ML20023E097

LER 83-021/03L-0:on 830504,three Hydraulic Snubbers Failed Functional Test During Dec Outage & 107 Snubbers Failed Test During Refuel Iv.Caused by Seal Failure & Valve Assembly Contamination.All Snubbers modified.W/830531 Ltr

ML20023E097
Person / Time
Site:	Crystal River
Issue date:	06/01/1983
From:	Taylor B, Westafer G FLORIDA POWER CORP.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
3F-0583-22, 3F-583-22, LER-83-021-03L, LER-83-21-3L, NUDOCS 8306090165
Download: ML20023E097 (13)

Text

_. _ _ _ _ _ .1 .. .

Nec FOmas 308 U.S. NUCLEAR nEGULATORY COMMISSION LICENSEE EVENT REPORT EXHIBIT A CoNTnot sLoex: i l i

l- I l' le@ , PtsAeE paint on Type ALL neouineo Nronanariom M lee r

Fl L luce c lsecoos R l P l 3 l@u0 l 01 -lucsasamu is 0 l 0 l ua 0 l 0 l 0 l as-l 0Nl 0 uceuss l@( Tves 4 l so1l 1 l1 l1se@ l@a con'T po i

= QJ@l 80 o Sil 5101o-10131012J@l CKET Nu eER E 015101418131@l 88 EVENT oATE 74 01610111813 Il Ms oRToATs l@

to EVENT DESCRIPHON AND PMotAELE CONSEQUENCES h rins l Durine the unplanned December outane. three hydraulic snubbers failed a i r, usa ifunctional test. During Refuel IV,107 additional snubbers failed a func- I o 4 ltional test. These snubbers are required to be operable by Technical Speci4 o s Ification 3.7.9.1. This is the eighth occurrence reported under Technical I

@ l Specification 3.7.9.1. I o 7 I I o l I

'c"o"ce" "c'E sN5e co onsNTeoos su oe su'e$s o e I x1 xlO LBj@ [A_j@ l S l UI Pl O l R l Tl@ TeD@ Z@

7 s 9 io is 32 i3 18 i LE R IVENTYEAR o.

@ g/Ro 8 3 10 l 211 l 24 38 y

27 Q

N N

[--J Ji y32 M i# N ! #!T.T 'Ml5" u. 22 l 0 l Of 0g1l ^E.WW "."'*.u* "s"u"Au"ill'-

A 'lll2"C.T..

@ g @ @ g @ l P l 31117l@

cause ossCnernON ANO ConRECnvE ACMONS h i o I Snubber inonerability was due to seal failure a_nd valve _ assembly contamina-I

, , i tion. Consequently, all 261 safety-related snubbers are being modified dura e1 ing Refuel IV. The modifications are described in detail in the attachment.1 l To prevent fluid contamination, new hydraulic fluid will be filtered before 1 4 1 use and fluid reservoirs now have filtered vents. 'l

'sT#u"s - s ,onsa oneensTATus @ Ea5 o.scoveny assemirvion i s [gj@ l 01010l@l N/A l @ Surveillance Observation @ l 7

s Evin $nsv7 '*

= uano on =tsau tocATiono,=um @

i

• 4=ov=To,4cnviw N /A @l l N/A l

. . LZJ@ e LzJ@l og,, . . u u .. w c .no @

i 7 l 01010 l@LZ_J@l N/A l u o.=.='t',= Jim-@

i e 1010101@l N/A l'

oo,on,,g'j,.auwg l

i e M1 i.

N/A

.o l

j ,gu inno @

Nac use oNLY 2 o LN_jh N/A l lllllIllIIIIl 1 ee io es a so NAME OF PREPARER B. C. Tavlor ,,,on g. (904) 795-3802 8306090165 830601 PDR ADOCK 05000302 S PDR

i SUPPLEMENTARY INFORMATION REPORT NO:- 50-302/83-021/03L-0 FACILITY: Crystal River Unit #3 REPORT DATE: May 31,1983 OCCURRENCE DATE: May 4,1983 IDENTIFICATION OF OCCURRENCE:

Florida Power Corporation has discovered several safety related hydraulic snubber failures.

Operability of these snubbers is required by Technical Specification 3.7.9.1.

CONDITIONS PRIOR TO OCCURRENCE:

Crystal River Unit 3 was in MODE 6 (Refueling) when the snubber failures were discovered.

DESCRIPTION OF OCCURRENCE:

In December 1982, during an unplanned outage (Letdown Cooler Outage),9 snubbers failed a visual inspection. When these snubbers were functionally tested, 3 failed and were subsequently declared inoperable.

