CN212256936U

CN212256936U - Nuclear fuel burnup depth measuring device based on active neutron space intensity distribution

Info

Publication number: CN212256936U
Application number: CN202021690226.6U
Authority: CN
Inventors: 韦峥; 姚泽恩; 张宇; 黑大千; 伍晓勇; 吴璐; 王俊润; 马占文; 王桢; 任亮; 高艮涛
Original assignee: Lanzhou University; Nuclear Power Institute of China
Current assignee: Lanzhou University; Nuclear Power Institute of China
Priority date: 2020-08-14
Filing date: 2020-08-14
Publication date: 2020-12-29
Anticipated expiration: 2030-08-14

Abstract

The utility model discloses a nuclear fuel burns up degree of depth measuring device based on initiative neutron space intensity distribution, including compact D-D neutron source, neutron moderation body, gamma shield, toper neutron collimation pore and thermal neutron image detector system, compact D-D neutron source wraps up neutron moderation body and gamma shield outward in proper order, and the vertical toper neutron collimation pore that sets up big-end-up on the neutron moderation body of D-D neutron source top, the thermal neutron image detector system of upper end installation in toper neutron collimation pore. The utility model discloses the reaction cross-section of different elements is different among well hot neutron and the nuclear fuel, makes the neutron flux that the transmission passed the nuclear fuel component sample in the toper neutron collimation pore have the difference in the space, recycles the response model of hot neutron transmission intensity and fuel burnup and can survey nuclear fuel component burnup degree of depth spatial distribution and average burnup. The utility model has the characteristics of it is quick, accurate, harmless, good spatial resolution.

Description

Nuclear fuel burnup depth measuring device based on active neutron space intensity distribution

Technical Field

The utility model belongs to the technical field of high radioactive nuclear material nondestructive test, especially, relate to a nuclear fuel burns up degree of depth measuring device based on initiative neutron spatial intensity distributes.

Background

The fuel element is a core component of the nuclear reactor, the performance index of the fuel element directly reflects the safety and the economy of the reactor, the burnup marks the consumption degree of the nuclear fuel in the operation process of the reactor, and the deeper the burnup is, the more the nuclear fuel is fully utilized, so that the power generation cost can be reduced. However, the burnup cannot be infinitely deepened, otherwise the chain reaction is difficult to maintain. The accurate measurement of the burnup depth of the reactor fuel element has great effect on improving the efficiency and the economy of the reactor, and has very important significance in the fields of nuclear power stations, burnup control, nuclear guarantee and the like.

The measurement of nuclear fuel burnup is generally an estimation of the burnup of fuel elements by measuring certain nuclear species in fissile fuel elements, the burn-up depth is a quantitative measure of the total energy produced by a unit weight of nuclear fuel loaded into the core, and the measurement methods are mainly divided into Destructive Analysis (DA) and non-destructive analysis (NDA). Destructive Analysis (DA) refers to chemical dissolution of spent fuel components, and radiochemical analysis or mass spectrometer analysis of some fissile nuclides in the dissolution liquid to determine burnup; non-destructive analysis (NDA) refers to the determination of burnup by measuring gamma rays associated with the burnup of a certain nuclide in a fissile species directly with a gamma spectrometer or by measuring spontaneous or induced fissile neutrons. Destructive measurement has the characteristic of directness, but factors such as long time period of measurement, high requirement on the measurement environment, complex measurement procedure and the like are generally used as a supplementary measurement means for the spent fuel burnup measurement. The nondestructive measurement method is simple, the measurement time period is short, the measurement is reliable, the use is convenient, the fuel consumption measurement requirement and the day of the spent fuel suddenly increase along with the development of the nuclear power station and the continuous accumulation of the spent fuel, and the nuclear fuel consumption nondestructive analysis technology has obvious competitive advantages.

