ML17311A372

Safety Evaluation Supporting Amends 84,72 & 56 to Licenses NPF-41,NPF-51 & NPF-74,respectively

ML17311A372
Person / Time
Site:	Palo Verde
Issue date:	10/27/1994
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML17311A373	List: ML17311A372 ML17333A064
References
NUDOCS 9411070245
Download: ML17311A372 (20)

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UNITED'STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0&i 9411070245 941027 PDR ADOCK 05000528 P,

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"'PDR, SAFE Y

V LUAT 0 BY TH OF C

OF NUC AR EACTOR REGU ON RELAT 0 TO AMENDMENT NO.

84 TO F CILITY OPERATING LICENSE NO.

NPF-41 AMENDMENT NO. 72 TO FACILITY OPERATING LICENSE NO. NPF-51 ND AMENDMENT NO. 56 TO FACI Y OPERATING LICENSE NO. NPF-74 RIZONA PUBLIC SERVICE COMPANY ET AL.

PALO VERDE NUCLEAR GENERATING STATION UNIT NOS.

1 2

AND 3 DOCKET NOS.

STN 50-528 STN 50-529 AND STN 50-530

1. 0 INTRODUCTION By letter dated August 23',

1993, the Arizona Public Service Company,(APS or the licensee) submitted a request for changes to the licenses for the Palo Verde Nuclear Generating Station (PVNGS), Units 1, 2, and 3 (Facility Operating License.Nos.

NPF-41, NPF-51, and NPF-74, respectively).

The Arizona Public Service Company submitted'his request on behalf of itself, the Salt River Project Agricultural Improvement and Power District, Southern California Edison

Company, El Paso Electric Company, Public Service Company of New

Mexico, Los Angeles Department of Water and Power, and Southern California Public Power Authori.ty.

The proposed changes would remove the Units 1 and 3

license condition regarding an augmented reactor coolant pump vibration monitoring program, and rescind the Confirmatory Order modifying the Unit 2 license regarding the same issue.

APS stated that an reactor coolant pump (RCP) monitoring system had been installed in each, unit to monitor and record RCP vibration data.

APS further stated that the vibration-'related parameters monitored by the new system provide better quality and safety than the parameters discussed in the existing license condition and Confirmatory Order.

By letter dated July 21,

1994, APS provided additional information related to the amendment and the new monitoring system, as requested by the staff during a conference call on May 17, 1994.

This additional information was clarifying in nature and did not affect the staff's previously published no significant hazards determination.

2.0 BACKGROUND

By letter dated October 8,

1987, APS informed the Commission that European RCPs similar to the Palo Verde Nuclear Generating Station (PVNGS)

RCPs in design and manufacture exhibited shaft cracking.

APS informed the Commission of planned inspections of the pump shafts at PVNGS Unit 1 during the current refueling outage.

On October 21,

1987, APS reported that ultrasonic testing

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(UT) revealed that crack indications of varying depths and lengths had.been identified on the shafts of the first two pumps.

Subsequently, crack indications were detected on the shaft of.the third pump.

The depth of the indications that were identified by.UT inspection on the PVNGS Unit 1 shafts exceeded those reported for the European RCP shafts which had not failed.

In addition, the operating hours for PVNGS Unit 1 pumps were significantly less than for the European pumps.

No shaft failures had been experienced. at PVNGS.

However, since the root cause of the phenomenon had not been identified and corrected, the staff was concerned that the information indicated an increased probability of a RCP shaft failure and the possibility of even more than one RCP shaft failure.

Following further meetings and discussions on inspection results for Unit 1

and 2, on November 19,

1987, NRC issued a Confirmatory Order modifying the license of PVNGS Unit 2, License No. NPF-51, to include commitments by the licensee related to the RCPs.

The modification required the licensee to implement an augmented vibration monitoring program for each of the four pumps and install modified RCP shafts during the next refueling outage.

The Order also allowed the Regional Administrator to relax or rescind any of the conditions upon a showing by the licensee of good:cause.

The Confirmatory Order modifying the Unit 2 operating license required APS to include the following commitments:

A.

Implement an augmented vibration monitoring program for each of the four RCPs that include the following activities:

Every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, monitor and record the vibration data on each of the four RCPs.

2.

3.

4.

On a daily basis, perform an evaluation of the pump vibration data obtained in 1 above, using an appropriately qualified engineering individual.

When any one vibration monitor on the RCP indicates a vibration level of 8 mils or greater, NRC shall be notified within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> via the emergency notification system.

In addition, when the vibration on any pump exceeds 8 mils due to a shaft crack or unknown cause, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> the affected pump shall have its orbit and spectra continuously monitored and evaluated by an appropriately qualified individual.

