Impact of HWC in BWRs on environmental radiation

An increase in radiation fields, due to the increase of the N-16 activity in the steam/turbine systems under hydrogen water chemistry (HWC) conditions, is a major concern in some BWR nuclear power plants, in which HWC is the only viable option to mitigate the intergranular stress corrosion cracking (IGSCC) of reactor internals. The N-16 activity is produced in the reactor coolant by the 16O(n,p)16N reaction from water in the core region. Under normal water chemistry (NWC) conditions, most of the produced N-16 stay in water with oxidized chemical forms (mainly NO3-). However, under HWC conditions, the N-16 activity is reduced to a more volatile form of NH3 (NH4OH) and carried away by steam to the mainsteam/turbine systems. Consequently, the mainsteam line radiation fields can be increased by as much as a factor of 5-8 under HWC conditions. Due to the radiation field increase from N-16 in mainsteam and turbine systems, the environmental radiation fields can be increased to varying degrees by direct and scattered gamma rays. This impact of radiation field increase may be serious enough in some cases to force plant operators to take appropriate corrective actions. This paper discusses the chemical and transport behavior of N-16 in steam and suggests some solutions to minimize the impact of environmental radiation field increase due to N-16. Some concern has also been raised regarding the release of tritium to the environment through the mainsteam and off-gas systems under HWC conditions. This paper will also address this potential impact issue. (author)