ML19338D909
| ML19338D909 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/02/1980 |
| From: | Zudans J Office of Nuclear Reactor Regulation |
| To: | Berlinger C Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19338D883 | List: |
| References | |
| NUDOCS 8009240179 | |
| Download: ML19338D909 (3) | |
Text
w UNITED STATES Enclosure g
g NUCLEAR REGULATORY COMMIS!
E V ASHINGTON. O. C. 20555 f
b k
Ay 0 21980 MEMORAF" JOR:
C. Berlinger, Acting Chief y
Operating Experience Evaluation Branch Division of Operating Reactors FROM:
J. Zudans, Engineering Branch Division of Operating Reactors
SUBJECT:
REACTOR COOLANT P!!MP SEAL DEGRADATION A review of available LER data on reactor coolant pump (RCP) seal failures and a preliminary review of the state-of-the-art RCP seal desiens has been conducted by the Operational Experience Evaluation Group (OEEG) with the following findings:
1.
Since 1969 there have been approximately 2] reported int. dents where seals in reactor coolant pumps or re:irculation pumps have failed lead-ing to or potentially leading to leakage of reacter coolant to the primary con".ainment.
Many more seal failures have c: curred which are not routi. ely reported and OEEB is rec:rrencing that AEOD consider changes to the LER reporting requirer.e.ts hich w:uld require liter. sees to routinely report RCp ard re:irculation pump seal failur,es/ problems.
3 1
2.
The root cause of nast of these incidents is unkn:wn, and therefore is neither identified in the LER nor in su;olerer.tal re;::rts.
While i
some causes are des:ribed, they represent preliminary findings.
Instead of root causes, LER's identify failure rodes.
Typical failure modes for seals have include:
a.
Inadequate seal spring pressure b.
Design errors i
c.
Themal shock d.
Cracking of piping which provides cooling to seals e.
Personnel errors f.
Debris OEEB has evaluated a failure code for pump seals in which a loss of off-site power could result in loss of component cooling and/or seal injection flows which might not be reestablish, except by operator action.
Although a variety of pump seal designs exist, it is generally true that RCP seals will be damaged during pump operation without these auxiliaries (cooling), and under certain conditions r.ay even be damaged when the pumps are idle.
5.
Total accumulated leakage and leakage rates into containments have been reported as high as 100,000 gallons and 100 GPM, respectively.
Leakage on the order of several thousand gallons and leakage rates of 5 to 10 GPM are more common.
Although leakage of this magnitude has occurred it has been contained and cleanup operations have apparently been orderly.
The design bases for plants as affected by small break LOCA should consider leak rates of this type to evaluate their impact on plant safety and safety margin.
This topic is addressed in " Generic Evaluation of Feed-
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7 MAY 0 2 f.: c'
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).C.Berlinger D]
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D water Transients and Small Break Loss-of-Coolant Accidents" (NUP.EGs-te 0635,-0611,-0626,-0555).
A very clear indication from our study is that seal degradation is 4.
quickly detected by several means:
seal staging pressure monitors a.
b.
increase in reactor coolant rakeup requirecents containment sump level indications c.
OEEB does not believe that an imediate safety concern exists relative to RCP seal failuresince detection of seal degradation is direct and It is however quick and any leakage is restricted to within containrer.t.
a potential concern since seal failures challenge safety systems, and were large leaks to occur a p:tential exists for exceeding techni:al specifica-OEE3 tion limits on cooldown rates for the reactor pressure vessels.
is requesting that AEC3 monitor operating experience to ider.tify significant increases in pump seal failures.
7 9
Most incidents of seal degradation have involved one of these three 5.
Each pump vendors; Byron Jackson, Ein; tar-Willarette, and Westing.ouse.
RCP vendor has a different seal design and also each vender uses different seals for BWR and PWR applications.
Specific details regarding seal design description of seals and seal auxiliaries for tr.ese ;rimary vandors are contained in EPRI report, NP-351, " Recirculating Pump Seal Investigation," dated December 1977.
Tr.is is due to the Seals are easily replaced when dama;ed or degraded.
6.
pump design which has a spacer coupling between the motor and pump shaft
.which, when removed, ellows easy access to the seals.
In summary, it seems that the safety rargin associated with RCP operation and seal failure is a Jequate since seal failures are easily detected and contained.
It remains to be detemined whether a full seal rupture will change the results As rentioned of a small break LOCA analysis and alter the design basis.
previously, this will be determined by the Bulletin and Orders task force.
A preliminary review of the three main pu~p vendor designs indicates that the Westinghouse design ray be more susceptible to large leak rates in the event of seal. failure (Westinghouse RCP's do not employ a canister assembly). '
However, OEEB does not believe that an in-depth staff review of state-of-the-art pump seal designs be conducted at this time because no irrediate safety concern exists and pump vendors have ongoing pump seal developrent programs aimed at increasing pump reliability and clant availability which the Encineerino Branch staff is followinc.
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F af MAY 0 21930 pgg REME
..., C. Berlinger n..
The more significant concern to this reviewer is that seal failures represegg potential challenges to safety systens which may or ray not have been cons.
idered in the original design review.
In addition, while these seal designs are quite sophisticated, failure modes are very diverse and.it is apparent that the role of the auxiliary systems (seal inject'an and component cooling) l should be more clearly defined.
The present confusior, in.this area is exemplified by the conflicting opinions of the vendors and NSSS suppliers who have indicated that loss of seal injection may be tolerated but not component cooling or vice versa.
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W e
W 7 John F. Zudens Engineering Branch Division of Operating Reccters cc:
D. Eisenhut 5
P.. Ernst D. Ross C. Michelson R. Riggs V. Noonan i
J. Zudans l
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