ML20198M337
| ML20198M337 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 10/22/1997 |
| From: | Boyce R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9710290064 | |
| Download: ML20198M337 (28) | |
Text
_ _ _ - _ - - _ - - - _ - - _ . - _ - _ _ _ _ - -
Robert t1 C yes Plant Manager A Limanck Generating Stat 6on v ~
PECO F~NERGY "="-a c --"<
Umench Generating Stat.on PO Box 2300 Sanaloga. PA 194644%I20 215 3271200 Lut. 2000 October 22,1997 Docket Nos. 50 352 50 353 Lloonee Nos. NPF 39 NPF45 U.s. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 l
SUBJECT:
Limerick Cacq 8tation, Units 1 and 2 .
Control Rod Failure to Scram Event and Associated BUNA-N Type Scram I solenoid Pliot Valve Aging lasues On September 25,1997, a Limerick Generating Statiori (LOS), Unit 1 control rod drift alarm was received in the Main Control Room (NCR) for oortrol rod 3443. During investigation and tr%-5:i:-ns, the control rod had failed to scram locally, and was manually inserted by Operations personnel from the MCR. The Scram Solenoid Pliot Valves (SSPVs) in the : lydraulic Control Unit (HCU) associated with this control rod were of the DUNA4J type. The attachment to this letter describes the LG8 investigation into this event and its resolution by LG8 on the industry issue of BUNA-N type SSPV aping.
If you have any questions, please do not hesitate to contact us.
Very truly yours, i -&
t oc: H. J. Miller, Administrator, Region I, USNRC wfattaement A. L Bunttt, USNRC Senior Resident inspector, LG8 * (
\
'9710290064 971 V PDR- ADOCK 0 2i l l
Docket Nos. 50 352 and 50 353 October 22,1997 Page 2 boc: D. M. Smith CB,63C 3 w G. R. Ra'e ey C8,63C 3 W. G. MecFarland - SM81 1 .
J. 8. Cotton 08,62C 3 .
T. J. Neeseen CB,63C 3 .
R. W. Boyce - GML51 .
J. D. von SuskN SSBS1 .
G. A. Hunger, Jr. - CB,62A 1 .
!- J. E. Cohen 8884 3 .
J. P. Grimes - 8883-1 .
F. A. Cook - 88851 .
J. A. Mutton - GML51 - .
C. T. SeN 88831 .
C. A. Hoffman - 88831 .
T. A. Moore 8882 4 .
S. A. Auve 8884 2 .
ISEG - SSd4 2 .
NRE Chairman - CB,62A 1 .
SecrWary. NCB CB,62A 1 (11 copies) =
PA DER BRP inspector 8682 4 - .
CommitmerW Coordinator- CB,62A 1 =
CorresN Release Point- SM812 =
DAC - SM812 .
\ k - - - . _ _ _ _ - - . _ _ . _ _ . . _ _ . . - _ . _ __
- ' Docket Nos. 50 352 and 50 353 Oolober 22,1997 Page3 i ^^^ RICK GiiiNERATING STATION. UNiin 1 AND 2 CONTROL ROD FAH llRE TO SCRAM EVENT AND ASW8ATED BUNA N TYFiii SCRAM sot FNOO PILOT VALVE AG!NG !BB'_8ES
SUMMARY
On September 25,1997, a Unit 2 control rod drtit alarm was reoelved for control rod $4 03.
During investigation and tre::i:-:^ig, the control rod failed to scram looelly, and was -
manually inserted from the Main Control Room. This control rod Hydraulic Control Unit (HCU) had Scram Solenoid Pilot Valves (88*V) that are of the SUNA-N type, and the cause has been attributed to aging of the diaphre0m material. The following desertbes the Limerick Generating Station (LG8) investiestion into this event and its resolution.
EVENT:
On September 25,1e97, dur6ng T side half scram testing, the Unit 2 control rod 34 03 showed Indications of a detfting control rod. Tre::' -:^1., led to the 9:=p that the 88PVs on its HCU were leaking air at the exhaust diaphre0me of the 217 and 218 valve endoap flan 0es (see attached diagram for 88PV confl0uration). Leaka0e out of the exhaust endoap of the 217 valve t,
i_
was attributed to be the cause of the control rod detft since, with the 218 valve de energized, only the 217 valve was keeping pressure on the scram valves. Sufflaient leakape could cause the 88PVs to begin to open.
The decision was made to insert the control rod 34-03 to position 00 to prevent further control rod delft events during subsequent half scram testing. When the Reactor En0ineers evaluated inserting the control rod to position 00, it was determined that inserting the control rod by single control rod scram would minimize PCIOMR ( Proconditioning interim Operating t+;: ,w' Recommendations) conoems, li was during this maneuver when the control rod failed to scram.
INDUSTRY BACKGROUNO:
in Odober 1993, General Electric (GE) leaued (SIL) Servios information Letter 575 *CRD Slow Start of Motion
- due to degrading scram times at 5% insertion (position 45 at LG8). The degradation was attributed to a0ing and temperature related hardening of the SSPV diaphra0ms.
