ML20072T126

Submits Addl Response to Violations Noted in Insp Repts 50-445/87-19 & 50-445/87-37.Implementation of Corrective Actions Re Need for Alarming Low Air Flow Conditions in HVAC Sys Due to Closed Gravity Damper Unnecessary

ML20072T126
Person / Time
Site:	Comanche Peak
Issue date:	04/08/1991
From:	William Cahill TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TXX-91119, NUDOCS 9104170234
Download: ML20072T126 (4)

Text

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.- .N FE 1 C Log # TXX 91119 File # 10130

= = -IR 87 37 IR 87 19 7UELECTRIC Ref. # 10CFR2,201 '

William J. ceWii, Jr'.

- becutive Vke PrwJent April 8, 1991 1 U S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C'. 20555

SUBJECT:

C0HANCHE PEAK' STEAM ELECTRIC STATION (CPSES)

DOCKET NOS. 50 445 AND-50-446 i ADDITIONAL INFORMATION T0 NRC INSPECTION RERRT NOS, 50-445/87-19 AND 50 445/87 37 4 REF: 1) .NRC Inspection-Report No. 50 445/87 19, dated October 15, 1987

-2L 7NRC InspectionLReport No. 50 445/87 37, dated February 8.- 1988

3) TV Electric letter (TXX 88205) from W.G. Counsil to the:NRC

' dated February-4,-1988

4) 'TU Electric letter!(TXX48332) from W.G. Counsil to the NRC.

dated April 11, 1988 4 b)- TU Electric ~ letter (TXX-89780) from W.G. Counsi.1' to the NRC dated November 8, 1989

6) Supplement 17 to Safety Evaluation Report (NUREG-0797) '

dated' November'1988 Gentlemen:-

1NRC-Inspection Reports' 50 445/87-19.and-50 445/87-37 identify an-open action-

' item (M 3) regarding the-potential need for alarming, low air flow conditions in.

R -Heating, Ventilating, and Air-Conditioning (HVAC) Systems-'due to a closed or L ' partially. closed gravity damper with the associated fan energized. (References l':and 2).

r TV Electric committed to implementing a design modification to add pitot tubes or to relocate pressure: taps.to resolve the potential = problem-of "no flow l

, . condition"-detection in HVAC systems prior to the:end of the-first refueling

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outage (References 3. 4 and 5). The NRC documented the ac.eptability of this- -/

-commitment in SSER 17 (Reference 6.-pace 4-82). TV Electric provided thi.s y - commitment as a- clenly conservative course of action which was feasible and not! cost prohibitive. Resources, which.were focused on activities needed.to-I', . .

9104170234 910408 / '

_PDR ADOCK 05000445 400 North Olivc Street L B. 8) Dal.as, Tem 75201 G: PLR

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4 TXV 91119 Page 2 of 4 obtain an operating license and prepare for operation, were not available at that time to pursue alternate solutions to the issue. Based on further review, TV Electric has determined that these corrective actions are not necessary.

This conclusion is based on the information below:

ij This open item is not a significant safety issue. All Safety Related HVAC Systems are provided with redundant fans and dampers which would start /open automatically during an emergency. With the single failure of a gravity damper to open, the redundant fan and damper will continue to perform the system safety function. Simultaneous failure of a gravity damper in one train nd a f ailure in the redundant train is not considered a credible event. The failure of a gravity damper would be detectable as described in item (3).

2) TV Electric considers the failure of an operating gravity damper a low probablity event at CPSES. This position is based on the following:

a) When a gravity damper is installed and the system is air balanced to provide the required air distribution, the gravity damper's counterweights are adjusted and welded such that the damper will open as soon as there is some air flow through the damper. The counterweight is adjusted to f acilitate the opening of the damper and maintain it in the open position while there is continuous air flow through the damper. As soon as there is no air flow through the damper, the design of the damper blades is such that the weight of the blades will cause the damper to close, b) All gravity dampers are inside buildings where they are not subject to direct outdoor conditions. Therefore the probability of a gravity damper failure due to weather induced cerrosion is judged to be low, c) On the Safety and Non-Safety Related Battery Room Exhaust System, each bcttery room is supplied with two 100% capacity exhaust f ans.

The equipment rotation program insures that each fan and gravity dumper is operated on a_ periodic basis. Since one of the two fans runs all the time, frequent use will reduce the potential for sticking gravity dampe.as. On the non-safety related fans there is no safety significar.ce to losing air flow due to a closed gravity damper.

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TXX 91119 Page 3 of 4 1

.1 3): The following would provide indication of gravity damper failure: l a)~ Change in area temperatures due to low air flow. Temperatures in certain areas serviced by various HVAC systems-are periodically surveilled=as per Technical Specification-4.7.10.

b) Differential pressure ~ changes inside of the ' buildings due to a fan not exhausting sufficient air or not supplying sufficient air.

Annunciators alert. the ! control room operators to high pressure in the  ;

Auxilliary, Safeguards and Fuel buildings (Primary Plant Ventilation d System), and low pressure in the Control Room (Control-Room i' Ventilation System).-

c) The-Engineered Safety Features-(ESF) filtration heaters =and associated fans would trip if air flow were restricted. A heater or

' fan trip is annunciated to the control- room' operators. - A

-modification has been proposed to- the ESF Primary Plant Ventilation .;

-System-(PPVS) to separate annunciation of fan or heater trips from:

the existing common annunciation for PPVS ESF heater and fan trip'and PPVS non-ESF fan trip. '

, d) . Other indications of1 abnormal air flow-conditions 1ere:

'1 )l Pressure indicators on the filter units 2)f Vane axial' fan trip when airflow is insufficient for motor :t

- cooling' 53)- Heaters would trip without sufficient-air flow, during the heating seasonL

4) -A maintenance' activity-has been implemented for Unit 1 safety related Li gravity dampers which-requires 1that maintenance be performed on safety related gravity damperslevery 12 monthsuto provide-the additional assurance.

ofithe gravity damper operability.. Maintenance activity for Unit-2 safety

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related= gravity dampers will be implemented by Unit J2: fuel load. Failure

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sof non-safety 1related gravity dampers Will not impact safety function of the plant. Therefore no action will be_-required on the-Unit 1 or.2 non-safety.related_ gravity dampers.

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! Page 4 of 4 Therefore, it can be concluded that postulating an undetected failure of a gravity damper is an extremely remote possibility and in the case of failure, the failure will not adversely affect the safe operation of the plant.

Based on the lack of safety significance and the information provided above. TU Electric concludes that implementation of the corrective action as identified in NRC open item H 3 does not impact safety of the plant. The existing design and the maintenance activity adequately addresses this item and the design modification to add pitot tubes or to relocate pressure taps will not be implemented on CPSES Units 1 or 2.

Sincerely, William J. Ca 11, Jr.

MCP/gj c - Mr. R. D. Hartin, Region IV Resident inspectors, CPSES (3)

Mr. J. W. Clifford, NRR Hr. Nel Fields, NRR

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