Role of Operational Radioprotection Simulation in the Dismantling of the Protection and Control Rods of VVR-S Reactor

The VVR-S nuclear research reactor owned by Horia Hubulei National Institute of Physics and Nuclear Engineering, has functioned between 1957 and 1997 at a nominal thermal power of 2 MW, using less-enriched nuclear fuel (10%), type EK-10, and highly enriched fuel (36%), type S-36. The reactor control was carried out by means of nine rods placed in the central part of the core. Four rods were used for the manual control of power, one for automatic control, three rods for reactor safety (emergency rods) and one for the fine control of power. One of the high hazard operations was the dismantling of the activated-contaminated control rods. Because of a higher radiological risk, simulation was performed to determine the expected maximum dose. The maximum gamma dose rate obtained using simulated results was 3.5 Sv/h, for the highly activated rod. In the real measurement, when the work was performed, the maximum gamma dose rate was 3 Sv/h. ⁹⁰Sr+⁹⁰Y are expected to be present in the control rods radioactivity.