OE recommended a four year servion life for the valves, with extension possible on a plant -
specific basis after examination of the diaphra0ms, in July 1994, GE leeued inCFR Part 21 Notification,
- Degraded SUNA-N Diaphre0ms in ASCO Dual Type Solenoid Valves" due to further ocounences of slowing and a failure of one control rod to scram at one plant. The safety basis of allowin0 the 88PVs to remain in service per the 10CFR Part 21 Notifloation was delineated based on a review of a sienificant number of slow control rod insertions on a scram and a failure of two control rods to insert on a scram. No further actions were recommended.
GE SIL 584 *8 cram solenoid pilot valve delayed responee" and SIL 585
- Scram solenoid pilot valve air system maintenanoe' leeued in January 1995, further explained the phenomenon relating to the SUNA-N diaphre0ms of the SSPVs. The 88PVs showing more rapid degradation were manufactured in 1989 and later, and the degradation was linked to a combination of the formulation process and possible contaminants. SIL 584 recommended sampling and evaluation of cunently installed diaphra0ms. SIL 585 recommended good maintenance predices relatin0 to valve rebuilds and checking air systems for contaminants.
l
.h
- , October 22,1997 i Page 4 I LIMERICK RACKGROUND 1
Unit i scram timing performed on Fetwuary 21,1995, showed 9 al ns of performance degradation
- i and a sample of the SSPVs was sord to GE for analysis. GE's final report stated that the SSPVs, which were in service for 4.6 years, showed near end-of-We condNions; however, they were still fundional. LG8's original schedule for replacement of a batch of appmmimately one. i third of the core was for December 1995, with replacements being an upgrade to Viton
- diaphra0ms.
so,*e Wo. GE recommended replacement by August 1995, prior to exceeding 5 years of i
- 1.G8 replaced the identmed batch on July 21,1995. Re=d batches, of appmmimately one.
third servius oflifetime, the core each on both units, were targeted to be replaced so as not to exceed a 5 year f ,
i LOS replacement frequency was :-;+2TC/ based on allowing some margin to the service life obtained by the samples analyzed by GE, which had only started to show signs of degradation at and of Wo. N was also noted by GE that the diaphragms at LOS are maintained in good i i
operating condRion. The original replacement schedule is shown below, and the resultin0 cunent j oore composition for both Units is shown on the attachments, !
i EllI.1 i-
'e Bate i replaced on Ju'/ 21,1995 with a servios life of 4 years 9 months. '
3 e Batch 2 replaced on November 17,19G6 with a servios life of 4 years 5 months.
e :
Batch 3 has been in service sinos December 1993, and scheduled for repiscomert in AprH 1996; the service Hfe will be 4 yuts 5 months.
1 AlNil.2
! e Batch 1 replaced on December 5,1994 with a service ilfe of 5 years 6 months.
l e Batch 2 replaced on January 8,1996 with a service life of 4 years 9 months.
L
- Batch 3 has been in service since March 1993, and scheduled for replacomord in December
.1997; the service We will be 4 years 9 months, 1_ >
4 in March 1997, during scram time testing following the fourth Unit 2 refueling outa0e (2R04), Unil .
2 control rod 50 31, a BUNA-N typw failed to scram. The SSPVs were removed and sent to GE for analysis. There were no other failures to scram of the remaining 184 control rods. The,e were no inormasing trends in core wide average scram Emes and no 2x2 arrays were out of -!
spoomcation. One control rod,3411, was slow to reach pt,sition 45 and the SSPVs for this
{ control rod were topiaced within a few days, ?
i-
- ' The resultant report from GE did not find a specific root cause for the failure. The diaphre0ms
' were not hardened to the poirt of failure, and the valve manufacturer could not duplicate the 1
failure on the test bench. In addition, there were some indications that some foreign material may have nterfered with SSPV operation.
FOLLOWUP FOR SEPTEunsR 25.1997 EVENT!
)'
The failure of the Unit 2 control rod 34-03 to scram was reviewed for reportability and determined not to be repostable. Additionally, it should be r oted that under an actual scram s30nal, control rod 34-03 would have scrammed as a result of operation of the backup scram valves, f
I l
l l
_ -. -- ..- . ,_., . _ . _ . - _ . - , . ~ ,
- - -.-. - - - .~..- - - - -
4
~ DoclW Nos. 50-352 and 50 353 -
October 22,1997
- Pa0e 5 i -
j "
i The fonowing plan was developed to addmes the potential genedc conoom m0an96ng the !
remaining population of sixty BUNA-N HCU 88PVs instated in una 2 and to wrtfy that the ;
j orleinal BUNA-N reAnent proprem concluelons were stiN valid, uneed on this hardening t i being premature mistive to any previously monnored performance at t.08: i i
l The 88PVs for HCU 34-03 were inspected and tested on the bench to determine the failure !
l mechanism. The inspection revealed that the BUNA-N diaphreoms were hardoned and that '
' crecidno had occurred. The hardening and cracking of the diaphre0ms led to increased air leakape both intomal and extemal to the 88PV. The hardening is believed to be the mechanism i
i resuming in the failure of control rod 3443 to scram.
l
) A welkdown of the Unit 2 HCus was performed to identify any air leaking from end caps as !
E possible procursors to failure. Seven HCU 88PVs were identified as having minor amounts of !
leaka0e:
3 i 1. 36 50 .
j~ 2. 50 51-
- 3. 46 55
. 4. 54 30 t i- 5. 22-03 i
- 8. 02 31 i 7. 08-47 p_
- A representative sample of the abdy BUNA-N HCus were sua time tooted to identify any :
- - problems. Twelve control rods were orl0inally chosen (two Groups of 10% samples) to
, encompass the seven identified HCU 88PVs with minor air leakage:
l 1. 36 59 4 2. 50 51 -
F- S. 6 55-l- 4. 54 39
- 5. .
