Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 22, 1997
NRC INFORMATION NOTICE 97-71: INAPPROPRIATE USE OF 10 CFR 50.59 REGARDING
REDUCED SEISMIC CRITERIA FOR TEMPORARY CONDITIONS
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.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to inform addressees of a licensee's inappropriate use of 10 CFR 50.59
regarding use of reduced seismic criteria for temporary conditions. It is
expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar
problems. However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action or written response is
required.
Description of Circumstances
In 1994, at LaSalle County Station, Units 1 and 2, the licensee, Commonwealth
Edison Company (ComEd), instituted a program for seismic loading for temporary
conditions (SLTC). The licensee's SLTC program allowed the application of
seismic criteria that are less stringent than those described in the updated
final safety analysis reports for these facilities, which are part of the
licensing bases for these facilities. The licensee applied the SLTC to
determine operability of Unit 1 recirculation piping with a failed snubber
removed, under the provisions of 10 CFR 50.59, "Changes, Tests and
Experiments." This regulation allows the licensee to change the facility or
facility procedures, as described in the safety analysis report, without prior
NRC approval provided that the change does not involve an unreviewed safety
question or a change to the facility technical specifications. During an
inspection, the NRC identified an unresolved item related to a licensee
procedure invoking this program (Reference 1).
The NRC staff met with the licensee and reviewed this matter (References 2-4).
The staff determined that the ComEd methodology for reduced seismic criteria
does not conform to its licensing basis, involves a change to the facility as
described in the safety analysis report, introduces a potential reduction in
the facility capability to withstand design-basis seismic events, and the
change thus constitutes an unreviewed safety question. Consequently, licensee
implementation of the SLTC program could not be done without NRC review and
approval, such as provided in 10 CFR 50.90 (Reference 5).
9709180074. IN 97-71
September 22, 1997
Page 2 of 3
Discussion
ComEd implemented a quantitative procedure for using seismic hazard curves to
determine reduced acceleration levels for evaluating seismic resistance for
safety-related structures, systems, and components (SSCs) for temporary
conditions of estimated short durations ranging from several days to months.
The procedure utilizes the facility design-basis safe-shutdown earthquake
(SSE) to determine corresponding reduced accelerations for temporary
conditions of estimated short durations. ComEd also used a method for
calculating a No Seismic Limit Duration (NSLD) corresponding to each hazard
curve such that for durations less than the NSLD, seismic effects do not have
to be considered as a load case. As a part of this method, ComEd used an
acceleration threshold of 0.02 g as one that is acceptably small so as not to
require a specific seismic evaluation.
The facility safety analysis report states that if the SSE occurs, SSCs will
remain functional. Application of the ComEd SLTC program could result in loss
of safety functions of temporary-condition SSCs. In particular, the safety
analysis report states that SSCs are designed for safe shutdown due to maximum
horizontal ground acceleration at the building foundation of 0.2 g. Adoption
of the ComEd program may result in some temporary-condition SSCs not being
designed for a minimum of 0.2 g SSE acceleration.. IN 97-71
September 22, 1997
Page 3 of 3
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
signed by D.B. Matthews for
Jack W. Roe, Acting Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contact: David Jeng, NRR
301-415-2727
E-mail: [email protected]
References
1. NRC Inspection Report 50-373/94-05 (NUDOCS Accession Number 9405130227)
2. Letter from I. Johnson, Commonwealth Edison Company, to W. T. Russell,
NRC, "Reduced Seismic Criteria at Commonwealth Edison Nuclear Facilities,"
dated March 23, 1994 (NUDOCS Accession Number 9403310205)
3. Notification of NRC meeting with Commonwealth Edison Company on
April 28, 1994, in Rockville, MD to discuss an alternate seismic loading
method (NUDOCS Accession Number 9404190047)
4. Letter from G. G. Benes, Commonwealth Edison Company, to W. T. Russell,
NRC, "Reduced Seismic Criteria at Commonwealth Edison Nuclear Facilities,"
dated August 8, 1994 (NUDOCS Accession Number 9408150288)
5. Letter from Jack W. Roe, NRC, to D. L. Farrar, Commonwealth Edison
Company, "Reduced Seismic Criteria for Temporary Conditions," dated
September 15, 1995 (NUDOCS Accession Number 9509200179)
6. Memorandum from S. L. Magruder, NRC, to D. B. Matthews, NRC, "Summary of
March 12, 1997, Meeting with the Nuclear Energy Institute (NEI) Reduced
Seismic Criteria Under Temporary Conditions," dated April 18, 1997 (NUDOCS
Accession Number 9704230269)
Attachment: List of Recently Issued NRC Information Notices
