ML070390148
| ML070390148 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 02/07/2007 |
| From: | Caldwell J Region 3 Administrator |
| To: | Crane C Exelon Generation Co, Exelon Nuclear |
| References | |
| EA-06-291, IR-07-006 | |
| Download: ML070390148 (8) | |
See also: IR 05000461/2007006
Text
February 7, 2007EA-06-291Mr. Christopher M. CranePresident and Chief Nuclear Officer
Exelon Nuclear
Exelon Generation Company, LLC
4300 Winfield Road
Warrenville, IL 60555SUBJECT:FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING AND NOTICE OF VIOLATION; NRC INSPECTION REPORT
NO. 05000461/2007006(DRS) FOR CLINTON POWER STATIONDear Mr. Crane:
The purpose of this letter is to provide you the final results of our significance determination of the preliminary Greater Than Green finding identified in Inspection Report No. 05000461/
2006011(DRS). The inspection finding was assessed using the Significance Determination
Process and was preliminarily characterized as Greater Than Green, a finding of greater than
very low safety significance, resulting in the need for further evaluation to determine
significance; and therefore, the need for additional NRC action. This Greater Than Green
finding involved the failure to select an appropriate method for calculating the minimum
elevation (i.e., the analytical level) of water above the high pressure core spray (HPCS) pump
suction line to preclude vortex formation and subsequent air entrainment in the pump's suction. As a result, the analytical level would result in significant air entrainment potentially causing the
HPCS to be incapable of completing its safety function. At our request, a Regulatory Conference was held on December 19, 2006, to further discussyour views on this issue. The public meeting summary, including the handouts, can be found in
the Agencywide Document Access and Management System (ADAMS) ML063520445. During
the meeting, your staff described the results of recent scaled model testing. Specifically, the
scaled model testing showed that a localized depression briefly formed which immediately
collapsed and resulted in significant (about 24 percent) air being entrained in the suction piping. You determined that this air/water mixture would result in a slowed level decrease in the reactor
core isolation cooling tank resulting in a delay in transferring suction to the suppression pool. However, your calculations showed that the suction valve from the suppression pool wouldopen and suction would be primarily from the suppression pool prior to the air reaching the
suction of the HPCS pump. Therefore, you concluded that the HPCS pump would be capable
of performing its safety function. In assessing the test model results, you assumed that flow
C. Crane-2-would not be characterized as slug flow, that is, the flow would be less than 24 percent airentrained. Your conclusion was based on: (1) visual confirmation during Alden Laboratory
Testing; (2) visual comparison of test results against a "known" flow having 24 percent air
entrainment; and (3) a computer model (RELAP) prediction that slug flow would exist above
24 percent. The NRC identified the following concerns with your conclusion: *During testing at Alden Laboratory, the pump was stopped immediately (about 5 seconds) upon visual observation of 'break through', i.e., air becoming entrained in
the suction pipe. This was done to preserve and prevent damage to the test pump.
This quick stopping did not allow time to verify the absence of slug flow.*The visual comparison of the test results against a "known" flow having 24 percent airentrainment was short in duration. This visual comparison may not represent actual test
or in-plant flow conditions. With flow and flow conditions unstable and oscillating, this
short time duration did not provide definitive proof that slug flow would not exist. Actual
void fraction measurements may typically have as much as 8 percent uncertainty.*The computer model (RELAP) is a generic 2-phase flow code and is not necessarilytuned or calibrated to this exact scenario. To consider results 'exact' and without any
consideration of analytical error is imprudent. The assumption of 24 percent air entrainment was key in assessing the ability of HPCS toperform its function for several reasons. First, the 24 percent provides a basis for the rate of
decrease in the RCIC tank. A greater void fraction would slow down the rate of change,
increasing the time to the swap-over point. This increase in time, would allow the air wave front
to travel further down the line and potentially reach pump suction prior to full opening of the
suppression pool suction valve. Secondly, although your staff calculated a 2-phase fluid flowvelocity, an increase in void fraction will increase the transport velocity, increasing the possibility
of air arrival at the pump. Lastly, should slug flow exist, there is a potential for system
waterhammer affecting system piping or the HPCS pump or both.In summary, the staff does not concur with your evaluation regarding the amount of airentrainment; and therefore, does not agree with your assessment on the past operability of the
HPCS pump. Your assessment is not conclusive, complete or robust, in that the basis for
24 percent was not well founded. Small changes to these assumptions may significantly impact
the conclusion regarding past HPCS pump operability. In addition, during the Regulatory Conference, you also provided your assessment of thesignificance of the finding. Specifically, you provided information regarding the potential for
operators to throttle HPCS flow and the estimated contribution to the risk from fire events. The
NRC reviewed the information regarding throttling the HPCS injection valve and determined
C. Crane-3-that it should be considered in the final significance determination. Based on the discussion atthe Regulatory Conference, operators would be directed to throttle HPCS in response to
