Ageing of electric cables in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 225

such as motor windings, sensors, transmitters, and detectors that may also be
detected using appropriate testing methods (AMS Corp., 2010).
Cable analysis and assessment methods require observing, measuring,
and trending indicators of cable condition that correlate to the physical
condition of the cable or its functional performance (U.S. NRC, 2010b).
According to the NRC, an 'ideal' condition monitoring technique should
have the following desired attributes: 'nondestructive and nonintrusive,
capable of measuring property changes or indicators that are trendable and
can be consistently correlated to functional performance during normal
service, applicable to cable types and materials commonly used in nuclear
power plants, provides reproducible results that are not affected by the
test environment or, if they are so affected, the results can be corrected
for those effects, able to identify the location of any defects in the cable,
allows the establishment of a well-defi ned end condition, and provides suf-
fi cient time before incipient failure to allow corrective actions' (U.S. NRC,
2010b). However, because the nuclear industry relies primarily on manufac-
turer qualifi cation data, it does insuffi cient testing to confi rm that cables can
operate dependably in the long term (IAEA, 2011).
Cable testing methods can be characterized in multiple ways (see
Table 6.1). In the broadest terms, two cable ageing methods are avail-
able: laboratory tests (involving microsampling, e.g. conducted in non-
operational conditions in a lab) and in-situ tests (conducted on cables as
installed in a plant) (U.S. NRC, 2010a; IAEA, 2011). However, another way
of categorizing cable ageing methods is life testing versus electrical testing.
Life-testing techniques involve testing - visually, physically, or chemically -
the physical properties (e.g. hardness) of spare cable samples of the same
cables actually installed and in operation at the plant. When such 'real-time'
testing is not possible or desirable, accelerated life testing can compress the
time required to test the ageing processes by 'pre-ageing' cable samples and
monitoring their performance when installed in the same environment as
actual in-service cables.
Electrical testing of cables involves the testing of electrical properties
such as insulation resistance/polarization index, voltage withstand, dielec-
tric loss/dissipation factor, time and/or frequency domain refl ectometry, and
partial discharge. These electrical testing methods can be further catego-
rized according to whether the inspection or test is performed in-situ on
electric cables in the plant or whether it is a laboratory-type test performed
on representative material specimens in a controlled laboratory setting.
Which of these testing techniques is used will depend on the type of insu-
lation material in the cable and type of environmental stressors to which
the cable is subjected (Hashemian, 2010). For example, historically, visual
and tactile inspection techniques have been the most commonly used meth-
ods for cables that are accessible. Some, such as the gel content and other

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