Fault tree analysis failure category

A study of the event trees allows one to determine the various containment failure modes and the characteristics of the radioactivity release to the environment following the possible accident sequences. By using the fault tree analysis we can then link each release to its associated probability of occurrence. It is found that many of the possible sequences in the event trees lead to similar types of radioactivity release, with the result that it is possible to summarize the consequences of the PWR accident in terms of as few as nine release categories, each with its corresponding probability. The corresponding figure for the BWR is six categories. 

This approach considered the unique aspects of the MARS reactor plant with respect to traditional PWRs. So, the HAZOP method was used to identify initiating events, the fault tree technique was used to evaluate the probability of failure of non-traditional components or systems and the event tree method was used to identify possible evolutions of accidental sequences. Twenty-eight different initiating events, grouped in 8 main categories, were identified and their evolutions were analyzed. The results of the probabilistic safety analysis are summarized in Figure IV-11. 

---