ML20209G123
| ML20209G123 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/28/1987 |
| From: | Lippold W BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8704300476 | |
| Download: ML20209G123 (9) | |
Text
A BALTIMORE GAS AND ELECTRIC CHARLES CENTER P.O. BOX 1475 BALTIMORE, MARYLAND 21203 W. JAMES LJPPOLD MANAGER PduCLEAR ENGINEERING SERVICES DEPARTMENT April 28,1987 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Station Battery (125 V DC)
REFERENCES:
(a)
Letter from Mr. J. A. Tiernan (BG&E), to Mr. A. C. Thadani (NRC),
dated April 14, 1986, Request for Amendment (b)
Letter from Mr. S. A. McNeil (NRC), to Mr. J. A. Tiernan (BG&E),
dated October 3,1986, same subject Gentlemen:
This letter is in response to Reference (b). We believe that this addresses all questions and concerns regarding Reference (a).
Reference (a), Change No. 5, proposed a change to the Surveillance Requirements for the 125-volt DC Station Batteries. provides the additional information requested. This information does not affect the Determination of Significant Hazards Considerations as provided in Reference (a).
Should you have further questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours, WJL/SRC/dlm Attachment k
8704300476 870428 PDR ADOCK 05000317 P
g Document Control Desk April 28,1987 Page 2 cc:
D. A. Brune, Esquire J. E. Silberg, Esquire A. C. Thadani, NRC S. A. McNell, NRC T. E. Murley, NRC T. Foley/D. A. Trimble T. Magette, DNR i
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ATTACHMENTI Item 1 NRC Request Provide a description or drawing of the physical design of the station battery. Include the following points of reference:
a.
top of the cell b.
top of the cell plates c.
maximum electrolyte level indication mark d.
minimum electrolyte level indication mark e.
orifice position in the funnel stem of the flame arresting vent f.
proposed short-term high and low electrolyte level limits g.
proposed long-term high and low electrolyte level limits Describe the design basis of the cells' maximum and minimum electrolyte level indication marks and any effects (physical, chemical, or electrical) on the battery which occur from permitting the electrolyte level range to be expanded.
BG&E Response Two sketches are enclosed that describe the points of reference discussed above.
The design basis for the cells' maximum and minimum electrolyte levels is predicated on overflow and uncovery of the plates, respectively. Additionally, the bottom of the stem on the Prevent Assembly should be covered in order to insure hydrogen exits the cell through an aluminum oxide material in the Prevent Assembly. The Prevent Assembly assists in dispersing and mixing the hydrogen generated in the cell. The apparent electrolyte level depends on the charging rate. As stated in IEEE Standard 450-1980, Section 4.4.1, when any cell electrolyte level reaches the low level line, water should be added to bring all cells to the high level line. If electrolyte level remains 1/2" or more below the top of the plates for an extended period of time the cell may have suffered irreversible damage due to plate exposure to air. Additionally, Section A.3 of Appendix A to IEEE Standard 450-1980 states that if electrolyte level is at or near the high-level mark at float voltage, it may rise above that mark on charge. That condition is not objectionable. This is a normal condition af ter the battery equalizes due to oxygen and hydrogen in solution. Af ter 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> on float, the levels will fall back to within the high level mark. The high level mark is the point of reference for the electrolyte specific gravity. All specific gravity measurements are corrected to the high level mark. A long-term limit of " $ 1/4" above maximum level mark" would provide additional flexibility in that corrective action would not be required when electrolyte level is slightly above the maximum mark. This condition would not adversely impact battery performance. For our battery cells, the maximum level mark is one inch below the overflow condition. Conservatively, an overflow condition would not occur as a result of a battery charge, even if electrolyte level prior to the charge was 1/4" above the maximum level mark. For the proposed short-term electrolyte level limits, NUREG-0452 l
states that the allowable values for electrolyte level ensure no physical damage to the plate vith an adequate electron transfer capability. --
r ATTACHMENT 1 There are no adverse chemical effects on the battery due to the expansion of the electrolyte level.. The electrolyte is a dilute solution of sulfuric acid and water. Because of evaporation and electrolysis, only water is lost from the solution under normal conditions.
For a nominal 1.215 specific gravity battery cell there is a fixed quantity of sulfuric acid available for the chemical reaction. In a NCX 1950 cell, approximately 10.93 lbs of acid is used. Since only water is lost from the cell, this acid will always be available for the chemical reaction, regardless of the electrolyte level.
A lowering of electrolyte level will cause the following electrical effect. The loss of electrolyte will result in higher concentrations of sulfuric acid that could cause accelerated aging of lead acid cells. This effect does not become noticeable until the specific gravity exceeds 1.250. The level in a nominal 1.215 cell would have to drop almost 1/2 inch below the low level mark in order for the specific gravity to reach 1.250.
Item 2 NRC Request Information should be provided demonstrating that the allowable value of 2.07 volts per cell is appropriate for the station batteries' design application, as related to the continuous or intermittent operation of the cells at this voltage. To permit the staff to place this proposed change in the proper perspective, the anticipated amount of time the cells would be in the short-term operating mode for a given 18-month period must be established.
Describe the events that could result in an ICV of less than 2.10 volts or an s.g. of less than 1.200. Provide an estimate of the amount of time that the ICVs will be less than 2.10 volts and/or the s.g.'s will be less than 1.20 during an 18-month period.
BG&E Response Cell voltage is not, by itself, an indication of the state of charge in a battery. IEEE Standard 450-1980 indicates that internal cell problems are usually not evident until cell voltage decreases to 2.07 volts. We believe that overall battery capability would be adequate in the short-term as long as all individual cell voltages are maintained above the 2.07 volt level.
