RBG-46465, Supplement to Amendment Request Amendment to Technical Specification 3.8.4 Actions for Inoperable Division 1 or 2 Battery Charger
| ML052290282 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 08/12/2005 |
| From: | King R Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-46465 | |
| Download: ML052290282 (9) | |
Text
= Entergy Entergy Operations, Inc.
River Bend Station 5485 U. S. Highway 61 N St. Francisville, LA 70775 Tel 225 336 6225 Fax 225 635 5068 rking~entergy.com Rick J. King Director, Nuclear Safety Assurance RBG-46465 August 12, 2005 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
REFERENCES:
Supplement to Amendment Request Amendment to Technical Specification 3.8.4 Actions for Inoperable Division 1 or 2 Battery Charger River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47 1.
Letter from Paul D. Hinnenkamp to USNRC dated December 17, 2005 (RBG-46375)
Dear Sir or Madam:
By letter (Reference 1), Entergy Operations, Inc. (Entergy) proposed a change to the River Bend Station, Unit 1 (RBS) Technical Specifications (TSs) to revise the requirements for direct current (DC) sources in TS 3.8.4, 'DC Sources - Operating".
On February 7, 2005, Entergy received from the staff one question related to the subject amendment request. Based on discussions, a supplement providing the response to the question is contained in Attachment 1.
There are no technical changes proposed to the amendment request. The original no significant hazards consideration included in Reference 1 is not affected by any information contained in this supplemental letter. There are three new commitments contained in this letter as summarized in Attachment 2.
If you have any questions or require additional information, please contact Greg Norris at 225-336-6391.
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RBG-46465 Page 2 of 2 I declare under penalty of perjury that the foregoing is true and correct. Executed on August 12, 2005.
Sincerely, RJKIGPN Attachments:
- 1. Response to Request For Additional Information
- 2. List of Regulatory Commitments cc:
Dr. Bruce S. Mallett U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 NRC Senior Resident Inspector P. O. Box 1050 St. Francisville, LA 70775 U.S. Nuclear Regulatory Commission Attn: Mr. Kaly Kalyanam MS O-7D1 Washington, DC 20555-0001 Louisiana Department of Environmental Quality Office of Environmental Compliance Attn: Mr. Ronnie Wascom Surveillance Division P.O. Box 4312 Baton Rouge, LA 70821-4312
Attachment I To RBG-46465 Response to Request for Additional Information
- to RBG-46465 Page 1 of 4 Response to Request for Additional Information Related to TS 3.8.4 Actions for Inoperable Division 1 or 2 Battery Charger Question:
In the licensee submittal, Section 2.0, Proposed Change, and Section 4.0, Technical Analysis, both state that the "first priority is to minimize the battery discharge". The proposed change to TS 3.8.4 is intended to assure that the discharge of the battery is terminated and the battery is restored to a proper float voltage. Please describe how the discharge of the battery will be minimized within the 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> proposed to restore the battery terminal voltage to greater than or equal to minimum float voltage.
Background:
Entergy conducted a conference call on March 17, 2005 with the NRC. During the call, additional questions emerged regarding the potential impact of a slow degradation of the battery charger and the associated alarm setpoint. Specifically, the reviewer asked if the charger output drifted below the technical specification value of 130.2 VDC (2.17 volts/cell) to just above the existing alarm set point of 123 VDC (2.05 volts/cell), what would be the potential impact on the battery? This required further review by Entergy to confirm alarm setpoints. A final conference call was conducted on July 19, 2005 to resolve comments.
Response
Transferring to the backup battery charger, BYS-CHGR1 D, in an expedited manner is a principal action taken to minimize battery discharge. RBS would also minimize the battery discharge by avoiding unnecessary breaker operations or other actions that could increase the battery loading above normal while transferring to the backup charger. Alarm Response Procedures (ARPs) at RBS currently provide instructions to transfer to the backup charger.
