The performance of self-interrogation neutron resonance densitometry in measuring spent fuel

Jianwei Hu, Holly R. Trellue, Stephen J. Tobin, T. J. Ulrich, Adrienne M. LaFleur, Corey R. Freeman, Howard O. Menlove, Martyn T. Swinhoe

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

The Self-interrogation Neutron Resonance Densitometry Technique (SINRD) is one of the fourteen nondestructive assay (NDA) techniques investigated under the Next Generation Safeguards Initiative (NGSI) effort. SINRD shows promising capability in determining the 239Pu and 235U content in spent nuclear fuel. SINRD is a relatively low-cost and lightweight instrument, and it is easy to implement in the field. SINRD makes use of the passive neutron source existing in a spent fuel assembly, and it uses ratios between the count rates collected in fission chambers that are covered with different absorbing materials. These ratios were correlated to certain attributes of the spent fuel assembly such as the total mass of 239Pu. Using count rate ratios instead of absolute count rates makes SINRD less vulnerable to systematic uncertainties. Building upon the previous research performed by Lafleur et al., this work focuses on the underlying physics of the SINRD technique: understanding the neutron energy spectrum at various locations inside and at the edge of the fuel assembly; understanding which isotopes have major impacts on the SINRD signal, by weighting the resonance absorption caused by each of a few isotopes deemed important in certain energy windows (dictated by the absorbing material covering the fission chambers); and understanding the spatial dependence of the count rate on each row of the fuel rods. The results of these studies show that water-filled gap of 0.5cm or more smears out the structure of the spectrum in the energy ranges important to SINRD; 239Pu is the most important nuclide that affects the count rate in the "Gd-Cd" window, and 235U has a significant impact as well, especially in the low burnup case; only the first three rows next to the detector has a significant impact on the signal. In short, this work provides insights into the factors that affect the performance of SINRD most and it will help to improve the hardware design and the algorithm used to interpret the signal for the SINRD technique.

Original languageEnglish
Pages (from-to)36-44
Number of pages9
JournalJournal of Nuclear Materials Management
Volume40
Issue number3
StatePublished - Mar 2012
Externally publishedYes

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