ML20141G137
| ML20141G137 | |
| Person / Time | |
|---|---|
| Issue date: | 04/21/1986 |
| From: | Norelius C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| References | |
| NUDOCS 8604230287 | |
| Download: ML20141G137 (8) | |
Text
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APR 21 1986 l
MEMORANDUM FOR: Edward L. Jordan, Director, Division of Emergency Preparedness and Engineering Response, IE FROM:
Charles E. Norelius, Director, Division of Reactor Projects Region III
SUBJECT:
POTENTIAL DEGRADATION OF RESIDUAL HEAT REMOVAL (RHR) SYSTEM J
l The attached draft of a proposed NRC Information Notice is transmitted to you for your review and action.
We believe that the condition described in the attached draft is generically important to nuclear safety in that it demonstrated that the RHR system can lose pumping capability.
During a refueling outage at Zion Unit 2 both tiains of the Residual Heat Removal (RHR) system lost pumping capability. This occurred when water level, that had been near the hot leg mid-point, dropped, permitting air to enter the RHR suction line, air-binding both RHR pumps. The attached draft informtion notice has been i
developed to inform licensees of this potential problem.
(NOTE:
fou may wish to consult PNO-V-86-12, dated-Narch 28, 1986
Subject:
Loss of Shutdown Cooling At San Onofre, for an additional example of recent RHR system problems.)
For further information please contact J. Suermann (FTS 388-5585), or W. Guldemond (FTS388-5574) of my staff.
14iitifiWsfeed by E.f~GFeessa?
Charles E. Norelius, Director Division of Reactor Projects
Attachment:
Draft of Proposed NRC Information Notice cc w/
Attachment:
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DRAFT IE Information Notice 86- :
DEGRADATIONOFRESIDUALHEATREMOVAL(RHR)
SYSTEM Addressees:
All pressurized water reactor nuclear power plants holding an operating license (OL) or construction permit (CP).
Purpose:
This information notice is provided as a notification of potentially significant problens pertaining to loss of shutdown cooling capability. This notice supplementsBulletin 80-12 and Information Notices 80-20 and 81-09, which discussed similar events.
It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude similar problems from occurring at their facilities.
However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required.
Description of Circumstances On December 14, 1985, during a refueling outage at Zion Unit 2 both trains of the residual heat removal (RHR) system lost pumping capability. This occurred
DRAFT when water level, that had been near the hot leg midpoint, dropped, permitting air to enter the RHR suction line, thus air-binding both RHR pumps. During the G5 minutes needed to restore one RHR pump and reactor vessel inventory, primary coolant temperature increased from 73'F to 87'F.
The drop in water level, attributed to a normal leakage rate of less than 1/4 gallon / minute, was not recognized by the operators. The control room strip chart recorder, which the operators relied on, for the reactor coolant system (RCS) vessel level was connected to a level transmitter; its sensing tap was located in close proximity to the RHR system return line. This spatial cor. figuration may have resulted in the tap being subjected to flow turbulence at half pipe conditions, with potentially adverse effects on level indication. Additionally, no frequency had been established for cross checks between the control room reactor vessel level indication and the temporary (Tygon tube) reactor vessel level indication which was capable of reading lower vessel level values. Additional details are provided in Attachment 1.
Discussion:
Loss of shutdown cooling capability is a significant event.
It is expected that licensees will review the circumstances of this event and take appropriate actions to assure shutdown cooling system operability.
1 No specific action or written response is required by the Information Notice.
If you have any questiuns about this matter, pledse contact the Regional Administrator of the appropriate NRC regional office or this office.
DRAFT Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response i
Office of Inspection and Enforcement Technical
Contact:
John Suermann (312)790-5585 William Guldemond (312)790-5574
Attachment:
Description of Recent Degradation of RHR System at Zion Unit 2 3
DRAFT Zion Unit 2 Event of December 14, 1985 Status of Zion-2 Prior to Loss of Residual Heat Removal (RHR) System 1.
Refueling was completed with Reactor Coolant System (RCS) temperature at 73*F. Approximately 14 weeks had elapsed since the unit was shutdown for refueling. Approximately one-third of the fuel was new and approximately two-thirds had been used in previous cycles.
2.
The head was de-tensioned with the holddown studs in place.
3.
Tygon tubing had been attached for RCS level indication.
4.
RHR pump B was running.
Sequence of Events DRAFT Time Event Cause/Connents 3:20 a.m.
Loss of RHR flow Operator reported no RHR flow on 2FT 972 and 2B RHR pump amps were abnonnally low 3:25 a.m.
RHR pump 28 turned off; No flow, no anips Declared Generating Stations Emergency Plan, Emergency Action Level 12 (GSEP-EAL-12)
(
3:30 a.m.
RHR pump 2A turned No flow, no amps on/off 3:55 a.m.
RHR pump 2A vented Air obtained during vent. No and turned on/off flow, no amps 4:05 a.m.
RHR pump 2A vented No flow, no amps.
and turned on/off Local suction pressure reading 0 psig.
l 2
l
DRAFT Time Event Cause/Connents 4:20 a.m.
Operator switched RHR pump Local suction pressure now suction from RCS Loop A hot reads 20 psig leg to RWST. Reactor vessel level increased to 589' elev.
(i.e. 2' below vessel flange) per control board recorder.
4:25 a.m.
Operator switched suction from Return RHR to normal shutdown RWST to RCS Loop A hot leg (to lineup and ensures RCS vented avoidoverfillingvessel).
4:30 a.m.
RHR pump 2B vented and turned Pump attained rated flow and on amps in 1-11 sainutes.
RCS temperature peaked at 87'F 4:40 a.m.
GSEP-EAL-12 tenninated 4:50 a.m.
RHR pump 2A vented and turned Normal flow and amps.
Pump on start attempt was delayed 20 minutes to prevent exceeding service rating for pump motor on successive start attempts 4:55 a.m.
RHR pump 2A turned off RCS temp. stable at approximately 82'F 3
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