ML20083K710

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Responds to NRC .Forwards Addl Info Re Decay Heat pump-1A Shaft Failure.W/Encl Tech Info & Test Repts
ML20083K710
Person / Time
Site: Crystal River Duke Energy icon.png
Issue date: 08/31/1978
From: Stewart W
FLORIDA POWER CORP.
To: Reid R
Office of Nuclear Reactor Regulation
Shared Package
ML20083K722 List:
References
NUDOCS 7901300120
Download: ML20083K710 (7)


Text

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mt, ou ?ee ,e se oC, e cu , e I50 e Florida gg W. P. STEWART. DIR ECTOR POWER PRODUCTION August 31, 1978 Mr. Robert W. Reid, Chief Operating Reactors Branch #4 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72 Decay Heat Pump Failure

Dear Sir:

In your letter of August 3, 1978, you requested additional information regarding the Decay Heat Pump - 1A shaft failure. That information is enclosed so that you can continue your review.

If you need any further information, please contact this office.

Sincerely, FLORIDA POWER CORPORATION W. P. Stewart WPS/ hew /

File: 3-B-15 R02 (8/31) iyg.JCP'I DOC'Ag M COPT gjg e

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7 9 013 0 0 /Ao a C6i,C.;! 7'ic" ?" * .:, ~w un Street South e P.O. Box 14042 St. Petersburg. F6orda 33733 813-866-5151

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STATE OF FLORIDA COUNTY OF PINELLAS W.P. Stewart states that he is the Director, Power Production, of Florida Power Corporation; that he is authorized on the part of said company to sign and file with the Nuclear Regulatory Commission the information attached hereto; and that all such statements made and matters set forth therein are true and correct to the best of his knowledge, information and belief.

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DO W.P. Stewart 4

Subscribed and sworn to before me, a Notary Public in and for the State and County above named, this 31st day of August, 1978

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i' Notary Public [.

p i Notary Public, State of Florida at Large, My Commission Expires: July 25, 1980-k

REQUEST FOR ADDITXONAL INFORMATION CRYSTAL RIVER 3 DHP-1A SRAFT FAILURE j l

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1. Additional assurance is needed that the corrective action proposed for DHP-1A will restore the ability of this pump to perform its intended function. Therefore, testing in the following areas is requested:

(1) Verification that the minimum required flow and head characteristics are maintained.

Response

The hydraulic characteristics of DRP-1A, following component inspection and reassembly, have been monitored by the performance of surveillance procedures. During the first 46 hours5.324074e-4 days <br />0.0128 hours <br />7.60582e-5 weeks <br />1.7503e-5 months <br /> of continuous run-in, SP-340 "ECCS PUMP OPERABILITY" was run on a i four hour interval. In all cases, the flow versus developed head characteristics were within the acceptable limits for this pump as specified by Section XI of the ASME codes. These surveillances are run with pump flow at rates required during accident conditions.

In addition, vibration data taken during this time as part of SP-340 indicate levels well within acceptable limite. Levels of

.40 to .68 mils displacement and .10 .20 in/sec velocity were recorded and are considered to be indicative of a smooth running condition.

New baseline, alert and action levels, will be developed and the running of SP-340 will revert to its normal monthly cycle.

(2) Verification that impeller rubbing has been eliminated and that -

excessive vibration levels do not exist at flow rates at which this pump may operate. This should be accomplished.using accelerometer data taken from the bearing housing in the velocity mode, to ascertain peak values at..various frequencies, and demodulated acceleration data taken for the pump casing, to ,

ascertain the degree of pump rubbing or impact with the stationary wear rings or casing. -

Response

Enclosed is a copy of the vibration analysis for DH Pump 1A obtained using external accelerometers. Also enclosed is a copy of the DH ' Pumps lA baseline external accelerometer ' report.

(3) A thorough inspection of'the pump at the conclusion of the-testing.

