ML14170A679
| ML14170A679 | |
| Person / Time | |
|---|---|
| Site: | Harris, Brunswick, Robinson  |
| Issue date: | 05/08/1980 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Jackie Jones CAROLINA POWER & LIGHT CO. |
| References | |
| NUDOCS 8007240113 | |
| Download: ML14170A679 (9) | |
Text
A
.~ oUNITED STATES NUCLEAR REGULATORY COMMISSION X
REGION 11 X
101 MARIETTA ST., N.W., SUITE 3100 ATLANTA, GEORGIA 3030 In Reply Refer To:
MAY 8 1980 RII:JPO 50-325, 50-324 50-400, 50-401 50-.02., 50-403 Carolina Power and Light Company ATTN:
J. A. Jones Senior Executive Vice President and Chief Operating Officer 411 Fayetteville Street Raleigh, North Carolina 27602 Gentlemen:
The enclosed Information Notice provides early notification of an event that may have safety significance. Accordingly, you should review the Information Notice for possible applicability to your facility.
No specific action or response is requested at this time; however, con tingent upon the results of further staff evaluation, a Bulletin or Circular recommending or requesting specific licensee actions may be issued.
If you have questions regarding this matter, please contact me.
Sincerely, Director
Enclosures:
- 1.
IE Information Notice No. 80-20
- 2.
List of Recently Issued IE Information Notices 800o7240 83
MAY 8 1980 Carolina Power and Light Company
-2 cc w/encl:
A. C. Tollison, Jr.
Plant Manager Box 458 Southport, North Carolina 28461 R. Parsons, Site Manager Post Office Box 101 New Hill, North Carolina 27562 R. B. Starkey, Jr., Plant Manager Post Office Box 790 Hartsville, South Carolina 29550
SSINS No.:
6870 UNITED STATES Accession No.:
NUCLEAR REGULATORY COMMISSION 8002280671 OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 May 8, 1980 IE Information Notice 80-20 LOSS OF DECAY HEAT REMOVAL CAPABILITY AT DAVIS-BESSE UN1T-1 WHILE IN A REFUELING MODE Description of Circumstances:
On April 19, 1980, decay heat removal capability was lost at Davis-Besse Unit 1 for approximately two and one-half hours. At the time of the event, the unit was in a refueling mode (e.g., RCS temperature was 90F; decay heat was being removed by Decay Heat Loop No. 2; the vessel head was detensioned with bolts in place; the reactor coolant level was slightly below the vessel head flanges; and the manway covers on top of the once through steam generators were removed).
(See Enclosure A, Status of Davis-Besse 1 Prior to Loss of Power to Busses E-2 and F-2 for additional details regarding this event.)
Since the plant was in a refueling mode, many systems or components were out of service for maintenance or testing purposes. In addition, other systems and components were deactivated to preclude their inadvertent actuation while in a refueling mode. Systems and components that were not in service or deactivated included:
Containment Spray System; High Pressure Injection System; Source Range Channel 2; Decay Heat Loop No. 1; Station Battery IP and IN; Emergency Diesel-Generator No. 1; 4.16 KV Essential Switchgear Bus CI; and 13.8 KV Switchgear Bus A (this bus was energized but not aligned).
In brief, the event was due to the tripping of a non-safeguards feeder breaker in 13.8 KV Switchgear Bus B. Because of the extensive maintenance and testing activities being conducted at the time, Channels I and 3 of the Reactor Protec tion System (RPS) and Safety Features Actuation System (SFAS) were being ener gized from only one source, the source emanating from the tripped breaker.
Since the SFAS logic used at Davis-Besse is a two-out-of-four input scheme in which the loss (or actuation) of any two input signals results in the actuation of all four output channels (i.e., Channels 1 and 3, and Channels 2 and 4), the loss of power to Channels 1 and 3 bistables also resulted in actuation of SFAS Channels 2 and 4. The actuation of SFAS Channels 2 and 4, in turn, affected Decay Heat Loop No. 2, the operating loop.
Since the initiating event was a loss of power event, all five levels of SFAS were actuated (i.e., Level 1 - High Radiation; Level 2 - High Pressure Injec tion; Level 3 -
Low Pressure Injection; Level 4 -
Containment Spray; and
IE Information Notice No. 80-20 May 8, 1980 Page 2 of 3 Level 5 - ECCS Recirculation Mode). Actuation of SFAS Level 2 and/or 3 resulted in containment isolation and loss of normal decay heat pump suction from RCS hot leg No. 2. Actuation of SFAS Level 3 aligned the Decay Heat Pump No. 2 suction to the Borated Water Storage Tank (BWST) in the low pressure injection mode. Actuation of SFAS Level 5 represents a low level in the BWST; therefore, upon its actuation, ECCS operation was automatically transferred from the Injection Mode to the Recirculation Mode. As a result, Decay Heat Pump No. 2, the operating pump, was automatically aligned to take suction from the containment sump rather than from the BWST or the reactor-coolant system.
