Data assimilation for verification of dry storage cask content

Dry cask storage is a method for the interim storage of spent fuel assemblies. These assemblies contain fissile isotopes of uranium and plutonium which can present a proliferation concern, and consequently there is a need for methods which can verify dry cask content. The loading (or partial loading in diversion scenarios) of a cask determines various physical quantities. On one hand, theoretical calculations of these quantities can be computed assuming a particular loading. On the other hand, experimental measurements of these quantities can be made directly. The discrepancy between theoretical calculations and experimental measurements is therefore a possible detection mechanism to highlight diversion scenarios. The Best Estimate Results with Reduced Uncertainties (BERRU) framework by Cacuci quantifies such discrepancies between calculated and measured results by a data consistency indicator χ². Conventional statistical tests using the χ² value can be used to eliminate proposed cask loadings which are too-inconsistent with experimental measurements, but cannot be used to accept any particular cask loading and therefore lack the predictive capability to identify any particular cask loading as being the most consistent. An extension of the BERRU framework and its χ² tests is then proposed in which we calculate the χ² indicator across various proposed cask loadings and experimental measurements. The cask loading which gives the lowest χ² value among all the proposed cask loadings will be accepted by the test as being the most consistent with the experimental measurements. This proposed test is applied to two physical models of dry cask storage to develop: (1) a neutronics test based on a neutron diffusion model of Bonner sphere measurements at the cask exterior, and (2) a thermal test based on an analytical natural circulation model of the gain in temperature of cooling air exiting a cask and its comparison with experimental thermocouple measurements. The particular physics of each model result in varying performance of each test in terms of what types of diversion scenarios it can predict, and the test's success rates in predicting them. Since both tests are partial glimpses into the common true state of the cask, we expect that considering both tests together ought to yield better results than the results from considering them as single tests in isolation. Two complementary applications of the neutronics and thermal tests are investigated where it is found that a multiphysics BERRU test yields improved prediction results and can be recommended as a preferred complementary application.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Tan, Zi Liang

Advisor dc:contributor.advisor

• Shwageraus, Evgeni

• data assimilation
• dry cask storage

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/107bd9b0-5a65-4b87-899f-35b3657a2280/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.104847

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/362953