ML18139A468

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Forwards IE Info Notice 80-20, Loss of Decay Heat Removal Capability at Davis-Besse Unit 1 While in Refueling Mode. No Response Required
ML18139A468
Person / Time
Site: Surry, North Anna  Dominion icon.png
Issue date: 05/08/1980
From: James O'Reilly
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To: Ferguson J
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
References
NUDOCS 8007240230
Download: ML18139A468 (9)
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Text

{{#Wiki_filter:* i-,-11 REG<,1 _ c," UNITED STATES (~,.~1-NUCLEAR REGULATORY COMMISSION REGION II 0 it v;, ~ 'i-0 ....... ~ In Reply Refer To: RII:JPO 50-338, 50-339 50-404. 50-405 ~,_50-::~~ 101 MARIETTA ST., N.W., SUITE 3100 ATLANTA, GEORGIA 30303 MAY 8 1980 , Viriinia Electric and Power Company Attn: J, H. Ferguson Executive Vice President-Power. P. O. Box 26666 Richmond, Virginia 23261 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.

Enclosures:

1.

IE Information Not~ee No. 80-20

2.

List of Recently Issued IE Information Notices Sincerely, ~---,~ James P. O'Reilly Director /

          • .,n

. I I / *l/

Virginia Electric and Power Company cc w/encl: W.R. Cartwright, Station Manager Post Office Box 402 Mineral, Virginia 23117 P. G. Perry Senior Resident Engineer Post Office Box 38 Mineral, Virginia 23117 ~- L. Wilson, Manager Post Office Box 315 Surry, Virginia 23883 MAY B 1980 ----- --------------------------

e e UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 May 8, 1980 SSINS No.: 6870 Accession No.: 8002280671 IE Information Notice 80-20 LOSS OF DECAY HEAT REMOVAL CAPABILITY AT DAVIS-BESSE UNIT---i 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. l; Station Battery lP and lN; 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 and3 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 Joss of power to Channels 1 and 3 bistables also resulted in a~_tuation of SFAS
  • '*Chiimels 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 £1.ve 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 * * *-~-----~_. --*

e IE Information Notice No. 80-20 e 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 pq,np was lost. As a result, the decay heat removal cap.ability was lost for app_roximately two and one-half hours, the time required tp vent the system. Furtherinore, 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'i~gle event (e.g., serving CJiannels 1 and 3 from separate sources), this event would have been precluded. Likewise, if mai~tenance activities had been planned or r~stricted 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.

  • Regirding the two-out-of-four SFAS logic used at Davis-Besse, even under nomal*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 orie source. Consequently, when the source £eeding 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 th~ir plants to losing decay heat removal capability by the causes described in this Informa-tion N9tice. No specific action or response is requested a~ this time. iicensees having questions regarding this matter should contact the director of the *appropriate NRC Regional Office.

Enclosure:

Davis-Besse Event of April 19, 1980 .-, *;, t' ~- ....,.. __ *::-*... *~,... -... --***....... -. *.

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e En.cloS'iJr"e A DAVIS-BESSE EVENT OF APRIL 19, 1980 STATUS OF DAVIS-BESSE 1 PRIOR TO LOSS OF POWER TO BUSSES E-2 AND F-2:

l. Refueling mode with RCS temperature at 90°F and level slightly below vessel head flange.

Head detensioned with bolts tn place. Hanway cover on ~op of OTSG removed. Tygon tubing attached to lower vents of RCS hot leg fer RCS level indication. Decay heat loop 2 1n service for RCS cooling.

2.

All non-nuclear instrument (NNI) power and Static Voltage Regulator YAR supplied from 13.8 KV Bus B via BBBF2. 13.8 K !us A energized but not connected. RPS and SFAS Channels l. and 3 being supplied from YAR..

3.

Equipment Out of Service -

a.

Sourcf! bnge Channel 2 - Surveillance ~

b.

Emergency Diesel Generator l - Maintenance. Ca Dec:ay Be.a: Loop 1 - Maintanauce. 4 *.Breakers for TIME 2:00 p.m. contaimnent spray and BPI pumps racked ou~. SEQUENCE OF EVENTS EVENT Loss of power to Busses E-2 and F-2 {non-essential 480 VAC) CAUSE/COMMENTS Ground short on 13.8 r,, breaker HBBF2 which caused breaker to open. Thi.s interrupted power to busse.s E-2 and F-2 vhi.ch were supplying all non-nuclear* instrument (NNI) power, channels land 3 of the Reactor Protection Systein (RPS) and .the Safety Features Actuation Signal (SFAS), the co%tlpuEer, and much of the control room indicators. 2;00 p.m.. SFAS Level _5 (rec:1.rcu-Two out of fo_ur logic tripped upon loss lation mod!!!) 'act:ua-of 8usses E-2 and F-2.. Actuation caused

  • tion.

ECCS pump suc~icn valves from containment -,- ~~-<c.-::c.J;~-<-i::::.'/1.,h',1,:~j~,"'-.. :*:.-.,;,:c~,::,.- __, ____,_:_-_:_:_,_-_*_.t_:_; 1 _*.-,*,-~---*'_-~.--,_:_*.*_,_,_.* __ *.~---i ;-_:-_::* enfflft to op*n and ECCS p*- suction v*lves *- ;., _,_-_

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~- --r -r fro~ Borated Water Storage Tank to close.