Since the emergency containment sump was dry, suction to the operating decay heat pump was lost. As a result, the decay heat removal capability was lost for approximately two and one-half hours, the time required to vent the system.
Furthermore, since Decay Heat Loop No. 1 was down for maintenance, it was not available to reduce the time required to restore decay heat cooling.
MAJOR CONTRIBUTORS TO THE EVENT:
The rather extended loss of decay heat removal capability at Davis-Besse Unit 1 was due to three somewhat independent factors, any one of which, if corrected, could have precluded this event. These three factors are:
(i) Inadequate procedures and/or administrative controls; (ii) Extensive maintenance activities; and (iii) The two-out-of-four SFAS logic.
Regarding inadequate procedures and/or administrative controls, it should be noted that the High Pressure Injection Pumps and the Containment Spray Pumps were deactivated to preclude their inadvertent actuation while in the refuel ing mode. In a similar vein, if the SFAS Level 5 scheme had been by-passed or deactivated while in the refueling mode, or if the emergency sump isolation valves were closed and their breakers opened, this event would have been, at most, a minor interruption of decay heat flow.
Regarding the extensive maintenance activities, it appears that this event would have been precluded, or at least ameliorated, if the maintenance activi ties were substantially reduced while in the refueling mode. For example, if the maintenance activities had been restricted such that two SFAS channels would not be lost by a single event (e.g., serving Channels 1 and 3 from separate sources), this event would have been precluded. Likewise, if maintenance activities had been planned or restricted such that a backup decay heat removal system would have been readily available, the consequences of the loss of the operating decay heat removal loop would have been ameliorated.
Regarding the two-out-of-four SFAS logic used at Davis-Besse, even under normal conditions, it appears that this type of logic is somewhat more suscep tible to spurious actions than other logic schemes (e.g., a one-out-of-two taken-twice scheme). This susceptibility is amplified when two SFAS channels are served from one source. Consequently, when the source feeding SFAS Channels 1 and 3 was lost, all five levels of SFAS were actuated. As stated
0 IE Information Notice No. 80-20 May 8, 1980 Page 3 of 3 previously, this particular event would have been precluded if SFAS Channels 1 and 3 were being served from separate and independent sources. In a similar vein, this specific event would have been precluded by a one-out-of-two taken twice type of logic that requires the coincident actuation of or loss of power of an even numbered SFAS Channel and an odd numbered SFAS Channel.
Since each LWR can be expected to be in a refueling mode many times during its lifetime, licensees should evaluate the susceptibility of their plants to losing decay heat removal capability by the causes described 'in this Informa tion Notice. No specific action or response is requested at this time.
Licensees having questions regarding this matter should contact the director of the,appropriate NRC Regional Office.
Enclosure:
Davis-Besse Event of April 19, 1980
0e A
Enclosue A DAVIS-BESSE EVENT OF APRIL 19. 1980 STATUS OF DAVIS-BESSE 1 PRIOR TO LOSS OF POWJER TO BUSSES E-2 AND 7-2:
- 1.
Refueling mode with RCS temperature at e9oF and level slightly below vessel head flange. Read detensioned with bolts in place. Manway cover on top of OTSG removed. Tygon tubing attached to lower vents of RCS hot leg for RCS level indication. Decay heat loop 2 in service for RCS cooling.
- 2.
All non-nuclear instrument (NNI) power and Static Voltage Regulator YAR supplied from 13.8 KV Bus B via HBBF2.
13.8 K Bus A energized but not connected.
RPS and SFAS Channels 1 and 3 being supplied from YAP.
- 3.
Equipment Out of Service
- a.
Source Range Channel 2 - Surveillance
- b. Emergency Diesel Generator 1 - Maintenance.
- c.
Decay Beat Loop 1 - Maintenance.
- 4.
Breakers for containment spray and BPI pumps racked out.
SEQUENCE OF EVENTS TIME EVENT 2:00 p.m.
Loss of power to Ground short on 13.8 IC breaker HBBF2 Busses E-2 ad 7-2 which caused breaker to open. This (non-essential 480 interrupted power to busses E-2 and F-2 VAC) which were supplying all non-nuclear*
instrument (NNI) power, channels 1 and 3 of the Reactor Protection System (RPS) and
.the Safety Features Actuation Signal (SFAS),
the computer, and much of the control room indicators.
2:00 p.m.
SFAS Level 5 (recircu-Two out of four logic tripped upon loss lation moda) actua-of Busses E-2 and 7-2.
Actuation caused tion.
