16.2 - Severe Accident Analysis (RRC-B) - EDF Hinkley Point

SUB-CHAPTER : 16.2PRE-CONSTRUCTION SAFETY REPORTCHAPTER 16: RISK REDUCTION AND SEVEREACCIDENT ANALYSESPAGE : 239 / 295Document ID.No.UKEPR-0002-162 Issue 043.2.2. Release from the Molten CoreRelease fractions from the molten core are given here for the most important radionuclides:• noble gases, iodine and caesium 100%• tellurium, selenium 25%• strontium 3%(Iodine is considered to be mainly in the form of aerosols, 2.5% in elemental form and 0.2%in organic form.)A list of all relevant elements is given in Section 16.2.3 - Table 1 with corresponding releasefractions.The proportions of radiologically significant nuclides released from the molten core materialgenerally correspond to the proportions usually seen in core melt accident analyses. Therelease fractions of noble gases, iodine and caesium isotopes are all equal to 1.In addition to the in-vessel release an ex-vessel release also occurs, resulting essentiallyfrom melt-concrete interaction. This second fraction of the total release plays a particular rolein terms of the release fractions for the less volatile fission products.Because of the effective basemat cooling in EPR, melt-concrete interaction is ruled out; therelease fractions for the alkaline earth-metals strontium and barium are at least one order ofmagnitude lower than for those cases in which melt-concrete interaction was consideredduring release. Furthermore, ruling out melt-concrete interaction means that, in the mostunfavourable cases, the main portion of the release of all relevant radionuclides into thecontainment atmosphere would occur within the first few hours of the accident.The release fractions from the molten core for the radionuclides most important forradiological consequences to an individual (noble gases, iodine and caesium) are quitesimilar to those taken into account for operating French plants. The French calculationspresented in this report (see section 3.4.) have been carried out considering the highestrelease level from the French and German approaches (See Section 16.2.3 - Table 1).3.2.3. In-containment aerosol behaviourThe quantity of airborne aerosols and (non-aerosol) elemental iodine decreases due todeposition in the containment.{ CCI Removed }