- !2-03 !
} 6. 02 i
- 7. 06-47 >
l S. 18 35 l
- 9. 02 19 '
- 10. 18 59 i 11, 58-19'
- 12. 30-43 i
- The 12 control rods all scrart,med suoosesfully within the required Technical Specifloations (TS) !
i surveillance time of 7 seconds to pochion 5. Two of the 12 control rods were silghtly slow to 3 ._ reach position 45 (0.43 sec). Contml rod 38-59 indicated 0.476 seconds and control rod 50 51 -
L indicated 0.460 seconds. These two control rods were in the population of the seven known to have minor airleakaos.
l Based on these times exceedin0 the required time to reach position 45, the avere0s scram times were compared per T8 to ensure operability. Scram time data for both units was reviewed and it wee confirmed that all previous scram times for BUNA-N control rods tested were satistadorv.
j The most recent test dates were September 13,1997, for UnN 1 and July 12,1997, for IXt 2.
l 7
I i-
1 Docket Nos. 50-352 ersd 50 353 2- October 22,1997 j Page6 ;
i i
) l An additional six more control rods were chosen (another 10% sample) to be scram time tested.
j- Those six control rods moremmed sucomesfully and showed no si 0 ns of slowed toepones. Also, '
the six additional control rods ensured that no two SUNA-N Hous with slowed toeponse times I were in the same 2X2 array. Additionapy, the post maintenance test of control rod 34-03 following 88PV replacement fulfilled the 19 control rods required to complete the portodic scram i
time purveillance test. !
- At the same time, a weekdown of Unit 1 HCUs was performed to identify any air leaks. Minor air leaks were identitled for the following two control rods
- l l[ :
- l. 1. 14 23 4
- 2. 46-27 j Based on this information, the folloudn0 con *ctive actions were taken:
- 1. Following replacement of the SSPV for control rod 34-03, all tested control rods
!- scrammed (19 in total) successfully.
7 I 2. A recommendation was made to replace the 88PVs for the Unit 2 cordrol rods 36 59
- and 50 51 at the earliest possible time. This is a conservative recommendation i based on an Indication of minor air leakape and an increase in the scram times. l 1.
i
! 3. The remaining SUNA-N 88PVs are tentatively planned to be repisoM no later than j the previously scheduled time frame of Deoomber 97, and consider.uon will be !
given to accoloratin0 that schedule. I 4
- 4. The Unit 1 BUNA-N 88PVs should be reviewed for similar actions. +
t 0
in co$nction with those plans, LG8 Site E,G:: 4 was involved in dinoussions with the ,
Senior NRC Resident inspedor to discuss the adequacy of these plans on September 25,1997.
i A folloussp phone call with NRC Region I was convened September 26,1997, to further discuss
, the suustion and Limortok's adion plan. Ro0 ion I submitted questions for olattfloation that were i
discussed in a telecon on October 3,1997.
I i
i ACTiGN PLAN f ,
l Anahrais of Contml Rod 34-03:
The GE industry materials expert on the topic of SUNA-N failures has inspected the F diaphra0ms from control rod 34-03 and forwarded the diaphre0ms to the orlGinal equipment .
- j. manufadurer.
L Monitorinn:
Monitoring of SSPVs for air leakape on Unit 1 and Unit 2 has been initiated on a weekly basis. A welkdown on October 6,1997, Identified one additional minor air leak on Unit 1 and '
i
- two additional minor air leaks on Unit 2. No new leaks were identified % ring a welkdown on L October 14,1997. ,
i a
I
~
- i. .
t.
'__ __ . a_ _ __ _...__ ._. _ ..___ _. _ _ _ . . . . _ _ - . _ _ _ _ , _ _ . . . _ _ _ ,_ _ . -~ . , _ _ . . . . . _ , . _ , _ _ , . _ , . . _ _
_.. _____._ _ _ _._ -..._ _._.._ _~__- _ - - - .-- - - --
! l l
- Docket Nos. 50 352 and 50 353 October 22,1997 Page 7 i.
i i Unit 2 Plan for Odober2.1997:
1 i
A Unit 2 load drop was performed on October 2,1997, to foollitate repleoing 88PVs for the slow control rods and to replace several other SSPVs that were sent to GE for analysis. ;
These sample 88PVs would allow the characterization of the remaining BUNA N r-:-r ""'m l by providing an SSPV that failed, an SSPV that had a minor air leak and was slow to reach ,
i position 45, an SSPV that had a minor air leak, and an 88PV that was neither leaking air nu !
slow. As a conservative measure, LG8 also made the dociolon to scram time test all I remaining Unit 2 BUNA-N 88PVs during that load drop to obtain additional information on :
1 the performance of the HCus that were part of the SUNA N batch. The roeuNs of that load ;
- drop are summarized below; - !
l l a. Replaced 88PVs on the slow control rods 36 50 and 50 51.
4
, b. Replaced 88PVs on 2 other control rods with BUNA-N: 46 55 (leaking, not slow) and 04.
!- 43 (ntA leaking, not slow). 6 l c. There were two addnional slow control rods,50 27 and 34 27, whloh had their 88PVs i repleood with Viton.
