ML20085L746

LER 75/003A:on 760209,while Opening Valve on Loop 2 Buffer Helium Recirculation,Loop 1,circulator 1B,tripped.Caused by Check Valve on Helium Supply.Spring Removed from Valve

ML20085L746
Person / Time
Site:	Fort Saint Vrain
Issue date:	05/13/1976
From:	Hillyard H PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085L744	List: ML20085L742 ML20085L746 ML20085L751 ML20085L761 ML20085L767 ML20085L772
References
LER-75-003A, LER-75-3A, NUDOCS 8311020439
Download: ML20085L746 (9)

Text

g UCENSEE EVENT REPgT CONTROL DLOCK:l l l l l l 1 (PLEASE PRINT ALL REQUNID INFORM ATION)

, 1 6 ':

NA E -

LCE**SE NUM91R VE YP  !

7 Oi 89 lelC1/=lslt'l/l 14 I C10l-l Cl Cl Ol CI (I-l 0101 15 14l / l / IF_l dl 16l31 25 28 30 31 32 CAJTCOpv T7pE sO N cc:KET NUMBER EVENT OATE REPORT DATE O 1 CONT l fl Ul 7 8

[(j l L_ l l [] 6l C l-l Ol 2l f-l 7} l [] 2l dl 9 l 7ld* l l Ol6 l/ l 3l 7l6;l 57 53 59 60 61 68 69 74 75 80 EVENT DESCRIPTION 5H!i l Equipment operator was returning a Loop 2 recirculator to service, opened discharge l 7 89 80 DE I valve. toop 1 circulator burrer supply accreased. acactor operator set circulator I 7 89 80 EE I brnka nnd seal but_ circulator trinned. Renorted as Sunnlement A to UE 75/03. I 7 89 80 DE I I 7 89 80 DE I (UE 75/03A) l 7 89 pA;ug 80 E CODE COMPONENT CODE F R VOLATON EE le 181 L8_]

7 89 10 Ivial'lviElYi 12 17 Izl IeI314101 44 Lv_]

11 43 47 48 CAUSE DESCRIPTION DE l Check valve on helium supply to one circulator caused abnormal operation which was l 7 89 80 0 l near unstable condition. Spring was removed f rom check valve. l 7 89 80 8I I STA  % POWER OTHER STATUS ISCOVERY D'SCOVERY DESCRIPTON 8

7 8 9 (fj lol cl Cl l N/A 10 12 13 l

44

[Ud 45 l M/A 46 l

80 ACTMTV CONTENT RELEASED OF RELEASE AMOUNT OF ACTIV.TY E

7 8 9 LzJ Lz;J 10 l NM 11 l

44 l M/A 45 LOCATON OF RELEASE l

80 PERSONNEL EXPOSURES NUMDER TYPE DESCRIPTON DE 1010101 Lz_1 INlA .I 7 89 11 12 13 80 PEASONNEL INJURtES NUMBER DESCR*PTON DE 1010101 i N/A I 7 89 11 12 80 OFFSITE CONSEQUENCES 8 i N/A 7 89 ' l 80 LOSS OR DAMAGE TO FACIUTY TYPE DESCR!PTON

@ [29 10i N /A 7 89 i 80 PUOLICITY 8311020439 760513 1

1 N/A PDR ADOCK 05000267 l 7 89 S PDR gg ADDITIONAL FACTORS DE I l 7 89 80 DE I _

l NAME:  % U S 71 - 75ll, E x l.1455

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. PHONE: .

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REPORT DATE: Mnv 11. 1976 UNUSUAL EVENT 75/03A

.,k SUPPLEMENT r OCCURRENCE DATE: February 9, 1976 Page 1 of 8 FORT ST. VRAIN NUCLEAR GENERATING STATION

• PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 i PLAITEVILLE, COLORADO 80651 REPORT NO. 50-267/75/03A SUP?LEMENT IDENTIFICATION OF OCCURRENCE:

On February 9,1976, while opening a valve on a Loop 2 buffer helium recircu-lator, Loop 1 circulator 1B tripped. This is being submitted as a supplemental report to Unusual Event Report No. 50-267/75/03, dated February 22, 1975.

CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown Hot Shutdown Routine Load Change X Cold Shutdown Other (specify)

Refueling Shutdown Routine Startup The major plant parameters at the time of the event were as follows:

Power RTR 0 MWth ELECT 0 MWe Secondary Coolant Pressure -1,387 psig Temperature _, 217 'F -

5

. Flow 125,000 #/hr.

