CN1866408A - Online measuring method for burn-up level of fuel element of sphere type modular high-temperature gas-cooling reactor - Google Patents

Abstract

The invention relates to the technical field of nuclear reactor testing, and is characterized in that it contains the following steps in sequence: the host computer starts the burnup depth measurement program; the fuel elements are radiated and cooled; and the programmable logic controller controls the fuel elements to be sent to the same axis as the collimator. The programmable logic controller notifies the host computer to perform measurements; the high-purity germanium γ spectrometer measures the count of 0.661642 MeV γ rays emitted by ¹³⁷ Cs in the fission product during the decay process, and the host computer calculates the γ The counting rate of rays is determined based on the preset threshold value to determine whether it is necessary to discharge the core or return to the core to continue the cycle; the measurement results of the host computer are sent back to the main control system through the programmable logic controller. The present invention has the advantage of being non-contact and capable of online measurement of the gamma ray rate that is linearly related to the burnup depth.

Description

On-line measurement method for fuel element burnup depth of pebble bed modular high temperature gas-cooled reactor

technical field

The invention is used for the burnup depth measurement method of the fuel elements in the pebble bed type modular high-temperature gas-cooled reactor, and particularly relates to the technical field of on-line measurement.

Background technique

Modular high-temperature gas-cooled reactor (MHTGR) is a reactor type recognized by the international nuclear energy community as having good safety. Its research and development work began in the 1970s. Unlike gas-cooled reactors, modular high-temperature gas-cooled reactors use ceramic-coated pellet fuel. Helium is used as coolant. Helium is an inert gas with good chemical stability, no phase change, and good cooling performance, so the outlet temperature of MHTGR coolant can be very high.

The pebble bed modular high temperature gas-cooled reactor (PBMHTGR) adopts the fuel management method of non-stop continuous loading and unloading, which utilizes the rolling characteristics of spherical fuel elements to form a fluid pebble bed core, making new fuel Replenishment of components and discharge of spent fuel components can be carried out continuously without stopping the stack. The fuel elements of PBMHTGR are unloaded as spent fuel elements through the fuel loading and unloading (FCA) system for multiple times through the core to achieve unloading burnup. The fuel management method of multiple passes can realize the average burnup depth of spent fuel elements.

The world's first pebble bed high temperature gas-cooled reactor (PBHTGR) is the AVR reactor in the Federal Republic of Germany. AVR uses spherical graphite fuel elements with a diameter of 6cm made of coated granular fuel, and 100,000 spherical fuel elements form a pebble bed reactor. core. The thermal power of the AVR reactor is 46MW, and the electric power is 15MW. It reached criticality for the first time in August 1966, and was connected to the grid for power generation on December 17, 1967. The AVR originally designed the helium outlet temperature to be 850°C. In February 1974, the helium outlet temperature was raised to 950°C. It was shut down in December 1988 and has been in operation for 21 years.

In the 1970s and early 1980s, the design of high-temperature gas-cooled reactor commercial power plants in the world was mainly developed in the direction of large-scale. After the Three Mile Island and Chernobyl nuclear power plant accidents, the United States launched an advanced reactor type development plan, making the modular high-temperature gas-cooled reactor the main development direction of high-temperature gas-cooled reactors. The basic feature of the modular high-temperature gas-cooled reactor is that under any accident conditions, the residual heat of the reactor core can be carried out in a passive way (that is, relying on natural laws such as gravity and natural circulation). would exceed the permitted limit. In this way, the possibility of core meltdown can be avoided, and the radioactive dose outside the nuclear power plant is still within the limit value under the condition of a serious accident, without using the emergency plan outside the site. Therefore, the modular high-temperature gas-cooled reactor is an advanced reactor type with passive safety.

The 80MW electric power HTR-Module developed by Siemens Interatom is the first design concept of small-capacity modular high-temperature gas-cooled reactor in the world. The mechanism is derived to ensure that the maximum temperature of the core fuel elements does not exceed the temperature limit under any accident conditions, avoiding the possibility of core melting. HTR-Module uses 6cm-diameter graphite spherical fuel elements made of coated granular fuel, and 360,000 spherical fuel elements are piled up to form a pebble bed core. In order to realize the passive load-out of residual heat from the core, the diameter of the core is limited, otherwise the maximum temperature of the fuel in the core may exceed the limit value of 1600°C.

