ML19260B238

LER 79-033/03L-0:on 791030,suppression Pool Level Discovered Below Tech Spec Limits.Caused by Suppression Chamber Narrow Range Level Instrumentation Responding Slowly to Change in Suppression Pool Level.More Water Added to Suppression Pool

ML19260B238
Person / Time
Site:	Quad Cities
Issue date:	11/27/1979
From:	Vahrenwald J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19260B230	List: ML19260B229 ML19260B238
References
LER-79-033-03L-03, LER-79-33-3L-3, NUDOCS 7912070450
Download: ML19260B238 (2)

Text

NRC FOPM I66 U.S. NUCLEAR REGULATORY COMMISSION (7 77) 1.lCENSEE EVENT REPORT CONTROL BLOCK: l 1

l l l l lJh 6 (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION) 7 o 1 8 9 ll l L LICENSEE l Q' l A CODE l D l 141 l@l0 15 l0 l0 l- l0 l 0 l 0 l - l 0 l 0 ! 025l@l26 4 l LICENSE LICENSE NUMt$ER 1 l1 l1 l1 l@(57 car TYPE J0 l

5d l@

CON'T 7

O 1 8

5OuRC lL l@l015 lo lo I 012 Sl4 @lIlo13101719 @ l 11 12 12 I7 I ol@

60 61 DOCKET NUMB ER 68 69 EVENT D ATE 74 75 REPORT DATE 60 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h o 2 l While addino nitrocen to the suooression chamber and after decreas*ng the drvwell- 1 o 3 l suppression chamber differential pressure from 1.48 osid to 1.23 osid, the suppress iori o 4 l 0001 level was observed to be approximatelv 3/8 inches below the Technical I o 5 l Specification 3 7.A.l.b limit for suppression pool inventory. Since the suporession ]

o 6 l pool temperature was moderate and because the limits for suopression cool level are l 0 7 l conservative, safe piant operation was not jeopardized. I o a l l 7 8 9 80 SYSTEM CAUSE CAUSE C OV P. VA LV E COCE CODE SUBCOCE COVPONENT CODE SUSCODE SUSCODE 7

O 9 8 9 l S l A l@ l B @ l A l@ ll N lS lT lR 10 11 12 13 U

18 l@ [Tl@ lZl @

19 20

,,_ SEQUENTI AL OCCURRENCE REPCRT REVISION LER RO EVENT YE AR REPORT NO. CODE TYPE N O.

@ aEPOAT l 7l 9l l-l l0l3l3l l/j l0 l3 l Ll l-l 0l 21 22 23 24 26 27 29 ;9 3L 31 32 ACTION EUTUAE EFFECT SMUTDOWN ATTSCHMENT NP R O.4 PRIVE COUP. CO?.*PO N E N T TAKEN ACTION ON PLANT VETHOO HOURS SU8 vlTTED FORV dO8. SUPPL:ER VANUFACTURER l33XlglJ4 Flg l35 Z lg l36Z lg l0l0[0 40 l

41 Y lg l Ylg {g 42 43 l B l 0 l 8 l 0 lg 44 47 CAUSE DESCRIPTION AND CORRECTi\T sCTIONs 3'h i o l The suppression chamber narrow range level instrumentation was slow in responding ]

1 i; to a small change in suppression pool level, the reading of which was compounded by I

. maintaining a differential pressure in the drywell and suppression chamber. l

, 3 [

Corrective action was to add more water to the suppression pool, bringing the level i ,, g within TS limits.  ;

7 8 9 80 STA S  % POWER OTHER STATUS 15 O RY DISCOVERY DESCRIPTION Operational Event 1 5 l E l@ l 0l 9l 8l@l ' "

NA l Al@l l A TIVITY CO TENT RELE ASED OC RELE ASE AMOUNT OF ACTIVITY LOCATION 09 RELEASE 6 NA l NA 7

1 8 9 l Z l @ 10l ZI@l 11 44 45 80 l

PERSONNEL EXPOSUAES NUVBER TYPE D ESC RIP TIO N 1 7 l0l0l0l@lZl@l NA PERSONNE L INJURIES NUM8E R CESCRIPTION y l0l0 0l@l ' '

NA ] 1d )?R l toss Os Oa oEmeSo rACiuTv43 TYDE D E SCRIP T ION

[h i 9 l Zlgl NA ~912078 4 I 7 4 9 10 80 Pb8 L ICI TV NRC USE CN' Y a D

2 o 'SSt#DL J8l ESt AIP7,oag NA l ll1llllll1ll l ;,

7 s 3 0 68 69 E0 ;

NAN 1E OF PREPARER PHONE: 309-654-2241 ext. los 2

1. LER NUMBER: LER/R0 79-33/03L-0 1I. LICENSEE NAME: Commonwealth Edison Company Quad-Cities Nuclear Power Station Ill. FACILITY NAME: Unit One IV. DOCKET NUMBER: 050-254 V. EVENT DESCRIPTION:

On October 30, 1979, while adding nitrogen to the suppression chamber and after decreasing the drywell-suppression chamber differential pressure from 1.48 psid to 1.23 psid the suppression pool level was observed to be approximately 3/8 inches below the Technical Specification 3.7.A.l.b limit for suppression pool inventory.

VI. PROBABLE CONSEQUENCES OF THE OCCURRENCE:

The safety implications of this event were minimal. Since the suppression pool temperature fwas moderate (85 F) and because the limits for suppression pool level are conservative, the pressure suppression system was always available and would have performed as designed. All other pressure suppression and emergency cooling systems were available.

Vll. CAUSE:

The instrumentation used for measuring narrow range suppression pool level is sometimes slow in responding to small changes in pool level as in the case of this report. The reading of the instrument is also compounded by maintaining a drywell-suppression chamber differential pressure. A small increase in drywell pressure will cause the water in the downcomers to be forced into the pool inventory and subsequently raise the pool level. A small decrease in drywell pressure will result in a small decrease in pool level. These small variations inherent to the level instrumentation do not affect the safety factors which have been established, nor in any way jeopardize safe plant operation.

The suppression pool level is closely monitored to assure that the proper level is maintained. In addition, it was not until a change in drywell to suppression chamber differential pressure was initiated that the control room level indicator showed slightly less than the required level. -

Vill. CORRECTIVE ACTION:

The immediate corrective action taken was to add water to the suppression pool bringing the level within the Technical Specification limits. The inability of the suppression pool level instrumentation to always promptly respond to small changes in pool level has been acknowledged in the past. At present an ef fort is being made to evaluate the instrument design to determine the feasibility of improving the instrument by adding a more advanced electronic package to the existing instrument configuration.

1514 229