TABLE OF CONTENTS During the past 45 years of peaceful use of nuclear energy, no case of a nuclear reactor pressure vessel rupture has occurred. This hypothetical event is not included in the design basis accidents (DBAs) nor, according to the most recent trends, among the severe accidents to be reasonably considered. This is not, as it will be discussed more extensively later, the only possible choice: it, however, has been considered acceptable and practicable.
It is also necessary to remember that the burst of a nuclear vessel without previous mitigation measures, would easily result in an accident of the severity of the Chernobyl one. Every effort, therefore, is made by technical experts involved to prevent a break by design, construction and operation provisions. In order to meet this goal, however, extraordinary efforts and means are necessary. Indeed, even though there is good design experience for ordinary industrial vessels built and operated at the best quality level, the resulting failure rate is unacceptable for the best nuclear vessels, where the risk is kept at minimum level. It must be remembered that the frequency of catastrophic ruptures in Class 1 industrial, non-nuclear, pressure vessels ranges between 10 ?4 and 10 ?3 per year. The total service time of nuclear pressure vessels for civil and military uses is now somewhat higher than 10 000 reactor-years.
Other additional facts must be considered in the operating experience of nuclear pressure vessels. An example was the...
