05000302/LER-1989-009, Submits Justification for Restart of Plant as Committed to in LER 89-009.Based on Test & Insp Data,Util Has Determined That Continued Operation W/Existing DHR Pumps Will Not Pose Unresolved Safety Concerns

Submits Justification for Restart of Plant as Committed to in LER 89-009.Based on Test & Insp Data,Util Has Determined That Continued Operation W/Existing DHR Pumps Will Not Pose Unresolved Safety Concerns

ML20247R363
Person / Time
Site:	Crystal River
Issue date:	05/30/1989
From:	Widell R FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0589-14, 3F589-14, NUDOCS 8906070214
Download: ML20247R363 (7)

LER-2089-009, Submits Justification for Restart of Plant as Committed to in LER 89-009.Based on Test & Insp Data,Util Has Determined That Continued Operation W/Existing DHR Pumps Will Not Pose Unresolved Safety Concerns

Event date:
Report date:
3022089009R00 - NRC Website

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May.30, 1989.

3F0589-14 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72' Report of Decay Heat Pump Test and Inspection

Dear Sir:

Florida Power Corporation (FPC) completed the Decay Heat Remova) (DHR)

Pump, DHP-1B, flow test described in our April 17, 1989 correspondence, and its follow-up disassembly and inspection. The preliminary assessment on the pump test and inspection data has been completed. Initial evaluations. indicate the DHR Pumps are capable of providing flow well below the vendor's minimum flow recommendations described in the April 1989 letter. A discussion justifying the restart of Crystal River Unit 3 as committed ' to in Licensee - Event Report 89-009-is prcvided herein.

FLOW TEST A general description of the flow test is outlined as follows:

1. The pump was tested in a recirculation mode to the Borated Water 4 Storage Tank (BWST).

o$ 2. The pump was tested over a range of flows, starting at 3000 gpm

@1C-O co and decreasing in pre-established increments to approximately 130 gpm. The pump was operated long enough at each flow increment to eg collect data, including a ten hour run at a total pump flow of

-g 400 gpm. The extended 400 gpm run was based on an expected oQ " worst-case" pump flow of 500 gpm for 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> during the T postulated small break loss of coolant accident (SBLOCA),

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$A adjusted for a 100 gpm and a 5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> margin.

ED GENERAL OFFICE: 3201 Thirty fourth Street South + P.O. Box 14042 + St. Petersburg, Florida 33733 + (813) 866 5151 A Florida Progress Company ,

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h. 6 May 30, 1.989 3F0589-14 Page 2

3. The parameters monitored during the flow test include:

a. Pump suction and discharge pressures to monitor the head characteristics of the. pump,

b. Pump flow to the BWST and flow in the pump minimum recirculation line to monitor total pump flow.

c. Pump- suction and . discharge. temperatures to monitor temperature rise across the pump.

d. Motor current to monitor the power consumption of the pump.

e. . Pump bearing cooling water inlet and outlet temperatures to monitor changes in bearing temperature rise.

f. Overall and filtered horizontal and vertical vibration at all four bearings, and overall filtered axial vibration at inboard end of pump to monitor bearing condition and dynamic loading of the bearings.

4. Satisfactory operation of the pump was assessed at each flow increment. Some of the key acceptance criteria (not all-inclusive) for this test were:

a. Vibration s 0.7 inches /second (ips).

b. Pump delta T S 15 0F.

c. Bearing cooling water temperature rise -

no absolute criterion, but baseline temperature was noted and any sudden increases were to result in termination of the test.

5. Bearing oil samples were taken before and after the test and analyzed to verify bearing condition was not affected by the test.

FLOW TES"l FVALUATION Following the flow test, data was provided to FPC's consultant, MPR Associates, Inc. for evaluation.

L 1. - Evaluations

a. Head-Flow -

Pump developed head for the various flow increments was measured during the test and compared against the vendor's pump curve. The test data was generally above, but within 5% of, the vendor's curve. Further, the pump

b . .

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May 30, 1.989 3F0589-14 Page 3 head at design flow (3000 gpm) remained unchanged as measured before and after the low flow test,. indicating no degradation of pump function as a result of the test. Based on this, the pump functioned as expected throughout the test. i

b. Motor Power -

The motor current data indicated the motor power was within 6% of the vendor's curve. Based'on this, the pump was drawing power as expected throughout the test.

c. Temperatures

~

Process -

The temperature rise across the pump was measured to determine if flow was adequate to prevent excessive pump heatup. Throughout the 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> test at 400 gpm, the temperature rise across the pump was about the same as for design flow and was insignificant.

