TSTF-08-14, Response to Request for Additional Information on TSTF-500, Revision 0, DC Electrical Rewrite - Update to TSTF-360.

Response to Request for Additional Information on TSTF-500, Revision 0, DC Electrical Rewrite - Update to TSTF-360.

ML082310334
Person / Time
Site:	Technical Specifications Task Force
Issue date:	08/18/2008
From:	David Bice, Gambrell R, Joseph Messina, Yates B Babcock & Wilcox, BWR Owners Group, Combustion Engineering Owners Group, PWR Owners Group, Technical Specifications Task Force, Westinghouse Owners Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TSTF-08-14, TSTF-360, TSTF-500, Rev 0
Download: ML082310334 (4)

Text

TECHNICAL SPECIFICATIONS TASK FORCE TSTF A JOINT OWNERS GROUP ACTIVITY August 18, 2008 TSTF-08-14 PROJ0753 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Response to Request for Additional Information on TSTF-500, Revision 0, "DC Electrical Rewrite - Update to TSTF-360"

REFERENCE:

Letter from Robert Elliott (NRC) to the Technical Specifications Task Force, "Request for Additional Information Regarding TSTF-500, Revision 0, 'DC Electrical Rewrite - Update to TSTF-360'," dated June 4, 2008.

Dear Sir or Madam:

In the referenced letter, the NRC provided a Request for Additional Information (RAI) regarding TSTF 500, Revision 0, "DC Electrical Rewrite - Update to TSTF-360." This letter responds to the NRC's request.

The TSTF requests that the Traveler be made available under the Consolidated Line Item Improvement Process.

Should you have any questions, please do not hesitate to contact us.

Bert Yates (PWROG/W) John Messina (BWROG)

David Bice (PWROG/CE) Reene' Gambrell (PWROG/B&W)

Enclosure cc: Robert Elliott, Technical Specifications Branch, NRC Matthew Hamm, Technical Specifications Branch, NRC 11921 Rockville Pike, Suite 100, Rockville, MD 20852 Phone: 301-984-4400, Fax: 301-984-7600 Email: tstf@excelservices.com Administered by EXCEL Services Corporation

Page 1 Response to Request for Additional Information on TSTF-500, Revision 0, "DC Electrical Rewrite - Update to TSTF-360" The following is the Technical Specification Task Force (TSTF) response to NRCs June 4, 2008, letter requesting the following information to complete the review of TSTF-500.

1. On page 14 of the August 31, 2007, submittal, the applicant stated that the float current requirements are based on the float current indicative of a charged battery. Define the term charged battery.

Response

The term "charged battery" means a battery that has been charged to the 95% to 100% range consistent with the limits established by the Technical Specifications and Commitment 1 discussed in Section 4.7.2.1 of the TSTF-500, Revision 0, justification.

2. On page 17 of the August 31, 2007, submittal, the applicant stated that the [2] amp float current value is an indication that the battery is [95] percent charged. Show that the Technical Specification float current value provides an indication that the battery is fully capable of performing its specified safety function.

Response

The Technical Specification float current value is selected such that when the charging current is less than the value, the remaining percent charge is less than or equal to the minimum design margin allowed by the commitment discussed in Commitment 1 of Section 4.7.2.1 of the TSTF-500, Revision 0, justification. When this condition is true, there is reasonable assurance that the battery is sufficiently charged to perform its specified safety function. For example, when the charging current has decreased to less than or equal to 5%

of the net charging amps, the percentage of charge remaining to be restored to the battery is less than or equal to 5%.

This relationship between battery state-of-charge and the value of the exponentially decaying charging current is discussed in more detail below in response to Question 3.

3. Describe the methodology for determining the design margin (e.g., 5%) that must be maintained in order to utilize float current monitoring as an indication of a batterys state-of-charge.

Response

Using the mathematical properties of an exponential decay curve, a table of the amounts of remaining charge to be restored versus the percentage of net charging amperes at a given time is given below. The required design margin to compensate for this remaining charge at this instant can then be determined from the table. This becomes the design margin to be maintained as discussed above.