1

Response

The 1A Decay Heat Pump was removed ~ frc< the DH Pit and inspected ,

i on August 16,11978. The ' inspection ~gy contact between the impeller and casing indicated that }heEs was no contact begw 1 -3790/Jk'0 /gc '

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thess parts. Also, thera was no contact with either the casing or bzck covar wear rings and impaller wtsr rings. The unit was completely disassembled. During the disassembly, it was noted that the shaft sleeve would not easily come off - the shaf t. The 1

shaft sleeve was pulled off by using the mechanical seal gland plate. This was the only way the sleeve could be removed without damage. This method of removal did, however, result in breaking the carbon ring in the mechanica.1 seal. The shaft and sleeve were inspected and there appeared to be corrosion on the shaft.

4 It is believed that this was responsible for the difficulty in removing the shaft sleeve. The shaf t and bearings were removed from the bearing housing. The bearings appeared acceptable. The only abnormal item was that' the oil slinger rings were both loose and riding against the-thrust bearing. There were no other indications in the unit that could have caused the high vibration

reading at approximately forty-five (45) times operating speed, as noted on the noise survey. Final. inspection-status of the pump showed that there was no contact between rotating and stationary parts in the pump and the bearings still appeared to be good.

l In order to re-assemble the pump with new bearings and in order

, to Liquid Penetrant Inspect the shaf t, the pump half coupling had to be . pressed of f the shaf t. During this operation, the bearing cover on the outboard end of the pump was broken.

The shaf t, .af ter all bearings, slinger rings, and coupling halves had been removed, was Liquid Penetrant Inspected. This

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inspection showed no defects in the shaf t in any location.

The following parts were ordered on Monday, August 14, 1978, from Worthington Pump Company:

Two (2) sets of Radial Bearings Two (2) sets of Thrust Bearings - Total of four (4) Bearings Two (2) sets of Inboard Oil Seals l Two Thrust Bearing Lock Nuts Two Thrust Bearing Lock Washers

.These parts arrived on Thursday, August 17, 1978. On Wednesday, August 16, 1978, the following parts were ordered:

Two (2) Carbon Rings for the Mechanical Seal One (1) Bearing Cover

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j. These parts are still not on site as of this report.

The pump was re-assembled, less the bearing cover, on August 17, 1978. The corrosion indications on the shaf t and matching marks on the sleeve were removed by using emory cloth. There was very

-little depth to the. indications and these were removed ~from both pieces quite easily. The impeller was placed on the shaf t and a rubbing / contact sound could be heard in the wear ring area. The

, impeller was removed, by using a pulley, on August 18,- 197.8, and I

the rubbing sound was detennined to be - caused by a' small piece of ~ trash between the wear rings on the impeller and back ' cover.

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Tha impaller waar rings and casing waar rings were cleaned up and the impeller re-installed. The unit rotated with no indication of contact or noise.

It was the recommendation of Engineering, B&W, Lynchburg, that the broken Bearing Cover, which had been brazed together by Florida Power personnel, be re-installed in the pump. The re-paired bearing cover is equal to or better than a new bearing c o ve r. Florida Power agreed and the repaired bearing cover was installed on the 1A Pump. l The unit was installed in the line and operated on August 19, 1978. The unit appears to operate smoothly.

2. What is the maximum time that the decay heat pumps must operate in the recirculation mode following a loss of coolant accident and approx-imately how long had DRP-1A operated in the recirculation mode prior to the most recent failure?

Response

A decay heat system design review was performed by B&W Safety Analysis and Systems Engineering personnel. The review included decay heat system operational requirements with regard to the capability of the decay heat system to perform its intended func-tion.

During LOCA, the decay heat pumps would be required to operate in the minimum recirculation flow mode (85-100 gpm) for a maximum time of fif teen (15) hours. This is the time required for a depletion of the BWST inventory during a small break LOCA. .Sub-s eq ue nt to this maximum time, the decay heat pumps would be placed in the " piggy-back" mode of operation with the HPI System, thereby increasing the pump flow rate to approximately 550 gpm.

Since the decay heat pumps have been determined to be suitable for at least 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> operation in the minimum recirculation mode, they would, in fact, perform their intended function during a LOCA.

From the time of the first failure of DEP-1A and its subsquent repair and the most recent failure, DHP-1A has not been operated. -

at all in the recirculation mode (85-100 gpm).

