05000285/LER-1993-001, :on 930108,discovered That Bast Level Surveillance Not Performed Properly.Caused by Inadequate Surveillance Test to Monitor Bast Levels.Mod Initiated to Provide Individual Annunciator Windows

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:on 930108,discovered That Bast Level Surveillance Not Performed Properly.Caused by Inadequate Surveillance Test to Monitor Bast Levels.Mod Initiated to Provide Individual Annunciator Windows
ML20128G230
Person / Time
Site: Fort Calhoun Omaha Public Power District icon.png
Issue date: 02/08/1993
From: Booth C, Gates W
OMAHA PUBLIC POWER DISTRICT
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-001, LER-93-1, LIC-93-0048, LIC-93-48, NUDOCS 9302120206
Download: ML20128G230 (6)


LER-1993-001, on 930108,discovered That Bast Level Surveillance Not Performed Properly.Caused by Inadequate Surveillance Test to Monitor Bast Levels.Mod Initiated to Provide Individual Annunciator Windows
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(1)
2851993001R00 - NRC Website

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Omaha Public Power District P.O. Dox 399 Hwy 75-North cf Ft Calhoun fort Calhoun, NE 680234399 i

402/636-2000 tebruary 8, 1093 LIC-93-0048 l

9, $ W clear Regulatory Commis for, Att Document Control Desk mao Station PI-137 Washington, DC 20555 Reference: Docket No. 50-285 Gentlement

Subject:

Licensee Event Report 93-001 for the Fort Calhoun Station Please find attached Licensee Event Report 93-001 dated February 8, 1993.

This i

report is being submitted pursuant to 10 CFR 50.73(a)(2)(1)(B).

If you should l

have any questions, please contact me.

Sincerely, NU. k W. G. Gates l

Vice President l

l WGG/jrg Attachment c:

J. L. Milhoan, NRC Regional Administrator, Region IV S. D. Bloom, NRC Project Manager R. P. Mullikin, NRC Senior Resident Inspector INP0 Records Center I

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ABSTRACT (umtt to 1400 spaces. I.e., approximately 15 single spaced typewritten lines) (15) on "B" Boric Acid Storage Tank (BAST)pervisor was reviewing maintenance to be performed On January 8, 1993, the Operations Su levelindication(floatswitchLAS-253)withthe Reactor Engineer. A potential 3roblem was discussed regarding the surveillance requirements for a channel checc. On review, it was identified that the BAST level surveillance was not being properly performed in that the existing surveillance test involved comparing two level indications (local and remote) from the same sensor (level bubbler), rather than comparing two independent sensors as required by Technical Specification (TS) 3.1, Table 3-2, Item IS.a.

The root cause of the event was determined to be an inadecuate surveillance test to monitor the BAST levels. A review of plant records showec that the original 1973 surveillance test incorrectly identified the local and remote indications from the level bubblers as meeting the intent of comparing independent indications.

Tem)orary " sight glasses" have been installed to provide independent level indication at eati tank.

Additional actions will include a modification to control room alarm indication for low BAST level to provide individual annunciator windows for float switches t.AS-260 and t.AS-253 for coigarison to level bubbler indications, we tem m paa,

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.mm % en BACKGROUND The Fort Calhoun Station (FCS) Chemical and Volume Control System (CVCS) includes two concentrated Boric Acid Storage Tanks (BASTS)._ The BAST 1cvels are monitored to ensure that a minimum Technical Specification required volume of boric acid is maintained in theavailabletank(s)toachieveacoldshutdownconditionatanytimeduringcorelife.

Permanent level indication on the BASTS is provided by two independent methods. The first is a level bubbler and transmitter that )rovides both a local indication and a remote (control room) level indication for eaci BAST. The local indicator provides a high level alarm in the control room at 94.2% level. The remote indicator provides alarms in the control room for low level at 80.0% level and low low level at 6.0% level.

L1T/LIA-261 provides indication for the "A" BAST and LIT /LIA-254 provides indication-for the "B" BAST.

The second level indication is an independent float switch for cach BAST that is activated at a level of 82.4%. Annunciator A2, Window C-4U in the control room alarms when a coincident low level is indicated by the float switches on both' BASTS. The float-switches for the "A" and "B" BASTS are LAS-260 and LAS-253 respectively.

FCSTechnicalSpecification(TS)3.1, Table 3-2,"MinimumfrequenciesforChecks, Calibrations and Testing:of Engineered Safety Features,-Instrumentation and Controls",

item 15.a. requires a daily check of " Boric Acid Tank Level".

The surveillance method-

- specified is to " Compare two independent sensors." This check is addressed by FCS SurveillanceTest(ST)OP-ST-SHIFT-0001,"OperationsTechnicalSpecificationRequired Shift Surveillance".