Primary Coolant Pressure 102 psig Temperature 202 'F Core Inlet 202 *F Core Outlet Flow 59.000 #/hr.

J lA circulator was shutdown,1B circulator was at 3,300 RPM,1C circulator was self-turbining, and 1D circulator was self-turbining.

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UNUSUAL EVENT 75/03A '-

SUPPLEMENT ,

Page 2 of 8 _

i

! e i DESCRIPTION OF OCCURRENCE:

i _.

i Loop 2 circulators 1C and 1D were self-turbining and Loop 1 circulator 1B was operating at 3,300 RPM when the operator was directed to return Loop 2 recircu-lator, C-2106, to service. The recirculator had been shutdown and isolated in an attempt to determine the source of a water leak. The operator opened V-21507 (reference PI-21-3, attached), then slowly " cracked" open V-21380.

' Opening V-21380 allowed helium from 1 1/2" L-21286 to flow into and pressurize C-2106 containment tank. The operator in the control room noted that circula-i tor 1B buffer helium supply flow had decreased to one (1) ACFM and immediately j

reduced speed to self-turbining, initiated the signal to set circulator 1B

' brake and static seal, and via the plant communications system, told the opera-tor to return C-2106 to its previous status. A time delay relay (28 seconds

' 12 seconds) prevents the seal from setting immediately following actuation of i

the brake in order to allow sufficient time for circulator speed to reach zero rpm.

During the 28 seconds time delay, circulator 1B was tripped by the Plant Protection System due to a negative buffer-mid-buffer differential. pressure.

~

APPARENT CAUSE OF OCCURRENCE: X Design t Unusual Service Cond.

Including Environ.

L Manufacture Component Failure Installation /Const. Other (specify)

Operator Procedure ANALYSIS OF

OCCURRENCE

j.

Prior to February 9,1976, circulator IB' buffer hel'ium supply line (l" .L-21122) had been altered by field change notice 2512A/2910, which installed a check valve upstream of HV-2189-3 (reference PI-21-8, attached). This check valve is part of a modification to facilitate opening the circulator mechanical shaft loop mary sealpressure.

with' the bearing water surge tank depressurized to less than_ pri--

Similar check valves were to be installed on the remaining-three circulators, pending completion of tests to determine that the installa-tion would facilitate opening of the mechanical shaft seal.

The check valve (Figure 1) was selected on the basis of; availability at the - '

i plant site. Note' that it is a spring loaded check valve.

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UNUSUAL EVENT 75/03A '

,e SUPPLEMENT i

, Page 3 of 8 l

, ANALYSIS OF

OCCURRENCE (continued)

' . In order to overcome the flow resistance of the check valve, added to 1B

[* circulator, the buffer helium supply pressure had to be increased. This i increase in buffer header pressure was accomplished by raising the purified j helium header pressure, which caused an . increase in bearing water surge tank pressure equal to the increase in buffer header pressure.

] The increase in surge tank pressure decreased the differengial pressure between the circulator helium-water drain and the surge tank. This differ-ential pressure maintains buffer helium return flow to the buffer recircu-lator suction which is at the same pressure as the bearing water surge tank.

j In this occurrence, the operator was directed to return recirculator C-2106o .

i to service. The operator opened V-21507, then slowly " cracked" open V-21380 .

'(reference PI-21-3, attached). Opening V-21380 allowed helium from 1 1/2" L-21286 to flow into _ and pressurize T-2103. The helium flow'into T-2103 re-duced the pressure in 1 1/2" L-21106 and therefore in 2" L-21116, which is

the buffer supply header to the circulators.

The effect of losing buffer helium supply flow to 1B circulator was to de--

l crease the pressure in the buffer seal cavity. The pressure decrease reduced the buffer cavity to surge tank differential pressure, which is the driving

} force for buffer helium return flow. This was followed by a flow reversal

, from the helium water drain to the buffer supply. This flow reversal caused

a negative buffer-mid-buf fer . pressure which was sensed by PDIS-21155, PDIS-21157, and PDIS-21159 (reference PI-21-8, attached). . When this flow reversal

=

4 reached a negative pressure differential of 9" water, the PDIS instrument outputs tripped af ter which the Plant Protective System tripped the circula-tor.

