Validation and Optimization of Activity Estimates of the FiR 1 TRIGA Research Reactor Biological Shield Concrete

Abstract

FiR 1 is a TRIGA Mark II-type research reactor in Finland. It was in operation between 1962 to 2015 and will be dismantled in 2022 to 2023. Preliminary calculations of the activities in the reactor main structures were performed in an earlier stage of the decommissioning project. Samples of the activated parts of the reactor biological shield concrete were drilled in December 2018 to validate these estimates. This paper describes the calculations and gamma activity measurements performed for the activated concrete samples to determine the boundary between radioactive parts and concrete that can plausibly be free-released from regulatory control. The activities have been estimated with a two-step calculation process using the MCNP and ORIGEN-S calculation codes and measurements using an ISOCS gamma spectrometer with a high-purity germanium detector.

Keywords:

• Concrete
• ISOCS
• TRIGA
• MCNP
• ORIGEN-S

Acknowledgments

The authors would like to thank Risto Koivusaari (Eurofins Expert Services Ltd.) and Mika Flander (Greental Ltd.) for conducting the diamond drilling of the concrete cores. The authors would also like to thank Tiina Lavonen (VTT) and Kirsti Helosuo (VTT) for the ICP-OES composition measurement of the steel shadow samples.

Disclosure Statement

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