Bearina Coolina Water - The temperature rise across the bearing cooling water jacket was monitored to ensure the bearing was not being overloaded or degraded. No temperature rise across the bearings was measured at any flow, indicating that the bearings did not produce an appreciable amount of heat. Thus, bearing overload does not appear to be a concern.

d. Pumo Bearina Vibration - The vibration at each bearing was measured to indicate whether dynamic loads from low-flow operation would result in bearing or shaft failure.

Vibration data was obtained for four bearings in three dimensions for each flow increment tested. All of the vibration data obtained was bounded by the 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />, 400 gpm test run and the 130 gpm minimum flow test run. These cases are discussed below.

At the indicated flow rate of about 400 gpm, thrust bearing vibration in the vertical direction was.0.46 ips (all other l measured vibrations were less) . This was the average value for this bearing and direction over the lo hours at this flow rate. The peak value during this 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> was 0.55 ips at the half hour mark when minor flow adjustments were in process. These flow adjustments are believed to be the cause of this high reading, because vibrations returned to a steady reading of around 0.46 ips after the adjustments were made.

During the 10 hour1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> run period at 400 gpm, all vibrations were fairly steady without an upward trend of vibration magnitude. When flow was throttled to minimum flow (130

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May 30, 1989 3F0589-14 Page 4 gpm), the thrust bearing vertical vibration increased to 0.54 ips. In addition, the vibration levels at the pump flow rate of 3000 gpm at the end of the test were not significantly different from the vibration levels measured at the same flow rate at the start of the cest. This result indicates that no significant degradation regarding vibration occurred as a result of the test.

Operating experience of the DHR pumps at Crystal River Unit 3 includes a shaft failure after nine days of operation at minimum recirculation flow (80 -

100 gpm). Based on the April 1989 test data, the vibration levels measured at the 130 gpm flow test were about 17% higher than the vibration levels measured at the indicated flow of 400 gpm.

Therefore, the vibration experienced during this previous failure should have been at least 17% higher than if the flow rate was at 400 gpm, indicating the pump could operate at 400 gpm for longer than nine days. In comparison, the requirement for operation at 500 gpm for only five hours (versus nine days) indicates substantial margin regarding vibration related failure.

The effects of available net positive suction head (NPSHA) on vibration were not evaluated during this test because NPSHA could not be reduced to the SBLOCA predicted NPSHA value of 14 feet in a practical manner. However, industry experiments done on a similar style of pump suggest that fluctuating radial and axial loads do not change significantly for a NPSHA above the required net positive suction head (NPSHR). The NPSHA during the Decay Heat l Removal Pump test was about 115 feet, and the NPSHA during a SBLOCA is about 14 feet. Both of these values are above the vendor's estimated NPSHR value of 7 feet. (This value is from the estimated performance curves for these pumps-Worthington Drawing E185234, "8HN194", dated May 9, 1967 at the lowest indicated flow, 1000 gpm.) Accordingly, the difference in NPSHA between the test and SBLOCA operating conditions are insignificant with regard to vibration.

In addition, the vibration levels at or above indicated flows of 1000-1250 gpm were as low as the vibration levels at the 3000 gpm design flow.

e. Bearina Oil Analysis - Oil samples taken before and after the test were analyzed and compared to each other to assess bearing degradation during the test. This oil analysis indicates that no bearing degradation occurred during the test.

May 30, 1989 '

3F0589-14 Page 5

2. Conclusion This test verified that the DHR pumps will operate acceptably during a SBLOCA. This is based on the DHR pump test where it operated acceptably for 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> at an indicated flow rate of approximately 400 gpm, and other historic operational data as referenced in correspondence from MPR dated May 26, 1989. The process temperature data did not indicate a concern for pump overheating. Bearing cooling water inlet and outlet temperatures did not diverge to indicate bearing overheating, and the before and after oil samples indicated no degradation of the bearings. There are substantial margins for the . vibration magnitudes expected during piggy-back operation. Also, the effect of NPSHA on vibration levels are considered insignificant. MPR has concluded the DHR pumps are capable of providing flow at or above 400 gpm for at least 3 days.

The test data also indicated that pump operating characteristics (i.e., vibration and process temperatures) at indicated flows of 1000-1250 gpm are no different from those found at the design flow (3000 gpm). This indicates indefinite pump operation at flows down to 1000-1250 gpm is as acceptable as operation at 3000 gpm.

The MPR interim report was made available for review to the NRC contractor. representatives at the CR-3 site.

