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Report to The American Physical Society of the study group on radionuclide release from severe accidents at nuclear power plants

1985; American Physical Society; Volume: 57; Issue: 3 Linguagem: Inglês

10.1103/revmodphys.57.s1

1539-0756

Richard Wilson, K.J. Araj, Augustine O. Allen, Peter Auer, David G. Boulware, F.C. Finlayson, Simon L. Goren, Clark H. Ice, L. J. Lidofsky, A.L. Sessoms, Mary LaSalle Shoaf, I. Spiewak, Thomas Tombrello, H. S. Gutowsky, Andreas Acrivos, Herman Feshbach, William A. Fowler,

Combustion and Detonation Processes

In 1983, The American Physical Society formed a study group on radionuclide release from severe accidents at nuclear power plants to "review the adequacy of the technical base upon which the phenomenological models for radionuclide release from postulated severe reactor ac- cidents are constructed, the adequacy of the models them- selves, and the correct use of the complex computer codes that incorporate these models in the analyses of accident sequences."The impetus to the existing research came from the ob- servation that much less radioactive iodine was released during the Three Mile Island accident than had been ex- pected in an accident of that magnitude.It is of obvious interest to inquire how general that observation is.Although this executive summary describes, explains, and paraphrases some of the conclusions of this report, any reference should be to the specific conclusion as writ- ten in Chapter VIII rather than to the executive sum- mary.This report is concerned with the release of radionu- clides from a hypothetical severe nuclear reactor accidentmore severe than any that has yet taken place.It discusses both the predictions and the scientific basis for making them.Although we have not calculated prob- abilities of individual accident sequences, we have chosen for detailed discussion those sequences deemed by others to be "risk dominant" or to involve a wide range of physi- cal and chemical phenomena.The study group finds considerable progress in develop- ing both a scientific basis and computational ability for predicting the consequences of hypothetical nuclear reac- tor accidents since the Reactor Safety Study of 1975 (WASH-1400) which is the current basis for regulation concerned with severe accidents.In several cases, the new calculations indicate that significantly smaller quantities of radionuclides reach the environment than calculated in the Reactor Safety Study.In other cases, the calculated quantities have not changed dramatically.A reactor accident can lead to severe consequences only if several barriers between the radioactivity and the envi- ronment are breached.One postulated scenario by which this could occur is the failure of the core heat-removal systems.This would cause the core to overheat, lose coolant, melt, fall to the bottom of the reactor pressure vessel, melt through the vessel, and be quenched in the water of the reactor cavity.This would release steam and noncondensible gases to the reactor containment building, and thereby increase the pressure, which would stress the containment.The Reactor Safety Study assigned a high probability one in tenthat the containment would fail at this time.This is now considered to be very unlikely.Once the water in the reactor cavity is evaporated, the core would remelt from the heat generated by the decay of the fission products and would attack the concrete floor.This interaction would be very complex, releasing gases and radioactive aerosols.Calculations indicate that this would cause the containment building to fail from overpressure many hours lateralthough it is possible (and claimed by some investigators) that the containment would hold for many days.If the containment does not APS Study Group on Severe Accidents at Nuclear Power Plants IV.D.6.The impact of hole size on the source term IV.D.7.Summary IV.E.Containment loads IV.E.1.Categorization IV.E.2.Hydrogen burning IV.E.3.Steam explosions (rapid phase transitions; superheat explosions) IV.E.4.Late containment failures IV.E.5~Earthquakes IV.E.6.Summary V. Computer Codes and Their Validation V.A.The uses of computer codes V.B.A sample suite of accident model codes V.B.1.The inventory of radionuclides in the fuel (ORIGEN) V.B.2.The thermal hydraulics code (MARCH) V.B.3.Details of MARCH V.B.4.MERGE V.B.5.Mode1ing of fission product releases ( CORSOR ) V.B.6.Transport and deposition of fission prod- ucts (TRAP-MELT) V.B.7.The core-concrete interaction (INTER/CORCON ) V.B.8.Production of H2 and CO (VANESA)V.B.9.Aerosol deposition code (NAUA)V.B.10.Removal by ice condensers (ICEDF)V.B.11.Water suppression pool removal (SPARC) V