L-PI-14-066, Supplement to License Amendment Request (LAR) to Revise Technical Specification (TS) 3.5.3, ECCS (Emergency Core Cooling System) - Shutdown

Supplement to License Amendment Request (LAR) to Revise Technical Specification (TS) 3.5.3, ECCS (Emergency Core Cooling System) - Shutdown

ML14258A089
Person / Time
Site:	Prairie Island
Issue date:	09/15/2014
From:	Davison K Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-14-066, TAC MF0728, TAC MF0727
Download: ML14258A089 (7)

Text

Xcel Energy L-PI-14-066 SEP .1 5 2014 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 Supplement to License Amendment Request (LAR) to Revise Technical Specification (TS) 3.5.3, "ECCS [Emergency Core Cooling System]- Shutdown" (TAC Nos. MF0727 and MF0728)

By letter dated February 20, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML13053A199), as supplemented by a letter dated June 25, 2013 (ADAMS Accession No. ML13178A024), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"),

submitted a license amendment request for Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, to remove Technical Specification (TS) 3.5.3 Limiting Condition for Operation (LCO) Note 1. By email dated June 23, 2014 (ML14174B394), NRC Staff requested additional information (RAI) on the February 20, 2013, LAR (ML13053A199).

The enclosure to this letter provides the response to the NRC Staff RAI. NSPM submits this supplement in accordance with the provisions of 10 CFR 50.90.

The supplemental information provided in this letter does not impact the conclusions of the Determination of No Significant Hazards Consideration and Environmental Assessment presented in the February 20, 2013 (ML13053A199) submittal as supplemented June 25, 2013 (ML13178A024).

In accordance with 10 CFR 50.91, NSPM is notifying the State of Minnesota of this LAR supplement by transmitting a copy of this letter and enclosure to the designated State Official.

If there are any questions or if additional information is needed, please contact Mr. Dale Vincent, P.E., at 651-267-1736.

1717 Wakonade Drive East

• Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on

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Kev1n Davison Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (1) cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC State of Minnesota

ENCLOSURE Supplement to License Amendment Request (LAR) to Revise Technical Specification (TS) 3.5.3, "ECCS [Emergency Core Cooling System]- Shutdown" TAG Nos. MF0727 and MF0728 By letter dated February 20, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML13053A199), as supplemented by a letter dated June 25, 2013 (ADAMS Accession No. ML13178A024), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"),

submitted a license amendment request for Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, to remove Technical Specification (TS) 3.5.3 Limiting Condition for Operation (LCO) Note 1. By email dated June 23, 2014 (ML14174B394), NRC Staff requested additional information (RAI) on the February 20, 2013, LAR (ML13053A199).

By email on August 26, 2014, the NRC provided further clarification on this RAI.

NRC Request for Additional Information (RAI):

Please provide an in-depth discussion to support use of a cold leg temperature of 218°F. Include consideration of the actual temperature requirement that is at the hot leg, the previous documentation of 226°F, and use of 200°F for the hot leg temperature that is addressed in the precedent referenced (ADAMS Accession No. ML12206A057).

Additional correspondence (email correspondence dated August 26, 2014 following conference call)

As a follow-up from our clarification call on August 25, 2014, the NRC staff indicates that the attached RAI is intended to develop a better understanding of plant conditions where one RHR [residual heat removal] system would be aligned for the ECCS mode. The staff needs to develop its reasonable assurance determination that one RHR system will not encounter flashing if a LOCA [loss of coolant accident] occurs when that system is required to perform ECCS cooling.

Therefore, the objective of the RAI is for the licensee to support a conclusion that one RHR system will not encounter flashing if a LOCA occurs when that system is required to perform ECCS cooling.

NSPM Response:

Background

This LAR proposes to remove Limiting Condition for Operation (LCO) Note 1 from TS 3.5.3. The specific note to be removed is:

Page 1 of 5

RHR LCO Note RAI

1. An RHR [residual heat removal] train may be considered OPERABLE during alignment and operation for decay heat removal, if capable of being manually realigned to the EGGS mode of operation.

