JPH0513592B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention scans and measures gamma rays emitted from contaminated radioactivity inside a pipe from outside the pipe using a gamma ray detection system having a collimator window. This invention relates to a measurement method for non-destructively quantifying precipitated radioactivity and aqueous radioactivity inside piping, or precipitated radioactivity and gaseous radioactivity.

(Conventional technology) Conventionally, in order to measure radioactivity inside a pipe, a part of the pipe was cut out from the measuring point, or the aqueous solution or gas inside was extracted as a measurement sample, and this sample was then measured in an analysis room, etc. The measurement method that determines the radioactivity in each state has been mainly used. This method involves cutting out the measurement sample and unsealing the radioactivity.
There were problems in that the measurement locations were limited and it took time to obtain measurement results.

In addition, as a non-destructive method, as shown in FIG.
A method has been used to find in this way,
When the radioactivity inside the pipe exists in the form of a deposit, an aqueous solution, or a gas, there is a problem in that it is not possible to separate and measure the radioactivity.

(Means for Solving the Problems) The present invention non-destructively quantifies radioactivity in the form of deposits, aqueous solution, or gas inside the radioactively contaminated pipes of the reactor primary cooling system in each state. This is a method devised for the purpose of

A principle diagram showing the measurement method of the present invention is shown in FIG. A gamma ray detection system 8, which has a structure in which a detector 7 is covered with a shield 6 having a rectangular collimator window 5, is placed in the center next to a pipe 9 to detect gamma rays emitted from the pipe whose interior is radioactively contaminated. Scanning measurements are performed by changing the angle 10 of the gamma ray detection system around the front surface of the detector, and the gamma ray count at each measurement angle is determined.

On the other hand, at each measurement angle, the number of gamma rays in each state reaching the detector is determined by the fact that the precipitated radioactivity 11 and aqueous radioactivity 12 or gaseous radioactivity 13 inside the pipe are uniformly distributed, and the unit radioactivity is If present, the distance from the axis of the pipe to the detector 14, the inner radius of the pipe 15, the outer radius of the pipe 16, the radiation absorption coefficient, the radiation absorption coefficient of water, the radiation absorption coefficient of gas, the vertical width of the collimator window 17 and thickness 18. The measurement result at each measurement angle is the sum of the number of gamma rays emitted from deposited, aqueous or gaseous radioactivity and counted by the detector, so if the radioactivity in each state is a unit of radioactivity. It corresponds to the sum of the products of the counts calculated for and the radioactivity of each state, which is an unknown quantity.

The point of view of the present invention is that since the ratio of gamma ray counts from deposited and aqueous or gaseous radioactivity measured by the above measurement method differs depending on each measurement angle, when the number of measurements is n, The reason is that the n-dimensional simultaneous linear equations are established independently. By solving this simultaneous equation, the deposited radioactivity and aqueous radioactivity inside the pipe, or the deposited radioactivity, gaseous radioactivity, and gaseous radioactivity can be quantified for each state.

(Example) An example of the present invention is shown in FIG. Assuming that the deposited radioactivity 20, aqueous radioactivity 21, or gaseous radioactivity 22 inside the pipe 19 is uniformly distributed and exists as a unit of radioactivity, the gamma ray detection system 23
Find the number of gamma rays in each state that reach the detector when measured at different angles.

In the calculation, each parameter used is defined as follows.

Piping inner radius 24: R1cm Piping outer radius 25: R2cm Distance from detector to piping axis 26: Lcm Collimator width 27: Wcm Collimator thickness 28: Hcm Detector system angle 29: B-degree piping Radiation absorption coefficient: Ap Radiation absorption coefficient of water: Aw Radiation absorption coefficient of gas: Ag Unit radioactivity in deposited state: σp Unit radioactivity in aqueous solution state: ρw Unit radioactivity in gas state: ρg. The origin 30 of the coordinates is the center of the front surface of the gamma ray detector, and the coordinates of the intersection of the center line 31 of the collimator window and the pipe are (x1, y1) as shown in Figure 3.
32, (x2, y2) 33 and (x3, y3) 34.

