BVY-92-136, Responds to NRC Re Unresolved Issues Noted in Edsfi Rept 50-271/92-81.Corrective Actions:Replacement of Degraded Grid Relays,W/Models W/Narrower Reset Tolerances, Under Review & Vehicle Barrier Protection Installed

Responds to NRC Re Unresolved Issues Noted in Edsfi Rept 50-271/92-81.Corrective Actions:Replacement of Degraded Grid Relays,W/Models W/Narrower Reset Tolerances, Under Review & Vehicle Barrier Protection Installed

ML20125D127
Person / Time
Site:	Vermont Yankee
Issue date:	12/07/1992
From:	Pelletier J VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-92-136, NUDOCS 9212150015
Download: ML20125D127 (8)

Text

..

~.

i L -c VERMONT YANKEE NOCLEAR POWER CORPORATION l

j .

p Ferry Road, Brattleboro, VT 05301-7002

/ ENGINEE I OFFICE 560 MA!N STREET

BOL TON, MA 01740

(508s779-6711 December 7,1992 l BVY 92136

I

-United States Nuclear Regulatory Commission l- ATTN: Document Control Desk l- Washington, DC 20555 i

References:

a) License No. DPR 28 (Docket No. 50-271) i- b) - Letter, USNRC to VYNPC, Electrical Distribution System

• l- Functional Inspection of Vermont-Yankee, Report t

No. 50-271/92-81, dated September 30,1992

!' c) NUMARC 90-12, " Design Basis Program Guidelines",

dated October 1990 '

, d)_ Letter VYNPC to.USNRC, BVY 92124, Response to NRC 2- - Electrical Distribution System Functional inspection 'of

Vermont Yankee, Report No. 50-271/92-81, Reply to

! Apparent Violations, dated October _30,1992

j. e) Letter VYNPC to USNRC, BVY 91-88, Station Blackout i (SBO) Supplemental Information on Coping Assessment,

[ dated September 30,1991-

Subject:

Response'to NRC Electrical. Distribution System Function -

' Inspection of Vermont Yankee, Report No. 50-271/92-81, j - Unresolved items and Other_lasues _

[

Dear Sir:

i l- This letter provides information requested by Reference' b) to:

F

1) Provide our resolution and conclusions on unresolved items pertaining.

, . to degraded grid relay settings and desel generator fuel oil transfer,_

t

' 2) Provide our schedule for resolution of the other issues identified at the - l

. exit meeting.

l i

14005?

j2A"*18acM*h o OI'

l

, VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission December 7,1992 Page 2 The degraded grid and fuel oli transfer unresolved items are addressed in Attachments A and B respectively. Attachment C to this letter provides our current schedule for resolution of all the items. If you have any further questions regarding these items, please contact Mike Metell (802-257 5271, Ext. 218) in my office.

Very truly yours, Vermont Yankee Nuclear Power Corporation PW James P. Pelletler Vice President, Engineering cc: USNRC Region l Administrator

- USNRC Resident inspector - VYNPS USNRC Project Manager - VYNPS

{

l

ATTACHMENT A DEGRADED GRID RELAYS Section 3.3 - Separation from Preferred Power Source - Item 92-81 04

.... In response to the NRC concerns, the licensee stated that they were now reassessing the degraded grid relay setpoint bases. This reassessment emerged as a scheduled work activity as a result of surveillance testing performed during the March 1992 plant outage when these setpoints were observed to have drifted outside the technical specification limits. The licensee also indicated that completion of a new voltage regulation analysis was expected by the end of 1992.

In view of the above, the acceptability of voltage regulation is unresolved pending the licensee's preparation of appropriate analyses addressing the potential spurious grid separations described above (50-271/92-81-04).

RESPONSE

We agree with the EDSFl inspection team that for 110KV/340KV minimum design line voltage in combination with maximum 4KV bus loading and concurrent accident signal, Vermont Yankee could be disconnected from the preferred power source and could be subject to an out of phase closure of a diesel generator breaker.

To address the postulated condition, Vermont Yankee has taken the following immediate actions:

• Vermont Yankee has examined worst case plant loadings and determined these loadings can only occur when the cooling towers are on line. Vermont Yankee has determined that without this cooling tower load, the postulated event should not occur.

Additionally, we have examined actual minimum / maximum voltages currently supplied by NEPEX (New England Power Exchange) and compared this data to those values used in our voltage regulation analysis. We have determined that the original voltage values used in our analysis were based on very conservative historical limits. We estimate that our actual minimum line voltages are about 115KV and 345KV respectively (versus 110KV and 340KV used in our original analysis). We estimate that our normal line voltages are typically greater than 117KV and 354KV respectively. Based on these more realistic values, Vermont Yankee has not, and does not anticipate being subject to the grid separation event as postulated in Reference b).