Since the 1970s, China has carried out a lot of related work in the field of high-temperature gas-cooled reactor technology, and has accumulated a certain amount of technology and experience. Considering the excellent safety characteristics and advanced performance of high-temperature gas-cooled reactor, China regards it as an advanced reactor type, and includes related technology development work in the national 863 high-tech research and development plan. With the Institute of Nuclear Energy and New Energy Technology of Tsinghua University as the main implementation unit of the project, an experimental reactor (HTR-10) with a thermal power of 10MW was built at the Changping site of the institute. Its basic structure is shown in Figure 2. The design of HTR-10 follows the design principles of PBMHTGR, and the following main technical and safety features basically reflect the main features of PBMHTGR:

(1) The HTR-10 core is composed of 27,000 graphite spherical fuel elements, and the fuel elements are composed of coated granular fuel. The coated fuel particles are miniature balls with a diameter of only 0.9 mm, and the core is uranium dioxide (UO ₂ ) particles with a diameter of 0.5 mm. UO ₂ particles are coated with a layer of low-density pyrolytic carbon, two layers of high-density pyrolytic carbon and a layer of silicon carbide. The coating layer fully retains the fission products produced in the _UO2 particles in the coated particles, and can withstand the internal pressure generated by the gas fission products.

The coated particle fuel is evenly dispersed in the inner layer of the graphite sphere, with a diameter of 5 cm. Its outer layer is a graphite shell to protect the coated particulate fuel from mechanical damage. The outer diameter of the fuel element is 6cm, and each fuel element contains an average of 8000 coated particle fuels.

(2) The most unique feature of the pebble bed high-temperature gas-cooled reactor is the fuel loading and unloading (FCA) system, whose structure is shown in Figure 1. HTR-10 adopts the continuous loading and unloading of fuel during the operation of the reactor, and the backup reactivity of the reactor (residual reactivity of the cold clean core) is small. The initial state core is composed of 57% fuel elements and 43% pure graphite balls. During the operation, the fuel management method of passing through the core core is adopted to gradually discharge the graphite balls unloaded from the core; The unloading burnup depth (i.e. the average burnup depth reached when the spent fuel elements are unloaded from the core) is 80GWD/tU (1GWD/tU=10 ⁹ W·day/tU), if the measured burnup of the fuel elements exceeds 72GWD/tU, it is discharged as spent fuel elements, and fuel elements smaller than this value are sent back to the core to continue circulation. Therefore, it takes an average of 5 cycles for each fuel element to be discharged from the core, so as to achieve a higher burnup depth and ensure a more uniform power distribution in the core, and also make the deviation of the burnup distribution of the discharged spent fuel elements smaller. Small.

Through the above analysis of PBMHTGR, the functional requirements of PBMHTGR for its FCA system can be summarized as follows:

(1) Under various working conditions of the reactor, fuel loading and unloading operations can be carried out without stopping the reactor;

(2) The fuel loading and unloading cycle realizes the following functions:

i) replenishing the core with new fuel elements;

ii) The fuel elements are unloaded from the core, and the fuel elements are changed from a stacked shape to a single arrangement through a special "single-arranger" device. During this process, it is necessary to prevent the formation of bridging blocks between the fuel elements and prevent them from flowing. Condition;

iii) Integrity testing of fuel elements to screen out fuel elements and fragments damaged by impacts during loading and unloading;

iv) Carry out burnup measurement of fuel elements one by one, discharge the spent fuel elements that have reached the unloading burnup into the spent fuel storage tank, and transport the components that have not reached the unloading burnup back to the core;

v) During the transition from the initial state core to the equilibrium state core, distinguish and identify the mixed graphite balls or graphite balls mixed with neutron poisons in the core, and exclude them one by one;

(3) In addition to relying on the rolling of gravity, the delivery of fuel elements can also be transported in the pipeline by pneumatic force. The inner wall of the delivery pipeline should be smooth, and the slope of the pipeline can ensure that the spherical elements can freely roll by gravity;

(4) To replenish new fuel elements into the reactor, or to discharge spent fuel elements out of the reactor, it is necessary to isolate and switch the atmosphere inside and outside the reactor, so as to minimize the leakage of coolant (helium) or the mixing of air during this process;

(5) The irradiated fuel elements are highly radioactive. During the loading and unloading process, the radiation impact on the operators should be prevented. In case of equipment failure, shielding facilities should be provided to ensure that personnel can approach for maintenance;

(6) The new fuel elements loaded, the spent fuel elements discharged, the damaged fuel elements discharged, the graphite balls discharged and the fuel elements recycled back to the core should be accurately counted.

