Enhancing future nuclear reactor safety A British company has recently investigated a late phase source term phenomena programme, which aimed at quantifying nuclear fission product and core material released from molten corium. The derived results are expected to aid the future development of severe accident management strategies, such as those associated with immersed core. Energy © Digital Vision With the primary aim of quantifying fission product, this programme had to examine the kinetics of release of the key fission products, namely lanthanides and actinides (as stimulants). It had also had to determine the importance of key phenomena such as sparging, slag formation and two-phase systems. To achieve the desired information, a number of experiments were executed, which created an aid to understanding the chemistry of species released during the late phase of an accident. This was further complemented with other experiments that examined the long-term behaviour of a solidified core immersed in a water pool. More detailed experiments studied the effect on the release process when fission product and core materials are released from molten pools, which included all forms of key phenomena.The releases from oxide pools and crust effects in the ceramic melts, and the transport and aerosol behaviour of ruthenium, which is released in the late-phase were also studied. Finally, the leaching behaviour on solidified core debris was studied by immersing it in water at temperatures of about 100 degrees Celsius for different periods of time. To conclude all the above-mentioned experiments, the programme also made an assessment of the experimental conditions so that they could be as representative as possible. The experiments and modelling studies were then integrated with plant assessments. These results will thus enable severe accident management strategies to be developed, with additional information providing data on fission product behaviour in the late phase of an accident. However, one of the fundamental benefits derived from this programme is the expected aid for the future design of plant calculations for Eastern European and advanced reactors.
