ML20236N515

Forwards Summary of Root Cause Investigations of Cable Issues Per G Kalman to Gc Andognini

ML20236N515
Person / Time
Site:	Rancho Seco
Issue date:	11/09/1987
From:	Croley B SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Miraglia F Office of Nuclear Reactor Regulation
References
DTS-87-103, NUDOCS 8711160201
Download: ML20236N515 (13)

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$SMUDSACRAMENTO MUNICIPAL UTILITY DISTRICT O P. O. Box 15830, Sacramento CA 95852+1830, (916) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA NOV 0 8 ISe7 DTS87-103

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U. S. Nuclear Regulatory Commission Attn: Frank J. Miraglia, Jr.

Associate Director for Projects Phillips Building 7920 Norfolk Avenue Bethesda, MD 20014 DOCKET 50-312 RANCHO SECO NUCLEAR GENERATING STATION LICENSE NO. DPR-54 1 CABLE DISCREPANCIES / ROOT CAUSE INVESTIGATIONS OF THE CABLE ISSUES l Re: NRC Letter, George Kalman to G. Carl Andognini, dated f August 14, 1987

Dear Mr. Miraglia:

i Please find attached a summary of the root cause investigations of the cable issues as requested in item (1) under Cable Discrepancies of the referenced-NRC letters.

Please. contact me if you have any questions. Members of your staff with questions requiring additional information or clarification may contact John Atwell at (209) 333-2935, extension 4916.

Sincerely, Bob Croley Director, Nuclear Technical Services l

cc: G._Kalman, NRC, Bethesda w/ attach A. D'Angelo, NRC, Rancho Seco w/ attach I J. B. Martin, NRC, Region V w/ attach 'I l

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RANCHO SECO NUCLEAR GENERATING STATION O 14440 Twin Cities Road, Herald, CA 95638 9799;(209) 333 2935 i

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INCIDENT ANALYSIS 87-04 3 -

' APPENDIX'"R" DEFICIENCIES I (Based on ODR 87-12, ODR 8-61, LER 87-02,~and LER 87-10)

SUMMARY

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' Evaluations' performed by. Nuclear Engineering Fire Protection resulted'in the identification of'two 10 CFR j Appendix 1 deficiencies. :One- is

, ,50, "R" the Diesel

' Generator '(GEA) . Breaker S4A08. control scheme. 'The j

, breaker's' protective trip circuit could'be actuated in a ~

fire. This ' deficiency was reported as LER ' 87-02. The second deficiency ' was in the Reactor Coolant System High ~

, Point Vent. Valves. A fire could cause spurious operation i

of . the ~ valves' and the loss' .of reactor coolant. This deficiency was reported as LER 87-10.

s Both oftthese deficiencies appear to have been-caused by human' error during the_ design and review stage of past Engineering Change Notices. The fact that these problems J-were: discovered.during the Appendix R review of present documentation indicates that the past Appendix R program

.D deficiencies are- being -searched for, found, and corrected . -

Deficiency 1 LER : 87-02 describes a problem in the control scheme of Diesel Generator. (GEA) - Breaker _ S4A08. Specifically, the control scheme of S4A08- is susceptible _ to a ' " hot short" which would ' actuate the breaker's protective . trip circuitry and - trip. the breaker. A " hot short" is a condition in which, 1) a fire burns off the insulation of _a ldeenergized cable, 2) an energized cable falls

- across;the deenergized cable, and 3) -the energized cable induces voltage into the deenergized cable. Since a loss of'offsite' power is assumed to occur at the same time'as a Control Room fire, the failure of breaker S4A08 would

. cause the--loss of the only Appendix R allowed source of on-site power for safe shutdown.

This deficiency was- discovered by the Fire Protection Group during the Appendix R assessment of the final electrical distribution system.

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( h Deficiency 2 i

LER 87-10 : ' describes an. Appendix- R deficiency associated with the Reactor Coolant: System- (RCS) High Point Vents.

