Environmental Engineering Reference
In-Depth Information
are minimized. The systems within the scope of MEM might be divided
into high and low risk-signifi cant categories. The risk signifi cance has been
defi ned quantitatively by PSA or qualitatively by expert judgement. The
MEM is an adaptation of 10CFR50.65 for the VVER-440/213 design fea-
tures, Hungarian regulatory environment and plant practice.
There are two basic methods applied in the MEM: deterministic method,
that is control of maintenance via testing/measuring performance parame-
ters of components, and probabilistic method, that is assessing the effective-
ness of maintenance via comparison of reliability/availability parameters
at the level of component/system or plant. Performance parameters are
defi ned in accordance with safety class and risk signifi cance. The determin-
istic method is based on ASME OM Code. For example in case of pumps
the performance criteria to be checked are the head, fl ow-rate and vibration
level. Plant level deterministic performance parameters include the capac-
ity factor, thermal effi ciency of the unit and leakage of the containment
(%/day). Risk signifi cance and the probabilistic performance criteria are
set on the basis of PSA. High risk signifi cant SSCs are those which are in
90% cut-set, have a high contribution to CDF or high Fussell-Vessely rank.
Performance criteria for MEM are based on the reliability or unavailability
data of performing safety function. System level performance parameters
are, for example, failure rates per demand (failure/start) or run failure rate
(failure/time) during operation. Plant level performance parameters are
the CDF or some selected contributors to the CDF and other safety fac-
tors (unplanned reactor scrams or safety system actuations per year). The
MEM is being implemented at Paks; for the implementation of ASME OM
Code, the existing in-service and post-maintenance testing programmes of
the Paks NPP have to be modifi ed and amended. Probabilistic performance
criteria are under development at present. It is expected that the MEM will
improve the safety factors and capacity factors for the plant while the main-
tenance effort will be optimal. MEM is a prerequisite for license renewal
in Hungary, since it provides assurance for the correct functioning of active
components.
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8.5.3 Maintenance of environmental qualifi cation
Performance and functioning of active systems can be tested during oper-
ation and can be ensured via maintenance under maintenance rule (MR),
that is evaluation and assessment of the effectiveness of the maintenance
along safety criteria, and/or via implementation of the programme for main-
taining the environmental qualifi cation (EQ).
For I&C components operating under harsh conditions environmen-
tal qualifi cation should be implemented. When the older VVER-440 and
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