I
i oxidation analysis.
Unit 1 Plan (next load dmo conogtunitv):
- 1. Scram time nineteen BUNA-N 88PV control rods inckwling the three control rods with minor airleaks:
14-23,02 21, and 46-27.
- 2. Replace SSPVs for control rods 14 23,02 23, and 46 27.
! RESULTS .
4 l Materials Analysis:
l \
l- A review of the batches of BUNA-N SSPVs installed on Unit 2 revealed two different 4 stock oodes that were installed. The susped batch associated with the Unit 2 control rod 1
{ 34 03 was investi0sted further. There were seven tctal HCUs fitted with this stock code: I t . 34 03 - failed and was replaced with Viton - *
! .. 38-59 and 50 had air leake and were slow; were replaced with Viton e 22 03 - airleaks
. 36 23,18 55, and 22 39 installed later than the rest (May 1994; corresponds to '
{
4 only 3 years and 5 months of service life) and no air leaks or slow response times
- were identified.
5 l
l
. , - . . , , _ - - , _ ~ . . , ,, , .,, , , , , - , - ... ,. _ . _ . , , ..r.,m.- -, ,_ . - _ _ - - -,y, .,-_yy_m,,.m.- -..,_._--m_< ~ ,
- . . . . . - - . - - - - _ . _ . - - .- - -= --
Docket Nos. 50-352 arid 50-353 October 22,1997 i Page 8 4
l- The SSPVs on control rods 22 03 and 10 51 were identified as leaking air on the welkdown performed on October 6 t997. The SSPVs on control rod 22 03 are of the
!- same vintage as 34 03, while 1H1 is rd. Based on the fed that the SSPV on control rod 22-03 has an air leak and is rA the same vinta0e es control rod 34-03, R was
! conservatively deJded to insert both control rods and a followup load drop was conducted on Octotser 7,1997, to accomplish that task.
l Materials analysis from the UnN 2 samples provided to GE has identified that the failurs
! r$f control rod 34-03 and degradation of control rod 50 51 are related to the batch in ,
- whidt they were made. Data from the oxidative stabliny study showed indications unlike
- previous batches that were analyzed which su00ests that the behavior of control rod 34-03 is clearty different than past batches of diaphra0ms that have boon analyzed (see t l attachment for GE report).
$ The stock codes for the valves installed on Unit 1 were researched to determine if any of I the suspect batch were installed. This review determined that six of these SSPVs were j installed on UnN 1. All have only boon in service 3 years and 10 months to date.
Conference Call With SSPV Manufadurer-A confotonos call with the SSPV manufacturer, was held on October 9,1997, with l representatives fan Station Engineering and observed by the Senior NRC Residerd inspector. The manufacturer discussed the failure mechanism for control rod 34-03 based on their review of the parts, and the impact of endcap air leaka0s.
The manufacturer concluded that control rod 34-03 failed to scram due to hardening and
- cracking of the BUNA-N diaphragms. The cracks allowed airflow to pass 'brough the
- diaphra0ms and did not allow the pmper differential pressures to develop to seat the
! pressure side diaphra0ms, allowing scram air header pressure to keep the SSPVs closed.
i
. Additionally, in the half scram condition, leakage throu0h the 217 exhaust diaphra0m '
allowed the control rod to drift until the differential pressure built up enough to seat the l exhaust diaphra0m, stopping the control red drift.
- The extemal air leaks were dia-ad, and the manufacturer indicated that the air leaks ,
that were observed would Dgi have contributed to the failure of the SSPV to operale.
- The extemal leaks are an indicator that the diaphragms have started to a0e and are not .
- completely sealing in their outer races. The capacity of the scram air header is adequate e except in the most extreme cases of leakage.
- This information fmm the manufacturer confirms that hserting the two control rods with -
minor air leaks was a conservative action, and is not required if the SSPV only exhibits
. extemal leakaos. Due to the fad that the SSPVs on Unit 1 have significantly less servios life than those on Unit 2, the three cordrol rods on Unit 1 with air looks will not be inserted at this time.
I
~
i i
i i
-. -- .- - - , - - , . - - . - - . ~ . . , , . . - .- - -- , , - - - . - - . _ - - - - - -
j .
Met Nos. 50 352 arid 50 353 October 22,1997 Pe08 9
Conclusion:
The failure of control rod 34-03 was due to an anomalous compostion of the BUttA-N diaphra0ms which led to premature a0in0 j This is substantiated in the GE Analysis Report which concludes:
- 1. The results indicate the SSPV diaphre0ms can be divided into two groups, one z.
being the suspect batch.
d 2.(a) Control rod 34-03 diaphre0rt onergy and temperature characteristic curves do ,
not Indicate end of life when r,ompared to results in the GEMAT data.
2.0 .'he results display additional different characteristics indicating another aging
, mechanism for this particular batch.
I i
jg2IE: All suspect batch diaphra0ms for Unit 1 and Unit 2 with more than 4 years of -
service life have been removed fror.1 the :--r g'i HCUs.
4
- 3. Results on the other group diaphra0ms removed from Unit 2 indicate terraining
- diaphra0m life, in-line with 1.GS's previous experience.
i
- The remaining suspect botch SSPVs in Unit 2 have s10 nificantly less servios life, and will be ,
removed from servios prior to the General Electric Laboratory Analysis Report
! recommendation of 4.25 years. ;
The updated schedule for replacement of all remaining BUNA N SSPVs is:
i' Unit 2: Week of November 8,1997.