This Note previously allowed one or both trains of RHR to be aligned to the shutdown cooling function as opposed to the normal EGGS lineup for vessel injection. TS 3.5.3 is applicable during much of Mode 4. Mode 4 is a transitional mode to progress a unit between normal operating pressure and temperature and shutdown conditions (Mode 5, Mode 6, defueled). The shutdown cooling function draws water from the reactor coolant system (RCS) hot leg and returns it to the RCS cold leg. EGGS draws water from the refueling water storage tank (RWST) and injects into the reactor pressure vessel. There are two concerns with operation of shutdown cooling in Mode 4 with the current note:

1. During a large LOCA, the RHR train aligned for shutdown cooling may lose suction prior to operator action to shut down and realign the pump for the remainder of the injection phase of the event.

2. There is also a concern that voids will form in some sections of EGGS piping as temperature and pressures change in the RCS. These voids will then transport to the pump and cause damage.

By removing LCO Note 1, an RHR train aligned for shutdown cooling cannot be considered operable for the EGGS function which will therefore require one train of EGGS to be aligned for injection while in the applicable portions of Mode 4. The other train can be aligned to shutdown cooling. The plant has experienced minimal impact on the ability of a unit to cool down to Mode 5 in a timely manner while running in this lineup.

Summary response The proposed change to require one train of RHR to be aligned for EGGS injection while in the TS 3.5.3 mode or other specified condition in the applicability (MOSCA) will ensure that at least one train will always be available to perform EGGS injection and recirculation functions required to mitigate an event. The referenced temperature of 218°F is the current lower temperature limit that defines the applicability of this specification. Current plant evaluations demonstrate that at all temperatures this specification is applicable and there is not sufficient void formation to cause damage to any RHR piping or pumps that would make the system inoperable.

EGGS operability during the injection phase of a LOCA occurring in Mode 4 is fundamentally no different than the requirements to mitigate a LOCA in Mode 1, 2 or 3.

The RHR system will draw water from the RWST to inject into the RCS. EGGS recirculation phase operability is affected by the potentially reduced pressures present in the containment atmosphere following a Mode 4 LOCA. The reduced pressures assumed during a Mode 4 LOCA will prompt void formation when RHR is first aligned to the containment sump; however, these voids have been evaluated to have no significant impact to the operability of the RHR piping or pumps.

Page 2 of 5

RHR LCO Note RAI Cold Leg Temperature of 218°F The RCS cold leg temperature of 218°F is the current "SI [safety injection] pump disable temperature" referred to in the applicability statement forTS 3.5.3, "Mode 4 when both RCS cold leg temperatures are> Sl pump disable temperature specified in PTLR."

The Sl pump disable temperature (218°F) limit protects the reactor pressure vessel from over-pressurization at low temperatures from an inadvertent Sl injection by requiring both trains of Sl to be disabled. Since a conflict would exist in TS 3.5.3 by requiring a train of ECCS to be operable while requiring both trains of Sl to be disabled, the lower bound of the applicability forTS 3.5.3 was established as the Sl pump disable temperature in the PTLR. Use of both cold legs above the Sl pump disable temperature in the TS 3.5.3 applicability statement is conservative in that it extends the TS applicability to a slightly lower temperature. The current value of 218°F is controlled in the PTLR and its associated change management process.

Previously documented temperature of 226°F The previously documented bounding temperature of 226°F was established for a scenario when a LOCA occurs and both trains of RHR are used to draw from the containment sump. Water temperatures above this limit would definitely create a void in the RHR piping that may affect operability. Since one train of RHR will not be connected to the RCS while the plant transitions through the TS 3.5.3 MOSCA, if a LOCA occurred, the temperature of the water already present in the RHR piping would be well below this limit. The water drawn from the containment sump would be temperature limited below the saturation conditions for the current containment pressure. The value of 226°F was developed using a conservative containment pressure of 13.3 psia. Any increase of containment pressure would map to a corresponding increase in saturation conditions and limiting temperatures.

