ML18082A414
| ML18082A414 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 05/08/1980 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Schneider F Public Service Enterprise Group |
| References | |
| NUDOCS 8005190576 | |
| Download: ML18082A414 (8) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION.
REGION I 631 PARK AVENUE KING OF PRUSSIA, PENNSYLVANIA 19406 Docket No. 50-272 50-311 May 8, 1980 Public Service Electric and Gas Company ATTN:
Mr. F. W. Schneider Vice President - Production 80 Park Place Newark, New Jersey 07101 Gentlemen:
The enclosed IE Information Notice No. 80-20, 11 Loss of Decay Heat Removal Capability at Davis*-Besse Unit 1 While in a Refueling Mode, 11 is forwarded to you for information.
Na writt~n response is required.
If you desire addi-tional information regartling this matter, please contact this office.
Sincerely,
~~~
~
Boyce H. Grier f.;...;- Di rector.
Enclosures:
- 1.
IE Information Notice No. 80-20 with Attachment
- 2.
List of Recently Issued IE Information Notices CONTACT:
W. Baunack (215-337-5253) cc: w/encls:
F. P.* Librizzi, General Manager - Electric Production E. N. Schwalje, Manager - Quality Assurance R. L. Mittl, General Manager - Licensing and Environment H. J. Midurq, Manager - Salem Generating Station
I.
ENCLOSURE 1 SSINS No.: 6870 UNITED STATES Accession No.:
NUCLEAR REGULATORY COMMISSION 8002280671 OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D. C. 20555 IE Information Notice 80-20 Date:
May 8, 1980 Page 1 of 3 LOSS OF DECAY HEAT REMOVAL CAPABILITY AT DAVIS-BESSE UNIT 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 bo.lts 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 Attachment 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 Channe 1 2; Decay Heat Loop No. 1 ; *
- 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 and 3 of the Reactor Protection System (RPS) and Safety Features Actuation System (SFAS) were being energized 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 Date:
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 approxi-mately 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 red~ced 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 mainten-ance 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 IE Information Notice No. 80-20 Date:
May 8, 1980 Page 3 of 3 1 and 3 was lost, all five levels of SFAS were actuated.
As stated 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.
Attachment A
.e Attachment A to I~nformation Notice No. 80-20 Encl.osu:re A DAVIS-BESSE EVENT OF APRIL 19, 1980 STATUS OF DAVIS-BESSE 1 PRIOR TO LOSS OF POWER Ttt_B~SES E-2 AND F-2:
- 1.
- 2.
0 Refueling mcde with RCS temperature at 90 F and level slightly below vessel head flange.
Head detensioried trl.th bolts in pl~c=.
Ma.n~ay cover on top of OTSG removed.
l'ygon tubing att,ched to lower vents of ncs hat leg fer RCS level. indication.
Dec:ay heat loop 2 in $Ervice fo~ RCS cooling.
All non-nuclear instrm:ent (NNI) power and Sta:~ic Voltage Regulator Y.\\R supplied f::om 13.8 KV Bus :B Via HBB'F2.
13.8 K Bc.s A euerg:f.zed but not ccnnected.
RPS and S7.AS Ch~nels l and 3 being supplied f-rQ111 YA.R.
Equipment Out of Service
- a.
Scu~c~ ~a~ge Cha~~l 2 - Survaillance
- b.
Emergancy Die.se1 G~~e~ato~ l - Maintenance.
- c.
Decay Heat Loop 1 -
Ma.inte:aan~e.
- 4.
- S:i:ea~ers for containm2nt spray and BPI p~s racked cut:'.
TIME 2:00 p.m.
~:02 p.m.
2:33 p.m.
SEQUENCE OP' EVmtI'S Loss of power to Busses E-2 and F-2 (non-essential 480 VAC)
CAUSE/COHMENTS Grouud short on 13.8 KV breaker HBBF2
- 1.ihich caused breaker to open.
This interruptad power to busses *E-2 and F-Z whic:h we:re supplying all non-nuclear**
instrument (NIU) po-..rer,. channels l and 3 of the Reactor Frotectiou System (RPS} and
.the Safety Features Actuation Signal (St'A.S)
- the computer, and much of the control rool:i 1.ndi.ca.tors.
SF.AS Levei S (recircu-Two out of f ou% log~c t%ipped upon loss lati.cn mode) ac:tua-of 3usses Z-2 and F-2.
Actuation caused
- tion.
~ccs pu:.p ~u~t!on valvsa from containm~nt sump.to open and ECCS pump suction valves from Boraeed Water Storage Tank to closa.
During valve t,ra.vel times, gravity flo"'
path existed fTo~ EWST to containment somp.
Decay P.eat *(low Operator turned off only oparating DH pressure saf aty in-pump to avoid spillage of RCS watar to jeccion) f~ow secured canta1nme~~ via th~ tygon tubing for RCS by operator level indicstion and open SG manway.
Parcial 4estoration of power Power ta Bus E-2 a~d SFAS channels l and 3 restored along with one channel of h'NI.
This restored ~ll essential p~er for ECCS.
1 l
. i
- ~;
/'\\:..
