ML20085M525
| ML20085M525 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/14/1976 |
| From: | Swart F PUBLIC SERVICE CO. OF COLORADO |
| To: | Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV), NRC OFFICE OF MANAGEMENT AND PROGRAM ANALYSIS (MPA) |
| Shared Package | |
| ML20085M528 | List: |
| References | |
| LER-75-016A, LER-75-16A, P-76233, P-76234, NUDOCS 8311080621 | |
| Download: ML20085M525 (14) | |
Text
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REPORT DATE: Octoher 14, 1976 UNUSUAL EVENT 75/16A Page 1 of 5 OCCURRENCE DATE: Detober 9, 1975 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O., BOX 361 4
PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/75/16A -
Final IDENTIFICATION OF OCCURRENCE:
Apparent f ailure of the control system for "C" circulator high pressure separa-tor resulted in flooding of the high pressure separator.
In discussion with the Nuclear Regulatory Commission on October 9,1975, this was identified as an unusual event per section 7.6 of the Technical Specifica-tions , paragraph (C) 2, Non-Routine Reports. .
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 Pressure 2,700 psig Temperature 1,100 *F Flow 40,000 #/hr.
Primary Coolant Pressure -0.4 psig Tempe ~rature 104 *F Core Inle't 106 *F Core Outlet-Flow 42,000 #/hr.
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UNUSUAL EVENT 75/16A Page 2 of 5 DESCRIPTION OF OCCURRENCE:
On August 30,'1975, with "C" helium circulator operating at 4,000 rpm on the Pelton wheel drive, the reactor operator called the Results Department to re-port "C" high pressure separator flow was high.
Results Department personnel reported to the control room and found the reac-tor operator had placed HC-2176 ("C" circulator main drain valve controller) in manual and to the full open position. (See attached drawing for schenatic of controls.)
Results went to check operation of PCV-2176 ("C" circulator main drain valve) and PDC-2176 local controller. Results also verified that LV-21304 ("C" high pressure separator drain valve was open and controlling level. PDV-2176 was full open and the setpoint on PDC-2176 was at -5 AP (equivalent to 3 psi or less from current to pneumatic converter, XEP-2176), which is a full open sig-nal.
The air line from the XEP output (s e tpoint for PDC-2176) was leaking. The air line was repaired and PDV-2176 was then manually operated f rom HC-2176 in the control room and after satisfactory operation, was placed in " auto".
The high pressure separator level and flow were controlling near normal.
Approximately twenty minutes later "C" high pressure separator level began to rise. The reactor operator placed HC-2176 in manual and drove the output to " fully open" signal for PDV-2176. The high pressure separator level rose to 60", and the buffer-mid-buffer measurement was re.duced to a slightly posi-tive pressure.
This represented a flooded condition which persisted for about five minutes before the reactor operator manually tripped "C" circulator.
Since an increase in PCRV moisture level was observed, "D" circulator speed was increased to 4,000 rpm and the purification system flow was increased to 120 ACFM to remove the moisture and maximize system cleanup rate.
APPARENT CAUSE OF OCCURRENCE: Design Unusual Service Cond.
Including Environment bbnufacture Component Failure Installation /Const. Other (specify)
Operator A
X Procedure
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- - V UNUSUAL EVENT 75/16A Page 4 of 5 APPARENT CAUSE OF OCCURRENCE (continued): .
It was first believed that a control offset signal was generated by a failure of the pneumatic low selector. A manual regulator in the system, set at 12
's psig (equivalent to a 25% open position on PDV-2176) supplies an input to the low selector to prevent the main drain valve from going beyond 75% shut. How-ever, no failures could be found to support this supposition. ,
ANALYSIS OF OCCURRENCE:
Analysis indicated that the high pressure separator flooding probably occurred during the manual stroking of PDV-2176 with the "C" circulator operating at 4,000 rpm. The valve was stroked af ter repairs were made on the broken air line to the XEP. Although PDV-2176 is a fail-open valve, a control signal of fset could have caused the valve to fail shut. This could cause the high pressure separator to flood.
A subsequent problem with IC nigh pressure separator level control has been discovered. An investigation identified the problem as being in the main drain to buf fer helium dif ferential pressure co'ntroller (PDT-2176-1 attached sketch).
This transmitter output would " lock up" in its minimum ouput signal position A if the buf fer to main drain dif ferential pressure was suf ficiently disturbed.
