[Federal Register Volume 68, Number 159 (Monday, August 18, 2003)]
[Notices]
[Pages 49529-49533]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-20994]


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NUCLEAR REGULATORY COMMISSION


Proposed Generic Communication; Risk-Informed Inspection Guidance 
for Post-Fire Safe-Shutdown Inspections

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 Regulatory Issue Summary (RIS) to inform 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, of the risk-informed 
inspection guidance that will be used by NRC inspectors to perform 
future post-fire safe-shutdown associated guidance inspections. The NRC 
is seeking comment from interested parties on the clarity and utility 
of the proposed RIS and the draft technical input that will be used to 
develop inspection guidance. The NRC will consider the comments 
received in its final evaluation of the proposed RIS.
    This Federal Register notice is available through the NRC's 
Agencywide Documents Access and Management System (ADAMS) under 
accession number ML032030584.

[[Page 49530]]


DATES: Comment period expires September 17, 2003. 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: Mark Henry Salley at (301) 415-2840 or 
by e-mail to [email protected].

SUPPLEMENTARY INFORMATION: 

NRC Regulatory Issue Summary 2003-XX: Risk-Informed Inspection Guidance 
for Post-Fire Safe-Shutdown Associated Circuit Inspections

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.

Intent

    The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
regulatory issue summary (RIS) to inform addressees of the risk-
informed technical input that will be used to develop inspection 
guidance used by NRC inspectors to perform future post-fire safe-
shutdown associated circuit inspections.

Background Information

    The regulatory requirements, guidance, and NRC staff's positions 
regarding post-fire safe-shutdown are contained in various NRC 
documents, including Title 10 of the Code of Federal Regulations, 
Section 50.48 (10 CFR 50.48), ``Fire Protection,'' and 10 CFR Part 50, 
Appendix A, General Design Criterion (GDC) 3. Nuclear power plants 
(NPPs) operating prior to January 1, 1979, were backfit to 10 CFR Part 
50, Appendix R, Section III G. NPPs licensed later were evaluated 
against Section 9.5-1 of NUREG-0800, Standard Review Plan (SRP). 
Regulatory Guide 1.189, ``Fire Protection,'' also provides regulatory 
guidance on post-fire safe shutdown. The extent to which these 
requirements or guidance are applicable to a specific NPP depends on 
the plant's age, commitments made by the licensee in establishing its 
fire protection plan, and license conditions regarding fire protection. 
One objective of the fire protection requirements and guidance is to 
provide reasonable assurance that fire-induced failures of associated 
circuits that could prevent the operation or cause maloperation of 
equipment necessary to achieve and maintain post-fire safe shutdown 
will not occur. As a part of its fire protection program each licensee 
performs an associated circuit analysis to evaluate and protect against 
these failures.
    Each NPP licensee has a post-fire safe-shutdown program that was 
reviewed and approved by the NRC either as a part of the licensee's 
compliance with the 10 CFR part 50, appendix R, backfit or as a part of 
the initial operating licensing basis reviews. Licensees are required 
to maintain and update this analysis as a condition of their operating 
license. The NRC routinely inspects the post-fire safe-shutdown program 
as a part of the triennial fire protection inspection of each licensee.

