PLA-7655, Response to Request for Additional Information, (CAC Nos. MF9131 and MF9132) PLA-7655

Response to Request for Additional Information, (CAC Nos. MF9131 and MF9132) PLA-7655

ML17338A516
Person / Time
Site:	Susquehanna
Issue date:	12/04/2017
From:	Berryman B Susquehanna, Talen Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CAC MF9131, CAC MF9132, PLA-7655
Download: ML17338A516 (11)

Text

Brad Berryman Site Vice President U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Susquehanna Nuclear, LLC 769 Salem Boulevard Berwick, PA 18603 Tel. 570.542.2904 Fax 570.542.1504 Brad.Berryman@TalenEnergy.com SUSQUEHANNA STEAM ELECTRIC STATION RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION, (CAC NOS. MF9131 AND MF9132)

PLA-7655 TALEN~.

ENERGY 10 CFR 50.90 Docket Nos. 50-387 and 50-388

References:

1. Letter PLA-7471, Susquehanna Nuclear, LLC to US. NRC, "Proposed License Amendments to Revise Diesel Generator Surveillance Requirements with new Steady State Voltage and Frequency Limits," dated January 25, 2017, (ML17044A149).

2. Letter PLA-7583, Susquehanna Nuclear, LLC to US. NRC, "Response to NRC Request for Supplemental Information for License Amendment Request to Revise Diesel Generator Surveillance Requirements with new Steady State Voltage and Frequency Limits," March 21, 2017, (ML17080A405).

3. Letter PLA-7619, Susquehanna Nuclear, LLC to US. NRC, "Response to Request for Additionallnformation, (CAC Nos. MF9131 and MF9132), "August 4, 2017 (ML17216A283 ).

4. NRC Email, "Request for Additional Information Regarding, (CAC Nos. MF9131 and MF9132)," October 27, 2017 (ML17317A022).

By letter dated January 25,2017 (Reference 1), Susquehanna Nuclear, LLC

("Susquehanna Nuclear") submitted a license amendment request for Facility Operating License Nos. NPF-14 and NPF-22 for the Susquehanna Steam Electric Station ("SSES")

Units 1 and 2. That proposal requests revised Surveillance Requirements (SRs) in Technical Specification (TS) 3.8.1, "AC [Alternating Current] Sources-Operating" for the use of new and more restrictive steady state voltage and frequency limits.

Susquehanna Nuclear provided supplemental information on this proposal on March 21, 2017, (Reference 2). The purpose of this letter is to respond to your request for additional information (RAI, Reference 4) on the requested licensing action. The response is provided in Attachment to this letter.

Susquehanna Nuclear has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration provided to the NRC in Reference 1. The additional information provided by this submittal does not affect those bases that support a conclusion that the proposed license amendment does not involve a significant hazards consideration, and that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment. PLA-7655 There are np new regulatory commitments asso.ciated with this response.

In the event that the NRC has any question concerning this response, please contact Mr. Jason Jennings at (570) 542-3155.

I declare under penalty of perjury that the information provided in this submittal is true and correct.

/IJ(/ 1 I~~ t1 Executed on:

w _; -

I Brad Berryman

Attachment:

Response to Request for Additional Information cc:

NRC Region I Ms. L. H. Micewski, NRC Sr. Resident Inspector Ms. T. E. Hood, NRC Project Manager Mr. M. Shields, PA DEP/BRP Attachment to PLA-7655 Response to Request for Additional Information Request for Additional Information (RAI-l):

Attachment to PLA-7655 Response to Request for Additional Information Page 1 of8 The NRC staff requested supplemental information, in a letter dated July 7, 2017(1), to complete its review. In response to the NRC request, the licensee submitted a letter dated August 4, 2017.

The licensee stated, in response to RAI-7a, that the impact ofthe DG voltage and frequency variations on the motors are explained in detail in the excerpts of calculation EC-024-1 03 5 Section 7, which were submitted with the license amendment request (LAR) as Attachment 3.

In Section 7.5, "Effects on Motors," ofthe LAR, the licensee determined the net effect of voltage and frequency variations on motor steady state speed using the change in speed (L'lS) equation.

The L'lS equation is approximated by considering the motor speed-torque curves in the area of intersection with the pump speed-torque curve as straight lines. The NRC staff notes that this approximation introduces enors which are functions of the slopes of the motor speed-torque curves. Provide a discussion of any enors introduced by this approximation for the L'lS equation based on the DG's motor and pump loads speed-torque curves.