BCCS pump suction valves from containment sump to open and ECCS pump suction valves from Borated Water Storage Tank to close.
During valve travel times, gravity flow path existed from RWST to containment sump.
2:02 p m.
Decay Beat (low Operator turned off only operating DB pressure safety in-pump to avoid spillage of RCS water to Jecticn) flow secured containment via the tygon tubing for RCS by ope ator level indication and open SC manway.
2:33 p.m.
Partial restoration of power Power to Bus E-2 and SFAS channels 1 and 3 restored along with one channel of INI.
This restored all essential power for ECCS.
-2 TIYE EVM CAUSE/COYMtNTS 2:44 p.m.
Attempt to reestab-Started DH pump 1-2 then stopped it when lish DHI flow it was determined that air was in suction line.
Pump secured to prevent damage.
3:34 p.m.
Source Range Channel 2 energized.
4:00 p.m.
Restoration of Busses Busses restored sequentually as efforts to
-(480 VAC) P-2, F-21, progressed to isolate ground fault.
4:06 p.m.
F-220 and F-23 4:25 p.m.
DE flow restored DE pump 1-2 starteg after venting.
RCS tempetature at 170 F.DH flow bypassing oh D li a
tcore TC's being taken and maximum 4:46 p.m.
Containment lump Precautionary measure to assure dontainmnt pump breakers sump water from BWST remained In sonltainment.
opened Incore TC's range from 161 to 164 F.
5:40 P.M.
Computer returned to Incore TC's range from 158 to 160F.
service.
6:24 p.m.
DE flow directed RCS cooldown established at less than 25 F through cooler per hour. RCS teaterature at 150 F. Incore TC's range from 151 to 564F.
9:50 p.m.
Power completely RCS temperature at approximately 1150F.
restored STATUS OF DAVIS-BESSE 1 AFTER RECOVERY FROM LOSS OF POWER TO BUSSES E-2 AND F-2!
- 1.
Refueling mode with RCS temperature at 115OF and level slightly below vessel head flange.
Head detensioned with bolts in place.
Manway cover on top of OTSG removed.
Tygon tubing attached to lower vents of RCS hot leg for RCS level indication. Decay beat loop 2 in service for RCS cooling.
- 2.
Bus E-2 being supplied from 13.8 KV Bus A via breaker HAAE2 and Bus 7-2 being supplied from 13.8 EV Bus B via breaker HBBF2.
- 3. Decay beat loop filled, all tags clear.
Maintenance work restricted so restoration of system will be less than two hours.
- 4. ECCS pump surtion valves (DH-9A and DH-93) from containment saump closed and breakers racked out.
This will prevent the suction of air into the decay T3
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2
-3 44:
g-3 heat loop during a level 5 actuation (recirculation mode) when there is no water in the sump.
- 5.
Equipment Out of Service:
Emergency Diesel Generator 1 -
maintenance
- 6. Broakers for containment spray and EPI pumps racked out.
vi..
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00 IE Information Notice No. 80-20 Enclosure May 8, 1980 RECENTLY ISSUED IE INFORMATION NOTICES Information Subject Date Issued To Notice No.
Issued 80-20 Loss of Decay Heat Removal 5/8/80 All holders of power Capability at Davis-Besse reactor operation Unit 1 While in a Refueling Licenses or construc Mode tion permit 80-19 NIOSH Recall of Recircu-5/6/80 All holders of a power lating-Mode (Closed-Circuit) reactor OL, Research Self-Contained Breathing Reactor License, Fuel Apparatus (Rebreathers)
Cycle Facility License and Priority I Material License 80-18 Possible Weapons Smuggling 5/5/80 All power reactor Pouch facilities with an OL, fuel fabrication and processing facilities and Materials Priority I licensees (processors and distributors) 80-17 Potential Hazards Associated 5/5/80 All radiography With Interchangable Parts Licenses On Radiographic Equipment 80-16 Shaft Seal Packing 4/29/80 All power reactor Causes Binding In Main facilities in your Steam Swing Check And Region with an OL or CP Isolation Valves 80-15 Axial (Longitudinal) 4/21/80 All Light Water Reactor Oriented Cracking In Facilities holding power Piping reactor OLs or CPs 80-14 Safety Suggestions From 4/2/80 All power reactor Employees facilities with an OL or CP 80-13 General Electric Type SBM 4/2/80 All light water reactor Control Switches - Defective facilities holding power Cam Followers reactor OLs or CPs 80-12 Instrument Failure Causes 3/31/80 All holders of power Opening of PORV and Block reactor OLs and CPs Valve 80-11 General Problems with ASCO 3/14/80 All holders of Reactor Valves in Nuclear Application OL, CP, fuel fabrica Including Fire Protection tion and processing Systems facilities