[Federal Register Volume 75, Number 174 (Thursday, September 9, 2010)]
[Pages 54918-54920]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-22490]




Draft Regulatory Guide, DG-1247, ``Design-Basis Hurricane and 
Hurricane Missiles for Nuclear Power Plants'' and Supporting Technical 
Basis Documents NUREG/CR 7004 and 7005

    DG-1247 is a proposed new regulatory guide. Issuance and 
Availability; Correction and Comment Period Extension:
AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of issuance; correction and comment period extension.


SUMMARY: On August 31, 2010 (75 FR 53352), the U.S. Nuclear Regulatory 
Commission (NRC) published a notice of issuance and availability of 
Draft Regulatory Guide (DG)--1247, ``Design-Basis Hurricane and 
Hurricane Missiles for Nuclear Power Plants.'' This Federal Register 
Notice did not provide all the information regarding the supporting 
technical basis documents NUREG/CR 7004 and 7005. Due to this 
correction the comment period has been extended to November 5, 2010.

Regulatory Commission, Washington, DC 20555-0001, telephone (301) 251-
7483, or e-mail [email protected].


I. Introduction

    The U.S. Nuclear Regulatory Commission (NRC) is issuing for public 
comment a draft guide in the agency's ``Regulatory Guide'' series and 
the supporting technical basis documents, NUREG/CR 7004 and 7005. 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, ``Design-Basis Hurricane 
and Hurricane Missiles for Nuclear Power Plants,'' is temporarily 
identified by its task number, DG-1247, which should be mentioned in 
all related correspondence. DG-1247 is a proposed new regulatory guide.
    This guide describes a method that the NRC staff considers 
acceptable to support reviews of applications that the agency expects 
to receive for new nuclear reactor construction permits or operating 
licenses under 10 CFR Part 50; design certifications under 10 CFR Part 
52, ``Early Site Permits; Standard Design Certifications; and Combined 
Licenses for Nuclear Power Plants'' (Ref. 9); and combined licenses 
under 10 CFR Part 52 that do not reference a standard design. 
Specifically, this regulatory guide provides new guidance that the 
staff of the NRC considers acceptable for use in selecting the design-
basis hurricane windspeeds and hurricane-generated missiles that a new 
nuclear power plant should be designed to withstand to prevent undue 
risk to the health and safety of the public. This guidance applies to 
the contiguous United States but does not address the determination of 
the design-basis hurricane and hurricane missiles for sites located 
along the Pacific coast or in Alaska, Hawaii, or Puerto Rico; the NRC 
will evaluate such determinations on a case-by-case basis. This guide 
also does not identify the specific structures, systems, and components 
that should be designed to withstand the effects of the design-basis 
hurricane or should be protected from hurricane-generated missiles and 
remain functional. Nor does this guide address other externally 
generated hazards, such as aviation crashes, nearby accidental 
explosions resulting in blast overpressure levels and explosion-borne 
debris and missiles, and turbine missiles. NUREG/CR 7004 is the 
technical basis for regulatory guidance on design-basis hurricane-borne 
missile speeds and NUREG/CR 7005 is the technical basis for regulatory 
guidance on design-basis hurricane wind speeds for new nuclear power 

[[Page 54919]]

