[Federal Register Volume 73, Number 49 (Wednesday, March 12, 2008)]
[Notices]
[Pages 13258-13261]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-4902]


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NUCLEAR REGULATORY COMMISSION


Proposed License Renewal Interim Staff Guidance LR-ISG-2008-01: 
Staff Guidance Regarding the Station Blackout Rule (10 CFR 50.63); 
Associated With License Renewal Applications; Solicitation of Public 
Comment

AGENCY: U.S. Nuclear Regulatory Commission.

ACTION: Solicitation of public comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is soliciting 
public comment on its Proposed License Renewal Interim Staff Guidance 
LR-ISG-2008-01 (LR-ISG) for clarification to its previously issued LR-
ISG-02, ``Staff Guidance on Scoping of Equipment Relied on to Meet the 
Requirements of the Station Blackout (SBO) Rule (10 CFR 50.63) for 
License Renewal,'' dated April 1, 2002, which has been incorporated in 
the License Renewal Standard Review Plan. This LR-ISG provides 
additional clarification to the staff position on the license renewal 
scoping requirements regarding the offsite power system for SBO 
recovery. The NRC staff issues LR-ISGs to facilitate timely 
implementation of the license renewal rule and to review activities 
associated with a license renewal application. Upon receiving public 
comments, the NRC staff will evaluate the comments and make a 
determination to incorporate the comments, as appropriate. Once the NRC 
staff completes the LR-ISG, it will issue the LR-ISG for NRC and 
industry use. The NRC staff will also incorporate the approved LR-ISG 
into the next revision of the license renewal guidance documents.

DATES: Comments may be submitted by May 12, 2008. Comments received 
after this date will be considered, if it is practical to do so, but 
the Commission is able to ensure consideration only for comments 
received on or before this date.

ADDRESSES: Comments may be submitted to: Chief, Rulemaking, Directives 
and Editing Branch, Office of Administration, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001. Comments should be delivered to: 
11545 Rockville Pike, Rockville, Maryland, Room T-6D59, between 7:30 
a.m. and 4:15 p.m. on Federal workdays. Persons may also provide 
comments via e-mail at [email protected]. The NRC maintains an Agencywide 
Documents Access and Management System (ADAMS), which provides text and 
image files of NRC's public documents. These documents may be accessed 
through the NRC's Public Electronic Reading Room on the Internet at 
http://www.nrc.gov/reading-rm/adams.html. Persons who do not have 
access to ADAMS or who encounter problems in accessing the documents 
located in ADAMS should contact the NRC Public Document Room (PDR) 
reference staff at 1-800-397-4209, 301-415-4737, or by e-mail at 
[email protected].

FOR FURTHER INFORMATION CONTACT: Ms. Stacie Sakai, Project Manager, 
Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001; telephone 301-415-1884 or by e-
mail at [email protected].

SUPPLEMENTARY INFORMATION: Attachment 1 to this Federal Register 
notice, entitled Staff Position and Rationale for the Proposed License 
Renewal Interim Staff Guidance LR-ISG-2008-01: Staff Guidance Regarding 
the Station Blackout Rule (10 CFR 50.63) Associated with License 
Renewal Applications,'' contains the NRC staff's rationale for 
publishing the proposed LR-ISG-2008-01. Attachment 2 to this Federal 
Register notice, entitled Proposed License Renewal Interim Staff 
Guidance LR-ISG-2008-01: Staff Guidance Regarding the Station Blackout 
Rule (10 CFR 50.63) Associated with License Renewal Applications,'' 
contains the additional clarification to the current staff position on 
the license renewal SBO scoping requirements.
    The NRC staff is issuing this notice to solicit public comments on 
the proposed LR-ISG-2008-01. After the NRC staff considers any public 
comments, it will make a determination regarding issuance of the 
proposed LR-ISG.

    Dated at Rockville, Maryland this 5th day of March, 2008.


