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LWR SEVERE ACCIDENT SOURCE TERMS: Part 2: Fission product release, transport and behavior in the containment

DOI: 10.1615/ICHMT.1995.RadTransfProcHeatMassTransfSevNuclReactAcc.250

T. Kress
Oak Ridge National Laboratory

R. Lee
U. S. Nuclear Regulatory Commission

D. Powers
Sandia National Laboratories

L. Soffer
U. S. Nuclear Regulatory Commission


Fission product releases to the environment, or source terms, are influenced by the highly diverse phenomena related to severe accident sequences. These phenomena govern fission product release and transport behavior in the core, the primary system and in the containment. The important parameters include core heatup. fuel element degradation and melting, pressure vessel attack and failure, possibly high pressure melt ejection, interaction of core debris with concrete, retention of fission products within the reactor coolant system, hydrogen burns or detonations, retention of fission products by suppression pools or ice beds, late revolatilization of fission products from surfaces, and containment integrity (containment bypass as well as the time and location of containment failure). Because of the multiplicity of accident sequences that can occur for a given plant as well as the diversity of the, as yet, imperfectly understood severe accident phenomena, it is not surprising that probabilistic risk assessments such as those documented in NUREG-1150 have indicated large uncertainties in source terms. The source term uncertainty significantly contributes to the overall uncertainty in the risk. Because of the impracticability of performing prototypic experiments, substantial reliance has been placed on the development and validation of detailed mechanistic computer codes for analyzing severe accident phenomena and the source terms associated with them. This paper discusses the extensive research and other efforts that have taken place over the last decade to address the technical issues which bear on being able to quantitatively describe source terms. It also summarizes our present state of knowledge and points out areas where additional research will add further to our understanding. Finally, this paper discusses the NRC's efforts in revising the licensing source term (TID-14844) and the implications of this revision, especially for siting and design of future power plants.

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