IR 05000250/1986002
| ML17342A376 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 01/28/1986 |
| From: | Jape F, Schnebli G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | |
| Shared Package | |
| ML17342A375 | List: |
| References | |
| 50-250-86-02, 50-250-86-2, 50-251-86-02, 50-251-86-2, NUDOCS 8602060167 | |
| Download: ML17342A376 (21) | |
Text
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Wp*y0 UNITED STATES NUCLEAR REGULATORY COMMISSION
REGION II
101 MARIETTASTREET, N.W.
ATLANTA,GEORGIA 30323 Report Nos.:
50-250/86-02 and 50-251/86-02 Licensee:
Florida Power and Light Company 9250 West Flagler Street Miami, FL 33101 Docket Nos.:
50-250 and 50-251 Facility Name:
Turkey Point 3 and
Inspection Conducted:
Jan ary 6-10, 1986 Inspector:
G.
Sc ne Approved by:
F. Jape, et>on se Engineering Branch Division of Reactor Safety License Nos.:
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Date Soigne SUMMARY Scope:
This special, unannounced inspection involved 32 inspector-hours on site in the area of followup on repetitive failure of the stop check valves in the steam supply system to the auxiliary feedwater pump turbines.
Results:
No violations or deviations were identified.
Four unresolved items were identified - Resolve NRC Concerns in the Use of'eaker Material for AFW Valve Repairs (paragraph 5b),
Resolve.
NRC concerns Over Licensee Actions to Obtain a More Permanent Solution for AFW Valve Problems (paragraph 5c), Resolve NRC Concerns Over No Actions Being Taken When Damage to Three AFW Valves Were Reported to Responsible Personnel, (paragraphs Sd and Se),
and Resolve NRC Concerns Over the Inadequate Search for the Missing AFW Valve Parts (paragraph 5f).
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REPORT DETAILS 1.
Persons Contacted Licensee Employees
- C. Baker, Plant Manager P. Banister, Production Supervisor B. Bryan, System Engineer
- J. Donis, Site Engineering Supervisor R. Hart, Licensing Engineer
- R. Longtemps, Mechanical Maintenance Department Head
- J. Mowbray, Senior Mechanical Engineer J. O'Brian, Project guality Control Supervisor W. Raasch, Systems Engineer
- R. Reinhardt, Operations guality Control Supervisor B. Sayers, Maintenance Field Supervisor Other licensee employees contacted included engineers, technicians, mechan-ics, security office members, and office personnel.
NRC Resident Inspectors
- T. Peebles, Senior Resident Inspector
- D. Brewer, Resident Inspector
- Attended exit interview 2.
Exit Interview The inspection scope and findings were summarized on January 10, 1986, with those persons indicated in paragraph 1 above.
The inspector described the areas inspected and discussed in detail the inspection findings listed below.
No dissenting comments were received from the licensee.
The following new unresolved items were identified:
Unresolved Item 250, 251/86-02-01, Resolve NRC Concerns in the Use of Weaker Material for AFW Valve Repairs, paragraph 5b Unresolved Item 250, 251/86-02-02, Resolve NRC concerns Over Licensee Actions to Obtain a
More Permanent Solution for AFW Valve Problems, paragraph 5c'.
Unresolved Item 250, 251/86-02-03, Resolve NRC Concerns Over No Actions Being Taken When Damage to Three AFW Valves Were Reported to Responsi-ble Personnel, paragraphs 5d and Se
Unresolved Item 250, 251/86-02-04, Resolve NRC Concerns Over the Inadequate Search for the Missing AFW Valve Parts, paragraph 5f At the exit interview the licensee made the following commitments that were to be completed prior to restarting Unit 3:
a.
The radiography surveillance frequency for all Unit 3 stopcheck valves would be accomplished in accordance with the schedule shown in para-graph 5.g. of this report.
b.
The strainers in all three TST valves would be inspected and the missing parts from the broken valves would be located and removed from the system.
c.
A failure analysis showing the acceptability of the valve repair would be completed and provided to Region II.
The licensee did not identify as proprietary any of the materials provided to or reviewed by the inspector during this inspection.
3.
Licensee Action on Previous Enforcement Matters t
This subject was not addressed in the inspection.
4.
Unresolved Items Unresolved items are matters about which more information is required to determine whether they are acceptable or may involve vio)ations or devia-tions.
Four new unresolved items identified during this inspection are discussed in paragraph 5.
5.
Followup on Repetitive Failure of Auxiliary Feedwater (AFW) Steam Supply Stop Check Valves (92702 and 61701)
This reactive inspection was initiated on January 6, 1986, to followup on the repetitive failures of the stop check valves in the steam supply system to the AFW pump turbines.
