ML20079E218
| ML20079E218 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/30/1991 |
| From: | James Knubel GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF ADMINISTRATION (ADM) |
| References | |
| FRN-56FR16130, REF-GTECI-023, REF-GTECI-NI, RTR-REGGD-01.XXX, RTR-REGGD-1.XXX, RULE-PR-50, TASK-023, TASK-23, TASK-DG-1008, TASK-OR, TASK-RE 56FR16130-00010, 56FR16130-10, C300-91-L199, C311-91-2109, NUDOCS 9110070073 | |
| Download: ML20079E218 (5) | |
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[}b Chief, Regulatory Publications Branch 5
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Division of freedom of Information and Publications Services Office of Administration U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Dear Sir:
Subject:
General Public Utilities Nuclear (GPUN)
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. DPR 50 Docket No. 50-289 Solicitation of Public Comments on Generic Issue 23, " Reactor Coolant Pump Seal f ailure".
The enclosed attachment provides specific 1Ml-1 comments on the subject issue as requested in the federal Register Notice Vol. 56, No. 76, dated Friday, April 19, 1991.
The format of the Attachment follows the sequence of questions raised in the Federal Register Notice.
In addition to these comments, NUM'.RC has developed comments on the generic elements of the NRC's analysis of 1-23 and proposed resolution.
The NUMARC comments, which are being transmitted to you via their September 30, 1991 1
letter, are also endorsed by GPUN.
Sincerely,
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Director, Licensing & Regulatory Affairs JK/EP/cb cc: Administrator, Region 1 TMl-1 NRC Resident inspector TMI-l NRC Project Manager 9110070073 910930 PDR PR 56FR16130 PDR GPU Nucica' CmpuaSm is a subshy N Gmew Puw Um n u rawn
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ATTACHMElll 1.1 Has your operating experience with the RCP seals changed since 1983?
If it has, then information regarding the history of RCP failures, including occurrences of forced outages is of interest.
Information regarding all types of operation, including startup is desired.
Response
Seal operating experience has changed since TMl-1 restarted in 1985.
Seal leakage trends and causes are more predictable and understandable after implementation of design changes pieviously recommended by Westinghouse (See 1.2 below).
TM1 1 experienced forced outages on the "D" aum) in September and December 1988 due to. erratic and abnormally 1i91 leakage of the No, 1 seal. The problem was attributed to excessive motor to pump coupling misalignment with a resultant high operating eccentricity between the seal runner and seal ring assembly.
Coupling realignment corrected-the_ problem.
1.2 If your operating experience has changed, to what do you attribute the change (e.g., improved quality assurance and quality control, improved maintenance, better procedures, improved instrumentation, dasignchanges)?
E21291112 Improved operating experience has resulted from on going improvements in the categories listed below:
Design upgrades based on Westinghouse field operating experience:
1)
Silicon Nitride No. I seal faces (replaced Aluminum 0xide).
- 2) _Hard (Chrome Carbide) facing of balance diameter elastomer location on No, I and i:o. 2 seal.
- 3) Changed the No. I seal balance diameter elastomer seal to an "o" ring inside a double delta channel seal of letralon material.
4). Changed hardness of selected "o" ring elastomers, 5)
Installed new seal injection filter housino which accepts one-micron filters.
Maintenance and Training:
- 1) Full scale' model is used to train craf t and engineers on _ seal assembly.
- 2) Dedicated crews are used for seal installation and pump alignment.
- 3) Maintenance procedure upgrades based on model experience plus feedback from actual seal assembly and inspection.
a
s C311-91-2109 Page 2 Improved Quality Control:
- 1) Westinghouse continues to upgrade Q.C. on elastomers and provides l
documentation on critical dimensions of individual seal s
components.
Technical manual and procedure changes are made to incorporate seal upgrades and refine RCP operation to cope with normal and abnormal conditions.
1.3 How often are seals being routinely replaced (e.g., every refueling)?
Response
The No. I seals are inspected after two operating cycles.
Elastomers are replaced and the seal faces reused if no rubbing has been encountered.
No.-2 and No. 3 seals on all units are examined every refueling outage.
Examination results indicate seal wear has been optimized with some parts being reused and others replaced.
We are working toward No. 2 and No. 3 seal examination after two operating cycles.
2.0 The NRC Staff is interested in obtaining any available data regarding degraded cooling or loss of cooling to the seals to support assertions that seals can survive long periods of time (i.e., hours) without
- cooling, i
Respong THI-l has not experienced any prolonged (greater than a few minutes) degraded cooling or loss of woling to RCP seals.
3.0 The Staff acknowledges that procedures related to the operation of the seals play an important role in avoiding a small-break LOCA caused by seal failure.
It is not clear that past and cuirent treatment of the seals reflect their'shfety importance.
The NRC staff is therefore considering the neeo for improvements in the related procedures, training and information provNed to operators and their actions.