First, finding the relationship between x1 and y1, we get y1=x1×tan(B). On the other hand, from the Pythagorean theorem, R1 ² =(L−x1) ² +y1 ² holds true. Coordinates (x1, y1) from the above two formulas
Solving, x1=2×L−√4×L ² −4×(1+tan(B) ² )×L
² −R1) ² /2×(1+tan(B) ² ) y1=2×L−√4×L ² −4×(1+tan(B) ² )×L
² −R1) ² /2×(1+tan(B) ² )×tan(B). Similarly, coordinates (x2, y2) and coordinates (x3,
y3), x2=2×L+√4×L ² −4×(1+tan(B) ² )×L
² −R1) ² /2×(1+tan(B) ² ) y2=2×L+√4×L ² −4×(1+tan(B) ² )×L
² −R1) ² /2×(1+tan(B) ² )×tan(B) x3=2×L−√4×L ² −4×(1+tan(B) ² )×L
² −R2) ² /2×(1+tan(B) ² ) y3=2×L−√4×L ² −4×(1+tan(B) ² )×L
² −R1 ² )/2×(1+tan(B) ² )×tan(B). Next, if the coordinates of the intersection of the uppermost line 35 of the range where the collimator window views the pipe and the pipe are coordinates (x4, y4) 36 and coordinate (x5, y5) 37, as shown in FIG. In the same way as above, x4=2×(L+(W/2)/sin(B))/2×(1+tan(
B) ² ) * *−√4×(L+(W/2)/sin(B))−4×(1+
tan(B) ² )×((L+(W/2)/sin(B)) ² −Rl ² )/
y4=2×(L+(W/2)/sin(B))/2×(1+tan(
B) ² ) * *−√4×(L+(W/2)/sin(B))−4×(1+
tan(B) ² )×((L+(W/2)/sin(B)) ² −Rl ² )/
×tan(B) x5=2×(L+(W/2)/sin(B))/2×(1+tan(
B) ² ) * *−√4×(L+(W/2)/sin(B))−4×(1+
tan(B) ² )×((L+(W/2)/sin(B)) ² −Rl ² )/
y5=2×(L+(W/2)/sin(B))−√4×(L+(
W/2)/sin(B))/2×(1+tan(B) ² )* *-4×(1+tan(B) ² )×((L+(W/2)/sin
(B)) ² −Rl ² )/ ×tan(B). In addition, the coordinates of the intersection of the lowermost line 38 of the range where the collimator window views the piping and the piping are determined by the third
As shown in the figure, if the coordinates (x6, y6) are 39 and the coordinates (x7, y7) are 40, x6 = 2 x (L-(W/2)/sin(B))/2 x (1+tan(
B) ² ) * *−√4×(L−(W/2)/sin(B))−4×(1+
tan(B) ² )×((L+(W/2)/sin(B) ² −R1 ² )/y6=2×(L−(W/2)/sin(B))/2×(1+tan(
B) ² ) * *−√4×(L−(W/2)/sin(B))−4×(1+
tan(B) ² )×((L+(W/2)/sin(B) ² −R1 ² )×t
an(B) x7=2×(L-(W/2)/sin(B))/2×(1+tan(
B) ² )* *+√4×(L-(W/2)/sin(B))-4×(1+
tan(B) ² )×((L+(W/2)/sin(B) ² −R1 ² )/y7=2×(L−(W/2)/sin(B))/2×(1+tan(
B) ² )* *+√4×(L-(W/2)/sin(B))-4×(1+
tan(B) ² )×((L+(W/2)/sin(B) ² −R1 ² )×t
an(B).

Using these coordinates, the deposited radioactivity (μCi/cm ² ), aqueous radioactivity (μCi/cm ³ ), and gaseous radioactivity (μCi/cm ³ ) inside the pipe can be calculated as follows: .