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Basic System Description (See sketch on sheet 9)
The steam supply system feeds three AFW pump turbines that are common to both units.
There are three main steam headers per unit that supply steam to the system for a total of six headers.
Each steam supply header contains a motor operated valve (MOV) and two stop check valves.
The MOY is normally shut and opens, when required, to provide steam flow to the turbines.
The stop check valves are located upstream and downstream from the MOV.
The stop checks are normally open to allow steam flow in the system when the MOV opens and the check feature of
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the valve is available to prevent backflow in the event of a steam line break.
The stop check valves are also used as a stop valve to isolate the steam line in the event of a steam generator tube rupture or to isolate the MOV for maintenance or testing.
Previous Valve Failure History (see sketch on sheet 10)
The stop check valves were installed new in November 1983 for Unit 3 and in May 1984 for Unit 4.
The valves are manufactured by Pacific
. Valves, Model 3"-660S-7-WE(80)-X, 600 LBS.
Carbon Steel, Stop Check Valve.
There were no reported problems with the valves until November 24, 1985, at which time the 320 valve on Unit 4 appeared to be defective.
When an operator attempted to shut the 320 valve for surveillance testing, the operator felt the valve did not close the appropriate number of turns based on previous experience.
The valve was then disassembled, inspected, and repaired in accordance with Nuclear Plant Work Order (PWO)
0462 and Non-Conformance Report (NCR)85-206.
Upon disassembly, it was found that disc guide stud was broken off of the disc and the stud was missing and, in general, the valve internals were in fairly rough shape (thrust plate bent and twisted, disc nut tack weld broken, disc nut beginning to unscrew from disc, and major degradation of the disc and seat).
The NCR also required radio-graphs (RTs) of Unit 4, 119 and 319 valves and all Unit 3 stop check valves to determine the internal condition of these valves.
The RTs were performed per Test Request (TR) 123-85 and the results indicated that the disc guide stud was missing from the 319 valve on Unit 4 and the 119 valve on Unit 3.
From November 24 through December 4, 1985, all 12 valves were disassem-bled, inspected, and repaired under NCR 85-206 and the following PWOs:
Unit 3 - 2479, 2480, 2481, 2482, 2483, and 2484; Unit 4 - 0462, 0463, 2424, 2425, 2426, and 2427.
In general, all valve internals were in rough shape requiring major repair and new parts.
The repairs wer'e accomplished with vendor assistance and new discs were installed in all valves except for the Unit 4 - 119 and 219 valves.
The original discs in the stop check valves were composed of ASTM A216 Gr.
WCB with measured physical properties of 61K yield and 86K tensile.
WCB is a
standard material supplied by Pacific Valve.
Replacement parts were supplied in AISI 1018 (ASTM A108) with properties of 36K yield and 55K tensile as estimated by hardness testing.
This material change was proposed by Pacific as an alternate to the WCB requested; the change was schedule related.
This area of concern is identified as Unresolved
.
Item 250, 251/86-02-01, Resolve NRC Concerns in the Use of Weaker Material for AFW Va'ive Repairs.
In addition to the repairs, NCR 85-206 and TR-123-85 required RTs of all valves in the flow path from the stop check valves to the AFW turbines in order to locate the missing disc guide studs from Unit 3-320 valve and Unit 4 - 319 and 320 valves.
The RT results were incon-clusive and no studs were located.
It should be noted that the long runs of piping to the turbines were not radiographed, nor were the
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steam strainers examined (which were later identified as being an integral part of the TST valves on the AFW pump turbines).
As repairs were completed, the units were restarted and placed in service.
Root Cause and Corrective Action The root cause determined by the licensee was that the, normally shut, MOVs in each steam supply header have seat leakage, thus, allowing slight steam flow through the system.
This low steam flow through the stop check valves causes the disc in the valve to vibrate, chatter, and bounce up and down on the seat, which, in turn, causes internal degra-dation of the valve.
The valve technical manual supports this conclu-sion in the following statement:
"NOTE:
Continuous throttling at less than 10% open causes exces-sive vibration, noise, wear, and damage to disc and seat ring."
The corrective actions included repairs to the valves as previously stated and the licensee is trying to obtain repair parts for the MOVs or new MOVs to replace the leaking ones.
Additionally, an inspection program was initiated to confirm operability of the valves.
The program required RT inspections of all 12 valves monthly to determine the internal condition of the valves.
The long term solution has been assigned to the licensee's AFW Task Force, who have been in discussions with the vendor to improve the stop check valves'esistance to fatigue.
