ML20029C105

LER 91-002-00:on 901209,ventilation Isolation Actuation Signal Generated by High Alarm on Process Radiation Monitor RM-062.Caused by Accumulation of Noncondensible Gases in Sample Piping.Valve Packing Leak repaired.W/910318 Ltr

ML20029C105
Person / Time
Site:	Fort Calhoun
Issue date:	03/18/1991
From:	Gates W, Molzer D OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-002, LER-91-2, LIC-91-0003L, LIC-91-3L, NUDOCS 9103250353
Download: ML20029C105 (6)

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pg - - . . . -iii Omaha Public Power District 444 South 16th Street MaH Omaha, Nebraska 68102 2247 402/636-2000 March 18, 1991 LIC-91-0003L U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station P1-137 Washington, DC 20555

Reference:

Docket No. 50-285 Gentlemen:

Subject:

Licensee Event Report 91-02 for the Fort Calhoun Station Please find attached Licensee Event Report 91-02 dated March 18, 1991. This report is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv).

If you should have any questions, please contact me.

Sincerely, Jo. 22. N W. G. Gates Division Manager Nuclear Operations WGG/djm Attachment c: R. D. Martin, NRC Regional Administrator W. C. Walker, NRC Project Manager R. P. Mullikin, NRC Senior Resident Inspector INPO Records Center

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On December 9,1990, the shift chemist was obtaining a san.ple from the Reactor Coolant System pressurizer surge line. A Ventilation Isolation Actuation Signal (VIAS was generated by a high alarm on process radiation monitor RM-062 when gas fr)om the drain header was exhausted to the plint stack via the sample sink fume hood. This was apparently caused by ac:umuiation of noncondensible gases in the sample piping due to a packing leak o,. a containment isolation valve, which caused a sampling line relief valve to lift and pressurize the waste disposal header.

. Following re-evaluations of reportability, it was determined that the VIAS caused the containment isolation valves on the Containment Atmosphere Samplina ~

Penetrations to close as designed. This actuation of a portion of the Containment Isolation En 10 CFR 50.73(a)(2)(iv). gineered Safety Feature System is reportable pursuant to Corrective actions include repair of the valve packin leak evaluation of and changes to the sampling procedure, and monitoring of he pr, i mary sample system.

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010 0l2 0F 015 m i n . ,< n e r , m . m the Ventilation Isolation Actuation Signal (VIAS At Fort is designed-to Calhounmitigate Station a re linit No.1, lease of significant radiciod reactor' coolant leaks. VIAS is initiated by a Safet (SIAS - a Containment Spray Actuation Signal or a Containment Radiation High $)lgnal (CRHS). -The CRHS feature five radiation employs monitors taking(CSAS),y-sa,nples from the containment and/or ventilation stacks. Those monitors are RM 050, RM 051, RM 060, RM 061, and RM-062. Activity detected above the  !

setpoint of any one of these mo.itors can initiate a CRHS. RM 061 and RM 062 i duplicate-the functions of RM-050 and RM 051, taking samples from the vent stack

• only, c The-VIAS performs the following functions: -i

1. ifopen),

2. Closes Closes the thecontainment containmentpressure purge valves relie (f valves (if open),

3. Stops the containment purge fans if runnin

4. Closes the containment air samplin(g valves,g),

a 5. 0) ens the inlet and outlet vents to the safety injection pump roons and

't3e spent regenerate tank rooms,

6. . Places the control room ventilation system in a filtered mode, and 7.- Isolates the Waste Gas Decay Tank. 3 The primary chemistry sampling panel is located in the radiologically controlled area of the Auxiliary Building. An enclosed sample sink is ad;acent to the ,

samaling panel. The sink drain discharges to the n4ste disposal header. -The sin ( enclosure is vented through a fume hood to the plant ventilation stack.

On December 9 1990, Fort Calhoun Statior, was in Mode 1 at 100% power. At 1213 hours0.014 days <br />0.337 hours <br />0.00201 weeks <br />4.615465e-4 months <br />, the shift chemist was realigning valves at the samplirl panel in preparation fcc obtainin pressurizer wrgo line. g a sample from the_ Reactor Coolant System (RCS)The valve chemist '

liguid :s to recirculate s aray up from RCS flow to the the sampling sinkVolume Control: Tank drain, located (VCT)to the sampling panel., when he adjacent T1e chemist was informed by Control Room parsonnel that.a VIAS had been generated:by a high alarm on a process radiation monitor.

-The Control Room 03erators confirmed that the VIAS had teen initiated by a high i alarm on RM 062. T,1ey then verified that all equi) meat required to function following a VIAS had operated as designed,:with tie pessible exce tion of the-Control Room HVAC System.- An Emergency Notification System telephone report was made to the NRC on December 9,pursuant 1990, to at 10 CFR1439 hours

-based on the fact that VIAS had actuated.

' December 50.72(b)(2)(ii)90 12, 19 verified that the Control Room HVAC System had functionedA folicw-up

. properly.

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0l0 0l 3 0F 0l5 i m in e N=e= = ,en,.,- - n er m o nn initial preparation of this Licensee Event Re ort, it was determined that the VIA During S isFortnot an Engineered ystem as defined by Section Station Ur.it No.Safety I pa Features (d d)t d ESF 6.1.2.1 of the Caltnun Safety Analysis Report and thus its actuation was not reportable.

