ML18152B586

SER Approving Request Relief Related to Inservice Testing Program at Surry Power Station Unit 1

ML18152B586
Person / Time
Site:	Surry
Issue date:	12/18/1998
From:	NRC (Affiliation Not Assigned)
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ML18152B584	List: ML18152B583 ML18152B586
References
NUDOCS 9812280258
Download: ML18152B586 (6)

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e UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 1 DOCKET NO. 50-280

1.0 INTRODUCTION

Title 10 of the Code of Federal Regulations, (1 O CFR) Section 50.55a, requires that inservice testing (1ST) of certain American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 pumps and valves be performed in accordance with the ASME Boiler and Pressure Vessel Code (ASME Code),Section XI and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to Section (a)(3)(i), Section (a)(3)(ii), or Section (f)(6)(i) of 1 O CFR 50.55a. In proposing alternatives or requesting relief, the licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility. Guidance related to the development and implementation of 1ST programs is given in Generic Letter (GL) 89-04, "Guidance on Developing Acceptable lnservice Testing Programs," issued April 3, 1989, and its Supplement 1 issued April 4, 1995. Additional guidance can be found in NUREG-1482, "Guidelines for lnservice Testing at Nuclear Power Plants," NUREG/CR-6396, "Examples, Clarifications, and Guidance on Preparing Requests for Relief from Pump and Valve lnservice Testing Requirements," and "Summary of Public Workshops Held in NRC Regions on Inspection Procedure 73756, 'lnservice Testing of Pumps and Valves,' and Answers to Panel Questions on lnservice Testing Issues."

The 1989 Edition of the ASME Code is the latest edition incorporated by reference in Paragraph (b) of Section 50.55a. Subsection IWP of ttw 1989 Edition, which gives the requirements for 1ST of pumps, refere*nces Part 6 of the American National Standards lnstitute/ASME Operations and Maintenance Standards (OM-6) as the rules for 1ST of pumps.

OM-6 replaces specific requirements in previous editions of Section XI, Subsection IWP of the ASME Code.

9812280258 981218 PDR ADOCK 05000280 p

PDR Enclosure

2.0 BACKGROUND

By letter dated October 19, 1993, Virginia Electric and Power Company (the licensee),

submitted the third 10-year interval 1ST program for Surry Power Station. Relief Request P-11, as contained in the licensee's October 19, 1993, 1ST program submittal, proposed to test the emergency service water (ESW) pumps within the tide level limits of a pump reference curve.

The staff evaluated the relief requests contained in the licensee's revised 1ST Program and issued a safety evaluation (SE) on October 20, 1994. For Relief Request P-11, the staff granted interim relief pursuant to 1 O CFR 50.55a(f)(6)(i) for one year or until the next refueling outage, whichever is later [see Technical Evaluation Report Section 2.3.1 and 1ST Program anomaly 5]. Prior to making its third interval 1ST program submittal (i.e., on June 29, 1993), the licensee had submitted Relief Request P-11. This version of P-11 was similar to the version contained in the 1ST program submittal except the earlier version was written against ASME Section XI, Subarticle IWP-3110. The NRC staff reviewed and approved the earlier version of P-11 in an. SE dated October 22, 1993. By letter dated October 12, 1995, the licensee responded to the 1ST program anomalies identified in the staff's October 20, 1994, SE, including anomaly number 5 related to P-11. By letter dated February 12, 1996, the NRC staff informed the licensee that continued use of P-11 was acceptable and that the staff's approval of P-11 was no longer considered "interim."

The Surry Power Station, Units 1 and 2, 1ST program for the third 10-year interval began on May 10, 1994. The Surry Power Station, Units 1 and 2, 1ST program was developed to the 1989 Edition of ASME Section XI of the ASME Boiler and Pressure Vessel Code. The 1989 edition of the Code specifies that the rules for the inservice testing of pumps and valves are stated in the ASME/ANSI Operations and Maintenance (OM) Standards, Part 6, "lnservice Testing of Pumps in Light-Water Reactor Power Plants," and Part 10, "lnservice Testing of Valves in Light-Water Reactor Power Plants."

3.0 EMERGENCY SERVICE WATER SYSTEM REVISED RELIEF REQUEST P-11 Relief Request P-11 pertains to the three ESW pumps for Surry Power Station, Unit 1 (17SW-P-1A, 1-SW-P-1B, and 1-SW-P-1C). These standby pumps are deep draft vertical line shaft pumps. The licensee has revised Relief Request P-11 to obtain relief from the hydraulic acceptance criteria for flow rate specified in Table 3b of OM-6. Table 3b establishes the acceptable range (0.95 to 1.1 O times the reference flow rate Qr), the alert range (0.93 to

< 0.95 Qr), and the required action range ( < 0.93. Qr and > 1.10 Qr). The ESW pumps provide the source of water to the intake canal during the design basis accident. In the event of a loss-of-coolant accident (LOCA) and a total loss of station power, with the requirement that the unit that did not undergo the LOCA must be cooled down, the maximum flow rate required would be 21,000 gpm. This would require two of the three ESW pumps to be operated.