Unit 1: By January 1998.
.! t l
)
l
- . , . . . , , . . . , . - , -n . - . - - .,.-n..,., . , , - , .. ,,,.,n.-.-.. .,, . ,
RPS "I" and SV-117 Enarpand RPS "B" and SV-118 EngM Y
Fuhauet h Supply air Preanus
$ Diapuragm air Presrere L-
\
h h Scram Valve air Pressurs ks =.~ x x~ D j F EndCap 9
. Ef(.:rg;L
- 6. i==w#f '4 End Cup
'.i.:c_ff.p_@ - :1 a MM i ,
- ~ '
5/.c47-1-i6 b\\
Con j
? '
s s
/ E.
E !
/
/ 4/
- h h
'N h nh
_ _-ss/r 9
( '
N.
i' N x N hEEEE" m
m; h_x wi d ? T -- _ , _ $ _n._ M
- gi ;'
3 sc _ ._.
z "*, =b6 SV-o47- E-d Exhaunt
- EndCap .
/ / ~ .ddbN E p;- yi.m$fNIN
- - YEMf End Cap i
< ,N N N g l
M /
T /
/
/ J /
/
/
F
/ f $
/
/
/
ma ~ ,)J
&s si/1, n n 2f ///sh;
' __ Q ,l-e '" Q:CG"# - A,
_ :...:=Ma .,;.dWy}ifMth 4y L,a-_
&&' m ; & m d * =E.o;v. ge .~ .
- WScrsun Valve Eshaust Scram Valve Cwj Closed g !
UNIT 1 02 06 10 14 18 22 26 30 34 38 42 46 50 54 58 59 Vo Vn Vo Vo Vo Vo 59 55 Vn Vo Voc Vn Vn Vo Vn 55 51 Vn Vo Vo Vo Vo 51 47 Vo Vn -Vo Vn Vo Vn Vn Vn 47 43 Vo Vo Vo Va Vn Vo VI: : Vn 43 39 Vn Vn Vo Vn Vn Vn Vo Vn Vnc Vn Vo Vo Vo Vn Vi 39 35 Vn Vn Vn Vn Vn Vn Vn Vn Vo l Vo Vo 35 31 Vo Vo Vn Vn Vo Vo Vn Vn Vn Voc Vn Vo 31 27 Vo Vo Vn Voc Vo Vo Vn Vn Vo 27 23 Vn Vnc Vn Vn Vn Vo Vn Vn 23 19 Vo Vn Vo Vn Vn Vo Vo Vn Vo Vo 19 15 Vo Vn Vnc Vn Vn Vn Vo 15 11 Vo Vo Vo Vo Vn Vo Vo- Vn 11 L 07 Vn Vo Vn Vo Vn Voc Vn 07
- 03. Vn Vo V-. Vo Vo Vo 03 02 06 10 14 18 22 26 30 34 38 42 46 50 54 58 Vo: Viton 'A' first batch Vn: Viton 'A'second batch c: Viton 'A' corrective maintenance V2: Viton 'B' D: Buna-N
>> nn U
! . UNIT 2 l t l
- i. ,
02 06 10 14 18 22 26 ~ 30 34 38 42 46 50 54 58' f 59 .Vn Vn V2 Vn 59 55 Vn Vo Vo Vn V2 55 l l 51 V2 Vn Vn Vnt Voc Vo Vn Vo Vn V2 51 , i 47 Vn Vo Vo Vn Vo Vn Vnc Vo Vo Vn 47 i i 43 Vn Vs - Vo Vn Vn Vn Vo Vn Vn Vo V2 43 ' i i 39 Vn Vo Vn Vn Vn Vn Vo Vn 39 35 Vn Vn Vo Vn Vn Vo Vo Vn Vn Vn 35 1 31 Vo Vnc Vo Voc 'Vn - Vo Vo Vo Vnc Vo Fn 31 I 27 Vn Vo Vn _Vn Vnc Vo V2 Vn Vn Vo V2 Vo Vn 27
]
3 23 Vo Vo Vo Vo Vnc Voc Vo L Vn 23 + 1 19 Vo Vn Vn Vo Vo Vnc Vo Vn- Vo Vo Vn 19 b =-r
- 15 Vn Vo Vn- Vo Vn Vo Vnc Vn Vo Vo Vn 15 11 Vn Vo Vn Vo Yo Vnc Vo Vn Vn 11 07~ Vo Vo Vo Vn 07 03 Vn V2 Vn Vn V2 Vo Vn 03 02 06 10 14 18 22 26 30 34 38 42 46 50 54 58 -
Vo: Viton 'A' first batch Vn: Viton 'A'second batch c: Viton 'A' corrective maintenanco l V2: Viton 'B' B: Buna-N l l l I ________________________________._j
i TodTT23: rs7 -ie:52AM oA cc tT8FIcaTION--- .p,3 O - Report:CPO97075 senesEscwcm 17$ Cwtnw Avenue son Jose, CA 8612:
. October 22,1997 CC: Letter File CPD97 '
T Carney LYChang K Faynshtein EY Gibo BWJoe RS Tunder DRF A0049965-003 e Mr. C. Hoffman _
- Limerick Nuclear Generating Station PECo Energy Company i Sanatoga, PA
Subject:
CPD97075, " Life Cycle Management (LCM) for the Post 1989 Vm' tage Buna-N SSW Diaphragms from Limerick Unit 2"
Dear Craig,
- This letter report documents the results for the Life Cycle Management program CE-NE has performed on the scram solenoid pilot valve (SSW) diaphragms =
- obtained from Limerick Unit 2. This program evaluates the components addressed above for life remaining. The scope of this evaluation has been conducted in accordance with PECo Energy Company 1997 Engineer of Choice Contract (Purchase Order No. BLNE270693).
