Title: The Significance of Boric Acid during a LWR Severe Accident and the Repercussions for Experimental Representativity
Citation: Proceedings of the International Congress on Advances in Nuclear Power Plants p. 11243 (1-12)
Publisher: French Nuclear Energy Society (SFEN)
Publication Year: 2011
JRC N°: JRC63998
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC63998
Type: Articles in periodicals and books
Abstract: In severe-accident (SA) evaluation, the importance of a parameter is determined by its influence on radioactivity released to the environment, the so-called source term. Beyond the released mass of a radioisotope, prediction of its chemico-physical forms is important. Light-water-cooled reactors (LWRs) contain large quantities of boron. In SAs, boron will be present in the primary system before, during and after fission products (FPs) are released from the core. This paper discusses the role boron would play during a SA and appropriate means and pitfalls of including it in a SA experiment. The quantity of boron to which the degrading core is directly exposed during a SA depends on the reactor type, its operating history and the SA scenario but can be estimated at somewhere between a few tens of kilogrammes and several tonnes. The impact of boron centres mainly on volatile-FP speciation changes altering the quantities and physico-chemical forms of these key elements that reach the containment; there are perhaps also important consequences for longer-term accident management if the water in the containment is appreciably borated. In the present state of knowledge, the full impact of boric acid during a LWR SA is somewhat uncertain and it is of most interest to study this in representative accident conditions maximizing the potential of boron to influence speciation of key FPs. This would be for a large-break scenario simulating core uncovery and initial core damage where boric acid is present in the steam in contact with the fuel in concentrations up to 1000ppm (boron by mass). This was finally studied in the Phébus FP programme in the test FPT2 carried out in October 2000; the Phébus FPT3 test conducted in 2004 is also relevant as it contained a boron-carbide-filled control rod in the fuel bundle. Data from these tests is not yet published and their interpretation continues but results tend to confirm the importance of the role of boron.
JRC Directorate:Nuclear Safety and Security

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