Airborne tritium emissions dynamics at Cernavoda NPP, 1997- 2007

Most of the tritium in a CANDU reactor is formed by thermal neutron capture reactions, 2H(n,γ)3H, which occur both in the moderator and primary heat transport system (PHT). Very low amounts of tritium may escape from heavy water circuits and auxiliaries of a CANDU reactor during normal operation and outages. Tritium emissions of Cernavoda NPP have been monitored since 1996, when the plant became operational. HTO has been continuously sampled on molecular sieves since the plant commissioning. Tritium samples have been measured twice a week and daily starting with 2007. Time series statistical methods were applied to study tritium emissions in air in order to estimate trends, to develop criteria for identifying abnormal emissions, and to predict further emissions. Tritium releases evolves stochastically around a slowly increasing trend but PHT and moderator events with significant leaks could have an important contribution to tritium releases to the environment. The standard deviation of time series residuals distribution, after detrending, could be used to establish investigation criteria for the emission levels. (authors)