II. Further Information

    Nuclear power plants must be designed so that they remain in a safe 
condition under extreme meteorological events, including those that 
could result in the most extreme wind events (tornadoes and hurricanes) 
that could reasonably be predicted to occur at the site. Initially, the 
NRC solely considered such conditions for tornadoes in Regulatory Guide 
(RG) 1.76, ``Design-Basis Tornado for Nuclear Power Plants,'' issued 
April 1974. The design-basis tornado windspeeds were chosen so that the 
probability that a tornado exceeding the design basis would occur was 
on the order of 10-7 per year per nuclear power plant. In 
March 2007, the NRC issued Revision 1 to RG 1.76, ``Design-Basis 
Tornado and Tornado Missiles for Nuclear Power Plants.'' Revision 1 to 
RG 1.76 relied on the Enhanced Fujita Scale which was implemented by 
the National Weather Service in February 2007. The Enhanced Fujita 
Scale is a revised assessment relating tornado damage to windspeed 
which resulted in a decrease in design-basis tornado windspeed criteria 
in Revision 1 to RG 1.76.
    Since design-basis tornado windspeeds were decreased as a result of 
the analysis performed to update RG 1.76, it was no longer clear that 
the revised tornado design-basis windspeeds would bound design-basis 
hurricane windspeeds in all areas of the United States. This prompted 
an investigation into extreme wind gusts during hurricanes and their 
relation to design-basis hurricane windspeeds. The NRC commissioned a 
report, NUREG/CR 7005, that considers peak-gust windspeeds and 
estimates maximum hurricane windspeeds for hurricanes that originate in 
the Atlantic and make landfall along the Atlantic and Gulf coasts of 
the contiguous United States. The NRC staff has determined that the 
design-basis hurricane windspeeds should correspond to the exceedance 
frequency of 10-7 per year, calculated as a best estimate. 
This is the same exceedance frequency used to establish the design-
basis tornado parameters in Revision 1 to RG 1.76. This exceedance 
frequency is also consistent with the Standard Review Plan (NUREG-0800) 
Section 2.2.3 (Evaluation of Potential Accidents) criterion for 
identifying design-basis events involving hazardous materials or 
activities on site and in the vicinity of a proposed site.
    To ensure the safety of new nuclear power plants in the event of a 
hurricane strike, NRC regulations require that a nuclear power plant 
design consider the impact of hurricane-generated missiles, in addition 
to the direct action of the hurricane wind. Hurricanes are capable of 
generating missiles from objects lying within the path of the hurricane 
wind and from debris of nearby damaged structures. To evaluate the 
resistance of barriers to penetration and gross failure, the hurricane 
missile velocities must also be defined. The NRC commissioned a report, 
NUREG/CR 7004, on design-basis hurricane-borne missile velocities. This 
report describes the method used to calculate velocities associated 
with several types of missiles considered for different hurricane 
windspeeds. The selected design-basis hurricane missile spectrum for 
nuclear power plants is the same as the design-basis tornado missile 
spectrum presented in RG 1.76. This spectrum includes (1) a massive 
high-kinetic-energy missile that deforms on impact (an automobile), (2) 
a rigid missile that tests penetration resistance (a pipe), and (3) a 
small rigid missile of a size sufficient to pass through any opening in 
protective barriers (a solid steel sphere).
    The hurricane missile analyses presented in NUREG/CR 7004 are based 
on missile aerodynamic and initial condition assumptions that are 
similar to those used for the analyses of tornado-borne missile 
velocities adopted for Revision 1 to RG 1.76. However, the assumed 
hurricane wind field differs from the assumed tornado wind field in 
that the hurricane wind field does not change spatially during the 
missile's flight time but does vary with height above the ground. 
Because the size of the hurricane zone with the highest winds is large 
relative to the size of the missile trajectory, the hurricane missile 
is subjected to the highest windspeeds throughout its trajectory. In 
contrast, the tornado wind field is smaller, so the tornado missile is 
subject to the strongest winds only at the beginning of its flight. 
This results in the same missile having a higher maximum velocity in a 
hurricane wind field than in a tornado wind field with the same maximum 
(3-second gust) windspeed. For example, the massive high-kinetic-energy 
tornado missile (a 1810 kg (4000 lb) automobile) in RG 1.76 is assigned 
a velocity of 41 m/s (92 mph) in tornado intensity Region I which has a 
design-basis tornado windspeed of 103 m/s (230 mph). The same missile 
is assigned a velocity of 68 m/s (152 mph) in a hurricane wind field 
with the same design-basis windspeed of 103 m/s (230 mph). The 1810 kg 
automobile missile will have a kinetic energy of 1.5x10 \6\ joules in 
the tornado wind field versus 4.2x10 \6\ joules in the hurricane wind 
    The NRC staff would like to point out that the missile speed 
analyses for both the tornado and hurricane massive high-kinetic-energy 
missile (the 1810 kg automobile) assume the missile starts its motion 
with zero initial velocity from an elevation of 40 meters above ground. 
Forces tending to increase the elevation of the hurricane missile with 
respect to the ground level (e.g., updrafts) are assumed to be 
negligible. However, rooftop mechanical (e.g., HVAC) equipment that is 
kept in place only by gravity connections is a source of heavy 
deformable debris when displaced during extreme-wind events. Buildings 
not designed for the hurricane winds can also continue to break up 
during the buildup of hurricane winds. Failures progress from the 
exterior building elements inward to the structural members (e.g., 
trusses, masonry units, beams, and columns). According to Section 7.1.1 
(Debris Potential at Safe Room Sites) of the Second Edition (August 
2008) of FEMA 361 (Design and Construction Guidance for Community Safe 
Rooms), the literature on hurricanes as well as tornadoes contains 
numerous examples of large structural members that have been 
transported by winds for significant distances by the wind field when a 
portion of exterior sheathing remains connected and provides an 
aerodynamic sail area on which the wind can act. An automobile 
hurricane missile with an initial elevation of 40 meters above ground 
could be considered a surrogate for such equipment and structures which 
can be found throughout a nuclear power plant site.
    Applications for new power plants will be expected to show that 
their applicable structures can independently withstand both the total 
design-basis tornado load and the total design-basis hurricane load as 
extreme environmental conditions. The staff plans to eventually revise 
the corresponding sections the Standard Review Plan to indicate that 
the design-basis hurricane windspeeds and hurricane-generated missiles 
specified in DG-1247 should be considered as loads to be sustained 
during extreme environmental conditions.
    The NRC staff is soliciting comments on DG-1247 and NUREG/CR 7004 
and 7005. Comments may be accompanied by relevant information or 
supporting data and should mention DG-1247 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).

