JPS61274285A - Method and apparatus for measuring element concentration - Google Patents

Abstract

PURPOSE:To eliminate any external radiation source as in the past, by detecting gammarays with a gamma rays detector as generated from gamma radioactive isotope in an object to be measured. CONSTITUTION:A circular arc collimator 23 is arranged in the vicinity of a bend part 21a of a bypass tube 21 and a gamma rays detector 24 inside. A pulse height analyzer 27 connected to the gamma rays detector 24 is provided with first and second memories 27a and 27b for temporarily memorizing spectrum data obtained by spectral analysis. A calculator 28 connected to the pulse height analyzer 27 performs a computation based on the spectrum data read out of the memories 27a and 27b.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method and apparatus for measuring the concentration of at least a T radioisotope in an object to be measured containing the T radioisotope.

"Conventional technology" For example, in the process of reprocessing spent fuel generated in a nuclear reactor, the concentration of U (uranium) and Pu (plutonium) must be accurately measured from the viewpoint of process control, safety management, safeguards, etc. This is extremely important. These concentration measurement methods can be roughly divided into non-destructive measurement and destructive measurement.Non-destructive measurement is incorporated into the fuel reprocessing process, and is used to measure the concentration of U and Pu in the object without taking it out. It has the advantage of being measurable.

FIG. 5 schematically shows an example of a conventional apparatus using absorption edge analysis for performing such non-destructive measurements. This device is equipped with a nozzle tube 1 connected to a main pipe (not shown) used in the fuel reprocessing process. A nitric acid solution 2 containing spent fuel is supplied to the bypass pipe 1 from the main pipe. The spent fuel consists primarily of USPu, fission products. Collimators 3.4 are arranged on both sides of the pass tube 1, respectively. A radiation source 5 consisting of an X-ray source or a gamma ray source is arranged outside the collimator 3 on the left side in the figure, and a radiation detector 6 is arranged outside the collimator 4 on the right side.

Photons generated by the radiation source 5 are collimated by the collimator 3 and then transmitted through the bypass pipe 1 . At this time, some of the photons are absorbed and scattered by U and Pu in the solution 2. The photons transmitted through the bypass pipe 1 are collimated by a collimator 4 and then enter a radiation detector 6. Radiation detector 6
generates a pulse signal with a wave height proportional to the energy of the incident photon and supplies it to the wave height analyzer 7. The pulse height analyzer 7 analyzes the heights of these pulse signals and supplies the results to the computer 8 as spectrum data.

The calculator 8 determines the energy distribution of photons incident on the radiation detector 6 based on this spectral data, and calculates the concentrations of U and Pu in the solution 2 from this energy spectrum.

By the way, in such a device, the intensity of the photons generated from the radiation source 5 needs to be relatively high in order to prevent measurement from being interfered with by the gamma rays generated by the fission products themselves in the solution 2. . For this reason, it is necessary to use, for example, a 150 kV, 10 mA X-ray generating tube as the radiation source 5, and the price of the entire device including this and ancillary equipment such as a power supply device becomes quite expensive. Furthermore, if maintenance costs for the X-ray generating tube and replacement of parts due to the short life of the target portion are taken into consideration, the cost becomes even higher.

In addition, when using an RI (radioisotope) gamma ray source as the radiation source 5 and performing concentration analysis by absorption edge (energy point where the mass absorption coefficient changes discontinuously) analysis method, it is possible to A gamma ray source that generates gamma rays with energy slightly lower than the absorption edge energy and a gamma ray source that generates gamma rays with energy slightly higher than the absorption edge energy are required. Since the half-lives of these γ-ray sources are different from each other, it is necessary to take measures such as measuring standard solutions for calibration.

Another problem is the attenuation of the intensity of the γ-ray source; for example, +69 Yb (ytterbium), which is said to be suitable for U concentration analysis, has a half-life of only 32 days, making it necessary to replace it in a short period of time. The cost will increase considerably.

``Problems to be solved by the invention'' As described above, conventional elemental concentration measuring devices require radiation R5 consisting of an The problem was that it was necessary to set up

In view of these circumstances, the present invention non-destructively reduces the concentration of T-radioactive isotope and other elements in an object to be measured containing T-radioactive isotope without using a radiation source such as an X-ray source or a γ-ray source. The object of the present invention is to provide a method and device for measuring elemental concentration, which can be used to measure elemental concentration.

"Means for Solving the Problems" In the present invention, two homogeneous objects to be measured containing a γ-radioactive isotope and having different thicknesses are both faced to a γ-ray detector, and the inside of the two objects to be measured is γ generated from the T radioisotope of
rays are detected by the gamma ray detector, and based on these detection results, the count rate of gamma rays generated from the T radioactive isotope in the two objects to be measured is calculated, and from these calculation results, the It is designed to determine the concentration of r-radioactive isotopes and other elements in substances.

