Determination of an Effective Detector Position for Pulsed-Neutron-Source Alpha Measurement by Time-Dependent Monte Carlo Neutron Transport Simulations

Sang Hoon Jang,Hyung Jin Shim

doi:10.1155/2018/2350458

Abstract

A simple method using the time-dependent Monte Carlo (TDMC) neutron transport calculation is presented to determine an effective detector position for the prompt neutron decay constant (α) measurement through the pulsed-neutron-source (PNS) experiment. In the proposed method, the optimum detector position is searched by comparing amplitudes of detector signals at different positions when their α estimates by the slope fitting are converged. The developed method is applied to the Pb-Bi-zoned ADS experimental benchmark at Kyoto University Critical Assembly. The α convergence time estimated by the TDMC PNS simulation agrees well with the experimental results. The α convergence time map and the corresponding signal amplitude map predicted by the developed method show that polyethylene moderator regions adjacent to fuel region are better positions than other candidates for the PNS α measurement.

Highlights

Since the early 1990s, accelerator-driven subcritical systems (ADS) for transmutation of radioactive wastes and energy production have been proposed and designed throughout the world with their advantages of high flexibility of fuel compositions and the enhanced safety concept [1,2,3]
The developed method to determine the optimum detector position for the PNS α measurement is applied for the Pb-Bi-zoned ADS experimental benchmark at Kyoto University Critical Assembly (KUCA) [22]
A simple method to determine an effective detector position for the PNS α measurement is proposed by comparing signal amplitudes at different detector positions estimated by the time-dependent Monte Carlo (TDMC) neutron transport calculations when their α estimates by the slope fitting are converged

Summary

Introduction

Since the early 1990s, accelerator-driven subcritical systems (ADS) for transmutation of radioactive wastes and energy production have been proposed and designed throughout the world with their advantages of high flexibility of fuel compositions and the enhanced safety concept [1,2,3]. The PNS α measurement may yield considerably different results at different detector positions and neutron sources, as reported in the experimental benchmarks on an ADS at Kyoto University Critical Assembly (KUCA) [15, 16]. This measurement dependency on the detector position and the neutron source can be attributed mostly to the signal contamination [11, 16] by the highermode components of the prompt neutron flux, which is caused by taking detector signals before the higher-mode components fully decay out. It is necessary to determine effective detector positions where the prompt neutron flux converges fast with larger signal strength than other candidate positions

Objectives

Results

Conclusion