To sum up, the technical characteristics of HTR-10 inevitably require the designer to propose an accurate and reliable fuel element burnup depth measurement method that can meet the online operation, and the method must meet the following requirements:

(1) The measurement results must be able to directly reflect the burnup depth value;

(2) The fuel element shall not be damaged during the measurement process;

(3) Allowing the reactor to operate in any manner and fuel elements to circulate in any manner;

(4) The measurement range of burnup depth is 100~105MWD/tU (1MWD/tU=10 ⁶ W·day/ton of uranium);

(5) The relative error of measurement is not greater than ±2%, and when the burnup depth is low, the relative error of measurement is allowed to be ±10%;

(6) The measurement time is about 60 seconds;

(7) It can run continuously for a long time;

(8) The measurement results must be sent to the FCA system and the reactor control system in real time, with high transmission rate and long transmission distance.

There are two types of fuel consumption units: (1) fima (Fima); (2) MWD/tU.

Among them, fima is the ratio of the number of fissioned atoms to the total number of heavy metal atoms in the initial charge, dimensionless:

In the formula: C ₅ is the enrichment degree of ²³⁵ U (nuclear fuel purity);

Φ is thermal neutron flux (the number of thermal neutrons entering a suitable small sphere centered on a certain point in space per unit time);

T is the irradiation time of fuel elements in the core;

σ _f is the microscopic fission cross section of ²³⁵ U (the probability of nuclear fission of an incident particle when there is one nucleus per unit area);

∑ _f is the macroscopic fission cross section of ²³⁵ U (the product of σ _f and the number of nuclei in the unit volume of U);

V _ball is the volume of the fuel element;

5 is the number of grams of U contained in each fuel element.

N _U is the number of atoms contained in each gram of U:

In order to intuitively illustrate the basic physical concepts, assuming that C ₅ , Φ, and T are all constants, the burnup depth expression is obtained:

In the formula: E _f is the energy released by each fission:

E _f = 197 MeV = 0.365 x 10 ^-21 MWD.

Therefore, the relationship between fima and MWD/tU can be obtained:

$\frac{\mathrm{<span\; class="notranslate">\; MWD</span>}}{\mathrm{<span\; class="notranslate">\; tU</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.927</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}\mathrm{<span\; class="notranslate">\; fima</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

It can be seen that, for a specific fuel (σ _f and C ₅ are known constants), the burnup depth is actually directly related to the integrated flux ΦT in the fuel element, and is also directly related to the fission products. Therefore, by measuring some fission products in the fuel element, the burnup depth of the fuel element can be estimated. From the perspective of measurement methods, it can generally be divided into two categories: destructive method measurement and non-destructive method measurement.

The destruction method measurement is to chemically dissolve the spent fuel elements, and perform radiochemical analysis or mass spectrometer analysis on certain fission nuclides in the solution to determine the burnup depth. The destructive method has the characteristics of directness and accurate and reliable data. However, during the measurement process of this method, the exposure of the staff is large, the measurement procedure is complicated, the work is difficult, the analysis period is long, the environmental requirements are high, and the analysis cost is high. As an auxiliary means of measuring spent fuel elements.

Non-destructive measurement usually directly uses a gamma spectrometer to measure the gamma rays related to the burnup depth of a certain nuclide in the fission products to determine the burnup depth. The principle of non-destructive measurement is clear, the operation is convenient, the result is reliable, and it has been widely used. Its characteristics of not destroying the fuel assembly are obviously suitable for the requirements of HTR-10.

