ML102600384

Requests for Additional Information (Eeeb) AFW Modification LAR (TAC Nos. ME1081 and 1082)

ML102600384
Person / Time
Site:	Point Beach
Issue date:	09/16/2010
From:	Beltz T Plant Licensing Branch III
To:	Hale S Point Beach
beltz T, NRR/DORL/LPL3-1, 301-415-3049
Shared Package
ML102600388	List: ML102600379 ML102600384
References
TAC ME1081, TAC ME1082
Download: ML102600384 (3)

Text

Requests for Additional Information Electrical Engineering Branch of the Office of Nuclear Reactor Regulation re:

Auxiliary Feedwater Modification License Amendment Request Point Beach Nuclear Plant, Units 1 and 2 License Nos. DPR-24 and DPR-27 Docket Nos. 50-266 and 50-301 EEEB 1 Loads Operated by Contactors BACKGROUND: Manufacturers provide a minimum drop out and pick up voltage for their products. These are guaranteed values for the life of the product for specified conditions.

Typical value for drop out voltage is 75%-65% of rated control voltage and the pickup is 85%-

110% of rated voltage. The licensee verbally indicated that approximately 55% of nominal voltage was considered for contactor drop out.

A Please provide justification for using voltages outside the manufacturer's recommended voltage range for safety-related contactor drop out and pickup.

B. If the licensee is using values other than manufacturer provided data (e.g. bench tested values), then please provide assurance that the assumed pick up and drop out values will be consistent for all conditions for the life of the product and there are plant controlled procedures for replacement of each device that has been analyzed at a value different than manufacturer provided data.

As applicable, please provide sufficient information to offer reasonable assurance that the conditions specified above are satisfied.

C. Depending on the number of voltage excursions below and above the nominal voltage, the motor loads may stall and restart. The low voltage and overvoltage conditions result in higher current flow.

Please verify that the evaluation for heating effect on the thermal protective devices included the effects of heating during the voltage transient and residual heating prior to the excursion.

D. The low voltage results in dropping out contactors and loads that were operating prior to a large motor start. The licensee has indicated that loads are capable of restarting and operating to meet design basis requirements.

Please verify that the process fluid systems were evaluated for potential effects such as voiding and water hammer.

E. According to the licensee response dated August 9, 2010, the licensee states the worst-case total loading of the EDG occurs with one EDG supplying both units during a design basis event with a LOOP/LOCA on one unit coincident with a LOOP on the other unit. The licensee evaluated the loads dropped out during EDG voltage excursions and concluded that all loads will start as long as the ESFAS was present. This is applicable to the unit with the LOCA condition.

Please provide details for impact on the Unit associated with the LOOP only event.

EEEB 2 Motor-Operated Valves (MOVs)

The licensee evaluated the stroke time of MOVs as discussed in the example for SI-860 Valve:

An example is provided for the SI-860 valves (CS pump discharge valves) based on the logic above. The minimum voltage requirements for these valves to operate is 365 V and the required stroke time is less than or equal to 16.5 seconds. The valves design stroke time is 11.73 seconds. The CS valves actuate on a high-high containment pressure signal, and therefore, are a random load on the system. The voltage dropped below 365 V a total of 5 times during the load sequence for a maximum total of 3.6 seconds, which was conservatively rounded to 4.0 seconds. The valve stroke time of 11.73 seconds was added to stall time of 4.0 seconds to determine a total stroke time of 15.73 seconds. This provides a 0.77 second margin to the required stroke time of 16.5 seconds.

It should be noted that at rated voltage, the motor delivers rated torque and speed. With the decrease in applied voltage, the torque produced varies with speed, both the torque and speed decreases resulting in an increase in slip. This lower speed due to degraded voltage will result in increased heating as well as reduced efficiency. The immediate effect of the degraded voltage is the reduction of the net torque produced which in turn means that the motor may not produce the desired thrust to satisfy the safety-related operation of the actuator.

For the SI-860 valves in the example above, the evaluated margin of 0.77 second is relatively small. There are also several factors that can impact the MOV stroke time.

Please provide a response to the following:

A. Verify the minimum voltage required for the 11.73 second stroke time.

B. Verify that this stroke time is consistently repeatable in the plant configuration and is for worst case loading on the valve.

C. Verify that effects that can reduce the thrust delivered by the motor operator under high differential pressure and flow conditions in relation to the thrust delivered under no-load conditions was considered.

D. Verify that the reduction in torque/speed was evaluated as the EDG output voltage is reduced during the transient caused by large motor starts.

E. Verify that the deceleration and acceleration time for the motor operator was considered during every event that the terminal voltage dropped below 365V.

F. The CS valves are a random load on the system. Verify that the stroke time is not extended if the Hi-Hi containment pressure signal is coincident with the worst case motor start on the EDG, resulting in delaying the MOV actuation until the voltage recovers to an adequate value.

G. Verify that the uncertainties associated with the accuracy of the MOV diagnostic equipment, frictional variations due to plant maintenance/lubrication activities, etc. were considered.

H. If the MOV is controlled by a contactor, verify that the total stall time was based on longer of the two, the pick-up voltage of the contactor or the adequate voltage needed for motor to operate.

I. Based on the field setting, the absolute EDG frequency can be at the lower end of the allowable range e.g. 58Hz. Based on the lowest allowable frequency value, coupled with voltage/frequency excursions during motor starts, verify that the valve stroke time is within acceptable limits.

J. Explain why the 0.77 second stroke time margin is adequate for MOV SI-860 considering the above, and account for uncertainties.

K. Identify the most limiting component when fed from EDG A and confirm that all safety-related equipment has adequate voltage with sufficient margin to account for uncertainties.

EEEB 3 According to the PBNP FSAR, a 550 gallon "day tank" is located near each unit. An additional 550 gallon storage tank is located in the base of each of the Train A units. The licensee has eliminated a 10% additional requirement for EDG fuel oil storage in the day tanks associated with each EDG. The licensee stated that the 10% additional margin is a requirement for fuel oil calculation after the transfer pump has started. The licensee indicated that PBNP intends to maintain 120 minutes worth of fuel for EACH EDG in each day tank.

Please confirm that this information is accurate.