How Cherenkov light intensities from irradiated nuclear fuel rods in wet storage depend on rod properties
(English)Manuscript (preprint) (Other academic)
Safeguards verification of irradiated nuclear fuel assemblies in wet storage is frequently done by measuring the Cherenkov light in the surrounding water produced due to radioactive decays of fission products in the fuel. This paper accounts for the physical processes behind the Cherenkov light production caused by a single fuel rod in wet storage, and simulations are presented that investigate to what extent various properties of the rod affect the Cherenkov light production. The work is intended to form a solid foundation for further development of the prediction models for Cherenkov light production which are used in the safeguards verifications.
It is concluded that the dominating source of the Cherenkov light is gamma-ray interactions with electrons in the surrounding water. Electrons created from beta decay may also exit the fuel and produce Cherenkov light, and e.g. Y-90 was identified as a possible contributor to significant levels of the measurable Cherenkov light in long-cooled fuel. The results also show that the cylindrical, elongated fuel rod geometry results in a non-isotropic Cherenkov light production, and the light component parallel to the rod's axis exhibits a dependence on gamma-ray energy that differs from the total intensity, which is of importance since the typical safeguards measurement situation observes that light component.
The results also show a relatively complex dependence between the Cherenkov light intensity and fuel properties such as fuel rod dimensions and fission product decay energy. It is also concluded that the radial distributions of the radiation sources in a fuel rod will affect the Cherenkov light production.
Nuclear safeguards, Geant4, Cherenkov light, DCVD, Nuclear fuel rod
Research subject Physics with specialization in Applied Nuclear Physics
IdentifiersURN: urn:nbn:se:uu:diva-309736OAI: oai:DiVA.org:uu-309736DiVA: diva2:1052807
FunderSwedish Radiation Safety Authority, SSM2012-2750Swedish National Infrastructure for Computing (SNIC), p2007011