ML20206G169

SER Approving Requirements of Istb 4.6.2(b) Pursuant to 10CFR50.55a(a)(3)(ii)

ML20206G169
Person / Time
Site:	Hatch
Issue date:	05/04/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20206G165	List: ML20206G161 ML20206G169
References
NUDOCS 9905070108
Download: ML20206G169 (5)

Text

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[j#"%g4-UNITED STATES s* j NUCLEAR REGULATORY COMMISSION ,

• WASHINGTON, D.C. 20656 4 001

\...../ ,

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION

l. RELATED TO THE THIRD TEN-YEAR INSERVICE TESTING INTERVAL PROGRAM SOUTHERN NUCLEAR OPERATING COMPANY. INC.

EDWIN 1. H' ATCH NUCLEAR PLANT UNITS 1 AND 2 ,

DOCKET NOS. 50-321 AND 50-366  !

1.0 INTRODUCTION

Title 10 of the Code of Federal Reaulations (10 CFR) Section 50.55a, requires that inservice testing (IST) of certain American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boiler and

Pressure Vessel Code (the Code) and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to paragraphs (a)(3)(i), (a)(3)(ii), or (f)(6)(i) of 10 CFR 50.55a. In proposing alternatives or requesting relief, tne licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would result in hardship c. unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility. Section 50.55a authorizes the Commission to approve alternatives ar:d to grant relief from ASME Code requirements upon making the necessary findings.- NRC guidance contained in Generic Letter (GL) 60 04, " Guidance on Developing Acceptable Inservice Testing Programs," provides alternatives to the Code requirements determined ecceptable to the staff. Further guidance was given in GL 89-04, Supplement 1, and NUREG-1482, " Guidelines for Inservice Testing at Nuclear Power Plants."

The third 10-year interval program for IST of pumps and valves at Hatch, Units 1 and 2, was submitted in a letter dated September 15,1995. The third 10-year interval for both units began on January 1,1996, and will end on December 31,2006. ' In accordance with the proposed alternative of Relief Request (RR) RR-G-1, which was approved in a :etter dated August 29, 1995, the applicable Codes used in the Hatch IST program are the ASME Operation and Maintenance (OM) Code-1990 for pumps and valves, with the exception of relief valves. The applicable Code for relief valves is the ASME OM Code-1995.

RR P-14 was initially submitted in a letter dated March 25,1397. The staff's safety evaluation (SE) dated August 21,1997, authorized the use of the proposed alternative testing method for an interim period of 120 days. RR-P-14 was subsequently revised and resubmitted to the NRC in a letter dated March 16,1999. The NRC's findings with respect to authorizing alternatives and granting or denying the proposed revised relief request are gben below.

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2.0 RELIEF REQUEST RR-P-14 (2"d Submittal)

The licensee proposes an alternative to the differential pressure measurement requirements of ISTB 4.6.2(b) for the four residual heat removal pumps (RHR) and two core spray (CS) pumps in each unit. The licensee proposes to measure the discharge pressure and calculate the  !

differential pressure by assuming a constant' suction pressure.

2.1 Licensee's Basis for Requesting Relief The licensee states:

The RHR and CS pumps are aligned to the suppression pool (torus) during all modes of normal plant operation which results in a virtually constant suction pressure. IST is performed utilizing a full flow test line which circulates water to and from the suppression pool. The Plant's Technical Specifications require that the suppression pool be maintained within a narrow range of level, temperature, and internal pressure during plant operation which results in a suction pressure l of approximately 5 psig. The Technical Specification operability limits for the l suppression pool are itemized below, j Unit 1/ Unit 2 l 1

Level 2 146" & s 150" l internal Pressure s 1.75 psig Water Temperature s100'F These Technical Specification operability limits for the suppression pool result in a maximum

- difference in calculated pump suction pressure of < 2 psig. This 2 psig maximum difference is insignificant when performing IST considering the normal discharge pressure of the RHR and CS pumps (see table below). This 2 psig variance is also insignificant in the calculation of differential pressure (AP = Po-P) when considering the Code acceptable operating range (i.e.,

95110% for vertical line shaft pumps and 90-110% for centrifugal pumps) from Table ISTB 5.2-V 2b and the allowable i2% instrument accuracy. Therefore, measurement of differential I

pressure provides no added benefit for determining pump operational readiness or for monitoring pump degradation.

Reference Discharge Maximum Pump Pressure Variance Unit 1 RHR 180 - 193 psig 1.11% max.

Unit 1 CS 305 - 310 psig 0.66% max.

Unit 2 RHR 172 - 190 psig 1.16% max.

Unit 2 CS 285 - 290 psig 0.70% max.

The following table summarizes several years worth of pump IST data. This summary confirms that the RHR and Core Spray pumps' suction pressures are consistent and are relatively insignificant in comparison with the pumps' discharge pressures. Applying an average suction

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I pressure of 5 psig, when calculating differential pressure, will provide data that is meaningful for l assessing operational readiness and for monitoring pump degradation.

