Probabilistic analysis of safety: Increasing the reliability and safety of nuclear power plant components - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 198

Table 6.1 Distribution of risk in relation to the location of the leak and the
state of the reactor

Contribu-
tion to
total risk of
TRMS

IE
frequency

IE IE code CDF

Large leak from hot loops,
power operation

2.05 ·
10 -8

LLOCA PO /HL 1.61 · 10 -5 29

Large leak from cold loop
power operation

5.03 ·
10 -8

LLOCA PO /CL 2.41 · 10 -5 70

Large leak from the hot loop,
hot shutdown

3.34 ·
10 -10

LLOCA HS /HL 1.79 · 10 -7 > 0.5%

Large leak from cold loop and
hot shutdown

7.21 ·
10 -10

LLOCA HS /CL 2.68 · 10 -7 1

7.18 ·
10 -8

Total 4.06 · 10 -5

￿ ￿ ￿ ￿ ￿

6.2 Main factors causing core melt under large-break LOCA.

Analysis of minimal cross sections (see Table 6.3) determines the most
significant failures of system components and erroneous personnel actions,
leading to reactor core melting. Large-break LOCA accidents include:
• in the AS 3 ET LLOCA PO/CL (leak from the cold loop, reactor at
power),
- failure to open the check valves on the injection lines into the cold
loop (21% of the total risk of CDF);
- common cause failures of emergency pumps make-up pumps (7% of
the total risk);
- failure of the control system for automatic switching to recirculation
through the sump due to human error when setting four relays (5% of the
total risk of CDF);