RS-14-086, Additional Information Re Request for License Amendment to Revise Battery Surveillance Requirements

Additional Information Re Request for License Amendment to Revise Battery Surveillance Requirements

ML14064A527
Person / Time
Site:	Quad Cities
Issue date:	03/05/2014
From:	Simpson P Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-14-086
Download: ML14064A527 (6)

Text

now 4300 Winfield Rond W_>.rrenville. L 60556 Exelon Generation 630 657 20,00 Office RS-14-086 March 5, 2014 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Quad Cities Nuclear Power Station, Units 1 and 2 Renewed Facility Operating License Nos. DPR-29 and DPR-30 NRC Docket Nos. 50-254 and 50-265

Subject:

Additional Information Regarding Request for License Amendment to Revise Battery Surveillance Requirements

References:

1. Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Request for License Amendment to Revise Battery Surveillance Requirements," dated June 10, 2013

2. Email from B. Mozafari (U.S. NRC) to K. Nicely (Exelon Generation Company, LLC), "Quad Cities, Units 1 and 2 - Second RAI for LAR Request Re: Battery Surveillance SRs (TAC Nos. MF2297 and MF2298)," dated January 24, 2014 (ADAMS Accession No. ML14027A316)

In Reference 1, Exelon Generation Company, LLC (EGC) requested an amendment to Renewed Facility Operating License Nos. DPR-29 and DPR-30 for Quad Cities Nuclear Power Station (QCNPS), Units 1 and 2, respectively. The proposed change revises Technical Specifications (TS) Surveillance Requirements (SR) 3.8.4.2 and SR 3.8.4.5 to add new acceptance criteria for total battery connection resistance.

The NRC requested additional information that is needed to complete the safety evaluation in Reference 2. In response to this request, EGC is providing the attached information.

EGC has reviewed the information supporting a finding of no significant hazards consideration, and the environmental consideration, that were previously provided to the NRC in Attachment 1 of Reference 1. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the additional information provided in this submittal does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

March 5, 2014 U.S. Nuclear Regulatory Commission Page 2 There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Kenneth M. Nicely at (630) 657-2803.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 5th day of March 2014.

Patrick R. Simpson Manager - Licensing

Attachment:

Response to Request for Additional Information cc: NRC Regional Administrator, Region III NRC Senior Resident Inspector - Quad Cities Nuclear Power Station Illinois Emergency Management Agency - Division of Nuclear Safety

ATTACHMENT Response to Request for Additional Information NRC Request 1 In response to NRC Request 1, the licensee stated that the proposed total battery connection resistance limits are the operability limits of the overall battery connection resistance. As indicated in the LAR, the total battery connection resistance values include inter-cell and terminal connection resistances.

Validate that the proposed total connection resistance values of 6.0E-3 ohm for the 250VDC subsystem and 2.4E-3 for the 125VDC subsystem, when used to demonstrate operability of the battery system(s), include measurement uncertainties, the sum of cable resistances and inter-tier, inter-cell, inter-rack, and terminal post connections resistances associated with the battery system, and the minimum voltage requirements considered in the plant design.

Response

The proposed total connection resistance values include measurement uncertainties, the sum of cable resistances and inter-tier, inter-cell, inter-rack, and terminal post connections resistances associated with the battery system, and the minimum voltage requirements considered in the plant design. The treatment of measurement uncertainties is discussed on page 9 of calculation QDC-8300-E-1587, which was submitted to the NRC as Attachment 4 of Reference 1. As discussed in Attachment 1 of Reference 1, the total battery connector resistance includes inter-cell and terminal connection (i.e., inter-tier and inter-rack connector cables and connections) resistance. Pages 5 and 6 of calculation QDC-8300-E-1587 provide a description of the steps used for each battery to determine the maximum allowable resistance.

NRC Request 2 In response to NRC Request 5, the licensee stated that the inter-cell, inter-tier, inter-rack, and terminal connection resistance limits will ensure that the minimum required battery terminal voltage (i.e., 105 VDC) for the 125 VDC batteries will be maintained. The response to NRC Request 2 states that the jumper cable resistance is excluded from the inter-cell measurements because it could mask a degrading inter-cell connector.

Clarify how the minimum required battery terminal voltages (i.e., 105 VDC and 210 VDC) for the 125 and 250 VDC batteries respectively, will be maintained without considering the resistance of the cables associated with the battery.

Response

The battery jumper cable resistances are considered in calculation QDC-8300-E-1587 for determining the maximum allowable intercell resistances, and thus, the minimum battery terminal voltages. The total allowable intercell resistance (RTotal-Allow) is determined as shown in the calculation on page 6, step 6. Note that the jumper resistance (RJumper) is subtracted from RTotal-Allow. In other words, as the jumper lengths increase, there is less allowable intercell resistance available for use when the intercell resistances are taken during the surveillances.

Also, note that only the jumper terminal connection resistance measurements are taken during the surveillances. Measurements through the length of the jumper cables are not necessary as Page 1

ATTACHMENT Response to Request for Additional Information they are not part of the intercell connector surveillance. As noted above, the jumper resistance is explicitly accounted for in determining the total allowed battery intercell connection resistance.

The resistances of these jumper cables are not expected to change over time.

NRC Request 3 In response to NRC Request 7, the licensee stated that the resistances for inter-cell connectors, terminal connectors and jumper cables are temperature corrected to 120°F (i.e., 50°C), the maximum temperature in the turbine building where the batteries are located. The licensee also stated that the voltage VMin, which is used to calculate the resistance RMargin due to the remaining battery margin, is temperature corrected to 65°F (i.e., 18.33 °C).

