JSIR2S code for delayed radiation simulations: Validation against measurements at the JSI TRIGA reactor

Highlights

• R2S methodology applied to a fission problem.

• Agreement between measured and simulated absolute absorbed dose rates.

• Methodology for cross-calibration of model detectors to absorbed dose.

• Delayed electron source term contributes a few percent to the detector signal.

Abstract

Interest on development of computational tools for calculations of radiation field due to decay of radioactive activation and fission products (delayed radiation) has increased in recent years, mainly due to requirements on shutdown dose rate for the future ITER fusion reactor and material testing reactors (MTR), where gamma heating values of several 10 Wg${}^{-1}$ can be reached in reactor structural components during reactor steady state operation and for characterization of research reactor irradiation facilities. Previous experimental work shows a roughly 30% contribution of delayed gamma rays to the total gamma ray flux.

An extensive experimental campaign at the JSI TRIGA reactor has been carried out using multiple ionization and fission chamber detectors for gamma and neutron field characterization. A series of reactor power steps was performed with said detectors in different irradiation positions during steady reactor power and after shutdown. The reactor and the used detectors, along with irradiation power steps have been modelled in detail using the JSIR2S code system framework to compare measured and calculated fluxes and dose rates. Simulated results are in good agreement with measurements and with experimentally obtained values of delayed gamma fractions from previous work.