ML070390148

EA-06-291, Clinton Power Station, Final Significance Determination for a White Finding and Notice of Violation; NRC Inspection Report No. 05000461/2007006 (DRS)

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, 2007

EA-06-291

Mr. Christopher M. Crane

President and Chief Nuclear Officer

Exelon Nuclear

Exelon Generation Company, LLC

4300 Winfield Road

Warrenville, IL 60555

SUBJECT: FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING

AND NOTICE OF VIOLATION; NRC INSPECTION REPORT

NO. 05000461/2007006(DRS) FOR CLINTON POWER STATION

Dear 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 pumps 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 discuss

your 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 would

open 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 air

entrained. 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 air

entrainment 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 necessarily

tuned 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 to

perform 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 flow

velocity, 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 air

entrainment; 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 the

significance 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 at

the 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 determined

that 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 additional

information 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 staffs determination of

significance 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 HPCS

system 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 enclosed

Notice of Violation (Notice). The circumstances surrounding the violation are described in detail

in 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 the

enclosed Notice when preparing your response.

Because plant performance for this issue has been determined to be in the regulatory response

band, 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, its

enclosure 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. Caldwell

Regional Administrator

Docket No. 50-461

License No. NPF-62

Enclosure:

Notice of Violation

cc w/encl: Site Vice President - Clinton Power Station

Plant 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

C. Crane -4-

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, its

enclosure 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. Caldwell

Regional Administrator

Docket No. 50-461

License No. NPF-62

Enclosure:

Notice of Violation

cc w/encl: Site Vice President - Clinton Power Station

Plant 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

DOCUMENT NAME:C:\FileNet\ML070390148.wpd

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To receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copy

OFFICE RIII D:OE1 RIII RIII RIII RIII

NAME GShear for DSolario for CPederson for GShear CPederson JCaldwell

PPelke CCarpenter AMStone

DATE 2/2/07 2/02/07 2/2/07 2/2/07 2/2/07 2/7/07

OFFICIAL RECORD COPY

1

HQ concurrence received via e-mail from D. Starkey, OE on February 2, 2007

Letter from J. Caldwell to C. Crane dated February 7, 2007

SUBJECT: FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING

AND NOTICE OF VIOLATION; NRC INSPECTION REPORT

NO. 05000461/2007006(DRS) FOR CLINTON POWER STATION

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NOTICE OF VIOLATION

Exelon/AmerGen Energy Company, LLC Docket No. 50-461

Clinton Power Station License No. NPF-62

EA-06-291

During an NRC inspection completed on November 17, 2006, a violation of NRC requirements

was 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 be

established 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 the

adequacy 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 which

identifies 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 parameters

as 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 the

adequacy 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 hereby

required 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 should

include 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, with

the 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 NRC

Public Document Room or from the NRCs document system (ADAMS), accessible from the

NRC Web site at http://www.nrc.gov/reading-rm/adams.html, to the extent possible, it should

not 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 must

specifically 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 working

days.

Dated this 7th day of February 2007