Ageing of electric cables in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 217

6
Ageing of electric cables in light
water reactors (LWRs)

H. M. HASHEMIAN , Analysis and
Measurement Services Corp. , USA

DOI : 10.1533/9780857097453.2.284

Abstract : This chapter will address the ageing of nuclear power plant
cables and test methods for these cables to manage ageing and verify
reliability. The focus will be on instrumentation and control (I&C) cables,
low-voltage cables and medium-voltage cables. Ageing due to long-term
exposure to temperature, radiation, humidity, and other environments
can cause the cable insulation material to deteriorate, allowing moisture
into the cable. This can in turn cause cable failure and jeopardize plant
safety. Various techniques are available to assess cable condition and
health, including electrical and mechanical measurements, and chemical
tests. Of these, electrical measurements are preferred as they allow in-situ
cable testing in operating plants. Prognostic techniques estimate residual
life of cables using data from periodic tests. To guard against ageing,
nuclear power plants are implementing ageing management programs
and regulators are writing new requirements for acceptable programs and
techniques for cable ageing management.

Key words : insulation resistance, high-potential (Hi-Pot), partial
discharge, quality factor, dissipation factor, AgeAlert TM , LCR (inductance,
capacitance, and resistance) tests, time domain refl ectometry, frequency
domain refl ectometry, reverse time domain refl ectometry.

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6.1 Introduction

The thousands of miles of electrical cable and wire in light water reactors
deliver the power and the signals enabling safety- and non-safety-related
equipment to operate in normal and in post-accident conditions (U.S. NRC,
2010a; Hashemian, 2010; AMS Corp., 2011). All plant instrumentation and
control (I&C) systems depend on reliable plant wiring (AMS Corp., 2010).
They bring the necessary signals to the operators, control equipment, and
safety systems, as well as delivering commands to activate relays, pumps,
valves and motors. Reliable instrumentation signals are often essential to
maintaining redundancy or containing an accident, and the loss of a cable
can result in the loss of crucial performance and operational data. Similarly,