Session: 05-05: Radiation Science and Nuclear Materials

Paper Number: 132066

132066 - Awcc Simulations Based on Monte Carlo Code Rmc 

Abstract: 

Neutron multiplicity measurement technology exploits the temporal correlation of fission neutron emission in nuclear materials. It utilizes mathematical tools to elucidate the processes of fission neutron generation, multiplication, and detection within nuclear materials. This process yields the point model equation, enabling the inversion of nuclear material mass based on neutron multiplicity counting. Due to differing spontaneous fission neutron yields of uranium and plutonium nuclear materials, neutron multiplicity analysis methods are categorized as active and passive. Passive methods for neutron multiplicity measurement primarily focus on Pu materials, where neutrons originate from ²⁴⁰Pu spontaneous fission neutrons, ²³⁹Pu induced fission neutrons, and neutrons produced by (α, n) reactions. On the other hand, active methods for neutron multiplicity measurement primarily target uranium materials, where neutrons mainly originate from ²³⁵U induced fission neutrons and external source random neutrons, with a minimal contribution from ²³⁸U spontaneous fission neutrons. Due to the higher spontaneous fission rate of plutonium, passive measurement methods have been developed and implemented. However, for uranium materials with a lower spontaneous fission rate, active measurement methods are essential. Existing Active Well Coincidence Counters (AWCC) can perform active neutron multiplicity measurements for uranium material mass. However, challenges such as low detection efficiency and significant accidental coincidences from Am-Li neutron sources persist. In order to enhance the efficiency and accuracy of uranium material measurements, in-depth research into active neutron multiplicity measurement methods is crucial. This paper, based on the independently developed Monte Carlo program RMC, models and analyzes the AWCC device, focusing on the active method. The study investigates active neutron multiplicity counting using two methods provided by RMC. The first method involves capturing output events in particle history and processing them using a multiplicity shift register. By setting pre-delay time, gate width, and long-delay time, neutron multiplicity counting is obtained. The second method involves analyzing the time sequence of neutrons captured in a specified detector element for a specific isotope at the end of each neutron history. Pre-delay time and gate width are also set to achieve neutron multiplicity counting. Both methods yield satisfactory results for single, double, and triple counting rates. Additionally, the study calculates the parameters of the point model equation and analyzes the impact of different physical parameters, such as pre-delay time and gate width, on the results. Furthermore, improvements are made to the point model equation for active neutron multiplicity counting, yielding promising results. This demonstrates the capability of the RMC program, expands its application in this field, and provides valuable insights for the design of subsequent experimental instruments.

Presenting Author: Yuanhao Gou Tsinghua University

Presenting Author Biography: PHD student in Tsinghua University

Authors:

Yuanhao Gou Tsinghua University
Zhaoyuan Liu Tsinghua University
Conglong Jia Tsinghua University
Dacai Zhang Tsinghua University
Hao Luo Tsinghua University
Kan Wang Tsinghua University