Introduction The post 1989 vintage, plant-aged, Buna N diaphrsgms from the Limerick Unit 2 scram solenoid pilot vales (v>Ws) were analyzed to determine their current - o condition after appromin w:ly 4.5 years of operation. The purpose of this life _ Cycle Management'/rogtsr t. rending analysis) is to determine the feasibility of operating the subject BunarN SSWs for a short term until the scheduled refurbi:hment in early November,1997. p e .
._ )
OCY 23 '97 10iS2AM QA'CERTZFICATION P.2 4 Summuv and Conchininna The plot ofinitial oxidative heats of degradation of one set of diaphragms (Set 1) versus operating time in the plant (Figure 9) indicates that the total expected life of these diaphragms collectively will be no more than 4.85 years and not quite the 5 years previously predicted. (This Batch is identified with a shelflife expiration date of 6/9/2002). The second set of diaphragms (Set 2) that exhibited circumferential cracking shows more degrade. tion than Set 1. (This Batch is identified with a shelflife expiration date of 7/1/2001). Similarly, the initial oxidative heats of degradation ss operating time in the plant plot (Figure 10) indicates a still sc.mewhat shorter expected life (about 4.25 years). The slightly shorter life for the Set I diaphragms (5 years previously predicted compared to 4.85 years currently predicted) could be due to contamination with extraneous materials (like an ester containing silicone grease such as Dow-Corning 55M) that may accelerate Buna N degradation. This grease was found on the surface of several of the plant-aged diaphragm samples, Reference Figura 11 in the Attachment. It is recommended that the Buna N diaphragms at Limerick Unit 2, which are from Set 2 and which have been in service 4.25 years or greater, be replaced immediately since they have reached their end oflife. Those diaphragms at Limerick Unit 2 from Set I need to be replaced at the earliest time before the end of their estimated life. Based on the results of this evaluation,it is concluded that replacement of these diaphragms in early November 1997 would be acceptable. Material Soecimens Diaphragms from HCUs 4&55(normal response time),50-27(slow response time), and 58-45(normal response tinie) exhibited localized hardness and in the case of 50-27,118P may be starting to show some sigm of cracking. The above diaphragms were all obtained from one batch of original material,i.e., Sct 1. Diaphragm samples from HCU 34-03(failed response), showed circumferential cracking in samples 118P and 117E. Diaphragm samples from HCUs 38-59(slow response time) and 50-51 gslow response time) were also from Set 2 and showed localized hardness. Diaphragm sample 38-59,118E had circumferential cracking and diaphragm sample 38-59,117E had non through-wall circumferential cracking. Reference is made herein to GEMAT which is an internal GE database containing data on previous materials testing, some of them being Buna-N. Information gz!ned from the past trending of these materials was used to help interpret results obtained in this evaluation. Page 2
~
OCT 23 '97 10854AN oA CERTEFICATICtf P.3 i
. Test Pmeedure The testing was via differential scanning calorimetry (DSC) at a constant temperature rate increase of 10*C/ minute with the sample under a 500 psi oxygen gas pressure. The temperature scan was from room temperature to 500*C. 4 i
A typical scan for a virgin Buna-N sample is given in Figure 1 of the Attachments to this report. There are two main features in the scan. First a preliminary, smooth peak occurs in the 150*C to 200*C range: for a virgin sample the peak temperature is approximately 200 *C. This peakis of greatest interest since it indicates the heat of reaction of the first degradative oxidation procer , a process which is proportional to the operating life of the diaphraFms. The larger the exothermic reaction of the material, the more operating life remains. For a virgin sample this value is -450J/g. The second peakin the ' oxidative ' DSC results is associated with a mechanistically different polymer oxidative degradation This peak is at a higher temperature than the first (- 400 'C) and has a much greater energy of reaction. Glass transition ternperatures, T, (i.e., phase change from a more crystallinr; to a more amorphous condition) were also obtained for some of the diaphragm samples using DSC testing. The process requires a DSC starting well below room temperature. For this work the 10*C/ minute scan under ambient pressure nitrogen to obtain glass transition temperatures were scanned from -120*C to 150*C. A gradualincrease in T,,also tends to parallel remaining life. However, T, may also be a factor characteristic of different batches of Buna-N. In general, the post-1989 vintage Buna-N diaphragms have a glass transition of--40*C. Results and_Discussioc The diaphragm material (labeled 34-03), i.e., Set 2, was originally supplied in its virgin state to Limerick from the Peach Bottom Atomic Power Station. This material exhibited the most circumferential cracking and showed the highest T, or glass transition temperature (reference Figures 7 and 8 in the Attachment) after
- 4.5 years of service at Limerick, Unit 2. It aho showed a low oxidative heat of degradation remaining (reference Figure 2). Furthermore, a third peak occurring at 450 *C is net:.d in the figure. This characteristic has nc,t been so obvious in previous studies, it may be related to this particular batch of diaphragms.
