[Federal Register Volume 75, Number 123 (Monday, June 28, 2010)]
[Pages 36698-36700]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-15629]




Draft Regulatory Guide: Issuance, Availability

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of Issuance and Availability of Draft Regulatory Guide, 
DG-1216, ``Plant-Specific Applicability of Transition Break Size 
Specified in 10 CFR 50.46a.''


Regulatory Commission, Washington, DC 20555-0001, telephone: (301) 251-
7662, e-mail [email protected], or, Richard Jervey, U.S. Nuclear 
Regulatory Commission, Washington, DC 20555-0001, telephone: (301) 251-
7404, e-mail [email protected].

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I. Introduction

    The U.S. Nuclear Regulatory Commission (NRC) is issuing for public 
comment a draft guide in the agency's ``Regulatory Guide'' series. This 
series was developed to describe and make available to the public such 
information as methods that are acceptable to the NRC staff for 
implementing specific parts of the NRC's regulations, techniques that 
the staff uses in evaluating specific problems or postulated accidents, 
and data that the staff needs in its review of applications for permits 
and licenses.
    The draft regulatory guide (DG), entitled ``Plant-Specific 
Applicability of Transition Break Size Specified in 10 CFR 50.46a,'' is 
temporarily identified by its task number, DG-1216, which should be 
mentioned in all related correspondence. DG-1216 is a proposed new 
regulatory guide written to support implementation of proposed 
rulemaking setting forth an alternate approach for evaluating the 
performance of an emergency core cooling system (ECCS). The proposed 
rule, 10 CFR 50.46a, ``Risk-Informed Changes to Loss-of-Coolant 
Accident Technical Requirements,'' was published in the Federal 
Register on August 10, 2009, (74 FR 40006). The NRC regulatory 
framework for nuclear power plants consists of a number of regulations 
and supporting guidelines, including, but not limited to, General 
Design Criterion (GDC) 35, ``Acceptance Criteria for Emergency Core 
Cooling Systems for Light-Water Nuclear Power Reactors,'' as set forth 
in Appendix A, ``General Design Criteria for Nuclear Power Plants,'' to 
10 CFR part 50, ``Domestic Licensing of Production and Utilization 
Facilities'' and 10 CFR 50.46a. GDC 35 states, in part, that the 
licensee must calculate ECCS cooling performance in accordance with an 
acceptable evaluation model. Furthermore, the licensee must calculate 
ECCS cooling performance for a number of postulated loss-of-coolant 
accidents (LOCAs) of different sizes, locations, and other properties 
sufficient to provide assurance that the evaluation considered the most 
severe postulated LOCAs. The proposed 10 CFR 50.46a would provide an 
alternative to the existing, conservatively-set deterministic 
requirements for evaluating the performance of ECCS systems.
    Section 50.46a would contain alternative requirements for ECCS at 
nuclear power reactors established by using risk information based on 
the likelihood of pipe breaks of different sizes. The rule would divide 
all coolant piping breaks currently considered in emergency core 
cooling requirements into two size groups: breaks up to and including a 
``transition break size,'' and breaks larger than the transition size 
up to the largest pipe in the reactor coolant system. Selection of the 
transition size was based upon pipe break frequency estimates, the 
associated uncertainties, and the need to provide regulatory stability 
to guard against changes resulting from any future increases in the 
LOCA frequency estimates. Because pipe breaks smaller than the 
transition break size are considered more likely they would be analyzed 
using existing criteria for ensuring the reactor core stays cool during 
and after an accident. Larger breaks are considered less likely and 
would be analyzed with less conservative methods, but plants would 
still have to mitigate the effects of failure of the largest pipe and 
maintain core cooling. After the final rule is issued, power plant 
operators could make plant design changes that could enhance safety 
and/or provide operational benefits. The rule also specifies risk 
acceptance criteria to ensure that modified designs would continue to 
provide adequate protection of public health and safety.
    This draft guide describes a method that the staff of the NRC 
considers acceptable for demonstrating that the generic transition 
break size (TBS) specified in the proposed 10 CFR 50.46a is applicable 
to a specific plant. The proposed rule would require a licensee to 
conduct the evaluation described herein either before, or as part of, 
the initial application to modify a nuclear power plant under the 
proposed rule. The proposed rule would also require a more limited 
evaluation to demonstrate the continued applicability of the TBS after 
each subsequent plant modification. The entire evaluation is greatly 
simplified for plants that the NRC has approved for license renewal. 
The evaluation is also simplified for plants that the NRC has approved 
for leak before break (LBB) or that have applied for license renewal.
    This guide only applies to light-water reactor designs that have 
received a construction permit or operating license prior to January 1, 
2000. This guide does not apply to new light-water (i.e., evolutionary 
and passive) or to non-light water (i.e., high temperature gas or 
liquid metal) reactor designs. Supplemental guidance for applying 10 
CFR 50.46a to these reactor designs will be developed at a later date 
as needed.
    The NRC staff is currently soliciting feedback on whether a pilot 
program should be conducted to demonstrate the use of this draft guide. 
Information gained from a pilot program would be used in the 
development of the final regulatory guide and the final 10 CFR 50.46a 
rule. The NRC staff is also seeking one or more pilot plants to 
participate in such a program. One or more public meetings may be 
arranged to discuss a possible pilot program and support public input 
to the guidance development process. Comments related to the need for, 
or suggestions for, pilot plants are encouraged at this time.

