Burnup Monitoring for Pebble Bed Reactor Systems

A pebble burnup monitoring system is a required component for domestic reactor safety and safeguards applications associated with pebble bed reactors (PBRs). One of the main requirements of a PBR burnup monitoring system is that it needs to be capable of rapid measurements to assess the burnup of each individual pebble to determine whether to recirculate it in the reactor or discard it as spent fuel. This report considers three different approaches for a burnup monitoring system for pebbles discharged from the reactor core in a pebble bed modular reactor-400: • passive gamma spectrometry measurement, • passive neutron coincidence measurement, and • active neutron counter based on the differential die-away technique. Conceptual designs have been created for each of these detectors, and preliminary analysis has been performed using Monte Carlo N-Particle and Oak Ridge Isotope Generation code simulations. The advantages and practical limitations (e.g., high radiation background) of each system were identified. Simulations suggest that each of the three measurement techniques can be successfully employed to distinguish between pebbles based on their number of passes through the core and to quantify the burnup of pebbles.. Authors: Mcelroy Jr., Robert [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)]; Hu, Jianwei [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000206581331); Kovacic, Donald N. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000176491182); Parada Iturria, Francisco [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0009000641147828); Shah, Manit D. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000236009504). DOE Contract: AC05-00OR22725. Subjects: 22 GENERAL STUDIES OF NUCLEAR REACTORS