Leading the way in nuclear safety research with the world’s first study on neutron-flux impact on radiation-induced expansion of rock-forming mineral

A research team led by Professor Ippei Maruyama and Associate Professor Kenta Murakami from the Graduate School of Engineering at the University of Tokyo, Associate Professor Takahiro Ohkubo from the Graduate School of Engineering at Chiba University, Dr. Osamu Kontani and Dr. Shohei Sawada from Kajima Corporation, Mr. Masaki Kawai and Mr. Junji Eto from Mitsubishi Research Institute, Inc., and Dr. Takafumi Igari from MRI Research Associates, Inc., has evaluated the expansion of rock-forming mineral under different neutron flux conditions. This study aims to enhance the assessment of the long-term safety of concrete used in nuclear power plants.

The results revealed that lower neutron flux leads to smaller expansion and larger mineral grains in the rock result in reduced expansion with the same neutron fluence. This expansion is caused by the amorphization of the crystal structure within the mineral, but the observed flux dependency suggests the presence of a annealing phenomenon, where the amorphized crystal structure partially realigns to its original state. The balance between the effects of neutron-induced disruption and the recovery phenomenon determines the expansion rate.

By modeling this phenomenon and predicting mineral expansion under the neutron flux environment experienced by biological shielding walls in an actual nuclear power plant reactor, the team found that the expansion could be significantly smaller—less than one-tenth—compared to previous estimates. These findings are expected to contribute to the long-term operation of nuclear power plants by enabling accurate evaluation and prediction of the performance changes in concrete exposed to radiation.

The paper can be found here:https://www.sciencedirect.com/science/article/pii/S0022311525000261