ML20065N750

Responds to Reporting Requirements Issued in NRC Bulletin 93-002,suppl 1, Debris Plugging of Emergency Core Cooling Suction Strainers

ML20065N750
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	04/19/1994
From:	Reid D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-94-44, IEB-93-002, IEB-93-2, NUDOCS 9404280075
Download: ML20065N750 (4)

Text

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{ e VERMONT YANKEE NUCLEAR POWER CORPORATION x .

r N: s Ferry Road. Bra tleboro. VT OC 101-7002

[ ENGINE I OFFICE N k

880 MAIN STREET 00LTON. MA 01740

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(508) 779-6711 April 19,1994 BVY 94-44 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

References:

(a) Ucense No. DPR-28 (Docket No. 50-271)

(b) NRC Bulletin 93-02, Supplement 1, " Debris Plugging of Emergency Core Cooling Suction Strainers", dated 2/18/94

Subject:

60 Day Response to NRC Bulletin 93-02, Supplement 1 This letter is in response to the reporting requirements issued in NRC Bulletin 93-02 (NRCB 93-02),

Supplement 1. The NRCB describes the staff concerns related to the potential loss of Emergency Core Cooling Systems (ECCS) due to suction strainer clogging. In addition, it requests licensees implement certain interim actions until the issue is resolved.

Attachment "A" to this letter describes Vermont Yankee's actions to date, our planned actions, and the schedule for completing them. Also, Vermont Yankee will continue to work with the Bolling Water Reactor Owners Group (BWROG) toward resolution of this issue.

We believe that the actions proposed are responsive to your concerns; however, if you have any further questions, please do not hesitate to contact us.

Sincerely, Vermont Yankee Nuclear Power Corporation s

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Donald A. Reid Vice President, Operations cc: USNRC Region 1 Administrator USNRC Resident inspector - VYNPS USNRC Project Manager - VYNPS

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STATE OF VERMONT ) a + -

WINDHAM COUNTY y NOTARY "\

} J Then personally appeared before me, Donald A. Reid, who, being duty sworn, did spieghat e 13f thNesilent, h Operations, of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to e anB.ple the foredoingh-document in the name and on the behalf of Vermont Yankee Nuclear Power Corporation, and th ter b M feln er C true to the best of his knowledge and belief. -

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Sally A. Sandstrum, Notary Public 9404280075 940419 My Commission expires FebrJary 10,1995 PDR'- ADOCK 05000271 Q PDR 1\ l l1

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9 Attachment A Rosponse to NRCB 93-02, Supplement 1 The following is Vermont Yankoe's response to the requested interim actions described in NRCB 93-02, Supplement 1:

Action Reauested Provide training and briefings to apprise operators and other appropriate emergency response personnel of tiu Information contained herein and in the referenced information notices regarding the potential for suppression pool strainer clogging.

VY Response The Operations Manager issued the BWROG's " Operator Guidance for Potential Blockage of ECCS Suction Strainers" to appraise operators of concerns with potential ECCS suction strainer plugging and potential mitigative actions.

In addition, this guidance as well as the Bulletin and information contained in the BWROG's " Safety Assessment - BWR Emergency Core Cooling System Suction Strainers", were utilized to develop an instruction module and simulator scenario to be utilized during operator requalification training (LOR 94.01). This training will be completed by May 20,1994. LOR cycle 94.02 will include training on the proposed new off-normal procedure c'escribed below. This training will be completed by July 22,1994, i l Appropriate emergency response personnel will receive training on this subject via the continuing I Engineering Support Personnel (ESP) training program. This training will be completed by June 17,  ;

1994.  !

Action Reauested Assure that the ernergency operating procedures make the operator aware of possible indications of l ECCS strainer clogging and provide guidance on mitigation.

Responce A combination of training, system operating procedures (ops), and a e,ew event-based off normal l operating procedure ON 3164 will be used to satisfy the requested action, in accordance with VYAP-0037, " Plant Procedures", an ON is used to address conditions resulting from system equipment malfunctions. This off-normal procedure will be drafted and made effective by May 27,1994. Training on this procedure will be performed during operator requalification training (LOR 94.02). This tralning will be completed by July 22,1994.