The conductors for both High Point Vent Valves (of a set) are routed in the same cables. / Additionally, the cables -

are . routed 'in the same trays ? or t vias. Because this

. commonality.is' downstream of-the fuses-for the High Point.

Vent . Valves, the : spurious - operation .of both High' Point Vant: Valves, due to a-fire,-is a credible accident. The spurious ' activation would be caused by a fire-induced.

g. " hot short" from another energized cable.

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.In order to prevent accidental ^ ' actuation ' of the . High

, Point Vent Valve circuits.the fuses are normally pulled.

This." hot short" ' deficiency was discovered. by the Fire Protection' Group during an engineering evaluation of the '

' electrical drawings:for the'RCS High' Point Vents' HMSIE .

.The direct cause of both'of these deficiencies appears to be personnel error that ' occurred during' the design and.-

review of coupleted Engineering Change Notices(ECNs).

The fact that these problems were discovered during the Appendix R review of present documentation-indicates that past Appendix R program deficiencies are being searched for,.found, and corrected.

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'^ f4 ROOT'CAUSE 86-10 lI REDUNDANT CABLING IN THE SAME FIRE AREA . i 2.'.

(Based.on'LER.86-10) i t.. - 1

SUMMARY

. On . May 22,: 1986', two Engineering Department engineers.

Jdiscovered a- cable routing error in Fire: Area .'17. The- >

engineerss found .an. ' empty conduit: while Llooking for .,

~ additional ' conduit space into the control Room. . The q 3 Cable' Raceway Tracking System (CRTS); indicated: that L the conduitScontained seven cables.- .A.walkdown.of the cable  :

routing resulted in the discovery thatLthe cables;were in

.  ? , non-firewrapped conduit.instead of firewrapped. conduit.

The'-misrouted1 cables- contained seven safe shutdo'wn' <

circuits = that were routed. from the Control nRoomL to ' the-  ;

Shutdown? Panel... through- .an isolation- cabinet.

Construction : Engineering had pulled the cables .in accordance with the original, routing; 'however, Nuclearo Engineering' revised; the ' cable routing 'twice.

Construction Engineering did not pull'back and repull the cables in agreement with the. revised' routings, t q

CAUSES The direct cause of the failure to reroute the cables is 1 personnel. error. .Although the Construction' field engineer was aware ' of the routing revisions, he did.not initiate the fieldi installation of the "C" revision of the cable routing. g The . underlying cause is 'that the CCG did not follow Engineering .and _ Inspection Instruction (EII) EC-10

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" Processing of Installation: Cards."

A.. contributing cause of this event was Quality Control's failure to perform adequate inspections of cable .j installations.

The. root cause is the failure of the Card Control Group 1 cognizant engineer to implement adequate managerial

. controls. He did not require the use of adequate and L ,

formal procedures for the processing of installation i cards by the CCG.  :

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. PULLED CADLES STORED'IN~ SAFETY--

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RELATED BREAKER CUBICLES , .q g ', 1 i

(Based.on LER 87-16)- , ;J

SUMMARY

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'5 '1987, were workingOn ' February ' on, Engineering Change: -

(ECN) NoticeElectrical

. R-0415B,- ' Mainte

" Installation ~20f . ' Synch Check _ Relays l. On All . Four - (4) 1 Diesel . Generators , And . Four ?(4) . Normalc Supply i Breakers. " ',,

While ' performing .the. ECN,:. Electrical' . Maintenance-j i

determined that the lock-out relays in;two safety-related cabinets could.be'. inadvertently actuated'if hit by cables. G coiled;in'the same-cabinet. '

On February 6,.1987, Nuclear. Engineering determined that- l

- the presence of these -coiled cables- invalidated the.. d seismic analysis' for the cabinets. - Nuclear Operations'-

and Electrical Maintenance checked.all,theJsafety-related-

't electrical cabinets and found, cables coiled in four' l additional cabinets. l CAUSES  !