At present, foreign research institutions mainly develop high-resolution gamma spectrometry and passive neutron measurement in the aspect of non-destructive analysis technology of nuclear fuel burnup. High resolution gamma spectrometry is directed to a certain nuclear species (e.g., a nuclear species¹³⁷Cs), measuring the activity of the calculated nuclide by a detector, and directly estimating the burn-up depth of the fuel according to a calibration curve. In addition, the gamma radioactivity ratio of the two radionuclides is measured (e.g.¹³⁴Cs/¹³⁷Cs) can eliminate the influence of factors such as geometric factors and detection efficiency, and the measurement precision is improved. The passive neutron measurement method is also called as a passive neutron method, and the basic principle is that neutrons emitted by spontaneous fission and nuclear reaction of fuel after irradiation are measured by a high-efficiency neutron detector, so that relative fuel consumption information of nuclear fuel is obtained. Passive neutron measurement is the most common method, post-irradiation combustionThe material can produce new heavy isotopes, neutrons are emitted through spontaneous fission and (alpha, n) reaction, the neutron counting rate of the spent fuel assembly is measured by using a neutron detector, and the average burnup is obtained through a series of data analysis and processing, and the burnup value obtained by the method is relatively accurate.

The problems existing in the prior art are as follows: the Destructive Analysis (DA) technology is used for measuring the burning depth of irradiated nuclear fuel, has long time period, high requirement on the measuring environment, complex measuring procedure and other factors, and is generally used as a supplementary measuring means for the burning measurement of the spent fuel; the high-resolution gamma energy spectrum measuring method of the nuclear fuel burnup depth after irradiation is limited by low measuring efficiency and difficult discrimination of complex gamma spectrums, so that the measuring precision of the nuclear fuel burnup depth is low; the passive neutron measurement method of the burnup depth of the irradiated nuclear fuel is limited by a neutron detector with high detection efficiency, the neutron intensity is exponentially reduced along with the cooling time, and the correction work of the measurement data is difficult.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a nuclear fuel burns up degree of depth measuring device based on initiative neutron space intensity distribution aims at solving the problem that prior art exists among the above-mentioned background art.

In order to achieve the above object, the utility model adopts the following technical scheme:

the nuclear fuel burnup depth measuring device based on active neutron space intensity distribution comprises a compact D-D neutron source, a neutron moderating body, a gamma shield, a conical neutron collimation pore channel and a thermal neutron image detector system, wherein the compact D-D neutron source is wrapped with the hydrogen-containing neutron moderating body with a certain thickness, the gamma shield is wrapped on the periphery of the neutron moderating body, the radiation safety performance of the periphery of the device is guaranteed, and the environmental radiation dose equivalent rate of the shield body at the position of 30cm on the outer surface is smaller than the national safety standard of 2.5 mu Sv/h. A conical neutron collimation pore channel with a large top and a small bottom is vertically arranged on the neutron moderating body at a certain distance above the compact D-D neutron source and used for obtaining a quasi-parallel neutron beam, and a thermal neutron image detector system is mounted at the upper end of the conical neutron collimation pore channel.

Preferably, the lower end of the conical neutron collimation pore channel is located above a neutron output port of the compact D-D neutron source, and the distance between the lower end of the conical neutron collimation pore channel and the neutron output port of the compact D-D neutron source is 15 cm.

Preferably, the upper end of the conical neutron collimation pore canal is positioned at the boundary of a gamma shield, and the thermal neutron image detector system is positioned outside the gamma shield.

Preferably, the thickness of the neutron moderator is 15 cm.

Preferably, the thermal neutron image detector system comprises⁶LiF fluorescence conversion screen, reflector and CCD camera, the⁶The LiF fluorescence conversion screen is aligned to the upper end of the conical neutron collimation pore channel and used for detecting neutron beams, and an optical lens is arranged on the CCD camera.