When any one vibration.monitor on the RCPs indicates a vibration level of. 10 mils or greater, within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, initiate action to place the unit in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and at least COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

In addition the affected RCP shall be secured after entering HOT STANDBY.

On a daily basis a spectrum analysis shall,'be performed on the RCP shaft vibration data and shall be evaluated for trends by an individual. qualified in that technique.

The evaluation shall

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consist of comparing the running speed (1XRPH) and twice running speed (2XRPH) spectral components to limits computed from baseline vibration.

The.limits shall be based on the lowest of:

(a) 1.6 times the baseline value; (b) the mean plus three standard deviations;,(c) 2 mils for the 2XRPH component;, or (d) 6 mils,for the 1XRPH component'.

When the ampl.itude exceeds any limit, further analysis shall be performed..

The analysis shall consist of an inspection of the amplitude versus time plots for a steadily increasing trend and a review of other plant data which might explain the change in amplitude.

If it is confirmed that the trend is not caused by plant or pump conditions unrelated to a shaft crack, the trend shall be extrapolated manually and/or by computer to predict the time at which the vibration is expected to reach 10 mils. If the projected time for reaching 10 mils is 1 week or less, within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> initiate action to place the unit in HOT STANDBY within +he next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in at least COLD SHUTDOWN within the. following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

In addition, the affected RCP shall be secured after entering HOT STANDBY.

B.

The licensees shall install modified reactor coolant pump shafts during the next refueling outage currently scheduled to start in February 1988.

The shafts shall include the modifications described in Figure DES-3 of the attachments to the licensee's November 5, 1987', letter.

The Unit 3 license condition was incorporated into the full-power license issued on November 25, 1987, and'he Unit 1 license condition was incorporated'nto the license by Amendment 32, dated Hay 10, 1988.

3. 0 DISCUSS ION APS dedicated several individuals to monitor and,record the vibration data on each of the four RCPs every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

Also, a qualified engineering individual was assigned to perform an evaluation of the RCP vibration data on a daily basis.

Since November 19,

1987, APS has dedicated thousands of, man-hours monitoring and recording RCP vibration data and performing a daily spectrum analysis, which is a manpower intensive task.

The installed RCP orbital monitoring system monitors the critical vibration related parameters, such as overall vibration, synchronous 1XRPH and 2XRPH amplitude, and phase angle for deviation from acceptable values defined as an acceptance region on the monitor.

The RCPs are continuously monitored by an analog vibration monitoring system with two proximity probes mounted just above the seal housing and an accelerometer mounted on the motor base.

The analog monitors have two set points for each channel which sound an alarm and flash an alarm window in the control.room.

In addi'tion to the analog alarm, a

'In the event new limits (or methods) are chosen, they shall. be evaluated by the licensee to assure that the new methods are equal to or,better than the above method.

The Commission shall be advised within 1 week if. new methods are chosen.

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computer system is installed which, approximately twice per minute, analyzes the vibration from the proximity probes for the amplitude and phase of the 1XRPH and 2XRPM components.

These vector components are compared to an acceptance

region, and if they are outside the region, the computer sounds an alarm in the control room.

The computer also monitors the condition of the analog monitor every 3 seconds and provides status reports, alarm logs, and 21 days of trend data for the overall vibration, IXRPH and 2XRPM amplitudes and phase and gap voltage.

The requirement to shutdown a unit on a low-amplitude vibration trend which cannot be identified as, an indication of a cracked shaft puts the unit at risk of being shutdown for reasons other than a cracked shaft.

Also, because low-amplitude symptoms of shaft cracks are similar to other nonsignificant pump conditions, the unit is at risk of being unnecessarily shutdown.

The data collector alarms need to be set very low in order to be sensitive;,however, this may cause many false alarms that must be manually evaluated.

APS considers the new monitoring system sensitive to fairly low amplitude trends and more realistic than most other plants'.

Further, the risk of shaft cracks has been greatly reduced, and the value of detecting low amplitude trends is also greatly reduced.

However, APS intends to continue to use the data collector at least once a month.

The original shafts that experienced cracking were martensitic steel, chrome plated over their. entire length to facilitate the assembly/disassembly of the impeller from the shaft.

The APS root cause analysis determined that the shaft cracking was the result of a reduction in the fatigue strength of the shaft material due to the presence/application of chrome plating.

Hicrocracks initiate in the chrome plate during normal operation, due to superimposed mechanical and thermal stresses, and propagate into the shaft base material.

APS has replaced all of the original shafts.

The replacement shafts in Unit I are spare shafts modified to address the cause of cracking.

The chrome plate has been removed in the keyway areas except where needed for assembling the impeller on the shaft, a thermal barrier to the shaft keyway area is provided, and stress concentrations are reduced in the diameter change areas.

