ML20206K320

Forwards Response to RAI Re Verification of Seismic Adequacy of Mechanical & Electrical Equipment

ML20206K320
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	05/07/1999
From:	Leach D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-99-63, NUDOCS 9905130132
Download: ML20206K320 (6)

Text

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VERMONT YANKEE y NUCLEAR POWER CORPORATION

' 185 Old Ferry Rcad, Brattleboro, VT 05301-7002 (802) 257-5271 May 7,1999  !

BVY 99-63 1 U.S. Nuclear Regulatory Commission ATEN: Document Control Desk Washington,DC 20555

References:

(a) Letter, USNRC to VYNPC, " Request for Additional Information Regarding Verification of Seismic Adequacy of Mechanical and Electrical Equipment (TAC NO. M69490)," NVY 99-36, dated March 23,1999.

(b) Letter, VYNPC to USNRC," Vermont Yankee Summary Report for Resolution of USI A-46," BVY 96-86, dated July 1,1996.

Subject:

Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)

Response to Request for Additional Information Regarding )

Verification of Seismic Adeauncy of Mechanical and Electrical Eauloment  !

4 Reference (a) requested Vermont Yankee (VY) to provide additional information in response to questions outlined in the enclosure to that letter. Attached for your use is a written reply to each of the staff's questions.

We trust that the information provided will enable you to complete your review of Reference (b); however, should you have any questions on this matter, please contact Mr. Wayne M. Limberger at (802) 258-4237.

Sincerely, VERMONT YANKEE NUCLEAR POWER CORPORATION 4x /?

/ M. .- -

ice Presi es,t,'Engineeri j Attachment /

cc: USNRC Region I Administrator USNRC Resident Inspector- VYNPS USNRC Project Manager-VYNPS VT Department of Public Service  !

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9905130132 990507 PDR P

ADOCK 05000271 '

PDR d

Docket No. 50-271 BVY 99-63 Attachment 1 Vermont Yankee Nuclear Power Station Response to Request for Additional Information Regarding Verification of Seismic Adequacy of Mechanical and Electrical Equipment i

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BVY 99-63 / Anachment I / Page 1 NRC RAl (a)

Describe what reviews were performed to determine if any local operator actions required to safely shut down the reactor (i.e., implement the SSEL) could be affected by potentially adverse environmental conditions (such as loss of lighting, excessive heat or humidity, or in-plant barriers) resulting from the seismic event. Describe how staffing was evaluated and describe the reviews that were conducted to ensure operators had adequate time and resources to respond to such events.

VY Response As described in GIP-2, Part II, Section 3.2.5, the only potential events which must be considered in the USI A-46 program are a safe shutdown earthquake (SSE) and loss of offsite power (LOOP). Vermont Yankee operating procedures used following a LOOP event have previously been validated as one of the FSAR Chapter 14 accident scenarios. In addition, FSAR Chapter 14 also requires that proper initial response to accidents be automatic and require no decision or manipulation of controls by operations personnel. This includes consideration of potentially adverse environmental conditions and the need for local operator actions to be perfo:med. Note that the USI A-46 accident scenario (SSE + LOOP) explicitly excludes loss of coolant accidents (LOCA) and high energy line breaks (HELB). Therefore, the environmental conditions in the plant and need for local operator actions to be performed as dismsed above are postulated to be equivalent to those in a Chapter 14 LOOP scenario.

The potential for failure of plant structures and equipment is not considered credible at eastern U.S.

earthquake levels. Earthquake experience has shown that typical industrial structures are able to withstand earthquakes larger than the SSEs for eastern U.S. nuclear plants without collapse or failure.

The potential for local failure of architectural features (such as suspended ceilings in the control room) and the potential for adverse seismic spatial interactions in the vicinity of safe shutdown equipment was explicitly evaluated as stipulated in GIP-2, Part II, Section 4.5 and Appendix D. For example, this review included a check that the masonry walls near safe shutdown equipment are seismically adequate based on the results of the IE Bulletin 80-11 program.

The systems and equipment selected for seismic review in the USI A-46 program are those for which Normal, Abnormal, and Emergency Operating Procedures are available to bring the plant from a normal operating mode to a hot shutdown condition. As stipulated in GIP-2, Part II, Sections 3.2.8 and 3.7, the safe shutdown equipment list (SSEL) was reviewed by a plant Operations Department representative to confirm that it is compatible with these plant procedures. Since these procedures had already been validated to ensure that adequate time and resources are available for operators to respond to a LOOP i incident, it was not necessary to re-velidate these procedures for the USI A-46 program. It is noted that '

during development of the SSEL a number ofinformational scenarios were developed and programmed l into the plant simulator. These scenarios were run with various training department instructors and Operations Depanttr:1t trainees in order to assess conformance and compatibility with existing {

procedures. I I

The only additional consideration, beyond those associated with the LOOP event, are those specifically associated with the vibratory motion of the SSE. Based on the results of the review of existing plant procedures, the FSAR requirements for initial response to be automatic and the informational simulator trials performed, it is concluded that there is sufficient time and resources available to cope with the A-46 scenario.

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BVY 99-63 / Attachment 1/ Page 2 l

NRC RAI(b)

As part of the licensee's review, were any control room structures that could impact the operator's ability to respond to the seismic event identified? Such items might include but are not limited to: MCR (main control room) ceiling tiles, nonbolted cabinets, and nonrestrained pieces of equipment (i.e., computer keyboards, monitors, stands, printers, etc.). Describe how each of these potential sources ofinteractions has been evaluated and describe the schedule for implementation of the final resolutions.

