[Federal Register Volume 70, Number 146 (Monday, August 1, 2005)]
[Notices]
[Pages 44127-44130]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-15124]


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NUCLEAR REGULATORY COMMISSION


Proposed Generic Communication Inaccessible or Underground Cable 
Failures That Disable Accident Mitigation Systems

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of opportunity for public comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to 
issue a generic letter (GL) to:
    Alert the licensees on the potential susceptibility of certain 
cables to affect the operability of multiple accident-mitigation 
systems;
    Request that addressees provide information regarding the 
monitoring of the inaccessible or underground electrical cables in 
light of the information provided in this letter. Adequate monitoring 
will ensure that cables will not fail abruptly and cause plant 
transients or disable accident mitigation systems when they are needed;
    Require addressees, to submit a written response to this generic 
letter pursuant to 10 CFR 50.54(f).
    This Federal Register notice is available through the NRC's 
Agencywide Documents Access and Management System (ADAMS) under 
accession number ML050880448.

DATES: Comment period expires September 30, 2005. Comments submitted 
after this date will be considered if it is practical to do so, but 
assurance of consideration cannot be given except for comments received 
on or before this date.

ADDRESSES: Submit written comments to the Chief, Rules and Directives 
Branch, Division of Administrative Services, Office of Administration, 
U.S. Nuclear Regulatory Commission, Mail Stop T6-D59, Washington, DC 
20555-0001, and cite the publication date and page number of this 
Federal Register notice. Written comments may also be delivered to NRC 
Headquarters, 11545 Rockville Pike (Room T-6D59), Rockville, Maryland, 
between 7:30 a.m. and 4:15 p.m. on Federal workdays.

FOR FURTHER INFORMATION, CONTACT: Thomas Koshy at 301-415-1176 or by e-
mail [email protected].

SUPPLEMENTARY INFORMATION: NRC Generic Letter 2005-XX, Inaccessible or 
Underground Cable Failures that Disable Accident Mitigation Systems.

Addressees

    All holders of operating licenses for nuclear power reactors, 
except those who have permanently ceased operations and have certified 
that fuel has been permanently removed from the reactor vessel.

Purpose

    The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
generic letter to:
    (1) Alert the licensees on the potential susceptibility of certain 
cables to affect the operability of multiple accident-mitigation 
systems.
    (2) Request that addressees provide information regarding the 
monitoring of the inaccessible or underground electrical cables in 
light of the information provided in this letter. Adequate monitoring 
will ensure that cables will not fail abruptly and cause plant 
transients or disable accident mitigation systems when they are needed.
    Pursuant to 10 CFR 50.54(f), addressees are required to submit a 
written response to this generic letter.

Background

    Cable failures have a variety of causes: Manufacturing defects, 
damage caused by shipping and installation, and exposure to electrical 
transients or abnormal environmental conditions during operation. Most 
of these defects worsen gradually over time as insulation degradation 
leads to cable failure.
    Electrical cables in nuclear power plants are usually located in 
dry environments. However, some cables are exposed to moisture from 
condensation and wetting in inaccessible locations such as buried 
conduits, cable trenches, cable troughs, duct banks, underground vaults 
and direct buried installations. Cables in these environments can fail 
due to various failure mechanisms such as water treeing (physical 
degradation), electrical treeing or other mechanisms of insulation 
degradation over varying voltage levels that decrease the dielectric 
strength of the conductor insulation.
    Information Notice (IN) 2002-12 described medium-voltage cable 
failures at Oyster Creek and Davis-Besse and several other plants which 
experienced long-term flooding problems in manholes and duct banks in 
which safety related cables were submerged. In response to the concern 
identified in IN 2002-12, several plants began manhole restoration 
projects to replace faulty dewatering equipment and cable supports and 
made other modifications. Several other plants have reported water 
removal problems but have not yet

[[Page 44128]]

reported any program for the early detection of potential failures.
    The rugged design of the electrical cables may prevent early 
failures even when they have been immersed in water for extended 
periods. When the staff observed that some of the cables qualified for 
40 years through the equipment qualification program were also failing 
at several nuclear stations, a detailed review was conducted. Even 
though there are only about a dozen cables susceptible for moisture-
induced damage in a nuclear station, the staff identified 23 Licensee 
Event Reports (LERs) and morning reports since 1988 on failures of 
buried medium-voltage cables from insulation failure. These reported 
events are believed to be only a very small fraction of the failures 
since not all cable failures are reportable. In most of the reported 
cases, the failed cables were in service for 10 years or more and none 
of these cables were identified as designed or qualified for long-term 
wetting or submergence.

