RS-14-332, Additional Information Regarding Request for License Amendment to Revise Battery Surveillance Requirements
| ML14338A176 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  (DPR-029, DPR-030) |
| Issue date: | 12/04/2014 |
| From: | Simpson P Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-14-332 | |
| Download: ML14338A176 (6) | |
Text
RS-14-332 December 4, 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 8. Mozafari (U.S. NRC) to K. Nicely (Exelon Generation Company, LLC), "Draft Quad Cities, Units 1 AND 2 - Third Draft RAI for LAR request re: battery surveillance SRs (TAC NOS. MF4589 AND MF4590),"
dated October 21, 2014 (ADAMS Accession No. ML14295A012)
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.
December 4, 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 4th day of December 2014.
l1fu;L R Patrick R. Simpson Manager - Licensing
Attachment:
Response to Request for Additional Information cc:
NRC Regional Administrator, Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station Illinois Emergency Management Agency-Division of Nuclear Safety
ATTACHMENT Response to Request for Additional Information Page 1 NRC Request 1 Provide a summary of the calculation which demonstrates that the proposed TS total connection resistance limiting values (i.e., 2.4E-3 ohms and 6.0E-3 ohms) will maintain the required minimum voltages (i.e., 105 VDC for the 125 VDC batteries and 210 VDC for the 250 VDC for the 250 VDC batteries) at the batteries' terminals under worst-case design basis loading conditions.
Response
The following is a summary of the methodology and conclusions of Calculation QDC-8300-E-1587, "Determination of Battery Intercell Connector Resistance Limits," in regards to the allowable battery connection resistances. This calculation was provided to the NRC as of Reference 1. The purpose of this calculation is to determine the acceptance criteria for the Technical Specifications surveillance which reads and sums all the intercell and terminal connection resistances for each battery.
A typical battery arrangement is shown below in Figure 1. The basic parts of the battery are the individual cells, the intercell connector plates, inter-rack connectors (jumper cables), inter-tier connector (jumper cable), and terminal connections. The concern with this type of battery is corrosion that can occur between the mating surfaces of the intercell connectors and cable connections at the battery terminal posts. This corrosion is due to the liquid electrolytes (sulfuric acid) that are contained within the cells which can penetrate these metallic connections over time. This corrosion increases the resistance at the mating surfaces which in-turn reduces the overall battery voltage as seen at terminals A and B as shown below.
Figure 1: Typical Battery Arrangement If an ideal battery existed in which there would never be corrosion on the mating surfaces, and the battery cells could be installed in a straight line (i.e., no jumper cables to connect sections
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Battery Cell (two posts per polarity)
Intercell Connector Plates Inter-rack Connector (cable)
Inter-tier Connector (cable)
A B
ATTACHMENT Response to Request for Additional Information Page 2 together), then a fully loaded battery would produce exactly 105 VDC for the 125 VDC batteries, and 210 VDC for the 250 VDC batteries, at terminals A and B, and the worst-case design basis loading conditions would be maintained. However, corrosion is a concern and the batteries are not installed in a straight line due to space limitations in the battery rooms. The batteries are installed in sections as shown on the layout drawings that were submitted to the NRC in of Reference 2. Due to these battery sections, large-gauge jumper cables are needed to connect the entire battery string together. These jumper cables are not part of the vendor's supplied battery assembly and are fabricated on-site. Any resistance added to the ideal battery (e.g., corrosion, jumper cables) would drop the voltage at terminals A and B below 105 VDC or 210 VDC, as applicable, which would make the battery inoperable.
The batteries at Quad Cities are not fully loaded and contain margin. In other words, the ideal battery discussed above would have higher voltages at terminals A and B under worst-case design basis loading conditions at Quad Cities.
For example, for the Unit 1 125 VDC battery, this minimum voltage is 106.1 VDC which is 1.1 volts of margin. This margin is determined using a battery sizing computer program known as ELMS-DC. This program uses the battery's specific performance curves which contain the battery cell's internal resistance and the resistance from clean (un-corroded) intercell connector plates (note that the jumper cables are excluded from this determination). Using Ohm's Law as shown below, this 1.1 volts of margin can be converted to a resistance value using 666 amps (A), which is the maximum current from the duty cycle.
