Real-Time Inventory Change Detection for the Protactinium Decay Inventory of the Molten Salt Breeder Reactor

Abstract

This work presents a novel monitoring method for detecting material loss from the decay inventory of the molten salt breeder reactor (MSBR) by monitoring for changes to the system dynamics using an isotopic ratio. The isotopic masses in the decay inventory of a MSBR were simulated under several material loss scenarios. In each case, the ratio of ²³¹Pa to ²³³Pa served as a sensitive and lasting indicator of material loss. This isotope ratio quickly decreased outside the normal range after a material loss, and the ratio remained depressed for several years after the loss. The dynamics of this ratio were driven by the periodic batch discard from the decay inventory every 220 days, which was specified in the MSBR design to periodically remove fission product buildup. For this method, isotopic ratios were found to be rapid and enduring indicators of inventory change if they comprise a pair with a short half-life (e.g., ²³³Pa) and a long half-life (e.g., ²³¹Pa) relative to the effective half-life induced by the driving system process (e.g., the batch discard cycle). Using such an isotope pair enabled a method to monitor for changes to the effective half-life of the system and by extension changes to the system inputs and outputs.

Keywords:

• Protactinium monitoring
• thorium safeguards
• molten salt breeder reactor
• special nuclear material monitoring

Acknowledgments

The authors would like to acknowledge support from the U.S. Department of Energy (DOE) National Nuclear Security Administration’s Office of International Nuclear Safeguards. This work was completed as a portion of a project for NA-241 by a multilaboratory team including S. Matt Gilbert from Sandia National Laboratories and Jeff Powers, T. Jay Harrison, and Natalie McGirl from ORNL. The authors would like to acknowledge the contributions of the rest of the team during the exploration stage of this work.

This paper has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the DOE. The U.S. government retains and the publisher, by accepting the paper for publication, acknowledges that the U.S. government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this paper, or allow others to do so, for U.S. government purposes. DOE will provide public access to the results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Notes

^a A significant quantity of ²³³U is defined as 8 kg by the International Atomic Energy Agency.⁵