First, determine the deposited radioactivity inside the pipe. Let the area 41 of the deposited radioactivity sandwiched between the coordinates (x4, y4) and the coordinates (x5, y5) be S1cm ² , and the deposited radioactivity sandwiched between the coordinates (x6, y6) and the coordinates (x7, y7) If ^the area ⁴² of
1) −sin ^-1 ((x5−(L+(W/2)/sin(B))/R1)
) S2=R1×(sin ^-1 ((L+(W/2)/sin(B)−x6)/R
1) −sin ^-1 ((x7−(L+(W/2)/sin(B))/R1)
).

Furthermore, if we approximate that these radioactivities reach the detector through the center line of the collimator, the distance 43T where radiation is absorbed by the pipe is the length from the coordinates (x1, y1) to (x3, y3). Therefore, it can be found by T=√(1-3) ² + (1-3) ² .

Therefore, the coefficient Np1 of the gamma ray detector due to the deposited radioactivity of S1 and the count Np2 of the gamma ray detector due to the deposited radioactivity of S2 are calculated as above, assuming that unit radioactivity σp exists in the deposited state. Using the values and coordinates, Np1=σp×S1/4×π×(x1/sin(B)) ² ×e ^-Ap×T Np2=σp×S2/4×π×(x2/sin(B)) It can be obtained as ² ×e ^-Ap×T . Therefore, if there is gas in the pipe, Np only needs to consider the absorption of S2, so the gamma ray detector count Np due to deposited radioactivity is Np = Np1 + Np2 × e ^{-Ag ×} It is calculated as ^(x2-x1) .

Under the above conditions, if there is water in the pipe, Np only needs to take into account water absorption for S2, so the gamma ray detector counts due to deposited radioactivity.
Np can be obtained as Np=Np1+Np2×e ^-Aw×(x2-x1) .

Next, the aqueous radioactivity and gaseous radioactivity inside the pipe are determined based on FIG. The radioactivity to be sought is the area surrounded by the upper line and lower line where the collimator wants the piping, namely coordinates (x4, y4) 44, coordinates (x5, y6) 45, coordinates (x6, y6) 46, and coordinates (x7, y7) This is the radioactivity of the area surrounded by 47. In order to perform the calculation, the integration range is approximated to a trapezoid 48 as shown in FIG. 3, and the integration range is calculated from coordinates (x1, y1) 49 to coordinates (x2, y2) 50.

In Figure 4, the coordinates of any point are (x, y)
51, and if the desired length 52 of the next collimator in the y direction is u, then from the relationship of similarity of triangles, u:W=x:H holds, and u becomes u=(W×x)/H. .

Therefore, the minute volume dv53 is dv=u×dx/cos(B)=(W×x)/(H×cos
(B)), and the aqueous radioactivity Nw is given by unit radioactivity ρw in the aqueous state. Considering the self-absorption of radiation by water, this minute volume dv is integrated from x1 to x2, and Nw = ∫ ^x2 _x1 [ρw×W×cos(B)／4×π×x ² ×e ^{-Aw×(x-
x1)/cos} (B)×e ^-AP×T 〕dx.

In addition, if gaseous radioactivity Ng exists in a gaseous state with unit radioactivity ρg, this minute volume dv can be calculated as x1 by considering self-absorption by the gas as above.
Integrate from to x2, Ng=∫ ^X2 _X1 [ρg×W×cos(B)/4×π×x ² ×e ^-Ag
X1)/cos (B)×e ^-AP×T 〕dx.

