ML20115A202
| ML20115A202 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Turkey Point |
| Issue date: | 06/13/1984 |
| From: | Shaw H, Zudans J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), Office of Nuclear Reactor Regulation |
| To: | Brammer H, Lanik G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20114G054 | List:
|
| References | |
| FOIA-84-616 NUDOCS 8406210107 | |
| Download: ML20115A202 (12) | |
Text
_ _...
a JUN 131984 MEMORANDUM FOR:
George F. Lanik, Section Leader
. Events Analysis Branch Division of Emergency Preparedness and Engineering Response, IE H. L. Brammer, Section Leader Mechanical Engineering Branch Division of Engineering, NRR FROM:
John J. Zudans Events Analysis Branch Division of Emergency Preparedness and Engineering Response, IE Horace K. Shaw Mechanical Engineering Branch Division of Engineering, NRR
SUBJECT:
MINUTES OF 5/15, 5/16-84 MEETING WITH FLORIDA POWER &
LIGHT (FPL) TO DISCUSS RESULTS OF THEIR MECHANICAL SNUB 8ER TEST PROGRAM FOR TURKEY POINT UNITS 3&4 On 5/15/84 - 5/16/84 NRC staff met with FPL and Pacific Scientic, the snubber vendor at the site, to discuss results of recent tests conducted at T.P. 3&4 on their mechanical snubbers.
The results of the meeting are contained in the enclosure.
Should you have any questions regarding this matter, please contact us accordingly.
Original si ned by 2
John J. Zudans Events Analysis Branch Division of Emergency Preparedness and Engineering Response, IE Origmel ai-'-
Horace K. Shaw Mechanical Engineering Branch Division of Engineering, NRR
Enclosure:
As stated cc:
R. Kiessel F. Jape, RII E. Brown M. Mcdonald E. Butcher Distribution DCS CERossi EAB R/F DEPER R/F JZudans HKShaw
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MINUTES of 5/15/84 - 5/16/84 MEETING WITH FLORIDA POWER & LIGHT (FPL) TO DISCUSS RESULTS OF
~
THEIR MECHANICAL SNUBBER TEST PROGRAM FOR TURKEY POINT UNITS 3&4 (TP 3&4)
As a result of the recently reported large number of inoperable mechanical snubbers found during surveillance testing, at FP&L T.P. 3&4, NRC I&E, NRR and RII staff members met with FP&L and the vendor, Pacific Scientific (PSA), to discuss the results-of the tests.
The meeting took place on May 15 and 16, 1984 at the. site,-with attendees as listed in Enclosure 1.
-Test Results and Conclusions FP&L provided an overview'of their surveillance program for mechanical snubbers.
Mechanical snubber testing has been conducted at T.P 3&4 during the past several weeks in compliance with plant technical specifications.
-All (* 200) TP 3&4 safety related snubbers were functionally tested in accordance-with approved test procedures.
The testing was performed by Wyle labs at the site with Wyle-test quipment.
The testing addressed three functional parameters namely (1) breakway (load at which snubber begins to move), (2) drag (rate of movement of snubber under load), and (3) acceleration (maximum acceler-ation which snubber will allow).
Three tests were conducted on each snubber in the following order:
1) breakaway / drag - stroke within 1/2" of each end 2)
Acceleration - 1 inch max. stroke J
(: -
3) breakaway / drag-stroke within 1/2" of each end Acceptance criteria for the tests were as follows:
1)
Breakaway 1 1% of snubber rated load 2)
Acceleration - snubber shall limit acceleration to 1 0.02g 3)
Orag rate - velocity 4 in/ min In addition to the above functional test acceptance criteria, certain types of visual abnormalities could also cause a snubber to be rejected.
These included deformation, lock up in place, and unstaking of the telescoping cylinder at the ball nut thread joint (only on TP 4)(see Fig. 1).
Of signifi-cance on T.P 4 was the incidence of unstaking, which resulted in classifica-tion of these snubbers as inoperable.
The vendor indicated that unstaking would not in itself cause snubber inoperability.
He provided documentation demonstrating the assertion.
(Enclosure 2.) As a result of the testing at T.P 3&4 the following preliminary test results were presented:
r-TP 4 17 - unstaked 1 - locked up as found 1
moving freely as found which would not provide any restraint 12 locked up during drag / breakaway. test 16 - failed breakaway 1 - exceeded 0.02g acceleration limit TP 3 7
exceeded 0.02g acceleration limit 8'
experienced erratic unstable acceleration response 7 - acceleration reduced to zero t
13 - failed drag / breakaway of these 6 would have passed with 2% breakaway acceptance criteria 10
. locked up - of these; 2 in final drag test, 1 in breakaway, 2 during initial acceleration, 4 frozen inplace (sizes PSA 1/4, 1/2, 3, 10), 1 during final drag 1 - free running All inoperable snubbers were replaced with new, off-the-shelf units.
Prior to installation they were tested by Wyle in accordance with the same test procedure as indicated above.
Of the new snubbers 3 locked up during test and
,4-failed the drag test.
Further discussions about these test results generated the following comments:
1.
Unstaked snubbers on TP 4 could have passed operability tests.
- However, tests were not performed on these snubbers since they had been defined as inoperable.
2.