The replacement shafts installed in Unit 2 and 3 are newly manufactured shafts of essentially the same design as Unit I replacements with enhancements.

The shafts are surface-rolled to increase their endurance fatigue strength and coated with chromium carbide instead of chrome plating, and a center bore is provided for UT examination access.

Since replacement of the original RCP shafts in the three units, no cracks have been detected by UT examination during each of the units past refueling outages.

In addition to the previously-discussed advantages, APS believes the newly-installed computer system will reduce the manpower burden and personnel radiation exposure.

APS will continue to monitor RCP vibration data through the use of the installed system, and intends to use the data collector at least once a month, and perform periodic RCP shaft UT inspections.

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UATIO Pursuant to the requirements of 10 CFR 2.204 and 10 CFR Part 50, the NRC issued the confirmatory order modifying the license of PVNGS Unit 2, License No. NPF-51, based-on the licensee's reports of cracks of varying length and depth found in the RCP shafts, a lack of any root cause analysis identification and correction of the cracking phenomenon, concern over an increased probability of a RCP shaft failure, and the potential for more than one RCP shaft failure.

Although shaft failure is an analyzed'vent which had not been experienced at the facility,.and considering that the reactor protection system would shut down the 'reactor upon a pump shaft failure, the increased probability of a shaft failure at the time raised immediate concerns relative to potential challenges to the reactor protection and emergency core cooling systems.

The license condition was subsequently incorporated into PVNGS Unit 1 and Unit 3 licenses.

The licensee performed a root cause analysis as described in APS letter dated Hay 20, 1988.

The root cause of the shaft cracking was determined to be a

reduction in'fatigue strength of the shaft material due to the presence and application of chrome plating.

Microcracks initiate in. the chrome plating during, normal operation, due to superimposed mechanical and thermal stresses, and propagate into the base metal as a result of high cycle fatigue loading.

.In laboratory tests it has been found that the presence of chrome plating significantly reduced the fatigue strength of the shaft material.

'Hydrogen embrittlement of the plating could occur during the shaft manufacturing and plating process as a result of released hydrogen being trapped between the base material and chrome plate.

Local shaft fatigue stress loading 'is also heightened by stress concentrations found in.the design of keyways and abrupt changes in shaft diameter.

APS replaced all of the original RCP shafts.

The replacement shafts in Unit 1

are spare shafts modified to address the cause of cracking.

The replacement shafts installed in Units,2 and 3 are newly manufactured shafts of the same basic design as the Unit 1 repl'acement shafts with additional fatigue reduction enhancements.

The replacement shafts were provided with a center bore to all'ow entry of a UT probe to facilitate and improve UT inspections.

The.Unit 1 shafts will be UT-inspected during each, refueling and the Unit 2 and 3 shafts will be UT-inspected during RCP mechanical seal replacements.

APS indicated that, if abnormal monitoring data trends are detected during any refueling outage, the trends will be evaluated on a case by case basis to determine if a UT shaft inspection is warranted.

Since replacement of the original RCP shafts in the three units, no cracks have. been detected by UT inspection during each of the units'ast refueling outages.

In the amendment

request, APS provided a summary of its safety analysis of a RCP shaft break and an evaluation of the potential for multiple shaft failures.

Based on the safety analysis, APS concluded that a single sheared shaft.would result in an uncomplicated shutdo'wn with no.fuel failure.

APS also stated that multiple shaft failures would not occur since the failure of one pump shaft will result in the reduction of other pumps'oads and subsequent reduction in their shafts'tresses and prompt shutdown of the

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unit.

Further, it was concluded that there would be no break in the reactor pressure boundary and the pump shaft seal would remain intact.

APS noted that the RCP shaft break event with a concurrent loss of offsite power has been previously evaluated in the Updated Final Safety Analysis Report, Subsection 15.3.4.

A APS installed a new monitoring system to monitor critical RCP-related vibration parameters.

APS considers that the proposed alternative o

sing the newly installed computer system provides a better level of qual and safety than existing license condition and Confirmatory Order requi ents since it monitors the IXRPH and 2XRPH components,

phase, and every few

seconds, and can quickly access trend data for fast evaluation.

The RCPs are continuously monitored by the system, which analyzes the monitored parameters, compares the results with acceptance limits, and sounds and flashes an alarm window in the control room if unacceptable conditions are detected.

The computer also monitors the system condition, provides status reports, alarm

logs, and 21 days of trend data of overall vibration levels.

The new system reduces manpower burden and radiation exposure of personnel.

In summary, the licensee's amendment request -proposes to remove the Units I and 3 license condition regarding an augmented RCP vibration monitoring.

program and rescind the Confirmatory Order modifying the Unit 2 license regarding the same issue.

Additionally, the staff noted that two additional items related to RCP vibration that are contained in the Unit 3 license have been completed.

