NEA Source Term Evaluation and Mitigation (STEM) Project

Past, recent and ongoing R&D programmes (e.g. Phebus FP, ISTP, ARTIST, OECD/BIP and THAI Projects) are mainly focussed on the reduction of uncertainties on the evaluation of the potential source term to the environment in case of a light water reactor (LWR) severe accident. This effort is sustained within the EU/SARNET Network of Excellence.

However, it has been recognised that known phenomenological uncertainties remain for some complex phenomena with a significant impact on source term. For public acceptance of lifetime extension of existing reactors, it must be demonstrated that their safety level continues to be enhanced.

Therefore, a new NEA project named STEM (Source Term Evaluation and Mitigation) was initiated in 2011 to improve the general evaluation of the source term. In addition, the reduction of known phenomenological uncertainties on certain phenomena is expected to help in

The NEA STEM Project deals with three main issues:

Within the frame of the NEA STEM Project, the first series of experiments (iodine behaviour under radiation) are dedicated to the analysis of radiation effects and will thus be realized in benches built on the EPICUR (Experimental Programme of Iodine Chemistry Under Radiation) facility. The second series of experiments (ruthenium transport) will aim to analyse the chemistry of ruthenium in pipes including the reactor coolant system and in filters. They will be performed in dedicated benches allowing the injection of different chemical compounds followed by their transport through high temperature gradient tubes up to aerosols filters and bubblers for gas trapping

Participating countries

Canada, Czech Republic, Finland, France, Germany, Korea and the United States of America.

Project Period

July 2011 to September 2015


EUR 3.5 million

Related links

Last updated: 11 April 2017