3F0997-27, Provides Description of HPI Sys Modifications to Improve Small Break LOCA Margins,Consistent W/Commitments Made in .Commitments Made by Util,Encl

Provides Description of HPI Sys Modifications to Improve Small Break LOCA Margins,Consistent W/Commitments Made in .Commitments Made by Util,Encl

ML20217A815
Person / Time
Site:	Crystal River
Issue date:	09/17/1997
From:	Holden J FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0997-27, 3F997-27, NUDOCS 9709230002
Download: ML20217A815 (5)

Text

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Florida Power C OMOR ATION DOC 9 fil .5 02 September 17,1997 3F0997-27 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

High Pressure Injection (HPI) System Modifications to improve Small Break Loss of Coolant Accident (SBLOCA) Margins

References:

A. FPC to NRC letter, 3F1096-22, " Crystal River Unit 3 Forced Outage," datad October 28,1996 B. NRC to FPC letter,3N0397-07, " Confirmatory Action Letter," dated March 4,1997

Dear Sir:

In Reference A, Florida Power Corporation (FPC) stated its plans to address eight specific design margin improvement issues prior to restarting the plant. "HPl System Modifications to Improve SBLOCA Margins" was one of the identified improvements (Ref.  !=ii!.

A, Issue 2). In its letter to the NRC, FPC stated that, "The CR-3 HPl system currently Q-meets all design and licensing basis functional requirements." However, FPC intends gida to reduce the operator burden created by the need for several manual operator actions, iEF as well as increase the system margin through hardware modifications. The purpose of _E_.

this letter is to describe FPC's plans for modification of the HPl System consistent with E its commitment in Reference A. g.

FPC identified three modifications to the HPl System that were being considered including installing cavitating venturis, installing cross-tie piping, and modifying the normal makeup line to ensure automatic isolation occurs upon Engineering Safeguards (ES) actuation. FPC has evaluated these three potential HPl modifications to select I appropriate options to pursue. The evaluation included an assessment of the impact of i each poten,tialyodiqcation on the boundary conditions including the reduction of {

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U.S..Nucber R gul tory Commission 3F0997-27 Page 2 of 5 operator burden and the reduction of peak clad temperatures during small break LOCAs.

Also included in the assessment were the potential timeliness of installation and the impact of the design on the plant. The conclusions .eached by this evaluation are discussed below:

HPl Cavitatina Venturis HP cavitating venturis were being considered by FPC for installation as a passive flow control device to limit ' low out a postulated line break and to aid in balancing HPI flow.

After further consideration, FPC has determined that cavitating venturis are not the preferred option for a passive flow control device for the CR-3 piping configuration.

Cavitating venturis can not be modeled with sufficient accuracy or shop tested sufficiently to determine tne anticipated vibrational amplitudes. As a result, in-plant testing of the cavitating venturis would have been required to obtain the final structural design requirements. In order to prevent equipment damage, limits would have been required on the testing that may have caused the testing to be aborted before required design hydraulic flow information for the SBLOCA calculations could have been attained. This may have resulted in the required design information not being attainable during Refuel Outage 11R.

FPC's plans called for a temporary installation of the cavitating venturis using flanged connections, followed by their testing and removal during the current outage. This plan was intended to allow time to make permanent design modifications, perform safety analyses, and amend the plant's license during Operating Cycle 11. Because of the unknown dynamic response of the piping system during cavitation and the potential severity of the induced vibrations, it was probable that additional supports and restraints would have been necessary after the 11R tests. This would have meant further testing and resultant modification during Refueling Outage 12R.

FPC has concluded that, given the ultimate goal of reducing operator burden and reducing peak clad temperatures, the best alternative is the installation of a passive flow control device such as preset throttle valves to balance HPl flow, along with the installation of cross-ties to minimize operator action and reduce peak clad temperature.

The installation of a passive flow control device such as preset throttle valves will serve primarily to minimize the need for operator action within the first 20 minutes of a SBLOCA, while the installation of cross-ties will result in a significant reduction in peak clad temperature.