It is difficult to estimate with any accuracy the amount of time ICVs will be less than 2.10 volts and/or the specific gravities will be less than 1.20 during an 18-month period.
The relative age of the battery cells will have the most significant effect on the actual time. We can say over the last year that the ICVs for all of our batteries, which are relatively new, have not been below 2.10 volts during the scheduled surveillances.
However, we have no data for any 18-month period.
l ATTACHMENT 1 An extended battery discharge would result in a lowering of the ICVs and specific gravities. Furthermore, the addition of an excessive amount of water to the cells would dilute the electrolyte and lower the specific gravity. Internal cell problems such as negative to positive plate shorts would also cause a gradual lowering of a cell ICV and specific gravity.
Item 3 NRC Request We request you provide the basis and rationale to demonstrate that tne trending of ICV and s.g. deviations is not necessary to detect overall battery capacity degradation below the minimum acceptable level during the period between consecutive performance discharge tests.
BG&E Response We are not suggesting that trending of ICV and specific gravity is not necessary to detect overall battery capacity degradation. We have and will continue to trend ICV and specific gravity. However, we propose to use this trending information to identify cells that may be developing problems but are still operable. We are not proposing to use this information as the sole determinant in verifying Technical Specification operability and availability.
A decrease in individual cell voltage or specific gravity during the time period since a previous test is not indicative of overall battery capability. However, we believe that by measuring and comparing individual cell deviations, for specific gravity, from the average of all connected cells that we can more accurately measure battery capacity. In addition, the specific gravity deviation of the average of all connected cells from the nominal specific gravity is more indicative of capacity also. We have proposed limits to these deviations in Reference (a).
Monitoring the differences in cell voltage and specific gravity between consecutive tests can be misleading. For example, ICV for a particular cell could be high, but within the limits, during a previous test and near the low limit for a current test. Based on the difference between the two tests, the cell may be out-of-specification for the allowed deviation. If you tie the deviation to a nominal value, we believe the specification will be more meaningful. We feel that the Institute of Electrical and Electronics Engineers recognized this and, therefore, did not include the requirement in their updated standard (IEEE Standard 450-1980).
r ATTACHMENTI Item 4 NRC Request The licensee has stated that even if the individual cells's.g.'s were.04 below 1.215, the Calvert Cliffs batteries will have sufficient capacity remaining for the design duty cycle, since the total ampere-hours demanded during the design duty cycle is less than one half of the design capacity of the cells. In this regard, provide a description comparing the design duty cycle to the design battery capacity in ampere-hours. Provide a quantitative description (and its basis) of the relationship of s.g. to battery capacity for your station battery including your battery capacity at s.g.'s of 1.195 and 1.175.
BG&E Response In our proposed Technical Specification change, the average of the specific gravities for all cells will be greater than 1.205 in the long term. In the short term (seven days or less), the average specific gravity of all cells can be no less than 1.195 for the battery to be considered operable. Therefore, the capacities of our batteries are being provided based on the average specific gravities of 1.205 and 1.195. Below is a summary of the capacities of our four vital 125-volt batteries at various initial specific gravities. These calculations are based on our Technical Specification duty cycle, a final individual cell voltage of 1.78 volts per cell, a design margin of 15% and an aging degradation factor of 25%.
Battery Capacity at Specific Gravity (SG) of:
Battery SG of 1.215 SG of 1.205 SG of 1.195 11 121.3 %
111.0 %
100.8 %
12 223.5 %
208.3 %
193.6 %
21 121.3 %
111.0 %
100.8 %
22 184.4 %
171.9 %
159.9 %
Reserve 121.3 %
111.0 %
100.8 %
The specific gravity of a lead-acid storage battery affects the capacity because it:
o Determines the potential of the plates; o
Affects the resistance of the electrolyte to the passage of the electric current; o
Affects the viscosity of the electrolyte and thereby the rate of diffusion; and, o
Differences in the concentration of the electrolyte in the pores of the plates and outside also affect the rate of diffusion. It has been shown that the concentration of electrolyte is directly related to the cell capacity, and that the capacity of the cells increases as the concentration of electrolyte increases, within allowable ranges.
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ATTACHMENT 1 Item 5 NRC Request State how the dummy load profile will be described and controlled in the FSAR, including its relationship to the battery duty cycle and to the duty cycle load survey.
Describe how the dummy load profile will be controlled in the interim until completion of the ongoing duty cycle load survey.
BG&E Response The design load cycle is controlled administratively in the updated FSAR. Table 8-10 in the updated FSAR describes the station batteries and the design load cycle. Any changes to the profile would continue to be controlled through the 10 CFR 50.59 process. There is no need to be concerned with any interim control since the updated FSAR administratively governs them currently. There are other control mechanisms in effect to ensure surveillance procedures are updated when design studies or modifications are completed which affect the design load cycles.
Item 6 NRC Request Provide the basis of the correlation of a charging current of less than 2 amperes when on a charge to an average s.g of all connected cells of greater than or equal to 1.195.
BG&E Response The pattern of charging current delivered by a conventional charger af ter a discharge provides a method for determining the state of charge for a battery. This is explained in Appendix B of IEEE Standard 450-1980. As the cells approach full charge, the battery voltage rises to approach the charger output voltage, and the charging current decreases. When the charging current has stablized at the charging voltage, the battery is charged, even though specific gravities have not stabilized.
The Bases in the l
Westinghouse Standard Technical Specifications state that a battery charger current that l
has stabilized at a low value is characteristic of a charged cell with adequate capacity.
For this reason, Table 4.8-1 proposes to define a charged cell in terms of either specific gravity or battery charging current.
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