Most of the burnup depth measurement methods developed at home and abroad link the burnup with fission products. However, none of the methods currently in use can fully meet the basic requirements of HTR-10 for burnup depth measurement, such as:

(1) A method of measuring short-lived fission products with a gamma spectrometer. It has been seen in the literature: measuring the decay rate of ¹⁴⁰ La and ¹⁵⁴ Eu (number of decays per unit time) and so on. Due to the short lifetime of the above-mentioned nuclides, their decay rate is not only related to the specific history of radiation (such as the power fluctuation of the stack, the fuel elements are in different radial regions when they pass through the core each time, etc.), but also strongly depends on the cooling time , which complicates the relationship between the measured quantity and the burnup, and cannot directly express the burnup depth value;

(2) Determination methods of chemistry (separation of specific fission products). This type of method usually requires destructive measurement of fuel elements, which does not meet the requirements of non-destructive measurement and online and real-time;

(3) The method of neutron measurement. This type of method may require an additional ²⁵² Cf neutron source, or the number of neutrons emitted by the fission product ²⁴⁴ Cm is small; in addition, in the case of low uranium enrichment in a single fuel element, excessive errors will be introduced; Meanwhile, ²⁴⁴ Cm becomes the main neutron emitter only after the cooling time is longer than 1.5 years. Therefore, it is difficult for this type of method to meet the basic requirements of timeliness and accuracy.

Contents of the invention

In order to meet the requirements of HTR-10 for burnup depth measurement, the present invention proposes a non-destructive method suitable for PBMHTGR fuel element burnup depth measurement. The solution adopted by the present invention to solve its technical problems is: taking high-purity germanium gamma energy spectrometer, tungsten collimator, and programmable controller (OMRON C200HS) as the core system equipment to form the basic structure of the burnup depth measurement and its control system , as shown in Figure 3; at the same time, the REXX script language is used to compile the automatic measurement software, which is used as the control and measurement software environment to design the online automatic measurement process; the above-mentioned hardware and software systems can realize the online measurement process of the burnup depth.

In principle, this method uses a high-resolution gamma spectrometer to measure the 0.661642 MeV gamma rays emitted by ¹³⁷ Cs in the fission products during the decay process to calculate the burnup depth of the fuel element. The total amount of ¹³⁷ Cs in the fission products is:

In the formula: _t1 is the cooling time after the end of irradiation;

Y ₇ is the share of ¹³⁷ Cs in the total fission products;

λ ₇ is the transformation constant of ¹³⁷ Cs.

It can be known from formula (1) that the total amount of ¹³⁷ Cs represented by formula (2) is proportional to the burnup depth, and its proportional coefficient is a known constant. The total amount of ¹³⁷ Cs can be determined by measuring the rate of γ-rays emitted by ¹³⁷ Cs (such as γ-rays with an energy of 0.661642 MeV), that is, the detection rate of ¹³⁷ Cs is:

In the formula: f is the self-absorption correction factor in the spherical source;

Ω is the solid angle of the spectrometer detector to the radioactive source after passing through the tungsten collimator;

ε is the detection efficiency of the spectrometer detector to gamma rays with an energy of 0.661642 MeV;

RI ₇ is the relative share of γ-rays with an energy of 0.661642 MeV in the decay of ¹³⁷ Cs.

The present invention is characterized in that said method comprises the following steps in sequence:

Step (1). Initialization

Install Genie 2000 spectrum processing software in the host computer, and start the REKX program for automatic measurement of burnup depth;

Step (2). After the fuel elements are irradiated in the core, they flow into the unloading pipe at the lower part of the core through the dequeue, and are cooled for about 40 days;

Step (3). After the programmable logic controller confirms that the last lifting operation is completed, it issues an instruction to start the broken ball separator, and sends the current fuel element to the ball receiving position of the lifter after sorting the broken balls;

Step (4). The programmable logic controller controls the lifter to send the fuel element from the receiving position to the lifting position, so that the fuel element and the collimator are on the same axis;

Step (5). The programmable logic controller sends a counting start command to the host computer, and under the control of the host computer, the following measurement process is completed: the gamma rays emitted by the nuclide produced by fission in the current fuel element during the decay process The solid angle defined by the collimator reaches the high-purity germanium crystal in the energy spectrometer and produces an ionization effect; under the action of the bias high-voltage power supply, it is collected by the input end of the preamplifier of the energy spectrometer into a charge pulse, which is amplified into a voltage pulse with low output impedance; after a long cable to the main amplifier of the energy spectrometer, it continues to amplify into a positive pulse signal of about 10V; enters the multi-channel pulse amplitude analyzer of the energy spectrometer, and is grouped according to the pulse height; The pulse amplitude spectrum after pulse height grouping is sent to the host computer for processing including dead time correction and background subtraction, and finally the count rate of 0.661642MeV gamma rays emitted by ¹³⁷ Cs in the decay process within 60s is obtained. R ₇ means; the relationship between R ₇ and fuel consumption (proportional to the irradiation time T) is calculated by the following formula:

Among them, f is the self-absorption correction factor in the spherical source;

Ω is the solid angle of the spectrometer detector to the radioactive source after passing through the tungsten collimator;

ε is the detection efficiency of the spectrometer detector to gamma rays with an energy of 0.661642 MeV;

RI ₇ is the relative share of γ-rays with an energy of 0.661642 MeV in the decay of ¹³⁷ Cs;

Y ₇ is the share of ¹³⁷ Cs in the total fission products;

V _ball is the volume of the fuel element;

Φ is thermal neutron flux, which is equal to the number of thermal neutrons entering a suitable small sphere centered on a certain point in space per unit time;

λ ₇ is the transformation constant of ¹³⁷ Cs;

T is the irradiation time of fuel elements in the core;

_t1 is the cooling time after the end of irradiation;

∑ _f is the macroscopic fission cross section of ²³⁵ U, which is equal to the product of σ _f and the number of nuclei in the unit volume of uranium, and this σ _f is the microscopic fission cross section of ²³⁵ U, which is equal to the probability of nuclear fission of an incident particle when there is one nucleus per unit area;

Step (6). After the above measurement process is completed, the count rate R ₇ of the 0.661642 MeV gamma rays emitted by ¹³⁷ Cs during the decay process within 60 s is obtained, and R ₇ is compared with the count rate threshold calculated according to the set burnup , to determine whether it is necessary to discharge the core or return to the core to continue the cycle;

Step (7). The measurement results are stored in the local historical database in real time and a report is generated, and the fuel consumption measurement results are sent to the programmable logic controller and the main control system DCS.

Choosing this method has the following advantages:

(1) Comply with the principle of non-destructive measurement;

(2) The half-life of ¹³⁷ Cs is as long as 30.2 years, the influence of cooling time can be ignored, and it is also conducive to further separation from other nuclides;

(3) The neutron cross-section of ¹³⁷ Cs (the effective cross-section where the nucleus interacts with neutrons) is small and will not be consumed by the neutron field in the core, so the operation mode of the reactor and the circulation mode of the fuel elements are not affected. Influence;

(4) There is a single value relationship between the measurement results and the burnup depth.

Description of drawings

Figure 1. Schematic diagram of HTR-10 fuel loading and unloading system; 1- core; 2- single train; 3- glove box; 4- crushed ball sorter; 5- pulse tank; 8-burnup depth measuring device; 9-dispenser; 10-lid sealing mechanism; 11-spent fuel shipping tank; 12-graphite component container; 13-ball receiving position; 14-lifting position; ;51-electric isolation valve; 52-solenoid valve; 53-counting sensor; 54-electromagnetic slide valve;-6-06-fresh fuel charging chamber;-6-09-reactor compartment; Compartment; -15-01-spent fuel storage; -15-07-burnup measurement room; -15-08-fuel loading and unloading room;

Figure 2. HTR-10 reactor structure; 16-control rod driving device; 17-absorption ball storage tank; 18-helium circulation fan; 19-heat shield; 20-top reflector; 21-cold helium gas header; 22 -Steam generator heat transfer tube; 23-pebble bed core; 24-intermediate heat exchanger; 25-side reflection layer; 26-core shell; 27-reactor pressure shell; 28-steam generator pressure shell; 29- Bottom reflection layer; 30-hot gas conduit; 31-hot helium gas header; 32-support structure of reactor internals; 33-unloading device; 34-hot gas conduit pressure shell;

Figure 3. Schematic diagram of the fuel consumption depth measurement system of the fuel handling system; 35-lifter; 36-lift position; 37-baffle; 38-fuel element; 39-tungsten collimator; source; 42-multi-channel pulse amplitude analyzer; 43-gateway; 44-Ethernet card; 45-Ethernet card; 46-host computer; 47-RS-232C interface; 48-RS-232C interface; 49-OMRON C200HS; 50 - Concrete walls;

Figure 4. Structural block diagram of the fuel handling system control system;

Figure 5. Genie 2000 software system architecture;

Figure 6. Flowchart of online measurement method for burnup depth;

Figure 7. Schematic diagram of the built-in processing environment of the Windows operating system;

Figure 8. Schematic diagram of the REXX binding processing environment.

