ML20066H910
| ML20066H910 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/09/1988 |
| From: | Kuncl L NEBRASKA PUBLIC POWER DISTRICT |
| To: | Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| IEB-88-004, IEB-88-4, IEIN-87-059, IEIN-87-59, NUDOCS 9102220179 | |
| Download: ML20066H910 (6) | |
Text
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GtNthAL OFFICE Nebraska Public Power Distdct
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armasswanems.wwawm-aavammmwnwaarreemuaustesen,emuummuurmammemnaamams NLS8800347 k
h Ih July 8, 1968 Mr. Robert D.
Martin Regional Administrator U.
S, Nuclear Regulatory Commission Region IV 611 Ryan Plara Drive, suite 1000 Arlington, TX 76011
Dear Mr. Martin:
Subject.
Response to NRC Bulletin No. 68 04 Cooper Nuclear Station NRC Docket No, 50 298, DPR 46 3
Reference:
1.
NRC Bulletin No. 88 04, " Potential Safety Related Pup Lo s s "
2.
NRC Information Notice 87 59, " Potential PHR Pump Loss a In accordance with the action requirements of Reference 1 the District has perforued an in depth ovaluation of all of its safety related pumps at CNS.
As a result of this evaluation, the District has identified six pumps which require further investigation, those being tho two Core Spray pumps and the four Service Water Booster pumps.
The District feels the Core Spray pumps presently have adequate minimum flow capacities; however, this can only be verified by testing.
The Service Water 3ooster pumps need further evaluation to verify that they will not experience adverse pump to pump interrections at minimum flow.
The District will perform the following items to resolve this issue:
1.
Test the Core Spray pumps to verify the adequacy of the $%
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existing mininum flow capacities.
4 2.
Evaluate
- and, if
- required, test the Service Water Booster pumps to show there are no advarme pump to pump interactions at minimum flow conditions.
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I Mr. Robert D. Martin July 8, 1988 Page 2 These test (s) will consist of vibration and flow monitoring at j
minimum flow conditions.
In the interim, the District will perform the following:
1.
Add statements to the applicable operating procedures which cautions-the operators to on1; run one SWB pump per loop when loop flow rates are less than 5,000 gpm.
2.
Add 's ta tements to the applicable operating procedures which caution'the operators to prevent dead. heading the
-Core Spray pump against a high reactor vessel pressure.
The above actions will be performed according to the following
{
-schedule.
1.
The. interim operating procedure changes will be De ef implemented.by August 5, 1988.
2..
The evaluation of the Service Water Booster pumps will pe+-f I
be completed prior to the next refueling outage.
(currently scheduled for Spring 1989) 3.
All testing'will be-completed prior to startup from the 9 a"4 next refueling outage.
4 All long-term resolutions,- including modifications if S
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appropriate,. will be completed prior to startup from-the; spring 1990 refueling. outage.
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LAs required by the
- Bulletin, a
Justification for-Continued Operation is attached.
If. you have any_ questions-regarding this -submittal, please
,contr.cc my office ~.
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C.
Kduc1 Nuclear Power Croup. Manager LCK:kk32.1c Attachment-
-c c :- Document Control Desk w/ attachment U.S. Nuclear Regulatory Commission NRC. Resident. Inspector w/ attachment Cooper Nuclear Station be:
NRC Distribution w/ attachment
Mr. Robert D.
Martin July 8, 1988 Page 3 STATE OF NEBRASKA)
)ss PLATTE COUNTY
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L.
G. Kunc1, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District, a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this request on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and belief, p.
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-Kunc1 Subscribed n my presence and sworn to before me this [ k day of
/
_______________, 1988.
COLLEEN M. KUTA if Coast la Aug 4,13 s
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i Attachment to i
NLSB800347 JUSTIFICATION FOR CONTINUED OPERATION FOR NRC BULLETIN 88 04
.The-concerns stated in NRC Bulletin 88-04 are summarized as:
-1.
With two pumps operating in parallel in the minimum flow mode, one of the pumps may be dead headed resulting in pump damage or failure.
2.
Install'ed minimum. pump flows may not be adequat'e to preclude pump-damage or failure.
=These conce rns _ are-addressed below. and provide the basis for i
concluding that continued operation of Cooper Nuclear Station is justified.
A.
- All Class 1.- 2, and 3 centrifugal and positive displacement-type. pumps _ installed at CNS are required to perform a
specific function in shutting down. the reactor or in Laitigating the consequenen of an. accident must undergo routine 'in service testing per ASME Boiler and' Pressure Vessel code Sec tion. XI, Article IVp 1000.