3. Provide the information or data which supports the revised restrie-tions for operation at minimum or recirculation flow rates.

Response

Based on results of a design review meeting with Worthington (DH Pump manufacturer) and with Worthington's authorization, B&W has informed Florida Power Corporation that the low-flow recircu-lation restrictions have been modified. The new restrictions, which allow operation of the DHP's during the recirculation mode for fif teen (15) hours continuously and up to eighty (80) hours

\ total within the life of the pump, were reported to you in our letter dated July 7, 1978. Attached is a copy of the B&W 1etter Simpson (InfoReq) D34

to Florida Powar Corporation revising these limits on the oper-ation of the DH Pumps at CR #3.

4. In order to facilitate our review of DRP-1A and the corrective actions to be taken, please provide detailed engineering drawings of the DRP showing critical dimensions.

Response

It is Worthingt'on's Corporate Policy not to release engineering draw-ings of pumps. This is being pursued.

5. Because of a similar but less severe misalignment between impellar and casing on DRP-1B is not precluded by its operating history and because inspection of the previous DRP-1B shaft at the time of its replacement

" revealed indications that could be interpreted as initiation of f atigue damage" (B&W Preliminary Significant Deficiency Report 5-77, May 3,1977), you are requested to verify by inspection proper align-

. ment between the DRP-1B impeller and casing and report the results of this inspection. Please inform us, in your seven day response to question 1, of your intent with respect to inspection of DEP-1B. You are also requested to provide the pump signature of DRP-1B which you refer to in your letter.

Response

DRP-1B was removed from the line for disassembly and inspection on Friday, Augus t 25, 1978. Initial observation indicated very minor contact between the impeller and casing.

The contact marks on the casing and impeller of the DRP-1B pump indi-cated that during some time in the pump's life the impeller had touch-ed the casing. The marks on the impeller were approximately 3/8" wide and in three different areas on the impeller. (The marks are on the

-front shroud of the impeller at the maximum outside diameter of the wheel.) Each area (3 areas) is 3 to 5 inches long and approximately 60* to 90* apart for approximately 240' on the impeller. The single

. contact mark on the casing is opposite the discharge splitter vein next to the pump casing pedestal foot. This ma'rk is approximately 1-1/2 inches long by 3/8 inch wide. The marks are dark in appearance compared to the machined areas on the pump casing and impeller. There is no evidence of metal removal from either the impeller or casing.

The appearance of these contact areas would indicate the marks are

' ld, o possibly made during Worthington shop testing.

The scratch marks on the suction wear rings were irregular in location on the ring and did not propogate around the impeller wear ring area.

Each mark had a start and stop point. This is typical of trash running through the rings.

Worthington is being contacted in regard to the thicker than normal Casing Gasket that was used in DRP-13.

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TMPELLER CASING Contact marks Contact mark 3" to 5" long 1-1/2" long by 3/8" wide by 3/8" wide 1

It was B&W Lynchburg's recommendation to remove 1/8 inch from the back of the impeller hub thus increasing the clearance between impeller and casing. The remaining observation on the pump was that what appeared to be trash going through the wear rings on the impeller suction had scuffed up the suction wear rings on both the pump casing and impeller.

The unit was completely disassembled and the shaf t dye checked on Friday night. There were no indications on the shaf t.

The-1/8 inch of material was removed from the impeller hub and the unit reassembled with new bearings, oil seals, and mechanical seal on Saturday. The old shaf t and impeller were returned to the DHP-1B pump.

The "B" pump shaf t showed some corrosion marks under the shaf t sleeve, similar to "A" pump shaft. These were removed with emory cloth. The completed unit, prior to reinstallation in the casing, was checked for impeller-to-casing clearance. Below are the readings taken:

Back Cover Flange to front Shroud at Impeller: 5-1/2".

Depth from Casing Flange to bottom of Casing Waterway:

A 5/8" B 7/8" C - 5/15/16" 4

D 7/8" Minimum clearance by measurement is 1/8".

The unit was installed in the system and operated on Sunday, August 27, 1978.

The pump signature of DRP-1B and a copy 'of the DH Pump 1B baseline -

external accelerometer reports are attach'd.e k

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