ML19341C215

Responds to NRC 810114 Ltr Requesting Auxiliary Feedwater Pump Endurance Test & Compliance W/Requirement to Automate Steam Driven Auxiliary Feedwater Pump.Test Confirmed Pump Vibrations Did Not Exceed Allowable Limits

ML19341C215
Person / Time
Site:	Millstone
Issue date:	02/19/1981
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
To:	Clark R Office of Nuclear Reactor Regulation
References
A01488, A1488, TAC-43559, TAC-44705, TAC-44746, TAC-46844, TAC-7544, NUDOCS 8103020399
Download: ML19341C215 (11)

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{, February 19, 1931 i c Docket No. 50-336 dii i A0ll.66

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Director of Nuclear Reactor Regulation Attn: Mr. Robert A. Clark, Chief Operating Reactors Branch #3 U. S. Nuclear Regulatory Commission Washington, D.C. 20555

References:

(1) T. M. Novak letter to W. G. Counsil, dated January lb ,1981.

(2) 'O. G. Eisenhut letter to W. G. Counsil, dated October 22, 1979 (3) W. G. Counsil letter to H. R. Denton, dated December 6,1979 (h ) W. G. Counsil letter to R. A. Clark, dated May 20, 1990.

(5) W. G. Counsil letter to H. R. Denton, dated November 28, 1979 Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Auxiliary Feedvater System In Reference (1), the NRC Staff issued Amendment No. 63 to Facility Operating License No. DPR-65 adding operability, trip setpoint and surveillance re-quirements for automatic initiation of the auxiliary feedvater system. In addition, the Staff documented the results of the review of Northeast Nuclear Energy Company's (NNEC0's) responses to the short and long-term recon =endations which resulted from the reliability evaluation of the M111ctone Unit No. 2 auxiliary feedvater system.

Eased on this review, the Staff requested that NNECO complete the following actions within thirty (30) days frcm receipt of Reference (1):

(1) Complete and document the results of a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> endurance test of the "A" auxiliu'y feedvater pump.

(2) Document our intentions regarding compliance with the Staff's re-quirement to automate the steam-driven auxiliary feedvater pump.

In response to these requests, NNEC0 hereby provides the following information.

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Item 1 A forty eight (h8) hour endurance test of the "A" auxiliary feedvater pump was initiated at 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on February 4,1981, and completed at 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> 81030203W

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on February 6,1981, in accordance witn the provisions of Reference (2) as supplemented by Reference (1).

The testing was performed during normal operation with the "A" auxiliary feedwater pump providing approximately 90-95 gpm to the Steam Generator No. 1. A flow schematic for the subject test is provided in Figure 1.

Prior to the test, NNECO perforned an engineering evaluation of the potential impact of the addition of cold auxiliary feedvater into the main feedwater flow. It was concluded that the auxiliary feedwater pump endurance test vould have negligible impact upon the fatigue life of the Steam Generator nozzle-to-pipe veld. This determination is based on the following:

As the main feedwater pipe vill be full, addition of cold auxiliary feedwater into the main feedwater flow will not result in thermal stratification.

The injection of r.uxiliary feedvater into the main feedwater is not expected to lower the main feedwater temperature significantly.

The one time application of this transient will result in negligible impact on the Steam Generator nozzle-to-pipe weld fatigue life.

Pump and motor bearirr; temperatures were measure.d by contact with the pump and motor casings near the bearings. The location of thy bearing tem-perature measurenents are shown in Figure 2.

A comparison of the "A" auxiliary feedwater pump design operating conditions and the test operating conditions is provided in Table 1.

A plot of the bearing temperatures versus time for the four measurement locations is provided in Figure 3 A plot of the "A" auxiliary feedvater pump room ambient temperature versus time is provided as Figure 4. Pump roca ambient humidity did not vary appreciably during the conduct of the test as the ventilation system maintains the pump room at the same humidity as the ground floor of the turbine building. The pump room humidity was approximately 23% throughout the test.

Following a review of the pump room smbient conditions during the auxiliary feedvater pump endurance test, UNECO has. determined that operation of the "A" auxiliary feedwater pump for extended periods of time vill not result in the environmental qualification limits for the safety-related equip-ment in the room to be exceeded.

Data collected during this test confirm that pump vibration did not exceed allowable limits during the conduct of this test.

. e Item 2 In Reference (3), NNECO provided the NRC Staff with the preliminary design of the control grade automatic initiation scheme for the Millstone Unit No. 2 auxiliary feedwater system. Subsequent to the docketing of Reference (3), NNECO investigated the capability of one electrically driven auxiliary feedwater pump to provide decay heat removal under the most 1Laiting con-ditions. The investigation determined that one electric auxiliary feedwater pump was capable of providing 100% of the required auxiliary feedwater flow to remove decay heat. Analytical justification was provided in Reference (h).

As such, NNECO revised its automatic initiation scheme for Millstone Unit No. 2. The revised scheme involves automatically starting two electric auxiliary feedwater pumps.

Conversations with the Staff indicated that the proposed scheme to auto-matically start only the two electric-driven auxiliary feedwater pumps would be unacceptable, however, no basis was given for this determination.

These discussions culminated in the issuance of Reference (1) whereby the Staff issued Amendment No. 63 to Facility Operating License DPR-65 which added operability, trip setpoints and surveillance requirements for the automatic initiation of the auxiliary feedwater system.

In response to the Referen' ; (1) request to document our intentions regarding compliance with the Staff's stated position requiring automatic start of the turbine driven auxiliary feedwater pump, NNECO maintains that the current design for the Millstone Unit No. 2 automatic auxiliary feedwater system, whereby two electric-driven pumps are started on low Steam Generator water level, is adequate and meets the intent of NUREG-0737 The basis for this determination is provided below.

