[Federal Register Volume 69, Number 216 (Tuesday, November 9, 2004)]
[Notices]
[Pages 64996-64998]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-24890]
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NUCLEAR REGULATORY COMMISSION
Notice of Availability of Interim Staff Guidance Documents For
Fuel Cycle Facilities
AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of availability.
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FOR FURTHER INFORMATION CONTACT: Wilkins Smith, Project Manager,
Technical Support Group, Division of Fuel Cycle Safety and Safeguards,
Office of Nuclear Material Safety and Safeguards, U.S. Nuclear
Regulatory Commission, Washington, DC 20005-0001. Telephone: (301) 415-
5788; fax number: (301) 415-5370; e-mail: [email protected].
SUPPLEMENTARY INFORMATION:
I. Introduction
The Nuclear Regulatory Commission (NRC) plans to issue Interim
Staff Guidance (ISG) documents for fuel cycle facilities. These ISG
documents provide clarifying guidance to the NRC staff when reviewing
either a license application or a license amendment request for a fuel
cycle facility under 10 CFR part 70. The NRC is soliciting public
comments on the ISG documents which will be considered in the final
versions or subsequent revisions.
II. Summary
The purpose of this notice is to provide the public an opportunity
to review and comment on a draft Interim Staff Guidance document for
fuel cycle facilities. Interim Staff Guidance-09 provides guidance to
NRC staff relative the requirements associated with the use of
Initiating Event Frequencies (IEFs) for demonstrating compliance with
the performance requirements of 10 CFR 70.61.
III. Interim Staff Guidance-09, Initiating Event Frequency, Draft
October 20, 2004 Issue
This guidance addresses the measures needed to assure the validity
and maintenance of initiating event frequencies (IEFs) used to
demonstrate compliance with the performance requirements for 10 CFR
70.61.
Introduction
The purpose of this Interim Staff Guidance (ISG) is to clarify the
use of IEFs for demonstrating compliance with the performance
requirements of 10 CFR 70.61. NUREG-1718, ``Standard Review Plan for
the Review of an Application for a Mixed Oxide (MOX) Fuel Fabrication
Facility,'' and NUREG-1520, ``Standard Review Plan for the Review of a
License Application for a Fuel Cycle Facility,'' provide methods for
reviewing integrated safety analyses (ISAs), employing a semi-
quantitative risk index method. While one of these methods is used
below to illustrate the use of IEFs, applicants and licensees may use
other methods which would produce similar results. There is no
particular method explicitly mandated, and sequences that are risk
significant or marginally acceptable are candidates for more detailed
evaluation by the applicant or licensee and reviewer.
Discussion
Each licensee or applicant is required to perform an ISA to
identify all credible high-consequence and intermediate-consequence
events. The risk of each such credible event is to be limited through
the use of appropriate engineered and/or administrative controls to
meet the performance requirements of 10 CFR 70.61. Such a control is
referred to as an item relied on for safety (IROFS). In turn, a safety
program must be established and maintained to assure that each IROFS is
available and reliable to perform its intended function when needed.
The safety program may be graded such that management measures applied
are graded commensurate with the reduction of risk attributable to that
item. In addition, a configuration management system must be
established pursuant to Sec. 70.72, to evaluate changes, to assure, in
part, that the IROFS are not removed without at least equivalent
replacement of the safety function.
The risk of each credible event is determined by cross-referencing
the severity of the consequence of the unmitigated accident sequence
with the likelihood of occurrence in a risk matrix with risk index
values. The likelihood of occurrence risk index values can be
determined by considering the criteria in NUREG-1520, Tables A-9
through A-11. Accident sequences result from initiating events which
are followed by the failure of one or more IROFS. Initiating events can
be (1) an external event such as a hurricane or earthquake, (2) a
facility event external to the process being analyzed (e.g., fires,
explosions, failures of other equipment, flooding from facility water
sources), (3) deviations from normal operations of the process
(credible abnormal events), or (4) failures of an IROFS in the process.
Additional guidance regarding initiating probabilities from natural
phenomena hazards are addressed in ISG-08, Natural Phenomena Hazards.