RBS will enhance the ARP to include additional instructions for the operator to minimize the battery discharge by shutting down any unnecessary 125 VDC loads. Abnormal Operating Procedure, AOP-0014 LOSS OF 125VDC, currently contains these instructions for the operator to shut down any unnecessary 125 VDC loads to conserve available battery capacity.
The normal typical steady state loading on the divisional battery chargers is less than 20 amps on the division with the largest DC loads per the System Engineer's performance monitoring log. The Division 1 and Division 2 batteries have approximately a 15 percent margin with one cell out of service for a Design Basis Accident (DBA). If a two hour discharge at the normal typical steady state charger loading is considered, the batteries still have positive margin after a DBA.
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Additional questions were asked during the initial conference call about possible failure mechanisms that might result in additional loading on the batteries during this two hour period. Specifically, it was asked if a loss of the battery charger's supply bus might also result in the inverters becoming a load on the battery. The loss of a battery charger's 480 volt supply bus would result in a simultaneous loss of the inverter's AC power, resulting in the transfer of that inverter's loads onto the associated divisional battery. However, a loss of that 480 Volt to RBG-46465 Page 2 of 4 AC supply bus requires entry into Technical Specification 3.8.9, Distribution Systems -
Operating, which would continue to be applicable even after the backup charger was placed in service.
The 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> limitation to restore Division I and 11 DC electrical power subsystems to OPERABLE status, as required by the current TS 3.8.4, is based upon guidance provided in Regulatory Guide (RG) 1.93. For the proposed amendment to TS 3.8.4, this 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> limitation remains applicable for restoring battery terminal voltage to greater than or equal to the minimum established float voltage. If unable to achieve the proposed Limiting Condition for Operation (LCO) requirements, the unit would begin an orderly shutdown after this time has elapsed.
The related DC system alarms provided at River Bend include:
[setpoint: 123 VDC]
- 2. -DIV I (11) 125VDC SWGR ENB-SWG01A(B) U.V. LOW-LOW",
[setpoint: 114.9 (114.4) VDC]
- 3. -DIV I (11) 125VDC SWGR ENB-SWGOIA(B) GROUND FAULT'
- 4. 125 VDC BAT CHGR ENB-CHGR1A(B) TROUBLE,
[setpoints: overvoltage relay 140 VDC, undervoltage relay 90% Voltage (for AC supply voltage), high temp device 140 degrees F, overcurrent relay 120%]
Upon a loss of AC power to the battery charger, the 125 VDC BAT CHGR ENB-CHGR1A(B)
TROUBLE alarm will annunciate. The loss of power would result in loss of the battery charger function and immediate loading of the respective divisional battery. The 125VDC SWGR ENB-SWG01A(B) U.V. LOW alarm would then provide notification that a battery discharge was occurring. That alarm is currently set at 123 VDC, which corresponds to the nominal open circuit voltage of the battery.
If a slow degradation of the battery charger were to occur, it would be observed during routine operator rounds which are conducted once each shift. Operator rounds require that battery charger output be verified to be between 131 VDC and 139 VDC, less than 200 amps, with the Float Timer setting equal to zero. Any deviation from these established criteria would be addressed upon discovery. If this degradation were to result in loss of the battery charger function, the 125VDC SWGR ENB-SWG01A(B) U.V. LOW alarm would provide notification as described above. RBS commits to modify this alarm setpoint to provide additional margin above the nominal open circuit voltage of the battery. The revised alarm setpoint will be set closer to the minimum float voltage of 130.2 VDC.
During a slow degradation, there would be no significant impact on the capability of a fully charged battery if the charger voltage degraded to a point slightly above the open circuit voltage for 24 to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The charger would still be carrying the load and battery would remain charged as long as the charger output was above the open circuit voltage of the battery. This is confirmed by the review of The Institute of Electrical and Electronics Engineers (IEEE) 450-1980 and IEEE 450-2002 which show that the recommended interval to RBG-46465 Page 3 of 4 for checking the charger output and voltage is monthly. This interpretation was validated by conversation with an IEEE 450 Working Committee member.
