05000368/LER-1980-018-03, Following Loss of Offsite Power Transient,Emergency Feedwater Flow Became Erratic. Probably Caused by Heating of Feedwater Train W/O Forced Flow,Allowing Water to Drain Back to Condensate Pump

Following Loss of Offsite Power Transient,Emergency Feedwater Flow Became Erratic. Probably Caused by Heating of Feedwater Train W/O Forced Flow,Allowing Water to Drain Back to Condensate Pump

ML19320D470
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/14/1980
From:	Clogburn T ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19320D465	List:
References
LER-80-018-03X, LER-80-18-3X, NUDOCS 8007210400
Download: ML19320D470 (2)

LER-1980-018, Following Loss of Offsite Power Transient,Emergency Feedwater Flow Became Erratic. Probably Caused by Heating of Feedwater Train W/O Forced Flow,Allowing Water to Drain Back to Condensate Pump

Event date:
Report date:
3681980018R03 - NRC Website

text

_

r

.( ;

UPDATE REPORT - PREVIOUS REPORT DATED 5/5/80 V

hRC FORM 364 U. S. NUCLE AR REGULATORY COMMISSION l.tCENSEE EVENT REPORT EXHIBIT A CONTROL 8 LOCK: l l l l l l lh (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) l 4

QlR l Al N] 0 l 2lgll0 l0 l -l0 l0 l 0l 0l 0 l-l 0 ;0 lgl4 l1 l 1l1 l 1lgl l lg o i 9

LICEN584 Coot to i

LICENSE NUM9EM 2S 26 LICLN:,E S TP( Jd 67 CAT be i

8 p'T CON

%',"' [L_)@l015 p 10101316181@l 014 101718101@l 01 71114 18101@

60 69 OOCK ET hLeMegn 68 69 EvtNTDaTE 34 FS HEPOHT OAft 40 8

EVENT DESCRIPTION ANO PROBABLE CONSEOVENCES h EID I Durina Mode 3 ooeration. following a loss of ofhi_tg oower transient.

I a

I 00:0 irmornonry ree mater ricu became erratic, indicating-that some cavitatier Iwas in progress. This event occurred approximately 15 minutes after a I

o.

iloss-of offsite power due to tornado damage on the power distribution I

o s Igrid.

EFW flow never was interrupted, however each train was independent-j o.

o 7 liv chut dnwn fnr a fnw mintiene tn allnw unntinn nf thn cru nimne fn11nuind 1301ation of the cause of the'cavitationE ThEfe havE'bEbii 56 !!imilaF6E" Icurrencestreportable oer T.S.6.9.1.9(b).

I o e

'un"

• ^s!

s&^sst u'Z' t s.Mo.

to.-,~<~TCoo E

I clH i@ la.J@ LZ.]@ 171717171717 l@ LIJ@ L11@

- ve~T,[..

i'?"oW[

• iN*c' k?"'

"' O "

@,a';,;,,;,'oIn I ni l--J 10 111 81 M

i 01 3 i LLJ L--J L1_l u

u 2n 22 23 14 26 2

2a 29 Ja 2

32 i KEN AC PLA T MET O HOUR $

$ Be TT FoR nH

$UPPL M

.AN 8A TURER Lnl@LZJ@ LIJ@

L2J@

l 0101010 i L_yj@

LN_lO LZJ @

IZ 19 l 919 l@

3J 34 36 36 33 40 48 4J 43 44 4;

CAUSE OESCRsPTION AND CORRECflVE ACTIONS 27 8 O l l

I See Attachment labeled "Cause Description and Corrective Actions"

_1

, 2 l l

El I

1 i

i.

STA

% POWER OTMf R $f ATU)

D5 V HT DISCovEMY O*SCHiPTION

[.20@ l 01010 l@l Natural Cire. I LAJ@l Low Feed Flow Alarm I

i s

' !nynv csiteur

'a auov=ToF4CriviTv @ l toCanono,cu.se@

asuist@o o, asuanLZ_J@l NA l

NA l

[2_j i o nou... et,,,osi%....C..P1,o~@

, so '

'a T P.

1010l Ol@[Z_J@l NA l

i i

, so.

't =;u'a'iis a

oisCainno=@ '

uuusi.

101010 l@l NA l

• u L 5 oF On D AC TOFACstlTV

@ [Z.j@l NA l

NFtC USE ONLY 8

DESC AiPTION 8 bsuto@l NA 1 lllllll111til f-8.9 10 Ga r,9 PO Tom Coaburn 501/968-2519 NAME OF PREPARER

,,,oy,.

8007210 VoO

o J

CAUSE DESCRIPTION AND CORRECTIVE ACTION (AttachmenttoLER50-3b8/80-018/03L-1)

The unit tripped from approximately 100% full power due to a loss of offsite power and 100% load rejection. Both emergency diesel generators came on automatically. The reactor established natural circulation with both emergency feedwater pumps (2P7A and 2P78) automatically feeding the steam generators. The emergency feedwater pumps were using a common suc-tion from the condensate storage tanks and the startup and blowdown demin-eralizer effluent. Approximately 15 minutes after the initial loss of off-site power, flow became erratic with flow rate oscillating approxi-mately 20% (between 80% and 100% of rated flow). This indicated that cav-itation was occurring in the EFW pumps. The source of the problem was determined to be the EFW suction from the startup and blowdown deminerali-zers and the operators isolated this source of EFW suction.

Since adequate steam generator level existed to allow natural circulation cooling and S/G levels were above the EFAS setpoint, EFW pumps 2P7A and 2P78 were stopped and vented. These venting operations were performed in series such that EFW flow was never interrupted. There was no complete loss of EFW suction during this event and no automatic switchover to ser-vice water suction occurred.

The cause of the cavitation (termed a loss of suction in Revision 0 of this report) was determined to be flashing of the effluent of the startup and blowdown demineralizers, which along with the condensate storage tank, was providing a common suction to the EFW pumps. A possible explanation was considered to be that loss of auxiliary cooling water to the steam generator blowdown heat exchangers might have caused the demineralizer effluent to heat up to the point of flashing. However, a more likely cause appears to be that reported in Revision 0 of this report: Heating of the feedwater train without forced flow allowed hot water to drain back through to the condensate pump discharge line which is also connect ed to the startup and blowdown demineralizer inlets. This hot water was flashing to steam and passed through the demineralizers and on to the EFW pumps suction.

In either case, the corrective action is the same.

That is, to isolate the startup and blowdown demineralizer effluent from the EFW suction. The plant startup and emergency feedwater operating proce-dures have been modified to require isolation prior to exceeding 5% power.

In addition, these valves are checked shut once per shift and documented on the shift turnover checklist. This administrative control is believed to be adequate to prevent recurrence.