Applicable Regulatory Requirements

    NRC regulations in title 10 of the Code of Federal Regulations 
(CFR) part 50, Appendix A, General Design Criterion (GDC) 4 states 
that, ``Structures, systems, and components important to safety shall 
be designed to accommodate the effects of and to be compatible with the 
environmental conditions associated with normal operation[.]''
    10 CFR, part 50, Appendix A, GDC 17 states that, ``Provisions shall 
be included to minimize the probability of losing electric power from 
any of the remaining [power] supplies, * * * loss of power from the 
transmission network, or the loss of power from the onsite electric 
power supplies.''
    10 CFR, part 50, Appendix A, GDC 18 states that, ``Electric power 
systems important to safety shall be designed to permit appropriate 
periodic inspection and testing of important * * * features, such as 
wiring, insulation, * * * the operability of the systems as a whole 
and, * * * the transfer of power among the nuclear power unit, the 
offsite power system, and the onsite power system.''
    10 CFR 50.65(a)(1) states that, ``Each holder of a license to 
operate a nuclear power plant * * * shall monitor the performance or 
condition of structures, systems, or components, * * * in a manner 
sufficient to provide reasonable assurance that such structures, 
systems, and components, * * * are capable of fulfilling their intended 
functions.''
    10 CFR, part 50, Appendix B, Criterion XI, requires, ``A test 
program shall be established to assure that all testing required to 
demonstrate that * * * components will perform satisfactorily in 
service is identified and performed[.]''
    These design criteria require that cables which are routed 
underground be capable of performing their function when subjected to 
anticipated environmental conditions such as moisture or flooding. 
Further, the design should minimize the probability of power 
interruption when transferring power between sources. The cable 
failures that could disable risk-significant equipment are expected to 
have monitoring programs to demonstrate that the cables can perform 
their safety function when called on. However, the recent industry 
cable failure data indicates a trend in unanticipated failures of 
underground/inaccessible cables that are important to safety.

Discussion

    Although nuclear plant systems are designed against single 
failures, undetected degradation of cables due to pre-existing 
manufacturing defects or wetted environments of buried or inaccessible 
cables could result in multiple equipment failures. The following are 
examples of risk-significant cable failures:
     The failure of power cables that connect the offsite power 
to the safety bus could result in an inability to recover offsite power 
far beyond the coping time considered for station blackout conditions. 
The incipient failures of these cables can go undetected because these 
cables generally remain de-energized when the plant is generating 
power.
     The failure of the power cables from an emergency diesel 
generator (EDG) to the respective safety bus (where the EDGs are 
located in separate buildings) would prevent recovery of standby power 
from the respective EDG and result in the unavailability of a full 
train of accident mitigation systems during a loss-of-offsite-power 
event (LOOP).
     The failure of the power cables to an emergency service 
water (ESW) or component cooling water pump can disable one train of 
emergency core cooling systems for long-term service unless the headers 
can be cross-connected and the redundant pump(s) can be lined up to 
supply sufficient cooling for both trains. If the EDGs are cooled from 
ESW or service water, the cable failure could disable the EDG and lose 
one train of standby power.
    At the Davis-Besse nuclear station, an underground cable insulation 
failure resulted in the trip of the 13.8kV circulating water pump 
breaker and loss of power to two other 4kV substations. The cable 
showed signs of insulation degradation caused by moisture intrusion 
(Inspection Report No: 05000346/2004017, ADAMS Accession No: 
ML050310426, issued on January 30, 2005). Generally, cable failure 
results in fault currents several orders of magnitude over the normal 
current. Until isolated by a breaker, the fault current or transient 
voltages travel on the immediate power systems, trip breakers that 
operate near their trip setpoint and fail other degraded insulation 
systems.
    As cables that are not qualified for wet environments are exposed 
to wet environments, they will continue to degrade with an increasing 
possibility that more than one cable will fail on demand from a cable 
fault or a switching transient. While a single failure may be 
manageable, multiple failures of this kind would pose undue challenges 
for the plant operators.
    Certain plants have reported failures in other safety systems such 
as auxiliary feedwater and containment spray systems with AC and DC 
power and control cables routed underground or along other inaccessible 
paths. Those degraded cables that are normally energized may fail to 
reveal their degraded condition, and the potential failure of the de-
energized safety systems might only be revealed during a demand for the 
mitigation capability.
    Certain licensees have attempted to periodically drain the 
accumulated water from the cable surroundings to avoid cable failures. 
In areas where the water table is relatively close to the cable, the 
water refills the cavity soon after the draining. In other cases, the 
water accumulates seasonally during snow fall or rain, filling the 
conduit or raceways, and cables may dry out whenever the humidity 
drops. In both cases, periodic draining may decrease the rate of 
insulation degradation but it does not prevent cable failures.
    Potential cable failures can be detected through state-of-the-art 
techniques for measuring and trending the condition of cable 
insulation. The cables that are susceptible to moisture-induced 
failures may vary from plant to plant, and they are generally routed in 
underground conduits, concrete duct banks, cable trenches, cable 
troughs, underground vaults or direct buried installations. Selective 
use of testing techniques, such as the partial discharge test, time 
domain reflectometry, dissipation factor testing, very low frequency AC 
testing, and broadband impedance spectroscopy, have helped licensees 
assess the condition of cable insulation with reasonable confidence,