As discussed in Section 2.0 above, the licensee previously obtained, for this current 10-year interval, relief from the requirements of Paragraph 4.3 of OM-6, which requires reference values to be at points of operation readily duplicated during subsequent tests where subsequent test results are compared to these reference values. For this reason, this particular aspect of Relief Request P-11 is not reevaluated in this SE.

e 3.1 Licensee's Basis for Request The licensee provided the following basis for the relief request:

)

Basis for Relief from Paragraph 4.3 [provided in this SE for background only]

The emergency service water pumps take suction from the James River and discharge into the intake canal. The James River near the plant is subject to a tide level variation of approximately five feet. Therefore, the total static head for the system can vary from test to test. There are no valves in the lines to throttle flow and to compensate for the change in system static head. The only way to duplicate flow and differential pressure from test to test is to perform the test at the same tide level each time. Trying to perform this test within a small enough tide level range to produce repeatable results has proven impractical. To compensate for the change in total system head, a pump reference curve will be prepared based on test results taken at different tide levels. Tests will be conducted within the tide level limits of the curve, and results will be compared to acceptance criteria based on the reference curve and the ranges given in OM Part 6, Table 3b. Inlet pressure will be calculated from tide level.

Basis for Relief from Table 3b [discussed in this SE]

The emergency service water pumps are standby pumps that are only operated during periodic tests. The pumps operate at adjusted speeds from 880 to 900 RPM and are driven by diesel engines. The suction bells containing the impellers for these pumps are submerged in the James River to a depth of approximately 9.8 feet. The brackish water of the James River provides a favorable environment for the growth of biological organisms. Between tests, organisms such as hydroids and barnacles attach to the inside of the suction bell and the pump impeller. As these organisms grow the hydraulic performance of the pumps degrades. The period of greatest growth occurs from mid-summer through early fall. During other portions of the year, biological growth does not cause significant degradation.

Surry Power Station has aggressively addressed this problem by coating the inside of the suction bells with antifouling material, by testing the pumps each month and by cleaning the suction bells and impellers when performance is projected to degrade to unacceptable levels before the next monthly test. Divers using specialized equipment clean the inside of the suction bells, the impellers and portions of the diffuser. This cleaning process restores the pumps to almost peak hydraulic performance levels.

In the past, the pumps have been completely removed for cleaning. However, frequent removal of the pumps is not practical because installation and realignment is a difficult and complex evolution. The suction bay has also been drained to allow cleaning of the pumps. This process involved construction of scaffolding, and removal of the suction bell and impeller. Also, any work that is being performed on the pump suction makes the circulating water pump sharing

l...

e the suction bay with the emergency service water pump unavailable. Draining the suction bay and removal of the pump takes several days. During certain summer periods, all eight circulating water pumps are needed to maintain both units at 100% electric power.

Currently, if the flow rate falls into the alert range of (0.93 to < 0.95 Qr) a trend of

• the degradation rate is performed to determine if the performance will decrease to ( < 0.93 Qr) before the next monthly test. If so, the divers are called in to clean the suction bell and impeller at a cost of approximately $4,000 per pump.

Experience has shown that when fouling occurs and the pumps degrade to the minimum acceptable limit there is still substantial margin between the minimum acceptable flow rate of 0.93 Qr and the design basis flow rate of.14,020.

Changing the acceptable range to (0.93 to 1.1 O Qr), the alert range to (0.90 to

<0.93 Qr), and the required action range to (< 0.90 Qr and> 1.10 Qr) for the monthly test would eliminate the need for at least one cleaning per pump during the high growth period, while maintaining adequate margin between pump performance and the design basis flow rate.

Given that 1) the mechanism of degradation is understood and can be trended,

2) the pumps are t~sted monthly as opposed to the Code required frequency of every three months, and 3) adequate performance margin exists, Surry Power Station believes that changing the acceptance criteria as described above will provide a sufficient level of safety while reducing the burden of maintaining the emergency service water pumps.

3.2 Proposed Alternate Testing The licensee proposed the following:

Tests will be conducted every month within the tide level limits of the pump reference curve, and flow will be compared to acceptance criteria based on the

• reference curve and the ranges given below. For flow rates that fall into the alert range, the test data will be trended and corrective action taken if the trend evaluation determines that the flow will fall below the required action range before the next monthly test.