On April 29,1983, during the present refueling outage, visual inspection revealed leakage on I safety related snubber. All 261 safety related snubbers were then functionally tested, indicating that 107 snubSers were inoperable.

DESIGNATION OF APPARENT CAUSE:

. As indicated in the attached report, the most frequently cited source of trouble has been hydraulic fluid contamination. The report gives a detailed description of other significant problems and their sources as well.

ANALYSIS OF OCCURRENCE:

There was no effect on public health as a result of this occurrence. Public safety was not compromised because a seismic or similar event did not occur.

CORRECTIVE ACTION:

All 261 safety related snubbers have been modified during the present refueling outage.

Design changes include machined 0-ring surfaces and mating surfaces to eliminate fluid leakage, and filtered reservoir vents to help prevent fluid contamination. New hydraulic fluid was filtered prior to entering the fluid reservoir in an additional attempt to eliminate the blockage problems associated with fluid contamination.

See parts 3 and 4 of the attached report for details concerning the modifications.

FAILURE DATA:

This is the the eighth occurrence reported under Technical Specification 3.7.9.1.

p.

1.0 INTRODUCTION

This report provides details of the testing and inspection problems, encountered since - l the 1981 refueling outage, with the snubbers at Crystal River Unit 3. It also addresses l the corrective actions that have been taken to eliminate these problems. The report is l presented chronologically, beginning with the 1981 refueling outage, through two plant repair outages in October and December,1982, and into the current 1983 refueling outage.

2.0 SNUBBER INSPECTION AND TESTING HISTORY l 2.1 1981 Refueling Outage l Visual Inspection Visual inspections during the 1981 refueling outage identified two predominant i problems. The first problem was the cracked aluminum reducer bushings, used to '

connect the. hydraulic cylinder to the shock sensing valve. The cracks could allow hydraulic fluid to leak out of the snubber and cause it to be inoperable. All aluminum reducer bushings were replaced with stainless steel fittings during the outage and this problem was eliminated.

The second problem ' involved the bearings used in the mounting attachment-pieces. The bearings were fabricated of hardened steel which, in some cases, cracked under operational loads. This failure could allow excess movement at i

the snubber attachment point. The hearings were heat treated to reduce the hardness, and the problem was eliminated (no bearing failures have been identified since the heat treatments were performed).

i Slight leakage at various fluid connections was also noticed during this outage, however, none of these leaks were of sufficient magnitude to cause the snubbers to be inoperable. Normal maintenance was initiated to stop the leaks.

Functional Testing Functional testing of all 261 snubbers during the 1981 refueling outage revealed hydraulic fluid contamination as the major source of functional testing problems.

Particulate matter (contamination) in the shock sensing valve system was plugging the bleed orifice and preventing snubber bleed-off following lockup. All of the snubbers were disassembled, cleaned, reassembled and filled with new hydraulic fluid. It was believed that the cleaning process would eliminate the contamination problem since the contaminants appeared to be particulate matter left in the fluid reservoirs after fabrication.

l 2.2 - October 1982 Outage i

Crystal River Unit 3 was shutdown in Octobtr 1982, to repair a leak in the reactor coolant drain tank. Seventy snubbers were inspected during the outage.

Nineteen snubbers had fluid leaks and were repaired. Ten of the nineteen snubbers were removed for functional testing because their fluid reservoirs were-l I

empty. All ten snubbers passed functional testing satisfactorily. Predominant

fluid leakage locations were reservoir-to-sightglass interface and the reservoir-to-valve block pipe nipple joints.

, 2.3 December 1982 Outage In December 1982, Crystal River Unit 3 was shutdown to replace leaking letdown system coolers. During the outage,107 snubbers were inspected . Nine snubbers had fluid leaks and were functionally tested. Three of the nine snubbers failed functional testing and were declared inoperable (see Table 1). Contaminants were found in the vaive assemblies upon investigation. Leakage was localized to l the reservoir-to-sightglass interface and the reservoir-to-valve block pipe nipple

joints. These are the same leakage locations identified during the October,1982 outage.

2.4 1983 Refueling Octage Visual Inspectio3 Crystal - River Unit 3 was shutdown on March 19, 1983 for refueling and maintenance. Visual inspection was performed on 100% of the safety related snubbers. One snubber failed this inspection because of fluid leakage at the reservoir-to-valve block pipe nipple joint (see Table 2).

i Functional Testing Functional testing has been performed on 100% of the safety related snubbers.