VY Response Control Room structures which could impact the operator's ability to respond to a SSE include equipment and features such as the overhead suspended ceiling, HVAC ductwork, electrical conduit and cabling, file cabinets and bookcases, furniture and non-essential operator aids such as computer terminals, keyboards and monitors. These structures and components were evaluated as part of Vermont Yankee's A-46 review.

The method used for evaluating these potential sources of seismic spatial interaction is described in GIP-2, Part II, Section 4.5 and Appendix D. As a result of performing this review, Vermont Yankee concluded that all of the above control room structures passed the GIP screening criteria except for components which include miscellaneous bookcases and file cabinets. To date, several of these components have been removed from the immediate area to locations where they do not pose an interaction hazard to personnel or equipment. A number of components that must remain local for access have been modified to upgrade their anchorage to preclude interaction concerns. Any remaining upgrades that have been identified are currently being developed in accordance with Vermont Yankee's schedule contained in our July 1,1996 submittal [ Reference (b)].

NRC RAI (c)

Describe what reviews were performed to determine if any local operator actions were required to reposition " bad actor relays." For any such activities describe how adverse environmental conditions (such as loss oflighting, excessive heat or humidity, or in-plant barriers) resulting from the seismic event were analyzed and dispositioned. Describe how staffing was evaluated and describe the reviews that were conducted to ensure operators had adequate time and resources to respond to such events.

VY Response The term " bad actor" relays is a colloquial expression which refers to the list of relays in Appendix E of EPRI Report NP-7148. These relays have low seismic ruggedness or demonstrated sensitivity to high frequency vibration. The term used in EPRI NP-7148 characterizes these relays as " low ruggedness" relays.

As a result of Vermont Yankee's relay screening and evaluation there were no operator actions required on " low ruggedness" relays to reset or restore systems for bringing the plant to a safe shutdown condition.

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BVY 99-63 / Attachment 1/ Page 3 l

NRC RAI (d)

Describe which of the operator actions associated with resetting SSEL equipment affected by postulated relay chatter are considered to be routine and consistent with the skill of the craft. If not considered skill of the craft, what training and operational aids were developed to ensure the operators will perform the ]

actions required to reset affected equipment? l VY Response There were no specific operator actions identified that were associated with resetting SSEL equipment as a result of the relay screening and evaluation. In all cases of relay chatter, the consequences were evaluated and determined to be acceptable. Any actions related to operator response were concluded to be consistent with existing Normal, Abnormal and Emergency Operating Procedures.

! NRC RAI (e) 1 l Assume the alarms associated with " bad actor relays" are expected to annunciate during the seismic i event. Do the operators have to respond to those annunciators and review the annunciator response l procedures associated with them for potential action? How would those additional actions impact the operator's ability to implement the Normal, Abnormal, and Emergency Operating Procedures required to place the reactor in a safe shutdown condition?

VY Resoonse l

l As discussed b our response to RAI (c) above, the term " bad actor" relays is a colloquial expression I which does not properly categorize these type of relays. As defined in the relay review procedure, EPRI Report NP-7148, these relays are called " low ruggedness" relays, j l

As described in EPRI Report NP-7148, Section 3.5.3, following an earthquake which causes the turbine to trip and the reactor to scram,50 to 100 or more alarms are expected to annunciate. In addition to this large number of alarms, there may be several earthquake-induced, spurious alarms resulting from events such as water sloshing in tanks, oil sloshing in transformers, actuation of vibration protective instrumentation on rotating equipment, and contact chatter of relays. When the profusion of alarms occurs, the operator will clearly be aware that the plant has tripped. Plant procedures and operator training require that operators respond to the turbine trip and reactor scram by confirming the trip and scram and checking important levels, temperatures, pressures, flows, and electrical switching resulting

. from associated power transfers. These confirmatory checks will take more than a minute to go through during which time the operators will be busy making these checks and not responding to specific alarms.

The earthquake motion is assumed to last less than a minute and the causes of the spurious alarms will have gone away during this period while the operators are responding to the plant trip. The NRC staff and SQUG representatives discussed this topic in detail, including discussions held at a meeting on August 3,1988, where this was a primary topic of discussion. The results of that evaluation and review are summarized in EPRI NP-7148, Section 3.5.3 where the following conclusion is reached.

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• BVY,99-63 / Attachment I / Page 4 "Accordingly, there appear to be no reasonable bases or evidence which would suggest that spurious alarms resulting from an earthquake may lead to abnormal operator responses. Therefore, special operating procedures or relay evaluation actions to address potential spurious alarms are not considered warranted and relays affecting alarms need not be seismically adequate."

The NRC staff accepted the relay functionality review procedure summarized in GIP-2 and described in detail in EPRI NP-7148 (including the above conclusion) in Supplemental Safety Evaluation Report No.

2 on GIP-2. Therefore, it is not considered necessary to perform any additional reviews of the effect spurious alarms caused by " low ruggedness" relays or other causes as a result of a seismic event.

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NRC RAI(O To the extent that Normal, Abnormal and Emergency Operating Procedures were modified to provide l plant staff with additional guidance on mitigating the A-46 Seismic Event, describe what training was required and provided to the licensed operators, nonlicensed operators, and other plant staff required to respond to such events.

VY Resnonse There were no modifications to plant operating procedures required in order to provide guidance on mitigating the USI A-46 seismic event. The reviews and simulator trials performed ensure that plant procedures are available and appropriate with operations response to the A-46 event scenario.