Detailed ways

In order to realize the above-mentioned burnup depth measurement process, this method equips the FCA system of HTR-10 with high-purity germanium gamma energy spectrometer, tungsten collimator, and programmable controller (OMRON C200HS) three core system equipment:

(1 ⁾ High-purity germanium gamma energy spectrometer: fission products emit gamma rays that are nearly a hundred times stronger than ¹³⁷ Cs. The high-purity germanium gamma energy spectrometer separates the gamma line of ¹³⁷ Cs. The relevant parameters are designed as follows:

i) Detector

P-type high-purity germanium detector, placed vertically, allowing temperature cycle, detection efficiency 19-20%, energy range for gamma-ray detection: 40KeV-10MeV;

Energy resolution: 1.8KeV～1.75KeV for γ of 1.33MeV;

Gaussian wave pattern: FW0.1M/FWHM=1.85～1.9, FW0.02M/FWHM=2.40～2.65, peak-comp ratio is 50.

ii) Multi-channel buffer

Amplifier gain: 4 to 1000 times, temperature coefficient of gain <±0.005%/℃. Effective input such as noise < 4.5μVRMS, integral nonlinearity ≤ ± 0.025%, anti-accumulation (integral) forming time is 1μs.

ADC processing time < 5μs, count rate > 10 ⁵ /s.

Digital spectrum stabilization, long-term stability ≤±0.018%, that is, <1 channel/24 hours, the number of channels is 16384, the channel width is ~0.5KeV, and there is an adjustable threshold for low-energy screening. High voltage power supply ±5000V, input FET protection.

Parameter adjustments such as amplifier gain, analog-to-digital conversion gain, amplifier forming time, digital voltage regulator setting, and zero pole adjustment are controlled by the host computer.

iii) Host computer and processing software

The upper computer CPU adopts Pentium 4 3.0GHz, and the operating system is Microsoft Windows 2000 ProfessionalSP4. The processing software is Genie 2000 spectrum software system, and its functions include: spectrum analysis, background fitting, dead time correction, calculation of peak area, and arbitrary opening of energy windows.

iv) cooling

Use a 30 liter Dewar or electric cooler.

(2) Tungsten collimator

The function of the collimator is to limit the solid angle of the spectrometer detector to the source. On the one hand, only direct rays pass through its inner cavity, that is, "transparent", and reach the spectrometer detector (the sensitive area) ; On the other hand, "all" block (ie "black") any rays that do not enter the inner cavity, preventing it from reaching the energy spectrometer detector. In order to achieve "transparency", the collimator adopts a double-cone geometric profile; in order to ensure "blackness", the collimator is finished by cutting high-density alloy material WNiFe.

(3) Programmable controller (OMRON C200HS)

The overall design of HTR-10 puts forward requirements for the burnup depth measurement system far beyond the requirements for the instruments in the laboratory, and the requirements for its control system are more stringent:

i) Continuous and stable operation;

ii) Multi-corner communication, control and interlocking: "Multi-corner" refers to including the reactor main control system DCS - FCA system programmable logic controller - host computer - high-purity germanium gamma spectrometer;

iii) Higher field signal transmission rate;

iv) Longer on-site signal transmission distance.

The structure of the FCA system control system is shown in Figure 4. In this method, the fuel consumption depth measurement system is connected to the local area network, and the local area network uses the baseband digital signal transmission of CSMA/CD (carrier sense multiple access and conflict detection) technology, the transmission distance reaches 1000M, and the transmission rate reaches 10 Mbit/s. Connect with coaxial cable RG62A/U.

In this method, the control system adopts the PLC product C200HS of Japan OMRON Company, and C200HS is a new type of PLC product developed by OMRON Company on the basis of its small PLC product C200H. C200H has the characteristics of modularization, bus type and high performance, and adopts a compact overall structure. The CPU unit is its core, and the CPU unit includes system power supply, microprocessor, storage system, control logic, bus interface and other interface circuits. The I/O system of C200H adopts a modular structure, and all I/O modules are connected to the CPU unit through the standard bus SYSBUS. The maximum number of I/O points is 480 points, supports remote I/O system, can expand its I/O points to 1792 points, and has the highest I/O density in the same size. C200H has strong adaptability and flexible application. Although it is a small PLC, it provides many functions of a large PLC configuration, especially in terms of processing speed, I/O system, network communication capability and anti-interference ability. The performance of C200HS has many improvements compared with C200H, but it is still consistent with C200H in terms of structure, working method, command system, I/O unit, etc., which makes C200HS and C200H have good compatibility characteristics.