According to the present invention, the gamma ray detector detects the gamma rays generated from the T radioactive isotope in the object to be measured, thereby eliminating the need for a conventional external radiation source.

"Summary of the Invention" For example, when focusing on an arbitrary γ-ray peak generated from T radioactive isotope in a nitric acid solution (hereinafter simply referred to as solution) containing spent fuel in a fuel reprocessing process, a sufficiently collimated measurement system can be used. Then, the counting rate C is expressed by the following equation.

C= f −n −(1−exp(−αT))
/ α--・(1) where f; γ-ray detection efficiency n; γ-ray generation rate in unit volume of solution α; γ-ray absorption coefficient T of solution; thickness of solution in the direction of γ-ray detector Among them, the T-ray detection efficiency f is the probability that γ-rays generated from the T radioactive isotope on the surface of the solution pass through the collimator, enter the γ-ray detector, and are detected. This γ-ray detection efficiency f is
Since it depends on the measurement system, it can be obtained by performing measurements in advance using a gamma ray source whose gamma ray generation rate is known. The thickness T of the solution can be set arbitrarily. Therefore, the T-ray generation rate n and the r-ray absorption coefficient α become unknown quantities.

Therefore, if the thickness T of the solution is set to two types, T1 and T2, and the counting rate C which is the measurement result when the thickness T is set to C5, and when the other thickness T2 is set to the counting rate C2, (1) The following simultaneous equations are obtained from the equations.

C+= f −n ・(1−exp (−αT+)
) / α−−42) C2□ f −n ・(
1-exp (-αr2) ) / α-(3) When these simultaneous equations (2) and (3) are solved for the T-ray generation rate n and the γ-ray absorption coefficient α, the γ-ray generation rate per unit volume of the solution is and the γ-ray absorption coefficient can be determined.

Therefore, by converting these using the gamma ray generation rate per unit mass of the T radioisotope and the mass absorption coefficient of the solute element, the concentration of the T radioisotope and the concentration of the solute element can be determined.

When focusing on multiple γ-ray peaks generated from T radioactive isotopes in a solution, by calculating the T-ray generation rate n and T-ray absorption coefficient α in a unit volume of the solution using the same method as above, The concentrations of multiple T radioactive isotopes are determined at once, and at the same time the T-ray absorption coefficient α for each γ-ray energy is calculated.
is required.

From this result, the energy dependence of the mass absorption coefficient is
The concentration of a specific element such as U or Pu can be determined by determining the concentration of a light element different from u or by absorption edge analysis.

In the above description, the measurement target is a nitric acid solution containing spent fuel in the fuel reprocessing process, but the measurement is not limited to this. If a substance is homogeneous, it is solid;
Regardless of whether it is a liquid or a gas, the concentration of the T radioactive isotope and the concentration of the solute element can be determined. Examples of solids include homogeneous solidified radioactive waste and P u O-[1
02 mixed powder is available. Examples of the gas include OF and gas.

Moreover, the element to be measured may be an atomic group, regardless of whether it is a solute or a solvent, as long as the elemental component ratio is known. In the case of the nitric acid solution in the previous example, since the elemental component ratio of nitric acid is known, its concentration can be determined as already explained.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 1 shows the main parts of an element concentration measuring device according to an embodiment of the present invention. This device is equipped with a bypass pipe 21 connected to a main pipe (not shown) of the fuel reprocessing process. A nitric acid solution 22 containing spent fuel is supplied to the bypass pipe 21 from the main pipe.

A predetermined portion of the bypass pipe 21 is bent in a Z shape.

An arcuate collimator 23 is arranged near the bent portion 21a. A gamma ray detector 24 is arranged inside the collimator 23. The gamma ray detector 24 has, for example, 10
It consists of a Ge detector whose detection efficiency for gamma rays of about 0 to 140 keV is the highest compared to the detection efficiency for gamma rays of higher energy.

The center of the detection section of the γ-ray detector 24 is located at the center of curvature of the collimator 23. Predetermined 2 of collimator 23
There are pores 25 and 26 with the same length and cross-sectional shape.
are provided so as to both extend in the radial direction of curvature. Therefore, the detection part of the γ-ray detector 23 faces the bent part 21a of the bypass pipe 21 through one of the pores 25, and faces the predetermined non-bent part 21b of the bypass pipe 21 through the other pore 26. It is supposed to be done. The thickness t2 of the solution 22 on the extension line of one of the pores 25 is twice the thickness tl of the same solution 22 on the extension line of the other pore 26. The thickness tl of the solution 22 at the non-bending part 21b is
If it is too small, there will be no absorption of gamma rays, and if it is too large, it will be considered to be virtually infinite due to the absorption of gamma rays at a distance. Therefore, the total concentration of U and Pu in solution 22 is 20
When it is about 0 g/β, it is desirable that the thickness t is about 1 to 2 cm.