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~-~,--~ -* During va.l'V'e travel ti.mes,* *gravity flow **-- path existed from B~ST to containment sump. .~. J" * * ~ -~.: ::* -':°:~;.;ff;;:::.. :. :1.:* Decay Heat (lo,,t Operator turned Qff only operating DB .. - pressure s.1fety in-pump to avoid spillage cf RCS water to ject1qn) fl.owl. 1u!c_ut'e_d ___ containment _via the tygon t_ubing for RCS -.-"':(~~:-; by ope~acor _;, -::.ti*,;;z-: , _level indicat:1.on and cpen SG manway. '}C,:;-,;_~&--~.1';. ';~-~~f~,i,'~iJ:~'t"{:~,:,'/ _ - -" _*':: _:,, ;: -~~ :~~:ci'I;;;cg~A~o~,,;'. c*.iF<:,-J-, * , *-*:.;, ** r*,, -~ 2:33 P**:,,..,.;,. -Parc:l.al re~t~~a,t,i:OD.;-;si-i1;*-,i/,'..':(::,_,,;:*/((i:/0 : \\--:,, !,i:\\:. * *-.--,-r -. * *",,of ponr: ' - ~ -- *

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'* Power to :Sus E.;..2 and SFAS cha.nn@ls 1 and 3 restored along wit.h one channel of ma. This restored all essential power for ECCS. -**.. -.. "*l*;..

j TIME 2:44 p.m. 3:34 p.m. 4:00_p.m. to ,~ 4:06 'P.m. 4:2S p.m-4:46 p.m. 5:40 p.m. 6~24 p.m. * .. 9:50 p.m. 2 - EVEN'l' Attempt to reestab-lish DH flow Source Range Channel 2 energized. CAUSE/COMMENTS S~arted DH pump 1-2 ~hen stopped it when it was deterinined that air was io suction line. Pump secured to prevent damage. Restorat~on of Busses Busses restored sequentually as efforts (480 VAC) F-2, F-21. progressed to isolate ground fault. F-22, and F-23 DH flow restored t Containment sump pump breakers opened Da pump l-2 starteg after ~enting. RCS temperature at 170 F.DH flow bypassing ~o1;06F~lncore TC's be~ng taken and maxi~~ Precautionary measure to assure ~ontainment. sump water fro~ BWST remained j.n sontainment. Incore TC's range from 161 to 164 F. Computer returned to Incore TC'a range from 158 to 160°F. serv.ice. DB flow directed through cooler Power eompletely restored 0 RCS coo1dovn established at less than 2S F per hour. RCS temperature a~ 1S0°F. Incore TC's range from 151 to l580F. RCS teJnperature at approxima~ely llS°F. STATUS OF DAVIS-BESSE l AFTEtl RECOVERY FROM: LOSS OF POWER TO BUSSRS E-2,A?,,"'O F-2:

1.

i: 0 Refueling mode with RCS temperature at 115 F and level slightly b~law vessel he4d flanga. Bead detensioned vith bolts in place. Hanway cover on top of OTSG

  • removed.

'Iygon eubin& attached t.o lower vent.s of RCS hot leg for llCS level.. ** indication. Decay beat loop 2 in service for RCS cooling. 1-:.r.~-",,<;::,,:*l)~2:~\\*Bus.£-2 being suppU.ed*fri,m.13.8 EV ~us A via breaker 'HAA!2 and 'Bus F*2*being - ¥,/;~*ik':;.J:LE~i:'f'i~l!,~~~lied:.. from l:3~~~'--~:;:!~~--~*;.c vi~c br,~a-~er.. HB~F2~c:. *::,:'.S!.\\\\!f:J?;{ ~:f{~?~~~~E> _;!/:,. *~: _. L,:,..,i _. },*;--{;l:".:.1)ecay beat loop filled *. all tags clear. Maintenance work. restricted so.,... - T., ** * ***,.. * ' -*

  • restorat.ion of system v.lll _b_e. less than tvo hours.

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  • 4 *. ECCS pump SUIC"tioil val~es (DB-9A and DB-9B) frcm conta.imnenf':'~ump closed and

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-~ .3 - heat loop du~ing a level S actuation (recirculation mode) when there is no ~ater 1n the sump.

5.

Equipcent Out cf Service: t~ergency Diesel Geuerator 1 maintenance

6. Breakers for containment spray and BPI pumps racked out.
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e IE Information Notice No. 80-20 May 8, 1980 Information Notice No. 80-20 80-19. 80-18 80-17 80-16 80-15 80-14 80-12 80-11 RECENTLY ISSUED IE INFORMATION NOTICES Subject Date Issued Loss of Decay Heat Removal 5/8/80 Capability at Davis-Besse Unit 1 While in a Refueling Mode NIOSH Recall of Recircu-5/6/80 lating-Mode (Closed-Circuit) Self-Contained Breathing Apparatus (Rebreathers) Possible Weapons Smuggling 5/5/80 Pouch Potential Hazards Associated With Interchangable Parts On Radiographic Equipment Shaft Seal Packing Causes Binding In Main Steam Swing Check And Isolation Valves Axial (Longitudinal) Oriented Cracking In Piping

,,1 Safety Suggestions From Employees General Electric Type SBM
  • Control Switches - Defective Cam Followers Instrument Failure Causes Opening of PORV*and Block Valve 5/5/80 4/29/80 4/21/80 4/2/80 4/2/80 3/31/80 General Probls with ASCO 3/14/80.
  • .. Valves in Nuclear Application
    • \\Including Fi~;; i.,,:.otection Systems
r.

.. - *-* -~--~-~----* Enclosure Issued To All holders of power reactor operation Licenses or construc-tion permit All holders of a power reactor OL, Research Reactor License, Fuel Cycle Facility License and Priority I Material License All power reactor facilities with an OL, fuel fabrication and processing facilities and Materials Priority I licensees (processors and distributors) All radiography Licenses 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 Ail holders of power reactor OLs and CPs Alf-holders of Reactor OL, CP, fuel fabrica-tion and processing facilities I}}

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