Summary of the Issue

    Beginning in 1997, the NRC staff noticed that a series of licensee 
event reports (LERs) identified plant-specific problems related to 
potential fire-induced electrical circuit failures that could prevent 
operation or cause maloperation of equipment necessary to achieve and 
maintain hot shutdown. The staff documented these problems in 
Information Notice 99-17, ``Problems Associated With Post-Fire Safe-
Shutdown Circuit Analysis.'' Based on the number of similar LERs, the 
NRC determined the issue should be treated generically. In 1998, the 
NRC staff started to interact with interested stakeholders in an 
attempt to understand the problem and develop an effective risk-
informed solution to the circuit analysis issue. Due to the number of 
different stakeholder interpretations of the regulations, the NRC 
decided to temporarily suspend the associated circuit portion of fire 
protection inspections. This decision is documented in an NRC 
memorandum from John Hannon to Gary Holahan dated November 29, 2000, 
(ML003773142). NRC also issued Enforcement Guidance Memorandum (EGM) 
98-002, Revision 2 (ML003710123).
    To address the differing interpretations of the regulations, the 
NRC contracted Brookhaven National Laboratory (BNL) to develop a post 
fire safe shutdown analysis letter report (ML023430533). This draft 
letter report provided a historical look at the essential elements of a 
post-fire safe-shutdown circuit analysis, regulatory requirements and 
NRC staff positions, successful industry implementations, and guidance 
for risk-informing the associated circuit analysis. During this period, 
the Nuclear Energy Institute (NEI) performed a series of cable 
functionality fire tests to be used in NEI's risk-informed guidance. 
Revision D, the latest revision of NEI 00-01, ``Guidance for Post-Fire 
Safe Shutdown Analysis,'' was issued in early 2003 (ML023010376). The 
results of the NEI cable functionality fire testing were reviewed by an 
expert panel. The purpose of this review was to develop risk insights 
into the phenomena of fire-induced failures of electrical cables. The 
Electric Power Research Institute (EPRI) coordinated this effort and 
issued the final report, ``Spurious Actuation of Electrical Circuits 
Due to Cable Fires: Results of an Expert Elicitation'' (Report No. 
1006961, May 2002).
    On February 19, 2003, the NRC conducted a facilitated, public 
workshop in Rockville, MD. The purpose of the workshop was to discuss, 
and gather stakeholder input on, proposed risk-informed post-fire safe-
shutdown circuit analysis inspection guidance. Using the above-
referenced documents as background, the goals of the workshop were to 
identify:
    (1) The most risk-significant associated circuit configurations;
    (2) other associated circuit configurations that require further 
research; and
    (3) low-risk-significant associated circuit configurations.
    The facilitated workshop was successful in meeting these goals. A 
complete transcript of the meeting is available in ADAMS (ML030620006).
    The staff has completed drafting the technical input that will be 
used to risk-inform inspector guidance for the most risk-significant 
associated circuit configurations (Item 1), identified other 
configurations that require further research (Item 2), and performed 
confirmatory research to verify the low-risk-significant configurations 
(Item 3) (ML030780326).
    In summary, the risk-informed inspection guidance will concentrate 
on associated circuits whose failure could cause flow diversion, loss 
of coolant, or other scenarios that could significantly impact the 
ability to achieve and maintain hot shutdown. The inspectors will pay 
particular attention to events that occur in the first hour. Inspectors 
will consider credible fire scenarios that could produce a thermal 
insult resulting in cable damage. The initial focus of the

[[Page 49531]]

inspectors will be on conductor-to-conductor shorts within a 
multiconductor cable, since risk insights gained from cable fire 
testing demonstrated that intra-cable shorting is the most probable 
cause of spurious actuations. Thermoplastic-cable-to-thermoplastic 
cable interactions are also highly probable and should be considered. 
To focus on the most risk-significant aspects, inspectors will assume a 
maximum of two concurrent spurious operations for each scenario 
evaluated. The details of this inspection are in the attached draft 
inspection guidance.

Backfit Discussion

    This RIS requires no action or written response and is, therefore, 
not a backfit under 10 CFR 50.109. Consequently, the NRC staff did not 
perform a backfit analysis.

Federal Register Notifications

    For some time the NRC staff has worked with NEI, members of the 
public, and other stakeholders to develop the technical input necessary 
to risk-informed the associated circuit inspection guidance referenced 
in this RIS. On February 19, 2003, the NRC staff held a facilitated 
public workshop in Rockville, MD, where public participation was 
solicited. A notice of the workshop was published in the Federal 
Register on December 27, 2002 (Vol. 67, No. 249, p. 79168).
    The draft RIS including the draft inspection guidance was published 
in the Federal Register to solicit public comments.

Paperwork Reduction Act Statement

    This RIS does not request any information collection.

Attachment: Draft Guidance for Risk-Informing NRC Inspection of 
Associated Circuits

