Abstract:
GRR-1 reactor is currently out of operation for inspection and refurbishment purposes. The GRR-1 inspection and refurbishment plan involves inspection and eventually replacement of the reactor’s primary cooling circuit. The health physics procedures to be implemented during inspection of the main water outlet are divided in three stages: a) pool dose rate survey from pool top, b) pool drainage by decreasing water level in steps and c) inspection of the water main outlet. Purpose of the present work is the evaluation of the gamma radiation fields inside and around the pool during the above procedures. The Monte Carlo neutron and photon transport code MCNP5 was employed in order to asses the activation of materials in the pool and predict gamma radiation levels during pool drainage. The code enabled simulation of the reactor core, pool and activated components within the pool. The MCNP predicted gamma dose rate results were calibrated against experimental measurements performed using a submersible GM detector.