Session: 05-05: Radiation Science and Nuclear Materials

Paper Number: 134218

134218 - Monte Carlo Simulation of Response of β-Delayed Neutron Inspection System for Fuel Cladding Damage 

Abstract: 

Damaged fuel elements can leak fission products into the coolant water system. The precursor nuclides (such as, ⁸⁷Br) will emit β-delayed neutrons, the half-life of nuclides ¹³⁷I (24.5s), ⁸⁷Br (55.6s), ⁸⁸Br (16.3s), which always are detected in the primary circuit coolant of pressurized water reactor (PWR) in order to inspect fuel cladding damage. The β-delayed Neutron Monitors usually only monitor neutron but not discriminate the background neutron, for example, the neutron from reaction D(γ，n)H, the contamination U fission and ¹⁷N decay. So, the β-n coincidence measurement should be used to monitor β-Delayed Neutron in the circuit coolant water. In this paper, one kind of β-Delayed Neutron Inspection System based on the β-n coincidence measurement was designed conceptually, and the efficiency of Neutron Monitors and the beta monitors were simulated by Monte Carlo code.    

 The neutron detection efficiency of traditional β-delayed Neutron Monitors was 2%-6%. In order to implement the β-n coincidence measurement, the detection efficiency of neutron monitors was needed to increase as far as possible. Two kinds of Neutron Monitors were designed and optimized through the Monte Carlo simulation (PHITS code). The [T-Deposit] and [T-Interact] tally cards of PHITS code were used to calculate the detector response, namely the efficiency, and [T-Product] was used to simulate the particles time distribution in detector. The first monitor mainly consisted of 12 He-3 proportional counters (10 atm gas pressure) which were evenly arranged in high density polyethylene (HDPE) moderator to provide neutron detection high-efficiency about 50% (spanning the energy range from 1 keV to 1 MeV) and flatness 1.1. In order to increase the neutron detection efficiency of ¹⁰B-coated counters, ¹⁰B-coated counters with multi-rings cathodes were simulated in different parameters including ¹⁰B-coated thickness and gas pressure. The final parameters were 1.5 um ¹⁰B-coated thickness and 0.5 atm P5 gas pressure. The second monitor mainly consisted of 108 B-10- coated counters and HDPE, which displayed neutron detection efficiency more than 30% and also flatness better than 1.1. Both two monitors were insensitive to gamma ray.  

   Considering the short range of beta particles in water, the beta monitors were designed as array detectors consisted of multiple thin-slice plastic scintillators, which were immersed in water in order to enlarge the detection efficiency. The thin-slice plastic scintillators were insensitive to gamma ray due to the intrinsic detection efficiency was nearly 2%. On the contrary, the intrinsic detection efficiency for high energy beta particles was almost 90%. In the water, detection efficiency for high energy beta of array detectors of thin-slice plastic scintillators was more than 20%.  

Presenting Author: Weihua Zhang Tsinghua University

Presenting Author Biography: 2023.7- present, Assistant Researcher, Tsinghua University.
Research on the radiation protection of reactor security, mainly including design of radiation monitors system of reactors.
Research on Boron Neutron Capture Therapy RBE and microdosimetry, including Monte Carlo simulation and experiments in the neutron and gamma radiation field.
2018.11 – 2022.11. Associate Researcher, Master's Supervisor, Institute of High Energy Physics, CAS.
Research on the neutron detection and radiation protection. Development of portable Single Sphere Neutron Spectrometer (SSNS) to detect neutron energy spectrum in near space and around nuclear facility. The SSNS was compact and low-power to mount in balloon cabin to detect atmospheric neutron energy spectrum during two flight tests in 2019 and 2020.
Research on the dosimetry and radiation effect. Development of Tissue-Equivalent Proportional Counter (TEPC) system and GEM-TEPC to study neutron microdosimetry and Relative Biological Effect (RBE). Development of kinds of free-air Ionization Chambers to monitor photon dose. Development of parallel Ionization Chamber to monitor proton beam for radiotherapy.
2008.08 – 2018.11. Associate Researcher (2015-2018), China Institute of Atomic Energy
Research on neutron microdosimetry and metrology. Development of TEPC system and GEM-TEPC to research the neutron/gamma microdosimetry and RBE in accelerator and reactor radiation fields. Development of Single Sphere Neutron Spectrometer based on NIM module electronics to measure the neutron energy spectrum. Investigation and design of neutron dosimeter and Linear Energy Transfer (LET) spectrometer.

Authors:

Weihua Zhang Tsinghua University
Liguo Zhang Tsinghua University
Jianzhu Cao Tsinghua University