JPH04147090A - Method for distinguishing radioactive contaminant - Google Patents

Abstract

PURPOSE:To efficiently distinguish contamination status by measuring a gamma-ray spectrum from a surface to be measured by a gamma-ray spectrum measuring detector and determining whether or not it is radioactive based on photoelectric peak and scattered light components of the spectrum. CONSTITUTION:A measuring surface of a gamma-ray spectrum measuring detector mounted on an arm or the like whose angle can be variably set to a desired angle vertically and horizontally around 360 degrees by remote control is directed to a floor, walls and a ceiling to be measured, and a shape of a surface to be measured is captured S11 by an image monitor S10 to determine an area of the surface to be measured. Then the detector is used to measure S19 a gamma-ray spectrum from the surface to be measured. The gamma-ray spectrum is roughly divided into photoelectric peak components and scattered ray components S21, S22, while after compensation, etc. S23 of geometric efficiency by a distance between measurements is done, a predetermined equation is used to calculate radioactive amounts of the surface to be measured S24, S25. By dividing the calculated radioactivity by the area of the surface to be measured, contamination density per unit area is calculated S26. The area to be measured is determined to be radioactive or not depending whether the calculated value exceeds a predetermined radioactive level.

Description

[Detailed description of the invention] [Objective of the invention] (Industrial application field) The present invention efficiently determines whether waste generated during decommissioning of nuclear reactor facilities is radioactive or not. This method is particularly relevant to building concrete, which accounts for most of the waste generated during decommissioning of nuclear power generation facilities, etc., and which is characterized by extremely low radioactivity levels. The present invention relates to a method for identifying radioactive contaminants that can quickly determine whether or not they are contaminated.

(Prior Art) It is said that the lifespan of a nuclear facility is 30 to 40 years, and after the nuclear facility has reached the end of its lifespan, the entire facility is dismantled and removed after being shut down and sealed for a predetermined period of time.

In the decommissioning (dismantling) process of this nuclear facility, first the radioactive equipment and piping located within the facility are dismantled and removed, and then the building is dismantled. A large amount of building concrete waste is generated during building demolition, and most of it is non-radioactive, and even if it is radioactive, the radioactivity level is very low, and concrete that is radioactive is
It has the characteristic that it is only superficial or borrowed. This 1
If concrete waste is dismantled without any sorting, some of the radioactive concrete will mix with a huge amount of non-radioactive concrete, turning the entire building concrete into radioactive concrete waste. If a large-scale storage facility or disposal facility is required to accommodate this waste, a major problem will arise.In addition, after the nuclear facility has been compiled, it will be necessary to measure and differentiate the building concrete waste for each disposal amount. In this case, since the number of targets 1 is huge, it is expected that it will take a considerable amount of time for measurement and discrimination even if a considerable number of measurement systems are involved. Conventional techniques for measuring and discriminating building concrete surfaces include scan surveys using contamination survey meters or smear sampling at representative points. Mya sampling can only detect loose surface contamination, but does not provide direct information about fixed contamination that has penetrated into the concrete surface. After the survey, decontamination such as wiping is performed, and the survey is conducted again to confirm that the contamination that was supposed to have been removed remains.It is only in this situation that it can be determined that the contamination is penetrative contamination. The target range that requires measurement discrimination is the floor within the controlled area of the nuclear reactor facility,
It covers a wide range of surfaces such as walls and ceilings, and measuring and discriminating them requires a huge amount of manpower and time.
Problems such as significantly lengthening the decommissioning process are also expected.

Therefore, regarding the floors, walls, and ceiling surfaces of building structures from which equipment, piping, etc. located in nuclear facilities have been removed, whether they are non-radioactive or radioactive, and furthermore, if they are radioactive, By providing a rational waste identification method that can quickly determine whether it is loose surface contamination or contamination that has permeated into the surface, it can significantly reduce the manpower and measurement time that was previously required. Can be shortened. In addition, regarding radioactive concrete, it is possible to appropriately classify waste by disposal destination, and the amount of radioactive concrete waste generated can be significantly reduced, making it possible to reduce the size of storage or disposal facilities for radioactive contaminated materials. At the same time, waste disposal costs can be significantly reduced.

