Monte Carlo Modeling of the Californium-Interrogation with Prompt Neutron (CIPN) Device for Spent Nuclear Fuel Measurements

摘要

Californium-Interrogation with Prompt Neutron detection (CIPN) is an active interrogation technique developed under the Next Generation Safeguards Initiative Spent Fuel (NGSI-SF) effort to improve capability to quantify the plutonium (Pu) mass in, and detect the diversion of pins from, spent nuclear fuel assemblies with non-destructive assay (NDA) techniques as well as estimate the initial enrichment, burnup and cooling time of the fuel. The CIPN detector consists of four neutron and two gamma-ray detectors in a compact, waterproof case. It is deployed on a pole and placed adjacent to an assembly in the spent fuel pool. A capsule of neutron-emitting californium-252 (Cf) is placed near the fuel assembly to induce fissions. The instrument is capable of measuring passive neutron background from the assembly as well as operating in the active-mode with the Cf source to analyze the fissile material content. Ion chambers can also provide a gross gamma count rate that can be related to the assembly burnup. Performance of the CIPN detector was evaluated with the Monte Carlo N-Particle transport code MCNPX using realistic spent fuel assembly libraries developed at Los Alamos National Laboratory (LANL). A large number of simulations provided data to correlate the detector response to specific assembly characteristics. These included the initial U-235 enrichment, irradiation history, and post-irradiation cooling time for each assembly. Future work will focus on integrating the CIPN detector signals to improve spent fuel assembly characterization and quantification of Pu mass.