An initiating event does not have to be an IROFS failure. An item
only becomes an IROFS if it is credited in the ISA for mitigation or
prevention per the definition in Sec. 70.4. If an item, whose failure
initiates an event, has strictly an operational function, it does not
have to be an IROFS. This applies to external events and can apply to
internal events. If the item whose failure initiates an event, has
solely a safety function that is credited in the ISA, then it should be
an IROFS. If the item has both an operational and a safety function,
the safety function should make it an IROFS (for its ISA credited
safety features only).
IEFs can play a significant role in determining whether the
performance requirements of Sec. 70.61 are met for a particular
accident sequence. Whether an initiating event is due to an IROFS or a
non-IROFS failure, licensees should take appropriate action to assure
that any change to the basis for assigning an IEF value to that event
is evaluated on a continuing basis to ensure continued compliance with
the performance requirements. For example, a non-IROFS component may
not be subject to the same QA program controls and other management
measures that an IROFS
[[Page 64997]]
would receive (i.e., surveillance, testing, procurement, etc.).
However, appropriate management controls should be considered, in a
graded manner, to provide assurance that performance requirements are
met over time. The ability to identify a non-IROFS component failure,
similar to that for IROFS, may be needed to provide feedback on failure
rates and IEFs to the ISA process. Changes to the IEF values may result
from changes to a component's design, procurement, operation, or
maintenance history, as well as new or increased external plant
hazards, and should be considered in a graded approach.
Regulatory Basis
10 CFR 70.61, Performance Requirements.
10 CFR 70.62, Safety Program and Integrated Safety Analysis.
10 CFR 70.65, Additional Content of Applications.
10 CFR 70.72, Facility Changes and Change Process.
Applicability
This guidance is for use in those cases where an applicant or
licensee chooses to use an IROFS or non-IROFS failure IEF for risk
determination.
Technical Review Guidance
1. IEF and Identification of an IROFS
Example. A licensee uses a heater/blower unit to heat a
UF6 cylinder in a hot box to liquify the contents prior to
sampling. The unmitigated accident sequence involves the failure of the
controller for the heater/blower resulting in overheating the cylinder.
This results in the cylinder becoming overpressurized and rupturing,
releasing the UF6 to the surrounding process area. Such a
release is analyzed to exceed the performance requirements of Sec.
70.61. The licensee has two basic choices: (1) Assume the initiating
event probability =1 and provide an appropriate level of mitigation or
prevention solely through one or more IROFS, or (2) assign a value to
the initiating event (blower/heater controller failure) and provide one
or more preventive or mitigative IROFS to bring the accident sequence
risk within the performance requirements.
If the licensee chooses (2) above and assigns an appropriate value
to the IEF, the indices of NUREG-1520, Table A-9, Failure Frequency
Index Number, may be used. The controller for the heater/blower unit
would be assigned an appropriate Frequency Index Number. The licensee
would then analyze the accident sequence and determine whether
additional IROFS are necessary to meet the performance requirements.
There are now two variables that feed into the risk determination: one
or more IROFS failure frequencies and the IEF of the non-IROFS
controller for the heater/blower unit. Changes to the initiating event
that impact the IEF of the non-IROFS controller for the heater/blower
unit in a manner that changes the licensee's previous determination of
compliance with the performance requirements must be evaluated per
Sec. 70.72(a).
2. IEF Index Use
Indices may be used to determine the overall likelihood of an
accident sequence. NUREG-1520, Table A-9, Failure Frequency Index
Numbers, identifies frequency index numbers based on specified
evidence. The evidence used by applicants and licensees should be
supportable and documented in the ISA summary as required by Sec.
70.65(b)(4). The evidence cited in the ISA documentation should not be
limited to anecdotal accounts and must demonstrate compliance with the
descriptive definitions of unlikely, highly unlikely, and credible, as
required by Sec. 70.65(b)(9). The rigor and specificity of the
documented evidence should be commensurate with the item's importance
to safety, and the data should support the frequency chosen (e.g., data
from 30 years of plant operating experience based on a single component
typically could not be expected to support a 10 E-2 failure
probability).
