ML17208A842

Forwards IE Info Notice 80-20, Loss of Decay Heat Removal Capability at Davis-Besse Unit 1 While in Refueling Mode. No Response Required

ML17208A842
Person / Time
Site:	Turkey Point, Saint Lucie
Issue date:	05/08/1980
From:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:	Robert E. Uhrig FLORIDA POWER & LIGHT CO.
References
NUDOCS 8007240206
Download: ML17208A842 (10)

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0-335, 50-38 50-250, 50-251 UNITED STATES NUCLEAR REGULATORY COMMISSION REGION II 101 MARIETTA ST., N.W., SUITE 3100 ATLANTA,GEORGIA 30303 SHAY 8 1980 Floiida Power and Light Company Attn:

R. E. Uhrig, Vice President Advanced Systems and Technology P. 0.

Box 529100 Miami, Florida 33152 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.

I Sincerely, James P. O'Reilly Director

Enclosures:

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IE Information Notice No. 80-20 2.

List of Recently Issued IE Information Notices 8007240 206

hfAY g )gag Florida Power and Light Company cc w/encl:

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M. Methy, Plant Manager Post Office Box 128 Ft. Pierce, Florida 33450 Nat Meems, Assistant l}A Manager Post Office Box 128 Ft. Pierce, Florida 33450 H. E. Yaeger, Plant Manager Post Office Box 013100 Miami, Florida 33101

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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT VASHINGTONs D C

20555 SSINS No.:

6870 Accession No.:

8002280671 May 8, 1980 IE Information Notice 80-20 IOSS OF DECAY HEAT REMOVAL CAPABILITYAT DA REFUELING MODE 1 WHILE IN A a

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 Ioop 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 1P and 1N; Emergency Diesel-Generator No. 1; 4.16 KV Essential Switchgear Bus Cl; 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 1 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 -'igh Radiation; Level 2 - High Pressure Injec-tion; Level 3 - Low preaanre Injection>'Level 4 Containment Spray; add'

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 Ievel 3 aligned the Decay Heat Pump No.

2 suction to the Borated Mater 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 s'ingle 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

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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'ppropriate NRC Regional Office.

Enclosure:

Davis-Besse Event of April 19, 1980

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DAVIS-BESSE ZVENT OP APRIL 19 1980 STATUS OF DAVIS<<BESSE I PRIOR TO LOSS OF POWER TO BUSSES E-2 AND F-2:

1.

Refueling mode with RCS temperature at 90 F and~evel slightly below vessel head flange.

Head detensioned with bolts in p1pce.

Manway cover on top of OTSG removed.

agon tubing attached to lower vents of RCS hot leg for RCS level indication.

Decay heat loop 2 in service for RCS coiling.

t 2.

Allnon-nucleaz instrument (NNI) power and Static Voltage Regulator YAR supplied from X3.8 KV Bus B via HBBF2.

13.8 K Bus h energized but not connected.

RPS and SFAS Channels 1 and 3 being supplied from VAR.

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+uipment Out of Sexvtc a.

Source Range Channel 2 - Suzveillance 1

b.

Emergency Diesel Generator 1 - Maintenance.

c Decay Heat Loop 1 - Maintenance.

4, Brea'kezs foz containment spray and HPI pumps racked out.

8 UENCE OF EVENTS 2:00 p.m.

Loss of power to Busses E-2 and F-2 (non-essential 480 VAC)

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CAUSE/COMMENTS Ground short on 13.8 KV breaker HBBF2 which caused breaker to open.

This interrupted power to busses E-2 and 7-2 which were supplying all non-nucleaz 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.

2'02 poRe 2 33 porno SFAS Level 5 (recizcu-Two out of fouz logic tripped upon loss lation mode) actua-of Busses E-2 and 7-2.

Actuation caused tion.

ECCS pump suction valves from containment sump to open and ECCS pump suction valves from Borated Water Storage Tank to close During valve travel times,'ravity flaw path existed from BWST to containment sump.

Decay Heat (low Operator turned off only operating DH

- pressure safety in-pump to avoid spillage of RCS water to

)ectiqn) flow secured containment via the tygon tubing for RCS.

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'evel indication and open SG -manway.

