ML17221A475
| ML17221A475 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 10/15/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17221A474 | List: |
| References | |
| NUDOCS 8710270461 | |
| Download: ML17221A475 (8) | |
Text
~R RE0II, (4
dp
~4 0
Cy 0
C O
I Vh O~
Cp n
0
+**++
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 24 TO FACILITY OPERATING LICENSE NO. NPF-16 FLORIDA POWER 5 LIGHT COMPANY, ET AL.
ST.
LUCIE PLANT, UNIT NO.
2 DOCKET NO. 50-389 INTRODUCTION By letter dated September 4, 1987, as supplemented September 11 and 15, 1987, Florida Power and Light Company (the licensee) submitted a proposed Technical Specification change pertaining to inservice inspection of steam generator tubes at St. Lucie Unit 2.
The proposed change is intended to ensure that all tubes subject to wear-induced degradation from adjacent "batwing" and vertical strap supports will be fully inspected (i.e.,
100Ã sample through U-bends) without involving unnecessary levels of sampling in regions of the tube bundle not subject to this degradation mechanism.
The application was noticed in the Federal Re ister on September 17, 1987 at 35161.
The staff proposed a no
~s gniF7cant azards consideration (NSHC) determination, which was based on the September 4 and 11, 1987 letters.
Additional information from the licensee was received by letter dated September 15, 1987.
Also, clarifications were made to the licensee's re-quest as a result of telephone conversations with the staff on September 29, 1987.
The additional information did not change, in any way, the staff's proposed NSHC determination or significantly alter the scope of the action noticed.
EVALUATION The tubes in the St. Lucie.steam generators are supported along their ver-tical lengths by seven full-diameter eggcrate supports and two partial diameter eggcrate supports.
The U-bend and horizontal lengths of the tubes are supported by batwing straps, which cross the tubes just below the start of the U-bend, and as many as five vertical support straps (depend-ing on the horizontal length of the tube).
The vertical straps are connected in the'ut-of-plane dimension by horizontal straps.
A stay cy-linder is installed at the central portion of the tubesheet to permit re-duction of tubesheet thickness.
The region above the stay c'ylinder cannot be tubed and forms a hollow cavity at the center of the tube bundle.
Tubes adjacent to this untubed stay cylinder region and contained within lines 65 to 103 and up to row 59 are supported by contact with the bat-87i02704bi 87iOis PDR ADOCK OS000389 PDR Q
~
~
wings and with as few as one vertical strap.
High-velocity two-phase flow up the untubed stay cylinder cavity imparts a force on the batwing suppports, resulting in out-of-plane motion of the batwing against the tubes, causing tube wear.
Vibration of. the batwings ceases when the leng'th of the tubes is long enough to encounter additional vertical supports.
Thus, tubes further out in the bundle are not subjected to batwing wear.
Combusion Engineering (CE) has performed extensive testing, including two-phase flow tests and vibration tests, to predict the extent of tubes po-tentially affected by batwing vibration (
Reference:
Combustion Engineering
- Report, CEN-328).
Results of these tests were used to develop a computer model to predict the extent and rate of wear for the affected tubes.
The model predicts that the wear phenomenum will be contained within a rela-tively narrow area adjacent to the stay cylinder cavity.
By letter dated September 15, 1987, the licensee provided additional information indicating that the inspection results at St. Lucie Unit 2 through the last, inspection in 1986 have been in good agreement with model predictions.
In its September 4,
1987 letter, the licensee proposed in part to inspect all tubes from line.66 to line 102, located 10 to 11 tubes from the untubed re-gion.
This proposal encompasses the full region of tubes predicted to wear to 40$ of the wall thickness over the 40-year plant lifetime.
Based on comments received by phone on September 29, 1987. from the NRC staf+
(discussed below), the licensee agreed to a modification of the proposed change by extending the inspection boundary from 10 to 11 tubes to 14 to 16 tubes in from the untubed region.
In addition, tubes located in lines 65 and 103 will be inspected from row 21 to row 35.
As identified in the September 4,
1987 letter, no credit will be taken for tubes inspected within the defined area of 100$ inspection in meeting the Technical Specification (TS) sampling requirements in paragraph 4.4.5.2 for tubes located outside the defined area (TS paragraph 4.4.5.2.d).