[[Page 44129]]

such that cables can be replaced in a planned way during refueling 
outages. The Oconee Nuclear Station relied on the partial discharge 
test to monitor the condition of the emergency power supply cable 
insulation and replaced the cable during a scheduled outage (Inspection 
Report 50-269/99-12, 50-270/99-12, ADAMS Accession No: ML0036767490 
issued on September 21, 1999).
    A diagnostic cable test program provides reasonable confidence that 
the cable will perform its intended function. The frequency of the test 
should be commensurate with the observed cable test results. To avoid 
unplanned outages and unanticipated failures, certain licensees have 
adopted a baseline frequency of 5 years for new cables or more frequent 
testing when insulation degradation is observed.

Requested Information

    Within 90 days of the date of this generic letter, addressees are 
requested to provide the following information to the NRC:
    (1) Provide a history of inaccessible or underground cable 
failures, that are within the scope of 10 CFR 50.65 (the Maintenance 
Rule), for all voltage levels indicating the type, voltage class, years 
of service and the root causes for the failure.
    (2) Provide a description and frequency of all inspection, testing 
and monitoring programs, including surveillance programs, to detect 
degradation of inaccessible or underground cables used to support EDGs, 
offsite power, emergency service water, service water, component 
cooling water and other systems that are within the scope of 10 CFR 
50.65 (the Maintenance Rule).
    (3) If a program as described in (2) is not in place, explain why 
you believe such a program is not necessary.
    The required written response should be addressed to the U.S. 
Nuclear Regulatory Commission, ATTN: Document Control Desk, 11555 
Rockville Pike, Rockville, Maryland 20852, under oath or affirmation 
under the provisions of Section 182a of the Atomic Energy Act of 1954, 
as amended, and 10 CFR 50.54(f). In addition, a copy of the response 
should be sent to the appropriate regional administrator.

Required Response

    In accordance with 10 CFR 50.54(f), addressees are required to 
submit written responses to this generic letter. There are two options:
    (a) Addressees may choose to submit written responses providing the 
information requested above within the requested time period.
    (b) Addressees who cannot meet the requested completion date or who 
choose an alternate course of action are required to notify the NRC of 
these circumstances in writing as soon as possible but no later than 60 
days from the date of this generic letter. The response must address 
any alternative course of action proposed, and the basis for the 
acceptability of the proposed alternative course of action.

Reasons for Requested Information

    This generic letter requests addressees to submit information. The 
requested information will enable the NRC staff to determine whether 
applicable requirements (10 CFR part 50, Appendix A, General Design 
Criteria 4, 17 and 18; 10 CFR 50.65, and 10 CFR part 50, Appendix B, 
Criterion XI) are being met in regard to the operational readiness of 
the power system and accident mitigation systems and whether additional 
action is necessary on those topics. The staff considers 40 hours of 
information collection burden to be reasonable in light of the benefit 
gained to identify and correct unanticipated failures of accident 
mitigation systems.