Using present PSA design specification (Enclosure 3) as the acceptance criteria for breakaway would have rendered a significant number of snubbers acceptable.
(2% of rated load vs. 1% as used by FPL).
The use of 1% as the acceptance criterian could be viewed as a conservatism of the test performed by FPL.
3.
Testing sequence was noted by PSA as a possible influence on test results.
Initial breakaway / drag followed by acceleration, followed by final breakaway / drag was considered by PSA to be unusually conservative.
PSA uses acceleration followed by breakaway / drag as their sequence for proof testing.
4.
Generally, except as noted above, more older snubbers were judged inoperable than new ones (Older means s 8 years, new means s 2 years.)
This appears to imply a less than 40 year service life for these components, which contradicts claims made by the vendor.
5.
PSA indicated that the snubbers may be sensitive to the test equipment used. This appears to be an engineering judgement based on their testing experience, not substantiated by any evidence.
l I
6.
PSA believed that due to the condition of many of the inspected snubbers that there is a good likelihood that they would pass a retest.
They also l
believed that load profile, load application rate and test sequence can i
severely impact test results.
Visual Inspection Results/Conclusioni FPL/NRC/PSA performed visual inspections of a number of snubber samples with t
different categories of inoperability.
The categories included: (1) drag /
breakaway, (2) lockup, (3) accelaration and; (4) overload.
As a result of inspections the following findings were noted:
1.
Overloading and installation provided clear evidence of the failure mechanism. As examples, overload was evidenced by bent dust covers, stripped threads and broken bearings while bent rods and unstaked snubbers were examples of poor installation methods.
Installation problems were most prevalent in small bore snubbers (PSA 1/4, 1/2).
Of significance is the fact that these catastrophic failures might not be detected during visual inspections.
2.
Inoperable snubbers discovered during f'unctional-testing often yielded no clear evidence of inoperability. The running elements of these snubbers
were often in good condition.
As previously mentioned the vendor felt that some of the test procedure, might have contributed to the results.
This condition was most prevalent in those that locked up during drag testing.
The ballscrew shaft and bearing would often exhibit smooth running, in addition to the satisfactory function of the capstan spring l
and torque transfer drum.
There does appear to be a question as to l
l whether the test or the component is affecting the results.
Pipe Analysis / Conclusions FPL delineated their approach to resolving potential problems with piping systems associated with inoperable snubbers.
All pipe locations with inoperable, locked up snubbers were investigated according to the following procedure:
1 1.
Locations with marginal stress in the existing pipe analysis and close to inoperable locked-up snubbers were identified in each affected system.
2.
Welds and heat affected zones (HAZ) at these potentially overstressed locations were liquid penetrant inspected.
In addition, piping in the affected run was examined for distortion or any other visible damage.
3.
Upon completion of examination all piping was reanalized with the inoperable snubber modeled as a rigid support, to categorize the extent of overstress.
Preliminary results of the procedure indicate that some piping locations on TP 3 may have been overstressed.
TP 4 analysis has not yet been completed.
No quantitative results were available for either plant.
The ISI performed on the affected piping showed no cracking in any welds or HAZ's.
No piping showed visible distortion.
The systems affected in each plant include:
Unit 3
+
1.
Pressurizer Spray 2.
Pressurizer Relief 3.
Component Cooling Water 4.
Chemical Volume Control System Unit 4 1.
Pressurizer Spray 2.
Pressurizer Relief 3.
Chemical Volume Control System 4.
Feedwater Conclusions FP&L has performed an indepth program which has identified problems with some of their safety related snubbers at their Turkey Point Units 3&4.
The program has identified certain areas which need to be evaluated when testing programs of this type are undertaken.
They include; 1) the test procedure that is used, 2) the loading sequence, 3) the range of acceptance criteria, 4) proper definition of inoperability and,
- 5) plant parameters (installation procedure, preventive maintenance techniques) which can affect test results.
As a result of the effort it appears that FP&L may want to revise some portion
-of their test procedures and acceptance criteria.
FP&L conservatively replaced all suspicious inoperable snubbers with new operable (demonstrated by test) ones.
The piping affected by those snubbers was analyzed, and welds at questionable locations were nondestructively examined.
L l
As a result of this meeting three generic issues have been identified,
- 1) Snubbers overloaded by such mechanisms as water hammer may be inoperable yet do not show visible signs, 2) Inadequate maintenance (or lack of mainte-nance) and improper installation (especially in small bore snubbers) may be a l
large contributor to snubber inoperability, 3) NRC should evaluate the need l
for consistent requirements in test methods, definitions of inoperability and acceptance criteria.
It is noted that the ASME Operations & Maintenance l
working group on snubbers (OM-4) is developing a standard, however it is not at this time available for implementation.
As a result of these findings it is recommended that NRC issue an Information Notice to all 0.L's and CP's to allert them of these findings.
In conclusion,.FP&L has taken effective measures to assure the integrity of the safety systems at T.P 3&4 and as such should be commended.
ENCLOSURE 1 List of Attendees Frank Jape NRC/RII Eddie Vaugn FPL/EPP Robert Franseth PSA Paul Hadnagy PSA Jerry Burford FPL/EPP Bryan Rotalante FPL-TECH. PLANT DEPT.
Mike Mowbray FPL Aria Jesus FPL John Gnecco TELEDYNE
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