ML20085L698
| ML20085L698 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/18/1975 |
| From: | Brey H PUBLIC SERVICE CO. OF COLORADO |
| To: | Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20085L694 | List: |
| References | |
| RO-50-267-75-5, NUDOCS 8311020349 | |
| Download: ML20085L698 (14) | |
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O pubHe Service Company of Odendo
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\. P. O. Box 361, Platteville, Colorado 80651 5
April 18, 1975
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Mr. E. horcis Howard, Director ,
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Uucicar Regulatory Cornission Region IV j.( fpg2O/g7g /~* j7
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Office of Inspection & Enforcement . 611 Ryan Plaza Drive # 6.)[3 /)'/ b Suite 1000
- Arlington, Texas 76012 fd
Dear Mr. Howard:
REF: Facility Operating License ho. Drn-3i4 Docket No. 50-267 Enclosed please find a copy of Unusual Event Report No. 50-267/75/5, preliminary, submitted per the requirements of the Technical Specifications. Very truly yours, t .Mw m II. Larry Brey Superintendent-Operations Fort St. Vrain Nuclear i Generating Station j
!!LB:il cc: Mr. Angelo Giambusso .
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i Letter Reports Reporta Reports _ San Francisco operations Office ERDA i 1333 Broadway e d Oakland, California 94612
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- P. O. Box 8160S San Diego, California 92138 Barbara Blick 1 1 1.
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D. Rodgers 1 E.11111 1 F. Mathie - 1 ) W. Hillyard 1 1 D. Alexander 1 J. Liebolt 1 ( K. Stannard 1 KRC, Director of Regulations, Washington,D.C. 20545 - ,1
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. REPORT DATE: April 18, 1975 UNUSUAL EVENT OCCURRENCE DATE: March 23, 1975 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/75/5 ;
Preliminary I
^
f IDENTIFICATION OF OCCURRENCE: A situation occurred while testing the helium circulator backup be,aring l water system which resulted in."A" and "B" circulators automatically tripping off and the buffer indication on "C" and "D" circulators to drop resulting in operator action to set the brake and seal. This is identified as an linusual Event, per Technical Specification ' definition AC 7.6c.3. i CONDITIONS PRIOR
! TO OCCURRENCE: _, Steady State Power Routine Shutdown Hot Shutdown Routine L'oad Change i X Cold Shutdown Other (specify)
Refueling Shutdown Routino Startup i The major plant parameters at the time of the event were as follows: I Power .RTR. O MWth Elcet. O MWe Secondary Coolant' Pressure N/A~ psig Temperature N/A ,
*F Flow N/A -#/hr.
Primary Coolant ~ Pressure 85~ psig Temperature'
~
200 *F Core Inlet
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200'- *F Core Outict Helium circulator self-turbining 4 e e a v- , ~u-, 4--- n v w -e -= , ,
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. DESCRIPTION OF ,
OCCURRENCE: ' The Emergency Feedwater header had been isolated via V-21453 in order to repair the pressure control for vcive PV-21105. Upon completion of this repair, pressurf =ation of the emergency feedwater header was initiated by slowly opening.the isolation valve V-21453. The following events then occurred: -
- 1. "A" and "B" helium circulators tripped un negative buffer /mid buffer.
- 2. HV-2366-1 and 2 changed froa supplying buffer to the helium circulators via the purified helium header to the helium storage system.At a PCRV pressure of 85 psig helium density is barely sufficient to place the purified helium compressors in service. Loss of a major helium user such as "A" and "B" buffers caused the purified helium compressor to trip and the automatic controls switched to the high pressure helium storage system.
- 3. The bearing water surge tank pressure in both loops went up to 140 psi, causing the buffer return flows to drop to .0 on the remaining circulators. "C" buffer vent 10" negative but didn't trip. "D" buffer dropped low but didn't go negative.
The operator set the brake and seal on both of these circulators because of the return flow being low. The Rix recovery compressors were then set up to vent to atmosphere in order to get the bearing water surge tank pressi. down. When surge tank pressure equalled reactor vessel pressure C" and "D" helium circulators were re-started. APPARENT CAUSE OF OCCURRENCE: X Design Unusual Service Cond. Including Environment Manufacture Component Failure Installation /Const. Other (specify) Operator Procedure The increased pressure in the surge tanks due to the water inflow displaced helium from these tanks thereby increasing the buffer helium recirculation suction pressure. This reduced the buffer return flow from the helium circulators causing them to trip an buf fer/mid-buf fer.