These quarterly
. tests are in addition
.to the Technical' Specification-surveillance requirements intenced to demonstrate compliance with the. plant safety analys~es.
The Section XI t,sts are intended to detect changes in pump performance; Article IUP 1500.(" Detection of Change")' states:
"The hydraulic'and mechanical condition of a pump, relative to a previous condition, can be determined by attempting.to duplicate, by test, a set of basic reference parameters.
Deviations detected are. symptoms of changes and, depending.upon the-degree of deviation,.
3 indicate need for further tests or corrective action."
The -in service tests measure speed (if_ variable speed)-,
inlet pressure, differential pressure, flow: rate, vibration amplitude, motor amps and bearing temperature.
Alert ranges
~
and required action rangen are' strictly defined, and require either-increased frequency of testing.or declaring the pump inoperative.
Performance outside of the required action range would require-prompt evaluation end resolution.
Although these tests themselves would not detect pump dead-heading. or inadequate minimum flow (since these are intended to be full flow tests), any deleterious effects of operating with inadequate flow would be detected in advance of significant pump performance degradation.
Therefore, any changes in pump performance would be detected and corrected per routine pump testing in advance "f pump degradation due to cumulative low flow effects from pump surveillance testing and normal rysten use.
Attachment co NLS8800347 Page -2 B.
The potential for pump extessive wear attributable to ninimum flow operation and/or dead heading is negligible, since system operation in the minimum flow mode is primarily limited for short durations duting monthly surveillance testing.
C.
BWR operating experience demonstrates that short term operation in the minimum flow mode and/or dead heading has little or no impact on pump life.
Recent inspections of BWR RHR pumps have indicated no pump impeller excessive wear due to minimum flow.
It is estimated that the pumps had been operating for up to 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> in the minimum flow mode in the period since the previous inspection.
There have been occurrences in the industry when pumps have operated dead headed inadvertently (i.e.,
dead heading was not caused by minimum flow operation but, for instance, by incorrectly closing a velve). These pumps have continued to function normally.
D.
Pump wear attributable to minimum flou and/or dead brading is not a
significant contributor to total system unavailability.
Other factors (such as loss of emergency power, I t, s s of cooling, etc.) are more significant.
BWR and CN3 operating history indicates no occurrences of system una w ahility due to pump excessive wear attributable to low flow operation.
E.
In a CNS specific evaluation, the four RHR pumps have been shown, by actual test results, to have adequate minimum flow capacities and to not have adverse pump to-pump interractions.
These pumps, therefore, are not adversely affected by the problems suggested in NRC Bulletin 88-04 F.
For the core spray pumps, the only design basis events that would lead to pumps running in the minimum flow mode and/or dead heading are events that result in an ECCS initiation signal while the reactor is at high pressure (above the pump shutoff head).
These events are typically small break LOCAs.
Of these, only certain small break LOCAs actually require ECCS inj e c tion from RHR or core spray after running at low flow.
Once initiated, the maximum duration that a core spray pump may operate in the mininum flow mode for the spectrum of hypothetical LOCAs is less than 30 minutes.
This is derived from postulated small break
- LOCAs, wherein reactor depressurization to below the shut off head of these pumps is delryed.
For large break LOCAs, the reactor inherently depressurizes through the break.
The present minimum flow bypass line is expected to provide adequate protection for these pumps for the short durations postulated during both the small and large break LOCAs.
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_-o A t ta c tin.e n c to NLS8800347 Page 3 For other scenarios, there is adequate time to secure the core spray pumps, and restart them as necessary, precluding extended operation in the minimum flow mode.
C.
As discussed in Item F above, only certain small break LOCAs actually require ECCS inj ec tion f r om RHR or core spray where the pumps may be operated for short periods in the minimum flow mode.
Because of the excess - ECCS capacity that is available, limiting LOCA scenarios do not depend on all 6 ECCS pumps to operate in order to satisfy 10 CFR 50.46 requirements and General Desi&n Criteria 35 of 10 CFR 50 Appendix A.
In fact, a realistic LOCA analysis would show that only one low pressure ECCS pump is typically necessary to satisfy core coolins requirements during and following a LOCA; therefore, even if both Core Spray pumps were to be r e r.d e r e d inoperable due to dead heading, and a
single failure is assumed to block one RHR loop, two RHR purps will etill-be available for short and long term core cooling.
Based upon the above, the District concludes that the continued operation of Cooper Nuclear Station is justified because 1) the potential for pump damage due to minimum flow operation or dead heading is negligible, 2) sufficient redundancy and ECCS capacity exists to meet the requirements of 10CFR 50.46 and CDC 35, and 3) routine testing is expected to detect any pump damage before system performance is degraded.
I kk(dk29.2b) 1
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