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Scientific paper

Sensitivity analysis of the Rossi-Alpha Distribution and the early die-away time τ from the DDSI instrument due to modelling assumptions

ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-Proliferation

Details

Identification
ISSN: 1977-5296, 10.3011/ESARDA.IJNSNP.2021.2
Publication date
1 June 2021
Author
Joint Research Centre

Description

Volume: 62, June 2021, pages 13-22,

Authors: Sophie Grape, Zsolt Elter, Erik Branger, Li Pöder Balkeståhl

Uppsala University

Abstract:

Under the Next Generation Safeguards Initiative, several different nuclear safeguards measurement techniques were studied. One of them was the Differential Die-Away Self-Interrogation technique, and the research showed that its early die-away time τ was proportional to the fuel assembly multiplication and thus sensitive to the fissile content of the fuel assembly under assay. A prototype instrument was later built and tested in the field, and the measurements showed that the instrument could be used successfully in the field. This work builds on previous efforts, and systematically studies the effects of assumptions about the fuel properties (such as its dimensions) and its irradiation conditions in the reactor, on the Rossi-Alpha Distribution (RAD) and τ. The motivation is twofold, firstly to better understand if and what impacts such assumptions have on the RAD and τ, and secondly to investigate how well the simulation model used to estimate the RAD and τ is able to generalize to other fuel types and irradiation conditions than those modelled. 20 spent nuclear fuel assemblies currently residing in the Swedish interim storage for spent nuclear fuel were measured by the prototype DDSI instrument. The assemblies were modelled using Serpent2 and MCNP6 in this work. Fuel depletion calculations were performed assuming both a standard irradiation cycle and the actual irradiation history as provided by the operator. Fuel properties and irradiation conditions were also modified and their effect studied. Based on the simulated DDSI instrument response in MCNP6, the RADs were created and τ determined. The analysis shows that each modelling assumption on its own affects both the RAD and the τ value. However, some of the individual effects work in opposite direction and cancel out when considered at the same time. For this reason, the default model is considered to be a good and valid approximation of the more complex one and results are expected to generalize well.

Keywords: Nuclear safeguards, DDSI, neutron coincidence, tau (τ ), modelling

Reference guideline:

Grape, S., Elter, Z., Branger, E., & Pöder Balkeståhl, L. (2021). Sensitivity analysis of the Rossi-Alpha Distribution and the early die-away time τ from the DDSI instrument due to modelling assumptions. ESARDA Bulletin - The International Journal of Nuclear Safeguards and Non-proliferation, 62, 13-22.
https://doi.org/10.3011/ESARDA.IJNSNP.2021.2

THMB_Bulletin-62_p.13-22-Grape

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Sensitivity analysis of the Rossi-Alpha Distribution and the early die-away time τ from the DDSI instrument due to modelling assumptions
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