TIME 2:44 p.m.
3:34 p.m.
4:00 p.m.
to 4:06 p.m.
4:25 p.m.
4:46 p.m.
5:40 p.m.
6:24 p.J.11.
e Attachment to IE trormation Notice No. 80-20 EVENT CAUSE/ COM?-!E?rrs
. Attempt; co reestab-
- Started DH pump 1-2 th;-n. sth'[>ped it tirnen lish DH flow it was detenrl.ned that air was in auction line.
Pump secured to p~event damage.
Source Range Channel 2 energized.
Rescorat~on of Busses Busses restorad sequentually as efforts (480 VAC) F-2, F-21, progressed ~o isolate ground fault.
F-22, and F-23 DB flow restcred
. I CQnt:aimnen't sump pump br~akers opened DH pump 1-2 sta~~ed after ~~nting. RCS t~lllparature at 170°F.DS flOtJ bypass~ng
.fgot,Obi'*. Ini:cre TC' s being taken and maxinnim Precautionary m!!asure to a.ssu:t'e contaimnent..
sump i.at:~r £::-c::n SWST r::-;:::.ained i:.l 5cnt.::d~en::~
Incore TC'~ range frQm 161 to 164 F.
Co-mput:er returned to !ncore TC's rang= from 158 tol60°F.
- service..
- I DR f lcw direc~~d
~hrough a:>oler 0
ii RCS ccoldcvn established a~ less Shan 25 F per hour.
RCS tempe~atu~e at l.SO F. Incc~e TC'~
range from 151 to isaor.
.. '9:50 p.m.
Paver completely
- restored RCS temperature ac approxi:za~ely l15°F.
- >>#*dfll'.....
. - ***~..
'.I
> ~
~TAl"US OF DAVIS-~ESSE l A..."'l:TER RECOVERY FROM LOSS OF PO~R TO BUSSES E-2 ANO F-2:
i J,:'
i
- ~
o I
l~,Refueling mode with RCS.temperature at ll.S 'F and level slightly below vessel head flange!..
Hea.d datznsia:;ied with bolts in place.
Manway cove.'t' en tap of O'ISG
- 2.
removed..
Tygon t:ubitig-atta.ched ta lcwer vents of RCS hot leg for RCS level.
indi~aEion. Decay heat loop 2 in service for RCS cooling.
Bus !.:t bei;:i~~t~~~~:~ ~~= 13. a xv ~us A via breaker HAAE2 and Bus P'-2 being supplied fr~ 13. 8 KV Bus B via breaker HB:S'F2.
- 3 *.......-l)ecay beat loop filled. all tags c1ear. Maintenance work restricted so
- restoracicn of system v.l.11 be less than tvo hours.
- 4.
ECCS Pl.mlP suction v~lva3 *cnH-9A and DB-9B) from containment sump closed and breakers racked out.
This vil1 prevent the suc:ion of air into the decay
- ~.~..
1
f
~ J Attachment to IE 9ormatfon Notice No. 80-20
.j
~ - i 3 -
heat loop during a lavel S actuation (recirculation mode) ~hen there is no vaeer in thfi!.. sunip.
S.
Equip:ent Out of Sel:'Vice:
Emergency Diesel Generator 1 - maintsnanca
- 6.
Breake~s for con~ainment spray and BPI pumps racked out.
i:
. J.
- i*
l*
~
Information Notice No. 80-11 80-12 80-13 80-14 80-15 80-16 80-17 80-18 80-19 ENCLOSURE 2 IE Information Notice No. 80-20 Date:
May 8, 1980 Page 1 of 1 RECENTLY ISSUED IE INFORMATION NOTICES Subject Date Issued Generic Problems With ASCO 3/14/80 Valves in Nuclear Applica-tions including Fire Pro-tection Systems Instrument Failure Causes 3/31/80 Opening of PORV and Block Valve General Electric Type SBM 4/2/80 Control Switches - Defective CAM Followers Safety Suggestions from 4/2/80 Employees Axial (Longitudinal) 4/21/80
.Oriented Cracking in Piping Shaft Seal Packing 5/5/80 Causes Binding in Main Steam Swing Check and Isolation Valves Potential Hazards 5/5/80 Associated With Interchangeable Parts On Radiographic Equipment Possible Weapons 5/5/80 Smuggling Pouch NIOSH Recall of Recir-5/6/80 culation-Mode (Closed-Circuit) Self-Contained Breathing Apparatus (Rebreathers)
Issued to All Power Reactor Facil-ities with an OL or CP, Fuel Fabrication and Processing Facilities All Power Reactor Facil-ities with an OL or CP All Power Reactor Facil-ities with an OL or CP All Power Reactor Facil-ities with an OL or CP, Fuel Fabrication and Processing Facilities and Materials Priority 1 Licensees All Power Reactor Facil-ities with an OL or CP All Power Reactor Facil-ities with an OL or CP All Radiographic Licensees All Power Reactor Faci-lities with an OL, Fuel Fabrication and Processing Facilities and Materials Priority I Licensees All Power Reactors with an OL, Research Reactors, Fuel Facilities and Priority I Material Licensees