Accordingly, this effect may address the condition of this diaphragm as being the most embrittled material found and the first to fail. This failure would be preceded by a slower valve regonse time due to incipientleakage through the diaphragm. Page 3
"' ^
OCT 23 '97 10155AM QA CERTIFICATION P4
. \
However, compared to the benchmark or reference Buna N, none of thz sampics !
- has an extremely long operating life left. The corresponding DSC figures, which
' determine the remaining exothermic heat of oxidative degradation, show that i
! _ values fallin the 200 to 250 Joules / gram range (reference Figures 3,4,5, and 6 in i I
- the Attachment). This must be compared to the 450 Joules / gram value of enthalpy of oxidative degradation determined for the unused Buna-N. According to the GEMAT data collected in the past, the threshold of end oflife indication is ,
dependent upon the particular batch of material and the condition of the plant-aged material. :In fact approaching the 130J/g value for the first DSC peak (or 150J/g for conservatirm) indicates end-of-life for the diaphragms in Set 1 according to past experience, as documented in the GEMAT database ( reference Figure 9 in the Attachment). For those diaphragms in Set 2, Figure 10 more . closely indicates their degradation procca, which is different in character from those evaluated previously. As sach it is recommended that the Set 2 diaphragms be replaced before the end of their estimated 4.25 years of service life. Please note the Figures in the Attachment which follow. Ifyou have any question
- i. regarding the above information, pleue do not hesitate to call me.
Sincerely, l W S4
~ C. P. Dulka, Ph. D Materials Engineering 610-251 /077 Page - 4 ,
l
CCT 23 '97 10iSER1 OA CERTIFICATION P.S f Attachment H 5ures 1 through 11 i Page 5
9 Mgure 1 g N w M o @ 5
- 'i qE. - m F
we ' E I *y .
- U E.S 3 '
Ng. El 4 ( I
-l-
= . .
. 1
- r. = 4'
[
,. t Fy n-
.k a
g. T g I. g: g.i. E- 3 *l Ci , 4- .
- g. 3 .. ,.
m Iest ,
; EM . .
x n PE ti 2 -8 og g y 3 t N I **
=
. alE h
. 4J f' o I
r.f.,8ke 1 ,
. 7 h2 EE -
em ..u ... NOIlO3IJI1N33 60 WerI:BI 46, E2 130 i
. .g
Sampid:118P.34-03.#6,HARD'BUNA-N
- 3 Fila: 5586E.01 I ,
Size: 9.9420 mg _
~ '
b Operator: RS2
-l Methoc RT->500*C,10*C/ MIN Rua Gate: 14-Oct-97 08:21
( m Comment: 971008.006, PDSC4. 02 500 PSI. 5'EEN PAN i 4 B-- 1
. ,z
?
n i i 6' P ( l
~
l _ E m 4- il j s
- 2 . .
E 2! g 166.81*C a r
- .p E t O 2-
- E "
S I 0.6573W/g lf
~ **
.l
.= ;
3 5 u L 0-m
~
186.8J/g l 407.51*C g 4
~
~
E h ' m
" 3 g
-2 . , , , , , '
~'
Q 0 100 200 3dc 400 00 ' kneral V4.00 Du nt 2300 g Temperature (*C) S
Sampi 118e HCU46-SS,#2 9 n Filo: 5541E.01 ( , 0122: 9.5430 og a V Operctor: . Icf Itethod: RT->500*C,10 *C/ MIN Run Date: 9-Oct-97 12:36 ji' Comeetst: 973008.006, POSC4. 02 500 PS1; OPEN PAN h
- v. . t
- a.
- g n
.m - a P
B
'6- p P
m R 4- ]. a , . Ic 5
$ , 365.11*C 3
h . r e . g - a-
$ I 0.7670W/g ~
> C - ,
,e .
{ e . 8 Y ,
, i m
Y
= ;; 0- t _
n - l- U e-I j 389.89'C 3 249.6J/g 3
- e. !
o. S
- -2 - , .
h 8 0 100 200 300 400-General v4.co g t 2:00 - Temperature ("c) g'
~ . . _ . _ _ _ _ . . _ _ _ _ _ _ _ _ . - _ . _ . . . _ _ . _ _ _ _ _ _ . _ - _ - - _ _ _ - .
~.
{- . (. { . , i Samp13: aite.HCU50-27,#6 ' m, (* (e Filo. 557AE.Gi operator: 'RS2
'j i
Size: 9.3200 mg 'N..
. Stun Date: 13-Oct-97 10:27 Hethod: RT->500*C SOT / MIN t 9 Comment: 971908.006, PDSC4. D2 500 PSI OPEN PAN HAIE) CRACK D-8 --
- - i, l r P
'?
6- P ( i L 1 k 4- n I.. 2!, Ec - 1
. 3 5 t 3
o - 7 :
. ~h.
265.84*C :
- a 2- ~
h 0.7968W/g e- - i
- 3 6 a i u . ,
3 - a , ,
' ?' !
' . % i. j y ,
m 0- t-I [ g t
- - 404.38*C 9' !
i 202.6J/g - .
