ML18051A587
| ML18051A587 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 09/01/1983 |
| From: | Dewitt R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8309070361 | |
| Download: ML18051A587 (5) | |
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~[ID UU1l ~ ~ Ulllf General Offices: 1945 Parnall Road, Jackson, Michigan 49201 * (517) 788-1217 September 1, 1983 Darrell G Eisenhut, Director Division of Licensing Nuclear Reactor Regulation US Nuclear Regulatory Commission Washington, DC 20555 Russell B. DeWitt Vice President Nuclear Operations CONSUMERS POWER COMPANY COMMENTS ON PROPOSED REQUIREMENTS RELATIVE TO STEAM-GENERATOR TUBE INTEGRITY The purpose of this letter is to provide you with Consumers Power Company (CP Co) comments on proposed NRC requirements relative to steam-generator tube integrity and the plant response to steam-generator tube ruptures.
It should be noted that these comments are those of Consumers Power Company only and do not necessarily represent the collective opinion of the Steam-Generator Owners Group (SGOG), of which CP Co is a participating and supporting member.
CP Co is both keenly aware and concerned about the issue of steam-generator tube integrity.
We support your efforts to evaluate the need for new requirements in this area and hope that the comments put forth below will assist you in developing meaningful and workable requirements.
Our general and specific comments on the proposed NRC requirements as presented to the SGOG at a meeting on July 6, 1983 are:
General Comments Consumers Power Company is currently operating one PWR (Palisades Plant, which experienced extensive steam-generator tube problems during the first three years of operation) and is planning to bring two additional PWRs into service in the next two years.
Thus, solving the steam-generator tube integrity problem is a vital concern to us, both from a nuclear safety and a plant reliability viewpoint.
We caution, however, that steam-generator tube integ-rity problems may be too complex to be treated generically.
While the indus-try has increased dramatically its understanding of the problems and their causes over the last few years, this deepened understanding tends to under-score the non-generic aspects of the problems.
Although each proposed re-quirement may be appropriate to address a given form of tube failure, the application of a specific requirement at a given plant may lack technical basis.
As a result, public health and safety may be served better by molding the generic requirements to fit each specific plant.
s3o9o7636-i -s369o1 PDR TOPRP EUTCPC PDR OC0883-0015A-NL02
DGEisenhut, Director Palisades Plant S-G TUBE INTEGRITY September 1, 1983 2
We are concerned that certain of the proposed generic requirements, as they presently stand, may be impractical to implement and/or unnecessary or poten-tially even counterproductive to nuclear safety.
And finally, we commend the NRC Staff for its recent efforts at integrating new requirements into existing plant plans and schedules consistent with the safety importance of the new requirements relative to actions and programs already planned.
We hope that any requirements in this area will be imple-mented in a similar manner and that the schedule for implementation of neces-sary actions will be negotiated between the NRC Project Manager and the Licensee.
Our specific concerns are as follows:
Visual Inspection of Secondary Side and Improved QA/QC Procedures While the concept of a detailed secondary side inspection for loose parts/
foreign objects is attractive in terms of preventing tube ruptures, the activity is not without risk.
The Palisades Plant, during a "dry-layup" condition similar to that which would exist during the proposed inspection, experienced damage requiring extensive tube plugging.
Since that time, we have kept the steam generator tubes in a wet-layup condition (except as required for modification of the steam generator).
The value-impact assess-ment performed by SAI (re:
Generic Letter 83-22) does not address this or other such corrosion-related events.
Therefore, the basis for concluding that this requirement is "very effective" may be incomplete.
Recent corrosion events at Oconee (following AFW modifications) and AN0-1 underscore the apparent sensitivity of steam generators to air.
Work by the Electric Power Research Institute also supports avoidance of a dry, moist layup environment for steam-generator tubes.
For secondary loose parts, proper follow-up of eddy current indications which are indicative of potential tube wear as well as prevention of the introduc-tion of foreign objects into the secondary side with appropriate procedural controls and QA/QC is sufficient.
Supplemental Tube Inspections The proposed requirement is to inspect 100% of the tubes in the effected steam generator if an initial 3% sample indicates more than one tube to be defective or more than 5% of the tubes inspected to be degraded.
The terms "defective" and "degraded" need to be defined more precisely.
Section 2.1.1 of the SAI report defines degrading as" *** have(ing) a previously undetected defect of 20% or greater depth or exhibit greater than 10% further wall penetration.
OC0883-0015A-NL02
DGEisenhut, Director Palisades Plant S-G TUBE INTEGRITY September 1, 1983 3
Defective is defined as" *** have(ing) defects with wall penetrations exceed-ing the plugging limit." Based upon this definition, a 100% inspection would be required virtually every inspection interval for our Palisades Plant with little perceived nuclear safety benefit.
