In-reactor simulation study of BWR coolant radiolysis and 16N carryover

Boiling water reactors (BWRs) have traditionally been operated using high-purity water coolant with no or minimal deliberate volatile or nonvolatile chemical additives. This results in oxidizing conditions in the coolant circuit due to the production of radiolytic species in-core. A number of structural components are susceptible to cracking when such conditions prevail. One solution to the problem of cracking is to inject hydrogen into the feedwater to suppress the water radiolysis and maintain reducing conditions. However, it is not clear that this technique can protect all of the core internals, due to stripping of the hydrogen into the steam phase. It is difficult to make in-core measurements of in-core electrochemical corrosion potential (ECP) to determine whether cracking has been suppressed. Furthermore, the minimum hydrogen injection levels that will protect any components in the coolant circuit are sufficient to cause up to a fivefold increase in the 16N carry-over into the steam with consequent large increases in dose rates at the turbines. This paper highlights important results obtained in the BWR coolant chemistry operating in the 5-MW research reactor MITR-II