This pressure reduction could not be immediately restored by the purified :

helium header and as a' result, the helium supply flow to IB circulator was j reduced. When the pressure decreased to the point that it could not over- ~

come the check valve resistance,1B circulator buffer helium supply flow de-creased to zero.

l CORRECTIVE ACTION: '

The spring in the check valve was removed, af ter it was determined that the valve. would perform its function without: the _ spring. As a result of removing the spring system operating pressures returned to near normal values. Due -

check valve (without spring) is being addod to the remaining circulator buffer helium supply lines.-

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UNU'SUAL EVENT 75/03A SUPPLMENT '

, Page 4 of 8 F

, CORRECTIVE ACTION (continued):

Approved test, RT-377, was written to verify that, with the spring removed from the check valve and the check valve installed on all circulators, a depressurized recirculator could be returned to service without tripping an operating circulator. This test was performed, with conditions similar to the conditions that existed at the time of this event. The test was success-fully completed on both loops without any circulator trips. No further corrective action is required.

FAILURE DATA /SIMILAR REPORTED OCCURRENCES:

None PROGRAMMATIC IMPACT:

None CODE IMPACT:

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UNUSUAL EVENT 75/03A s EDW!di) -

SUPPLEMENT ,g!

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Page 7 of 8 gl PISTON CHECK VALVES eN-ir g FIGURE 1 w .'

' h HORIZONTAL OR VERTICAL ' J ;bf . J

, 600 lb, 2000 psi CWP (screwed or socket werdMg) (d['3, L

D 600 lb 1440 psi CWP (Flanged) ~ " ~ i 1500 lb',3600 psi CWP g .,

80!!cd Bonnet. Screwed, Socket Welding or Flanged Ends. .

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q STANDARD flATERIA1.S-Dodies and covers are of forced carbon s*# l st:11 or chromium molybdenum F11 alloy steel. Piston disks for 1" g 5122 and smaller are of cobalt chromium tungsten stain!ess steel. }

Piston disks for 1 %

• and larger are of Fil a!!oy steel hardfaced with '

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projection welded Stellite. Spr'*;;is cf stainless steel to insure 'ast pistun-check action. See material specifications on pages 48 & 49. ,_j 2" Fig. 858 Piston Check -

Q DESCRIPTION -

Sins (Inches) %. %. %. M.1,1 % 1 % 2 ~'k D . ..

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Pressure Class Fig. No. Type .s- ,

Ends 838 Horizontal or Vertical Screwed

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rer flanged end ratings, see pace 11.

2" Fig.1038 Piston Check 600 lb. Pr < nary Service . . 3000 psi Hydrostatic SheII Test Pressure ' -

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FIGURE NUMBERS 838-838Yd 858 DIMENSIONS SIZE (faches)  %  %  %  % 1 1% 1% 2  %  % 1 1% 1% 2 A-End to End 3.00 3.00 3.00 3.63 4.25 5.75 5.75 6.50 C-Contact Face to Contact Face E-Center to Top- 6.50 7.50 8.50 9.50 9.50 11.50 2.75 2.75 2.75 3.25 3.75 4.56 4.56 5.13 Weight its. 2 2.25 2.69 3.13 4.19 4.19 4.69 2 2 3.5 5 11 10 14 6.5 11 13 21 26 29 FIGURE NUMBERS 1038-1038Y 1058 DIMENSIONS Size (inches)  %  %  %

% 1 1% 1% 2  %  % 1 1% 1% *:

A-End to End 3.00 3.00 3.00 3.63 4.25 5.75 5.75 6.50 C-Contact Face to Contact Face

gr E-C:nter to Top 8.50 9.00 10.00 12.00 12.00 14.50 2.75 2.75 2.75 3.25 3.75 4.56 4.56 5.13 2.69 3.13 3.13 4.19

__ Weight sbs. 2.5 2.5 2.5 3.5 4.19 4.69 5.5 11 11 15 14 17 24 32 41 69

'Upon materialprolonged esposure of weld.ng and valves to temperatures above 800 F. the carbide phase of carbon steel may be converted es rerommended.

g For Valve End Preparation see paees 50 & St -

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, UNUSUAL EVENT 75/03A .

SUPPLEMENT Page 8 of 8 t

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~~~.. l Submitted by: c _/t f / h #'

H.' W. " Hilly (fd, Jr.

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, 7' Technical $6rvices Supervisor Reviewed by: S.'(U A*d D kw% r.vg H.LarryBryy {

Superintenddnt, Operations Approved by: _. ,.,),, M .mj

• N Ffederic E. Swart Superintendent, Nuclear Production l

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