transient (i.e., non- Loss of Coolant Accidents and non- Anticipated Transient Without a Scram)
scenarios. If operators successfully throttle the HPCS injection valve, the system flow
rate will be low enough that air entrainment during suction swap-over to the suppression pool
would no longer be a concern. For the final significance determination, the NRC assumed that
HPCS would fail in response to transient initiating events only if the operator failed to properly
throttle the HPCS injection valve. For all other initiating events, HPCS was assumed to fail
during the suction transfer, consistent with the assumption in the preliminary significance
determination. Given the inherent uncertainty in estimating human error probabilities, the NRC
used its best estimate of 2.6E-2 for the human error probability in the final significance
determination.The NRC also reviewed the estimation of fire risk contribution that you provided and determinedthat it was the best available information; and therefore, it was used directly in the final
significance determination.After considering the information presented at the Regulatory Conference and the additionalinformation you provided in your letter dated December 21, 2006, the NRC has concluded that
the inspection finding is appropriately characterized as White, an issue with low to moderate
increased importance to safety, which may require additional NRC inspections. Using the
estimation of fire risk contribution and best estimate for human error probability, the NRC
determined the total change in core damage frequency to be about 4.4E-6 per year. You have 30 calendar days from the date of this letter to appeal the staff's determination ofsignificance for the identified White finding. Such appeals will be considered to have merit only
if they meet the criteria given in NRC Inspection Manual Chapter 0609, Attachment 2.The NRC has also determined that the failure to ensure the adequacy of design of the HPCSsystem by performance of design reviews or by use of alternate or simplified calculational
methods is a violation of Title 10 Part 50, Appendix B, Criteria III, as cited in the enclosedNotice of Violation (Notice). The circumstances surrounding the violation are described in detailin Inspection Report No. 05000461/2006011(DRS). In accordance with the NRC Enforcement
Policy, NUREG-1600, the Notice of Violation is considered escalated enforcement action
because it is associated with a White finding.You are required to respond to this letter and should follow the instructions specified in theenclosed Notice when preparing your response.Because plant performance for this issue has been determined to be in the regulatory responseband, we will use the NRC Action Matrix, to determine the most appropriate NRC response for
this event. We will notify you, by separate correspondence, of that determination.
C. Crane-4-In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, itsenclosure and response will be made available electronically for public inspection in the
NRC Public Document Room or from the Publically Available Records (PARS) component
of NRC's document system (ADAMS), accessible from the NRC Web site at
http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).Sincerely,/RA/James L. CaldwellRegional AdministratorDocket No. 50-461License No. NPF-62Enclosure:Notice of Violationcc w/encl:Site Vice President - Clinton Power StationPlant Manager - Clinton Power Station
Regulatory Assurance Manager - Clinton Power Station
Chief Operating Officer
Senior Vice President - Nuclear Services
Vice President - Operations Support
Vice President - Licensing and Regulatory Affairs
Manager Licensing - Clinton Power Station
Senior Counsel, Nuclear, Mid-West Regional Operating Group
Document Control Desk - Licensing
Assistant Attorney General
Illinois Emergency Management Agency
State Liaison Officer, State of Illinois
Chairman, Illinois Commerce Commission
1 HQ concurrence received via e-mail from D. Starkey, OE on February 2, 2007C. Crane-4-In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, itsenclosure and response will be made available electronically for public inspection in the
Public Document Room or from the Publically Available Records (PARS) component
of NRC's document system (ADAMS), accessible from the NRC Web site at
http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).Sincerely,/RA/ James L. CaldwellRegional AdministratorDocket No. 50-461License No. NPF-62Enclosure:Notice of Violationcc w/encl:Site Vice President - Clinton Power StationPlant Manager - Clinton Power Station
Regulatory Assurance Manager - Clinton Power Station
Chief Operating Officer
Senior Vice President - Nuclear Services
Vice President - Operations Support
Vice President - Licensing and Regulatory Affairs
Manager Licensing - Clinton Power Station
Senior Counsel, Nuclear, Mid-West Regional Operating Group
Document Control Desk - Licensing
Assistant Attorney General
Illinois Emergency Management Agency
State Liaison Officer, State of Illinois
Chairman, Illinois Commerce CommissionDOCUMENT NAME:C:\FileNet\ML070390148.wpd
G Publicly Available
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G Non-SensitiveTo receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copyOFFICERIIID:OE 1RIIIRIIIRIIIRIIINAMEGShear forPPelkeDSolario forCCarpenterCPederson forAMStoneGShearCPedersonJCaldwellDATE2/2/072/02/072/2/072/2/072/2/072/7/07
OFFICIAL RECORD COPY
Letter from J. Caldwell to C. Crane dated February 7, 2007SUBJECT:FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING AND NOTICE OF VIOLATION; NRC INSPECTION REPORT
NO. 05000461/2007006(DRS) FOR CLINTON POWER STATIONADAMS DISTRIBUTION
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SECY
L. Reyes, EDO
W. Kane, DEDR
C. Carpenter, OE
D. Solorio, OE
D. Starkey, OE
J. Caldwell, RIII