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Partial restozatLon of power Power to Bus E-2 and SFAS channe1s 1 and 3

restored along with one channel of NNI~

This restored all essential power for ECCS-1

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2 2:44 p.m.

. Attempt to reestab-lish DH flow CAUSE/CO%ANTS Started DH pump 1-2 then stopped it when it was determined that air was

$ n suction line.

Pump secured to prevent damage.

3e 34 p e'me Source Range Channel 2 energized.

4:00,p.m.

, to 4:06 'p.m.

Restoration of Busses Busses restored sequentually as efforts (480 VhC) F-2, F-21, progressed to isolate ground fault.

F-22, and F-23 4:25 p.m, 4:46 p.m.

DH flow restored Containment sump pump breakers opened DH pump 1-2 started after venting.

RCS temperature at 170 F. DH flow bypassing gao$ pd

. Xnnote TC'e being taken and maximum 0hZ.

Precautionary measure to assure containment sump ~at~r from BtdtST remained im containment.

Incoze TC's range from 161 to 164 Z.

5:40 p.m.

Computer returned to Incorc TC's range from 158 to 160 F.

service.

6:24 p.m.

9:50 p.m, DH flow directed through cooler Power completely restored RCS cooldown established at less than 25 F per hour.

RCS temperature at 150 F.

range from 15l to 158oF RCS temperature at approximately 115 F.

STATUS OF DAVIS-BESSE 1 AFTER RECOVERY FRY LOSS OF POWER TO BUSSES E-2 AND F 2:

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1.

Refueling mode with RCS temperature at 115 F and level slightly below vesse1 head flange.

Head detcnsioned with boles in place.

Hanway cover on top of OTSG removed.

Tigon tubing attached to lower vents of RCS hot leg for RCS level indication.

Decay heat loop 2 in service for RCS cooling.

2.

Bus Vr2 being supplied from )3.8 KV Bus h via breaker HAAE2 <<nd Bus F 2 being supplied from 13.8 iW Bus B via breakez HBBF2.

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Decay heat loop fQIad,'11 tags clear.

Haintenance work restricted so restoration of system vi11 be less than two hours.

I 4e ECCS pump sue tion valves (DH-9h and DH-9B) from containment sump closed and breakers racked out.

This villprevent the suction of air into the decay I

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heat loop during a level 5 sctuat1on (recirculation mode) when there is no water in the sump.

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Equipment Out of Service.

Emergency Diesel Generator 1 - maintenance 6.

Breakers for containment spray end HPI pumps racked out.

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IE Information Notice No. 80-20 May 8, 1980 RECENTIY ISSUED IE INFORMATION NOTICES Enclosure Information Notice No.

Subject Date Issued Issued To 80"20 80"19 Ioss of Decay Heat Removal Capability at Davis-Besse Unit 1 While in a Refueling Mode NIOSH Recall of Recircu-lating-Mode (Closed-Circuit)

Self-Contained Breathing Apparatus (Rebreathers) 5/8/80 5/6/80 All holders of power reactor operation Iicgnses or construc-tion permit All holders of a power reactor OL, Research Reactor License, Fuel Cycle Facility License and Priority I Material License 80-18 80-17 Possible Weapons Smuggling 5/5/80 Pouch Potential Hazards Associated 5/5/80 With Interchangable Parts On Radiographic Equipment All power reactor facilities with an OL, fuel fabrication and processing facilities and Materials Priority I licensees (processors and distributors)

All radiography Licenses 80-16 80-15 80-14 80-13 80-12 80-11 Shaft Seal Packing Causes Binding In Main Steam Swing Check And Isolation Valves Axial (Longitudinal)

Oriented Cracking In Piping Safety Suggestions From Employees General Electric Type SBM Control Switches - Defective Cam Followers Instrument Failure Causes Opening of PORV and Block Valve General Problems with ASCO Valves in Nuclear Application "Including Fire Protection Systems 4/29/80 4/21/So 4/2/so 4/2/80 3/31/80 3/14/80 All power reactor facilities in your Region with an OL or CP All Light Water Reactor Facilities holding power reactor OLs or CPs All power reactor facilities with an OL or CP All light water reactor facilities holding power reactor OLs or CPs All holders of power reactor OIs and CPs All holders of Reactor OL, CP, fuel fabrica" tion and processing facilities