Preliminary evaluations have shown that preset throttle valves are the most likely candidate for use as the passive ficw control device in this application at CR-3. Unlike cavitating venturis, the throttb valve option allows the flows for the fluid model calculation to be established and the analysis to be completed with high confidence of

• success when installed and tested. The use of throttle valves has proven industry experience and the use of throttle valves for this purpose is common at other nuclear

U.S..Nucinr Regul: tory Commission 4

3F0997-27 Page 3 of 5 plants. In addition, the installation of throttle valves does not have the severity of vibrational concems that are associated with cavitating venturis. Thus, risk to the plant and the risk of delayed implementation are significantly reduced. FPC is currently basing its design on preset throttle valves.

Cross-tie Pipino FPC has been evaluating cross-tie designs. Properly designed cross-tie piping will improve HPI flow delivery, thus reducing peak clad temperature, as well as reducing operator burden. Given design issues involving potential single failure susceptibility, recent industry experience with leakage past check valves and the potential irnpact on HPl nozzles and piping, further evaluations of the cross-tie design are necessary.

However, the evaluations of cross-tie designs will be completed in time for both the cross-ties and the passive flow control devices to be installed during Refuel Outage 11R.

Automatic Isolation of Norma! Makeup As a requirement of the implementation of Technical Specification Change Request Notice (TSCRN) 210, FPC is adding a 1500 psig low Reactor Coolant System (RCS) pressure automatic isolation signal to the normal makeup valve, MUV-27. This isolation signal will ensure that the normal makeup valve will automatically close if the electrical train from which it is powered remains available (operator s9ctable A or B powered).

The addition of this automatic isolation signal will aid in the reuuction of operator burden, and slightly improve pump margin and/or reduce peak clad temperatures due to improved HPl System response time.

In Reference A, FPC stated that this modification, " involves modifying the power supply to the existing isolation valve (MUV-27) and adding another isolation valve powered from the opposite train in series with MUV-27." The addition of a series isolation valve powered from the opposite train was being considered by FPC to ensure isolation of the normal makeup line under all conditions. Later hydraulic analyses determined that isolation of the normal makeup line would not have been required with the installation of cavitating venturis. FPC proceeded with the 1500 psig isolation signal to the normal makeup valve as an interim improvement to HPI response time until cavitating venturis could have been installed. The need for the additional series isolation valve now needs to be evaluated using the preset throttle valve option. It is likely that the need for the additional isolation valve will be eliminated.

Also as a requirement of the implementation of TSCRN 210, FPC is revising the HPI line isolation criterion contained in the Emergency Operating Procedures (EOPs). This new criterion is logically similar to the existing criterion, but is much simpler and will ensure proper identification of a line requiring isolation.

U.S Nucinr R::gul: tory Commission 3F0997-27 Page 4 of 5 Summary Potential HPl System modifications to improve SBLOCA margins have been evaluated.

FPC has concluded that the combination of the installation of a passive flow control device, of which throttle valves are the most likely candidate, cross-tie piping, and automatic isolation of the normal makeup line is the solution that best satisfies FPC's evaluation criteria outlined above. In addition, this solution fully meets FPC's commitment in Reference A to reduce the operator burden and increase the margin of the HPl System through hardware modifications. Commitments made in this letter cre provided in Attachment A.

Should you have any questions or require additional information concerning these HPI l System modifications, please contact David Kunsemiller, Manager, Nuclear Licensing at (352) 563-4566.

Sincerely, t

'h([

J.J. Holden Director Site Nuclear Operations JJH:kdw Attachment xc: Regional Administrator, Region ll NRR Project Manager Senior Resident inspector

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O U.S Nucisar Rtgul: tory Commission

. 3F09&7-27 Page 5 of 5-Attachment A List of Regulatory Commitments The following table identifies those actions committed to by Florida Power Corporation in this document. Any other actions discussed in the submittal represents intended or planned actions by Florida Power Corporation. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Manager, Nuclear 1.icensing of any questions regarding this document or any associated regulatory commitments.

10 NUMBER COMMITMENT DATE OR OUTAGE I

3F0997-27-01 Install HPl System cross-ties and During Refuel Outage passive flow control devices 11R l

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