Mockup experiments for the irregular shield of the first nuclear ship of Japan

Abstract Shielding mockup experiments were performed in order to obtain useful experimental data for complicated configurations of the primary shield of the first nuclear ship of Japan, a special cargo ship of 8350 gross tons, with a pressurized water reactor of 36 MWt. Spatial distributions of gamma-ray dose rate and thermal neutron flux were measured around the primary shield mockups placed in the pool of JRR-4, a swimming pool type research reactor of 2.5 MW, stalled at Japan Atomic Energy Research Institute for special shielding research purposes. The calculations were carried out to compare the experimental results using point kernel integration codes SPAN-3 and SPAN-SLAB. The computed results with SPAN-SLAB seem to give a rather good agreement with measured values for some points which were little influenced by air voids. But the calculated thermal neutron flux densities in the coolant nozzle, neglecting the streaming radiation through the nozzle, were less than the measured data by a factor of about 10. The experiments showed that the preliminary design is sufficient for the primary shield except around the coolant nozzle. The detail design will be proceeded taking the results of the mockup experiment into consideration.