The basic composition of C200HS and the optional modules of this method:

Provides the installation rack (motherboard) for the system bus and module slots;

·CPU unit;

· User memory unit;

· Handheld programmer;

·Basic I/O unit;

Position control unit NC111: The position control unit is one of the special function I/O units of C200HS PLC, and it is an intelligent unit dedicated to position control. The position control unit is suitable for stepping motor or servo motor driver with pulse input. On the one hand, it can independently output pulses to control the stepping motor or servo motor to drive the controlled point to move. On the other hand, it can accept the control instructions and control sent by PLC. parameters, complete the corresponding control actions, and return the results and status information to the PLC. Among them, NC111 is used for single-coordinate control, and this method uses NC111 as the position control unit of the lifter.

·Communication module

On the basis of completing the measurement system and control system architecture, according to the FCA system design principle and sub-system operating procedures in HTR-10, this method optimizes the operation logic relationship of the FCA system, and designs the online automatic measurement software for the fuel consumption depth to realize the fuel consumption Automatic operation of depth measurement process and automatic database building of measurement results. On the one hand, it reduces the possibility of misoperation due to human factors, and on the other hand, it improves the operating efficiency and reliability of the system.

The burnup depth automatic measurement software runs on the host computer. This software is based on the development toolkit provided by Genie 2000 spectrum software system, and is developed on the host computer by using the REXX script language. Genie 2000 is a comprehensive nuclear measurement tool set dedicated to multichannel spectrum acquisition and analysis (Multichannel Analyzers, MCA). Its system architecture is shown in Figure 5. In addition to standard functions such as MCA control, spectral line display and adjustment, routine analysis and reporting, Genie 2000 also provides comprehensive spectral line analysis for α and γ spectrometers, quality assurance and overall support for special professional applications.

The core of the Genie 2000 software system is the virtual data manager (Virtual Data Manager, VDM) module. The task of VDM is to manage all information flows in the system and complete the communication with data files and MCA equipment. The user layer application software communicates with the VDM through the internal processing communication (Inter Process Communication, IPC) layer. IPC provides support for stand-alone and network users. Users can combine their own needs through the built-in processing environment of the operating system or the binding processing environment. analysis, both processing environments are based on the same computing modules.

The REXX language was born in the IBM UK Science Center. It was originally used for the Conversation Monitor System (CMS) component of IBM's general-purpose virtual machine (Virtual Machine, VM) operating system. Its design motivation is to refer to the PL/I language development An interpreted language that is easier to use than it was developed to overcome the shortcomings of IBM's command language at that time. The MS Windows operating system is associated with MS-DOS as the basic instruction processing environment, as shown in Figure 7. It is undeniable that DOS cannot show satisfactory performance in terms of interactivity, computing power, logic processing, branching, etc. As an "instruction filter", REXX directly sends the instructions that Windows itself can run to the system instruction processor, while REXX syntax instructions are interpreted by the REXX instruction processor as instructions that Windows can run, and then sent to the operating system for processing, as shown in the figure 8. S561 (Genie 2000 binding program support module), as an optional part of the huge application software package of Genie 2000 software system, provides a REXX script command processor for advanced automatic process development. Therefore, this method adopts REXX script language to compile ASCII command files to customize the automatic measurement process of burnup depth.

The automatic measurement process of burnup depth is shown in Figure 6:

(1) Initialization of the burnup depth measurement process (hereinafter referred to as "measurement process");

(2) The measurement process enters the monitoring state, waiting for the programmable logic controller burnup depth measurement command (hereinafter referred to as "combustion test command");

(3) After the lifter receives the fuel element at the ball receiving position, it sends the fuel element to the lifting position;

(4) After the lifter reaches the ball-catching position, the programmable logic controller prompts the operator that the current operating state is "permissible fuel consumption depth measurement", and sends a fuel measurement command to the measurement process through the communication interface;