As an example of the above calculation, the outer diameter of the pipe is 20 cm, and the thickness is 1 cm.
Co-60 exists as a radionuclide inside the pipes in the form of a deposit and an aqueous solution, or in the form of a deposit and a gas.
Based on this measurement method, gamma rays with an energy of 1.33 MeV were measured. Each parameter is as follows: Inside radius of the pipe: R1 = 9cm Outside radius of the pipe: R2 = 10cm Length from detector to pipe axis: L = 20cm Collimator thickness: H = 5cm Collimator length: W = 0.5cm Radiation absorption coefficient of piping: Ap = 0.414 (cm ^-1 ) Radiation absorption coefficient of water: Ah = 0.0204 (cm ^-1 ) Radiation absorption coefficient of gas: Ag = 0.0000242 (cm ^-1 ) Unit radioactivity of deposited state: σp = 37000 (1μCi/cm ² ) Unit radioactivity in aqueous solution state: ρw = 37000 (1μCi/cm ² ) Unit radioactivity in gas state: ρg = 37000 (1μCi/cm ² ) Substitute into the above formula to detect gamma rays. Calculations were performed for increasing the angle at which the system desired piping from 0 degrees to 30 degrees. FIG. 5 shows calculation results 54 and 55 for the case where deposited radioactivity and aqueous radioactivity exist inside the pipe. Calculation results 56 and 57 for the case where deposited radioactivity and gaseous radioactivity exist inside the pipe are shown in FIG. The above calculation results show that the ratio of the gamma ray counts of radioactivity in the deposited form and in the aqueous form, or in the deposited form and that in the gaseous form, differs depending on the angle at which the piping is viewed.

For this reason, the deposited radioactivity in the piping that should be determined is
Cp (μCi/cm ² ), aqueous radioactivity Cw (μCi/cm ³ )
It is calculated as follows. If n measurements are performed by changing the desired angle of the piping of the gamma ray detection system, let the counts of gamma rays measured for each of the n measurement angles be M(1) to M(n), and according to the above calculation, Np(1) ~ Np
(n), count by aqueous radioactivity is Nw(1) ~ Nw(n)
Then, for each measurement point, Cp×Np(1)+Cw×Nw(1)=M(1) Cp×Np(2)+Cw×Nw(2)=M(2) Cp×Np(n)+Cw× An n-element simultaneous linear equation of Nw(n)=M(n) is established. These n equations are independently established because, as shown by the above calculation, the ratio of counts due to radioactivity in each state differs depending on the measurement angle. Therefore, since this simultaneous equation has two unknowns, Cp and Cw, it can be solved by changing the angle at two or more locations, and can calculate the deposited radioactivity and aqueous radioactivity, respectively. Can be quantified.

In addition, the deposited radioactivity in the pipe to be determined is Cp
(μCi/cm ² ) and when gaseous radioactivity is Cw (μCi/cm ³ ), it can be determined in the same manner as above.

(Effects of the Invention) The measurement method of the present invention enables scanning measurement of gamma rays emitted from radioactivity inside the pipe by changing the angle of the gamma ray detection system with the front surface of the detector as an axis. The mechanism of the scanning device that measures the whole can be downsized.

As described above, by using the measurement method of the present invention, it is possible to nondestructively quantify each type of radioactivity in the form of deposits, aqueous solution, or gas inside a pipe, which was not possible with conventional techniques. Therefore, it becomes easy to measure the radioactivity inside the piping, including the existing state, when cutting the reactor primary system piping. Furthermore, it becomes possible to easily perform monitoring work for radioactivity in the pipes and maintenance work during the operation of the nuclear reactor.

[Brief explanation of drawings]

