Medium Voltage Underground Cable White Paper NEI 06-05

EXECUTIVE SUMMARY
The Nuclear Energy Institute (NEI) offers the attached White Paper for your information
concerning the NRC concerns related to potential common-mode failure of medium voltage
underground cables. These concerns were expressed in a letter dated February 05, 2004. A
public meeting was held in June 2004 to discuss the staff concerns and review available
information. Following this meeting, NEI agreed to consider the concerns. After consultation
with our industry representatives, we decided that there was benefit in developing the attached
White Paper.

In December 2004, Nuclear Energy Institute (NEI) formed a Medium Voltage Underground
(MVU) Cable Task Force to address the performance questions. Following a meeting in January
2005, an industry survey was prepared to collect data concerning MVU cable installations,
manufacturing types, failure modes, and cable replacement attribute data, if failures had
occurred.

As a result of the survey, a more complete understanding as to the extent of the cable issue was
developed. A large segment of the installed MVU cables throughout the industry have not
experienced any problems at all. While several nuclear sites experienced some cable degradation
and failures due to specific cable designs and manufacturing types, virtually all were corrected
by cable replacement.

The purpose of this White Paper is to address the potential aging issues involved with MVU
cables, review cable construction, design improvements made over the years, and document
actual operating histories based on a comprehensive survey of installed MVU cables.
The Task Force analysis of the Survey results led to a recommended approach for the
management of cable aging. In addition, this White Paper identifies transition issues to be
considered by plants renewing their operating licenses.

MVU cables that experience prolonged, wet conditions may have degraded insulation, based
upon the insulation material. Thus, some MVU cables are more susceptible to the effects of
voltage surges, such as lightning, that can lead to failure. Increased care during installation and
the use of modern cable insulation have resolved the historic troubles. NEI Survey evaluations
conclude that MVU cable failures are random and are not a common-mode failure. Thus, we do
not believe that there is a generic regulatory concern that needs to be addressed.









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