[[Page 13259]]


    For the Nuclear Regulatory Commission.
Pao-Tsin Kuo,
Director, Division of License Renewal, Office of Nuclear Reactor 
Regulation.

Attachment 1--Staff Position and Rationale for the Proposed License 
Renewal Interim Staff Guidance LR-ISG-2008-01: Staff Guidance Regarding 
the Station Blackout Rule (10 CFR 50.63) Associated With License 
Renewal Applications

Staff Position

    Consistent with the requirements specified in Title 10, Sec.  
54.4(a)(3), of the Code of Federal Regulations (10 CFR 54.4(a)(3)) and 
10 CFR 50.63(a)(1), the scope of license renewal should include the 
offsite recovery path from the transmission system to the Class 1E 
distribution system. Accordingly, the offsite recovery paths that must 
be included within the scope of license renewal, in accordance with 10 
CFR 54.4(a)(3), consist of circuits from two independent sources. Both 
paths start from the switchyard breaker to the plant Class 1E safety 
buses. This path includes (1) switchyard circuit breakers that connect 
to the offsite power system (i.e., grid), (2) power transformers, (3) 
intervening overhead or underground circuits (i.e., cables, buses and 
connections, transmission conductors and connections, insulators, 
disconnect switches, and associated components), (4) circuits between 
the circuit breakers and power transformers, (5) circuits between the 
power transformers and onsite electrical distribution system, and (6) 
the associated control circuits and structures.

Rationale

    The license renewal rule, 10 CFR 54.4(a)(3), requires that the 
scope of license renewal include ``All systems, structures, and 
components relied on in safety analyses or plant evaluations to perform 
a function that demonstrates compliance with the Commission's 
regulations for * * * station blackout (10 CFR 50.63).'' The station 
blackout (SBO) rule, 10 CFR 50.63(a)(1), states that each light-water-
cooled nuclear power plant licensed to operate must be able to 
withstand and recover from an SBO of a specified duration that is based 
on factors that include ``(iii) The expected frequency of loss of 
offsite power; and (iv) The probable time needed to restore offsite 
power.'' In this regard, the SBO rule is consistent with the staff 
findings identified in the statement of considerations for the SBO rule 
and NUREG-1032, ``Evaluation of Station Blackout Accidents at Nuclear 
Power Plants,'' issued June 1988.
    During its evaluation of licensee compliance with the requirements 
in 10 CFR 50.63, ``Loss of All Alternating Current Power,'' the staff 
has assessed the offsite power recovery paths that are credited in the 
licensee evaluation of SBO coping duration. The SBO coping duration 
evaluation is based on the criteria specified in 10 CFR 50.63(a)(1). 
The staff's regulatory assessment and acceptance of licensees' 
compliance with the SBO rule for offsite power is based on the site-
related characteristics and power design characteristics as defined in 
Regulatory Guide (RG) 1.155, ``Station Blackout,'' issued August 1988, 
and also the availability and reliability of the offsite power 
including the protective coordination of switchyard breakers. The staff 
developed this guidance to ensure that scoping of SBO equipment in 
accordance with the requirements of 10 CFR 54.4(a)(3) is conducted in a 
manner consistent with the original staff evaluations of licensee 
compliance with the requirements of the SBO rule (10 CFR 50.63) to 
include equipment necessary for recovery.

Attachment 2--Proposed License Renewal Interim Staff Guidance LR-ISG-
2008-01: Staff Guidance Regarding the Station Blackout Rule (10 CFR 
50.63) Associated with License Renewal Applications

Staff Position

    Consistent with the requirements specified in Title 10, Sec.  
54.4(a)(3), of the Code of Federal Regulations (10 CFR 54.4(a)(3)) and 
10 CFR 50.63(a)(1), the scope of license renewal should include the 
offsite recovery path from the transmission system to the Class 1E 
distribution system. The offsite and onsite power circuits must permit 
functioning of structures, systems, and components necessary to respond 
to the event. The rationale for this position follows.