Response to RAI-l:

The change in speed (~S) equation, as presented in the calculation, is a close approximation to the actual speed change that will be experienced by the motor caused by voltage and frequency variations of the diesel generator. In lieu of plotting and interpreting motor speed/torque curves, algorithms are derived that can be used to provide a close and valid approximation of the change in steady state (rated) speed of a motor as a result of voltage and frequency variations.

The change in speed (~S) equation, as used within calculation EC-024-1035, is derived from the relationship between the torque developed by the motor and the change in voltage and/or frequency. The speed-torque curves of the motor and pump are used to help demonstrate the above mentioned relationship.

If the motor, running at rated voltage, shall have a change in voltage, the torque, developed by the motor, will change to a value that is proportional to the square of the motor's rated terminal voltage.

T2 = T1 ( ~~ )

2

where, T1 =torque at voltage V1 T2 = torque at voltage V2 V1 = baseline voltage V2 = new voltage equation 1 (I)

NRC Letter, "Request for Additional Information Regarding License Amendment Request to Revise Diesel Generator Surveillance Requirements with new Steady State Voltage and Frequency Limits (CAC Nos.

MF9131 and MF9132)," dated July 7, 2017, (ML17180A200).

Attachment to PLA-7655 Response to Request for Additional Information Page 2 of8 The same relationship holds true for changes in frequency, but, the change in the motor's torque will be inversely proportional to the square of the supply frequency.

T2 = Tl ( 11 )2 f2

where, equation 2 Tl =torque at frequency fl T2 = torque at frequency f2 fl = baseline frequency f2 = new frequency As seen above, when the frequency and/or voltage of a motor shall change, so does the motor's torque value. But another motor parameter is also impacted by voltage and/or frequency changes and that parameter is speed. A motor's synchronous speed is defmed by the fmmula:

Ss = 1201 p

where, f = frequency P = number of poles Ss = synchronous speed equation 3 A change in the motor's frequency will cause a proportionate change in the motor's synchronous speed.

Using the speed torque curve of the motor and plotting the pump curve on top, the rated (steady state) speed of a motor is determined by the intersect point where the motor curve intersects the pump curve. If the motor is operated at a different voltage and/or frequency, other than its rated nameplate value, the motor curve shall shift parallel to the x-axis by a proportionate value. The effect on motor torque, as caused by a change in voltage and/or frequency, can be closely approximated by evaluating the operational region (the region representing the point of maximum torque to the end of the synchronous speed) ofthe motor speed-torque curve. For motors used in pump applications, mainly those of design A, B and some C qualities, the motor speed-torque curve will have a slope that is very steep in the operational region. As a result, the slope of the motor curve can be represented as a linear function.

The change in rated speed (actual) is determined by taking the point of intersect Sl of the rated motor curve to the pump curve and subtracting the point of intersect S2 of the new motor curve (caused by a change in frequency) to the pump curve. By representing the slope of the motor curve as a linear function, a delta (enor) is introduced and is identified as the difference in speed between the intersect point S2 of the new motor curve and the newly created point of S2'. S2' is defined as the intersect point of where a horizontal line from S 1 intersects the new motor curve.

The delta value is dependent on the slope of the new motor curve. (Note: A change in voltage and/or frequency will alter the slope of this curve within the operational region in accordance with equations 2 and 3, however the slope of the curve shall remain steep and the impact to the overall results (enor) will be minimal). Based on the change in voltage and/or frequency, the relationship between torque and rated speed is defined as:

s J S's.

Load (pump curve)

Motor @ condition 1 Motor @ condition 2 Attachment to PLA-7655 Response to Request for Additional Information Page 3 of8 ll.

~ Q.C1o:Ja./ A$

Figure 1 By linear interpretation,

~

_ (ss-s1)

Tl-T2 T2 Solving for £lS, LlS = G~- 1) (ss-s1)

where,

£lS = change in speed Ss = synchronous speed S 1 = speed at condition 1 T1 =torque at condition 1 T2 = torque at condition 2 and speed S 1 equation 4

Attachment to PLA-7655 Response to Request for Additional Information Page 4 of8 Equation 4 above represents the change in rated speed (assumed) caused by a change in voltage and/or frequency.

