Source term evaluation in a hypothetical core disruptive accident in the PEC fast reactor

The Italian PEC reactor is a semi-integrated loop-type fast reactor, characterized by a power of about 120 MW(th). As a result of severe accident analysis for the PEC reactor, the main issues are presented to verify the capability of the containment to withstand an energetic core disruptive accident. The hypothetical initial scenario includes a nuclear power excursion that causes melting of a large zone of the core. Subsequently, a reaction between sodium and melt fuel is expected, with a consequent release of mechanical energy related to sodium bubble expansion. The effects of mechanical energy release on the reactor block unit have been investigated using either qualified computer codes or experimental tests. Transport phenomena of radionuclides have been considered as the basis for determining the source term including the amount and type of radioactive materials released to the environment during the accident examined. The performance of containment engineered safety features and the effects of natural aerosol depletion processes are taken into account in the source term evaluation. The leakage of radioactive materials through the containment barriers to the environment has been evaluated taking into account the capability of the containment barriers and suitable leakage hypotheses. To allow for the special features of the PEC in the radionuclide transport analysis, suitable models have been developed. The time dependent radioactivity in the critical reactor areas and the integrated radioactivity release to the environment have been calculated. Subsequently, the radiological dose to operators in the main control room has been evaluated in order to verify control room accessibility during the accident evolution. Such evaluation is useful to establish the time for which operators can remain inside the control room to apply suitable corrective actions. (author). Poster presentation. 4 figs, 1 tab