Rationale

    In the license renewal rule, 10 CFR 54.4(a)(3) requires that the 
scope of license renewal include ``All systems, structures, and 
components relied on in safety analyses or plant evaluations to perform 
a function that demonstrates compliance with the Commission's 
regulations for * * * station blackout (10 CFR 50.63).'' In the station 
blackout (SBO) rule, 10 CFR 50.63(a)(1), states that each light-water-
cooled nuclear power plant licensed to operate must be able to 
withstand and recover from an SBO of a specified duration that is based 
on factors that include ``(iii) The expected frequency of loss of 
offsite power; and (iv) The probable time needed to restore offsite 
power.'' In this regard, the SBO rule is consistent with the staff 
findings identified in the statement of considerations and NUREG-1032, 
``Evaluation of Station Blackout Accidents at Nuclear Power Plants,'' 
issued June 1988. In particular, with regard to factor (iv), the staff 
found that restoration of offsite power (0.6 hours median time to 
restore) is more likely to terminate an SBO event than restoration of 
the emergency diesel generators (8 hours median time to repair).
    In Appendix A, ``General Design Criteria for Nuclear Power 
Plants,'' to 10 CFR part 50, ``Domestic Licensing of Production and 
Utilization Facilities,'' General Design Criterion (GDC) 17, ``Electric 
Power Systems,'' requires that two physically independent circuits 
shall supply electric power from the transmission network to the onsite 
electric distribution system. These circuits must be designed and 
located so as to minimize to the extent practical the likelihood of 
their simultaneous failure under operating and postulated accident and 
environmental conditions. A switchyard common to both circuits is 
acceptable. Each of these circuits shall be designed to be available 
soon enough after a loss of all onsite alternating current (ac) power 
supplies and the loss of the other offsite electric power circuit to 
ensure that specified acceptable fuel design limits and design 
conditions of the reactor coolant pressure boundary are not exceeded. 
One of these circuits (the immediate access circuit) shall be designed 
to be available within a few seconds following a loss-of-coolant 
accident to ensure the maintenance of core cooling, containment 
integrity, and other vital safety functions.
    Plants not licensed in accordance with GDC 17 were licensed to 
satisfy plant-specific principal design criteria presented in the plant 
updated final safety analysis report (FSAR). These criteria are similar 
to GDC 17. The electric grid is the source of power to the offsite 
power system. Therefore, all operating plants have offsite power 
requirements similar to GDC 17. The plant technical specifications 
embody the operational restrictions for the design requirements for the 
loss of offsite power sources.
    SBO is the loss of offsite and onsite ac electric power to the 
essential and nonessential switchgear buses in a nuclear power plant. 
It does not include the loss of ac power fed from inverters powered by 
station batteries or loss of ac power from an alternate ac power 
source. The U.S. Nuclear Regulatory Commission added the SBO rule to 
the

[[Page 13260]]

