ML20237J408
| ML20237J408 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 08/14/1987 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| TAC-65965, TAC-65966, NUDOCS 8708180168 | |
| Download: ML20237J408 (5) | |
Text
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DUKE POWER GOMI%NY L
P.O. HOx 33180 CHARLOTTE, N.C. 28242 HALU. TUCKER TELEPHONE vsos enemment (704) 373-4531
, poos.aan emonoorsom August 14, 1987 U'. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555
Subject:
Catawba Nuclear Station Docket Nos. 50-413 and 50-414
Dear Sir:
Mr. Steven A. Varga's letter of August 7, 1987 requested information relating to the adequacy of Catawba's Nuclear Service Water (RN) System. The Staff's concern apparently stems from a scenario previously identified by Duke in which one unit is shutdown with one of two diesel generators out of service.
Specifically, the
-Staff questioned conformance to General Design Criteria 5 and 44, and requested
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"(1) an analysis justifying the adequacy of (one) RN pump to serve both units o_r (2) a description of actions implemented or planned to be implemented that ijustify continued plant operation". These issues are discussed below.
Conformance to General Design Criteria 5 and 44 The RN System is described in Section 9.2.1 of the Catawba FSAR and shown diagramtically on FSAR Figurea 9.2.1-1 through -12.
A simplified schematic is provided as Attachment 1.
The RN System consists of two redundant trains, A and B, of essential equipment per unit. The A train is supplied by the two A RN pumps and the B train by the two B pumps. An A and a B pump are designated for each unit and are powered from separate emergency power sources associated with that unit. The A and B pumps are interconnected by a common discharge header such that operation of any two of the four pumps is sufficient to supply all cooling water requirements for the two units for startup, cooldown, refueling, or post-accident operation. Only one pump is needed for normal operation. The crossover connections are provided with isolat. ion valves that are automatically closed on a High-High containment pressure or Lcw RN Pump Pit level signal to ensure train integrity. As previously concluded in Section 9.2.1 of the Catawba Safety Evaluation Report (NUREG-0954) the RN System meets GDC 5 and 44.
The
. h Staff's previous conclusions remain valid.
n y $ Single Pump Operation n
- b. In the' event of a station blackout and single unit LOCA, while the non-LOCA unit Io is operating with a single emergency diesel generator removed from service, a single failure of the RN pit supply valve on the opposite train from the
.hg inoperable _ diesel generator would result in the loss of both RN pumps on that
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train, leaving a single RN pump to supply cooling for both units. The more l
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'$4 limiting case with respect to pump capacity would be the pre-event inoperability
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~ U. S. Nuclear Regulatory Commission August. 14,-1987' Page 2:
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lof the RN pump on the non-LCOA unit rather than a diesel generator,' sines this j
condition will result in actual heat loads, e.g.,
the diesel generator, on that unit.
An anal" sis has been performed which demonstrates the adequacy of a single RN i
pump under these conditions. This analysis is based on the following:
LOCA Non-LOCA Unit Unit COMPONENT COOLING 5200 GPM 2500 GPM CONTAINMENT SPRAY 3800 GPM 0 GPM ASSURED AUXILIARY FEEDWATER 0 GPM 500 GPM
'D/G COOLING 1100 GPM 1100 GPM COMPONENT COOLING RN HX FOULING FACTOR - 0.0045 CONTAINMENT SPRAY RN HX FOULING FACTOR - 0.005 I
D/G COOLING RN FOULING FACTOR - 0.0035 PUMPHOUSE DFMANDS - 2186 GPM CONTROL ROOM COOLING - 1400 GPM
. Operator action to re-throttle flow rates between components is not. required' until transfer to containment sump recirculation (approximately 40 minutes after start of the event).-
The crossover valve (47A or 48B) associated with an out of service diesel generator is closed and de-energized at the time of removal from service.
-Actions Justifying Continued Opere. tion In the absence of the above analysis establishlug the adequacy of a single RN pump to supply both units, alterna'e actions have been taken at the plant to t
assure safe operation within the bases for the Technical Specifications at any time that a diesel generator or RN pump was removed from service.
