阅读说明：本技术 一种通过测量中子得到钆浓度的在线监测方法及系统 (On-line monitoring method and system for obtaining gadolinium concentration by measuring neutrons ) 是由 刘伟容 张伟 王欣 谢永骥 林爽 吴志强 宋晓鹏 于 2021-07-07 设计创作，主要内容包括：本发明涉及一种通过测量中子得到钆浓度的在线监测方法及系统,将中子源和中子探测器分别布置在装有含钆溶液的测量腔两侧,中子源发射的中子束穿过测量腔,部分中子与含钆溶液中的核素～(157)Gd和～(155)Gd发生俘获反应转换成γ射线,中子探测器测量经过测量腔而未反应的中子,根据中子探测器的脉冲信号计数率推导计算出含钆溶液的钆浓度值。本发明实现了可溶中子毒物溶液中钆浓度的在线监测,测量过程中不需要对溶液进行取样,保证了分析人员和测量设备免受辐射危害的影响。(The invention relates to an on-line monitoring method and system for obtaining gadolinium concentration by measuring neutrons 157 Gd and 155 gd is subjected to capture reaction and converted into gamma rays, a neutron detector measures unreacted neutrons passing through the measuring cavity, and the gadolinium concentration value of the gadolinium-containing solution is deduced and calculated according to the pulse signal counting rate of the neutron detector. The invention realizes the on-line monitoring of the gadolinium concentration in the soluble neutron poison solution, does not need to sample the solution in the measuring process, and ensures that analysts and measuring equipment are not influenced by radiation hazard.)

1. The on-line monitoring method for obtaining gadolinium concentration by measuring neutrons is characterized in that a neutron source and a neutron detector are respectively arranged at two sides of a measuring cavity filled with gadolinium-containing solution, a neutron beam emitted by the neutron source passes through the measuring cavity, and part of neutrons and nuclides in the gadolinium-containing solution¹⁵⁷Gd and¹⁵⁵gd is subjected to capture reaction and converted into gamma rays, a neutron detector measures unreacted neutrons passing through the measuring cavity, and the gadolinium concentration value of the gadolinium-containing solution is deduced and calculated according to the pulse signal counting rate of the neutron detector.

2. The method for on-line monitoring of gadolinium concentration through neutron measurement as claimed in claim 1, wherein the pulse signal count rate of said neutron detector is related to gadolinium concentration by the following equation:

X＝1/n＝A₀P²+B₀P+C₀

A₀＝β²/2n₀

B₀＝β/n₀

C₀＝1/n₀

wherein the content of the first and second substances,

p is the gadolinium concentration;

n is the neutron counting rate detected by the neutron detector when the gadolinium concentration is P;

A₀、B₀、C₀is a constant;

β is a constant related to the structure of the detection device and the absorption cross section of gadolinium;

n₀the count rate of neutrons detected by the neutron detector in the absence of gadolinium.

3. The method of claim 2, wherein the measuring device is calibrated by a solution with known gadolinium concentration to obtain a data curve of gadolinium concentration and neutron detector count rate, and the data curve is fit by least squares to obtain A in the formula₀，B₀And C₀A constant.

4. The method for on-line monitoring of gadolinium concentration by measuring neutrons as claimed in claim 1 wherein said gadolinium containing solution may be gadolinium nitrate solution.

5. An on-line monitoring system for obtaining gadolinium concentration by measuring neutrons for realizing the method of any one of claims 1 to 4, comprising a neutron source and a neutron detector respectively arranged at two sides of a measurement cavity filled with gadolinium-containing solution, wherein a neutron beam emitted by the neutron source passes through the measurement cavity, unreacted neutrons are received by the neutron detector, the neutron detector is connected with a data processing unit, and the data processing unit calculates gadolinium concentration value of gadolinium-containing solution in the measurement cavity according to pulse signal counting rate of the neutron detector.

6. The system for on-line monitoring of gadolinium concentration through neutron measurement as claimed in claim 5, wherein the neutron detector can be a proportional counter tube, a scintillator detector or a semiconductor detector; and acquiring pulse signals generated by the neutron detector through a detector pulse signal measurement channel to obtain pulse signal counts output by the neutron detector.

Technical Field

The invention belongs to the technology of soluble neutron poison online monitoring, and particularly relates to an online monitoring method and system for obtaining gadolinium concentration by measuring neutrons.