E (USAR of the),E gineered Safeguards Controls and instrumentation in USAR SectionThe VIAS is def 6.1.2.3. Section 6.1 of the llSAR had been updated in late 1989 to better categorize ES equipment and provide guidance on what ES equipment actuation was reportable. USAR Section 6.1.5 notes that nenerally only actuation of equipment within an ESF Syatem as per Section 6.1.2.1 i t reportable.

The Acting Resident inspector was notified and the ENS call was retracted.

However, subsequent discussions of this event's reportability among NRC and Omaha Public Power District (OPPD) personnel prcmpted further evaluation.

During this event, the normally open containment air sampling isolation valves had closed upon receipt of the valid VIAS. These valves are part of the Containment 1 solation System which is an Engineered Safety Feature as defined inSection6.1.2.1oftheUSAR. Therefore, OPPO determined on Februar that the event should be reported pursuant to 10 CFR 50.73(a)(2)(iv). y 15, 1991

- An irivestigation into this event determined that when the chemist opened samplin SL-171lifted, g valve SL-170 causing thetowaste recirculate disposal theheader RCS sample to become to the VCT, the relief valve momentarily pressurized. The discharge from relief valve SL-171 aoes directly i.o the waste disposal header. Given the close proximity to where SL-171 discharges into the waste header :md the location of the sarci' sink drain, the pressurization of the headce caused tlie liquid:in the samplo sink's drain trap to be blown out

-into the sam >1e sink enclosure. Th.s allowed gas from the drain header and a portion of tie liquid / gas mixttire being discharaed from the relief to be exhausted to the plant stack ~ via the sa'nole sink fume hood. The activity was

--high enough that it caused RM-062 to go into . alarm. Wit,in 15 seconds of the initial spike on RM-062 the reading dropped be'ow the computer alarm setpoint (40^0 cpm) on the alarm printer.

The 9rimary sampling )rocedure the chemist was usir.g specified that the sample system pressure must 3e maintained below 40 psig as indicated on the local pressure indicator. This was to ensure system pressure did not exceed the 50

sig relief setpoint of SL-171. The chemist was aware of this requirement and atiranted to maintain pressure below 40 psig by slightly cracking open the samp.e vt' e, but was unsuccessful due to the pressure fluctuations caused by the gas contained in the sample flow. Consequently, relief valve SL-171 lifted, w

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. Discussion with the chemists indicated th;t the only time an excessive amour.t of gas was observed during primary sampling was when a sample was drawn from the ';

pressurizer-surge line. The most probable explanation for this phenomenon is that the reactor coolant water contaim 1 in the sample tubing between the sample valves and the containment iso 1Gion Mve became depressurized, causing noncondensible cases to N released from solution. The gas then accumulated in the highest seMn ef ciping which is located downstream of the sample point

- for the urastariza sorge line. When a sample was draw. from the pressurizer

' surge the 'he <.s contained in this elevated portion of piping was carried along with,tne : giu flow. The inost likely cause for the sample coolant ,

'depressurizatSn was a known packing leak on the sampling containment isolation 1 valve HCV-2504A located inside containment.

Although it could not-be positively determined, the most probable primary cause 1 of this event was the difficultly the chemist experienced in controlling sample system pressure due to the excessive amount of gas present when the pressuriter surge.line was sampled. This apparently resulted from the packing leak on HCV-

-2504A. y

-The following corrective actions have been taken:

(1) The packing leak on containment isolation valve HCV-2504A was repaired. l

(2) Chen.rt.y has monitored the primary sampling system to identify any  !

i.oticaable decrease in noncondensible gases during sampling following the -!

)acking. leak repair on HCV-2504A. The amount of noncondensible gases has  !

aeen substantially reduced.

(3)- The chemistry sampling procedure was evaluated and minor changes were made i to prevent-recurrence of this event.

n This event has been evaluated as having minimal safety significance. The gas that was exhausted into the ventilation duct via the sasiple hood had a high

'enough activity to cause radie ion monitor RM-062 to alarm (VIAS setpoint is 10,900 cpm), a'id consequcatly initiate a VIAS. However, the maximum activity on RM-062-cannot be positively determined; the multipoint strip chart recorders  :

(RR-49,>49A activity for) RM 062 since-the actual release was of too short a duration.for the' process Therefore,~an estimate of the instantaneous site boundary concentrations was assuming a-thirty second release duration based on the Control Room

= performed (to ensure the release did not exceed the ' requirements of 10 CFR

-alarm 20.106.log)he.

T assum)tions used in the dose calculations were very conservative 1 order to provide tie most limiting radiological conditions that would have occurred 1as a result'of this event. Results of this analysis show the requirements of 10 CFR 20.106 were not exceeded. The estimated maximum MPC

- fraction at the site boundary for the most limiting isotope was calculated to be 0.1768, and the to al activity released was 0.0549 Ci.

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LERs 87-20 and 39-04 were written to address other valid VIAS actuations. Other inadvertent actuations of VIAS were reported in LERs 87-05, 87-06, 87-08, 87-09, 87-12, 87-24, 88-15 88-26, 88-38, and 90-02. None of these previous LERs resulted from the same cause as this event, 4

NRC Poca 30.A (&89)

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