3.1 Are there procedures currently in place that are intended to prevent seal leaks from becoming small break LOCAs during normal plant operation and loss-of-seal cooling events such as station blackout?
Are the required operator actions (e.g., isolating leakoff lines) the same for normal plant operation and loss of-seal cooling events? -
Response
TMl-1 has procedures in place to mitigate the consequences of loss of seal cooling.
for normal operation and loss of seal cooling events, operator actions may vary depending on seal leak-off rate and temperature.
TMI-l is also committed to comply with the Station Blackout Rule before restart from Cycle 9 refueling outage.
Compliance will be by installation of an alternate AC power supply that will limit the loss of AC power to 10 minutes.
The use of an alternate AC supply precludes tl a need for an additional cooling system for a loss of cooling water incident.
. ~
C311-91-2109 Page 3 3.2 Has the RCP instrumentation been evaluated to determine whether operators have sufficient information to implement the procedures?
Responte The RCP seal instrumentation installed at TMl-1 provides sufficient monitoring to determine seal performance plus any changes or abnormalities that are encountered, thus allowing the operators to implement the procedures.
Manufacturer's operating recommendatists have been incorporated into plant operating procedures, utilizing existing instrumentation.
3.3 How is RCP seal vendor information used in establishing operation and maintenance practices for the RCP seals?
Response
Vendor seal technical data and operation recommendations as appropriate along with actual operating experience are incorporated into plant procedures.
Procedures are updated as required based on new vendor data which is refined to reflect actual plant operation.
3.4 In se'"e cases, industry practice allows continued plant operation with the RCP seal when first or second stages have failed.
Do you limit this practice?
If so, what are the limiting conditions?
Response
TMl-1 procedures permit continued plant operation at reduced power, given a No,1 or No. 2 seal f ailure assuming no further complications exist. Continued plant operation is disallowed, however, if the leak off exceeds Technical Specification limits for recoverable losses.
3.5 What additional quality assurance and procedural measures can be takEa regarding RCP seals to improve safety?
Resoonse The existing Westinghouse Quality Assurance Program provides critical seal parts (runners and seal rings for No. I and No. 2 seals) to 10 CFR 50 Appendix B and 10 CFR 21 criteria.
Other seal components are manufactured to Westinghouse standards.
Operating experience has not indicated any component deficiencies that were directly attributed to poor or inadequate Quality Assurance. Addition of more stringent quality requirements therefore would not be warranted.
4.0 As part of the probabilistic risk assessment performed for Gl-23, a seal nodel (Appendix A of NUREG/CR-5167) was developed for use in estimating the core damage frequency associated with loss of RCP seal cooling.
4.1 is the Staff's model, or other models, adequate to predict RCP seal leakage (i.e., modes of seal failure, time dependent failure probability, and leakage estimates) and handle the uncertainties in the models? Do the models correlate to actual plant or test data?
C311-91-kl09 Page 4 R m an12 The NRC model (Appendix A of NUREG/CR-5167) is an extension of the Westinghouse Owners Group Analysis (WCAP 10541).
The model and the Westinghouse analysis are based on design, actual field operation plus testing by Westinghouse and other laboratories. It is suggested that comparison of models be reconciled directly with Westinghouse and/or other model generators in order to benefit from their in depth knowledge and experience with such models.
4.2 Of particular interest to the staff are alternatives to the probabilistic RCP seal leakage developed for Westinghouse seals and alternative models for other seal designs (i.e., for seals by Byron Jackson, Bingham International, or Combustion Engineering /KSB) to predict seal leakage during loss-of-all scal-cooling events.
Can you provide information regarding any alternative models?
ResDonse GPUN does not have an alternative model.
See the response to 4.1 above.
5.0 in exploring alternatives to providing additional seal cooling, one approach might be to test the existing seals to demonstrate conclusively that they will not leak excessively if not cooled for extended periods of time, even though such conditions exceed the seal design basis and possibly the conditions of the warranty.
If testing was an option to demonstrate acceptable seal performance under loss of cooling conditions, what conservative conditions should be imposed on the RCP seal for the test program (e.g., length of time, maximum wear on seal, number of tests)?
Resoonse Testing should expose the various seal designs to actual pressures, temperatures, radiation levels, wear (aging), etc., encoi '] red in normal operation and off normal operation. The tests show be run until leakage re.'ches an established maximum consistent with analysis provided by seal vendors.
6.0 if, after consideration of public comments, the NRC decides that additional RCP seal requirements are necessary what method of imposition should be used (e.g., by rulemaking, order, or generic letter)?
Resnan12 If the NRC determines the need to ettablish new requirements and request plant modifications, we believe it should proceed with rulemaking or orders since there doesn't seem to be a legal basis to support implementation of draft Regulatory Guide DG 1008.
This is consistent with NUMARC's response and the Commission's recent ruling in connection with NRC Generic Issue B-56, Emergency Diesel Generator Reliability.
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