Environmental Engineering Reference
In-Depth Information
a pronounced tendency to decompose in the presence of high temperature
and moisture conditions releasing sulphide which is a known promoter of
SCC. In the United States, to manage ageing of vessel head penetrations and
nozzles, the utilities are forced to conduct a regular inspection under ASME
Code Case 694. Some plants also conduct supplementary inspections on the
PWSCC sensitive zone. Many power plants conduct supplemented inspec-
tion and replace their RPV heads with new ones (IAEA, 2007).
7.3.5 Management practices in selected countries
In Japan, utilities inspect in accordance with JEAC-4205 (Japan Electric
Association Code for ISI Requirements), and the inspection requirements
are similar to those in the United States. For the RPV weld lines, a volu-
metric examination is conducted on a regular basis. In France, utilities con-
duct inspection according to their RSE-M (Rules for In-service Inspection of
Nuclear Power Plant Components), and also undertake water pressure test-
ing with acoustic emission monitoring, non-destructive inspection during the
outages, loose-parts (noise) monitoring during operation, leak detection dur-
ing operation and fatigue monitoring. The range of inspection covers the belt-
line region of the shell, all welds, top and bottom heads, nozzles and safe end
welds, penetrations, control rod drive housings, studs, threaded holes and sup-
ports. In Germany, utilities conduct regular inspection using the non-destruc-
tive inspection method in accordance with German Code KTA 3201.4.
7. 4
Case studies of management strategies
In this section we look at applied management practice around the world.
7.4.1 Degradation of reactor vessels
There have been no cases of ageing degradation of reactor vessels. Thermal
annealing at high temperature (475 ± 15°C) for 100-150 h has been applied
to plants operating in Russia since 1987 as a preventative measure (Badanin,
1989 ; Cole and Friderichs, 1991 ).
7.4.2 Degradation of reactor internals
There is a report that a guide tube support pin made of Alloy 750 was dam-
aged in Mihama Nuclear plant in Japan in 1978. The damaged pin was mov-
ing around as a foreign body and it was discovered in the steam generator
chamber. It was determined that the damage was from high stress in pri-
mary water at high temperature. After this incident, research studies were
conducted over many years to understand the damage mechanisms. It was
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