ML19323F248

Application to Amend License DPR-65,submitted as Proposed Revision to Tech Specs,In Response to NRC 791221 Ltr. Summarizes Status of Implementation of Automatic Initiation of Auxiliary Feedwater.One Pump Sufficient

ML19323F248
Person / Time
Site:	Millstone
Issue date:	05/20/1980
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML19323F249	List: ML19323F248 ML19323F255
References
A00803, A803, TAC-42410, TAC-44705, TAC-44746, NUDOCS 8005280696
Download: ML19323F248 (8)

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May 20, 1980 Docket No. 50-336 A00803 Director of N'.clea r Reactor Regulation Attn: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1) W. G. Counsil lette: to D. G. Eisenhut dated April 11, 1980.

(2) R. Reid letter to W. G. Counsil anted December 21, 1979.

(3) W. G. Counsil letter to R. Clark dated May 9,1980.

(4) W. G. Counsil letter to J. Hendrie dated November 30, 1979.

(5) W. G. Counsil letter to R. Reid dated January 25, 1980.

(6) W. G. Counsil letter to H. R. Denton dated December 6,1979.

(7) W. G. Counsil letter to D. G. Eisenhut dated November 28, 1979.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Automatic Initiation of Auxiliary Feedwater The most recent docketed correspondence on the subject of Automatic Initiation of Auxiliary Feedwater for Millstone Unit No. 2 is Reference (1) which summarized the implementation status as of that date. Reference (1) also requested the Staff to defer the implementation date f rom June 1,1980 to the 1980 refueling oucage for reasons stated therein. Although that request remains valid in Northeast Nuclear Energy Company's (NNECO) judgment, subsequent events have altered the implementation effort. Therefore, NNECO is docketing this letter to summarize the impact of those changes.

The unit is currently shutdown because the service water system was declared inoperable for reasons involving its capability to withstand a seismic event.

Consequently, NNECO has taken the opportunity to attempt to install the automatic initiation scheme to the point that implementation can be readily accomplished subsequent to receipt of a Staff directive. Although expeditious ef forts are in progress, NNECO's ability to complete the installation prior to startup f rom the current outage is a function of the duration of this outage. NNECO will maintain communications with the Staf f in this regard in an attempt to secure the deferral if the installation cannot be completed prior to startup.

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Although the Staff has stated that they do not intend to review the control-grade installations prior to authorizing implementation, NNECO has modified its control-grade scheme substantially f rom the concept presented in Ref erence (6) and is providing the following discussion for information purposes.

Previous submittals have indicated that upon low steam generator level, automatic start signals would be given to each of the two electrically driven auxiliary feedwater pumps and the one steam-driven auxiliary feedwater pump. The basis for this scheme was that it would be necessary to start all three pumps to ensure adequate auxiliary feedwater flow in the event of a single failure. Since the time of those submittals, NNECO has investigated the capability of one electrically driven auxiliary feedwater pump to provide decay heat removal under the most limiting conditions, and has determined that one pump is, in fact, capable of fulfilling this function. Consequently, it is no longer necessary to start all three pumps to satisfy the single failure criterion. NNECO's revised automatic initiation scheme involves only the two electrically driven pumps. The steam-driven pump is, therefore, classified as a manual backup. This does not invalidate NNECO's commitment to make one auxiliary f eedwater train AC-independent as stated in Reference (7).

Cperational history has demonstrated the adequacy of one electrically driven pump to provide adequate heat removal capability, and this fact was the original motive for investigating this alternative. The concept has the significant advantage of eliminating the steam-driven pump from the automatic initiation scheme thereby rendering the redundant trains fully independent.

The upgrading of the scheme to safety-grade stat'us can be more readily accomplished as there are no longer any components associated with both redundant divisions.

The analytical justification of this chcnge is provided as Attachment 1.

These analyses demonstrate that the installed auxiliary feedwater pump capacity represents 400 percent of design requirements as opposed to the original concept of 200 percent. The design basis event for this evaluation is a total loss of main feedwater with the single failure being one electrically driven pump. To conservatively reflect the nominal three-minute time delay and the associated allowance for instrument uncertainty, a 228-second delay from the low-level initiation setpoint to the start of auxiliary feedwater flow was assumed. A conservative calculation was also performed to ensure that primary system pressure remained below the PORV setpoint throughout the duration of the transient. The attac.ed analysis supports NNECO's conclusion that one electrically driven auxiliary feedwater pump is sufficient to provide the required flow rate to the steam generator for the most limiting design basis event.

In Reference (2), the Staff provided model Technical Specifications for an automatic initiation scheme. These Specifications have been modified to reflect the Millstone-unique design. Therefore, pursuant to 10CFR50.90, NNECO hereby proposes to amend its operating license, DPR-65, by incorporating the revisions identified in Attachment 2 into the Millstone Unit No. 2 Technical Specifications.

The proposed initiation setpoints and response times are conservatively reflected in the analysis presented in Attachment 1.