Background

Due to the fact that¹⁵⁷Gd and¹⁵⁵gd has a physical property of having a large thermal neutron absorption cross section (¹⁵⁷The thermal neutron absorption cross section of Gd is about 60900 target,¹⁵⁵gd has a thermal neutron absorption cross section of about 254000 target), and its compounds can be used as soluble neutron absorbers. Based on this physical property, gadolinium nitrate is often used as a soluble neutron poison added to process equipment involved in nuclear reactions to modulate reactivity.

Because the influence of the gadolinium concentration on the reactivity is great, the gadolinium concentration needs to be ensured to meet the requirement, and the critical safety is ensured. At present, the concentration of gadolinium is mainly obtained by a sampling measurement method (such as a spectrophotometry method) in the industry, and the concentration of gadolinium is measured by a Qin mountain heavy water reactor. However, the sampling measurement method has time delay, cannot give the current gadolinium concentration value in real time, and the sample generally has high radioactivity and may cause radiation damage to the analysts and equipment.

Disclosure of Invention

The invention aims to provide a method and a system for obtaining gadolinium concentration by measuring neutrons aiming at the defects of the prior art, so as to realize online monitoring of gadolinium concentration in a soluble neutron poison solution.

The technical scheme of the invention is as follows: an on-line monitor method for obtaining gadolinium concentration by measuring neutron features that the neutron source and neutron detector are respectively arranged at both sides of measuring cavity containing gadolinium solution, the neutron beam emitted by neutron source passes through measuring cavity, and part of neutrons and nuclide in gadolinium solution¹⁵⁷Gd and¹⁵⁵the Gd is subjected to capture reaction and converted into gamma rayAnd the neutron detector measures unreacted neutrons passing through the measuring cavity, and the gadolinium concentration value of the gadolinium-containing solution is deduced and calculated according to the pulse signal counting rate of the neutron detector.

Further, the above-mentioned online monitoring method for obtaining gadolinium concentration by measuring neutrons is provided, wherein a relation between a pulse signal count rate of the neutron detector and gadolinium concentration is as follows:

X＝1/n＝A₀P²+B₀P+C₀

A₀＝β²/2n₀

B₀＝β/n₀

C₀＝1/n₀

wherein the content of the first and second substances,

p is the gadolinium concentration;

n is the neutron counting rate detected by the neutron detector when the gadolinium concentration is P;

A₀、B₀、C₀is a constant;

β is a constant related to the structure of the detection device and the absorption cross section of gadolinium;

n₀the count rate of neutrons detected by the neutron detector in the absence of gadolinium.

Further, the above-mentioned online monitoring method for obtaining gadolinium concentration by measuring neutrons is characterized in that the measuring device is calibrated by a solution with known gadolinium concentration to obtain a data curve of gadolinium concentration and neutron detector counting rate, and a least square fitting is performed to obtain a in a formula₀，B₀And C₀A constant.

Further, the method for on-line monitoring of gadolinium concentration by measuring neutrons as described above, wherein the gadolinium-containing solution may be a gadolinium nitrate solution.

An on-line monitoring system for obtaining gadolinium concentration by measuring neutrons for realizing the method comprises a neutron source and a neutron detector which are respectively arranged at two sides of a measuring cavity filled with gadolinium-containing solution, wherein neutron beams emitted by the neutron source pass through the measuring cavity, unreacted neutrons are received by the neutron detector, the neutron detector is connected with a data processing unit, and the data processing unit calculates the gadolinium concentration value of the gadolinium-containing solution in the measuring cavity according to the pulse signal counting rate of the neutron detector.

Further, the on-line monitoring system for obtaining gadolinium concentration by measuring neutrons as described above, wherein the neutron detector may be a proportional counter tube, a scintillator detector or a semiconductor detector; and acquiring pulse signals generated by the neutron detector through a detector pulse signal measurement channel to obtain pulse signal counts output by the neutron detector.

The invention has the following beneficial effects: the invention uses a neutron detector to measure the non-nuclide when the neutron beam irradiates the gadolinium-containing solution¹⁵⁷Gd and¹⁵⁵gd captures the reacted neutrons, the higher the gadolinium concentration in the measuring cavity is, the more the reacted neutrons are, the fewer the neutron detectors are counted, and the gadolinium concentration can be calculated in real time through counting of the neutron detectors very accurately according to a relational expression between counting of the neutron detectors and gadolinium concentration of gadolinium-containing solution. The invention realizes the on-line monitoring of the gadolinium concentration in the soluble neutron poison solution, does not need to sample the solution in the measuring process, and ensures that analysts and measuring equipment are not influenced by radiation hazard.