The technical specifications for emergency diesel generators require that two be operable when the associated unit is in Modes 1, 2, 3 or 4.
Similarly, two independent Nuclear Service Water Loops are required to be operable when in these
. modes. The bases states that this redundancy is provided to cover the assumption of a single failure, and thus be consistent with the safety analysis which assumes only a' single train is operating. Operation without this redundancy is permitted for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, clearly suspending the requirement to be able to withstand an additional single failure while meeting the safety analysis for that
' limited period of time.
Plant procedures were revised in 1986 to require both 1
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U. S. Nuclear Regulatory Commission
-August'.14, 1987
.Page 3.
. units to enter-72 hour action statements anytime a diesel generator on either unit was removed from service.. For the unit with the inoperable diesel generator, there are numerous failures of opposite train components, e.g.,
emergency power, ECCS or containment cooling components, which would place that unit in an unanalyzed condition.
Included in this listing of components is the nuclear service water pit supply valve from the SNSWP. Operation without the assumption of any of these failures is clearly permitted for this limited period j
of time. Recording the unaffected unit into a degraded mode at the same time
-assures that no unit specific degradations of the unaffected train occur without immediate compensatory actions being taken as required by Technical Specification 3.0.3.
Prior to an emergency diesel generator being out of service for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, plant procedures require that the unaffected unit be placed in a non-degraded condition by (1) pre-aligning the unaffected train for SNSWP recirculation and (2) isolating or otherwise restricting flow to the degraded train of the degraded i
unit in a manner which insures adequate post-accident flows to components on this train of the other unit. The unit with the diesel generator out of service is placed in a shutdown operating mode as required by the Technical Specifications.
.After completion of action (2) above, action (1) while not required by the Technical Specifications nor the safety analysis to support the operating unit, has provided an additional margin of safety to the shutdown unit.
Planned Actions for Safety Improvements The transfer from Lake Wylie to the SNSWP as a source of water for the Nuclear Service Water System in the absence of a loss of Lake Wylie represents an 3
unnecessary challenge to the associated valves from the SNSWP. To improve the l
overall reliability of the RN System, two modifications are in process to reduce
]
i the potential for these challenges One modification would remove the containment pressure signal that realigns the RN pumps suction from Lake Wylie to the SNSWP. This signal is unnecessary since suction is also swapped on loss of Lake Wylie as sensed by low RN Pump Pit level.
This modification should be completed prior to the upcoming Unit I refueling j
outage in early October, 1987.
l In order to improve the reliability of the pit level instrumentation, thus reducing challenges from spurious signals, additional transmitters will be added to go from a 1 out of 2 logic to a 2 out of 3 logic. Because this change requires additional hardware, it is targeted for 1988.
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Conclusions
.It is Duke's conclusion that the Catawba Nuclear Service Water System meets General Design Criteria 5 and 44 as previously concluded by the NRC in the Catawba SER.
Present plant procedures adequately address the steps to be taken when a diesel generator is removed from service.
These steps are consistent with the Technical Specifications, their bases and the plant safety analysis.
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t U. S. Nuclear Regulatory Commission
< August 14,.1987
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.Other scenarios which lead to a single RN pump supplying both units have been analyzed. Adequate cooling water is supplied to all operating components as required,in the safety analysis.
l I,dditional improvements are planned for increasing the RN System reliability.
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l Due'to the complexity of the Catawba RN System and the many scenarios that have
)
.been discussed, Duke would welcome a meeting to discuss the issues raised by Mr.
Varga's letter.
I declare under penalty of perjury that the above statements are true and correct i
to the best of my knowledge.
Very truly yours.
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Hal B. Tucker ROS/54/sbn xc:
Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900' Atlanta, Georgia 30323 Mr. P. K. Van Doorn NRC Resident Inspector Catawba Nuclear Station Dr. K. Jabbour Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555
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