OM-6, Table 3b (vertical line shaft pumps)

Proposed in P-11 for the three Emergency Service Water Pum s 3.3 Evaluation Flow Rate (Q)

Acceptable Range

0. 95 to 1.1 0 Q r 0.93 to 1.10 Qr Alert Range 0.93 to <0.95 Qr 0.90 to <0.93 Qr Required Action Range

<0.93 Qr

>1.10 Qr

<0.90 Qr

>1.10 Qr The licensee stated that the primary hydraulic degradation mechanism for the ESW.pumps is the growth of biological organisms such as hydroids and barnacles which occurs at a significant rate from mid-summer through early fall. The expanded acceptance criteria will reduce the burden of maintaining the pumps by reducing the frequency of cleaning the pump suction bells and impellers during the period of high biological growth. To justify the expanded acceptance criteria, Surry Power Station has proposed an alternative which involves: 1) testing the pumps monthly, and 2) taking corrective action if the measured flow rate falls into the alert range and if the trend evaluation determines that the flow will fall below the required action range before the next monthly test.

Surry Power Station has attempted to address this problem by coating the inside of the suction bells with antifouling material, by testing the pumps each month, and by cleaning the suction-bells and impellers when performance is projected to degrade to unacceptable levels before the next monthly test. The licensee stated that divers use specialized equipment to clean the inside of the suction bells, the impellers and portions of the diffuser. The licensee stated that this cleaning process restores the pumps to almost peak hydraulic performance levels.

The licensee's experience has shown that when fouling occurs and the pumps degrade to the minimum acceptable limit, the.re is still substantial margin between the minimum acceptable flow rate of 0.93 Qr and the design basis *flow rate. The reference flow rate for one ESW pump is approximately 17,000 gpm (0.93 X 17,000 gpm = 15,810 gpm). According to the licensee's Updated Final Safety Analysis Report (UFSAR), in the event of a LOCA and a total loss of station power, with the requirement that the unit that did not undergo the LOCA must be cooled down, the maximum flow rate required would be 21,000 gpm. This would require two of the three ESW pumps to be operated. Even with each of two ESW pumps degraded to 0.90 Qr (15,300 gpm) there would be more than sufficient flow to meet this criteria.

From a risk perspective, testing the ESW pumps monthly as opposed to quarterly will reduce the fault exposure time and common mode failure probability associated with the ESW pumps and thus will tend to reduce overall plant risk. This reduced plant risk is potentially offset by the reduced hydraulic margin associated with lowering the flow rate required action acceptance criteria from 0.93 Qr to 0.90 Qr*

I e The flow rate acceptance criteria in the ASME Code of record for the licensee's second 10-year 1ST interval (Table IWP-3100-2) specified an acceptable range (0.94 to 1.02 times the reference flow rate Qr), an alert range (0.90 to < 0.94 Qr and 1.02 to 1.03 Qr), and a required action range (< 0.90 Qr and> 1.03 Q J When the revised OM Code was published, the "low

alert range for flow rate measurements of vertical line shaft pumps was made more stringent (0.93 to 0.95 Q J The licensee's third (current) 10-year interval 1ST program uses the more stringent flow rate acceptance criteria. As stated in NUREG/CP-0111 (page 43-44), more stringent hydraulic acceptance criteria are necessary for these pumps because there am inherent deficiencies in vibration testing vertical line shaft pumps and degradation will be identified sooner through changes in hydraulic parameters. The pump performance information obtained by testing the ESW pumps monthly (as proposed by the licensee) will be much more beneficial than using more stringent flow rate acceptance criteria to evaluate a quarterly test in terms of assuring that the ESW pumps will be capable of performing their design basis function when required. Therefore, the alternative proposed by the licensee will provide reasonable assurance of operational readiness.

Because the licensee did not request relief from the requirements of Section 6.1 of OM-6, the licensee is required to comply with these Code requirements (i.e., using the revised test frequency and hydraulic acceptance criteria approved by this SE).

The proposal will reduce the burden of maintaining the pumps by reducing the frequency of cleaning the pump suction bells and impellers during the period of high biological growth. This involves securing the ESW pump and circulating water pump in the shared suction bay, tagging both pumps out, and sending a diver into the bay to scrape off the hydroids and barnacles. The licensee estimates that the proposal would eliminate the need for at least one cleaning per pump during the high growth period. During certain summer periods, when all eight circulating water pumps are needed to maintain both units at 100 percent electric power, it would be a hardship to clean the ESW pumps.

The staff finds that the licensee's proposed test strategy for the ESW pumps will provide reasonable assurance of the operational readiness of the ESW pumps to perform their intended.

safety function when required because: 1) the licensee has taken reasonable steps to correct the root cause of the flow degradation such as coating the inside of _the suction bells with antifouling material; 2) the flow degradation mechanism is understood and can be trended;

3) the pumps will be tested monthly as opposed to quarterly as required by the Code; 4) when ESW pump flow is found to be in the alert range, the test data will be trended and corrective action taken if the trend evaluation determines that the.flow will fall below the required action range before the next monthly test; and 5) adequate system performance margins will be maintained.

3.4 Conclusion In light of the reasonable assurance provided by the alternative testing and expanded acceptance criteria, the proposed alternative is authorized pursuant to 1 O CFR 50.55a(a)(3)(ii) based on the determination that compliance with the specified requirements results in a hardship without a compensating increase in the level of quality and safety.

Principal Contributor: D. Fischer Date:

December 18, 1998