Drawings

FIG. 1 is a schematic diagram illustrating the principle of an on-line monitoring method for obtaining gadolinium concentration by measuring neutrons according to the present invention;

FIG. 2 is a graph of neutron count versus gadolinium concentration in an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The measurement principle of the invention is shown in figure 1, the monitoring system is provided with a neutron source, a measurement cavity, a neutron detector, a data processing unit and the like, the measurement cavity is filled with a gadolinium-containing solution (gadolinium nitrate solution) to be measured, and the neutron source and the neutron detector are respectively arranged at two sides of the measurement cavity. Controlling neutron sourcesThe neutron beam moving direction enables the neutron beam emitted by the neutron source to pass through gadolinium nitrate solution in the measuring cavity from one side, the material of the measuring cavity needs to be corrosion-resistant and cannot influence incident neutrons, and the measuring cavity is usually stainless steel with the thickness not more than 2mm and gadolinium nitrate¹⁵⁷Gd and¹⁵⁵gd has a large capture cross section for thermal neutrons, and part of neutrons can generate capture reaction with the two nuclides to be absorbed, so that the neutrons cannot penetrate through the measurement cavity. Unreacted neutrons penetrate out from the other side of the measuring cavity, and the neutrons which pass through the measuring cavity but are not reacted are measured by a neutron detector, wherein the neutron detector can be a common proportional counter tube, a scintillator detector or a semiconductor detector. The greater the gadolinium concentration in the measurement cavity, the greater the number of neutrons that react and the fewer the counts of the neutron detector. The counting rate of the pulse signals output by the neutron detector is in direct proportion to the number of thermal neutrons received by the neutron detector. The pulse signals are collected through the pulse signal measuring channel, and the data processing unit can calculate the gadolinium concentration in the measuring cavity according to the relation between the neutron counting rate and the gadolinium concentration.

The physical conversion method of the pulse signal counting rate and the gadolinium concentration in the solution of the neutron detector comprises the following steps:

the attenuation characteristic relation of neutrons in gadolinium nitrate solution is as follows:

n＝n₀e^-βP (1)

(1) the formula can be transformed into:

n₀＝ne^βP (2)

wherein the content of the first and second substances,

n₀-the count rate of neutrons detected by the neutron detector in the absence of gadolinium;

n is the neutron counting rate detected by the neutron detector when the gadolinium concentration is P;

beta-a constant related to the structure of the detection device and the absorption cross section of gadolinium, wherein the constant can be determined by multiplying the absorption cross section, the gadolinium isotope ratio and the product of a measurement cavity;

p-gadolinium concentration.

(2) The formula can be transformed into:

lnn＝-βP+lnn₀ (3)

let Y be lnn, c₀＝lnn₀And then:

Y＝-βP+c₀ (4)

this is a linear equation, and coefficients β and c can be fitted using a linear fit method₀。

When beta P < 1, (2) can be expanded in two stages according to Taylor series:

let X be 1/n, C₀＝1/n₀，B₀＝β/n₀，A₀＝β²/2n₀And then:

X＝A₀P²+B₀P+C₀ (6)

this is a quadratic equation, and a quadratic fit method can be used to fit the coefficient A₀，B₀，C₀。

With incident neutrons as 10⁶s^-1The yield of neutrons emitted by the DT neutron generator, the detector is a He-3 proportional counting tube with the diameter of 2.5cm and the length of 15cm, the volume of the solution is 10L, and Gd is utilized₂(SO₄)₃·8H₂The Gd-containing solutions with different concentrations were prepared for O, and the calculated relationship curve is shown in fig. 2.

Therefore, a good relation curve between neutron counting and gadolinium concentration can be obtained between 0.0g/L and 0.8g/L, so that the method for calculating the gadolinium concentration in the measuring cavity in real time by using the pulse signal counting rate output by the neutron detector and the gadolinium concentration calculation equation is feasible and accurate when the gadolinium concentration is between 0.0g/L and 0.8g/L, and the corresponding gadolinium concentration measuring range can be adjusted by adjusting the neutron yield and the detector size in the system according to engineering requirements, so that the practical requirements can be better met.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.