Background

    In 1997, the NRC noticed that a number of licensee event reports 
(LERs) identified plant-specific problems related to potential fire-
induced electrical circuit failures that could prevent operation or 
cause maloperation of equipment necessary to achieve and maintain hot 
shutdown in the event of a fire. The staff documented this information 
in Information Notice 99-17, ``Problems Associated With Post-Fire Safe-
Shutdown Circuit Analysis.'' On November 29, 2000, inspection of 
associated circuits was temporarily suspended (ML003773142). During 
this period, the Nuclear Energy Institute (NEI) developed NEI 00-01, 
``Guidance for Post-Fire Safe Shutdown Analysis'' Rev. D (ML023010376). 
The staff contracted Brookhaven National Laboratory (BNL) to develop a 
post-fire safe shutdown analysis guidance letter report (ML023430533). 
The Electric Power Research Institute (EPRI) assembled an expert panel 
and issued ``Spurious Actuation of Electrical Circuits due to Cable 
Fires: Results of an Expert Elicitation'' (Report No. 1006961, May 
2002). Using the above-referenced documentation as background, the NRC 
conducted a facilitated public workshop on February 19, 2003, in 
Rockville, MD. The transcript of the meeting is available in ADAMS 
(ML030620006). Based on the information above, especially the 
facilitated workshop discussions, the staff developed the technical 
input for draft risk-informed inspector guidance. This guidance, 
initially transmitted in a memorandum to Cynthia Carpenter from John 
Hannon dated March 19, 2003 (ML030780326), is essentially the same as 
the guidance provided below with two notable exceptions. First, 
additional technical review of the probability of hot-shorts indicated 
thermoplastic cable-to-cable interactions should have been located in 
Bin 1 rather than Bin 2. Second, the statement ``Inspectors will not 
consider the impact of degraded control room instrumentation and 
indication circuits that might confuse operators pending additional 
research'' can be easily misinterpreted and has been deleted. A new 
section on instrumentation has been added in place of this statement. 
These changes have been made in the following guidance.

Discussion

    The discussion summarizes the general guidance that would be needed 
to develop an inspection procedure.
Basic Risk Equation
    The risk due to associated circuits can be evaluated using the 
following basic risk equation:

Risk = (fire frequency) x (likelihood of fire effects & cable 
attributes that
contribute to failure) x (likelihood of undesired consequences)

    The three factors in this equation are defined as follows:
    1. Fire Frequency. The fire frequency is based on a statistical 
analysis of nuclear power plant (NPP) operating experience. The fire 
protection significance determination process (SDP) provides a method 
and bases for estimating fire frequencies for plant areas. One unique 
aspect of circuit analysis is the potential need for evaluation of 
multiple areas (i.e., areas through which a cable or common set of 
cables is routed).
    2. Likelihood of Fire Effects & Cable Attributes that Contribute to 
Failure. There needs to be a credible fire threat in the area under 
review to damage the cable of concern. This threat may consist of in 
situ combustibles, or the actual or maximum allowable amount of 
transient combustibles as controlled by plant-specific procedures, or a 
combination thereof. The fire protection SDP provides methods and bases 
for the identification and analysis of these fire scenarios. The NRC 
has published fire dynamics tools (i.e., Draft NUREG-1805) which can be 
used to approximate the fire and its effects when more than a 
qualitative analysis is necesaary. The cable attributes should also be 
considered in assessing the likelihood of cable failure. Failures due 
to thermal insult from the fire result from heating in the hot gas 
layer, immersion in the plume, immersion in the flame zone (direct 
flame impingement), or radiant heating. All modes of heat transfer 
should be considered as appropriate to a given fire scenario.
    A. Thermoplastic Cables. Thermoplastic cables (typically non-IEEE 
383 qualified) should be assumed to fail if exposed to the hot gas 
layer or plume temperatures of 425[deg]F or greater for a minimum of 5 
minutes. In the case of radiant heat transfer, the cable should be 
assumed to fail if exposed to a minimum 5kW/m\2\ for 5 minutes. When a 
thermoplastic cable is within the flame zone of the fire (direct flame 
impingement) or in a cable tray that is burning, damage should be 
assumed to occur in 5 minutes.
    B. Thermoset Cables. Thermoset cables (typically IEEE 383 
qualified) should be assumed to fail if exposed to hot gas layer or 
plume temperatures of 700[deg]F or greater for a minimum of 10 minutes. 
In the case of radiant heat transfer, the cable should be assumed to 
fail if exposed to a minimum 10kW/m\2\ for 10 minutes. When a thermoset 
cable of concern is in the flame zone of the fire (direct flame 
impingement), or in a cable tray that is burning, damage should be 
assumed to occur in 10 minutes.
    C. Cable Failure Modes. For multiconductor cables testing has 
demonstrated that conductor-to-conductor shorting within the same cable 
is the most common mode of failure. This is commonly referred to as 
``intra-cable shorting.'' It is reasonable to assume that given 
failure, more than one conductor-to-conductor short will occur in a 
given cable. A second primary mode of cable failure is conductor-to-
conductor shorting between separate

