Experimental Benchmark of MCNPX Calculations Against Self-Interrogation Neutron Resonance Densitometry (SINRD) Fresh Fuel Measurements

摘要

We have investigated the use Self-Interrogation Neutron Resonance Densitometry (SINRD) tomeasure the ~(235)U concentration in a PWR 15x15 fresh LEU fuel assembly in air. Differentmeasurement configurations were simulated in Monte Carlo N-Particle eXtended transport code(MCNPX) and benchmarked against experimental results. The sensitivity of SINRD is based onusing the same fissile materials in the fission chambers as are present in the fuel because the effectof resonance absorption lines in the transmitted flux is amplified by the corresponding (n,f) reactionpeaks in fission chamber. Due to the low spontaneous fission rate of 238U (i.e. no curium in the freshfuel), ~(252)Cf sources were used to self-interrogate the fresh fuel pins. The resonance absorption ofthese neutrons in the fresh fuel pins can be measured using ~(235)U fission chambers placed adjacent tothe assembly. We used ratios of different fission chambers to reduce the number of unknowns weare trying measure because the neutron source strength and detector-fuel assembly coupling cancelin the ratios. The agreement between MCNPX results and experimental measurements confirms theaccuracy of the MCNPX models used. The development of SINRD to measure the fissile content inspent fuel is important to the improvement of nuclear safeguards and material accountability. Futurework includes the use of this technique to measure the fissile content in LWR spent fuel in water.