ML20086A069
| ML20086A069 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 05/20/1976 |
| From: | Hillyard H PUBLIC SERVICE CO. OF COLORADO |
| To: | Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20086A058 | List: |
| References | |
| AO-76-011, AO-76-11, NUDOCS 8311110236 | |
| Download: ML20086A069 (1) | |
Text
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I CONTROL 8 LOCK:[_ l l l l l l [PLEASE PRINT ALL REQUIREO INFORMATIDsi) 1 6 iAME UCENSE NUMBER Y o i Ic lo l rl sl vl il 10101-10 10 10 10101-10101 141 111121 of in li l' 7 89 14 15 25 26 30 31 32 CATEGony " ypE T ER$ ooCxET NUMBER EVENT DATE REPORT DATE O 1 CONT l D l I l 7 8 57 58 [I] 59 b_j 60 l 0 l 5 l O l-l 0 l 21 6 l 7l 61 68 l 0 l 5 l 21017l 6l 69 74 l0l1l0l6l7l7l 75 80 EVENT DESCRPTON HE I Unexpected trip of Helium Circulator 1C due to negative buf fer-mid-buf fer differen- l 7 89 80
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3E l tial pressure. Cause was flow blockage buf fer gas return system. Plunged filter l 7 89 80 3E l cleaned. In operable alarm returned to service (A0 76/11) No miemif f enne efface nn l 7 89 80 DE I plant, which was in cold shutdown status. l 7 89 80 3G l ) (A0 76/11A) ! 7 89 ,,,uf 80 E COMPONENT Coof s ton as I si nl Lv_] I zl zl zl ziz Iz 1 Lz_1 l zl zi zl zl tm_J l 7 8910 11 12 17 43 44 47 48 i CAUSE DESCRPTON EE l System complexity; confusion associated with shif t change. l 7 89 80 8I 7 89 SO l DI l l 5 POWER OTHER STATUS oecoVERY oESCMPTON b gd 7 8 1 010 10 l l N/A 10 12 13 l 44 45 l N/A 46 80 l ASE AMOUNT or ACTmTv LocATON or RELEASE DE 7 8 U orLzJ l w/i 9 10 , 11 l 44 IN/A 45 30 I PERSONNEL EXPOSURES NUMBER TYPE DESCNPTON M l Ol 010 l [0] l N/A l 7 89 11 12 13 m PERSONNEL NJURIES NUMBER DESCmPTON DE 10l 0l d l N/A i 7 89 11 12 - SO OFFSITE CONSEQUENCES
@@ l N/A l 7 89 30 j LOSS OR DAMAGE TO FACluTY TYPE DESCmPTON l D3 llj lN/A l 7 89 10 8311110236 760804 a0 N" PDR I&E PNO-76-137 PDR DE l N/A l 7 8, 9 30 ADDITION.:.L FACTORS
@ l (Event Description. cUnl) Discussed indications with ooerator. in deenfl. Al a rm en I 7 89 m
@ l be added on buf fer-mid-buffer dif ferential pressure. l unna e in m M1 M W 't
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O REPORT CATE: January 6,1977 ABNORMAL OCCURRENCE 76/11A Page 1 of 5
' OCCURRENCE DATE: (Determined) May 20, 1976 PORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 REPORT NO. 50-267/ 76/11A Final Supplement IDENIIFICATION OF OCCURRENCE:
On May 10, 1976, during the afternoon shift ch.ange, helium circulator 1C tripped due to negative buffer-mid-buffer differential pressure. Initial indications were that the trip was associated with an approved test in progress. Subsequent investigation has indicated no connection with the test in progress. The trip was therefore unexpected and reportable per the Fort St. Vrain Technical Specifications, Paragraph 2.1(f). CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown Hot Shutdown Routine Load Change I Cold Shutdown other (specify) Refueling Shutdown Routine Startup The major plant parameters at the time of the event were as follows: Power RTR 0 Wth ELECT 0 We Secondary Coolant Pressure 255 psig Temperature 80 'F Flow 31,800 f/hr.