In addition, non-radioactive concrete waste that can be treated as general waste can be used effectively, such as in landfills. Furthermore, since the amount of radioactive contaminants generated can be significantly reduced and decontamination work can be made more efficient, the exposure of workers to radiation can be significantly reduced.

(Problem to be solved by the invention) Until now, radioactive concrete waste has been measured,
Work related to decontamination, packaging, and other disposal is currently being carried out individually, and there is currently no study on systematizing the efficient determination of whether generated concrete waste is radioactive or non-radioactive. It had not been done.

Radioactive concrete waste is classified into radioactive concrete and contaminated concrete. Concerning radioactive concrete, the main targets are concrete structures such as bio-shielding walls placed around the reactor core, and these structures are being radioactive by analysis and evaluation using the neutron flux from the reactor core. It is possible to accurately predict the extent of radioactivity and the radioactivity level of radioactive concrete. Furthermore, since the entire interior of radioactive concrete is radioactive, decontamination is not effective and it is disposed of appropriately depending on the radioactivity level.

On the other hand, contaminated concrete is generated when radioactive substances adhere to the building concrete surface for some reason during the operation or maintenance of nuclear facilities, and some of the radioactive substances attached to the concrete surface penetrate into the inside of the concrete surface. In the case of contaminated concrete, the contaminated location (floor, wall, ceiling) and the form of contamination of the contaminated concrete (
The radioactivity temperature of contaminated materials (contamination only on the surface/contamination that has permeated to the inside) greatly depends on the radioactivity concentration of the reactor water, etc. with which it came into contact, the time of contact, and the contact time. It is impossible to easily evaluate the range and radioactivity concentration using analytical methods. If the building were to be demolished without clarifying the extent of the contaminated concrete, the contaminated concrete would be mixed with non-radioactive building concrete, potentially making the entire building concrete radioactively contaminated. Therefore, in order to avoid this, before dismantling the building, check the floors, walls, and walls of each room in the building.
Clarify the scope of contamination of the ceiling and its radioactivity concentration,
It is important to completely remove the contaminated concrete before demolishing the building.

Regarding concrete waste generated during decommissioning of nuclear facilities, although a measurement and discrimination system for radioactive concrete generated during equipment dismantling and removal is being considered, it is necessary to rationalize contaminated concrete waste before demolition of buildings. No consideration has been given to a system for measuring and discriminating them.

The present invention has been made in consideration of the above points, and its purpose is to treat building concrete waste, which accounts for most of the decommissioning waste of nuclear facilities, by dismantling building concrete waste from each room before dismantling the building. An object of the present invention is to provide a radioactive contaminant discrimination method that can efficiently measure and discriminate the contamination status (presence or absence of contamination) and contamination form (surface contamination/penetration contamination).

[Structure of the invention]

(Means for Solving the Problem) As a means for achieving the above object, the present invention provides a method for measuring the floor, wall, ceiling surface or a part of these of a building structure in a controlled area of a nuclear power facility such as a nuclear power facility. Set the target surface,
Measuring the spectrum of γ-rays from the surface to be measured using a detector for measuring the γ-ray spectrum, and determining whether or not the surface to be measured is radioactive based on the photoelectric peak component and scattered ray component of the measured spectrum. , if the surface to be measured is radioactive, it is determined whether the surface to be measured is surface contamination or penetrative contamination, and in the case of penetrative contamination, it is determined how far the contamination has penetrated from the surface. do.

(Function) In the method for determining radioactive contaminants according to the present invention, a gamma ray spectrum is measured with a gamma ray spectrum measuring detector on a surface to be measured on a building structure.

Then, based on the photoelectric peak component and the scattered radiation component of the measured spectrum, it is determined whether the surface to be measured is radioactive or not, and if it is radioactive, it is determined whether the surface to be measured is surface contamination or penetrating contamination; In the case of penetration contamination, a determination is made as to how far the contamination has penetrated from the surface.

