ML20084S892

Ro:On 710508,suction Deflector Found in Plenum of Loop 1 Steam Generator & Cap Screw from Pump B Found in Suction Pump A.Caused by Welds Cracked Through & Locating Pin Presumed to Have Been Installed.Deflectors to Be Replaced

ML20084S892
Person / Time
Site:	Palisades
Issue date:	05/18/1971
From:	Haueter R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P, Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084S888	List: ML20084S892
References
NUDOCS 8306200054
Download: ML20084S892 (5)

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Consumers

- a d W e QjgP. K j )/ Power Company Wl con.<.i on.ce. osa wou u.cn.a.n Avenue. sacuan. u.cn.g n 4920s . Are coo. si7 7sa osso May 18, 1971 Dr. P. A. Morris, Director Re: Docket 50-255 Division of Reactor Licensing License No DPR-20 United States Atomic Energy, Commission Washington, DC 20545

Dear Dr. Morris:

Att: Mr. D. J. Skovholt This letter is written to apprise you of a recent difficulty with the pr! mary coolant pumps at the Palisades Plant. At the time the difficulty was detected, the post-core-loading hot functional testing had been successfully completed and the nuclear steam supply system was being cooled down to 2600F preparatory to the initial approach to criticality.

A noise in the suction piping of the "A" primary coolant pump was detected at 8:00 PM on May 8, 1971 and the plant was cooled down. Subsequent inspection revealed that the noise was caused by the hexagonal head cap screw from the suction deflector on the "B" primary coolant pump (see attached figure from the FSAR). In addition, the suction deflector was found in the plenum of the steam generator common to the suction piping for the "A" and "B" primary coolant pumps. Damage to the impellers of both pumps indicated that one or both of the loose parts had impacted against the impellers during a period of pump operation.

Sequence of Events Heat-up of the primary system for the post-core-loading hot functional testing was initiated on April 29, 1971. During the heat-up and subsequent testing, the "A" pump operated approximately 116 hours0.00134 days <br />0.0322 hours <br />1.917989e-4 weeks <br />4.4138e-5 months <br /> and experienced nine start-stop cycles. The "B" pump operated approximately 125 hours0.00145 days <br />0.0347 hours <br />2.066799e-4 weeks <br />4.75625e-5 months <br /> and experienced ten start-stop

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cycles. Both pumps were stopped on May 7 when two of the four seals in the "B" pump started showing excessive leakage. The remainder

((}/b of the testing was accomplished with only "C" and "D" pumps in opera-g^ tion.

On May 8, a noise was detected in the suction piping to

/. the "A" pump, apparently from a foreign object. The sound could be 2 14 1, 3

/, heard distinctly without the aid of a hearing device. Cooldown of

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fri I the primary system was started at 1:00 AM on May 9 Y~V 8306200054 710802 q ow PDR ADDCK 05000255 S PDR

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O O Dr. P. A. Morris 2 May 18, 1971 Following cooldown and draining of the primary system to below the loop nozzles, the steam generator manway was removed for entry into the "A" primary suction pipe. A suction deflector (%314 lb) was found in the pienum of the loop 1 steam generator and the 1-1/2 inch x 10 inch cap acrew, which held the deflector in place, was found in the 30-inch suction pipe to the "A" primary coolant pump.

(Parts were later determined to be from the "B" pump.) Thevisualf inspection of the inlets to "A" and "B" primary coolant pumps was l accomplished by entry into the suction pipes.

Following the discovery of the problem in the No 1 loop, the manway on the No 2 steam generator was also removed and the inlets to the "C" and "D" primary coolant pumps were inspected and found to ,

be normal.

Cause of Incident The suction deflector cap screw and the suction deflector dropped off the lower end of the "B" primary coolant pump shaft. An investigation as to the cause is currently under way; however, the results are inconclusive at this time. The cap screw had been welded to the deflector to prevent the cap screw from backing out. Inspec-tion of the "A" and "B" pump disclosed the following:

"B" Primary Coolant Pump - The auction deflector and cap screw were found missing from the impeller hub. Wear marks about 1-1/2" by 1/2" were found on one edge of each of two impeller-to-shaft hexagonal head cap screws protruding from the bottom of the impeller. Matching marks were noted on two of the suction deflector ribs. AM SS locating pin M2" diameter, 7/8" long)_is-presumed to,have been installed and has not been located as yet. Impact marks

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wh e found Vn se'vefal of'the impe31er vanes, the most significant one being about 3" by 1-1/2" with about a 1/2" deflection at the lead-ing edge of the impeller vane.

Several impact marks were noted in the pump suction line, none of which showed any indication of significant penetration.

"A" Primary Coolant Pump - Cap-screw-to-suction-deflector velds were found cracked through on five_of the six sides of the hex-agonal head cap screw. Impact marks were noted on all of the impeller vanes and one vane has a tear approximately three inches into the lead-ing edge. One flap of the tear is bent back about 60 0. Several gouges were also noted in the pump casing. However, none of these are more than1/32"deeporgreaterthantwosquareinchesinarea. The suction line elbow from the steam generator has numerous impact marks caused by the bouncing of the cap screw. Preliminary inspection disclosed no cracks or deep penetrations in the clad surface.

Inspection of "C" and "D" primary coolant pump suction lines revealed nothing unusual.

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. .  ; O Dr. p. A. hbrris O

3 May 18, 1971 A possible mode of failure is stresses set up in the welds due to differences in heating rate of cap screw and deflector, or from the welding operation. These welds had been reinforced prior to the last installation of pump intervals.

Corrective Action The "C" and "D" primary coolant pump suction deflectors will be replaced by 2" flat plates (13-1/4" diameter) milled to recess the eight impeller-to-chaft hexagonal head cap screws. A hole will be machined through the center of each plate to allow free f3ow and assist in reducing thermal stress in the plate-to-impeller cap screws.

The plate will be attached with two 3/4" socket head cap screws anchored in the jacking bolt holes. The cap screws will be staked to the plate. The stake pins will be anchored in the plate.

The "B" primary coolant pump will be repaired in a similar manner. The shaft seal cartridge on the "B" pump has been replaced.

The "A" primary coolant pump suction deflector cap screw welds will be removed and the cap screw tack welded on two faces 1800 apart.

Plans for Resumption of Testing The low power physics testing vill resume when the above modifications are complete; however, we plan to run only the "C" and "D" pumps during this testing. Following the completion of the low power physics testing, other primary coolant pump modifications (addition of an auxiliary impeller to increase the differential pressure across the hydrostatic bearing) are planned. Permanent re-pairs to the pumps will be accomplished at this time.

Conclusions We conclude that the modifications described above will effectively prevent any further failure of pump components. The "A" and "B" pumps are operable but will not be used during the low power testing. We do not plan to run these two pumps until repairs to the impeller vanes are accomplished.

The 1/2" x 7/8" locating pin is sufficiently light so that there are no concerns about significant cladding wear if it reached the bottom of the reactor vessel. Also, the size nr tha pin precludes it from being carried up into a fuel bundle.

Yours very truly, Robert L. Haueter (Signed)

RBS/sm Robert L. Haueter l

Electric Production CC: BHGrier Superintendent - Nuclear Div of Compl USAEC L_

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