The staff notes that typical insulated power cables have a rated temperature of 90°C (i.e.,

194°F), and thus, analytical calculations conservatively use a bounding temperature of 90°C.

a. Provide the temperature correction factor for RMargin. If RMargin is temperature corrected to 65°F, clarify if adding RMargin to RVendor, the vendor's resistance that is temperature corrected to 120°F, is conservative.

b. Explain how the change in resistance due to load current heating effect and the resultant increase in temperature of all current carrying components is accounted for in the RTotal-Allow value and the above total battery connection resistance limits.

Response

RMargin is temperature corrected to 65°F via the ELMS-DC program for sizing the battery. The value of RMargin is calculated per step 5 on page 6 of calculation QDC-8300-E-1587 as shown below.

Vx RMargin =

IMax Note that Vx is obtained from step 2 by using the ELMS-DC program. This program uses 65°F as the minimum battery electrolyte temperature to determine a minimum battery voltage since it is the minimum allowable temperature permitted by Technical Specifications 3.8.6, "Battery Cell Parameters," for the battery to remain operable. Since lower temperatures produce lower values of Vx, using 65°F is conservative. From step 6, RVendor is divided by the 120°F temperature correction factor. A higher intercell temperature will produce lower RVendor values which is also conservative.

In regards to conservatism, when adding RMargin and RVendor together, the following should be noted when temperatures are considered. RMargin is a function of the chemical reactions in the battery itself and is not affected negatively when the ambient temperature rises the way copper conductors do. A rising ambient temperature in the battery room will improve the battery's ultimate minimum voltage. Conversely, a rising ambient temperature will have a negative impact on the copper conductors of the intercell connectors and jumper cables and will reduce battery minimum voltage. For conservatism, the subject calculation uses the worst-case highest temperature when calculating RVendor and the worst-case lowest temperature for RMargin. This Page 2

ATTACHMENT Response to Request for Additional Information tends towards over-conservatism as the battery room cannot be 65°F and 120°F at the same time.

The subject calculation is set-up using the worst-case battery loading conditions to ensure the absolute minimum RTotal-Allow values are obtained. For Quad Cities Nuclear Power Station (QCNPS), as shown on the ELMS-DC load profiles (i.e., Attachment A of the calculation), the worst-case LOOP/LOCA loading on the batteries occurs during the first minute of the event (e.g.

678 amps for the Unit 2 battery). A large portion of the 678 amp loading is due to inrush currents from the starting of spring charge motors when the various circuit breakers actuate, and from the emergency diesel generator (EDG) starting sequence due to the LOOP. These inrush currents start at the very beginning of the event and quickly subside (i.e., 1-2 seconds).

An estimate of the power that would be generated in the cables and intercell connectors can be determined by looking at the jumper cables for the 125 VDC batteries. These jumper cables are four paralleled 350 MCM conductors. From Table 3 on page 9 of the calculation, these parallel cables have a resistance of 35 µ / 3.92 feet = 8.9 µ / foot. Since power is expressed by P = I2R, the power that would be dissipated as heat in the cables would be (678 amps)2(8.9 µ) = 4.1 watts per foot in the first two seconds of the event. This small amount of energy dissipation would have an insignificant and negligible effect on voltage drop along the battery string during the first two seconds of the event. Periodic testing confirms the battery system will deliver sufficient DC power to meet accident loads (i.e., service and duty performance tests).

In addition, as discussed above, the values of RMargin and RVendor are calculated at the two ends of the temperature range. An ELMS-DC test run was performed raising the minimum battery electrolyte temperature from 65°F to 95°F to mimic the 120°F conditions of the jumper cable and intercell connectors. The results showed an increase of 1500 µ to the value of RMargin.

This indicates that there is a significant amount of margin built into the use of the 65°F battery electrolyte temperature. In contrast, for the same 30°F temperature rise in the copper conductors, the resistance only changes by 160 µ. The temperature change due to heating of the conductors due to current flow is enveloped by the extra margin in the battery via RMargin.

Therefore, for temperatures at 65°F, the heating produced by the current is accounted for in the 120°F temperature correction factor for the jumper cables and RVendor. For temperatures above 65°F, the margin built into the 65°F correction factor envelopes the heating effects from current flow.

NRC Request 4 In Attachment 4 of the LAR, the licensee stated that the minimum required battery voltages used to determine the maximum allowable connection resistance value are 105 VDC and 210 VDC for the 125 and 250 VDC batteries respectively.

The staff notes that equipment manufacturers typically specify 210V and 105V as the minimum allowable voltage at the device terminals.

Validate that the minimum required battery voltages at the batteries terminals are adequate for operability of all DC equipment after allowing for voltage drop due to intervening conductors and connections.

Page 3

ATTACHMENT Response to Request for Additional Information

Response

Components powered by DC sources are much more tolerant to voltage drop than their AC counterparts. This is due to the nature of DC which never drops to zero volts the way an AC sine wave does. Although some equipment is specified with a minimum voltage requirement of 85% of its nominal rating (210 VDC), bench testing has shown that much of this equipment can function well below this value. Exelon Generation Company, LLC has performed extensive testing on DC motor operated valves (MOVs) in support of the Generic Letter 89-10 program and found them to operate as low as 25% of rated voltage in some cases.

In applications where equipment is expected to operate at the minimum allowable voltage (e.g., 105 VDC), voltage drop calculations for that equipment considers vendor/site testing to validate the equipment will operate at those voltages. It should also be noted that periodic surveillance tests, which place large loads on the batteries during a simulated LOOP/LOCA event, have not identified any components which would be incapable of performing their required design functions. This validates that critical components such as relays and solenoids can function properly at voltage levels below that of their published ratings.

There are no concerns with intercell connection resistances provided that the battery terminal voltages of 105 and 210 VDC are maintained.

Reference

1. Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Request for License Amendment to Revise Battery Surveillance Requirements," dated June 10, 2013 Page 4