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pgge 3 ANALYSIS OF ' OCCURRENCE: It appears that PC-21105 failed to control as did PCV-2191 and PCV-2192. With these valves not operating while V-21453 was being opened, there was no control of the Backup bearing water flow. The large amount of flow into the bearing 1102 surge tanks causes a displacement of the helium from the surge tanks (due to a level increase). This helium flows back the equilization line to the suction of the buffer helium recirculators thus reversing the buffer helium flow from the helium circulators. This is the loss of buffer /mid-buffer and. consequently a trip. The icvel increase would not occur under normal circumstances because when the normal bearing unter pumps are tripped, (and thus backup bearing water initiated), the feedforward signal from the control system opens the surge tank drain valves. This climinctes the possibflity of high rate of change in the surge tank level, and thus the reduction of return helium f, low from the circulator. CORRECTIVE ACTION: . The ability of the backup bearing water control systems to properly respond is currently undergoing review and testing. FAILURE DATA / SIllILAR REPORTED OCCURRENCES: , Unusual Event No. 50-267/75/3. A review of the failure of PV-21105-1 in the backup bearing water system which occurred on 4/10/75 is attached to this report for your information. , PROGRAM'!ATIC TMPACT: None CODE IMPACT: None Recommended: LW Cu H.' Larr'y Bre)\ i Superintendent-Operations Fort St. Vrain Nuclear Cencrating Station f
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Approved: _ a [t_ d .c _ '
- t. W , Ik Fr deric E. Swart perintendent huclear Production
'ublic Service Company of Colorado
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O ! O - Page 5 FAILURE OP pV21105-1 DESCRIPTION OF , OCCURRENCE: . On April 10, 1975, while testing the helium circulator backup bearing water system a pressure control valve (PV31105-1) experienced a mechanical failure requiring shutdown of the emergency feedwater header and' 1oss of the backup bearing water system. , This valve is a pneucatically operated Valtek Mark Two valve with 1" internal trim. The failure occurred in the following manner: Emergency Fecdwater 11cader pressure pushing up against the valvo plug was approximately 4,000 psig. The yoke clamp failed, causing the plug assembly to push upward lifting the operator assembly, packing spacers and packing retainer (not shown in attached drawing). This allowed high pressure water to blow out of the st'em guide area. ANALYSIS OF OCCURRENCE: Examination of the yoke clamp revealed a fractured area. This fracturpd , area appeared to have existed for a considerable time, as evidenced by discolored surfaces in the fracture. CORRECTIVE ACTION: A manufacturer's representative investigated the failure on April 11, 1975. Damaged parts were replaced and this valve (PV-21105-1) along with two other Valtek valves (PDV-2191-1, 2192-1) were disassembled and incpected. All yoke clamps were dye penetrant checked. The pressure containing components on PV-21105-1 were also radiographed or dyc penetrant checked. As a follow-up a review of the piping and valves making up this system is in process to verify pressure capabilitics, surge responses, relief valve capacitics, and proper supports and hangers. , l l - c . Jl
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(, d \_s a . Anrf1 18, 1975 UNUSUAL r. VENT REPORT DATE: , OCCURRENCE DATE: Marc _h 2 3, 197 5 FGRT SI. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE CO !PANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT N0. 50'267/75/5 Prelimindry IDENTIFICATION OF _OC.C..U. RRE':CE : A situation occu" red while testing the helium circulator backup bearing water system which resulted in "A" and "B" circulators automatically trippingoff)andthebufferindicationon"C"and"D"circulatorstodrop resulting in operator action to set the brake and seal. This is identified as an Unusual Event, per Technical Specification definition AC 7.6c.3. CONDlTIONS PRIOR Steady State Power Routine Shutdown TO OCCUTMENN._ Hot Shutdown Routine Lodd Change X Cold Shutdeun Other (specify) Refueling Shutdova Routine Startup The rejor plant par,' meters at the tine of the event were as follows: Power RTR. O NWth Elect'. O MWe Secondary Coolant Pressure N/A psig Temperature _ N/A *F Flow N/A #/hr. Primary Coolant Pressure 85 psig Temperature ~200 F Core Inlet
~200 *F Core Outlet Ecliun circulator self turbining 1l 1u -)
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C/ V Page 2 DESCRIPTION OF OCCURRENCr.: The Emergency Teedwater header had been isolated via V-21453 in order to repair the pressure control for valve PV-21105. Upon completion of thin repair, pressurication of the emergency feedwater header was initiated by slowly openin;: the isolat. ion valve V-21453. The following events then occurred:
- 1. "A" and "B" helium circulators tripped on negative buffer /mid buffer.