regulations in 10 CFR part 50 because, as operating experience 
accumulated, concern arose that the reliability of both the offsite and 
onsite ac power systems might be less than originally anticipated, even 
for designs that met the requirements of GDC 17 and GDC 18, 
``Inspection and Testing of Electric Power Systems.'' The results of 
risk studies indicate that estimated core melt frequencies from SBOs 
vary considerably between plants and could be a significant risk 
contributor for some plants.
    As a result, the SBO rule required that nuclear power plants have 
the capability to withstand and recover from the loss of offsite and 
onsite ac power of a specified duration (the coping duration). In their 
plant evaluations, licensees followed the guidance specified in 
Regulatory Guide (RG) 1.155, ``Station Blackout,'' issued August 1988, 
and NUMARC 87-00, ``Guidelines and Technical Bases for NUMARC 
Initiatives Addressing Station Blackout at Light Water Reactors,'' to 
determine their required plant-specific coping duration. The agency 
based the criteria specified in RG 1.155 to calculate a plant-specific 
coping duration on the expected frequency of loss of offsite power and 
the probable time needed to restore offsite power, as well as the other 
two factors (onsite emergency ac power source redundancy and 
reliability) specified in 10 CFR 50.63(a)(1). In requiring that a 
plant's coping duration be based in part on the probable time needed to 
restore offsite power, 10 CFR 50.63(a)(1) specifies that the offsite 
power system be an assumed method of recovering from an SBO. 
Disregarding the offsite power system as a means of recovering from an 
SBO would not meet the requirements of the 10 CFR 50.63 rule and would 
result in a longer required coping duration.
    The use of the offsite power system within 10 CFR 50.63(a)(1) as a 
means of recovering from an SBO should not be construed to be the only 
acceptable means of recovering from an SBO. A licensee could, for 
example, recover offsite power or emergency (onsite) power. It is not 
possible to determine before an actual SBO event which source of power 
can be returned first. As a result, 10 CFR 50.63(c)(1)(ii) and its 
associated guidance in RG 1.155, Sections 1.3 and 2, require procedures 
to recover from an SBO that include restoration of offsite and onsite 
power.
    Based on the above, licensees rely on both the offsite and onsite 
power systems to meet the requirements of the SBO rule. Elements of 
both offsite and onsite power are necessary to determine the required 
coping duration under 10 CFR 50.63(a)(1), and the procedures required 
by 10 CFR 50.63(c)(1)(ii) must address both offsite power and onsite 
power restoration. It follows, therefore, that both systems are used to 
demonstrate compliance with the SBO rule and must be included within 
the scope of license renewal consistent with the requirements of 10 CFR 
54.4(a)(3). The onsite power system is included within the scope of 
license renewal on the basis of the requirements under 10 CFR 
54.4(a)(1) (safety-related systems). The equipment that is relied upon 
to cope with an SBO (e.g., alternate ac power sources) is included 
within the scope of license renewal on the basis of the requirements 
under 10 CFR 54.4(a)(3). The offsite power system is therefore 
necessary to complete the required scope of the electrical power 
systems under license renewal.
    The staff has recently noted during the review of license renewal 
applications that some applicants have not included all of the 
components and structures within the scope of license renewal needed 
for recovering the offsite source from an SBO event as required by 10 
CFR 54.4(a)(3). Failure to include all of the structures and components 
within the scope of license renewal will result in those structures and 
components not being subject to aging management review, and the 
effects of aging will not be adequately managed so that the intended 
function(s) will be maintained consistent with the current licensing 
basis for the period of extended operation in accordance with 10 CFR 
54.21(a)(1) and (a)(3).
    During its evaluation of licensee compliance with the requirements 
in 10 CFR 50.63, ``Loss of All Alternating Current Power,'' the staff 
has assessed the offsite power recovery paths that are credited in the 
licensee evaluation of SBO coping duration. The SBO coping duration 
evaluation is based on the criteria specified in 10 CFR 50.63(a)(1). 
The staff's regulatory assessment and acceptance of licensees' 
compliance with the SBO rule for offsite power is based on the site-
related characteristics and power design characteristics as defined in 
RG 1.155, and also the availability and reliability of the offsite 
power including the protective coordination of switchyard breakers.
    The offsite power systems of U.S. nuclear power plants consist of a 
transmission system component and a switchyard that provides a source 
of power and a plant system component that connects that power source 
to a plant's onsite electrical distribution system which powers safety 
equipment. The staff considers each plant design individually, 
reviewing the plant's FSAR and associated electrical drawings. The key 
to performing the scoping for the SBO recovery path is defining the 
boundary of the offsite power source at the switchyard. A switchyard 
can have multiple offsite lines supplying the switchyard buses. 
Although switchyard designs vary, most plants have either a ring bus or 
breaker-and-a-half scheme.
    The scoping boundary, as outlined in the Standard Review Plan-
License Renewal (SRP-LR), Section 2.5.2.1.1, should be from the breaker 
or breakers from the switchyard (connections to the line side). If 
there is a circuit breaker between the power transformer (startup, 
reserve, auxiliary, or main transformer) and the switchyard bus, and 
the circuit breaker is directly bolted to the switchyard bus, then that 
circuit breaker is acceptable as the scoping boundary. If there is a 
disconnect switch, but no circuit breaker exists between the 
transformer and the switchyard bus, then the circuit breaker(s) 
connected to the switchyard bus that feeds the power transformer 
(startup, reserve, auxiliary, or main transformer) should be acceptable 
as the scoping boundary.
    The circuit breaker, as the scoping boundary, provides connection 
to offsite power via the switchyard bus, which can be powered by any of 
the incoming transmission lines. This breaker should be at the 
transmission system voltage to ensure adequate protection of safety bus 
and the recovery of offsite power. The staff believes that the circuit 
breaker needs to be within the scope of license renewal because of its 
ability to provide plant power, protect downstream circuits and provide 
plant operator-controlled isolation and energization ability. In 
addition, a circuit breaker coordinates with other protective devices 
to minimize the probability of loss of offsite power and prevent 
transients from affecting the onsite distribution system as offsite 
power is being restored. For these reasons, a circuit breaker remains 
as the scoping boundary. Using a disconnect switch or other component 
downstream of the breaker is not consistent with the staff position of 
compliance with the SBO rule and is not acceptable for meeting the SBO 
scoping requirements for license renewal.
    As discussed above, for purposes of the license renewal, the staff 
has determined that the offsite recovery paths that must be included 
within the scope of license renewal, in accordance with 10 CFR 
54.4(a)(3), consist of circuits from two independent sources. Both 
paths start from the switchyard breaker to the plant Class 1E safety

