ML20085L772

AO 50-267/75/3:on 750123,dew Point Moisture Monitors Failed to Initiate Reactor Scram When Moisture Content Exceeded Trip Setpoint.Caused by Failure of Sample of Primary Coolant to Reach Monitor.Tech Specs Revised

ML20085L772
Person / Time
Site:	Fort Saint Vrain
Issue date:	02/12/1975
From:	Brey H PUBLIC SERVICE CO. OF COLORADO
To:	Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20085L744	List: ML20085L742 ML20085L746 ML20085L751 ML20085L761 ML20085L767 ML20085L772
References
AO-50-267-75-3, NUDOCS 8311020445
Download: ML20085L772 (5)

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~?.s 3s[T\'zO Mr. E. Morris Howard, Director Region IV, Office of Inspection and Enforcement Nuclear Regulatory Commission REF: Facility Operating License P. O. Box 5039 No. DPR-34 White Settlement, Texas 76108 Docket No. 50-267

Dear Mr.Howard:

Enclosed please find a copy of Abnormal Occurrence Report No. 50-267/75/3, submitted por the requirements of the Technical Specifications.

Very truly yours, /) j d . - U e h -

• OE Frederic E. Swart Superintendent Nuclear Production Fort St. Vrain Nuclear Generating Station FES:11 cc: Mr. Angelo Giambusso 8311020445 760513 PDft ADOCK 05000267PDR S

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REPORT DATZ: 1/31/75 .ABh0RMAL OCCURRENCE

. .* t i OCCURRENCE DATE: 1/23175 ..

FORT ST. VRAIN NUCLEAR CENERATING STATION -

PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COLORADO 80651 s9 V kn\.1 - sf Y.} ,

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REPORT No. 50-267/75/3 .

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IDENTIFICATION OF (\

OCCURRENCE: N .

Failure of the Dew Point Moisture Monitors to initiate a reactor scram t when moisture content of the primary coolant exceeded the trip setpoint.

This is identified as an Abnormal Occurrence per definition 2.lb of the Technical Specifications and a violation of Limiting Condition for Operation, LCO 4.2.11, Loop Impurity Levels, Low Temperatures.

CONDITIONS PRIOR TO OCCURRENCE: -Steady State Power Routine Shutdown Hot Shutdown Routine Load Changu Cold Shutdown X Other (specify)

Refueling Shutdown Reactor critical at approximately Routine Startup 10-5%.of. Rated Thermal Power for training purposes.

t The major plant parameters at the time of the event were as follows:

Power PTR 0 MWth ELECT. O MWe Secondary Coolant Pressure 1250 psig Temperature 182 'F Flow 349,000 t/hr.

Primary Coolant Pressure 234 psig Temperature 182 'F Core Inlet 193 'F Core Outict  !

Flow 2 x 105 #/hr.

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DESCRIPTION , ,

OF OCCURRENCE: ,

Page 2 On January 23, 1975, preparations were made to take the reactor critical ,

for training purposes. Two helium circulators, A and B, were accelerated i to approximately 2300 rpm at approximately 0130. Moisture levels in the ,

primary coolant at this time was < 1000 ppmv,-well within the limit of 5000 ppmv stated in LCO 4.2.11. An increase in moisture concentration was noted on the panametrics moisture monitors shortly following acceleration of the helium circulators. This was considered normal from our past experience ,

under similiar circumstances. ~ ~

The reactor was taken critical at approximately 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br /> and power raised to 10-5 %. It was noted that the moisture level was continuing to rise'in the ' . i primary coolant but the trace on the chart indicated an approach to an equilibrium condition of about 1500 ppmy, still within the limits of LCO 4.2.11.

It should be noted that the panametric monitor on I-05 had alarmed at 500 ppm.

As the morning progressed, the indicated moisture level in the primary coolant stabilized at approximately 1500-2000 ppmv. At the same time it was noted that-it was necessary to continuously adjust the control rods into the core to maintain the desired power level. This initial control rod movement was, at the time, thought to be due to overcooling of the, core with helium flow. As core reactivity continued to change the mechanism causing it was not immediately obvious. The reactor was scrammed when the core reactivity reached .008AK-greater than expected.

