Source Terms und Release Frequencies

Contact: Klaus Gufler

Inventories of nuclear power plants, source terms and release frequencies are not among the easily accessible data of nuclear power plants. Although the available data contains some uncertainties, a sufficiently good data set has been created on the basis of collected information for European facilities (operating and planned). Data was collected from plant-specific probabilistic safety analyses (PSA), reports of the IAEA and OECD NEA, the EU as well as publications in journals, etc.

Within the Flexrisk domain 257 nuclear power plants, nuclear fuel cycle facilities and large research reactors were identified and appropriate characteristics were allocated. The relevant information comprises:

  • Location
  • Plant type
  • Startup and planned shutdown
  • Detailed power plant specifications
  • Safety features
  • Thermal and electrical power
  • Accident- and release frequencies

The selected nuclear plants were grouped in facilities with similar characteristics and appropriate release scenarios (release shapes) were defined. For every group two release scenarios from the broad spectrum of different accident scenarios were selected. A scenario with early and one with late release was chosen to be able to consider two accidents with different characteristics. Since the accident progression, release quantities and frequencies vary greatly and are very reactor specific, only limited comparison is possible. In order to obtain a meaningful picture, the analysis was focused to one accident scenario per reactor, where both, frequency and release quantities, appears plausible, to characterize the threat posed by a reactor.

For all postulated accidents starting time of release, duration of release and the release height were determined and, if necessary, up to two phases of the release were defined.

Based on the release shapes, the fractions of the released radio nuclides that were identified according to their radiobiological relevance in work package 4, were elaborated and assigned for each reactor type. The most relevant groups include iodine, noble gases, caesium, tellurium, strontium, and ruthenium.

The core inventories for different reactor types were identified for LEU and MOX cores. In order to assort them to the different facilities the inventories were scaled linearly, according to the thermal reactor power.