Backfit Discussion

    Under the provisions of section 182a of the Atomic Energy Act of 
1954, as amended, and 10 CFR 50.54(f), this generic letter transmits an 
information request for the purpose of verifying compliance with 
applicable existing requirements. Specifically, the requested 
information will enable the NRC staff to determine whether applicable 
requirements (plant Technical Specification in conjunction with 10 CFR 
part 50, Appendix A, General Design Criteria 4, 17 and 18; 10 CFR 
50.65, and 10 CFR part 50, Appendix B Criterion XI) are being met in 
regard to the operation readiness of the power system. No backfit is 
either intended or approved in the context of issuance of this generic 
letter. Therefore, the staff has not performed a backfit analysis.

Federal Register Notification

    A notice of opportunity for public comment on this generic letter 
was published in the Federal Register on (xx Frxxxxx) on {date{time} . 
Comments were received from {indicate no of commentors by type{time} . 
The staff considered all comments that were received. The staff's 
evaluation of the comments is publicly available through the NRC's 
ADAMS under Accession No. ML052020036.

Paperwork Reduction Act Statement

    This generic letter contains information collection requirements 
that are subject to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 
et seq.). These information collections were approved by the Office of 
Management and Budget, approval No: 3150-0011, which expires on 
February 28, 2007.
    The burden to the public for these mandatory information 
collections is estimated to average 40 hours per response, including 
the time for reviewing instructions, searching existing data sources, 
gathering and maintaining the data needed, and completing and reviewing 
the information collection. The U.S. Nuclear Regulatory Commission is 
seeking public comment on the potential impact of the information 
collection contained in the generic letter and on the following issues:
    1. Is the proposed information collection necessary for the proper 
performance of the functions of the NRC, including whether the 
information will have practical utility?
    2. Is the estimate of burden accurate?
    3. Is there a way to enhance the quality, utility, and clarity of 
the information to be collected?
    4. How can the burden of the information collection be minimized, 
including the use of automated collection techniques?
    Send comments regarding this burden estimate or any other aspect of 
these information collections, including suggestions for reducing the 
burden, to the Records and FOIA/Privacy Services Branch (T-5 F52), U.S. 
Nuclear Regulatory Commission, Washington, DC 20555-0001, or by 
Internet electronic mail to [email protected]; and to the Desk 
Officer, Office of Information and Regulatory Affairs, NEOB-10202, 
(3150-0011), Office of Management and Budget, Washington, DC 20503.

Public Protection Notification

    The NRC may not conduct or sponsor, and a person is not required to 
respond to, a request for information or an information collection 
requirement unless the requesting document displays a currently valid 
OMB control number.

Contacts

    Please direct any questions about this matter to the technical 
contact listed below or the appropriate Office of Nuclear Reactor 
Regulation (NRR) project manager. Bruce A. Boger, Director, Division of 
Inspection Program Management, Office of Nuclear Reactor Regulation.

[[Page 44130]]

    Technical Contact: Thomas Koshy, NRR, 301-415-1176. E-mail: 
[email protected].

End of Draft Generic Letter

    Documents may be examined, and/or copied for a fee, at the NRC's 
Public Document Room at One White Flint North, 11555 Rockville Pike 
(first floor), Rockville, Maryland. Publicly available records will be 
accessible electronically from the Agencywide Documents Access and 
Management System (ADAMS) Public Electronic Reading Room on the 
Internet at the NRC Web site, http://www.nrc.gov/NRC/ADAMS/index.html. 
If you do not have access to ADAMS or if you have problems in accessing 
the documents in ADAMS, contact the NRC Public Document Room (PDR) 
reference staff at 1-800-397-4209 or 301-415-4737 or by e-mail to 
[email protected].

    Dated in Rockville, Maryland, this 22nd day of July 2005.

    For the Nuclear Regulatory Commission.
Patrick L. Hiland,
Chief, Reactor Operations Branch, Division of Inspection Program 
Management, Office of Nuclear Reactor Regulation.
[FR Doc. 05-15124 Filed 7-29-05; 8:45 am]
BILLING CODE 7590-01-P