The minimum signal from the controller force the main drain valve to its mini-mum opening cad ther~efore forces additional water up the circulator shaf t.
This additional water cust go to either the high pressure separator or into the primary coolant. It is believed the main drain controller malfunction was the cause for flooding circulator 1C high pressure separator.
CORRECTIVE ACTION:
The low selector was recoved, disassembled, inspected, and cleaned since failure of this component could be the only wa9 PDV-2176 could have shut. No problems of any kind were found with the pneumatic low selector. The main drain con-trol system and valve were completely checked out and operated under simulated conditions for all inputs. The system operated correctly as designed. LV-21304, high pressure separator drain valve, was observed to be operating properly.
The main drain differential pressure transmitter manufacturer has supplied a A procedure to calibrate and align the instrument. This will prevent the lockup of the ins trument output. The instruments controlling the main drain valve on all four circulators have been checked and correctly calibrated and aligned.
No further carrective action is anticipated or required.
. 4 FAILURE DATA /SIMILAR REPORTED OCCURRENCES:
None -
PROGRAMMATIC IMPACT:
None
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UNUSUAL EVENT 75/16A Page 5 of 5 CODE IMPACT:
None -
's Submitted by: -
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- 11. W. Hillyard/, Jr. /
Technical Services Supervisor Reviewed by:
-f o c-rTLLL L 1 IMGM H. Larry Br h Sup e rint ende nt. , Nuclea c Production Approved by: _.?g o , J< a a.s Ffederic E. Svart Nuclear Production Manager O
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,s 'public Service Company ?Oderrde P. O. Box 361, Platteville. Colorado 80651
, y October 14, 1976 Fort St. Vrain g$/ ,@ [Qg',-g,Q ,
i Unit No.1
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Nuclear Regulatory Commis (sibt') Y Mr. E. Morris Howard, Dir G[t OI$/
Region IV Office of Inspection and Enforcement Suite 1000 j Arlington, Texas 76012
- REF: Facility Operating License No. DPR-34 Docket No. 50-267
Dear Mr. Howard:
Enclosed please find a copy of Unusual Event Report No. 50-267/
75/16A, Final, submitted per the requirements of the Technical Speci-fications.
Also, p' lease find enclosed one copy of the Licensee Event Report for Unusual Event Report No. 50-267/75/16A, Final.
Very truly yours, d& (.N%
Frederic E. Swart Nuclear Production ibnager FES/alk cc: Mr. Roger S. Boyd
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NAME PHONE:
, - - - . . - . . - _ , .a.- ._..,____,,_--_.--....?***.'
.R$ PORT DATE:
O October 14, 1976 >
UNUSUAL EVENT 75/16A OCCURRENCE DATE: '
October 9, 1975 !
FORT ST. VRAIN NUCLEAR CENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 8'0651
. REPORT No. 50-267/75/16A -
Final IDENTIFICATION OF OCCURRENCE:
Apparent failure of the control system for "C" circulator high pressure separa-tor resulted in flooding of the high pressure separator.
In discussion with the Nuclear Regulatory Commission on October 9,1975, this was identified as an unusual event per section 7.6 of the Technical Specifica-tions, paragraph (C) 2, Non-Routine Reports.
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 W Jart Pressure 2,700 psig Temperature 1,100 'F s
Flow 4'O,000 #/hr.
Primary Coolant Pressure -0.4 psig Rmperature 104 *F Core Inlet 106 *F Core Outlet Flow 42,000' f/hr.
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UNUSUAL EVENT 75/16A Page 2 of 5 DESCRIPTION OF OCCURRENCE:
On August 30, 1975, with "C" helium circulator operating at 4,000 rpm on the Pelton wheel drive, the reactor operator called the Results Department to re-port "C" high pressure separator fl6w was high.
Results Department personnel reported to the control room and found the reac-tor operator had placed HC-23 76 ("C" circulator main drain valve controller) in manual and to the full open position. (See attached drawing for schematic of controls.)
Results went to check operation of PCV-2176 ("C" circulator main drain valve) and PDC-2176 local controller. Results also verified that LV-21304 ("C" high pressure separator drain valve was open and controlling level. PDV-2176 was full open and the setpoint on PDC-2176 was at -5 AP (equivalent to 3 psi or less from current to pneumatic converter, XEP-2176), which is a full open sig .
nal.