[[Page 49532]]

cables, commonly referred to as ``inter-cable shorting.'' Inter-cable 
shorting is less likely than intra-cable shorting. At this time, the 
following configurations should be considered:
    [sbull] For any individual multiconductor cable (thermoset or 
thermoplastic), any and all potential spurious actuations that may 
result from intra-cable shorting, including any possible combination of 
conductors within the cable, may be postulated to occur concurrently 
regardless of number. However, as a practical matter, the number of 
combinations of potential hot shorts increases rapidly with the number 
of conductors within a given cable. For example, a multiconductor cable 
with three conductors (3C) has 3 possible combinations of two 
(including desired combinations), while a five conductor cable (5C) has 
10 possible combinations of two (including desired combinations), and a 
seven conductor cable (7C) has 21 possible combinations of two 
(including desired combinations). To facilitate an inspection that 
considers most of the risk presented by postulated hot shorts within a 
multiconductor cable, inspectors should consider only a few (three or 
four) of the most critical postulated combinations.
    [sbull] For any thermoplastic cable, any and all potential spurious 
actuations that may result from intra-cable and inter-cable shorting 
with other thermoplastic cables, including any possible combination of 
conductors within or between the cables, may be postulated to occur 
concurrently regardless of number.
    [sbull] For cases involving the potential failure of more than one 
multiconductor cable, a maximum of two concurrent spurious actuations 
should be assumed. For cases where more than two concurrent spurious 
actuations can occur as the result of intra-cable shorting within a 
single multiconductor cable they should be considered. The 
consideration of more than two concurrent spurious operations in more 
than two cables will be deferred pending additional research.
    [sbull] Inspectors will consider the potential spurious operation 
of a direct current (DC) circuit given failures of the associated 
control cables even if the spurious operation requires two concurrent 
hot shorts of the proper polarity (e.g., plus-to-plus and minus-to-
minus) provided the required source and target conductors are each 
located within the same multiconductor cable.
    [sbull] The consideration of thermoset cable inter-cable shorts 
will be deferred pending additional research.
    D. Instrumentation Circuits. Required instrumentation circuits are 
beyond the scope of this associated circuits guidance and must meet the 
same requirements as required power and control circuits. There is one 
case where an instrument circuit could potentially be considered as an 
associated circuit. If a fire-induced failure of an instrument circuit 
could interfere with the post-fire safe-shutdown capability, but not 
have a direct effect on systems and equipment needed to achieve and 
maintain hot shutdown, then the instrument circuit may be treated as an 
associated circuit and handled accordingly.
    3. Likelihood of Undesired Consequences. The inspectors must assess 
the potential consequence of the associated circuit failure. The 
inspector should review the specific NPP process and instrumentation 
diagrams (P&IDs)\1\ for flow diversions, loss of coolant, or other 
scenarios that could significantly impair the NPP's ability to achieve 
and maintain hot shutdown.\2\ For the specific area under evaluation, 
the inspector may wish to consider components that could prevent 
operation or cause maloperation as the components of interest. When 
considering the potential consequence of such failures, the inspector 
should also consider the time at which the prevented operation or 
maloperation occurs. Failures that impede hot shutdown within the first 
hour of the fire tend to be most risk-significant in a first-order 
evaluation. Consideration of cold shutdown circuits will be deferred 
pending additional research.
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    \1\ For NPPs that do not use P&IDs, the inspector will have to 
gather the same information from flow diagrams and cable routing/
logic diagrams.
    \2\ Hot shutdown is defined in the NPP technical specifications.
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Items To Be Deferred at This Time, Pending Additional Research
    The following items are either considered of relatively low risk 
significance and/or are being deferred pending additional research:
    [sbull] Inter-cable shorting for thermoset cables is considered to 
be substantially less likely than intra-cable shorting. Hence, the 
inspection of potential spurious operation issues involving inter-cable 
shorting for thermoset cables is being deferred pending additional 
research.
    [sbull] Inter-cable shorting between thermoplastic and thermoset 
cables is considered less likely than intra-cable shorting of either 
cable type or inter-cable shorting of thermoplastic cables. The 
inspection of spurious actuation issues involving inter-cable shorting 
between thermoplastic and thermoset cables is therefore being deferred 
pending additional research.
    [sbull] Pending further research, inspectors will not consider 
configurations involving three or more concurrent spurious operations 
involving more than three cables.
    [sbull] Recent testing strongly suggests that a control power 
transformer (CPT) in a control circuit can substantially reduce the 
likelihood of spurious operation. The power output of the CPT relative 
to the power demands of the controlled device(s) appears critical. 
Pending additional research, inspectors may defer the consideration of 
multiple (i.e., two or more) concurrent spurious operations due to 
control cable failures if they can verify that the power to each 
impacted control circuit is supplied via a CPT with a power capacity of 
no more than 150% of the power required to supply the control circuit 
in its normal modes of operation (e.g., required to power one actuating 
device and any circuit monitoring or indication features).
    [sbull] Recent testing strongly suggests that fire-induced hot 
shorts will likely self-mitigate (e.g., short to ground) after some 
limited period of time. Available data remains sparse, but there are no 
known reports of a fire-induced hot short that lasted more than 20 
minutes. This is of particular importance to devices such as air-
operated valves (AOVs) or pressure-operated relief valves (PORVs) which 
return to their de-energized position upon mitigation of a hot short 
cable failure. Pending further research, inspectors should defer the 
consideration of such faults if they can verify that a spurious 
operation of up to 20 minutes duration will not compromise the ability 
of the plant to achieve hot shutdown.
Items Not To Be Considered at This Time in Inspections
    The following items are considered of very low likelihood and/or 
low risk, and will not be considered in the risk-informed inspection 
process:
    [sbull] Open circuit (or loss of conductor continuity) conductor 
failures will not be considered as an initial mode of cable failure. 
Note that cable shorting (e.g., a short to ground) may result in an 
open circuit fault due to the tripping of circuit protection features.
    [sbull] Inter-cable short circuits involving the conductors of an 
armored cable will not be considered. Such failures are considered 
virtually impossible unless the short involves the cable's grounded 
armoring.
    [sbull] Inter-cable short circuits involving the conductors of one 
cable within a

