Importance of Severe Accident Radiological Releases and Definition of Large Release

摘要

Analysis results are presented on the determination of the importance of severe accidents radiological releases into the environment, in terms of various off-site consequences. It is shown that in addition to iodine, the release of tellurium, barium, cerium, cesium, curium, lanthanum, molybdenum, niobium, plutonium, ruthenium, strontium, yttrium and (radioactive) zirconium are important to early fatality health effects, provided ah equal and complete release of these nuclides were to be postulated; however, considering the conditions under which fission product releases occur, only the nuclides of iodine, cesium, tellurium, and to a lesser extent, the nuclides of molybdenum, strontium, and barium are consequentially of significance, because, quantitatively significant releases of the other nuclides are not envisioned. Furthermore, in terms of latent health effects, it is shown that nuclides of americium, cesium, cobalt, curium, and plutonium are important, if an equal and complete release were to be postulated. Here again, during severe accidents, large releases for the aforementioned nuclides other than cesium are not likely. Therefore, cesium remains as the nuclide of greatest significance from a standpoint of long-term effects of severe accidents. The noble gases are shown to be inconsequential. The paper also examines the potential implications of various definitions of "large release" based on the results of level-2 probabilistic safety assessments for typical light water reactors. It is shown that the definition of alternatives that are based on latent effects are more restrictive than those based on early effects, and for large reactors, those alternatives that are defined on the basis of simple release thresholds are generally less ambiguous and easier to define, implement, and verify.%Es werden Ergebnisse von Untersuchungen zur Bestimmung radiologischer Freisetzungen in die Umwelt bei schweren Störfällen im Hinblick auf verschiedene Folgen außerhalb des Anlagenstandorts behandelt. Neben der Freisetzung von Jod erweisen sich Freisetzungen von Tellur, Barium, Cer, Cäsium, Curium, Lanthan, Molybdän, Niob, Plutonium, Ruthen, Strontium, Yttrium und (radioaktivem) Zirkon, unter der Annahme einer gleich starken und vollständigen Freisetzung dieser Nuklide, als wichtig im Hinblick auf gesundheitliche Folgen mit früher Todesfolge. Berücksichtigt man allerdings die Bedingungen, unter denen Spaltprodukte freigesetzt werden, spielen nur die Nuklide Jod, Cäsium, Tellur und, in untergeordnetem Maße, Molybdän, Strontium und Barium eine Rolle, da quantitativ bedeutsame Freisetzungen anderer Nuklide nicht zu erwarten sind.