[[Page 13261]]

buses. This path includes (1) switchyard circuit breakers that connect 
to the offsite power system (i.e., grid), (2) power transformers, (3) 
intervening overhead or underground circuits (i.e., cables, buses and 
connections, transmission conductors and connections, insulators, 
disconnect switches, and associated components), (4) circuits between 
the circuit breakers and power transformers, (5) circuits between the 
power transformers and onsite electrical distribution system, and (6) 
control circuit cables and connections and structures associated with 
components in the recovery path. The SBO recovery path scoping boundary 
ends at the line side of the switchyard breaker(s) at transmission 
system voltage. For the switchyard breakers, bolted connections to the 
switchyard bus and structural components supporting the breakers are 
within the scope of license renewal. The control circuit cables and its 
connections for the switchyard breakers are not within the scope of 
license renewal. Figures of different configurations of the SBO offsite 
power recovery path that are acceptable to the staff and meet the 
license renewal scoping requirements in accordance with 10 CFR 
54.4(a)(3) are available via ADAMS at Accession No. ML080520620.
    The ownership of switchyard components is not a factor in ensuring 
that the effects of aging will be adequately managed for components and 
structures needed for recovering the offsite circuits from an SBO event 
consistent with the requirements in 10 CFR 54.4, ``Scope,'' and 10 CFR 
54.21, ``Contents of Application--Technical Information.'' The staff 
recognizes that there are interface and control agreements between the 
licensee and transmission system operator. These agreements do not 
preclude the applicant from complying with requirements specified in 10 
CFR 54.4 and 10 CFR 54.21.
    Designating the appropriate offsite power system long-lived passive 
structures and components that are part of this circuit path as subject 
to an aging management review will ensure the maintenance of the bases 
underlying the SBO requirements over the period of the extended 
license. This is consistent with the Commission's expectations in 
including the SBO event under 10 CFR 54.4(a)(3) of the license renewal 
rule.

[FR Doc. E8-4902 Filed 3-11-08; 8:45 am]
BILLING CODE 7590-01-P