_3_

NNECO's determination regarding the unreviewed safety question issue remains as stated in Reference (4). Therefore, it is our position as well as our understanding of the Staf f's evaluation that formal docketed approval of this installation is required prior to implementation. Despite the fact that this installation constitutes an unreviewed safety question, NNECO's analyses and evaluations presented in this letter and in Reference (5) ferm the basis of NNECO's conclusion that the installation is acceptable from a safety perspective. The change is not judged to be necessary to ensure continued saf e operation, but is acceptable.

The Millstone Unit No. 2 Nuclear Review Board has reviewed and approved the attached proposed changes and concurred in the above determinations.

NNECO has reviewed the proposed license amendment pursuant to the requirements of 10CFR170 and has determined that the fee associated with this change has been forwarded in Reference (3). The Staff has advised of their intention to issue the subject Technical Specification change in conjunction with the Cycle 4 reload license amendment. The Class 4 amendment fee forwarded in Reference (3) is, therefore, applicable in this instance.

In summary, we will keep the Staff verbally informed regarding the potential need for deferral of the implementation date to the 1980 refueling outage.

It is also noted that of the three commitments noted in Reference (1), the only remaining commitment is to provide the final safety grade design for the automatic initiation scheme. This design, which is expected to reflect the uprating of the electrically driven pumps to 100 percent capability, will be the subject of future correspondence.

Very truly yours, NORTHEAST NUCLE g ENERGY MPANY

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W. G. Counsil A('A' Vice President Attachment

DOCKET No. 50-336 ATTACID1ENT 1 MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 AUTOMATIC INITIATION OF AUXILIARY FEEDWATER MAY, 1980

Introduction The auxiliary f eedwater system contains two electric motor-driven pumps and one steam turbina driven pump with twice the rated capacity of each electric driven pump. For the purposes of this analysis, the two electric motor-driven pumps are considtred to be automatically initiated on low steam generator level with a 228-second delay time between initiation signal and pump start. A single electric motor-driven pump is considered as failed; with turbine bypass to condenser unavailable for the worst-case analysis.

Summary Analyses have been performed, which have shown that one auxiliary feedwater electric driven pump is suf ficient to provide heat removal under the most limiting conditions following a total loss of main feedwater event. Since this event is the most limiting of the design basis events assumed for the system (auxiliary f eedwater) from the standpoint of minimum flow requirements, the analysis justifies the upgrading of one electric motor-driven pump flow to 100% capacity.

Method of Analysis A simplified one volume, two junction model using the RETRAN code was developed to determine the time of minimum steam generator inventory for various auxiliary feedvater flow rates. The limiting case of the design basis events for minimum necessary auxiliary feedwater flow rates is the total loss of feedwater event. A non-conduction heat exchanger option was selected to model heat transfer from the primary to the secondary side. This effectively uncouples primary-secondary responses leaving onl/ the total amount of heat transferred. A flow capacity of

! 300 gpm at 1000 psi was used for the one electric motor auxiliary feedwater pump flow rate case. The flow rate was doubled for the two electric motor-driven pump cases.

Since this model cannot provide the RC system pressure response, the limiting case was also analyzed using the Long-Term Cooling (LTC) code to determine if prit: to steam generator level recovery the pressurizer PORV would lift.

Results of Analysis For the total loss of feedwater event with automatic initiation of auxiliary feedwater pumps, a flow rate of 600 gpm can be expected for two electric motor-driven pumps operating or for the turbine driven pump operating alone.

In the event of one electric motor-driven pump failure, 300 gpm would be available to the steam generators from automatic initiation of auxiliary feedwater.

Should the turbine bypass to condenser be unavailable, the secondary safeties would open at their setpoints keeping steam generator pressure levels to i

approximately 1000 psi. Figures 1 and 2 show these cases (steam generator inven-tory vs. time) for two electric pumps operating, and one electric pump operating, respectively. The worst case seen (Figure 2) shows a steam generator inventory of about 9,400 lbs, per steam generator at 4180 seconds from reactor trip.

This corresponds to about 6% tuba coverage in the steam generators. At th is point , the steam generators begin to refill from auxiliary f eedwater flow. This analysis conservatively assumes ANS + 20% for decay heat.

Recovery would be expedited by operator actuation of the available steam driven pump. The analysis shows that, in the unlikely event of concurrent failure of one motor-driven auxiliary feedwater pump and turbine bypass, the operator will have ample time to start backup flow and reduce steam generator level recovery time. The worst case (one electric motor driven pump; turbine bypass to condenser unavailable) was run to determine the primary pressure response and any possible impact on the PORV. The greatest primary pressure occurred at 540 seconds into the event. Since the PORV high pressure setpoint (2400 psi) was not reached for this case, it can be concluded that the automation of the two electrically driven pumps and not the steam driven pump will not result in increased challenges to the FORV.

Conclusions In all cases examined, one electric motor driven auxiliary feedwater pump is capable of providing heat removal capability and refill of the steam generators. One electric motor driven auxiliary feedwater pump is sufficient

to provide the minimum required flow rate to the steam generators for the most limiting auxiliary feedwater system design basis event.

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