A Reliability Physics Model for Aging of Cable Insulation Materials (NUREG/CR-6869, BNL-NUREG-73676-2005)

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Publication Information

Manuscript Completed: February 2005
Date Published: March 2005

Prepared by:
T.-L. Chu, M. Subudhi, and J. Lehne

Energy Science and Technology Department
Brookhaven National Laboratory
Upton, New York 11973-5000

A.J. Buslik, NRC Project Manager

Prepared for:
Division of Risk Analysis and Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6371

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Abstract

This report presents a method for predicting the probability that the insulation of an aged instrumentation or control cable inside of containment will reach a critical level of embrittlement. The critical level of embrittlement can be used to support an assessment of the probability that the cable will fail to perform its function if exposed to a loss of coolant accident (LOCA). However, there are instances where cables with severely embrittled insulation have performed their function, in tests. The method predicts the probability distribution for the time it takes for the insulation of a cable subjected to a constant dose rate and temperature to reach a critical level of embrittlement. The embrittlement level is measured by the elongation at break (EAB), a condition of the cable, the greater the EAB the less the embrittlement. In order to incorporate the results in a probabilistic risk assessment, it would be necessary to estimate the probability that a cable which has reached a critical level of embrittlement would fail to perform its intended function in a LOCA.