Optimisation of hydraulic tests, technical certification and planned–preventative maintenance - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 268

carried out during operation);
- determine the time of next technical inspection; deadline for the next
technical inspection is determined depending on the actual characteristics
of residual defects, strength, useful life, safety, reliability and survivability
of EP;
- Determine the conditions of operation, maintenance and operational
control up to the next technical inspection, which would provide the level
of residual defects, reliability and safety in accordance with the established
requirements.
Below are the results of studies of the effect of periodicity of technical
inspection (TI) on the reliability of the main circulation line (MCL) and
the pressurizer (PRZ) of the VVER-1000 reactor. The inspection method
was described in Ref. 115. Initial data for calculation (defectiveness of
metal, mechanical properties, operating conditions, etc. correspond to
power units of the Balakovo NPP on the condition of compliance with the
standard terms of design, manufacture and operation, including inspection,
maintenance and repairs).
Figures 8.17 and 8.18 show the results of analysis aimed at determining
the effect of periodicity of MCL and PRZ technical inspection in the range
of up to 10 years. Reliability was determined by the criteria of resistance
to formation of leaks and damage during operation. The solid lines on the
graphs show the change in the probability of a leak or fracture during the
time between two adjacent TIs. It is evident that in both the MCL and PRZ,
the probability of leakage or failure varies only slightly and at a 10-year

Leak

Leak

￿ ￿ ￿ ￿ ￿

Rupture

Rupture

Frequency of TI, years Frequency of TI, years

8.17 (left) Dependence of probability of leakage and rupture on
frequency of TI under the conditions of NI and repair of identified
defects for MCP Du 850.
8.18 Dependence of probability of leakage and rupture on periodicity
of TI under the conditions of the NC and repair of identified defects
for the casing of the pressure compensator.