To date, no permanent solution is available.
This area of concern is identified as Unresolved Item 250, 251/86-02-02, Resolve NRC Concerns Over Licensee Actions to Obtain a
More Permanent Solution for AFW Yalve Problems.
Current Failure History On January I, 1986, during the per formance of Surveil 1 ance Test 4-0SP-075.3 (AFW Nitrogen Backup System Low Pressure Alarm Setpoint and Leakrate Yerification)
on Unit 4 problems were encountered with the Unit 4, 320 valve.
This valve is shut, per the procedure, to isolate the steam supply to A and C
AFW turbines in order to prevent the turbines from running during the test.
During performance of the test, A and C AFW pumps started, which indicated an internal problem with the valve.
The valve was declared out of service and the unit was placed in a
72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Limiting Condition for Operation (LCO) per Technical Specification (TS) 3.8.5.
At 0030 on January 2, 1986, the emergency response team was notified to expedite valve repair to prevent exceed-ing the LCO.
The valve was disassembled at 0500 on January 2,
1986, per PWO 0501 and it was discovered that the disc guide stud was sepa-rated from the disc and was found laying in the bottom of the valve body.
NCR 86-001 was initiated to repair the valve and required that the remaining 11 stop check valves be RT'ed immediately to determine the condition of the disc guide studs.
The NCR further stated:
"Any missing guide studs shall be identified for immediate repair.
Damaged
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valves are considered out of service."
TR-001-86 was initiated to request the RTs.
The acceptance criteria on the TR stated:
"Verify vertical guide stud is still attached to the valve disc assembly.
Reject missing or misaligned disc assemblies/guide studs."
In addi-tion, the TR stated that the RT results were required
"ASAP".
The radiography of the valves was completed at 1915 on January 2, 1986, and the results of the inspection were stated on the TR as follows:
"All of the valves are acceptable, except for the following:
Unit 4, valve 4-10-319, vert. guide stem approx.
15'nit 3, valve 3-10-119, vert. guide stem approx.
10'nit 3, valve 3-10-219, vert. guide stem approx. 30'"
The cognizant engineer was notified, at home, at 2030 on January 2,
1986.
No actions were taken.
Region II's Involvement in the Valve Issue As previously stated, this inspector was sent to the site to followup on the repetitive failure of the valves.
The inspector arrived late in the afternoon on January 6,
1986, and spent the remainder of the day obtaining a badge for unescorted site access.
The inspection commenced on the morning of January 7,
1986, in discussions with maintenance personnel, visual inspection of the damaged valve internals, and a
review of the PWOs and NCRs concerning past work on the valves.
In discussions with the cognizant engineer, a
copy of TR-001-86, which identified the three additional unacceptable valves, was obtained.
When questioned as to the disposition of the unacceptable valves, the engineer stated that the valves were alright because there was enough
"slop" between the disc guide stud and its guide to allow the disc to lift even if the guide stud was bent.
The inspector disagreed with the licensee engineer and requested to see the radiographs of the ll valves taken on January 2,
1986.
The engineer agreed and also stated that this would be the first time he looked at the RTs.
Upon initial observation of the RT films, it was obvious to both,. this inspector and the cognizant engineer, that the three valves were unacceptable as previously reported and, in fact, it appeared that the disc guide stem was broken off the disc on Unit 3 - 119 and 219 valves and Unit 4 - 319 valve.
The 320 valve on Unit 3 looked questionable and the 319 valve on Unit 4, although the stud was definitely at an angle, it was hard to determine if it was disconnected from the disc.
These two valves were RT'ed again later that day and it was confirmed that the 319 valve stud was broken off the disc and the 320 valve was. satisfactory.
Plant management was notified by the cognizant engineer and after a
management meeting, the three valves were declared inoperable.
Unit 3 was then shut down at about 1830 on January 7,
1986.
Unit 4 was placed in a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO, as required by TS 3.8.5, and subsequently shutdown at about 0600 on January 10, 198 'I N
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When the cognizant engineer and his supervisor, the site engineering supervisor, were questioned by the NRC as to why no actions were taken on January 2,
1986, when the radiographers informed the engineer that three of the valves were unacceptable, a definitive answer was hard to come by.
Their final official stand was as follows:
(1)
When informed, at home, by the radiographers that the RTs indicat-ed that three additional valves were unacceptable, the cognizant engineer assumed the RTs were unsat and considered the valves operable based on the fact the guide studs were still in the valve.
(2)
The cognizant engineer then informed the site engineering supervi-sor that the RTs were unsat but that he considered the valves operable based on the discussion above.
