ML20004B088

LER 81-003/01T-0:on 810428,MSIVs HCV-1041A/HCV-10242A Failed Closed Upon Loss of All 125 Volt Dc Power Feeding Bus A1-41B.Caused by Damaged Cable on 100 Amp Switch.Switch & Cable Replaced.All Breaker Panel Lugs Checked for Tightness

ML20004B088
Person / Time
Site:	Fort Calhoun
Issue date:	05/03/1981
From:	Mueller R OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20004B083	List: ML20004B082 ML20004B088
References
LER-81-003-01T, LER-81-3-1T, NUDOCS 8105270214
Download: ML20004B088 (5)

Text

,NRCfo7M44 U, S. NUCLEAR REGULATORY CoMMISSIGN (7.7 75- .

LICENSEE EVENT REPORT CONTROL clock: l 1

l l l 1 l lh 6

(PLE ASE FRINT OR TYPE ALL REQUsRED INFORMATION) l0 I1b 1 V lE !F lC !S l1 !@l0 l0 l0 l0 l0 l0 l0 l0 l0 l0 l0 -25l@lh l1 LiESid CODE 14 15 L6 CENSE NUMtsEH 26 l1 l1 l1 lhl LiCtf dSE TYPE Jo l

o r LAI Sa l@

CC N'T ICI'!

$$ Shl0 I s IO l0 10 l9 l8IsIhlnlh 19 lR l A l1 lh[0 l5 l0 l9 l8 l1 lh L0 b' DCCKET NUMSER 68 63 EVENT DATE 14 75 REPORT D ATE 80 EVENT DESCRI? TION AND PROBABLE CONSEQUENCES h l a I z ! IDuring normal operations aLapproximstely h55 power. n11 19s vnit m pnynr una 4 rg % !

l% ' a 8 {.AI kl3 was los1 The main stean isolation valves (HCV-10h1A/HCV-10h2A) failed closed i j o 4 4 l [upon this loss of control power to AI-h1B. These valves failing closed initiated an l

! Ia !,l [EHC turbine trip, which in turn, caused a reactor trip. The loss of DC power would notl l l 3 !s I thave affected the ability of the plant to safely shutdown should an accident have oc- I lo!:; l curred since redundant safeguards equipuent was available and operable on DC panel I ta;s! lAI-h1A. l 7 g 3 80 SYSTEM CAUSE CAUSE COMP. VALVE CCDE CODE SUSCOCE ' COMPONENT CODE SUSCODE SUSCODE 10t9! I n I c l @ [x_l@ (z_J @ I C l x l T 18 l a I r l@ IE l@ [7,._J @

7 ;t 9 10 11 12 13 18 13 20

,_ SE 3UENTI AL OCCURRENCE REFORT REVISION LER RO EVE NT YE AR REPORT NO. CODE TYPE NO.

@ .g.g 18111 21 1-1 23 1010131 74 kJ 27 10 11 I 28 29 IT I 30 l-j 31

[ 0_]

32 J1 d6 T A T O PLA T .tE T HOURS SB IT FO 4 UB. S PPLIE MAN FACTURER

!a !-@ll'@ l A lh 1Clh (0lOl5l1i

- 8 h 30 37 40 LY_]h 41

(,Ljh 42

[L]h lTI2l0l3lh 43 44 41 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h 11 i 3 I [One lead of .the cabl.e fo!ma on .the aintributien nian nf tha 19s W - inn n u _cv4*nk l (which feeds bus AI-h13) was found to be burnt loose from the switch completely. It i1 11 i lis believed that thin enbl kna hean nepnrntad ana *n tha kant onm na by l o o n " ~* - I l1 ;.} lnection between the cable and the switch landing lug. The damaged section of cable l lij,) Ivas replaced as was the 100 amp switch. All lugs on the entire DC bus breaker panels,j li!$ l lEE-8F and EE-oG vere checked to ensure proner tightness. I i n ') 80 17 f ,8GWER CTHER S TATUS IS O Y OtSCOVERY DESCRIPTION RY l_E_jh i E l0 lh 15 lh! NA l [,,,a,,jhl via turbine & reactor trins l A TiVlTY CO TENT

! GELEASED OF DELEASE A*.100NT OF ACTIVITV LOCA TION OF RELEASE

! Ii In l [2_J @ 10L J@l nA I I n I 1 44 45 80 ll l

/ M PE G' 'JEL t xPOSbOES 11 I NUMBFO TN rF DE SCRIP TION 39

< l i l ii 1010 10 l@l 7, l@l NA I 1 H 9 11 12 13 80 PERSONNE L sNJUDIES YP.'9En D C,CRIP TIOS 111 I 1d -I9'101010 l@l12 11 NA 80 i t GNS OF OH DA%'.E TO F ACILITY ,

I TYPE CESCHIP flO"4 lio 17, l@l UA 80 j7 M 9 19 Pullt ICI T Y NRC USE ONLY 8,

i

'l2loj [2_j l muto@Of SCRIPTION HA \b/ l llllllllllll li

'f 4 9 10 t 68 69 80 5

! 810 5 2 LhnEPARER ndy Meller  :

PHONE: h02-h26-h011 E

LFR No.81-003 Omaha Public Power District Fort Calhoun Station Unit No. 1 Docket No. 05000285 ,

ATTACHMENT NO. 1 Safety Analysis The Fort Calhoun Station Unit No. 1 is so designed that no single failure can prevent the safe shutdown of the plant. The failure of the 125 volt DC power to panel AI41B would not have prevented the complete and proper loading or operation of essential safeguards equipment should the need have arisen. The loss of 125 volt DC power to panel AI-41B can u .sidered as a very conservative instance of the total loss of 125 VDC to DC bus #2. Total loss of 125 volt DC power to DC bus #2 has previously been analyzed per the Final Safety Analysis Report (refer to sections 7.3.5 and 8.3.4) as being: a single failure resulting in loss of control function redundancy but having no effect on safeguards systems performance.