As stated earlier, as frequency changes, so does the synchronous speed of the motor. The effect a motor's synchronous speed change has on steady state speed can be closely approximated as shown below:

51 Ssl Ss.:<..

Load (pump curve)

Motor @ condition 1 Motor @ condition 2 Figure 2

Attachment to PLA-7655 Response to Request for Additional Information Page 5 of8 By linear interpretation, Solving for ~S 52 = 51 (ssz)

Ss1 LIS = 51 - 52 = 51 (1 - SsZ)

Ss1

where,

~S = change in speed Ss1 =synchronous speed at condition 1 Ss2 =synchronous speed at condition 2 S 1 = speed at condition 1 S2 = speed at condition 2 equation 5 The overall effect of voltage and frequency variations on steady state speed can be closely approximated as the sum of the changes due to voltage plus the sum of the changes due to frequency and is expressed below:

LIS = G~- 1) (ss-S1) + S1 ( 1- ~;~)

or

where, f1 = rated frequency f2 = postulated frequency

~S = change in speed Ss = synchronous speed S 1 = rated speed at V 1 and f1 V1 =rated voltage V2 = postulated voltage equation 6 At SSES, all motors (Core Spray, RHR, RHRSW and ESW) are design B motors and follow the characteristics of a typical pump motor curve with steep slopes in their operational region. As the slopes of these curves approach infinity (vertical), the delta (as defined above) approaches "0". This small delta that is incorporated in the ~S equation is insignificant and will not produce a negative impact to the performance of the motor or its intended safety functions.

RAI-2

Attachment to PLA-7655 Response to Request for Additional Information Page 6 of8 In Section 7.5, Table 11, "Speed & HP [horsepower] Variation Matrix of Major Motor Loads,"

provided the results of changes in motor speed and HP of major motor loads due to the changes in DG steady state voltage and frequency. The licensee stated that the maximum change in motor HP would occur when the DG is operating at maximum steady state voltage and frequency (i.e., 4400 V and 60.5 Hz).

The NRC staff notes that, based on Table 11, the HP of the major pumps loads would increase by at least 3% when the DG is operating at maximum steady state voltage and frequency (i.e.,

4400 V and 60.5 Hz). For some major motor loads such as the reactor core spray (CS) pumps motors, the increased pump HP would be higher than the respective motor nameplate rating provided in the Susquehanna Updated Final Safety Analysis Report (UFSAR), Table 8.3-1.

For each DG major motor-pump sets loads (CS, residual heat removal (RHR), RHR service water, emergency service water), provide the following:

a)

Provide the values for the pumps' maximum brake HP and the motors' service factors. Also, provide a discussion ofthe impact of the increased HP on the motors' capabilities and performance.

The licensee also discussed, in Section 7.5 of Attachment 3, the change in motor rise temperature due to the DG frequency variations. Table 11 of Attachment 3 shows that the motor speed and HP are impacted by the cumulative DG voltage and frequency variations.

b)

Provide a discussion of the impact of the increased speed and HP resulting from the DG operating at maximum steady state voltage and frequency on all the DG motor loads operating temperatures.

Response to RAI-2:

a)

The maximum brake HP for the major DG pumps and their associated motor's service factor are as follows:

Core Spray RHR RHRSW ESW BHP = 691 BHP = 1798 BHP = 574 BHP=440 Service Factor 1.0 Service Factor 1.0 Service Factor 1.15 Service Factor 1.15 The capabilities of the major motor loads of the DG to meet their safety design requirements will not be impacted as a result of the increased horsepower output of the motors.

Changes to the motor's horsepower output are the result of voltage and frequency changes/variations that are caused by the source power supply, the diesel generators. As stated in the proposal, the voltage and frequency outputs of the DGs are strictly controlled by the DG's Static Exciter Voltage Regulator (SEVR) and electronic governor,

Attachment to PLA-7655 Response to Request for Additional Information Page 7 of8 respectively. The SEVR is designed to maintain a constant generator output voltage of 4250 volts nominal. The output is controlled through the Diesel's Power Driven Potentiometer PDP-4 (with a range of 4150 to 4350 volts). If the measured generator output voltage is different from the nominal setpoint of 4250 volts, the regulator will respond by varying the field current to conect the voltage to 4250 volts. The only time voltage is allowed to swing outside of this range is when the DGs are to synchronize with offsite sources.

