Environmental Engineering Reference
In-Depth Information
For low-cycle fatigue analysis of Safety Class 1 and 2 piping and
mechanical components, ASME BPVC was adapted for the calculations
(Katona, Rátkai and Pammer, 2011). This task also includes identifi ca-
tion of needs for fatigue monitoring. The most critical ones are the high
stresses in the body and sealing block of the main circulating pumps.
These, however, could be managed via focused non-destructive examina-
tion programmes.
Analysis of thermal ageing of Class 1 and 2 components focuses on
components manufactured from 15Ch2MFA, 22K, 08Ch18N9TL cast
stainless steel materials and also on welds (Sv04Ch19H11M3, EA400/10T,
Sv10ChMFT, IONI 13/55) which are sensitive to thermal embrittlement.
Signifi cant changes of material properties due to thermal embrittle-
ment are to be expected above 220°C operational temperature in case
of ferrit-pearlit materials or cast stainless steel. Only a few components
match these conditions at the Paks NPP. According to fatigue analyses
performed, there are no cases where crack propagation due to fatigue
might be expected. The analysis performed for the main gate valve cast
stainless steel body shows that crack propagation should not be expected
even if the J-R curve for C8 steel is changing due to embrittlement and a
crack is postulated.
For analysis of thermal stratifi cation for Class 1 and 2 pipelines, a mea-
suring system was operated at the Paks NPP Unit 1 pressurizer surge line
in 2000-2001. Assessment of the measured data shows signifi cant thermal
stratifi cation (110°C), which moved periodically from the pressurizer to the
hot leg. This temperature swing was maintained by the swing of water level
control in the pressurizer during the heat-up and cool-down. During normal
operation, the temperature differences were decreased to a negligible level.
A similar temperature monitoring system has been operating on both legs of
the surge line at Unit 3 since 2007. Evaluation of the measured data and the
subsequent fatigue analysis justify LTO for the pressurizer surge lines. Other
pipelines have also been identifi ed where thermal stratifi cation might occur.
These are the pipelines connecting coolant cleaning system No 1 to the pri-
mary system; the pipeline of the passive emergency core cooling system and
the feed-water system pipeline and also the auxiliary emergency feed-water
pipelines. Experience gained at other VVER-440/213 plants (Mochovce and
Dukovany NPP) has been taken into account in identifying the pipelines of
interest. Implementation of monitoring programmes is ongoing for these
pipelines with temperature and displacement measurements.
High-cycle fatigue analysis of fl ow-induced vibration of internal struc-
tures of the steam generator tubes shows that the fl ow-induced vibration
of the heat-exchange tubes does not cause signifi cant stresses compared to
those from operational loads. Taking into account 60 years of operation and
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