- - - - - - . - . = . . _. -

.. l 4

i Our short and long term actions are as follows:

• Short term actions - Vermont Yankee has contacted NEPEX and has initiated discussions on changing NEPEX procedures to ensure that minimum supplied line voltages are specified/ maintained at 115KV/345KV levels. Other New England nuclear stations have pursued and secured similar requested change's. -We will also complete the in-house voltage regulation study using the new limits.

We anticipate that these changes can be accomplished by Spring 1993.

~

• Lona term actions - Vermont Yankee plans to investigate other

- potential improvements which could further ensure preferred power _

source availability. These include a) limited shedding of nonessential loads such as the cooling towers; b) replacement of _the degraded grid relays with models that have narrower reset. tolerances; c) modification

. of the initiation' logic of the degraded grid relays. The need for any improvements beyond the short term actions to be taken will also be considered. These investigations are scheduled to be completed by the Fall of 1994.

. I

l 7 .

l ATTACHMENT B j

DIESEL GENERATOR FUEL OIL TRANSFER SYSTEM l

j Section 4.2.1 - Fuel Oil Transfer Pump Submersion - Item 92-81 09 i

l During a walkdown of the fuel oil transfer pump house, the team noted that the pumps were located in a single pit adjacent to the storage tank pit. They also l observed that a conduit penetrating the_ wall between the two pits had not

! been sealed. Because of the pumps vulnerability to common mode failure due to flooding, the team asked the licensee to address maximum flood level, tank i rupture resulting from a design basis missile, and qualification of pump motors for submersion. The licensee's preliminary review indicated that the maximum flood level was severalinches below the pump house access door.and the rim j around the tank pit. However,if the tank contained more than 68,000 gallons, i a rupture of the tank at or-below ground level could flood the tank pit above l the 8' 4" level of the conduit penetration-and hence the pump room. The i pump motors were not quallfled for submersion.

In view of the above, the capability of the transfer pumps to operate in tN event of the postulated tank rupture is an unresolved item pending -the j licensee's further evaluation of the issue and NRC review (50 271/92-81-09).

i

[ RESPONSE Vermont Yankee has determined that the only design purpose for the above mentioned -

l wall penetration is to provide accecs for the subject conduit.--To enhance the existing L berm oil retention capability, the subject conduit-is scheduled to be-sealed by I

December 15,1992. We conclude that this enhancement addresses all flooding / pump l submersion items.

Section 3.2.1 - Fuel Oil Temperature Control - Item 92-81-10 i

.... Although, on the basis of the temperature specified in Section 10.12.3 of -

the FSAR, the requirements.of the fuel oil procurement specification met those

! of the ASTM Standard and, hence, those of the Technical Specification, the team expressed concern for those times when the temperature fell below the i pour point of the oil. Extended severe weather conditions could cause gelling;

of the fuel oil and clogging of both transfer pump strainers. Vermont Yankee's cold weather procedure, OP 2196 required that the temperature'of fuel oil at 4

the pump suction be noted once each shift. However, the primary purpose of-the temperature reading was to ascertain the operability of the heat tracing, i

i

- _ _ .- - _ , _ . _ , . _ _ .s. ,.

l i

.... The inspectors agreed that the mass of the oil would retard gelling, but noted that this and past experience with fuel analysis could not be used to ensure that a common mode failure of the fuel transfer system would not occur. Therefore fluidity of the fuel oil is unresolved pending appropriate j analysis and corrective actions by the licensee (50 271/92 81-10).

j RESPONSE Vermont Yankee will enhance OP 3140 " Alarm Response" by December 15,1992 to alert the operators of potential loss of fuel oil transfer capability for sub zero weather conditions. Specifically:

• We have analyzed fuel usage in sub zero weather, and have determined i that fuelis transferred about once every two hours to meet house heating s needs. Therefore by monitoring the house heating boiler day tank level (via level alarm switch LSL-108-6B), we effectively and automatically monitor fuel oil transfer. We will update OP 3140 to note that if alarm switch LSL-108-6B is alarmed, that fuel oil transfer /EDG operability may be impacted.

• To aid the operator in troubleshooting the LSL-108-6B alarm, we have also updated OP 3140 to compare the pump suction line temperature during transfer, to the fuel oil tank oil pour point (0 degree F

, specification,-10 to -20 degrees F typical actual values) if fuel oil transfer

gelling is suspected. During fuel oil transfer, representative internal storage tank oil temperatures can be read at the fuel oil transfer pump suction line sensor.