The failure rate was approximately 40% Most of the failures have been

, attributed to fluid contamination causing the snubber to have no bleed-off after achieving locking velocity. These failures are similar to those discovered during.

the 1981 refueling outage. -

3.0 INVESTIC ATION OF PROBLEMS ENCOUNTERED SINCE 1981 3.1 Hvdraulic Fluid Leakage at the Reservoir-to-Sightglass Interface

, Leakage at the reservoir-to-sightglass interface was determined to arise from

! misalignment of- the fluid port and sightglass attachment nut that is welded

, inside the reservoir body, (see Figure 1). The misalignment prevents proper seating of the O-ring gasket against the reservoir body. To eliminate this  !

problem, all reservoirs have been replaced with a new style that have a threaded fluid port rather than a nut welded on the inside. The new style reservoirs also have a machined 0-ring seating surface. These modifications have eliminated the sightglass misalignment problem and associated leakage.

3.2 Hydraulic Fluid Leakage at the Reservoir-to-Valve Block Pipe Nipple Joint

! The fluid connection between the reservoir and valve block is a 1/4 inch pipe j nipple. Leakage has occurred at these joints because of thread wear resulting i

t t

. .-. -- =- _ - _. - _ - - _ . ..

~

i

{ from numerous assemblies and disassemblies of the joint during snubber maintenance. All reservoirs, pipe nipples and valve blocks have been replaced

~

i with new ones, thereby providing all new sealing surfaces. . The joints are being assembled with a thread sealing compound. These changes have eliminated leakage at these joints. The new nipples have wrench flats to aid installation and ,

removal. L 3.3 Source of Hydraulic Fluid Contamination 1

Fluid Contamination was assumed to originate in the reservoirs when the problem was discovered during the 1981 refueling outage. When contamination was found again in 1982, other sources were investigated, and the following actions have been taken to eliminate their possibilities:

POSSIBLE CONTAMINATION SOURCE CORRECTIVE ACTION

1) Fluid Reservoir The manufacturer has been required to flush.

each reservoir with a cleaning solution prior to shipment to Crystal River.

lndependent pre-shipment inspections are performed to verify cleanliness prior to sending new reservoirs to Crystal River.

Reservoirs are flushed with cleaning solution prior to assembly of the snubber.

2) Reservoir Vent Opening Reservoir Vents that were open to the atmosphere have been replaced with filtered i vents.

I 3). New Hydraulic Fluid New hydraulic fluid is being filtered prior to use. (Contaminaras have been found in new 4

fluid.)

In addition to actions listed above, clean hydraulic fluid is being pumped into the snubbers through a filter. Following filling, the snubber is stroked several times with the displaced fluid passing through a filter and returned to the snubber each stroke, (see Figure 2). These corrective measures should preclude further fluid contamination

' problems.

4.0 SHOCK SENSING VALVE DESIGN CHANGE 1

A new style shock sensing valve has been installed on all of the snubbers. The new design eliminates the stationary needle valve type bleed orifices. Bleed orifices are 3 -now machined into the poppet valves. The new design allows the orifice groove to move out of the seating area and be cleaned when hydraulic fluid passes over it. The old design required the orifice groove to remain stationary where contaminants could collect and plug the opening. (Figures 3 and 4 show the old and new style valve blocks.)

i _ - . . . ~ . _ _ , , _ . _ _ - . .

5.0 COMPUTERIZED DATA BASE Florida Power Corporation is developing a Computerized Data Base to assist in tracking the operating and maintenance history of the Crystal River Unit 3 snubbers.

6.0 CONCLUSION

S

. The snubber design changes, combined with the fluid cleaning process, implemented during the 1983 refueling outage provide a high degree of confidence that the snubbers will function properly over the next fuel cycle.

l l

{

r

_4_

. .. . . . . . = . - _ . . . . . . _ - .-

l

TABLE 1

! DECEMBER 1982 SNUBBER FAILURES MSH 161 RCH 34 RCH 87

- These snubbers failed visual inspection and functional testing in 1982.

.i t

r I

TABLE 2 APRIL 1983 SNUBBER FUNCTIONAL TEST FAILURES

(* indicates failure of visual inspection also)