The frequency of the DG is in direct proportion to the DG' s speed and is controlled by the DG' s electronic governor. The tuning ofthe electronic governor is controlled by procedures that set the frequency ofthe DG to 60Hz+/- 0.1 Hz. If the DG's SEVR or the electronic governor were to fail, additional controls are in place that will restrict the operation of the DG to be within the newly proposed voltage limit of 4000-4400 VAC and a frequency limit of 59.3-60.5 Hz. The operation of the DG at the newly proposed limits will only occur on a temporary basis until the DG's SEVR or electronic governor is repaired or replaced.

The major motor loads of the DG were designed to meet the requirements ofNEMA Standard MG-1. The NEMA Standard requires that at a minimum, the AC induction motors shall operate successfully under running (continuous) conditions at rated load with a variation in voltage and frequency up to the following:

Plus or minus 10 percent of rated voltage with rated frequency Plus or minus 5 percent of rated frequency with rated voltage A combined variation in voltage and frequency of 10 percent (sum of absolute values) of the rated values, provided the frequency variation does not exceed plus or minus 5 percent of rated frequency With the operation of the DG within the limits as described above, the major motor loads of the DG shall continue to be within the criteria established by the MG-1 standard for the successful operation of AC induction motors. The major motor loads of the DG shall continue to operate safely meeting their safety related functions and their design requirements for which they were intended.

During motor operation at the higher limits, motor performance will be affected but not to a degree where it presents a negative impact to the motor itself or to its safety design functions.

As stated earlier, the increase in horsepower output is the result of variations in voltage and/or frequency. Such variation, will have a direct impact on the speed of the motor which in tum impacts attributes such as pump flow, net positive suction head (NPSH) availability and of course horsepower output. Using the affinity laws established in Table 3 of calculation EC-024-1 03 5, with the motors operating at maximum steady state voltage and frequency, an increase in motor speed of approximately 0.8% will be experienced. This will cause an increase in the pump flow by approximately 0.8% and a decrease in the margin ofNPSH, caused by an increase of flow loss component ofNPSH by approximately 1. 7%.

Attachment to PLA-7655 Response to Request for Additional Information Page 8 of8 Although the performance of the motor and associated parameters are impacted, the impact remains minimal and the motor and associated equipment shall continue to operate safely meeting their safety related functions and their design requirements for which they were intended.

b)

The speed of a motor and its HP output are controlled by voltage and frequency settings.

Temperature of the motor is also impacted when either the frequency, voltage or both shall change.

The effect of frequency variations on an induction motor's operating temperature is based on the proportional relationship of the square of the HP to rated HP ratio (Equation 10 of calculation EC-024-1035). The change in motor HP is related to the cube of the frequency change (Affinity Laws). This explanation is provided in section 7.5 of calculation EC-024-1035 with the use of the affinity laws as documented in Table 3.

Based on these relationships, changes in motor rise temperature due to the diesel generator operating at maximum frequency of 60.5 Hz shall be approximately 5.1% of temperature rise. During diesel generation operation at minimum frequency of 59.3 Hz, the change shall be approximately -6.9% of temperature rise.

For voltage variations, when a motor is carrying full load, the in-phase or power-producing component of its line current will vary inversely with terminal voltage. Lower the voltage and the current will rise. With the increase in current, both stator and rotor I2R losses will rise. The net result is a greater rise in winding temperature. When the voltage is above rated voltage, the in-phase component of line current will now decrease, and both stator and rotor eR losses will decrease along with the winding temperature.

Figure 6-58 ofEPRI's Power Plant Electrical Reference Series Volume 6 (Motors) provides the relationship between voltage and temperature rise. Per this figure, a 1 0%

decrease in voltage produces approximately a 5°C increase in temperature and a 10%

increase in voltage produces a -3 to -4°C decrease in temperature.

When both voltage and frequency values are changed simultaneously, the motor can operate successfully with little temperature change, if the voltage to frequency ratio is kept constant to its rated values. Other variations will produce a cumulative effect on the motor's temperature rise. Under the conditions requested, with the motor operating at maximum voltage and frequency, the net effect would be a temperature rise of approximately 1 to 2°C (a 5.1% rise ( ~4°C) for frequency plus an~ -3°C drop for voltage).

The increase in operating temperature of the motor by an approximate 1 to 2°C will not have a negative impact to the motor.