NEA Source Term Evaluation and Mitigation Project Phase 2 (STEM-2)

The STEM Project was initiated with a first phase in 2011 to improve the general evaluation of the fission-product (FP) source term in the event of a severe accident of a water-cooled reactor in relation to two major FPs, iodine and ruthenium. The STEM Project is conducted in IRSN facilities at Cadarache, France. The first phase of the project, which ended in 2015, addressed three main issues: experiments on radioactive-iodine release due to irradiation of iodine-bearing aerosols that would contribute to mid- and longer-term source in the containment; a literature survey on interactions between iodine and paints; and experiments on transport of volatile ruthenium species through steel pipes representing the reactor coolant system (RCS). This new four-year phase, STEM-2, pursues experimental investigations of iodine and ruthenium issues undertaking the following investigations concerning iodine:

Regarding ruthenium, experiments in more representative conditions than in STEM will be performed on simulations of ruthenium transport in the RCS. In particular, this means more representativity for the deposition surface, the use of stronger oxidising conditions characteristic of air radiolysis products (such as ozone and nitrous oxides) and the use of representative gaseous and/or aerosol “pollutants” (i.e. seed particles, silver aerosols, aerosol deposits) that could influence ruthenium behaviour.

It should be noted that the STEM has strong scientific links with the BIP project including complementary objectives and many common partners.

Participating countries

Canada, Finland, France, Germany, Japan, Korea, United Kingdom and the United States of America.

Project Period

January 2016 to December 2019


EUR 2.48 million

Related links


Last reviewed: 11 April 2017