(5) After receiving the instruction, the measurement process calculates the count rate of 0.661642MeV gamma rays emitted during the decay of ¹³⁷ Cs within the specified time according to the preset acquisition and analysis algorithms and parameters in the initialization process, and displays the measurement process in real time;

(6) After the measurement and analysis process ends, the measurement process automatically saves the measurement results of the current fuel element locally, and the data file format is a .cnf file;

(7) According to the measurement result, the measurement process transmits the measurement result to the programmable logic controller through the communication interface;

(8) After the programmable logic controller receives the measurement results, it prompts the operator to measure the current type of element (fuel element, spent fuel element, graphite ball), and performs corresponding operations according to the processing commands of different types of elements (lifting to the core, unload);

(9) After the PLC confirms that the lifting or unloading operation of the current element ball is completed, the signal of the burnup depth measurement result is reset to the initial state, and the process returns to step (2) to continue to monitor the PLC instructions and prepare Next burnup measurement.

Claims (1)

1. spherical-bed MHTR fuel element burn-up level On-line Measuring Method is characterized in that, described method contains following steps successively:

Step (1). initialization

Genie 2000 frequency spectrum processing softwares are installed in host computer, and are started the automatic measure R EXX program of burn-up level;

Step (2). fuel element passes through irradiation in reactor core after, in single-row device flow to the discharge duct of reactor core bottom, through about 40 days cooling;

Step (3). programmable logic controller (PLC) confirm to finish once promote operation after, send instruction and start broken bulb spacer, current fuel element is delivered to the lifter position of receiving after broken ball sorting;

Step (4). this programmable logic controller (PLC) controls lifter is delivered to fuel element and is promoted the position from the position of receiving, fuel element and collimating apparatus are on the same axis;

Step (5). this programmable logic controller (PLC) sends the counting sign on to host computer, under this PC control, finish following measurement flow process: the solid angle that the gamma-rays that the nucleic that produces owing to fission in the current fuel element sends limits through collimating apparatus in decay process, arrive the HpGe crystal in the energy spectrometer, produce ionisation effect; Under the effect of biasing high-voltage power supply, be gathered into charge pulse by the input end of the prime amplifier of energy spectrometer, after amplifying, become potential pulse, and have low output impedance; Continue to be enlarged into the positive pulse signal of about 10V to the main amplifier of energy spectrometer through long cable; Enter the multichannel pulse scope-analyzer of energy spectrometer, divide into groups according to pulse height; Pulse amplitude spectrum after degree of the leaping high grouping of feeling the pulse is delivered to the processing that host computer comprises that the dead time is revised, deducts background, finally obtain ¹³⁷The counting rate of the gamma-rays of the 0.661642MeV that Cs is launched in decay process in 60s used R ₇Expression; R ₇Calculated by following formula with the relation of burnup, burnup is proportional to exposure time T:

Wherein, f is the self-absorption modifying factor in the spherical source;

Ω is by behind the tungsten collimator, the solid angle that the energy spectrometer detector is opened radioactive source;

ε is that the energy spectrometer detector is the gamma-ray detection efficiency of 0.661642MeV to energy;

RI ₇For energy is that the gamma-rays of 0.661642MeV accounts for ¹³⁷The relative share of Cs decay;

Y ₇For ¹³⁷Cs shared share in gross-fission-product;

V _BallVolume for fuel element;

Φ is a thermal neutron flux, and equaling to enter in the unit interval with the space point is that center suitable spherular pined for subnumber;

λ ₇For ¹³⁷The disintegration constant of Cs;

T is the exposure time of fuel element at reactor core;

t ₁Be the cool time after the irradiation end;

∑ _fFor ²³⁵The macroscopic fission cross section of U equals σ _fWith the product of nuclear number in the uranium unit volume, this σ _fFor ²³⁵The microscopic fission cross section of U, the probability of a particle generation of incident nuclear fission when equaling unit area an atomic nucleus being arranged;

Step (6). above-mentioned measurement flow process obtains after finishing ¹³⁷The counting rate R of the gamma-rays of the 0.661642MeV that Cs is launched in decay process in 60s ₇, with R ₇With according to setting counting rate threshold ratio that burnup calculates, determining whether needs to discharge reactor core or returns reactor core and continue circulation;

Step (7). measurement result is deposited in local historical data base in real time and generates report, simultaneously the burnup measurement result is sent programmable logic controller (PLC) and master control system DCS.

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