by a radiation source placed at a certain point r→ _i is expressed by equation (1).

D(r→ _j )=S(r→ _i )C(r→ _i −r→ _j )…(1) Here, S(r→ _i ) is the intensity of the radiation source placed at point r→ _i , C(r→ _i −r→ _j ) is D(r→ _j ) and S(r→ _i )
There is a certain correlation between 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 located, and each piece of equipment usually has a certain spatial extent. 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 will be treated as if there were multiple devices each having multiple radiation sources for each category. Therefore, in reality, a certain evaluation point r→
The dose rate D(r→ _j ) of _j is given as a plurality of radiation sources and is given by equation (2).

D(r→ _j )= 〓 ⁱ S _i (r→ _i ) C _ij (r→ _i −r→ _j ) …(2) Here, S _i (r→ _i ) and C _ij (r→ _i −r → _j ) respectively represent the i-th source intensity and its corresponding correlation. If the position r→ _i of the radiation source and the position r→ _j of the evaluation point are determined, and the shape and geometrical arrangement of the radiation source are given, the value of this correlation C _ij (r→ _i −r→ _j ) can be determined. can be calculated theoretically by an electronic computer using the Shiyahei calculation code.

This device allows you to learn about the facility in advance.
The values of C _ij (r→ _i −r→ _j ) are calculated theoretically for all i, that is, for all radiation sources, and for all j, that is, for all evaluation points, and are stored in the storage device 3. Save it. Note that C _ij (r→ _i −r→
_j ) is performed by an external electronic counter or the like, and only the results are stored in the storage device 3 of this device.

Generally, the radiation source intensity S _i (r→ _i ) changes depending on the operational status of the nuclear facility, aging, etc. Therefore, in order to accurately determine the air dose distribution within a facility,
It is necessary to use the latest data on the source strength S _i (r→ _i ). Therefore, in this device, the value of each radiation source intensity is periodically determined 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 meter 1a installed at four locations
1d measures the dose rate at each measurement point. The dose rate measured by each radiation dose rate meter is measured by the first device 9.
and the second device 10, respectively. As explained in Figure 1,
The output signal of each radiation dose rate meter 1 is input to the arithmetic processing unit 4 via the process input device 2 . This signal is a quantity corresponding to D(r→ _j ) on the left side of equation (2). The arithmetic processing unit 4 calculates each source intensity S _i (r→ _i ) based on equation (2) using data regarding C _ij (r→ _i −r→ _j ) stored in advance in the storage device 3. Calculate the value of . In addition, D by the installed radiation dose rate meter
If the value of (r→ _j ) alone is insufficient, measure the dose rate at any measurement point using a portable dose rate meter such as survey meters 11a and 11b as shown in Figure 3, and use this value. can also be input from the operator console 5. Generally, 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 arrangement is uniform. In addition, if the source intensity of a certain radiation source cannot be determined by the arithmetic processing unit 4 despite the above methods, the operator can directly input the source intensity from the operator console 5. . In this way, in this device, the arithmetic processing unit 4 calculates D(r→ _j ) obtained by the radiation dose rate meter and C _ij (r→ _i −r→ _j ) stored in the storage device 3. Based on this, the value of the source intensity S _i (r→ _i ) is always calculated at regular intervals, and the latest value is stored in the storage device 3. This constant period is preferably about 1 hour.

The processing unit 4 generates an air dose rate distribution as shown in FIG. 2 based on the data of C _ij (r→ _i −r→ _j ) and S _i (r→ _j ) stored in the storage device 3. Calculate,
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 the Yasuhei body is placed in 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. step
In S1, the operator inputs evaluation conditions such as the evaluation location, the size, shape, and position of the leprosy body from the operator console 5. According to this condition, the arithmetic processing unit 4 retrieves C _ij (r→ _i − r→ _j ) of each evaluation point necessary for evaluation from the storage device 3 in step S2, and then retrieves the latest S _i in step S3. Search for (r→ _i ). Next, in step S4, it is determined whether or not there is a shrinkage body between the radiation source and the evaluation point, and if there is a shrinkage body, a correction coefficient due to the shrinkage effect is calculated in step S5.
This correction coefficient R _ij (r→ _i −r→ _j ) 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).

D _i (r→ _j ) =S _i (r→ _i )C _ij (r→ _i −r→ _j )R _ij (r→ _i −r→
_j )...(3) Here, D _i (r→ _j ) is the dose rate at the j-th evaluation point caused by the i-th radiation source. Therefore, the dose rate D(r→ _j ) at the j-th evaluation point is determined by equation (4).

D (r→ _j )= 〓 ⁱ D _i (r→ _j )...(4) Therefore, a loop is constructed by step S7 and step S8, and D _i (r→ _j ) is obtained for all i, and this is Total in step S9. Steps to determine dose rate at all required evaluation points
Construct a loop by S10 and step S11,
Find D(r→ _j ) for all j and step
In S12, an isodose rate curve is created to show 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 Yayahei body is placed in a nuclear facility such as a nuclear power plant by simply inputting data regarding the Yayahei 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, and FIG. 2 is an example of an isodose rate curve diagram showing an air dose rate distribution created by the apparatus according to the present invention.
Fig. 3 is an explanatory diagram showing an example of the positional relationship between a plurality of radiation sources and a plurality of radiation dose rate meters, and Fig. 4 is a method for predicting and evaluating spatial dose distribution when a shield body is placed using the apparatus according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Radiation dose rate meter, 2... Process input device, 3... Storage device, 4... Arithmetic processing device, 5...
...Operator console, 6...Display unit, 7...
Radiation source, 8... Shiyahei body, 9... First equipment, 1
0...Second equipment, 11...Survey meter.

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 of the radiation dose rate meter as an input and outputs a signal according to the output signal. , a storage device in which a correlation between the radiation source and the radiation dose rate caused by the radiation source at an evaluation point located at a predetermined position is stored in advance; and an operator directly inputs 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 map based on data regarding the human body; and a display device that displays the spatial dose rate distribution map.