The licensee discussed these items with the staff, on October 25,

1994, and requested their removal.

The first item. required the licensee to submit a report to the staff following the first Unit 2,refueling outage detailing RCP inspection findings.

This report was submitted by letter dated Hay 20,

1988, and the staff evaluation was issued by letter dated January 4,

1989.

The second item required the installation of modified RCP shafts.

The licensee's letter dated August 23, 1993, states that all shafts have been replaced.

Accordingly,, these additional items are deleted from the Unit 3 license.

The licensee has proposed to continue to monitor RCP vibration data through the use of the newly-installed computer system, use the data collector at least once a month for very low amplitude trend assessments, and perform periodic UT inspections of the RCP shafts.

The staff finds the amendment acceptable based on (I) licensee's root cause analysis, (2) corrective action and safety analysis, (3) proposed continuing monitoring program and inspection

actions, and (4) burden and exposure reductions considerations inherent with

'he proposed alternatives.

6.0 S AT CONSULTAT ON In accordance with the Commission's regulations, the Arizona State official was notified. of the proposed issuance of the amendments.

The State official had no comments.

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7. 0 ENVIRONMENTAL CONSIDERATION The amendments change a requirement with respect to the instal.lation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.

The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.

The Commission has previously issued a proposed finding that 'the amendments

.involve no si'gnificant hazards consideration, and there has been no public comment on such finding (58 FR 50963).

Accordingly, the amendments meet the el'igibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to-10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection.with the issuance of the amendments.

8. 0 CONCLUSION The Commission has concluded, based on the considerations discussed

above, that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed

manner, (2) such activities will be conducted in compl,iance with the Commission s regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the 'health and safety of the public.

Principal Contributors:

F. Grubelich B. Hol'ian Date:

October 27, 1994

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t UNITED STATES t NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001.

October 27, 1994 MEMORANDUM TO:

FROM:

SUBJECT:

Sholly Coordinator Brian E. Holian, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV Office of Nuclear.Reactor Regulation REQUEST FOR PUBLICATION IN BIWEEKLY FR NOTICE NOTICE OF ISSUANCE OF AMENDMENTS TO FACILITY OPERATING LICENSES (TAC NOS. H87322,

H87323, AND H87324)

Arizona Public Service Com an et al.

Docket Nos.

STN 50-528 STN 50-529 and STN'0-530 Palo Verde Nuclear Generatin Station Units 1

2 and 3

Harico a Count Arizona Date of a lication for amendments:

August 23,

1993, as supplemented by letter of July 21, 1994 Brief descri tion of amendments:

These amendments remove the Units 1 and 3

license condition regarding an augmented reactor coolant pump vibration monitoring program and the confirmatory order modifying the Unit 2 license regarding the same issue.

Date of issuance:

October 27, 1994 Effective date:

October 27, 1994 Amendment Nos.:

84, 72, and 56 Facilit 0 eratin License Nos.

NPF-41 NPF-51 and'PF-74:

The amendments revised the Technical Specifications.

Date of initial notice in FEDERAL REGISTER:

September 29, 1993 (58 FR 50963)

The additiona'I information in the letter dated July 21,

1994, was.

clarifying in nature and did not affect the staff's previously published'o significant hazards determination.

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Sholly Coordinator October 27,,

1994 The Commission's related evaluation. of.the amendments is contained in a Safety Evaluation dated October 27, 1994.

No signi'ficant-hazards consideration comments received:

No.

Local Public Document Room location:

Phoenix Public Library, 12 East McDowell Road,

Phoenix, Arizona 85004 DISTRIBUTION:

~Docket F'Ue~

PDIV-2 'Reading File BHolian LTran DFoster-Curseen Sholly Coordinator (Orig+1)

OGC (015B18)

DOCUMENT NAME:

PV87322. BWI DRPW LA PDIV-2 P

PDIV-2/PM NAHE DFoster-Curseen LTran BHolian:

DATE 6

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194 OFFICIAL RECORD COPY

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I Sholly Coordinator October 27, 1994.'he Commission's related evaluation of the amendments is contained in a Safety Evaluation dated October.

27,,

1994.

No significant hazards consideration comments received:

No.

Local.Public Document Room location:

,Phoenix Public Library, 12 'East HcDowell Road, Phoenix, Arizona 85004 DISTRIBUTION:

Docket File PDIV-2 Reading File BHolian LTran

'DFoster,-Curseen Sholly Coordinator (Orig+1)

'OGC (015B18)

DOCUHENT NAHE:

PV87322. BWI OFF lCE MAHE DATE DRPW/LA DFoster-Curseen 0

94 PDIV-2/P PDIV-2/PH LTran

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/94 OFFICIAL RECORD COPY

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