ML19323H557
| ML19323H557 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 06/09/1980 |
| From: | Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | |
| References | |
| NUDOCS 8006130174 | |
| Download: ML19323H557 (3) | |
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VrnoxxrA EI.ECTRIC AND Powan CoxPrxy RICIIMOND, VIRGIN EA 202f71 June 9, 1980 Mr. James P. O'Reilly, Director Serial No. 1160B Office of Inspection and Enforcement N0/RWC:ms U. S. Nuclear Regulatory Commission Docket No. 50-338 50-339 Region II 101 Mariettu Street, Suite 3100 Atlanta, Georgia 30303
Dear Mr. O'Reilly:
On October 31, 1979 a report was made under the provisions of 10 CFR 50.55(e) concerning the Safeguards Area Exhaust System, North Anna Power Station, Unit 2.
Pursuant to North Anna Station Technical Specifications, the Virginia Electric and Power Company also submitted License Event Report No. LER-79-149/
01T-0 dated November 15, 1979.
The report indicated that the Safeguards Area Exhaust System which provides post LOCA ambient cooling for the Recirculation Spray and Low Head Safety Injection Pumps is not entirely seismically designed as stated in the Final Safety Analysis Report Section 9.4.6.1.
Our follow up letters dated November 30, and December 28, 1979 indicated that
}
further evaluation showed the system design basis is not in conflict with the system description or design criteria as stated in the FSAR.
However, we stated we were continuing our review to determine if modifications are requir-ed to ensure that the Safeguards and Central Area Exhaust systems will perform their intended functions.
The exhaust duc twork from the Safeguard Area ventilation fans and other fans ventilating potentially contaminated areas up to and including the ventilation stacks was not designed to Seismic Category I requirements, since it was assuned that a postulated failure of the fan discharge ductwork would result in a break in the exhaust ductwork rather than a crimp or full closure of the exhaust path.
Under the assumed failure mechanism, the Ventilation System would still perform its required function of providing adequa te cooling of Engineered Sa:eguards equipment.
Further evaluation of this design basis in-dicated that we could not show conclusively by analysis that the exhaust duct-work from the fans up to and including the ventilation stack will not fall by crimping during a seismic event.
Therefore, a review was conducted to deter-mine what equipment required to nitigate the consequences of.1 LOCA might not receive adequate cooling assuming a loss of ventilation due to crimping of the non-seismic exhaust ductwork.
It was concluded that the outside recirculation spray pumps and the low head safety injection pumps ventilated by the Safe-guards Area exhaust fans and the charging pumps ventilated by the Auxiliary Building Central Area exhaust fans are the only essential equipment that might not receive adequate cooling during this postulated event.
S noun l79
V noix A Et.zctuic Axu Powra COMPAW TO Mr. James P. O'Reilly 2
9 Based on this review the Auxiliary Building Central Area Ventilation Exhaust System has been modified to ensure operability following a seismic event.
The modification consisted of installing a mechanical means of opening the Central Area exhaust ductuork on the Auxiliary Building roof and seismically support-ing the exhaust ductwork from the Central Area fans up to and including the new exhaust port.
Should ventilation flow be lost by crimping downstream of this exhaus t port, the exhaus t port will be opened and ventilation flow re-established.
The exhaust from this path can be monitored by lining up the existing Ventilation Vent sampler radiation monitor to the Auxiliary Building Central Area exhaust.
The Safeguards Area Exhaust system, as originally designed is with the suction ducts to the fans,
-HV-F-40A and B, seismically supported, and the discharge duct to the ventilation stack "B",
non-seismically supported.
If the Sa fe-guards Area Exhaust system failed to operate the seismically supported local ventilation fans
-HV-F-71 A and B were designed to recirculate air over the pumps and motors to dissipate the heat in the Safeguards Area.
This backup system requires manual fan initiation and opening an outside door at grade elevation to allow heated air to vent to the atmosphere.
The source of cool air to the area is through the non-seismic supply air unit,
-HV-HV-4.
k It has been determined that it is not feasible to seismically upgrade the supply air units h-HV-HV-4.
Therefore, the Safeguard Area Exhaust system exhaus t ducts will be seismically upgraded in a manner similar to the modifi-cations to the Central Area Exhaust System and the outside door at grade level vill be used as the supply of cool air.
The discharge duct from fans
-HV-F-4 0A and B will be selsnically supported up to and including a new exhaust port.
This pressure relief door would open and alarm in the control room should the ventilation ficw be lost due to crimping downstream.
The exhaust port will be located downs t ream of the existing ventilation vent sampler radiation monitor.
We are continuing to evaluate the use of louv'rs in the roof of the Safeguards Area to allow aut' matic operation and improvei o
supply air distribution.
In the intertm, the backup recirculation fans,
-HV-F-71A and 3 will be used to dissipate heat in the event of a LOCA followed by a seismic event causing the Safeguard Area Exhaust system exhaust ducts to crimp causing a loss of flow.
Should the seismic event cause the supply air unit to become i
inoperable the Safeguards Area door will be used as the supply of cool air.
i
Vinoix14 Et.rcruic Aso Powra CoxPrxy To Mr.
James P.
O'Reilly 3
It is currently scheduled to have the seismic upgrade of the Safeguards Area Exhaust Ventilation system exhaust duct and the pressure relief door installed prior to full power operation on Unit No. 2.
Very truly yours, f-
/-
B. R. Sylvia Manager-Nuclear Operations and Maintenance cc:
Mr. Victor Stello, Director Office of Inspection and Enforcement o
m.