The direct cause of the coiled cables. being left. in all the ~ cabinets, other . than A405 and A409, is a planning .T error: the cable. terminations should have been scheduled

.to occur immediately following the cable pull,' but were. -

J. not.

The~ direct- cause of the coiled cables being lef t ' in cabinets 4A05 and 4A09 is a design error: the effects of the coiled spare-cables on the seismic analysis were not I considered. .i The ' Root Cause of cables being left coiled and unrestrained in safety-related breaker cubicle cabinets

- is: inadequate procedures for the installation =of =!

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4 ROOT CAUSE 87-03 CABLE RACEWAY TRACKING SYSTEM ,

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SUMMARY

- As a result of Licensee Event Report 87-13 and several I

' Occurrence _ Description Reports. related' to the'  !

installation .of cables at--Rancho .Seco,. the . Incident-Analysis Group initiated a ' review of the . Rancho Set:o i Cable. Raceway Tracking- System (CRTS). Although no

. specific cabling. problems appear'to have been directly '

associated with or caused:by the CRTS, there do appear tio

.be .significant . indications of CRTS problems. These" problems. include:

o The NRC's questions about the quality of the CRTS data. base g

o. Indi' cations that the CRTS data base did not match the actual plant configuration ~

.o Allegations that the ' CRTS ..was not.used correctly and that errors were being entered into the data base.

'CAUSES The root cause of . the problems: related to the CRTS and its:use is that neither Nuclear Engineering management or i

the CRTS Supervisor were adequately involved in the CRTS.

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1 ROOT CAUSE 87-05 OVERWEIGHT CABLE TRAYS (Based on LER 87-24)

SUf01ARY On February 25, 1987 it was determined that up to sevon cable trays inay exceed the 50 pounds per linear foot limit of the USAR. This event was reported to the NRC via IER 87-24. None of these trays contained Class 1 circuits.

Cable tray weights for all of the 3,459 cable trays at Rancho Seco were calculated. These preliminary calculations indicated no more than seven cable trdys were potentially overweight.

Subsequent calculations determined that only one tray, 740BGlA, was overweight. In a final calculation, tray 740BGlA was calculated to weigh 50.35 lb/ft. This overage is acceptable due to the conservatism of the calculation.

CAUSES The exact limits for cable tray weight and fill are defined in the Rancho Seco USAR. These limits are:

o 50 lb/ft for cable tray weight o 40% fill for cable trays associated with the Reactor Protection System and Safety Features Actuation System.

Electrical Engineering uses a fill-to-weight correlation to prevent exceeding these limita. Although the use of the fill-to-weight correlation appears acceptable; 19 Class 1E and 171 non-Class 1E cable trays were filled -

beyond the applicable fill limit without verification f that the cable tray weight limits had n.4 been exceeded. i The direct cause of the overweight cable tray problem is inadequate procedural guidance.

.The root cause of the overweight cable tray problem is l the failure to ensure adequate implementation of USAR l requirements. l I

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, . ' ROOT CAUSE.87-09 ,j UNACCEPTABLE INTERMIXING OF POWER / CONTROL' 3

, AND INSTRUMENTATION CABLES'  !

SUMMARY

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' In _ March -1987, the . District determined tha't .561 C3 ass ' 1E- -

Jinstrument cables- were. internixed- with.Eeither- power icables or, control cables._ The intermixing. . involved 20

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- powerj cables and ~ 14 ' control cables 'which were routed :.in instrumentation-cable trays, and!6 Instrumentation cables >

routed in? power / control cable trays. In addition, a. M total of 15 ~. Reactorc:. Protection . System / Safety ,. Features d

' Actuation System (RPS/SFAS) Instrumentation cables .were 3

-l found' routed:in instrument trays instead-of conduit.  ; 4-The maj ority -.o these problems.were identifiod durihg1a .