A pulse height analyzer 27 is connected to the γ-ray detector 24 .

The pulse height analyzer 27 includes first and second memos J27a and 27b for temporarily storing spectrum data obtained by spectrum analysis. A computer 28 is connected to the wave height analyzer 27. Calculator 28 is a memo! J2
Based on the spectrum data read from 7a and 27b, calculations are performed as described later.

An arc-shaped moving member 31 is disposed on the outer circumference of the collimator 23 so as to be able to reciprocate along the outer circumference of the collimator 23 via a plurality of guide rollers 32 . Moving member 31
A rack 33 is provided at a predetermined location on the outer peripheral surface of the rack 33, and a pinion 34 is meshed with the rack 33. The pinion 34 is rotated forward or reverse by a motor (not shown). A shield 35 made of tungsten or the like is provided at another predetermined location on the moving member 31.

The shielding body 35 selectively shields the two pores 25 and 26 of the collimator 23 as the moving member 31 moves.

FIG. 2 schematically shows the circuit configuration of this device. This device is equipped with a CPU (central processing unit) 51, and is connected to various parts through a path line 52 such as a data bus. Among these, the external storage device 53 is a storage device using a floppy disk, a magnetic drum, etc.
Concentration measurement programs and necessary data for analysis are stored. RAM (Random access)
The memory 54 is used not only for writing necessary data, but also for temporary storage of data for performing various data processing. The operation panel 55 is a keyboard for operating the CPU 51.

The first and second limit switches 56 and 57 are used as switches for detecting the movement limit position of the shield 35. The morph driver 58 is a circuit that drives a motor 59 for moving the shield 35.

The pulse height analyzer 27 is connected to the gamma ray detector 24 via an amplifier 61. The results calculated by the CPU 51 are sent to the printer drive section 62 and CR connected to this device.
The printer 64 is driven by the T (cathode ray tube) drive unit 63.
or output to CRT65. The CRT 65 is also designed to display data necessary for program execution.

Next, the operation of this measuring device will be explained with reference to the flowchart shown in FIG.

A program is set in the RAM 54 of this device, and when the operator operates the operation panel 57 to start executing the program, the CPU 51 starts normal rotation of the motor 59 (step 2). As a result, the shielding body 35 is moved clockwise in FIG. 1 together with the moving member 31. The moving member 31 comes into contact with the first limit switch 56, turning it on. In particular, the CPU 51 detects this and stops the motor 59 (step ■).

As a result, the shielding body 35 reaches a predetermined position for shielding one of the pores 25 and is held at that position.

After that, the CPLI 51 detects the gamma ray detector 2 at a predetermined timing.
4 and the pulse height analyzer 27 are both turned on, and the non-bending portion 21 is turned on.
Measurement of γ-rays generated from the solution 22 in part b is waited for a certain period of time (step ■). That is, the non-bending portion 2
A part of the photons generated from the solution 22 in the part 1b pass through the other pore 26 of the collimator 23 and reach the gamma ray detector 2.
4. The γ-ray detector 24 outputs a pulse signal with a wave height proportional to the energy of a photon to the wave height analyzer 27 every time a photon is detected. The pulse height analyzer 27 analyzes the energy of the γ-rays incident on the γ-ray detector 24 from the height of this pulse signal. The analysis results are stored in the first memory 27a as spectral data.

When such measurement is completed (step ■; Y), CP
Thereafter, U51 starts reverse rotation of the motor 59 at a predetermined timing (step 2). When the motor 59 reverses,
Together with the moving member 31, the shield 35 is moved counterclockwise in FIG.

When the moving member 31 comes into contact with the second limit switch 57 and turns it on (Step ■; Y), the CPU 51 stops the rotation of the motor 59 (Step ■). As a result, the shielding body 35 reaches another predetermined position for shielding the other pore 26 and is held at that position.

Thereafter, the CPU 51 activates the gamma ray detector 24 at a predetermined timing.
and the wave height analyzer 27 are turned on again, and the bending section 21 is turned on again.
Measurement of γ-rays generated from the solution 22 in part a is waited for a certain period of time (step ■). That is, some of the photons generated from the solution 22 at the bent portion 21a pass through the other pore 26 of the collimator 23 and enter the γ-ray detector 24. Thereafter, the spectrum data at this time is stored in the second memory 27b in the same manner as in the case of the non-bent portion 21b.

When such measurements are completed (step ■: Y), the CPU
51 reads out the spectrum data stored in both memories 27a and 27b, and performs a predetermined calculation based on these data (step 2).