As a part of the investigation into the noted reactivity changa, the two high ,

level moisture monitors were switched to the indicate mode and~both indicated 4500-4600 ppm moisture. ,

Because of the discrepancy noted between the dew point and panametric moisture monitors, sampics of primary coolant were drawn and analyzed for moisture in the gas chromatograph. These analyses indicated moisture levels in excess of 10,000 ppm.

APPARENT CAUSE OF OCCURRENCE: X Design , Unusual Service Cond.

Including Environ.

Manufacture Component Failure .

Installation /Const. I~ Other (Specify)

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Operator ,

X Procedure '

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• n A check of the dewpoint moisture monitor mirror temperature setting ~ indicated

[ . it was set at 105'F which corresponds to a moisture level of 5000 ppm at 220 psia.

s In reality, the primary coolant pressure was at'246 psia and at this pressure,.

the 105*F dewpoint temperature corresponds to 4800 ppm. This still did not . .

! - explain the difference between the chromatograph reading and the dewpoint moisture monitor readings.

Apparently a representative sample of primary coolant was'not reaching the moisture monitors..

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ANALYSIS OF OCCURRENCE:

At the time of the incident in question, the PCRV cooling water system was maintaining the concrete temperature at approximately 105'F. The sample lines to the dew point moisture monitors from the helium circulator outlets must come through the concrete and therefore, the sample line temperature ,

is controlled by the PCRV concrete temperature. .

Assuming the concrete / sample line temperature to .be 100f l05*F, condensation '

of moisture would take place in the sample line at moisture concentrations of 4100-4800 ppm in the primary coolant. With this in mind, it is reasonable to assume the sample being received by the moisture monitors was saturated at some temperature between 100-105*F and that the monitor would never have indicated a moisture level higher than 4600 ppm until such time as the sample line condensation accumulated to the point that a drop of liquid water reached the monitor and caused it to trip.

The sample line for the Panametric moisture monitors also comes through the PCRV wall and runs for a number of hundreds of feet through areas of the plant whose temperature is less than 100-105'F.

If we assume a minimum sample line temperature of 80*F, the maximum moisture concentration that could be indicated at 246 psia would be approximately 2000 ppm.

It should be noted that after a number of hours, liquid water was seen flowing from the sample lines at both the dew point and panametric moisture monitors.

In conclusion, it can be said that the dew point moisture monitors were functioning properly and were correct,1y indicating the moisture concentration in the sample delivered to them. The limiting factor on the ability of the moisture monitors to see the correct concentration is the sample line temperature.

CORRECTIVE ACTION:

Because of discrepancies in LCO 4.4.1, LCO 4.2.11, and LSSS 3.3 of the Technical Specifications which all concern allowable primary coolant moisture levels, a revision for the Technical Specifications had been developed and submitted to the NRC for consideration prior to the problems experienced -

on January 23, 1975.

This proposed Technical Specification revision takes into account the sample line temperature effects to assure a dew point monitor temperature trip setting of < 100*F.

Following removal of moisture from the primary coolant to allow operation of the reactor within the limits of LCO 4.2.11, the reactor will again be taken critical to determine its reactivity status which will be reported at that time.

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s FAILURE DATA /

SIMILIAR REPORTED OCCURRENCES:

, Unusual Occurrences 50-267/74/7 and 8 dealt with spurious trips of these, ,

moisture monitors.

PROGRA3DIATIC IMPACT: is

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The programmatic impact of this moisture monitor failure to initiate a scram is not significant; however, removal of moisture from the primary coolant is delaying continuation of the plant testing program. U r

CODE IMPACT:

None RECOSDIENDED: .

4W APPROVED:p m - ,. ,

H. Larry'Brey l' ) Frederic E. Swart

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Superintendents 0perationd Superintendent Nuclear Prod.

Fort St. Vrain Nuclear Public Service Company Generating Station of Colorado O

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