The air line from the XEP output (setpoint for PDC-2176) was leaking. The air line was repaired and PDV-2176 was then manually operated from HC-2176 in the control room and af ter satisfactory operation, was placed in " auto".
The high pressure separator level and flow were controlling near normal.
Approximately twenty minutes later "C" high pressure separator level began to rise. The reactor operator placed HC-2176 in manual and drove the output to " fully open" signal for PDV-2176. The high. pressure separator level rose to 60", and the buffer-mid-buffer measurement was reduced to a slightly posi-tive pressure.
This represented a flooded condition which persisted for about five minutes before the reactor operator manually tripped "C" circulator.
Since an increase in PCRV moisture level was observed, "D" circulator speed was increased to 4,000 rpm and the purification system flow was increased to 120 ACFM to remove the moisture and maximize system cleanup rate.
APPARENT CAUSE OF OCCURRENCE: Design Unusual Service Cond.
Including Environment:
Manufacture Component Failure Installation /Const. Other (specify)
Operator ,
1
^ X Procedure
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. . O O UNUSUAL EVENT 75/16A Page 4 of 5 APPARENT CAUSE OF OCCURRENCE (continued):
It was first believed that a cersrol offset signal was generated by a failure of the pneumatic low selector. A manual regslator in the system, set at 12 .
h psig (equivalent to a 25% open position on PDV-2176) supplies an input to the low selector to prevent the main drain valve from going beyond 75% shut. How-ever, no failures could be found to support this supposition. .
ANALYSIS OF .
OCCURRENCE:
Analysis indicated that the high pressure separator flooding probably occurred during the manual stroking of PDV-2176 with the "C" circulator operating at 4,000 rpm. The valve was stroked after repairs were made on the broken air line to the XEP. Although PDV-2176 is a fail-open valve, a control signal offset could have caused the valve to fail shut. This could cause the high pressure separator to flood.
A subsequent problem with IC high pressure separator level control has been discovered. An investigation identified the problem as being in the main drain to buffer helium dif ferential pressure controller (PDT-2176-1 attached sketch).
This transmitter output would " lock up" in its minimum ouput signal position A if the buffer to main drain differential pressure was sufficiently disturbed.
The minimum signal from the controller forces the main drain valve to its mini- _
mum opening and ther'efore forces additional water up the circulator shaft.
This additional water must go to either the high pressure separator or into the primary coolant. It is believed the main drain controller malfunction was the cause for flooding circulator 1C high pressure separator.'
CORRECTIVE ACTION:
The low selector was removed', disassembled, inspected, and cleaned since failure of this component could be the only way PDV-2176 could have shut. No problems of any kind were found with the pneumatic low selector. The main drain con-trol system and valve were completely checked out and operated under simulated conditions for all inputs. The system operated correctly as designed. LV-21304, high pressure separator drain valve, was observed to be operating properly.
The main drain differential pressure transmitter manufacturer has supplied a A procedure to calibrate and align the instrument. This will prevent the lockup of the instrument output. The instruments controlling the main drain valve on all four circulators have been checked and correctly calibrated and aligned.
No further corrective action is anticipated or required.
FAILURE DATA /SIMILAR REPORTED OCCURRENCES:
None PROGRAMMATIC IMPACT: .
None
. I 1 l
1 ___--__--______--._-----.--------.--_--.--_____o
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~
. . UNUSUAL EVENT 75/16A Page 5 of 5 CODE IMPACT:
None s
Submitted by: - s,r - 't<
/ - '.
H. W. Hillyar#, Jr. /
Technical Services Supervisor Reviewed by: LOM H. Larry Br$ ,
Superintenddnt, Nuclear Production I
f Approved by: _u , d , s-n
.Ffederic E. Swart .
Nuclear Production Manager S
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P. O. Box 361, Platteville, Colorado 80651
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tC , A-October 14, 1976
([(, *$$0 gg%F Fort . St. Vrain T
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.<x Unit No. 1 P-76234 yg.g Office of Information & Program Control U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Enclosed please find a copy of Unusual Event Report No. 50-267/ 75/16A, Final, and the Licensee Event Report for this unusual event.
Sincerely, H. W. Hil yard, Jr.
Technical Services Supervisor Fort St. Vrain Nuclear Generating Station HWH/alk
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