. Primary Coolant Pressure 195. _ psia Core Inlet Temperature 86 'F Core Outlet Temperature 86 'F l Flow * #/h .
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I O ABNORMAL OCCURRENCE 76/11A Page 2 of 5 CONDITIONS PRIOR TO OCCURRENCE (continued): Circulators *1A Self-turbining
*18 Self-turbining
*1C 2,000 RPM
*1D Shutdown l
DESCRIPTION OF OCCURRENCE: With the plant in a cold shutdown condi* ion and primary coolant circulation provided by running helium circulator 1C at 2,000 RPM, circulator 1C tripped. The plant alarm system indicaced that the parameter causing the trip was ab-normal buffer-mid-buffer differential pressure. This trip occurred during the period when the off-going operator was being debriefed by the swing shift relief operator. APPARENT CAUSE OF OCCURRENCE: X Nsign Unusual Service Cond. Including Environment Manufacture Component Failure Ins tallation/ Cons t. Other (specify) I Operator Procedure ANALYSIS OF OCCURRENCE: Refer to attached PI-21-3 for component identification. A check of the re-cordings of circulator auxiliary system parameters revealed that a perturba - tion in the Loop 2 buffer helium return system caused reversal of flow. Since the buffer supply flow continued to be normal, enough reverse flow, across the buffer-mid-buffer pressure dif ferential taps, occurred to cause
-10" water pressure differential and the subsequent trip of the circulator.
It was first thought that the trip was the result of an approved test being performed. Subsequent investigation revealed this was not the case. In addi-tion, the blockage of flow in the buffer return system was discovered in discus-sions with the Supervisor of the Instrument Department. Be i'ndicated that difficulty in re-establishing the tripped circulator to operation was experi-enced because of an inability to obtain return flow with either Loop 2 recir-culator. When the filter (M-21129) down stream of the recirculators was hy-passed by opening V-21742, return flow was re-established without further i difficulty. The filter was later cleaned and returned to service. e
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, ABNORMAL OCCURRENCE 76/11A Page 3 of 5 ,
1 ANALYSIS OF OCCURRENCE (continued): The fact that the circulator return flow reached a value of zero, was dis-cussed with the Reactor Operator on duty. He stated that he had not been svare of the existence of the low flow condition. In subsequent tests of alarm operability, no problems with the circulator low flow alarm could be detected. The setpoint for circulator low flow was observed to be set at a value of 2.5 acfa, which is its proper setting. In addition, the recirculator low flow alarm FAL-2142, had been removed from service due to a previous abnormal operating condition, and was not operable. When M-21129 became plugged, no loop low flow alarm occurred to alert the operator. Although the low flow alarm was out of service, the recirculator standby start was fully operable. The circulator system is complex, and problems involving return flow are hard to recognize with the current system and instrument configuration. The fact l that the operator failed to recognize the trouble was compounded by the pro-l cess of debriefing the of f-going operator while maintaining an awareness of the status of operating equipment, and by the lack of operability of FAL-2142. CORRECTIVE ACTION: This occurrence has been thoroughly reviewed with the operator on duty at the time. The recognition of symptoms, particularly those related to loss o,f recirculation flow, have been reiterated with him in detail. A change notice has been written and approved to install a buffer-mid-buffer A differential pressure alarm. This alarm will alert operators to buffer-mid-buffer problems prior to resching the trip point. No other corrective action is anticipated or required at this time. FAILURE DATA /3IMILAR REPORTED OCCURRENCES: Similar to Unusual Event Report No. 50-267/75/03B, in which two circulators tripped when all buffer gas return flow was stopped causing abnormal buffer-mid-buffer differential pressure. PROGRAMMATIC IMPACT: l l None OODE IMPACT: None
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' . ABNORMAL OCCURRENCE 76/11A j i .' ,
Page 5 of 5 ; 1 l Submitted by: s [ H. N. Hillya ~ Z. / Jr. [ Technical Se ices Supervisor .
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Reviewed by: Mk s . ,
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H. Larry Brey { Superintenden't, Operatiob,s - Approved by: fj n y/ t, federicE. Swart Nuclear Production Manager l I l )}}