In other words, the contamination density per unit area is calculated based on the number of counts in the measured spectrum, the area of the measurement target surface, and the distance from the measurement target surface to the detector, and it is determined whether this value exceeds the predetermined radioactivity level. Depending on whether or not the surface to be measured is radioactive, it is determined whether or not the surface to be measured is radioactive.

In addition, if it is radioactive, the photoelectric peak component and scattered radiation component of the measured spectrum are examined in detail, and it is determined whether the surface contamination is surface contamination or penetrating contamination based on whether a gamma ray spectrum occurs in the scattered region. It will be judged.

Additionally, in the case of penetrating contamination, the photoelectric peak and scattered radiation components of the measured spectra are considered in more detail, and based on a comparison with the scattered radiation components in the absence of penetrating contamination, the extent to which the contamination originates from the surface is determined. It is determined whether it has penetrated to the depth.

(Example) Examples of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a general flowchart showing a method for discriminating radioactive contaminants according to an embodiment of the present invention.

In determining radioactive contaminants, first the shape of the surface to be measured is determined with respect to the floor, wall, and ceiling surfaces of the building structure after the removal of equipment, piping, etc. (step S1), and based on this,
Determine the measurement target area to be measured at one time (step S2
).

Next, γ is adjusted to match the aspect ratio of the area to be measured.
The aspect ratio of the collimator of the detector for line spectrum measurement is set (step S3), the detector is moved so that the area to be measured becomes the measurement field of view, and the measurement distance is adjusted (step S4). , the detector measures the spectrum of γ-rays incident from the area to be measured (Step S5), and based on this measurement result and the radioactivity level of the disposal, determines whether the area to be measured is non-radioactive. (Step S
6) and a determination as to whether it is radioactive (step S7).

If it is determined that the area to be measured is radioactive, the results of the gamma ray spectrum measurement in step S5 are analyzed in more detail, and it is determined whether the area to be measured is Δ surface contamination (step S8); A determination is made as to whether it is penetrative contamination (step S9).

FIG. 2 shows the flowchart shown in FIG. 1 in more detail.

In Figure 2, first, by remote control, 360
γ attached to an arm etc. that can be variably set to any angle
Detector for line spectrum measurements (fl.

For example, the measurement surface of a Ge semiconductor detector, Na1 (T, p) scintillation detector, etc.) is directed toward the floor, wall, or ceiling surface on which the measurement is to be performed. Then, based on the image on the image monitor installed near the detector (step 510), the size, aspect ratio, etc. of the surface to be measured are determined.
l) Based on this, a measurement target area to be measured is determined (step 512).

Once the area to be measured has been determined, the aspect ratio of the collimator of the detector is set to the same aspect ratio as that of the area to be measured (Step 813), and the collimator is mounted within the detector to determine the distance at which the entire area to be measured falls within the field of view of the detector. The measuring distance is adjusted by moving the detector to the point where the measuring distance is reached (step 514).

This adjustment involves emitting ultrasonic waves from an ultrasonic oscillator installed near the detector (step 515), and detecting the reflection of the ultrasonic waves using an ultrasonic receiver installed at the same position (step 5).
16), and measure the time difference (step 517). Then, from this time difference, the distance between measurements [(detection time/2)
mJ constant] with high accuracy (step 518).

This distance between measurements can be finely adjusted;
It is possible to eliminate the incidence of extra radioactivity from areas other than the measurement target area that would cause disturbance in measurement, and the measurement accuracy can be improved.

Next, the gamma ray spectrum from the measurement target area is measured by the detector (step 519). The gamma ray signal incident on the detector from the measurement target area is processed by an amplifier, a linear amplifier,
A signal processing system that includes a wave height discriminator, a computer, etc. amplifies the signal, distributes it to channels corresponding to each energy level, performs integration, etc., and calculates the gamma ray spectrum (count number by energy) for the measurement target area. is obtained (
step 520).