In addition, Electric Power Research Institute (EPRI) TR-100248 states, "Batteries lose capacity because of self discharge if consistently undercharged. An undercharged battery may not be at full capacity and can become permanently damaged from sulfation.
Undercharging results in a harmful build up of lead sulfate on the plates, called sulfation." Table 8-1 of EPRI TR-1 00248 shows for a lead calcium battery, with a specific gravity of 1.210, the nominal open circuit voltage is 2.05 (123 volts for 60 cells), the minimum float voltage is 2.17 (130.2 volts for 60 cells) and the typical float voltage is 2.20 to 2.25 (132 to 135 for 60 cells). This document also recommends a monthly battery float voltage check.
The Technical Specification Bases state that the current surveillance requirements (SR 3.8.4.1) for checking the battery charger float voltage every 7 days are consistent when compared with the battery manufacturer's recommendations and IEEE 450. No specific float voltage verification frequency is specified in GNB (GNB Industries) "Station Battery Installation and Operating Instructions" Section 08-05. IEEE 450-1980 and IEEE 450-2002 show that the recommended interval for checking the charger output and voltage is monthly.
RBS commits to revise Technical Specification Bases for SR 3.8.4.3 to clarify that the 7 day check is conservative with respect to the recommendations (vs. being consistent).
Section 11.1.3.1 of EPRI TR-100248, Purpose of Float Voltage Checks for Vented Lead Acid Batteries, states "during normal operation the charger voltage is high enough so that a trickle charge overcomes the batteries' tendency to self-discharge and keeps the battery in a fully charged condition.... The purpose of the float battery checklis to verify the battery is maintained within the battery manufacturer's recommended limits. Float voltage checks are important to perform; however the float voltage alone does not confirm adequate cell capacity." This is based on an example of over 1000 cells where float voltage was compared to capacity measured by a discharge test. This discussion is intended to cover normal or near normal voltage variations, the capacity of a cell with a grossly low voltage such as 1.8 volts is clearly questionable.
In summary, slow degradation of battery chargers is relatively rare. Alarms are provided for the loss of the charging function. The impact of undercharging for a short period of time is not significant as inferred by the monthly frequency of float voltage checks specified in the standards. The battery capacity would not rapidly degrade as the charging voltage drifted low.
The battery charger would provide a small charge and carry the steady state load as long as it was above the open circuit voltage of the battery.
In addition to the above response, RBS commits to revise Section 8.3.2 of the Updated Safety Analysis Report (USAR). It is currently stated in the USAR that "Operation of the backup battery charger is under strict administrative control. No credit was taken for a backup charger in mitigating the consequences of an accident." This statement will be modified to indicate that, when used as a substitute for a safety-related battery charger, the backup battery charger will be credited for accident mitigation.
to RBG-46465 Page 4 of 4
References:
- 1. EPRI TR-100248
- 4. GNB (GNB Industries) "Station Battery Installation and Operating Instructions"
- To
-RBG-46465 List of Regulatory Commitments to RBG-46465 Page 1 of 1 List of Regulatory Commitments The following table identifies those actions committed to by Entergy in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
TYPE (Check one)
SCHEDULED ONE-CONTINUING COMPLETION COMMITMENT TIME COMPLIANCE DATE (If ACTION Required)
Modify the alarm setpoint for 125VDC SWGR x
Prior to ENB-SWG01A(B) U.V. LOW to provide Implementation additional margin above the nominal open circuit of Change voltage of the battery. The revised alarm setpoint will be set closer to the minimum float voltage of 130.2 VDC.
Revise Technical Specification Bases for SR x
Prior to 3.8.4.3 to clarify that the 7 day check is Implementation conservative with respect to the of Change recommendations (vs. being consistent).
Revise section 8.3.2 of the USAR. It is currently:
x Prior to stated in the USAR that "Operation of the Implementation backup battery charger is under strict of Change administrative control. No credit was taken for a backup charger in mitigating the consequences of an accident." This statement will be modified to indicate that, when used as a substitute for a safety-related battery charger, the backup battery charger will be credited for accident mitigation.