Environmental Engineering Reference
In-Depth Information
The integrated reliability indices of operating units and specific
indicators of reliability for some types of equipment are analysed in Ref.
48. Analysis was performed for three groups of units:
• put into operation from 1960 to 1965;
• put into operation from 1965 to 1970;
• put into operation from 1970 to 1975.
This grouping of equipment allows to perform the analysis of
developments in the operating time range from 10 to 40 years. Given the
fact that the age of most nuclear power units is 10 to 30 years (for example,
in France in 2008, just one block reaches the operating life of 30 years),
trend analysis of reliability of similar equipment in the period from 30 to
40 years can be very useful to develop measures to manage the ageing
nuclear power plant.
The main conclusion concerning the integral indices of reliability is
that unplanned unavailability of blocks decreases or remains constant over
time. In other words, further experience with the reliability of blocks is
gained, i.e. there is an effective feedback of operating experience.
With regard to the specific reliability parameters, the increasing trend
was identified for some types of equipment such as pumps, fans, valves,
switches, heat exchangers, etc. The parameters of 'ageing' for the linear
model are comparable with TIRGALEX data
49
.
Another practical conclusion concerns application of the strategy of
'minimum maintenance' which can lead to an increase in failure rate.
In addition, we show that even with a constant or decreasing failure
rate of equipment, the total unavailability may increase with time due to
increased frequency and duration of repairs related to non-critical equipment
failures, as shown in Fig. 2.11.
2.5.2
Data from operating experience of NPP
equipment
The main sources of data on the reliability of nuclear power plant equipment
are shown schematically in Fig. 2.12. In general, we can distinguish between
generalised (at the national level, according to the type of reactor, of
equipment, etc.) and specific data.
If we talk about specific data, in terms of analysis of ageing in the PSA,
the most qualitative and representative data are the data on the frequency of
initiating events, and reliability of components for use in PSA. These data
can be the basis for further analysis. However, these data are insufficient
for trend analysis of ageing and for developing time-dependent reliability
models.
The required additional information can be obtained from the primary
operation and maintenance of data and documents and/or summarised
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