-1986/87 review (Impell Task 241/271) - of the ECable ( and ;

Raceway- Tracking. System. (CRTS) ^ " data base'. . Eleven 1 , j

. power / control cable intermixes / ..were . identified . byL walkdowns ' performed , as a . ' part; of: : the Cable . and ; Wire ,

u Sampling Plan'.

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q The. -intermixing- of power / control cables with instrumentation. cables l: and the' routing f. of. - RPS/GFAS' instrumentation cables in trays rather,'than conduit >

ij constitute,. installations ' contrary ' to! Section 8.2.2.-11'.H of the. Updated Safety.Analy' sis Reporti-(USAR).

The .--intermixing- of. the ? power / control 'and instrumentation cables is' reportable to the NRC in accordance with 10'CFR l 50.73: '(a)-(2) (ii) , (v) and (vii). The-routingLof RPS/SFAS~ ,

instrumentation cables Ein raceways 'rather than conduits ]

is reportable' to the NRC' in accordance with '10 CFR 50.73 g (a) (2) (v) .' These ; events were reported: to'the NRC.vla o Licensee Event Report'87-26, "UnacceptableLIntermixing:of "

Power / Control and Instrumentation Cables." '

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CAUSES i

Direct 6auses l

f. PJ;EeI/ Control Cables Jysociated "wlth Cable Trays A28AA1 gjlSi A28AB3 .

The direct cause of the intermixing of cables in cable trays A28AA3 and A20AB3 is a construction error. The cables were repulled into their original routing instead of the revised routing.

The underlying cause is the failure to follow procedure i ECa10 " Processing of Installation Cards." The pull cards 4

were signed by the field engineer instead of the craft foreman who performed the work. Procedure EC-10 required ,

the signature of the field installation personnel

performing the work.

A contributing cauce was the. failure of the Electrical QC Group to identify the construction error. The error was f not identified because of the failure of the electrical QC Inspectors to follow the requirements of procedure EC-11 " Cable Installation During Construction and Major Modifications. This was also identified in RC 86-10.

Powerffontrol cables Associated with Cable Tray AggAlil The direct cause of the intermixing of instrumentation cables with power / control cables in cable tray A28AN3 is n-design error. The two power cables were not scheduled to be removed following the predesignation of the tray.

The contributing cause of the intermixing is a lack of a comprehensive service level designator in the cable tracking systems used. The tracking systems could not be

> used to check'for intermixing conditions when the routing I for the instrumentation cables was laid outt therefore, an intermixing condition would not be identified.

l Power / Control Cables Associated with Cable Tray A28AA1

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The direct cause of the intermixing in cable tray A28AAl

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l is either a design or construction error during construction of the Plant.

The contributing cause of the intermixing in cable tray A28AAl_ is a lack of a comprehensive service level designator in the cable tracking systems.

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RoutincU of "15 " Instrument Cable's in ' Travs ' I'nstead of 4

5 Dedicated' Conduit .,. l g' -The direct ' Leause of d the 'RPSkand SFAS ' instrumentation -

. cables;being; route'd; in_ cable; trayss rather than' dedicated n .cor.duit is design error, f :.This. design. error 'isipresent in; t 4

two EONS C however,

the cableLroutings-for both;ECNs'were 1 performed >byx t hesame group.

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'The underlyingfcauseLof?the: cables'being misrouted'islthe' ,

h y :. lack of training of NED pers,onnel'on.USAR requirements.. y 5  ?

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Cables J Associated' with ' the Decav Heat System Cross Tie.

Flow Transmitters' "

The' direct Jcauseiof the -inte mixing of; the 6eDecay Heat;

System < crossitie Lflow instrumentation cables is design

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3 error. This; design error occurred duringt the original' 1 l;, . design 1 phase iof ~ Rancho Seco. . The original design. error-was- exacerbated ' when the . routing ' was incorrectly ]l redesigned in 1984..

q The .underlyingL4causes are the: .use of: only contract l

, engineers:ae'the. Physical Layout Group and their lackTof' l training)on USAR. requirements.