Compare in prior art's shortcoming and not enough, the utility model discloses following beneficial effect has:

the utility model provides a nuclear fuel burns up degree of depth measuring device based on initiative neutron space intensity distribution utilizes compact D-D accelerator neutron source to provide the neutron, and D-D accelerator neutron source periphery sets up neutron moderation body and gamma shield, and D-D accelerator neutron source top sets up toper neutron collimation pore, and the neutron is surveyed by the detector system after moderation collimation, the utility model discloses the thermal neutron fluence in the imaging field of vision among the detector system is greater than 10⁴n/(cm²s), the space uniformity of neutron fluence is more than 95%, and the parallelism of thermal neutrons is better than 93%. The reaction cross sections of the thermal neutrons and different elements in the nuclear fuel are different, so that the neutron flux transmitted through a nuclear fuel element sample has difference in space, the thermal neutrons after the sample is transmitted are converted into a digital transmission image through a thermal neutron image detector, the two-dimensional spatial distribution of the thermal neutron transmission intensity is obtained, and the burning depth spatial distribution and the average burning rate of the nuclear fuel element are measured according to the established response model of the thermal neutron transmission intensity and the fuel burning rate. The utility model relates to a novel nuclear fuel burnup nondestructive analysis technique (NDA), have characteristics quick, accurate, harmless, good spatial resolution, provide the independent mashup of china for the online short-term test of china's nuclear fuel burnupAnd moreover, the safe and efficient development of nuclear energy in China is guaranteed.

Drawings

Fig. 1 is a schematic structural diagram of a nuclear fuel burnup depth measuring device based on active neutron spatial intensity distribution provided by an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a thermal neutron image detector system provided by an embodiment of the present invention.

In the figure: 1-compact D-D neutron source; 2-neutron moderators; a 3-gamma shield; 4-a conical neutron collimation channel; 5-thermal neutron image detector system; 501-neutron beam; 502-⁶LiF fluorescent conversion screen; 503-mirror; 504-optical lens; 505-CCD camera.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in 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.

Referring to fig. 1, the nuclear fuel burnup depth measuring device based on active neutron space intensity distribution comprises a compact D-D neutron source 1, a neutron moderating body 2, a gamma shielding body 3, a conical neutron collimation pore channel 4 and a thermal neutron image detector system 5, wherein the compact D-D neutron source 1 which has good radiation safety performance and is movable is adopted to provide exogenous neutrons, the D-D neutron yield is more than 10⁹n/s and neutron output stability of better than 99 percent, a compact D-D neutron source 1 is externally wrapped with a hydrogen-containing neutron moderator 2 (boron-containing polyethylene) with the thickness of 15cm, the compact D-D neutron source 1 can effectively moderate D-D fast neutrons of 2.45MeV into thermal neutrons, the proportion of the thermal neutrons is more than 85 percent, the compact D-D neutron source 1 is arranged in the middle of the hydrogen-containing neutron moderator 2, a gamma shield 3 is wrapped at the periphery of the neutron moderator 2 to ensure the radiation safety performance of the periphery of the device, and the environmental radiation dose equivalent rate at the position of 30cm of the outer surface of the shield is less than the national safety standard of 2.5 mu Sv/h. A conical neutron collimation pore channel 4 with a big top and a small bottom is vertically arranged in the neutron moderating body 2 at a certain distance above the compact D-D neutron source 1 and is used for obtaining a quasi-parallel neutron beam, and the lower end of the conical neutron collimation pore channel 4The thermal neutron image detector system is located above a neutron output port of the compact D-D neutron source 1, the lower end of the conical neutron collimation pore channel 4 is preferably 15cm away from the neutron output port of the compact D-D neutron source 1, the upper end of the conical neutron collimation pore channel 4 is located at the boundary of the gamma shield 3, the thermal neutron image detector system 5 is installed at the upper end of the conical neutron collimation pore channel 4, and the thermal neutron image detector system 5 is located outside the gamma shield 3. The length of the whole device is 1.8m, the width is 1.0m, and the height is 1.0 m. The thermal neutron image detector system 5 has good spatial position resolution up to 100 μm, and has a structure shown in FIG. 2 including⁶A LiF fluorescent conversion screen 502, a reflecting mirror 503 and a CCD camera 505,⁶the LiF fluorescence conversion screen 502 is aligned with the upper end of the conical neutron collimation channel 4 and is used for detecting the neutron beam 501 of the conical neutron collimation channel 4, and the CCD camera 505 is provided with an optical lens 504. Transmitting thermal neutrons of nuclear fuel⁶LiF interaction, nuclear reaction occurs⁶Li+n→³H+⁴He +4.78MeV to generate charged particles t and alpha, wherein the charged particles deposit energy on the crystal ZnS to excite atoms to emit fluorescence, the optical signal is reflected by the reflector 503 and enters the CCD camera 505, and the CCD camera obtains the transmission image information of the sample to be detected.