An item's failure rate should be determined from actual data for
that specific component or safety function in the current system design
under the current environmental conditions. When specific failure data
is limited or not available, the applicant or licensee may use more
``generic'' data with appropriate substantiation. However, when less
specific failure data is available, appropriate conservatism should be
exercised in assigning frequency indices. The footnote to Table A-9
that states ``indices less than (more negative than) -1 should not be
assigned to IROFS unless the configuration management, auditing and
other management measures are of high quality, because without those
measures, the IROFS may be changed or not maintained,'' should also be
applied to non-IROFS IEFs. In this case, appropriate management
controls should be provided to assure that any changes to the evidence
supporting IEF indices will be identified and promptly evaluated to
ensure that the performance requirements of Sec. 70.61 are met. A
graded approach may be used in applying management controls based on
the IEF values; however, how this will be done should be identified in
the ISA Summary.
Possible changes to IEFs, failure rates, and the assumptions they
are based on should be periodically evaluated by the licensee to assure
that any change to an IEF has been accounted for in the ISA process.
Over time an IEF may change because of component aging or
deterioration. Maintenance and performance experience should be fed
back into the IEF evaluation. IEF changes could involve, for example,
the introduction of new or hazards from nearby processes or new
materials, changes in design, maintenance, or operation activities,
etc. The applicant or licensee should establish management measures,
which may be graded, to periodically confirm that there have been no
changes to the ISA assumptions. For example, an applicant or licensee
may choose to verify that there have been no changes to hazards from
maintenance activities during a certain period of time based on an
appropriate documented technical review or audit under the QA program.
Whatever strategy the applicant or licensee chooses to employ
should have an outcome of timely identification, and periodic
evaluation, of failure rates followed by a prompt evaluation of the
failure rate change on the ISA assumptions. This can be accomplished in
accordance with the corrective maintenance program and/or the Quality
Assurance (QA) problem identification and corrective action system.
Indices particularly relied upon (i.e., <-1) for overall likelihood
will be reviewed during the ISA review process.
3. External IEFs
Possible changes to non-natural phenomena external events should be
periodically evaluated by the licensee to assure that any change to an
IEF has been accounted for in the ISA process. Such changes could
involve, for example, the introduction of new hazards from an adjoining
industrial site, changes in adjoining transportation activities, etc.
The applicant or licensee should establish management measures, which
may be graded, to periodically confirm that there have been no changes
to the ISA assumptions. For example, an applicant or licensee may
choose to verify that there have been no changes to outside hazards
based on a two- to three-year review under the QA program.
[[Page 64998]]
4. Assurance
The Safety Program required by Sec. 70.62(a) should have
provisions for implementing the appropriate management controls to
maintain the validity of the IEFs. Consideration should also be given
to commitments in the QA program or a specific license condition.
References
U.S. Code of Federal Regulations, title 10, part 70, ``Domestic
Licensing of Special Nuclear Material,'' U.S. Government Printing
Office, January 1, 2003.
NUREG-1520, ``Standard Review Plan for the Review of a License
Application for a Fuel Cycle Facility,'' U.S. Nuclear Regulatory
Commission, Office of Nuclear Material Safety and Safeguards, March
2002.
NUREG-1718, ``Standard Review Plan for the Review of an Application
for a Mixed Oxide (MOX) Fuel Fabrication Facility,'' U.S. Nuclear
Regulatory Commission, Office of Nuclear Material Safety and
Safeguards, August 2000.
IV. Further Information
Comments and questions should be directed to the NRC contact listed
above by December 9, 2004. Comments received after this date will be
considered if it is practical to do so, but assurance of consideration
cannot be given to comments received after this date.
Dated in Rockville, Maryland, this 3rd day of November, 2004.
For the Nuclear Regulatory Commission.
Melanie A. Galloway,
Chief, Technical Support Group, Division of Fuel Cycle Safety and
Safeguards, Office of Nuclear Material Safety and Safeguards.
[FR Doc. 04-24890 Filed 11-8-04; 8:45 am]
BILLING CODE 7590-01-P