In addition, any indications found within the defined area of 1005 inspection would not be counted in establishing the results category for inspections performed outside the defined area (see note (2) at bottom of page 3/4 4-12a of the TS).
At the staff's request, the licensee agreed by phone on September 29, 1987 to a modification of note (2) to make it clear that only indications in the defined area involving batwing and vertical strap wear need not be considered.
Finally, for reasons discussed below, the licensee also agreed by phone on September 29, 1987 to the staff's request that the subject TS changes shall be footnoted such that they shall apply only to the upcoming refueling outage.
The staff has not yet had an opportunity to review the tests,
- analyses, and operating experience in sufficient detail to reach a conclusion regarding a permanent change to the TS.
However, it is clear, based on the staff's review to date, that there is adequate basis for an interim change to the TS applicable to the upcoming refueling outage only.
Therefore, the staff has granted only part of licensee's request and will act on the request for a permanent change at a later date.
~
a a
w I
The staff's review indicates that the inspection boundary initially pro-posed in the licensee's September 4,
1987 letter was generally, but not entirely, conservative with respect to bounding locations where batwing-induced wear indications have been found in the past.
Although the licensee continues to believe that its initial inspection boundary propo-sal is conservative with respect to pluggable (greater than or equal to 40%}
indications that may be found in the future, it nevertheless agreed to extend its proposed inspection boundary deeper into the tube bundle to as far as row 65.
Beyond row 65, a second vertical support becomes fully effective in limiting tube motion relative to the batwing.
The revised inspection boundary encompasses the location of all batwing-induced wear indications to date and all tubes predicted by the CE wear model to develop greater than 10% indications by the end of the 40-year plant lifetime.
Based on the above, the staff finds the proposed inspection boundary to adequately bound the region of the tube bundle which could be potentially affected by batwing-induced'ear at the upcoming inspection outage.
Since this defined area will receive a 1005 inspection under the proposed change to the TS, it follows that the proposed change will provide more, rather than less, assurance that defective tubes will be identified during the upcoming inspection.
The staff concludes, therefore, that the TS change requested in the licensee's September 4, 1987, letter is acceptable.
This conclusion is subject to modifications to the September 4,
198?
- letter, as discussed earlier.
In addition, the staff concludes that the inspection boundary defined in TS paragraph 4.4.5.2.d shall be expanded as necessary to incorporate a minimum of two rows of indication-free tubes at the periphery of the inspection pattern.
Although this latter item is not addressed by the proposed TS change, the licensee stated in its September 4,
1987 submittal that it would follow this approach.
FINDINGS The staff has concluded that the proposed TS changes, as modified by the staff, may be granted in part and are acceptable based on the details discussed above.
IV.
EXIGENT CIRCUMSTANCES The Commission's regulations, 10 CFR 50.91, contain provisions for issuance of amendments when the usual 30-day public notice period cannot be met.
One type of special exception is an exigency.
An exigency is a case where the staf+ and licensee need to act promptly, but failure to act promptly does not involve a plant shutdown, derating, or delay in startup.
The exi-gency case usually represents an amendment involving a safety enhancement to the plant.
Under such circumstances, the Commission notifies the public in one of two ways:
by issuing a
Federa1 Recefster notice providing an opp'ortunity for hearing and allowing~at east two weeks for prior pubiic comments, or by issuing a press release discussing the proposed
- changes, using the local media.
In this case, the Commission used the first approach.
The proposed
C
~
~
~
V.
changes were discussed in the September 17, 1987 Federal Re ister notice at page 35161, with a request for pubiic comments bby into er 3, 1987.
The St. Lucie Plant, Unit No.
2 is scheduled for refueling in early October.
One of the requirements during refueling is to inspect steam generator tubes.
The existing TS do not address the recently-identified need to inspect steam generator tubes in the batwing region of the steam generators where wear is occurring.
The proposed change would add a
special inspection region associated with the batwings, in order to fully, characterize the region, monitor tube wear and take remedial action as necessary.