For this calculation, first note both! Appropriate γ-ray peaks (for example, 1s4Eu 123.1keV peak, 14'ce
133.5 keV peak, etc.) of each count rate C1, C2
This is done by calculating each. Next, these counting rates C3 and C2 are calculated using the simultaneous equations (2) and (
3) and solve for α to obtain γ of solution 22.
A linear absorption coefficient is calculated. At this time, the thickness of the solution is T+ = t + , T2 = t 2 , and t2 = 2i+, so the T-ray absorption coefficient α of the solution 22 is expressed by the following equation.

α==! , (C2/Cl-1) / t,...
-(4) By the way, since the main components of the solution 22 are Pu, U, and the solvent (nitric acid consisting of light elements), the absorption effect of γ-rays is mostly due to Pu and U.

Further, since Pu and U have close atomic numbers and substantially equal mass absorption coefficients, if the value is σ, the total concentration ρ of Pu and U is calculated by the following equation.

ρ==! . (C2/Cl-1) / t+・σ・・・・
(5) The total concentration of Pu and U obtained in this way is displayed on the CRT 65, and also displayed on the printer 6 as necessary.
4 is printed out (step 0).

When all series of measurement operations are completed (step ■; Y)
, the contents of both memories 27a and 27b are initialized and prepared for the next measurement operation.

"Other Embodiments" FIG. 4 shows the main parts of an element concentration measuring device in another embodiment of the present invention. In this figure, parts with the same names as those in FIG.

In this device, a predetermined portion of the bypass pipe 21 is bent into an L shape. The detection part of the γ-ray detector 23 is located in one of the pores 2
5, facing the non-bent portion 21b of the bypass pipe 21,
It faces the bent portion 21a through the other pore 26. The total concentration of U and Pu in solution 22 is 200g
/β, the thickness tl of the solution 22 on the extension line of one pore 25 is about 1 to 2 am, and the thickness t2 of the solution 22 on the extension line of the other pore 26 is ioam It has become more than moderate. When the thickness of the solution 22 is 10 cm or more, the thickness of the solution 22 can be considered to be substantially infinite due to γ-ray absorption at a distance. Therefore, t2 becomes infinite. As a result, the total concentration ρ of Pu and U in this device can be determined by the following equation.

p=-ff1n(1-CI/C2)/T ・cy--
-(6) In the above example, the case where the total concentration of Pu and U in a solution containing Pu and U is determined is not limited to this. For example, the U concentration in a solution containing only U can also be determined. in this case,
Focusing on the 135 keV gamma ray peak of 235 U, the gamma ray absorption coefficient α and the U concentration are determined in the same manner as in the above example. Then, by substituting the obtained γ-ray absorption coefficient α into one of the simultaneous equations (2) and (3) to obtain the γ-ray generation rate n in unit volume, and converting this to 23 Sua degrees, the U concentration and 235U concentration can be determined at once.

"Effects of the Invention" As explained above, according to the present invention, element concentrations can be measured without using an external radiation source such as an X-ray source or a T-ray source, resulting in a significant cost reduction. I can do it. Further, there is no need to take measures for calibration. Furthermore, since no external radiation source is used, there is no need to adjust its arrangement.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing the main parts of an element concentration measuring device according to an embodiment of the present invention, Fig. 2 is a block diagram showing the main parts of the electric circuit of the device, and Fig. 3 shows the operation of the device. FIG. 4 is a schematic diagram showing the main parts of an element concentration measuring device according to another embodiment of the present invention, and FIG. 5 is a schematic diagram showing an example of a conventional elemental a-plane measuring device. 21... Bypass pipe, 22... Solution, 23... Collimator, 24... T-ray detector, 27... Wave height analyzer , 27a...first memory, 27b...second memory, 28...calculator, 35...shielding body, 51...・cpu. 59...Motor, 64...Printer, 65...CRTo Applicant: Japan Atomic Energy Corporation, Agent

Claims (1)

[Claims] 1. Two homogeneous objects to be measured containing a γ-radioactive isotope and having different thicknesses are both faced to a γ-ray detector, and the γ-radioactive isotope in the two objects to be measured is Detecting the generated γ rays with the γ ray detector, calculating the counting rate of the γ rays generated from the γ radioactive isotopes in the two objects to be measured based on these detection results, and using these calculation results. A method for measuring element concentration, characterized in that the concentration of at least T radioactive isotope in the object to be measured is determined. 2. A γ-ray detector, and 2.
When the gamma ray detector detects the gamma rays generated from two homogeneous objects to be measured and the gamma radioactive isotope in these objects, the A count rate calculation means for calculating the count rate of γ rays generated from the radioisotope, and a concentration for calculating the concentration of at least the γ radioisotope in the object to be measured based on the calculation result by the count rate calculation means. An element concentration measuring device comprising: a calculation means; and a display means for displaying calculation results by the concentration calculation means.