Livre blanc du Tritium & bilan des rejets de tritium pour les INB
ASN Position Statement Tritium is a hydrogen isotope that is a low-energy beta emitter (mean energy 5.7 keV). The most commonly- found form in the biosphere is tritiated water and the dominant exposure route is ingestion. The radiotoxicity of tritium is low. The overall impact of tritium releases in France is also low, with an annual effective dose of roughly one µSv or less for the reference groups. Radioactive releases in the environment around civilian nuclear facilities have significantly decreased over the last few decades, with the exception of tritium. Discharges of this element are forecast to increase due to expected changes in the fuel management methods used by tne NPP, and also due to new tritiumemitting facilities, including new power plants that are to be built, and the ITER project. In late 2007, papers published in the UK (RIFE 11 report, study by the HPA’s Advisory Group on Ionising Radiation (AGIR)) raised questions as to the behaviour of tritium in the environment, in particular focusing on potential accumulation in organisms of organically bound tritium (OBT) from tritium released into the environment and on methods for assessing the biological impact of tritium in humans. Given this context, ASN wanted to get a clear analysis of the existing studies into the issue and in early 2008 decided to establish two broad working groups, chaired by Dr Patrick Smeesters of the Belgian Federal Agency for Nuclear Control (AFCN) and Mr Roland Masse of the Académie des technologies . The groups were formed of experts (from the CEA, CNRS, GSIEN, Institut Curie, IRSN, universities and European Commission “Article 31” experts), representatives of operators (ANDRA, AREVA, CEA, EDF and ITER), associations (ANCCLI, ACRO and CLI) and safety authorities (ASN, DSND). Their findings and recommendations were submitted in early April 2010. The ASN is pleased with the high quality of the work and the large bibliography provided, which have led to the recommendations issued at the end of each group’s summary. The studies highlight the small impact that tritium releases have in France. However, they do also show the need to carry out further study and research in order to supplement current data and knowledge on the behaviour of tritium in the environment. The ASN has drawn up the following action plan on the basis of the recommendations made by the two working groups. It also hopes that research bodies take into account the requests made by the working groups, as described below. ASN action plan Measurements There is currently no standardised measurement protocol for the various physico-chemical forms of tritium, in particular the various organic forms of tritium (exchangeable and non-exchangeable). The fact that there is no standardised method makes it difficult to interpret existing studies and data. The CEA’s CETAMA (commission for the establishment of analysis methods) has started work to define shared and recognised measurement protocols. In the ASN’s view, this work: must lead to the production of a guide to the measurement of organically bound tritium; is a vital first step prior to launching further studies. Control of discharges It is currently felt to be unrealistic to detritiate discharges from nuclear reactors and the La Hague fuel reprocessing plant at an acceptable cost using the best technologies currently available. In addition, detritiation would only have a limited effect on the radiological impact from these facilities. Given the increase observed in tritium discharges from civilian nuclear facilities and the absence of a detritiation method, the ASN, as part of the development of defence in depth, considers that: publishing the quantities discharged for each facility on an annual basis will ensure a long-term, reliable inventory of sources of tritium production. The public should be regularly and specifically informed of this inventory of tritium discharges by nuclear operators; accounting for discharges from all facilities should continue to be managed in all circumstances, as is the case today; a “technology watch” should be set up with respect to detritiation technologies.