The utility model discloses a theory of operation:

the utility model discloses a compact D-D neutron source 1 provides the exogenous neutron, wrap up hydrogeneous neutron moderation body 2 outside compact D-D neutron source 1, wrap up gamma shielding body 3 in neutron moderation body 2 periphery, through the D-D fast neutron of the 2.45MeV of the output of compact D-D neutron source 1 of neutron moderation body 2 slowing down into thermal neutron or epithermal neutron, thermal neutron or epithermal neutron after the moderation get into the interior irradiation of toper neutron collimation pore 4 of vertical setting in compact D-D neutron source 1 top neutron moderation body 2, it is greater than 10 to shine the interior thermal neutron flux in the field of vision, it slows down the body 2 to shine the neutron flux of internal heat⁴n/(cm²S), the irradiated high radioactive nuclear fuel element is placed in an irradiation field, the neutron flux transmitted through the nuclear fuel element has difference in space due to different reaction cross sections of thermal neutrons and different elements in the nuclear fuel, the thermal neutrons transmitted through the nuclear fuel element are detected by a thermal neutron image detector system 5 at the upper end of a conical neutron collimation pore passage 4 and are converted into digital transmission through the thermal neutron image detector system 5And imaging to obtain two-dimensional spatial distribution of thermal neutron transmission intensity, and measuring the spatial distribution of the burnup depth of the nuclear fuel element and the average burnup according to the established response model of the thermal neutron transmission intensity and the fuel burnup.

The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, as any modifications, equivalents, improvements and the like made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims

1. The device for measuring the burnup depth of the nuclear fuel based on the active neutron space intensity distribution is characterized by comprising a compact D-D neutron source, a neutron moderating body, a gamma shield, a conical neutron collimation pore channel and a thermal neutron image detector system, wherein the compact D-D neutron source is wrapped with the hydrogen-containing neutron moderating body with a certain thickness, the gamma shield is wrapped on the periphery of the neutron moderating body, the conical neutron collimation pore channel with a large top and a small bottom is vertically arranged on the neutron moderating body at a certain distance above the compact D-D neutron source and used for obtaining quasi-parallel neutron beams, and the thermal neutron image detector system is installed at the upper end of the conical neutron collimation pore channel.

2. The active neutron spatial intensity distribution based nuclear fuel burnup depth measurement device of claim 1, wherein a lower end of the tapered neutron collimation channel is located above a neutron output port of the compact D-D neutron source, and a distance between the lower end of the tapered neutron collimation channel and the neutron output port of the compact D-D neutron source is 15 cm.

3. The active neutron spatial intensity distribution based nuclear fuel burnup depth measurement device of claim 2, wherein the upper end of the tapered neutron collimation aperture is located at a gamma shield boundary and the thermal neutron image detector system is located outside the gamma shield.

4. The active neutron spatial intensity distribution based nuclear fuel burnup depth measurement device of claim 1, wherein the neutron moderator has a thickness of 15 cm.

5. The active neutron spatial intensity distribution based nuclear fuel burnup depth measurement device of claim 1, wherein the thermal neutron image detector system comprises⁶LiF fluorescence conversion screen, reflector and CCD camera, the⁶The LiF fluorescence conversion screen is aligned to the upper end of the conical neutron collimation pore channel and used for detecting neutron beams, and an optical lens is arranged on the CCD camera.