[[Page 54920]]

DATES: The comment period closes on November 5, 2010.

ADDRESSES: You may submit comments by any one of the following methods. 
Please include Docket ID NRC-2010-0288 in the subject line of your 
comments. Comments submitted in writing or in electronic form will be 
posted on the NRC Web site and on the Federal rulemaking Web site 
Regulations.gov. 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 disclosed.
    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.
    Federal Rulemaking Web site: Go to http://www.regulations.gov and 
search for documents filed under Docket ID NRC-2010-0288. Address 
questions about NRC dockets to Carol Gallagher 301-492-3668; e-mail 
[email protected].
    Mail comments to: Cindy Bladey, Chief, Rules, Announcements and 
Directives Branch (RAD), Office of Administration, Mail Stop: TWB-05-
B01M, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or 
by fax to RAD at (301) 492-3446.
    You can access publicly available documents related to this notice 
using the following methods:
    NRC's Public Document Room (PDR): The public may examine and have 
copied for a fee publicly available documents at the NRC's PDR, Room O1 
F21, One White Flint North, 11555 Rockville Pike, Rockville, Maryland.
    NRC's Agencywide Documents Access and Management System (ADAMS): 
Publicly available documents created or received at the NRC are 
available electronically at the NRC's Electronic Reading Room at http://www.nrc.gov/reading-rm/adams.html. From this page, the public can gain 
entry into ADAMS, which provides text and image files of NRC's public 
documents. If you do not have access to ADAMS or if there are problems 
in accessing the documents located in ADAMS, contact the NRC's PDR 
reference staff at 1-800-397-4209, 301-415-4737, or by e-mail to 
[email protected]. DG-1247 is available electronically under ADAMS 
Accession Number ML100480890. In addition, electronic copies of DG-1247 
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/. The 
regulatory analysis may be found in ADAMS under Accession No. 
    Regulatory guides are not copyrighted, and NRC approval is not 
required to reproduce them.

    Dated at Rockville, Maryland, this 1st day of September 2010.

    For the Nuclear Regulatory Commission.
Harriet Karagiannis,
Acting Chief, Regulatory Guide Development Branch, Division of 
Engineering, Office of Nuclear Regulatory Research.
[FR Doc. 2010-22490 Filed 9-8-10; 8:45 am]