Abstract
Effect of high concentrations of soluble neutron poison gadolinium nitrate, Gd(NO3)3, in the moderator system of a proposed advanced Indian nuclear reactor, was evaluated from the safety point of view. The radiolytic yields of H2 and H2O2 was expected to be high as moderator water system pH would be lowered and conductivity also would be high by the addition of higher concentration Gd(NO3)3 solutions during various shutdown states. Experiments were carried out to estimate this increase in radiolytic yield of molecular products with the addition of Gd(NO3)3 in the concentration range of 15–400mgkg−1. Both the H2O2 and H2 yields were found to increase with absorbed dose and also with increasing Gd3+ concentration up to 100mgkg−1 but the increase were marginal in 100–400mgkg−1 range. For a given concentration of Gd(NO3)3 solution, radiolysis in high purity D2O showed a lower D2 formation than H2 in light water. In a simulated moderator temperature of 65°C, a higher yield of H2 was observed. The headspace provided above the liquid phase in irradiation zone had shown to have a substantial effect on the generation of H2. With decreasing headspace, H2 generation increased and went through a maximum. Considering the expected long operational life (~100 years) for the proposed reactor, the corrosion rate of the structural materials (stainless steel 304 LN) in contact with this high concentration Gd(NO3)3 solution was also estimated at 65°C which showed a negligible effect.
Published Version
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