Evaluation of Safety Parameters for Gharr-1 After Nineteen (19) Years of Operation

ABSTRACT

Evaluation of safety parameters of GHARR-1 after nineteen years of operation was performed and are presented herein. This work serves as an input into periodic evaluations of safety parameters. Due to fuel depletion, the excess reactivity for GHARR1 drops to the allowed lower limit of 2.3 mk from 4 mk in about 2 years. Beryllium is added to the top shim tray of the core to compensate for reactivity loss. The addition of beryllium to the top of the core requires evaluations of safety parameters. The objective for this work was to evaluate the safety parameters of GHARR-1after 19 years of operation and compare them with those provided in the SAR and other literature. Four codes namely; REBUS/ANL, MCNP, PARET/ANL and PLTEMP/ANL were used in this work. The REBUS/ANL code was used to generate an inventory of isotopes in the fuel after 19 years of operation. The masses for the isotopes were used to update the material card in the MCNP model for GHARR-1 and 9 mm of beryllium was also added to the top shim tray in the model.

The MCNP code was used to predict neutronics and kinetic parameters of GHARR-1. The neutron generation time, delayed neutron fraction, axial power peaking factors, fuel temperature reactivity coefficient, moderator temperature coefficient and the moderator void coefficient were used in the PARET/ANL code to predict the transient and steady state parameters of the reactor. The existing PLTEMP/ANL input deck was updated with the axial and radial power peaking factors obtained from the MCNP simulations. The code was used to predict the steady state parameters; DNBR, ONBR, FIR, saturation and ONB temperatures respectively. The delayed neutron fraction, neutron generation time, moderator reactivity coefficient were 2 predicted as; 3 8.17507 10- ´ Dk k/ , 5 8.147 10- ´ s ,-0.1218 mk which compared with those provided in the SAR as 3 8.08 10- ´ Dk k/ , 5 8.12 10- ´ s ,-0.13 mk. The maximum power peaking factor was predicted as 1.3522 compared to 1.3525 for the clean core and it was with the expected range of 1.3 to 1.5 for light water reactors. The reactor power for reactivity insertion of 2.1 mk was predicted as 39.3 kW compared to 36.1 from experimental work. The DNBR, ONBR and FIR for 30 kW were predicted as; 19.12, 1.25, and 4.37, respectively. The results obtained indicate that the reactor’s neutronic and thermal hydraulic characteristics meet requirements set out in the Safety Analysis Report.