Environmental Engineering Reference
In-Depth Information
It is diffi cult to inspect the inside of a nuclear reactor, but it is possible
to obtain information on physical damage, leakage and mechanical and
structural states through visual inspection of the accessible zone. When an
in-service inspection is being conducted, all fl ange closure studbolts and
heads are removed. At this time, damaged equipment can also be removed.
Equipment moved to the pool or which remains in the pressure vessel can
be inspected using a remote control camera. It is diffi cult to conduct ultra-
sonic testing on this equipment or to interpret the results, but eddy-current
testing is effective in measuring reduced thickness of pipes. Inspecting the
inaccessible zone using the monitoring systems is complicated. Therefore,
more effective remote control inspection equipment is needed (Morgan
and Livingston, 1995).
The general regulation of in-service inspection of reactor vessel internals
in ASME Section XI requires a visual inspection every ten years. Recently
the requirement has become a visual inspection (VT-1, VT-3) supplemented
with ultrasonic inspection of the baffl e former bolts. The baffl e former bolts
comprise the weakest part of the internals. Supplementary ultrasonic exam-
ination is carried out in accordance with ASME Section XI subsection IWB,
examination category B-N-3 in the United States and some other countries.
Development of the ultrasonic examination equipment used for inspecting
these bolts should take into consideration the existence of locking bar style
bolts and the accessibility problems.
7.3.3 Management techniques for steam
generator tubes
Degradation management in steam generators is possible with the help of
research and development or a technical support programme. Strategies
can be established by supplementing inspection and repair programmes
based on operating experience in power plants. Management of ageing can
be divided into the understanding, prevention, detection, monitoring and
mitigation of ageing. A measure to systematically combine the management
strategies is needed for steam generators which are widely used globally. An
effective strategy could also be established and efforts to reduce duplication
made through the cooperation of the equipment vendors and energy utility
companies as shown in Fig. 7.1.
With the techniques developed to date, such as shot peening, rotopeen-
ing and heating and temperature reduction of the hot leg side, it is possible
to reduce the tensile stress inside steam generator tubes. These measures
markedly postpone PWSCC initiation. Plugging, sleeving or changing the
affected pipes is effective in terms of repair. Secondary water chemis-
try control is the best defence against ageing damage on steam gener-
ator tubes. Measures to expand the life of the steam generator include
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