- 2. HV-2366-1 and 2 changed from supplying buffer to the helium circulators via the purified helium header to the helium storage system.At a PCRV pres.sure of 85 paig helium density is barely sefficient to place the purified.hclium compressers in service. Loss of a naj or helium user such as "A" and "B" buffers caused the purified helium compressor to trip and the automatic controls switched to the high pressure helium storage system.
- 3. The bearing water surge tank pressure in both loops went up to 140 psi, causing the buffer return flews to drop to 0 on the remaining circulators. "C" buffer went 10" negative but didn't trip. "D" buffer dropped low but didn't go negative.
The operator sct the brake and seal on both of these circulators
. because of the return flow being lov. The Rix recovery compressors vere then set up to vent to atmosphere in order to get the bearing water surge t'ank pressurc down. When surge tank pressure equalled reactor vessel pressure "C" and "D" helium circulators were re-started.
APPARENT CAUSE OF OCCURRENCE 1 X Design Unusual Service Cond. Including Environment Manufacture Component Failure Installation /Const. Other (specify) Operator Procedure The increased pressure in the surge tanks due to the water inflow displaced heliun from these tanks thereby increasing the buffer helium-recirculatien suction pressure. This reduced the buffer return flow from the helium circulators causing them to trip on buf fer/mid-buf fer. I c
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(._)\ (V Page 3 ANAINSIS OF OCCUDMi:NCE : It appears that PC-21105 failed to cont rol as did PCV-2191 and PCV-2192. Uith these valves not operating while V-21453 was being opened, there was no control of t he ilackup bearing water flow. The large amount of flow into the bearing I! 3 0 surge tInks causes a displacement of the helium from the surge tanks (due to a level increase). This hellum flown back the equilization line to the suctica of the buffer helium recirculators thus reversing the buf fer helium flow from t he helium circulators. This is the loss of buffer /mid-buffer and consequently a trip. The icvel increase would not occur under normal circumstances because when the ncrmal bearing water pumps are tripped, (and thus backup bearing water initiated), the feedforward signal from the control system opens the surge tank drain valves. This eliminates the possibility of high rate of change in the surge tank level, and thus the reduction of return hellun flow from the circulator. CORRECTIVE ACTION: The ability of the backup bearing water control systems to properly respond is currently undergoing review and testing. FAILURE DATA / SU!II.AR RFP0 U.D OCCGRENCES: Unusual Event No. 50-M7/75/3. A review of the failure of PV-21103-1 in the backup bearing water system which occurred on 4/10/75 is attached to thi.s report for yc ur inforeation. PROCFOJ_'_:IATIC IYPACT: None CODE I! PACT: None Recommended: Lm att<
- 11. 1.arry Brey 1 Superintendent-Operations l Fort St. Vrain Nuclear Cencrating Station /. l l
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Approved: _ _g ,_3 )4. .s .d s. , r . '\ Fr deric E. Swart Saperintendent Nuclear Production fublic Service Company of Colorado
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O ! C' (_) Page 5 i FAILURE OF PV21105-1 e
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[ DESCR1pTION OF [ OCCURRE'CE: 10, 1975, while testing the helium circulator backup bearing water 1 On April experienced a mechanical failure systen a pressure centrol valve (PV21105-1) requiring shutdown of the emergency feedwater header and loss of the backup bearing water system. This valve is a pneucatically operated Valtek >hrk Two valve with 1" internal trin. The failure occurred in the following manner: Emergency Feedvater Hender pressure Thepushing up against yoke clamp failed, the valve causing plug was appraximately 4,000 psig. the plug asscrbly to push upward lif ting the operator assembly,(not shown in atta packing spacers and packing retainerThis allowed high pressure water to blow ANALYSTS OF OCCURRENCE: This fractured Exanination of the yoke cla p revealed a fractured area. ; area appeared to have existed for a considerable time, as evidenced by discolored surfeccs in'the fracture. CORRECTIVE ACTION: - 11, 1975. '
-A manufacturer's representative investigated the failure on Aprilalong with two other (PV-21105-3)
Danaged parts vere replaced and this valvewere disassembled and inspected. All Valtek valves (PDV-2191-1, 7192-1) The. pressure containing components yoke clamps were dye penetrant checked. checked. on PV-21105-1 were also radiographed or dye penetrant As a follow-up a review of the piping anc) valves surgenaking up thisrelief responsos, systen is valve in process to verify pressure capabilitics, . capacitics, and prcper supports and hangers. l 1 a
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