This γ-ray spectrum is roughly divided into a photoelectric peak component and a scattered ray component (steps 821 and 522), and after correction of geometric efficiency based on the distance between measurements, etc. (step 52B).
), the amount of radioactivity possessed by the area to be measured is calculated using the following formula (step S24, 525).

A−C/ (Ir XεXG) −=−[
) However, A: γ-ray radioactivity C: Count number Ir of the γ-ray spectrum measuring detector: γ-ray emission rate ε: Counting efficiency of the detector G: Geometric efficiency of the detector Ir in the above formula (1) depends on the nuclide of interest for measurement, and ε
is a value that can be determined by the detector used. Furthermore, as shown in equation (2), G changes depending on the measurement distance between the area to be measured and the detector, but as mentioned above, the accurate value can be determined by an ultrasonic oscillator installed near the detector. I understand. The radius of the detector used may be used as the radius of the detector.

Therefore, the amount of radioactivity A can be easily calculated.

By dividing the calculated radioactivity amount A by the area to be measured, the contamination density per unit area can be calculated (step 526). Then, depending on whether the value exceeds a predetermined radioactivity level, it is determined whether the area to be measured is radioactive or non-radioactive.

By the way, when there is contamination penetration in the area to be measured, a γ-ray spectrum as shown in FIG. 3 is obtained.

In FIG. 3, the horizontal axis is the energy level, and the vertical axis is the count number of the gamma ray spectrum measuring detector.

If contamination has not penetrated inside the surface, a sharp gamma ray peak waveform (photoelectric peak) will be obtained at the energy level of the nuclide to be measured, but if contamination has penetrated inside the surface, , γ of the contaminating nuclide present inside the surface
The effect of the rays scattering out of the concrete while losing energy from within the concrete appears, so a gamma ray spectrum of the scattered ray component occurs in the scattering region other than the photoelectric peak (region with lower energy than the photoelectric peak component). .

Furthermore, the γ-ray spectrum in this scattering region is proportional to the amount of contamination present inside the concrete.

In other words, it is possible to determine whether or not there is contamination penetration based on whether or not a γ-ray spectrum occurs in the scattering region, and if it is determined that there is contamination, the scattering when there is no penetration contamination can be determined. By comparing with the line components, it is possible to determine how deep the contamination has penetrated from the surface.

FIG. 4 shows the relationship between the penetration depth of contamination and the γ-ray spectral ratio (γ-ray spectral ratio between penetrating contamination and surface contamination).

As is clear from FIG. 4, when the form of contamination is surface contamination, the radioactivity ratio is 1. As the penetration of contamination progresses, the amount of radioactivity present inside the concrete increases, so the scattered gamma ray spectrum on the side of the penetration contamination increases. Therefore, as shown in FIG. 2, the fourth
The depth of contamination penetration may be identified as shown (step 828).

By removing the contaminated parts using mechanical cutting methods such as a scrubber, breaker, or brainer depending on the degree of penetration, most of the remaining building concrete can be made non-radioactively contaminated ( Step S29,
530).

The radioactivity concentration of the removed radioactive concrete can be calculated from the measured radioactivity amount since the removal amount can be determined from the peeling thickness of the applied decontamination technique (step 531).

The present inventors made a trial calculation to discriminate building waste of a nuclear power generation facility, which generates a total of 500,000 tons, using the waste discrimination method according to the present invention, and obtained the results shown in Table 1.

Table 1 Classification of general waste and radioactive contaminants 104Bq/
If it is l.

Table 1 shows the levels and weights of general waste and radioactive (contaminated) waste after applying the radioactive contaminant identification method according to the present invention to 500,000 tons of concrete for building structures of nuclear power facilities. This shows the relationship. The weight of contaminated waste is estimated to be approximately 15 mm when the method of the present invention is applied to remove 15 mm of contaminated waste from an area of approximately 15,000 yen within a managed area that has been found to have percolated contamination. This is an example of a trial calculation of the amount of radioactive contaminants to be produced, and it is clear that this method can separate a large amount of building concrete into a disposal layer. In addition, in the conventional example where measurement and discrimination were performed after the building was dismantled, all 500,000 tons could have been radioactively contaminated, but by applying this method, in the example in Table 1,
It is possible to significantly reduce radioactive contaminants to about 1/1000.

