Environmental Engineering Reference
In-Depth Information
long time to begin oxidizing has substantial antioxidant levels, and therefore
minimal degradation (U.S. NRC, 2001).
Fourier transform infrared (FTIR) spectroscopy, a laboratory technique
for studying the molecular structure of materials,, can identify operating
conditions where heat may cause cable insulation to become brittle or
crack. FTIR involves applying infrared radiation to a small piece of cable
insulation using a spectroscope. The spectroscope measures the ability of
the material to absorb or transmit the radiation. When the chemical bonds
in the sample absorb the radiation they begin to vibrate at specifi c wave-
lengths. The FTIR technique compares the actual measured maximum
vibrations of these chemical bonds to their known maximum vibrations to
ascertain to what extent the bonds have already oxidized or degraded over
time. The more the cable surface has been exposed to heat over time, the
more likely the measured vibrations of the sample chemical bonds will dif-
fer from the original values.
FTIR is extremely accurate - measuring to one tenth of a degree
Fahrenheit - and enables relatively easy, trendable, non-destructive degra-
dation monitoring. However, it requires expensive equipment and a small
sample, which may be diffi cult to obtain from remote sections of a cable
circuit (U.S. NRC, 2001; 2010a; 2010b).
6.3.4 Limitations of individual analysis and
assessment methods
The techniques outlined here are often applied individually to assess cable
problems. However, none of these techniques can characterize the ageing
condition of a cable with confi dence, and most have never been evaluated
comprehensively to determine if the changes they identify in a cable are
correlated to cable age. Moreover, performing all these destructive/non-
destructive mechanical, electrical, and chemical tests on the 9.1 million feet
of cable and wiring in an LWR would be daunting and time consuming (AMS
Corp., 2010). To more accurately determine or model the residual life in the
cable network of a plant, a system and program is needed that combines
and integrates these methods in such a way as to provide a more objective
assessment of the health and ageing condition of low- and medium-voltage
cables (AMS Corp., 2010 ).
6.4
Residual life modeling
The servicing and maintenance of the miles of I&C, low- and medium-voltage
cables in each light water plant has historically been reactive in nature. Such
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