PUMP MPL MIN. MAX. AVG. REMARKS No. PRES. PRES. PRES i 1E11-C002A 3.9 3.8 5.1 (52) Or=8000 gpm, Apr=116 psid 1E11-C002B 3.2 6.25 4.8 (47) Or=7700 gpm, Apr=185 psid 1E11-C002C 3.0 6.2 4.8(46) Or=7700 gpm, Apr=176 psid 1E11-C002D 3.4 6.0 4.6 (40) Or=7700 gpm, Apr=183 psid 1E21-C001 A 2.5 5.8 4.1 (68) Or=4625 gpm, Apr=289 psid 1E21-C001B 1.7

• 5.9 3.7 (47) Or=4625 gpm, Apr=282 psid 2E11-C002A 3.0 6.8 5.2 (50) Or=8000 gom, Apr=187 psid 2E11-C002B 4.3 7.1 5.3 (48) Or=7800 gpm, Apr=180 psid 2E11-C002C 3.0 6.9 5.3 (55) Or=7900 gpm, Apr=182 psid 2E11-C002D 3.8 6.2 4.9 (47) Or=7700 gpm, Apr=175 psid 2E21-C001 A 4.15 6.9 5.1 (43) Or=4750 gpm, Apr=302 psid 2E21-C001B 3.3 6.4 5.0 (53) Or=4750 gpm, Apr=303 psid AVERAGE 3.3 6.4 4.9 N/A Number in parenthesis "()" indicates the number of test valves averaged to get indicated value.

• One time occurrence only.

Additionally, a test gage is required to be installed to perform IST of each pump. The permanently installed pump suction pressure gages encompass a wider range of pressures than does IST and thus exceed the OM Code allowable range limit (3 times the reference value). The installed RHR pump gages must account for the pressure experienced with the RHR loop in the shutdown cooling mode of operation. The installed CS pump gages must account for the pressure experienced with the CS suction aligned to the Condensate Storage Tank. Therefore, a test gage, which satisfies the Code range limits, must be temporarily installed each time that IST is required.

Applying a constant pump suction pressure, when calculating differential pressure, will allow the IST to be performed with the installed pressure gages thus lessening the burden on operations personnel responsible for the testing. Since test gages are required to be calibrated both prior to and after usage, it also eliminates the possibility of invalidating test data due to a gage being damaged during transportation, installation or removal.

Mechanical degradation of centrifugal pumps, which experience significant differences in suction (inlet) pressure, would be indicated by changes in the differential pressure. However, for these pumps, the suction pressure variance is insignificant in comparison to the developed

4 head (pressure). Therefore, monitoring discharge pressure and calculating differential pressure assuming a constant 5 psig suction pressure provides an adequate method to determine operational readiness and detect potential degradation.

2.2 Alternative Testing The licensee proposes:

Pump suction pressure will be assumed to be 5 psig based on a review of several years of IST data which support suction pressure being virtually constant. During IST, pump differential pressure will be calculated by measuring pump discharge pressure and subtracting 5 psig. This value will then be compared to the corresponding reference value. The acceptance criteria of Table ISTB 5.2-2b will be applied for assessing pump operational readiness and for monitoring potential pump degradation. This testing method meets the intent .

of the Code for monitoring pump operationa! readiness and degradation, and j relieves the Licensee the burden associated with the use of temporary test l

gages. Therefore, the proposed alternative is requested pursuant to 10 CFR l 50.55a(a)(3)(ii).

2.3 Evaluation 1 l

The licensee requests relief from the requirements of ISTB 4.6.2(b) for the residual heat removal pumps,1E11-C002A, B, C & D and 2E11-C002A, B, C & D, and the core sprey pumps, 1E21-C001 A & B and 2E21-C001 A & B. If a direct indicating instrument is not provided, this section of the Code requires that differential pressure be determined by the difference between the pressure at a point in the inlet pipe and the pressure at a point in the discharge pipe. The licensee proposes to measure the discharge pressure and calculate the differential pressure by assuming a constant suction pressure of 5 psig.

The range of the permanently installed pressure gauges at the pumps' inlet exceed the OM Code allowable range limit (3 times the reference value), and so temporary gauges would need to be installed for each test. Accordingly, these temporarily installed gauges would need to be calibrated both prior to and after usage. These extra steps which are necessary for  !

compliance with the requirements of ISTB 4.6.2(b) create a hardship for the licensee without a compensating increase in the level of quality and safety.

Discharge pressure can be used in lieu of differential pressure for evaluating pump hydraulic performance if variations in pump inlet pressure are small. NUREG/CR-6396, Section 3.3.2 provides items to consider for justifying the use of discharge pressure instead of differential pressure, it includes:

(1) The inlet pressure'is small in comparison with the discharge pressure (maximum deviation of 2%).

(2) The maximum expected variation in the inlet pressure from test to test is relatively small as determined by control procedures and technical specification limits and as verified by historical data.

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.. . L (3) The Code required acceptance criteria are not relaxed.

(4) Everithough some uncertainty is introduced by this method, applying the Code -

' acceptance criteria for differential pressure for this application adds conservatism.

'(5)~. If a significant blockage occurs at the pump suction, this condition would affect the discharge pressure and/or flow measurement and would not go undetected.

The licensee's submittal meets all'the above criteria. The proposed alternative testing method provides an acceptable means of evaluating pump performance without causing a significant decrease in the ability to monitor operational readiness.

3.0 CONCLUSION

The proposed alternative to the requirements of ISTB 4.6.2(b) is authorized pursuant to 10 CFR 50.55a(a)(3)(ii). Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Principal Reviewer: M. Kotzalas Date: May 4, 1999 i

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