ML20085N194

Ro:On 710315,during Functional Tests of Recirculation Sys, Low Flow Indication Observed on Recirculation Jet Pump 11. Caused by Welding Purge Dam Lodged in Transition Casting of Jet Pump.Flushing Program Being Conducted

ML20085N194
Person / Time
Site:	Dresden
Issue date:	03/27/1971
From:	Burke L COMMONWEALTH EDISON CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085N191	List: ML20085N194 ML20085N213
References
NUDOCS 8311100311
Download: ML20085N194 (2)

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Drecden Huclear Power Station h[f N

Rural Route No. 1

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. (;gj su March 27, 1971 Dr. Peter A. Morric, Director Divicion of Reactor Licencing U.S. Atomic Energy Commiccion 1

Washington, D.C.

20515 Gubject:

Licence DPR-25, Drecden Uuelcar Power Station Unit #3 Ref:

Telegram dated March 19, 1971 "Information Concerning a Dresden Unit 3 Jet Pump Problem"

Dear Dr. Morris:

This in to inform you about the low flow condition obcerved in a s

Recirculation System jet pump at Dresden Unit 3 during startup testing.

One purpoco of these tects ia to obtain an initial calibration of jet pump flow instruments.

Since these tectc were conducted with the

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reactor in the cold, depreccuriced condition, there wac no nuclear

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or thermal effect on the core.

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Problem and Invectication N

On March 15, 1071 during functionM MQf the Recirculation q

Uycten, cub!equent to fuel loading but prior to cigniricariT; nuclear heating. a low flow indication was obcerved on recirculation :let pump no. 11.' ~ITormal flow indications were recorded up to and including l

Ma1Tli~l t, 1971. The problem was believed to be acccciated with the flow trancmitter.

Initial checka revealed no problems with the flow transmitter or indicators.

Subsequent back-fluching of the inctrument lines, removal of various components within the cyctem (i.e. inctruraent excecc flow q

check valves, etc.) and recording of preccure data cortfirmed that the F

problem was accociated with the jet pump itcelf.

On March 17, the P

decision wac made to remove the reactor head and veccel internals to e

l gain access to the jet pumpc.

j At 5:30 A.M. on March 23, the reactor head, dryer, separator and q

Jet pump 11 ram's horn had been removed. Work on the jet pump and 9

l-cubcequent removal of the dam was performed with the water level at l

approximately2/3coreheight.

Radiation levels were approximately j

35mr/hourandthedocestoperconnelwerelow. The cauce for the j

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reduced flow in jet pump no.11 was found to be a weldina nurge dam,

lodged in the trancition cacting of the jet pump at a point where the{

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flow is divided from the ricer inlet to two noczles for jet pumps nos.

y 11 and 12.

The purge dam was lodged adainst the canting and blocked Sjy approximately three-four_tta of the flow to jet pump no. 11.

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831110o311 72o402 SENT REGION _

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s Dr. Peter A. Morric March 27, 1971 removal, the purge dam was revealed to be a standard plywood and rubber dam, approxinately 16 inchec in diameter, commonly used in construction heliarc welding operations.

Analycic and Corrective Action Preliminary evaluationc of the occurrence indicate that, due to the ci".e and characterictica of the dam, it originated from the 16 inch low preccure coolant injection (LPCI) synte:r diceharge piping.

The LPCI Gycten in the only cource of 16 inch pipe that dicchargea directly into the recirculation piping.

The cyctem v;an last crerated.;ith flow into the vercel on December 21> 1970.

It is believed that the Weldera

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,diurge dam was wached to a noint ahead of the tectable check valve

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A0 W l'901-25A or into the recirculation piping at that time, and finally wac forced into the jet pump inlet ricer during the Heelrculation Gyctem functional tecta between the period of March 12 - 15, thereby blocking flow through the. jet pur.p.

The possibility of other dama remaining in the cystem has been concidered.

All cyctens leadlig into the Recirculati.on Gyctem have now been operated at htll flow for a long zaough period to i

dislodce any objects of thic type.

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t Precautions were ta! en to prevent droppin,; frc:menta into the :ycte:1 l

durind removal and a fluchi lcyrogra::. ic being conducted to remove piece.1 l

which may remain in the cycter:..

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Very truly y9urc,

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'L. ~ Bu rke Guperticing Engineer Gtation Conctruction Dept.

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