(3)
The next day (January 3,
1986),
the site engineering supervisor assumed that the cognizant engineer would look at the RTs and since he had no feedback from him still considered the valves operable.
(4)
The whole matter was dropped until January 7,
1986, as discussed in paragraph 5.e. of this report.
This area of concern is identified as Unresolved Item 250, 251/86-02-03, Resolve NRC Concerns Over No Actions Being Taken When Damage to Three AFW Valves Were Reported to Responsible Personnel.
Location of Missing Disc Guide Studs and Thrust Washer As previously stated, the three disc guide studs that had broken off prior to November 24, 1985, were missing, in addition, a thrust washer was missing from the internals of one of the damaged valves.
The studs are approximately 2 1/2" long and 3/8" in diameter and the thrust washer is a metal disc about 1 1/8" in diameter and 1/8" thick.
On January 7,
1986, this inspector expressed a concern to the site engineering supervisor and the cognizant engineer as to the adequacy of the search for the missing parts.
The major area of concern was the possibility of damage to components downstream from the stop check valves as the parts were accelerated down the steam line with steam flow.
They stated, as previously discussed, that all valves in the flow path down to the turbine were radiographed and the parts were not located.
The inspector pointed out that there were long runs of piping from the valves to the turbines and that the parts could be anywhere in the flow path, not just in the valves.
They then stated that it did not make any difference because there was a strainer in the steam lines to the turbines and this would catch the parts.
The inspector then questioned where the strainer was located, the mesh size, and the strainer
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thickness and received answers that showed a definite lack of knowledge concerning the strainers, in particular, their location.
The inspector then questioned that if strainers were in the supply lines, why didn'
they inspect them for the missing parts.
Their response indicated they considered the radiographs of the valves to be sufficient.
The inspector then questioned the AFW system engineer as to the loca-tion and design of the strainers.
He stated that he was unaware of the strainers, however, he would look into the matter.
We then walked down the steam supply portion of the system and were unable to locate the strainers.
The system engineer informed this inspector on January 9, 1986, that they had determined the location of the strainers to be an integral part of the TST valve on the inlet to each turbine.
The strainers are constructed of '14 gauge steel, 0.0747 inches thick with 0.109 inch holes.
The engineer also stated that they would take one pump out of service at a time during the upcoming Unit 4 outage and inspect the strainers to locate the missing parts.
On January 10, 1986, the T&T valve for "C" AFW pump was disassembled and one of the missing studs was located.
This area of concern is identified as Unresolved Item 250, 251/86-02-04, Resolve NRC Concerns Over the Inadequate Search for the Missing AFW Valve Parts.
Additional Corrective Action In order to return Unit 3 to service, an interim Unit 3 valves was implemented.
The repairs were per NCR 86-009, utilizing an oversize guide stud and a stronger material (AISI 8620) for the stud.
surveillance fr equency for all six valves was to following schedule:
repair for all six to be accomplished, (1/2" versus 3/8"),
In addition, the RT be increased to the (1)
One inspection after the AFW pump operability check (2)
One inspection per week for six weeks (3)
One inspection per two weeks for two months (4)
One inspection per month for the remainder of the fuel cycle Summary of NRC Concerns in This Issue Four Unresolved Items have been identified:
(1)
The valve discs substituted due to scheduling were made of a
weaker material than the original discs that failed.
No analysis or justification for using the weaker material was performed.
This is identified as Unresolved Item 250, 251/86-02-01 (see paragraph 5b).
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(2) It appears that the root cause of the problem, seat leakage past the NOYs, needs increased management attention to obtain a more permanent fix for the problem.
Until the NOVs are repaired or replaced, the stop check valves wi 11 be susceptible to damage.
This is identified as Unresolved Item 250, 251/86-02-02 (see paragraph 5c).
(3)
The major area of concern was that problems with the valves were identified to responsible licensee personnel on January 2,
1986 and no actions were taken unti 1 January 7,
1986, as a direct result of this inspection.
This, in turn, caused a
LCO to be exceeded by approximately five days on Unit 3 and eight days on Unit 4.
This is identified as Unresolved Item 250, 251/86-02-03 (see paragraphs 5d and 5e).
(4)
The attempt to locate the missing parts from the valves appeared to be inadequate, in that the licensee radiographed only the valves in the flow path and ignored the long piping runs and system low points.
In addition, if it was known that strainers were present in the system, it appears that this would be the most logical place to look.
However, this was also ignored until the issue was raise during this inspection.
This is identified as Unresolved Item 250, 251/86-02-04 (see paragraph 5f).
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