This is because a relatively small number of tubes may be found to exceed the plugging limit each inspection due to statistical variations in measurement results even though little or no tube degradation is actually being experienced.
Consumers Power Company has employed the following criteria for deciding if additional tube inspection should be performed at our Palisades Plant:
- 1.
For tubes with previous indications of 30% or greater wastage:
- a.
consider additional inspections of up to 100% of one or both steam generators if the sample indicates a statistically significant increase in wastage of between 2 and 10%;
- b.
perform additional inspections of up to 100% of one or both steam generators if the sample indicates a statistically significant increase in wastage of more than 10%.
- 2.
For tubes with no previous indications of flaws, the same criteria as described in item 1 above are applied.
- 3.
For tubes which cannot be examined (ie, blocked tubes) due to denting:
- a.
perform an inspection of all adjacent unplugged tubes if the number of blocked tubes is less than 25.
- b.
perform an inspection of all adjacent tubes, of an additional 50 surrounding tubes and of 30% of the tubes in "high stress" areas if more than 25 tubes are blocked.
(A "high stress" area is defined as a region in the steam generator wherein the tubes are particularly.
susceptible to denting.)
- c.
perform an inspection of up to 100% of one or both steam generators (both hot and cold legs) if more than 100 tubes are blocked.
Conduct secondary side inspections of the support plate and to identify possible loose parts.
- d.
perform tube inspections in the areas surrounding any small clusters of blocked tubes in order to determine the extent of the cluster and consider performing a secondary side inspection.
OC0883-0015A-NL02
DGEisenhut, Director Palisades Plant S-G TUBE INTEGRITY September 1, 1983 4
It is important to point out that these criteria were selected specifically for the Palisades steam generators, and that the selection of similar criteria for another set of steam generators should be based on the actual conditions of the steam generators and the environmental factors affecting their opera-tion.
Reviewing the Palisades experience since 1974 (one forced outage due to a steam-generator tube leak), we conclude that our inspection program has been effective.
Thus, the benefits derived from conducting 100% inspections at each interval would not, in our opinion, justify the increased cost. We estimate that an additional $300,000 and 10 days additional inspection time would be required each inspection interval.
These costs would be in addition to the $500,000 and 45 days presently required for a normal inspection.
Full Length Inspections Inspections at our Palisades Plant have not shown any significant defects in the cold-leg portion of the steam-generator tubes.
Therefore, we believe that the present number of tubes being inspected in the cold legs is adequate and that an adequate basis exists for applying the inspection criteria separately to the hot and cold leg portions of the steam-generator tubes.
Our Technical Specifications presently require a 1% sample although traditionally we have inspected more than 1% depending on the observed condition of the steam generators and as a matter of good business practice.
Full-length inspections of all tubes would be time-consuming and expensive (we estimate an additional cost of $100,000 and 10 days additional inspection time per inspection inter-val if a 100% inspection of the cold-leg portion is required) and would have an adverse impact on exposure to inspection personnel.
Secondary Water Chemistry Program This requirement is technically justified and supportable from a good business perspective.
We have already implemented such a program at our Palisades Plant and our Technical Specifications include requirements to monitor certain secondary water chemistry control parameters.
Placing additional specific requirements in our operating license would have little effect on the way we do business, nor would it result in any nuclear safety benefit.
- However, replacing current license requirements with a more general requirement to develop and maintain a suitable secondary water chemistry program which is sufficiently flexible to permit change as new knowledge is gained through industry research and experience would enhance steam generator reliability.
OC0883-0015A-NL02
DGEisenhut, Director
-Palisades Plant S-G TUBE INTEGRITY September 1, 1983 Condenser Inservice Inspection Program 5
A condenser inservice inspection program should not be required as a license condition.
Steam-generator performance is the safety issue, not condenser performance.
The goal should be to control steam generator water chemistry (ie, a secondary water chemistry program).
Depending on plant-specific conditions, utilities may decide to perform various forms of condenser inspec-tion and/or maintenance to support meeting this goal.
Controlling both the goal and a means for meeting the goal is unnecessarily prescriptive.
Safety Injection Signal Reset Implementation of this requirement would necessitate a detailed review of existing SIS circuitry and, possibly, some plant modification.
If modifica-tion is required, the cost could significantly exceed (by a factor of 2 to 5) the $20,000 estimated by the NRC.
Consumers Power Company generally concurs with the remaining requirements (ie, Maximum Inspection Interval, Primary to Secondary Leakage Rate Limits and Coolant Iodine Activity Limits) as presented during the July 6, 1983 meeting as being prudent.
Russell B DeWitt, Vice President Nuclear Operations OC0883-0015A-NL02