The inspection of'he remaining tubes in the steam generators will be conducted per the existing TS.
Although the wear is a long-term phenomenon which is expected to occur over the life of the steam genera-tors, it is prudent to take action now, during the early stages of the wear.
The staff has determined that failure to act in a timely manner would result in requiring the licensee to follow the existing TS regarding steam generator tube sample selection and inspection.
The inspection of the steam generator tubes is one of the first major outage-related efforts undertaken because of the length of time that is required to inspect tubes during the outag'e.
Therefore, the staff determined that the overall safety of the plant would be enhanced if the special inspection area was added to the TS prior to the scheduled inspection.
STATE/PUBLIC CONSULTATION VI.
The proposed TS changes, as modified by the staff, were discussed with the State of Florida representative.
No objections to the issuance of the amendment were made.
In addition, there were no public comments in re-sponse to the notice pub1ished in the Federal
~Re ister.
FINAL NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION The standards used to arrive at a proposed determination that a request for an amendment involves no significant hazards consideration are included in the Commission's regulations, 10 CFR 50.92, which state that the opera-tion of the facility in accordance with the proposed amendment would not (1) involve a significant increase in the probability or consequences of an accident previously evaluated; or {2) create the possibility of new or different kind of accident from any accident previously evaluated; or (3) involve 'a significant reduction in a margin of safety.
The following evaluation in relation to the three standards demonstrates that the proposed amendment does not involve a significant hazards consi-deration.
First Standard - Involve a significant increase in the probability or consequences of an accident previously evaluated.
Operation of the facility in accordance with the proposed amendment would not involve a significant increase in the probability or consequences of an accident previously evaluated.
The proposed amendment would increase the surveillance requirements for a defined area of tubes in the steam generators.
This inspection pattern ensures that the area within the steam generator tube bundle representing the highest likelihood of damage will be examined.
The inspection of the remainder of the tube bundle will continue to be governed by the current TS requirements.
The probability of not detecting a steam generator tube problem becomes very low.
Second Standard - Create the possibility of a new or different kind of td tp 1
1y 1
d.
Use of the modified specification would not create the possibility of a new or different kind of accident from any accident previously evaluated.
This modified specification applies to the inspection of a specific region of tubes in the steam generator while maintaining the intent of the speci-fication.
Since no changes to the design or operation of the systems or components of the plant are involved, this change will not create the pos-sibility of a new or different kind of accident from any accident previously evaluated.
Third Standard - Involve a significant reduction in a margin of safety.
Use of the modified specification would not involve a significant reduc-tion in a margin of safety.
The margin of safety involved in steam generator tube inspections depends on the accuracy and completeness of the examination.
The wear mechanism seen at St. Lucie Unit 2 is well-defined and well within the capability of inspection techniques.
Using the predictive models based upon experiments and analysis, the area of concern is identified and will be inspected.
The current TS will be applied elsewhere in the steam generator to ensure that future problems (if any) are identified.
Therefore, this change will not involve a significant reduction in a margin of safety.
A conference call was held with the licensee on September 29, 1987.
The licensee agreed to a number of changes in the TS.
The changes are dis-cussed above in the evaluation section.
Also, additional information was submitted by the licensee by letter dated September 15, 1987.
The results of the conference call and the additional information submitted by letter dated September 15, 1987 did not change, in any way, the staff's proposed NSHC determination or significantly alter the scope of the action noticed.
Based on the foregoing, the Commission has concluded that the standards of 10 CFR 50.92 are satisfied.
There<ore, the Commission has made a final determination that the proposed amendment does not involve a significant hazards consideration.
VII ENVIRONMENTAL CONSIDERATION This amendment involves a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change to a surveillance requirement.
The staff has determined that the amendment involves no significant increase in the amounts, and'no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission previously published a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such find-ing.
The Commission has made a final no significant hazards consideration finding with respect to this amendment.
Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 551.22(c)(9).
Pursuant to 10 CFR 51.22(b),
no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
VIII CONCLUSION Me have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, and. (2) such activities will be conducted in compliance with the Commission's regulations, and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Date:
october 15I 1987 Princi al Contributors:
E. Murphy E. Tourigny
t e
'hrl 4