R =
I V
=
A 6
6 6
V 1
1
= 1651 µ The 1651 µ of resistance is the starting point in determining how much connection resistance is allowed when station personnel take the micro-ohm readings as part of the Technical Specifications surveillance. This value is what is known as RMargin in the calculation. As discussed above, the resistance of the clean intercell connector plates is already contained in the ELMS-DC program via the performance curves with an assumed value by the vendor of 26.67 µ. However, when the micro-ohm readings at the connections are taken during the surveillance, these intercell connector plates will be part of that reading and will be accounted for twice. To alleviate this unnecessary conservatism, this value known as RVendor will be added to RMargin to arrive at the amount of total connection resistance that is available to counteract the effects of corrosion. However, the ELMS-DC program is unaware of how many jumper cables were used to construct the battery string, or their length. For this reason, the resistance from the jumper cables (RJumper) must be subtracted from the RVendor and RMargin summation as a penalty to reduce the Technical Specifications acceptance criteria to ensure the 105 VDC or 210 VDC requirement, as applicable, is maintained. In addition, inaccuracies from the micro-ohm meter could produce readings on the low end which is non-conservative. Similarly, the inaccuracies from the meter (RMeter) must also be subtracted from the Technical Specifications acceptance criteria.
The complete equation for determining the connection resistance of the intercell connector plates, jumper cable connections (inter-tier and inter-rack), and terminal connections (feed
ATTACHMENT Response to Request for Additional Information Page 3 cables at terminals A and B) is shown below. Note that the metallic components are corrected for worst-case temperature conditions. As discussed previously, the values that are subtracted below reduce RTotal-Allow, leading to a more conservative limit.
RTotal -Allow =
Corr Temp Vendor R
+ RMargin - RJumper - RMeter RTotal -Allow =
1.096
)
(59)(26.67
µ + 1651 µ - 35 µ - 34 µ = 3017 µ RTotal -Allow Technical Specifications Acceptance Criteria 3017 µ 2400 µ For the Unit 1 125 VDC battery, 3017 µ is the maximum amount of connection resistance that would be allowed to accumulate at the intercell and terminal connections to maintain battery operability. As this value may change over time due to added load on the battery (e.g.,
modifications), a lower Technical Specifications surveillance acceptance criteria is established at 2400 µ for the Unit 1 125 VDC battery. The difference between 3017 µ and 2400 µ is the amount of margin available for future load additions to this battery.
The RTotal-Allow values and proposed Technical Specifications acceptance criteria values for each of the six safety-related batteries at Quad Cities are summarized in Table 5 of Calculation QDC-8300-E-1587 on page 14. This calculation was provided to the NRC as Attachment 4 of Reference 1.
NRC Request 2 Provide the margins available between the proposed TS total connection resistance limiting values and the overall battery resistances for maintaining the required minimum voltages for the 125 VDC and 250 VDC batteries.
Response
The latest surveillance on the Unit 1 125 VDC battery had 1700 µ of total connection resistance. If the jumper cables were included in the resistance measurements, the total would be 1735 µ which is below the 2400 µ acceptance criterion. As discussed above, including the jumper cable resistances as part of the surveillance is not necessary because the proposed connection resistance limits have been reduced to account for the jumper cables.
The following table shows the relationships between RTotal-Allow, the Technical Specifications Acceptance Criteria, and the actual measured values (i.e., total connection summations) for each of the six safety-related batteries. Note that RTotal-Allow is the overall battery resistance for maintaining the required minimum voltages. The Actual Measured Values are the summed-up as-found connection resistances from the latest battery surveillances. The minimum margin between the actual measured value and RTotal-Allow is 881 µ for the Unit 2 Alternate 125 VDC battery (i.e., the limiting battery).
ATTACHMENT Response to Request for Additional Information Page 4 Battery RTotal -Allow Technical Specifications Acceptance Criteria Actual Measured Values Unit 1 Normal 125 VDC 3017 µ 2400 µ 1700 µ Unit 1 Alternate 125 VDC 3017 µ 2400 µ 1296 µ Unit 1 250 VDC 11,800 µ 6000 µ 3814 µ Unit 2 Normal 125 VDC 2713 µ 2400 µ 1713 µ Unit 2 Alternate 125 VDC 2713 µ 2400 µ 1832 µ Unit 2 250 VDC 11,557 µ 6000 µ 3615 µ 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. Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Additional Information Regarding Request for License Amendment to Revise Battery Surveillance Requirements," dated October 24, 2013