Current limiting temperature The current evaluated limiting temperature is 211 oF which is assumed in all the RHR piping that would have been used during the shutdown cooling mode of operation. This temperature was developed as part of the operability recommendation in the Corrective Action Program that justifies current operability. The operability recommendation analysis assumes that a loop has been used for shutdown cooling recently then is transitioned to recirculation following a LOCA. Using this assumption creates a scenario when the water in the piping is at an elevated temperature. While this assumed configuration is utilized to create a bounding analysis, it is not a credible alignment under the changes proposed in this LAR.

The temperature of 211 oF was found to create several voids in specific portions of the RHR piping. A scoping analysis shows that the voids formed at 211°F would bound other larger voids formed at higher temperatures. The small voids have less steam Page 3 of 5

RHR LCO Note RAI mass and result in higher peak pressures when they collapse. Further analysis shows that the voids formed at this temperature would not cause sufficient damage to affect operability of the RHR pump and piping.

The limiting temperature of 211 oF bounds all higher temperatures. Therefore, the system is expected to remain operable within the entire range of applicability under TS 3.5.3. If the lower limit of applicability of 218°F for this specification were revised in the PTLR in the future, this RHR system limiting value would have to be revisited to determine if it would then need to represent the lower bounds of the applicability of this specification.

Note that since the credited train of ECCS (RHR) is not supplying the shutdown cooling function when the plant is within TS 3.5.3 applicability, the water temperature in the piping of the credited train is expected to be comparable to conditions during swapover from ECCS injection to ECCS recirculation for a LOCA occurring in Mode 1, 2, or 3.

The RHR trains are not swapped between the shutdown cooling and ECCS functions.

Page 5 of 14 in the enclosure to the LAR (ML13053A199) stated:

Note that the RHR trains for each unit do not have identical piping configurations.

On Unit 1, only RHR Train B can discharge to an RCS cold leg. Conversely, on Unit 2, only RHR Train A can discharge to an RCS cold leg. Two trains of RHR can be used for RCS cool down by cross-connecting the two trains. However, if only one train is used for cool down, Train B must be used on Unit 1 and Train A must used on Unit 2.

Thus, the RHR train that is aligned for ECCS will not be used for cooldown and will remain nominally at ambient temperatures.

Use of 200°F in the Referenced Precedent NSPM does not have access to the full basis for the decision to use 200°F as a limiting temperature in the Bryon and Braidwood submittals. The referenced precedent was submitted for a Westinghouse 4-loop Nuclear Steam Supply System (NSSS) design.

There may be enough differences in design between PINGP and the precedent that a comparison may not prove useful in justification of limiting temperatures.

The referenced precedent quotes a normal hot leg temperature limit of 260°F for which the similar lineup that PINGP calculates a limit of 249°F. The precedent quotes a 200°F RCS temperature limit when swapping lineup from shutdown cooling to the ECCS sump. Similar cases analyzed for PINGP determined the limiting RHR pump suction temperature when initiating suction from the recirculation sump following a LOCA. The resultant RHR pump suction temperatures are 226°F and 228oF for 2-pump and 1-pump operation, respectively. Since the exact details of the differences in piping configuration, measured temperature locations, and assumptions are not known, it is difficult to draw useful conclusions from any comparison of these values.

Page 4 of 5

RHR LCO Note RAI Continued Operability This license amendment request proposes removal of LCO Note 1 from TS 3.5.3 which removes the non-conservatism in the TS and assures that one train of ECCS remains operable to mitigate a postulated Mode 4 LOCA while in the MOSCA forTS 3.5.3.

Formal calculations are being prepared to determine the full expected response of the RHR piping during a Mode 4 LOCA which may determine a different limiting set of inputs, including temperature. However, these calculations do not affect the performance of the train of ECCS which is isolated from the RCS and operable to meet TS 3.5.3.

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