In addition, when conducting a contamination survey of floors, walls, and ceiling surfaces using conventional technology before demolition of a building, in order to measure high walls and ceiling surfaces, it is necessary to conduct a contamination survey for approximately 300 rooms to the north. Measurements must be made after all scaffolding, etc. have been tightened, and the number of man-hours involved in measurement and work such as assembling the scaffolding is enormous, mixing efficiency is extremely poor, and radiation exposure for workers is a problem. When the determination method of the invention is applied, it is possible to reliably determine the presence or absence of contamination and the presence or absence of contamination penetration in one room in about one hour.Furthermore, it is possible to perform measurements by remote control, which reduces the amount of human labor involved in measurement. Moreover, measurement efficiency can be greatly improved. Therefore, the number of man-hours required by conventional methods can be significantly reduced, and measurement efficiency can be greatly improved, reducing radiation exposure and
It is expected to reduce costs and radiation exposure for workers.

FIG. 5 shows another example of implementing the present invention, in which it is determined on a room-by-room basis whether or not the room is contaminated, prior to gamma ray spectrum measurement performed on each measurement target surface. This is what I did.

That is, prior to gamma ray spectrum measurement performed on each surface to be measured, a batch measurement is performed to determine whether or not each room is contaminated (step 541).

For example, in the center of the room to be measured,
It is conceivable to place a detector (for example, a NaI scintillation detector, etc.) under conditions without collimation, allow γ-rays from the entire room to enter the detector, and measure the γ-ray spectrum.

Through this measurement, it is determined whether or not there is a contaminated part in the room (step 542). If it is determined that there is a contaminated part in the room, each target surface is If it is determined that there is no contaminated part in the room, detailed measurement of that room is not performed (step 544).

In this way, by room-by-room batch measurement, it is possible to narrow down the rooms that require detailed measurements, making it possible to improve work efficiency and shorten measurement time.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to efficiently measure and evaluate the residual radioactivity in the controlled areas of nuclear facilities, etc., and it is possible to efficiently measure and evaluate a huge amount of concrete waste according to its radioactivity level. can be processed. For this reason,
The amount of radioactive contaminants can be significantly reduced, and it becomes possible to rationally classify and discriminate waste. This makes it possible to significantly shorten the working time and the number of working man-hours, and also to significantly reduce the exposure of workers to radiation.

[Brief explanation of the drawing]

Fig. 1 is a schematic flowchart showing a method for identifying radioactive contaminants according to an embodiment of the present invention, Fig. 2 is a similar detailed flowchart, and Fig. 3 is a flowchart showing a method for identifying radioactive contaminants according to an embodiment of the present invention. FIG. 4 is a graph showing the γ-ray spectrum, FIG. 4 is a graph showing the relationship between the penetration depth of contamination and the γ-ray spectrum ratio, and FIG. 5 is a flowchart of main parts showing another embodiment of the present invention. Applicant's Representative Sato - Male Energy Group S Selection 2I

Claims (1)

[Claims] The measurement target surface is set on the floor, wall, ceiling surface, or a part of these, of a building structure in the controlled area of a nuclear power facility such as a nuclear power facility, and the gamma ray spectrum measurement detector is used to measure the radiation from the measurement target surface. Measure the γ-ray spectrum, and based on the photoelectric peak component and scattered ray component of the measured spectrum,
Determination of whether the surface to be measured is radioactive or not, if radioactive, determination of whether the surface to be measured is surface contamination or penetration contamination, and in the case of penetration contamination, to what extent the contamination has penetrated from the surface. A method for identifying radioactive contaminants, characterized by determining whether or not they are present.