DHR PUMP INSPECTION The DHR Pump utilized to perform the low-flow test was disassembled and inspected on May 10, 1989. The inspections witnessed by NRC contractor personnel included casing and stuffing box wear rings, volute tongues, shaft, shaft sleeve, impeller vanes, impeller wear rings, impeller shroud, and pump bearings. A liquid penetrant examination (PT) was performed on the DHR Pump shaft at the impeller end (100%, 3600, from bearing shoulder to impeller, excluding threads), the impeller vane to hub attachment area (both top and bottom), and the impeller shroud. No cracks were identified during the inspection process. The test was viewed by a qualified QC inspector, an Engineering representative and a NRC representative.

There were no indications of unusual wear or damage on any of the components.

JUSTIFICATION FOR RESTART OF CR-3 The flow rate and duration requirements for the DHR pumps are outlined below, including the basis for these requirements and the justification as to why the pumps are able to satisfy these requirements.

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May 30, 1989 3F0589-14 Page 6 Recirculation Flow (Flows of 80 - 100 gpm for 1 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />):

1. A pump flow of approximately 100 gpm is needed for minimum-flow recirculation after an Engineered Safeguards (ES) actuation, when Reactor Coolant System (RCS) pressure is higher than DH pump pressure. This flow rate is based on the orifice size in the minimum flow recirculation line on the DHR pumps.

2. This recirculation is a " stand-by" mode of operation until RCS pressure drops below DHR pump shut-off pressure. As such, the-duration of operation in this mode will be minimized by plant procedures, with an upper limit of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

3. The DHR pumps are capable of meeting this 80 -

100 gpm for i 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> requirement, based on correspondence between Dresser Pump Division and FPC on September 6, 1988. Dresser stated,

" Analysis of history of shaft failures, coupled with an appreciation of recirculating loading, leads us to a conservative position that two hours cumulative operation at 80 gpm minimum flow should not result in shaft or bearing failure due to recirculation on the 8HN194 decay heat pumps."

Low Pressure Injection and Decay Heat Removal Flows (>100 gpm to 1500 gpm):

1. A DHR pump flow of > 100 gpm may be required for low pressure injection supply to the high pressure injection pumps (commonly referred to as a piggy-back operation), or to support low pressure injection to the RCS ,as a result of a SBLOCA. The flow rate takes into account the 100 gpm recirculation flow and allows for additional makeup flow as a result of the LOCA. For pump operation from 100 gpm to 400 gpm, procedural guidance will be available to limit operation in this range to i 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The procedure will provide guidance to increase the DHR pump flow rate to > 400 gpm by increasing the flow through operator action.

For low pressure injection pump operations from 400 gpm to 1500 gpm, DHR pump operating time is sufficient to allow for depressurization of the RCS and establishment of decay heat removal cooling flows in excess of 1500 gpm.

2. The DHR pumps are capable of meeting the 100 gpm to 400 gpm for 1 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> needs based on the Dresser correspondence referenced above. The 400 gpm to 1500 gpm capability is supported by the MPR Associates, Inc. correspondence dated May 26, 1989 which concludes the DHR pumps will operate at 400 gpm and above for at least 3 days.

May 30, 1989 3F0589-14 Page 7 Decay Heat Removal Flow-(Flow 2 1500 gpm for Unrestricted Duration):

1; Based on current practice, a pump flow of 2 1500 gpm is used for most normal DHR system operations. Plant operating procedures will be revised to ensure that all normal DHR system operations are performed at a pump flow rate of 2 1500 gpm.

2. Operation at a DHR pump flow rate of 2 1500 gpm can occur for essentially unrestricted periods of time, such as during extended refuel or maintenance outages.

3. The DHR pumps are capable of meeting this 2 1500 gpm/ unrestricted duration requirement based on the- successful testing and evaluation of DHP-1B already discussed.

Based on the test and inspection data, FPC has determined that continued operation with the existing DHR Pumps does not pose any unresolved safety concerns. Based on the test and inspection data, no hardware changes are necessary. FPC has proved that the vendor recommendations for operation of these pumps are too conservative to be the basis for restricting CR-3 pump operation.

Revisions to operating and emergency procedures which would enhance operator awareness of the DHR Pump performance capabilities will be made before restart. The final report summarizing the test, inspections, and evaluations performed on the DHR Pump low flow capabilities will be provided to the NRC within 30 days of plant restart as stated in FPC's April 17, 1989 letter.

Sincerely, t

Rolf C. Widell, Director Nuclear Operations Site Support RCW:JWT:wla xc: Regional Administrator, Region II Senior Resident Inspector l

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