BSH 15 FWH 132 MUH 42 RCH 63 CFH 13 FWH 140 MUH 46 RCH 64 CFH 15 FWH 144 MUH 47 RCH 65 CFH 16 MSH 149 MUH 48 RCH 66 CFH 17 MSH 159 MUH 49* RCH 67 CFH 18 MSH 162 MUH 51 RCH 68 DHH 17 MSH 163 MUH53 RCH 69 DHH 18 MSH 165 MUH80 RCH 70 DHH 21 MSH 167 MUH 81 RCH 71L DHH 23 MSH 168 MUH 82 RCH 76 DHH 24 MSH 169 MUH 83 RCH 77 DHH 25 MSH 207 MUH 85 RCH 79 DHH 27 MSH 210 RCH 26 RCH 80 DHH 35 MSH 243 RCH 28 RCH 81 DHH 36 MSH 250 RCH 29 RCH 82E DHH 37 MSH 567U RCH 30 RCH 84 DHH 38 MSH 568L RCH 32 RCH 85 DHH 39 MSH 568U RCH 36 RCH 86 DHR 24U MSH 575 RCH 40 RCH 89 DHR 37 MSH 576L RCH 47N RCH 90 DHR 49 MSH581 RCH 47S SWH 483 EFH14L MUH 33 RCH50 SWH 493U EFH 15U MUH 36 RCH 51 SWH 493L EFH 15L MUH 37 RCH 52 EFH 94 MUH 38 RCH54 FWH 122 MUH 39 RCH 55 FWH 123 MUH 40 RCH 60 FWH 131 MUH 41 RCH 61

w Fluid Port 0-Rin

-Reservoir Body Sightglass Housing - -

g Weld 2 - i 1. I E III I al . .d -Nut Q .

" " ^ "

O-Ring jS hss

~~'

rd' -

~

Mounting Bolt and  ; g-Fluid Connection Figure 1.- Old Style Reservoir.

Sightglass - =

Misaligned nut on inside of reservoir has caused fluid leaks at the interface between the reservoir body and sightglass.

This has been resolvd by threading the fluid port and eliminating the nut.

k 1

I.

l i

i

r. t:

i .. . ..  % -

- 10 3 -

g _r  ;

J Outside Reservoir Inside Reservoir

Figure 2a.

Snubber fill lineup

_ X Transfer valve

\

Shut-off v Shut-off hvalveB dvalveA Ef

~'

Valve 1 ick Discannect Flow p C meter 7' Fittings rN V V 11tey f x --

7N .) I Valye 4 heservoirVent

• ** ~ ~

2.---- Snubber Valve Block Valve 2

^

Snubber Cylinder Figure 2b.

Tank A Fluid recirculation lineup Tank B l-Transfer Valve

[ Shut-off Shut-off [ h Valve A

{

m' "9 i Disconnect Flow alv. 1 Fitt qgs Meter -

Filte I

g - --

Neservoir Vent Valve 4 Valve 3 -

' Snubber Valve Block

~

Valve l - Snubber Cylinder I

'I Figure 3 Old Style Valve Block 4

1 i

I 1

Bleed Orifice Needle. Valve Groove

y /

/ /

lM

- - 11 Lll l[ ] [;j;j

[

C f WL / \ Ilf

" ^T I ooR j o. a --

.bbbON,

" ] IIIEIIlllfll i,o g of koo I.

L_

Cylinder Fluid Inlet Fitting Poppet Valve.

Spring Reservoir Port l

l 1

t'

Figure 4 New Style Valve Block Fill Port Plug Fill Port

..=p

[ .

- - =

Cylinder Fluid n et Fitting Bleed Orifice

],. Groove

'" ' p,, m i r- I

. .. , , j ooA- l I eo o o l

, e 0 ,_ __ _ - _ _ _ ,Q, l) f;' i

'h_ h_

((__ _ o

! g f,1 00 o- 9oo gm , _ . , --

1-  ;  ;

[

i ,

i .3 I Poppet Valve "

i, Inte'rnal

[ Ball-Check Balve Spring i Reservoir Port l

O

.h

coa 1%

oo

, - 4g e Vp itQf!

en $hhd

%b[ wlu f!

m >-

ca -

M ' e$

C Power coaroaarios

& M g s,

' fr May 31,1983 ~0 In?

3F-0583-22

• OU

.. -g N 3L' Mr. James P. O'Reilly Regional Administrator, Region II U.S. Nuclear Regulatory Commission Office of Inspection & Enforcement 101 Marietta Street N.W., Suite 2900 Atlanta, GA 30303

Subject:

Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72 Licensee Event Report No.83-021

Dear Mr. O'Reilly:

Enclosed is Licensee Event Report 83-021/03L-0 and the attachments which are submitted in accordance with Technical Specification 6.9.1.9.

Should there be any questions, please contact this office.

Sincerely,

/

1

/ /

G. R. Westafer Manager, Nt clear Licensing and Fuel Management BCT/ caw Enclosure cc: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555 0ft/lClAbC.

W A1 General Office 320 Trurty-fourth street soutn . P O. Box 14042. St. Petersburg. Fiorda 33733 813-866-5151 /