The capacity of the two electric motor-driven auxiliary feedwater pumps has been demonctrated to be 200% of that required to adequately remove decay heat. Analytical justification has been provided in Reference (4).

Elimination of the steam turbine-driven auxiliary feedwater pump fram the automatic initiation scheme will render the redundant electric driven trains fully independant and capable of satisfying the single failure criterion.

The steam-driven pump is classified as a manual backup train which will be started from the control roan. In addition, as was described in Reference (5), the stemn-driven train will be made A.C. independent.

The Staff has documented, in Reference (1), that the turbine-driven auxiliary feedwater pump is required to be automatically started in order to provide reliable flow to the steam generators in the event of a station blackout. This requirement far exceeds present design criteria for other safety-related systems such as the High Pressure Safety Injection (HPSI) or Containment Spray Systems. The precedent which will be set should NNECO be required to design the auxiliary feedwater system to the station blackout criterion has far reaching knplications, and has not been substantiated by the Staff in docketed correspondence.

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It is NNECO's opinion that a IiUREG document is not the appropriate vehicle for the Staff to prcnulgate a requirement with such ramifications.

In light of the preceding arguments, MIECO has performed best estimate cal-culations to determine the times to dry-out for the steam generators at Mill-stone Unit No. 2 under various trip conditions, including a loss of main feedvater as a result of station blackout (loss of off-site and on-site power). The analyses demonstrate that, should a station blackout occur, the operator would have in excess of forty five (k5) minutes to manually start the turbine-driven auxiliary feedvater pu=p from the control room and its associated A.C. independent train prior to dry-out of the steam generators.

Table 2 lists the analyses performed and the calculated dry-out times, miECO concludes that the amount of time available to the cperator prior to steam generator dry out during a station blackout during which he must manually initiate auxiliary feed with the turbine-driven pump is more than adequate. It is also noted that emergency procedures utilized during a station blackout explicitly direct the operator to initiate auxiliary feedvater flow with the turbine-driven pump. In actual plant transients vbere auxiliary feedvater has been required to be manually initiated, it has successfully been acco=plished within one minute cf the start of the transient.

Two additional points of concern exist should the Staff ultimately require EiECO t provide _ for the automatic initiatica of the turbine-driven as well 9 electric-driven auxiliary feedvater pumps. The se t.re : 1) potential pump cavitation concerns and 2) steam generator overfill conditions.

The potential for pump cavitation with 71 tant pump da= age has been identified during those times when both the e2 e -driven and turbine-driven auxiliary feedvater pumps are operating. It inconsistent for the Staff to require a system to automatically start when required because of a lack of confidence in operator action when operator action is required (to throttle flow) to prevent a potential failure of that system, i.e., pump cavitation.

~ Operation of all three auxiliary feedvater pu=ps at Millstone Unit No. 2 vill potentially result in the delivery of 400% of the required auxiliary feedvater if operator action to throttle feed flow is not assumed. The addition of 400% of the required auxiliary feedvater flow vill result in an overfilling of the steam generators unless appropriate action by the operator to throttle flow is assumed.

NNECO understands that the Staff of the Office of nuclear Reactor Regulation has considered steam generator overfill truisients as a candidate for in-clusion as part of the proposed new Unresolved Safety Issues (USI) on

" Safety Implications of Control Systems." Overfill of the steam generators will effect the response of the primary system, including pressurizer level shrinkage, potentially over cooling the primary system such that the reactor vessel nil ductility transition temperature (UDIT) limits could be violated, as well as impacting the structural integrity of the steam generator components.

Althought it is realized this is a low probability event, Staff concern is obviously present. It would again be inconsistent for the Staff to require a system to respond in such a way as to increase the potential for con-sequences detrimental to plant safety.

It is NNECO's conclusion, based on the information presented above, that automatic initiation of the turbine driven auxiliary feedwater pump is neither required for safe mitigation of loss of feedwater transients nor desired for several philosophical and technical reasons. Demonstration of a substantial dry-out time for the loss of main feedwater transient with a concurrent station blackout together with explicit emergency operating procedures ensures appropriate and timely operator action to mitigate the event without an automatic initiation scheme for the turbine-driven auxiliary feedwater pump.

It would be inconsistent for the Staff to continue to require NNECO to automate the turbine driven auxiliary feedwater pump in light of the in-formation provided herein as 3 has been clearly illustrated that safe plant operation is assured vi the current automatic initiation scheme.

All prerequisites for NRC acc=ytance of this position, both written and verbal, have been addressed by the docketing of this suhaittal. The potential concerns associated with automatic initiation of the turbine-driven auxiliary feedwater pump are not balanced by an increase in safety.

We trust you find this information responsive to the Reference (1) requests.

Very truly yours, NORTHEAST NUCLEAR ENERGY TPANY 4 ,

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W. 'G'. Counsil '

Senior Vice President

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Table 1 "A" AUXILIARY FEEDWATER Ptf6 Design Operating Test Operating Conditions Cond itions Pump Flow 300 gpm 90-95 gpm Discharge Pressure 1056 psi 1207-1215 4 psi

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Table 2 BEST ESTIMATE STEAM GE:iERATOR DRY OUT TDiE CALCULATIO:IS Millstone "uclear Power Station, Unit No. 2

1. Loss of Main Feedvater

• dry out: 22 minutes off-site power available reactor trip on lov steam generator water level

2. Loss of Main Feedvater

• dry out: 30 minutes reactor trip on low steam generator water level ,

loss of off-site power at time of reactor trip

3. Loss of Off-site Power dry out : >h5 minutes reactor trip on loss of off-site power

• Approximate Values