FIG. 1 is a diagram showing deposited radioactivity inside a pipe measured by a conventional non-destructive measurement method. FIG. 2 is a diagram showing the principle of the measurement method of the present invention. FIG. 3 is an explanatory diagram when measuring deposited radioactivity inside a pipe by the measuring method of the present invention. FIG. 4 is an explanatory diagram when measuring aqueous radioactivity and gaseous radioactivity inside a pipe by the measuring method of the present invention. FIG. 5 is a distribution diagram showing the results of measurement and calculation of deposited radioactivity and aqueous radioactivity inside a pipe using the measuring method of the present invention. (Assuming that the deposited radioactivity (1 μCi/cm ² ) and the aqueous radioactivity (1 μCi/cm ³ ) inside the pipe are uniformly distributed, the gamma ray detection system detects gamma rays with an energy of 1.33 MeV inside the pipe. Calculations were made for the case where the desired angle was increased from 0 degrees to 30 degrees in 1 degree increments.) Figure 6 shows that the deposited radioactivity and gaseous radioactivity inside the pipe can be determined by the measurement method of the present invention. It is a distribution diagram showing the results of measurement and calculation. (Assuming that the deposited radioactivity (1 μCi/cm ² ) and gaseous radioactivity (1 μCi/cm ³ ) inside the pipe are uniformly distributed, the gamma ray detection system detects gamma rays with an energy of 1.33 MeV inside the pipe. Calculations were made for the case where the desired angle was increased from 0 degrees to 30 degrees in 1 degree intervals) 1... Gamma ray measurement system, 2... Collimator window, 3... Piping, 4... Deposited radiation on the inner surface of the pipe. Function, 5... Rectangular collimator window, 6... Shielding body, 7... Gamma ray detector, 8... Gamma ray detection system, 9... Piping with radioactive contamination inside, 1
0... Angle of gamma ray detection system (measurement angle),
11... Deposited radioactivity inside the pipe, 12... Aqueous radioactivity, 13... Gaseous radioactivity, 14... Distance from the axis of the pipe to the detector, 15... Radius inside the pipe, 16... ...Radius of the outside of the pipe, 17...Length of the collimator, 18...Thickness of the collimator, 19
... Piping to be measured, 20 ... Deposited radioactivity inside the pipe, 21 ... Aqueous radioactivity, 22 ... Gaseous radioactivity, 23 ... Gamma ray detection system, 24 ...
...Radius inside the pipe, 25...Radius outside the pipe, 2
6... Distance from detector to piping axis, 27... Vertical width of collimator, 28... Thickness of collimator, 2
9... Angle of detection system (measurement angle), 30...
...Origin of coordinates, 31...Center line of collimator, 3
2... Coordinates (x1, y1), 33... Coordinates (x2, y2),
34...Coordinates (x3, y3), 35...The uppermost line of the range where the collimator wants the piping, 36...Coordinates (x4, y4), 37...Coordinates (x5, y5), 38...The collimator The lowest line of the range where you want the piping, 39
...Coordinates (x6, y6), 40...Coordinates (x7, y7),
41...Area of deposited radioactivity (perigee), 42...
...Area of deposited radioactivity (apogee), 43...Distance at which radiation is absorbed by piping, 44...Coordinates (x4, y4), 45...Coordinates (x5, y5), 46...Coordinates (x6, y6), 47...coordinates (x7, y7), 48...
...integration range approximated to a trapezoid, 49...coordinates (x1,
y1), 50...Coordinates (x2, y2), 51...Coordinates of any point, 52...Length in the y direction desired by the collimator, 53...Minimum volume, 54...When there is water in the pipe Calculation results of deposited radioactivity, 55... Calculation results of aqueous radioactivity in piping, 56... Calculation results of deposited radioactivity when there is gas in piping, 5
7...Calculation results of gaseous radioactivity in the pipe.

Claims (1)

[Claims] 1 Radioactivity almost uniformly deposited on the inside of the pipe and aqueous radioactivity almost uniformly distributed inside the pipe, or radioactivity almost uniformly deposited on the inside of the pipe and gas almost uniformly distributed inside the pipe A gamma ray detection system in which gamma rays with a specific energy emitted from radioactive nuclides in piping contaminated with radioactivity are covered around the detector by a shield with a rectangular collimator window from the side of the piping. In the method of determining the radioactivity inside the pipe by measuring the spectrum using Measure gamma rays emitted from radionuclides inside the pipe at two or more locations,
The measured gamma ray counts are calculated by taking advantage of the fact that the ratio of gamma ray counts emitted from deposited radioactivity and aqueous radioactivity, or between deposited radioactivity and gaseous radioactivity, differs depending on the measurement angle. , the inner and outer radii of the pipe, the distance from the axis of the pipe to the detector, the radiation absorption coefficient of the pipe, the radiation absorption coefficient of water, the radiation absorption coefficient of gas, and the dimensions and thickness of the collimator window. , a pipe internal radioactivity measuring method characterized by quantifying deposited radioactivity and aqueous radioactivity, or deposited radioactivity and gaseous radioactivity inside the pipe.