Using probabilistic methods for solving the problem of ensuring leak tightness of heat exchanger tubes of nuclear power plant steam generators - Probabilistic Safety Assessment for Optimum Nuclear Power Plant Life Management (PLiM) - page 306

9.4 Application of the generalised method of
probabilistic analysis and systematic method-
ology for analyzing and ensuring integrity of
steam generator heat exchanger tubes in nuclear
power plants with VVER-1000 and VVER-440
reactors

This section presents the results of application of the generalised method
of probabilistic analysis (see section 5.3) and system concept of strength
safety 138,139, etc to ensure integrity of the steam generator heat exchanger tubes
in nuclear power plants with VVER-440 and VVER-1000 reactors. The
section includes:
- a brief description of the system concept for strength safety;
- description of the guidance document (GD) developed on the basis of
the system concept, and conditions of its use;
- results of application of the GD 137 ;
- associated technical results obtained during the development of system
technology ensuring integrity of the steam generator tubes, namely the
impact of the technology on:
- kinetics of defects in the tubes;
- detectability of eddy current testing;
- detectability of the pneumohydraulic inspection method.
As already mentioned, the problem of ensuring the integrity of the heat
exchanger tubes was solved by the generalised method of probabilistic
analysis and system concept of strength safety which was then used to
formulate the document 137 .
The system concept to ensure the integrity of HETs has been
implemented in a number of power units in Russia and Ukraine. In all
cases, after applying the recommendations prepared on the basis of the
system concept the tube bundles of steam generators worked in these units
with high efficiency without unplanned shutdowns cused by unacceptable
leakage from the primary and secondary circuits.
Below are the results of applying this approach to ensure the integrity
of the steam generator heat exchanger tubes for reactors VVER-1000 and
VVER-440 reactors of nuclear power plants in operation in accordance
with the document in Ref. 137. These results represent a special case of
practical implementation of the system concept to ensure strength, operating
life, reliability, survivability and safety. The concept is described in greater
detail in Ref. 138.
The system concept is based on a systems approach which allows for
detailed consideration of the problem to find fast the optimum solution.
The central concept of the system approach is the concept of the system.
The following issues were resolved in considering the problem of
ensuring integrity of heat exchanger tubes using the system concept:

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