title: Optimization of hybrid-type instrumentation for Pu accountancy of U/TRU ingot in pyroprocessing.
abstract: One of the final products of pyroprocessing for spent nuclear fuel recycling is a U/TRU ingot consisting of rare earth (RE), uranium (U), and transuranic (TRU) elements. The amounts of nuclear materials in a U/TRU ingot must be measured as precisely as possible in order to secure the safeguardability of a pyroprocessing facility, as it contains the most amount of Pu among spent nuclear fuels. In this paper, we propose a new nuclear material accountancy method for measurement of Pu mass in a U/TRU ingot. This is a hybrid system combining two techniques, based on measurement of neutrons from both (1) fast- and (2) thermal-neutron-induced fission events. In technique #1, the change in the average neutron energy is a signature that is determined using the so-called ring ratio method, according to which two detector rings are positioned close to and far from the sample, respectively, to measure the increase of the average neutron energy due to the increased number of fast-neutron-induced fission events and, in turn, the Pu mass in the ingot. We call this technique, fast-neutron energy multiplication (FNEM). In technique #2, which is well known as Passive Neutron Albedo Reactivity (PNAR), a neutron population's changes resulting from thermal-neutron-induced fission events due to the presence or absence of a cadmium (Cd) liner in the sample's cavity wall, and reflected in the Cd ratio, is the signature that is measured. In the present study, it was considered that the use of a hybrid, FNEM×PNAR technique would significantly enhance the signature of a Pu mass. Therefore, the performance of such a system was investigated for different detector parameters in order to determine the optimal geometry. The performance was additionally evaluated by MCNP6 Monte Carlo simulations for different U/TRU compositions reflecting different burnups (BU), initial enrichments (IE), and cooling times (CT) to estimate its performance in real situations.
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea. Electronic address: hseo@kaeri.re.kr.
authors.forename: Hee
authors.initials: H
authors.lastname: Seo
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea.
authors.forename: Byung-Hee
authors.initials: BH
authors.lastname: Won
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea.
authors.forename: Seong-Kyu
authors.initials: SK
authors.lastname: Ahn
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea.
authors.forename: Seung Kyu
authors.initials: SK
authors.lastname: Lee
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea.
authors.forename: Se-Hwan
authors.initials: SH
authors.lastname: Park
authors.affiliation: Korea Atomic Energy Research Institute, Yuseong, Daejeon 305-353, Korea.
authors.forename: Geun-Il
authors.initials: GI
authors.lastname: Park
authors.affiliation: Safeguards Technical Solutions, Los Alamos, NM 87544, USA.
authors.forename: Spencer H
authors.initials: SH
authors.lastname: Menlove
keywords: Nondestructive assay; Nuclear material accountancy; Nuclear safeguards; Pyroprocessing