= :
g El 'N l 3 i h -2 . O 100 200 300 400 Temperature (T) General V4.00 nt 2100 3 l
= ;
i
. . _ _ _ _ _ _ _ _ _ _ _ _________________J
_ - .. . . _ . - . . . . . . _ . - ~ _ . - , - - - . . . . . - . . .- - . . - - . . _ - . . . - . .
.. t t ( (- -
l Samp3e: 118P.HCU58-43.f5 i' r7 Filo: 5570E.01 ,n 51ze: 9.4390 mg a La Operator: RS2- ' e$ - ! Mathod: RT->500*C,10*C/ MIN . Run Dato: 23-Oct-97 09: 12 ;ii - M Comment: 971008.006,PDSC4.02 500 PSI,DPEN PAN, FLEXIBLE DIAPH k -! t.' .4 . j 8 8 .i 2
~
?
P 6- ~ 1 I I 4-m
.]
a E . !! 2 E R- i 3
~
162.58*C - 1 l'
, (n. I 5 o !
E
- 2-u n '
t' I i j u
~
0.6336W/g
$ i i
8 , , 5 0- b , . g . ! s 407.56*C I
=
199.0J/g l
? e i
1N 3 ; W l$ -2 0 100 200 M 4do I l Temperature (*C) kneral V4.2 t 2200 @
! ;,'!,i.t,!j l ; lfi ,lIi:
iIi ii : . n _ i9 g 2.p Pa P eG 3 ne.R .
, H i$ ,98 Eo i !0 0
_ , 0 1
.( - 2 Im$ *. t gn
\ bo 5 o 4
- o o
5 0 . 4 _. 7 v _ 9 .Ir C l
-
- a t 1 0
c 6 r 1 O ,
,0 n 0e 2 - 2
_ C. S 4 0 4e s - ER5 4 2 8: : 5re . 5ot - t a .
- aD l
or en ipuM . . FOR'AR .
~
. 0 C 0] 3C
- D '
- s. R (
. A
_ ( H . e . . .' r N . u A t P a _ r . N e p E ' P m _ O 0 e
. C g 0T I
- g 2 S 2 J
[/ - / P 7 W I
' t 0 5 1 9 0 6 8 2 5 1 8 2 2 0 9
_ 1 W4 MC
# /S 0
,l cD 0 1
~ 9
- P '
. 5 0 .
- 1 6 8 ,0 -
_ 3gC0 Um* - C 08 .
- H000
. 250 e3>1
_ 7 . 9 1 1 9R
- 9. T 9
( : - 0
- : t .
2 h:dn pehm oe 8 6 4 2 - mzt m eieo =I SSMC e2 2o m. Li .,e !b5 8 5 S _n i- t .-8
. _ . . - - - . - - .- - . .- - . - ... . _ - - - .. - . -.-~. - - -. - - - - -
.i 1
' N, 8 MOCHEM N. R. C . A. c . 310 m 31m i m te-as it u em . . 11 Figure 7.
l w
^
J *5 l e a d f 4- ! 8 h I l aHf
$Ill
= f .g p l ~
- wF i
l - o3 . J t ln
- l. OB .
r
- en h Y
l R.ee 1 6 H
=
1,$g r - 9 l~ lillg
< = i
?
w
?
1 n r
?
v
?
- 3. g
! jg tem meu seau 8 'd - NOI163I.:lI1MJ? 60 LM41:01 46, E2 130
, ll Figure 3.
a 7 , S a 8
. g '
S ' s ' I . 3 O , g Ej . I . 'Eg y m. a; .
'l
. }e
< e n> i . s'g . 9' llgl y 9 t I lr?l
~
- 9. .
~
!!!I N
h
. 'f
?
,T .
?
a I 7 f . (s/m mots seau . 6*d fDIlO3IJIld33 60 t.pJ41:0! 46. E2 130
f ( (. ( r l l .- ie l2 Figure S. Estimate of Remaining Life for the post-1989 Vintage Buna-N SSPV Diaphragms at umerick U2 450 :
"a w -
\ l
- 350- '
'300- \ ,
l I 5 E \
\ \
, e Limench Date 5 \ h a GEMATData
-Unear (Lunenck Data) i 200 ,s,
- --Linear (GEMAT Data) 3 3
l$ I i so
\ \ '
'@ g \ \ \\ \ \ \ \ \ \' ,,\ _ N \ \ \^ S i '
"8 100 -
g y = -61.M4x + 450 E ,h b 0 I
.s 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -
m Years in Service N ' F-i I
t Figwe 10. Essmate of Remaining 1.ife for the post-1989 Vintage Buna-N SSf'V Diaphragms (PB Batch) at Limerick U2 450- l 400 N,
\
s* w
. + ,
E h N
!=
s s-- u x s s
.v.-o - ,
Lmeer(Lirnerid Data (PB Bakh)) g# - , N
\ \
s .
% .\
t
\ \ \
s
\ \' i e
e 150 - - b; >
- e 5
u d 100 - y = -56.317x + 450 g i; r-50 I 5 g 0 O 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 m y Years in Service 8
irwy-iser oeispM muzM cosme4TE LASS O@( EIS 571 7123 P. 3 i Figure 11, - d
-l'
- 1 s" !
i r . l i 2
) ..
2
.g
. ~
i w E-a
-i n'W es Yt -
E 4 see~
~
NMh Ia d 2T*d HOIlO3IJIld33 t#) LRJ81:01 46, E2 l'X) _ __ _ .}}