II. Further Information

    The NRC staff is soliciting comments on DG-1216. Comments may be 
accompanied by relevant information or supporting data and should 
mention DG-1216 in the subject line. Comments submitted in writing or 
in electronic form will be made available to the public in their 
entirety through the NRC's Agencywide Documents Access and Management 
System (ADAMS).
    Because your comments will not be edited to remove any identifying 
or contact information, the NRC cautions you against including any 
information in your submission that you do not want to be publicly 
    The NRC requests that any party soliciting or aggregating comments 
received from other persons for submission to the NRC inform those 
persons that the NRC will not edit their comments to remove any 
identifying or contact information, and therefore, they should not 
include any information in their comments that they do not want 
publicly disclosed. You may submit comments by any of the following 
    1. Mail comments to: Rules, Announcements, and Directives Branch 
Mail Stop: TWB-05-B01M, Office of Administration, U.S. Nuclear 
Regulatory Commission, Washington, DC 20555-0001.
    2. Federal e-Rulemaking Portal: Go to http://www.regulations.gov 
and search for documents filed under Docket ID [NRC-2010-0229] Address 
questions about NRC dockets to Carol Gallagher, 301-492-3668; e-mail 
[email protected].
    3. Fax comments to: Rules, Announcements, and Directives Branch, 
Office of Administration, U.S. Nuclear Regulatory Commission at (301) 
    Comments would be most helpful if received by August 25, 2010. 
Comments received after that date will be considered if it is practical 
to do so, but the NRC is able to ensure consideration only for comments 
received on or before this date. Although a time limit is given, 
comments and suggestions in

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connection with items for inclusion in guides currently being developed 
or improvements in all published guides are encouraged at any time. 
Requests for technical information about DG-1216 may be directed to the 
NRC contact: Robert L. Tregoning, U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001, telephone: (301) 251-7662, e-mail 
[email protected], or, Richard Jervey, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001, telephone: (301) 251-7404, e-
mail [email protected].
    Electronic copies of DG-1216 are available through the NRC's public 
Web site under Draft Regulatory Guides in the ``Regulatory Guides'' 
collection of the NRC's Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/. Electronic copies are also available in 
ADAMS (http://www.nrc.gov/reading-rm/adams.html), under Accession No. 
ML100430356. The regulatory analysis may be found in ADAMS under 
Accession No. ML101530472.
    In addition, regulatory guides are available for inspection at the 
NRC's Public Document Room (PDR) located at 11555 Rockville Pike, 
Rockville, Maryland. The PDR's mailing address is USNRC PDR, 
Washington, DC 20555-0001. The PDR can also be reached by telephone at 
(301) 415-4737 or (800) 397-4205, by fax at (301) 415-3548, and by e-
mail to [email protected].
    Regulatory guides are not copyrighted, and Commission approval is 
not required to reproduce them.

    Dated at Rockville, Maryland, June 17, 2010.

    For the Nuclear Regulatory Commission.
Andrea D. Valentin,
Chief, Regulatory Guide Development Branch, Division of Engineering, 
Office of Nuclear Regulatory Research.
[FR Doc. 2010-15629 Filed 6-25-10; 8:45 am]