The new event-based procedure will address the following:

The operating conditions and parameter changes which would identify potential plugging of ECCS suction stralnors including;

• ECCS flow rate less than expected for the current operating conditions

• Decreased suction pressure as indicated by local Instrumentation

• Pump motor amperage indications erratic or decreasing

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• ' Erratic and significant fluctuations in pump discharge pressure 4

• inability to control and maintain RPV and containment parameters (i.e., temperature, pressure, level)

The operator actions and initiation of activities required to stop the degradation of conditions and/or mitigate their consequences including;

• Secure from service, or throttle flow from the suscopitble ECCS systems not needed to restore and maintain EOP parameters

• Align Core Spray suction to the CST one loop at a time, conditions permitting

• Initiate makeup to the CST; contact maintenance for asalstance in providing additional makeup capability Action Reauestg Institute procedures and other measures to provide compensatory actions to prevent, delay, or mitigate a loss of available NPSH margin under LOCA conditions. Such measures should be consistent with providing the design basis emergency system functions for core and containment cooling Actions to assure sufficient core and containment cooling may include:

• Reduction of flow (consistent with delivering the required ECCS flow) through the strainers to reduce head loss and extend the time for debris deposition

• Operator realignment of existing systems to allow backflushing of clogged strainers 8 -

• Operator realignment of existing systems to allow Injunction to the core from water sources other than the suppression pool e Intermittent operation of the containment sprays, when possible, to reduce the transport of debris to the strainers e Other plant-specific measures which assurn availability of sufficient core and containment cooling to meet the des!gn basis of the plant

Response

The following is Vermont Yankee's position on each of the above suggested compensatory actions:

Reduction of flow (consistent with delivering the required ECCS flow) through the strainers to .

reduce head loss and extend the time for debris deposition I The new off-normal operating procedure (ON 3164) will provide direction to the operator consistent with this objective. )

Operator realignment of existing systems to allow backflushing of clogged strainers This action is not poscible since Vermont Yankee's existing systems cannot be realigned to provide an effectivs mean3 for backflushing of clogged suction strainers. .

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Operator " realignment of existing systems to allow injection to the core from water sources other than the suppression pool Most of the preferred injection sources identified in the Emergency Operating Procedures (EOPs) have suction sources external to the suppression pool (i.e., condensate /feedwater, HPCI, RCIC, CRD, and Core Spray). The new off-normal operating procedure (ON 3164) will provide direction to the operator for realignment when conditions warrant this action. In addition, the new procedure wl!! direct the operator to initiate action for augmenting normal makeup capability to the CST. Th4 should prolong the usefulness of HPCI and RCIC, other operating conditions permitting. In addition, it should ensure long term availability for the Core Spray subsystems when aligned to the CST. If the preferred sources are inadequate of unavailable, the EOPs direct the operator to utilize alternate in}ection systems to restore and maintain level. These alternate injection systems include the RHR Service Water System, the Fire Protection System, and the Condensate Transfer Syaism, all of which utilize suc ion sources external to the suppression pool.

Intermittent operation of the containment sprays, when possible, to reduce the transport of debris to the strainers The EOPs direct the operator to operate containment sprays when necessary to maintain drywell temperature and pressure below the limits specified in the Emergency Procedure Gu'delines.

Operation of the containment sprays in accordance with the guidance provided by the EOPs may result in intermittent operation of the sprays, depending upon the specific accident conditions. The current procedures require initiation of drywell sprays when pressure is above 14 psig. (to preclude cyclic oscillation (i.e., chugging) at the downcomer openings of the drywell vents), and termination when pressure is less than 2.5 psig. (to permit resetting of PCIS and RPG high drywell pressure logic).

Other plant-specific measures which assure availability of sufficient core and containment cooling to meet the design basis of the plant As described above, Vermont Yankee has a number of normal and alternate methods for assuring adequate core cooling in the event conditions occur which result in debris generation and deposition on the ECCS suction strainers.