Due to the variations in the portions of total charge represented under the exponential curve, a range of percentages is tabulated to illustrate that the method applies to all conditions.

The table is arranged from a fully charged condition in the top row to the particular

Page 2 Response to Request for Additional Information on TSTF-500, Revision 0, "DC Electrical Rewrite - Update to TSTF-360" remaining percent charge in the bottom row. The bottom row represents the transition in charging current from the bulk charging region to the exponential decay region. Notice that the first 3 columns basically show the exponential properties for the different time constants.

The other columns are derived from these using the portion of charge represented under the exponential curve.

Table 1 - Charge Remaining in Percent

1. Net Charge 100% 50% 20% 10% Notes Time Amps (%) charge in charge in charge in charge in const. curve curve curve curve 5 Float Limit 0% 0% 0% 0% Fully Charged 4 2% 2% 1% 0.4% 0.2%

3 5% 5% 2% 1% 0.5%

2 14% 14% 7% 3% 1%

1 37% 37% 18% 7% 4%

0 100% 100% 50% 20% 10% Start of decay The percent of remaining charge under the exponential curve is typically 20 to 30%;

however, the 100% column is shown to provide the worst-case remaining charge values.

Net charge amps is the difference between the charger DC output rated amps and the continuous house loads running at the time the battery is being charged. The actual amps value would be selected based on the charger sizing calculation. This is the minimum value expected over time since it is the percentage of this value that determines the return to service limit for the battery.

As an example, at three time constants the charge remaining is 5% and in all other columns the values are less than 5%. Therefore, this is the minimum design margin that must be maintained for use with the corresponding float current of 5% of the net charging amps.

Existing batteries with limited design margins may have to use float current values at 4 and 5 time constants. The actual limit for each battery at a given plant will be based on all the pertinent site specific factors.

This illustrates the methodology to be used for selecting the appropriate float current limit and the corresponding design margin to be maintained.

4. Describe how licensees will show that the float current limit for determining a batterys state-of-charge will remain valid for future replacement batteries.

Response

For replacement batteries of the same size and model number there would be no change required. Verification by the manufacturer that the use of float current monitoring is acceptable would be obtained for any replacement batteries. For replacement batteries of a different model/size and/or manufacturer, this verification would be part of the documentation package for the design change used to install the replacement battery.

Page 3 Response to Request for Additional Information on TSTF-500, Revision 0, "DC Electrical Rewrite - Update to TSTF-360"

5. Describe how electrical isolation will be maintained in accordance with Regulatory Guide 1.75, "Criteria for Independence of Electrical Safety Systems," between non-Class 1E and Class 1E circuits when an alternate means (i.e., non-Class 1E spare battery charger) is maintaining the charge on the Class 1E battery. If double isolation (e.g., two breakers in series, a breaker and a fuse, or a breaker supplied with a loss-of-offsite power signal) is not used, provide a detailed discussion on how a fault on the non-Class 1E electrical circuit will not propagate to the Class 1E electrical circuit.

Response

Meeting licensee commitments to Regulatory Guide 1.75 is ensured by the procedures governing temporary or permanent changes to plant equipment. These procedures are developed, used, and maintained in accordance with the licensees Quality Assurance program. The use of a non-safety-related charger to supply a class 1E battery would be governed by these existing procedures. The requirements of 10 CFR 50.59 and 10 CFR 50.65 apply to permanent design changes and temporary alterations supporting maintenance, respectively. This is beyond the scope of TSTF-500.

6. On page 15 of the August 31, 2007, submittal, the TSTF stated that the minimum temperature necessary to support operability of the battery can vary depending on the available excess capacity of the associated battery. Describe the available excess capacity that is being credited.

Response

The excess capacity being credited is that percentage of margin above what is required to account for aging and design. The remaining margin could be applied to the temperature adjustment to establish a relaxed minimum design temperature limit. If the battery is verified to be fully charged, then it could be possible to use the design margin normally reserved for this purpose to establish a relaxed minimum temperature limit. Margins will be clearly documented and controlled under the licensees program for design calculations.