ML19270H812

Updates LER-79-149/01T-0 Submitted 791115:exhaust Ductwork from Safeguards Area Ventilation Sys Does Not Conflict W/ FSAR Design Basis.Mods to Ensure Adequate Seismically Qualified Emergency Cooling Expected by 800115

ML19270H812
Person / Time
Site:	North Anna
Issue date:	12/28/1979
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8001030756
Download: ML19270H812 (3)

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VraoxxxA Ex.ncTaxc ann Powna COMPANY Rxcnxown.VxnouxxA 23261 December 28, 1979 Mr. James P. O'Reilly, Director Serial No. 1160 Office of Inspection and Enforcement P0/RMB:suv U.S. Nuclear Regulatory Commission Docket No. 50-338 Region II License No. NPF-4 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

Pursant to North Anna Power Station Technical Specifications, the Virginia Electric and Power Company submitted Licensee 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 Lov Bead Safety Injection Pumps is not entirely seismically designed as stated in FSA2 Section 9.4.6.1. The original design of the system scened to be in contrast to the FSAR criteria since the fan discharge ductwork up to and including the ventilation stack is not designed to Seisuic Category I require-ments.

Further evaluation of the design criteria as stated in the FSAR indicates, however, that the systen design basis is not contrary to the description con-tained in the FSAR. Specifically, FSAR Section 9.4.6.1 states that:

" Spaces containing the recirculation spray and safety injection pumps and their valve rooms are subject to potential radioactive contamination from gland leakage, and consequently their exhaust systen is designed for seismic Category I..."

The portion of the Safeguards Area Exhaust System designed to Seismic Category I requirements is described in detail in Table 3.2.1-1. The table clearly in-dicates that only the Safeguards Area Ventilation Exhaust Fans and exhaust ductwork up to the fans are Seismic Category I. '"he seismic design categories for all parts of the Enginee red Safety Feature Area Ventilation System is further described in the Supplement to the FSAR in response to Comment 9.44.

The response states that:

'*The entire Engineered Safety Feature (Safeguards) Area exhaust sys-tem, including the ducts and fans in the auxiliary building are de-signed to Seismic Class I requirements."

The entire system referred to in the response should be interpreted as the exhaust fans and the ductwork up to the fans as defined in Table 3.2.1-1 re-ferenced above. The exhaust from the Safeguards Area fans discharge into a common ventilation duct along with the exhausts free several other plant areas. 7 1675 003 k? '

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I Mr. James P. O'Refily, Director The Seismic Category I ductverk is also shown in the Supplement to the FSAR in response to Corusent 9.85. Figure 59.86-1 indicates that the exhaust ductwork from the Safeguards Area Fans as well as exhaust ductwork from other poten-i tially contaminated area fans up to and including the Ventilation Stacka are not designed to Seismic Category I requirements. It is therefore concluded that the design of the Safeguards Ares Ventilation System is not in conflict with the system description or design basis contained in the FSAR as reported j in License Event Report 1.ER-79-149/01T-0.

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The exhaust ductvork from the Safeguards Area ventilation fans and other fans l ventilating potentially contaminated areas up to and including tha ventilation stacks was not designed to Seismic Category I requirements, since it was assumed 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 adequate cooling of f

Engineered Safeguards equipeent. Further evaluation of this design basis in-dicates that we cannot show conclusively by analysis that the exhaust ductwork frcm the fans up to and including the ventilation stack will not fail by crir: ping during a seisnic event. Therefore, a review has been conductM to determine what equipment required to mitigate the consequences of a LOCA might not receive adequate cooling assuming a loss of ventilation due to crimping of the non-seismic exhaust ductvork. It was concluded that the outside recircu-lation spray pumps and the low head safety injection pu=ps ventilated by the Safeguards 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.

The Safeguards Area Ventilation Syste= is provided with an emergency supply

, system designed as Seismic Class I. This system may be manually initiated following a loss of normal ventilation flow. Therefore, adequato protection exists to ensure that equipexnt in this area can be adequately cooled during the postulated failure in tbo ventilation exhaust system. However, there is no present neans of providing emergency backup ventilation for the charging pu=ps.

Since we are unable to prove by analysis that the Ventilation System is ade-quate to provide the necessary cooling requirements for the charging pumps, and since there is no seismically qualified backup emergency cooling, we plan to codify the Auxiliary Building Central Area Ventilation Exhaust System to ensure operability following a seismic event. The modification will consist of installing a mechanical means of opening the Central Area exhaust ductwork on the Auxiliary Building roof and seismically supporting the exhaust ductwork from the Central Area fans up to and including the new exhaust port. Should ventilation flow be lost by cri= ping downstream of this exhaust port, the ex-haust port vill 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.

This modification will be implemented as soon as possible. The current pro-i jected completion date is January 15, 1980 provided suitable materials are available.

l According to our current schadule for start-up of Unit No.1, the unit vill be i returned to service prior to completion of this modification. It is our in-

tent, therefore, to complete the nodification during pcr " t t ti 1675 004 W Oh ki'l.

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s Mr. James P. O'Reilly, Director No. 1. Station emergency procedures will be revised as necessary to reflect the required operator actions to maintain ventilation flow following the postu-lated failure of the non-seismic ductwork. We vill continue our evaluation of the Ventilation System design basis to determine what other long term correc-tive action is necessary, if any, to ensure the adequacy of the system to pro-vide the required cooling to all Engineered Safeguards equipment.

In summary, although the original design basis is not in conflict with FSAR criteria, we cannot show analytically that the exhaust ductwork from the Safe-guards Area exhaust fans and the Auxiliary Building Central Area exhaust fans vill be adequate to ensure an operable flow path following a seismic event.

Therefore, corrective action will be taken as described above.

We would appreciate your prompt review and response on this matter.

Very truly yours.

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C.11. Stallings Vice President - Power Supply And Production Operations RMB/suv:1N3 Enclosures (3 copies) cc: Mr. Victor Stello, Director Office of Inspection and Enforcement P00R ORGINAL 1675 005