' i Cables Associated with ' the Reactor ~ Coolare System Flow' ]

' Transmitters  ;

1The? direct cause' of ? the ' intermixing of t h e. 14'Reactor L Coolant System flow transmitter' cables fis design error. .

This : design :errorJoccurred during' . the ' original design l

. phase . of Rancho Seco. The original design l error was exacerbated when the routing ' was incorrectly redesigned in 1983.

The underlying ..cause was the use of only contract engineers for the Physical Layout Group and.their lack of craining on plant.wspecific USAR requirements.

.r Root Cause i

The root cause of the cable intermixing problems is the failure to.have and/or use procedures for cable design, o installation, inspectjon, and repulling, i.

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4 , comprehensive $designproceduresdidnotexistuntil-1986.-

The - present; procedure system does not address USAR i requirements.-

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In-the 1983 outage, installation cards'were not processed in accordance with procedure EC-10 " Processing of l Installation Cards."

, I From 19812to 1986, the' Electrical QC Inspectors did not i always inspect cable routing in accordance with procedure EC-11 " Cable' Installation During Construction and Major  !

< Modifications."

The procedures for cable insta11ation have not and do not specifica11y' address the process used to pull-back and repull cables in a revised routing.  !

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, , CLOSURE OF~DHR' VALVE-1

.(Based on LER 85-16)~ i

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SUMMARY

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[OnJA ugustf8,?AugustL14, and September- 23,(1985,- the' Decay 4 j; HeatL Removals. System! suction. block . valve' W (HV-20002)'

- spuriously 1 closedi. resulting- in .a . temporary : loss - of the j' - , DHS 1 system.. Licensee Event ' Report ' 85-16 was . Written Lto :

at ~ address thefclosures..

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, 1 -(Valve,r HV-20002,-_-is designed E to close automatically- when-the RCS s precsurel exceeds ;255. psig. Pressural indication - ,

is -transmitted to the .HV-20002. circuitry from PT-21099. I

^ OnJAugust~8,Jthe RCS pressure was 223Lpsig, on August 14

-the RCS. ' pressure . was 217 4 psig, on September 23 the RCS pressure ' was: 217L ;psig.- Between Augusti 23, 198 5, ; "andL January - 21, 1987, a chart ' recorder was ~ intermittently

connected . to the -- output. of 0 PT-21099. During _ this1 time' period'1the recorder logged over 45 instances;of pressure s ,

'spikest emanating from-the transmitter.

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The spurious' closures ~wereLcaused by the intermixing' of

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instrument;cabletwith power / control. cables. The spurious- ,

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' decay (; heat.~ isolation 1 signal- was Etraced to' , improperly -

d a routing. shielded ' instrument cable (lRISO4B6A) through L Channell B : power ~ trays J and conduit; to a penetration,. as documented. inL NCR: E-5263, Revision ' 3.

This; cable was installed during'plantLconstruction.

, A: special-Ltest was conducted to demonstrate that a

' voltage ' spike' appeared ' when the power circuit to motor operated . valve ' HV-20002 was energized. The existing  ;

misrouted cable wa's' abandoned in place. A new instrument '

cable was routed'in instrument cable raceways. The test j was repeated following the new cable installation with no indication of a voltage spike.

Furthertinvestigation of the power tray involved revealed that 47 additional power cables were also routed with PT-21099' ' instrument ~ cable. Any one of these cables could

-have caused a voltage spike similar to that found during testing of HV-20002. i 4

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Becauso. this' item' i's similar to the intermixing discussed in Root'Cause Report 87-09, the.MRT' determined 1 <

that no further investigation was required.

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'Causes The direct cause of intermixing- instrument cable 1R1SO4B6A with power cables is a design'or construction error that occurred during Plant construction.

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