[[Page 49533]]

conduit and the conductors of any other cable outside the conduit will 
not be considered. As with armored cables, such faults are considered 
virtually impossible. Note that intra-cable shorting for thermoplastic 
or thermoset cables and inter-cable shorting between thermoplastic 
cables inside a common conduit are possible.
    [sbull] Inspectors will not consider multiple high-impedance faults 
on a common power supply. Although such faults have been considered 
using deterministic methods for critical safe-shutdown circuits, such 
faults are considered of very low likelihood and often can be readily 
overcome by manual operator actions.
    [sbull] Inspectors will not consider three-phase, proper-polarity 
hot short power cable failures. In theory, such failures could cause a 
three-phase device to spuriously operate. However, such failures are 
considered of very low likelihood because the three distinct phases of 
power would have to align in the proper phased sequence to operate. 
Note that three-phase devices may still be subject to spurious 
operations due to faults in their related control and/or 
instrumentation circuits.
    [sbull] Inspectors will not consider multiple proper-polarity hot 
shorts leading to the spurious operation of a DC motor or motor-
operated device when the postulated failures involve only the DC 
device's power cables (e.g., those cables that run from the motor 
control center (MCC) to the device). Such failures are considered 
unlikely because a shunt and a field require five separate conductors 
to have the correct polarity and sequence in order to operate. DC 
devices may still be subject to spurious actuation given failures in 
their control and/or instrument circuits.

Summary

    In summary, the inspectors should focus on associated circuits 
whose failure could cause flow diversion, loss of coolant, or other 
scenarios that could significantly impair the ability to achieve and 
maintain hot shutdown, paying particular attention to those events that 
occur in the first hour. The inspectors should be able to develop 
credible fire scenarios that could produce a thermal insult resulting 
in cable damage. The inspectors should focus on conductor-to-conductor 
shorts within a multiconductor cable, since risk insights gained from 
cable fire testing have demonstrated that intra-cable shorting is the 
most probable cause of spurious actuations. The inspectors should also 
consider inter-cable shorting between thermoplastic cables. The 
inspectors should assume a maximum of two concurrent spurious 
operations for each scenario evaluated.

End

    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 at Rockville, Maryland, this 11th day of August, 2003.

    For the Nuclear Regulatory Commission.
William D. Beckner,
Chief, Reactor Operations Branch, Division of Inspection Program 
Management, Office of Nuclear Reactor Regulation.
[FR Doc. 03-20994 Filed 8-15-03; 8:45 am]
BILLING CODE 7590-01-P