Regional Basic Professional Training Course in Korea

Regional Basic Professional Training Course (BPTC) on Nuclear Safety
• Pressure waves formed inside the reactor system acting on reactor internals;
• Pressurized thermal shock;
• Reactor vessel melt‐through;
• Mechanical impact of the escaping coolant jet and the corresponding reaction
forces on plant components and systems;
• Environmental impact of the escaping coolant on system and compo-
nent qualification requirements (humidity, temperature and radiation);
• Direct coolant radioactivity releases due to containment bypass;
• Containment pressurization;
• Radioactivity releases from the containment;
• Containment basemat melt‐through.
Any initiating event may be analyzed with respect to these safety aspects. Acceptance
criteria are basically related to these safety aspects.
In general, there are lots of initiating events, and it is not only very difficult, but also not
effective to analyze all initiating events. For practical reasons, it is recommended that all
initiating events are classified by groups with safety aspects and dominant phenomena. A
traditional categorization of the PIEs is based on frequency and potential consequences of
the event. The classification is intended to 1) ensure that a sufficiently broad spectrum of
initiating events has been considered, 2) categorize the initiating events by type and
expected frequency of occurrence so that only the limiting cases in each group need to be
quantitatively analyzed, and 3) permit the consistent application of specific acceptance
criteria for each postulated initiating event. In classifying all initiating events by the
frequencies, it is very difficult to accurately quantify the event frequency; there are
several guidelines to group initiating events into plant conditions. Table 8‐1 shows
❙ 476 ❙