Abstract

In this work, distributed measurements of capacitance on a nuclear power plant (NPP) cable are examined for their effectiveness as a method of nondestructive evaluation. Many U.S. NPPs are approximately 40 years old and undergoing a costly process of license renewal, motivating inspection of cables, concrete, and other materials whose integrity are critical to the safe functioning of the plant. In particular, a shielded, tri-core instrumentation cable insulated with flame-resistant ethylene propylene rubber (FR-EPR) and jacketed with chlorinated polyethylene (CPE) was studied. A half-meter section of a 28.5-meter-long cable was thermally aged at 140 °C in an air-circulating oven for 1,600 h. Open-circuit capacitance measurements were made by connecting an Agilent LCR meter to the cable sample by means of a two-point probe test fixture, by which one conductor was maintained at positive potential (1 V) whereas the other two conductors and the cable shield were maintained at 0 V. Portions of cable were cut from the end of the cable and the capacitance remeasured after each portion was removed, developing a dataset from which the minimum value of damage ratio at which the damage is detectable via this method, approximately 12 %, could be inferred. This method is promising for practical application in NPPs since it offers the potential to detect unacceptable levels of aging in insulation polymers at locations along the cable that are remote from the cable end and are perhaps inaccessible. It is also capable of providing an estimate of the extent of the damage. The method offers the additional advantage of being applied via an existing cable connector or exposed cable terminal ends, which are typically accessible, unlike most of the cable length which is likely to be in cable trays or conduits thereby restricting direct access.

How to Cite:

Gagliani, R. ., Bowler, N. ., Glass, S. W. & Fifield, L. S., (2019) “Capacitance measurements for nondestructive testing of aged nuclear power plant cable”, Review of Progress in Quantitative Nondestructive Evaluation .