EVENT DESCRIPTION

On January 7, 1993, while operating in Mode 1 at 100% power, the Operations-Supervisor

'was involved in discussions to determine if on-line maintenance could be performed on the "B" BAST level switch (LAS-253), or if the maintenance should be scheduled during an-

.. outage. The maintenance was required in order to correct a " false" low level signal

--being provided by LAS-253 to the coincident alarm circuitry.

The' TS requirements for BAST level indications were reviewed by the-Operations l Supervisor and a Shift Supervisor.

The level indication at that time concisted of one channel, LIT /LIA-254 (local / remote), on_"B" BAST and two channels, LIT /LIA-261 (local / remote)andLAS-260,on"A" BAST.

This was considered an allowable configuration,-however, it was noted that the loss of one level channel on "A" BAST would put the plant in: a 24-hour Limiting Condition for Operation (LC0).

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.ac, we emn On January 8, 1993, the Operations Supervisor reviewed the issue and its implications with the Reactor Engineer.

The Reactor Engineer expressed concern that a problem could exist with the Surveillance Requirements for a channel check.

On review it was identified that the BAST level surveillance specified that LIT-254 be compared to-LIA-254, and that LIT-261 be compared to LIA-261.

The surveillance method specified in TS 3.1, Table 3-2, Item 15.a is to " Compare two independent sensors".

The ST, therefore,didnotcompare"lndependentsensors",butrathercomparedtwodifferent indicators from the same sensor.

On January 9, 1993, administrative controls were established to maintain "A" BAST at a minimum icvel above the alarm setpoint of LAS-260.

This would allow the level surveillance to be performed on "A" by comparing the indication from LIT /LIA-261 to the.

. alarm condition on Window C-4U, which, due to the continuous low level signal from LAS-253, would now annunciate on a low level-signal from LAS-260.

On January 12, 1993 a temporary modification was installed that would allow monitoring ofbothBASTs'levelslocally. This: modification installed a tem orary " sight glass" on each BAST.- The Auxiliary Building Operator began logging the "si ht glass" level indication every two hours in addition to the local level indicat on.

Surveillance Test OP-ST-SHIFT-000h was then revised to address comparing " sight glass" and bubbler readings.

.This event resulted in the identification of a failure to meet the IS 3.1 requirement

.for a daily comparison of independent sensors of boric acid tank level.

This report is beingsubmittedpursuantto10CFR50.73(a)(2)(1)(B).

SAFETY ASSESSM NT The event did not impact nuclear safety. BAST levels are logged every two hours-and-unexplained trends in level would have been identified by'the. operators..

Similar logs have been taken since before 1977.). An increasing level would provide ind cation ofsa.

1 plugged. bubbler or unexplained BAST in-leakage.

Corrective action would.then be taken to identify and correct the problem.. Historically, the LAS float switches are generally =

a highly reliable method for monitoring a minimum tank level. /. condition resulting in an actual low level, below that needed to reach cold shutdown, would-have been identified by the available instrumentation, a

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The root cause of the event has been determined to be an inadequate surveillance test to monitor the BAST levels. A review of plant records showed that the original 1973 surveillance test incorrectly identified the local and remote indications from the level bubblers (originally designated LIA-254 X & Y and LIA-261 X & Y) as meeting the intent of comparing independent indications.

A 3rinciple contributing factor in this event was found to be that incomplete action was tacen in responding to one corrective action identified in LER 91-008. The LER indicated that each surveillance procedure would be reviewed to ensure they met the intent of TS surveillance requirements.

Individuals were assigned-to review each i

surveillance procedure except OP-ST-SHIFT-0001, which, because of its multiple parts, was to be divided among several reviewers. However, due to an administrative oversight, the intended multi-reviewer review of OP-ST-SHIFT-0001 was not assigned, and therefore was not completed.

CORRECTIVE ACTIONS

The following corrective actions-have been or will be completed:

1.

Temporary Modification 93-005 installed a temporary " sight glass" level indication on each BAST, and OP-ST-SHIFT-0001 was revised to address comparing.

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" sight glass" and bubbler readings, in order to meet TS 3.1, Table 3-2, Item 15.a.

2.

Surveillance Test OP-ST-SHIFT-0001 has been reviewed and determined to adequately meet _the intent of associated TS surveillance requirements.

3.

Modification MR-FC-93-001 has been initiated to split the current single:

annunciator associated with LAS-260 and LAS-253. The modification will provide each BAST with an individual annunciator window.. Necessary procedure changes, including a-change to OP-ST-SHIFT-0001 to specify LAS-260 and LAS-253 as the independent sensors for comparison to LIT /LIA-261 and LIT /LIA-254-respectively, will be completed when the modification is accepted for operation.

This modification will be installed at the first outage of sufficient duration to support the work, but not later than the~1993 Refueling Outage.

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PREVIOUS SIMILAR EVENTS

.LERs91-008, 91-001,89-002, 88-008,87-037 and 87-010 discuss other events involving surveillance tests that did not meet TS surveillance requirements.

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