G. Grant, RIII
L. Chandler, OGC
B. Jones, OGC
J. Dyer, NRR
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M. Tschiltz, Chief, SPSB, NRR
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J. Stang, NRR
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K. Fuller, Enforcement Officer, RIV
R. Pascarelli, Enforcement Coordinator, NRR
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P. Pelke, RIII
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J. Lynch, RIII
S. Minnick, RIII
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NOTICE OF VIOLATIONExelon/AmerGen Energy Company, LLC Docket No. 50-461Clinton Power Station License No. NPF-62EA-06-291During an NRC inspection completed on November 17, 2006, a violation of NRC requirementswas identified. In accordance with the NRC Enforcement Policy, the violation is listed below: Title 10 Part 50, Appendix B, Criteria III states, in part, that measures shall beestablished to assure that applicable regulatory requirements and the design basis, as
defined in § 50.2 and as specified in the license application, for those structures,
systems, and components to which this appendix applies are correctly translated into
specifications, drawings, procedures, and instructions. It further states that design control measures shall provide for verifying or checking theadequacy of design, such as by the performance of design reviews, by the use of
alternate or simplified calculational methods, or by the performance of a suitable testing
program.Title 10, Part 50.2 states, in part, that "design bases" means that information whichidentifies the specific functions to be performed by a structure, system, or component of
a facility, and the specific values or ranges of values chosen for controlling parametersas reference bounds for design. These values may be (1) restraints derived from
generally accepted "state of the art" practices for achieving functional goals, or (2)
requirements derived from analysis (based on calculation and/or experiments) of the
effects of a postulated accident for which a structure, system, or component must meet
its functional goals.Contrary to the above, prior to August 12, 2006, the licensee had not ensured theadequacy of design of the high pressure core spray (HPCS) system by performance of
design reviews or by use of alternate or simplified calculational methods. Specifically,
the initiation of suction swap-over from the reactor core isolation cooling tank to the
suppression pool, a controlling parameter to ensure continued function of the HPCS
pump, was required to occur at 740.19 feet as derived by calculation IP-M-384,
Revisions 0, 1, and 1B. However, this calculated value did not prevent significant air
entrainment in the suction of the HPCS pump and subsequent loss of function of the
HPCS pump.This violation is associated with a White SDP finding.
Pursuant to the provisions of 10 CFR 2.201, Exelon/AmerGen Energy Company, LLC is herebyrequired to submit a written statement or explanation to the U.S. Nuclear Regulatory
Commission, ATTN: Document Control Desk, Washington, DC 20555-0001 with a copy to the
Regional Administrator, Region III, and a copy to the NRC Resident
Inspector at the Clinton Power Station, within 30 days of the date of the letter transmitting this Notice of Violation (Notice).
Notice of Violation-2-This reply should be clearly marked as a "Reply to a Notice of Violation; EA-06-291 and shouldinclude for each violation: (1) the reason for the violation, or, if contested, the basis for
disputing the violation or severity level, (2) the corrective steps that have been taken and the
results achieved, (3) the corrective steps that will be taken to avoid further violations, and
(4) the date when full compliance will be achieved. Your response may reference or include
previous docketed correspondence, if the correspondence adequately addresses the required
response. If an adequate reply is not received within the time specified in this Notice, an order
or a Demand for Information may be issued as to why the license should not be modified,
suspended, or revoked, or why such other action as may be proper should not be taken.
Where good cause is shown, consideration will be given to extending the response time. If you contest this enforcement action, you should also provide a copy of your response, withthe basis for your denial, to the Director, Office of Enforcement, United States Nuclear
Regulatory Commission, Washington, DC 20555-0001. Because your response will be made available electronically for public inspection in the NRCPublic Document Room or from the NRC's document system (ADAMS), accessible from the
NRC Web site at http://www.nrc.gov/reading-rm/adams.html, to the extent possible, it shouldnot include any personal privacy, proprietary, or safeguards information so that it can be made
available to the public without redaction. If personal privacy or proprietary information is
necessary to provide an acceptable response, then please provide a bracketed copy of your
response that identifies the information that should be protected and a redacted copy of your
response that deletes such information. If you request withholding of such material, you mustspecifically identify the portions of your response that you seek to have withheld and provide in
detail the bases for your claim of withholding (e.g., explain why the disclosure of information will
create an unwarranted invasion of personal privacy or provide the information required by
10 CFR 2.390(b) to support a request for withholding confidential commercial or financial
information). If safeguards information is necessary to provide an acceptable response, please
provide the level of protection described in 10 CFR 73.21. In accordance with 10 CFR 19.11, you may be required to post this Notice within two workingdays. Dated this 7
th day of February 2007