The loss of 125 VDC power at AI-41B caused several significant events.

These events, as well as an analysis on their relation to a safe shutdown of the plant in case of an accident, are listed below:

1. The component cocling water system valves feeding the SI tank leakage coolers, the Nuclear Detector Well Cooling units and the RC p mp seals and bearing coolers closed as designed. In all cases where component cooling water feeding safeguards equipment was involved, all equipment (normally fed from AI-41B) acted as designed and attained the proper safety position. The Raw Water valves fed from AI-41B attained the fail-safe position and were properly aligned should Raw Water have been needed as a backup to the com-ponent cooling water system feeding the Safety Injeccion and Con-tainment Spray Pump bearing coolers, the Conta ament Air Cooling and and Filtering Units, the Shutdown Cooling h,at Exchangers and the Control A/C units.

2. Although the Nuclear Detector Well Cooling System is not required to be operable should a shutdown be deemed necessary, Technical Specification 2.13 states that the " annulus exit temperature from the nuclear detector cooling system shall not exceed a temperature found to correlate to 150 F concrete temperature." Contrary to this technical specification, the moss of component cooling water to the nuclear detector well cool:.ng system caused a rise in con-crete temperature of part of the biological shield to 170 F. This rise to 170 F from the normal 120 F temperature was caused due to the loss of componcat cooling water corresponding to a period of 1.33 hours3.819444e-4 days <br />0.00917 hours <br />5.456349e-5 weeks <br />1.25565e-5 months <br />. Therefore, using two conservative assumptions, i.e.,

a. The temperature was at 170 F for the full 1.33 hours3.819444e-4 days <br />0.00917 hours <br />5.456349e-5 weeks <br />1.25565e-5 months <br /> rather than rising from 120 F to 170 F over the 1.33 hour3.819444e-4 days <br />0.00917 hours <br />5.456349e-5 weeks <br />1.25565e-5 months <br /> period, and

b. the thin film convection heat transfer coefficient (h) has been postulated in the analysis to tend to infinity (44, whereas in actuality it is probably in the range of 10-20 even in rapid thermal transfer processes. ,(

( 'N s

Attachment No. 1 (continued)

2. continued An analysis was performed in an effort to assess possible concrete damage caused'ay the temperature rise to 1700F. The results of.

this analysis ahoved that the temperature of the biological. shield concrete would drop to below 1500F (for a surface temperature of 1700F) at less than 1.5 inches into the concrete. It is OPPD's engineering judgement that the conditions described above could not create any detrimental effect or deterioration of the biological shield concrete. It is worthwhile to note that the duration time of 133 hours0.00154 days <br />0.0369 hours <br />2.199074e-4 weeks <br />5.06065e-5 months <br /> came about as the time it took the CCW system feeding the Nuclear Detector Well Coolers to be restored to fully opersble status.

3. Although control power for certain safeguards equipment was lost for a period of approximately 20 minutes, all redundant equipment-was availsble and operable as designed. Both diesel generators were verified / operated automatically as a result of the turbine /

plant trip. The DC sequencer circuitry corresponding to Sequencer S2-1 was unavailable for a time period of 20 mintues (the length of time it took to return power to AI-41B via .the' manual transfer switch which allowed AI 41B to be fed from DC bus #1). However, during this 20 minute interval, the AC sequencer . circuitry associated with the "B" safeguards train, Sequencer S2-2 as well as the AC and DC sequencer circuitry associated with the "A" safeguards train, sequencer Sl-1 (DC) and Sl-2 (AC), were available and capsble of properly sequencing safeguards loads should the.need have arisen.

4. Numerous containment isolation valves, radvaste system isolation valves, as well as safety injection actuation signal actuated valves, attained their fail-safe positions as designed upon de-energization of AI-41B.

It is important to note that the loss of 125 DC power to AI klB lasted for a period of 20 mintues, at which time the manual transfer switch was operated and 125 volt DC power was returned to AI-41B via 125 volt DC bus #1. Upon re-energi ation all safeguards related. circuits were restored to immediate opersbility with the exception of the CCW system which required an additional one hour to restore to the fully operable state due to lost inventory.

LER No.81-003 Omaha Public Power District Fort Calhoun Station Unit No. 1 Docket No. 05000285 ATIACE4ENT NO. 2 Corrective Action It was deter =ined that a loose connection on ont cf the cables which extends from the 125 VDC panel switch to the transfer switch vnich feeds AI k13, had caused the switch lug to be compl. ely disconnected from the cable due to heat. As a result, both the switch itnelf (an ITE EH2-S100) as well as a section of damaged cable, were irreparable and were replaced wi* h spares. All lugs on both DC distribution panels (EE-8F-fed from the 125 VDC bus #1 and EE-8G-fed from the 125 VDC bus #2) were checked for adequate tightness and adjusted if necessary to ensure a

" good connection" between cables and lugs. The system was then returned to normal, i.e. the AI-h1B bus feed was returned to DC bus #2.

e 6

LER No.81-003 -

Omaha Public Power District Fort Calhoun Station Unit No. 1 Docket No. 05000285 ATTACHMENT NO. 3 Failure Data This is the first failure of this type to occur at Fort Calhoun Station Unit No. 1.

i k

,. l ',

. x

\

_-