We have also examined the potential for analytically predicting, under severe cold weather conditions, when the fuel oil gelling potential could be a problem. We have determined that:

• A pure analytical model may not give the desired accurracy, relative to the large number of variables to be considered, such as radiational cooling, air temperature, underground heat' transfer, wind heat loss, precipitation, etc.

• Collecting data at the above mentioned conditions and tank oil temperature during transfer would allow evaluation of the potential for fuel oil gelling.

We have decided to collect and analyze this data during the 1992-1993 winter season.

Please note that Vermont Yankee does not anticipate an oil transfer problem in that we have transferred fuel oil successfully without gelling for the past 20 years of 4

operation, including severe sustained cold spells. We have concluded that these actions provide sufficient warning of a possible fuel oil gelling problem and address this issue.

Section 3.2.1 - Fuel Oil Transfer Pipino Damaae ltem 92-81-11 During a walkdown of-the fuel oil transfer system, the team noted that approximately 15 feet of transfer piping downstream of each pump had been Installed within inches- from - each other, outside the pump house. No protection had been provided against external damage from hazar_ds in the area, e.g. backing up vehicle or missile during a tornado. The piping was in an exposed area adjacent to a roadway. The team was concerned that damage from such hazards might cause a common mode failure of both fuel oil supply lines and the shutdown of both EDGs upon depletion of the 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> supply of fuel oil stored in the day tanks.

The licensee was not able to satisfactorily address the issue during the inspection. Therefore this item is an unresolved item pending review by the licensee (50-271/92-81-11).

RESPONSE

We agree with the EDSFilnspection Team that enhancing protection of these lines can improve their safety performance. On this basis, Vermont Yankee has completed the following actions:

• Fuel Oil Transfer Line Vehicle - Protection - Vermont -Yankee has determined that vehicle traffic could impact fuel oil transfer line performance. Therefore, during November 1992, -Vermont Yankee completed installation of vehicle barrier protection for these fuel oil transfer lines.

• Tornado impact on Fue! Oil Tonsfer Line Assessment .- We have reviewed this concern relative to -our Station Blackout response

! (Reference e). The probability of experiencing a tornado at Vermont Yankee is about 2 E-05 occurrence per year (i.e.'9.8 E-S occurrence pe-year per square mile). We. estimate that the probability of damage occurring at these lines (based on previous similar studies and Reference e),if Vermont Yankee experienced a tornado, would be less than 1 E-06.

This is sufficiently small, such that further immediate action-_is not warranted at this time. Vermont _ Yankee will more formally address this item in our IPEEE Program.

i i.

4 Attachment C- Schedule for Addressina EDSFI Items Planned Completion Date Separation from Preferred Power Source Analysis immediate Complete Unresolved item 1 -(50-271/ 92-81-04) Short term Spring 93 Long term Fall 94 Diesel Generator Loading Analysis Summer 93 Unresolved item 2 - (50-271/ 92-81-05) 120 Vac Protective Devices Coordination Analysis Winter 93/94 Unresolved item 3 -(50-271/ 92-81-06) 125 Vdc Protective Devices Coordination Analysis Fall 93 Unresolved item 4 - (50-271/ 92-81 07)

DC Bus Cross Connections Analysis Spring 93 Unresolved item 5 - (50-271/ 92-81-08)

Fuel Oil Transfer Pump Submersion - Hardware Upgrade Dec 15,1992 Unresolved item 6 (50-271/92-81-09)

Fuel Oil Temperature Control- Procedural Enhancement Dec 15,1992 Unresolved item 7 (50-271/92-81 10)

Fuel Oil Transfer Piping Damage - Short term analysis Complete Unresolved item 8 - (50-271/ 92-81 11) - Hardware Upgrade Complete

- IPEEE calculation Spring 95 Diesel Generator Room Temperature Calculation Feb 93 Unresolved item 9 -(50-271/ 92-81-12)

Battery Room Ventilation Calculation Spring 93 l Unresolved item 10-(50-271/ 92-81 13) l Cable Ampacity Calculation Summer 94

120 Vac Control Circuit Analysis Winter 93/94 L

AC System Short Circuit Analysis Spring 93 120 Vac Voltage Drop Study Winter 93/94 125 Vdc Voltage Drop Study Spring 94 l Switchgear Room Ventilation Calculation Feb 93 Note 1: In accordance with NUMARC 90-12 (Reference c) and noted in Reference b), Vermont Yankee had already scheduled many of the above enhancements, l .

Note 2: The above schedule is for Vermont Yankee planning purposes only. Vermont Yankee does not consider this schedule as a commitment. It may be adjusted based on arising priorities.

-. .- . -.