ML20237C557
| ML20237C557 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 08/20/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20237C555 | List: |
| References | |
| NUDOCS 9808210271 | |
| Download: ML20237C557 (4) | |
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UNITED STATES g
j NUCLEAR REGULATORY COMMISSION WASHINGTON. D.C. SoseH001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT NO.125 TO FACILITY OPERATING LICENSE NO. NPF-43 DETROIT EDISON COMPANY FERMI 2 DOCKET NO. 50-341
1.0 INTRODUCTION
By letter dated April 2,1998, the Detroit Edison Company (DECO or the licensee) requested an i
amendment to the Technical Specifications (TS) appended to Facility Operating License No.
NPF-43 for Fermi 2. The proposed amendment would permit entering Operational Conditions 1 l
l and 2 prior to completion of Surveillance Requirements for the primary containment hydrogen i
and oxygen monitors in order to establish the conditions necessary (inerted containment) to properly perform calibrations. Also, the amendment would allow an increase in the calibration 1
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- frequency for the oxygen monitors from once every 18 months to quarterly and correct the nomenclature for the hydrogen and oxygen monitors in tables 3.3.7.5-1 and 4.3.7.5-1.
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2.0 EVALUATION
2.1 Background
r The hydrogen and oxygen monitors are part of the primary containment monitoring system l
(PCMS). The PCMS hydrogen and oxygen monitors provide control room operators with information regarding hydrogen and oxygen concentration following an accident. As described in the Updated Final Safety Analysis Report, the hydrogen and oxygen (14/0 ) monitoring 2
I system consists of two divisions, each division including one channel for each parameter. The H /0 system continuously samples the containment atmosphere during Operational 2 2 Conditions 1 and 2 when required to be operable by the TS. One division is normally aligned to the drywell, with the other division aligned to the torus.
During power operation, the Fermi 2 containment is inerted with nitrogen gas as required by TS to maintain a deliberately low concentration of oxygen in the containment atmosphere. Because
' the containment is inerted, the oxygen concentration is the limiting parameter for preventing the l
accumulation of an explosive gas mixture in the event of a loss-of-coolant accident (LOCA). The hydrogen and oxygen concentrations are monitored during operation and following a LOCA by the primary containment hydrogen and oxygen monitors and are displayed in the control room.
During plant shutdown for refueling and maintenance, the containment is de-inerted with air (approximately 20 percent oxygen) to permit personnel access. TS currently require the hydrogen monitors be calibrated quarterly and the oxygen monitors be calibrated once every 9808210271 980820 PDR ADOCK 05000341 P
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l 18 months._ Normally, these calibrations occur during plant operation with the containment inerted. However, if the plant is in an outage when the surveillance lapses, the monitors would be calibrated with the containment de-inerted. As reported in Licensee Event Report 97-004, the oxygen monitors exhibited a zero-shift when calibrated in an environment other than a nitrogen environment. Thus, if the monitor is calibrated while operating in a de-inerted environment during an outage, the monitor would be inaccurate and inoperable as soon as the transition is made to an inerted environment when the containment is ine ted on startup.
The hydrogen and oxygen monitors each utilize an electrochemical cell. The electrochemical cells contain electrodes and an electrolyte. A membrane separates the electrolyte from the gas sample. The electrodes, electrolyte, and membrane are selected to make the cell responsive to a particular gas of interest (e.g., hydrogen or oxygen). The cell produces a voltage which is a j
function of the concentration of the gas of interest in the electrolyte. Because the sample gas diffuses through the cell membrane into the electrolyte, the concentration of a particular gas in the electrolyte is proportional to the concentration of that gas in the sample. The sample gas continuously flows through an outer chamber and is normally directly exposed to the cell membrane through the inner chamber. During calibration, the calibration gas is injected into the inner chamber, displacing the sample gas which continues to flow through the outer chamber.
Thus, the cell membrane sees only the calibration gas during calibration. The licensee stated that the calibration itself is controlled by the instrument's microprocessor which determines the appropriate calibration factors that correlate cell output to calibration gas concentration, including compensation for temperature of the sample gas that continues to flow during the calibration cycle.
The licensee stated that testing conducted at Fermi demonstrated that it is possible to adequately calibrate the oxygen monitors with the containment de-inerted by simulating an inerted environment by purging the instrument with humidified nitrogen for approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> before running the calibration. Although it is possible to calibrate the instrument in this manner, this method of calibration places greater reliance on manual operations. For example, the nitrogen purge gas pressure must be manually set to match the normal sample gas pressure to provide for accurate calibration. While possible, the licensee stated that this method is neither considered to be practical nor desirable.
2.2 Prooosed Chance Specification 4.0.4 requires that surveillance requirements be completed prior to entry into an operational condition where the subject equipment is required to be operable. The licensee l~
proposed an exception to Specification 4.0.4 for the hydrogen and oxygen monitors calibration.
i The licensee-proposed TS exception for the hydrogen and oxygen monitors reads as follows:
The provisions of Specification 4.0.4 are not applicable provided that the surveillance is completed for one channel within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and for both channels within seven days after exceeding 15% of RATED THERMAL POWER.
In addition, TS Table 4.3.7.5-1 specifies the " Channel Calibration" for the Drywell Oxygen Concentration to be at 18-month intervals. The licensee proposed to increase the calibration frequency for the oxygen monitoring channel from once every 18 months to quarterly.
. The licensee also proposed to revise the nomenclature in Tables 3.3.7.5-1 and 4.3.7.5-1.
Specifically, the oxygen monitor would be changed from "Drywell Oxygen Concentration" to
" Primary Containment Oxygen Concentration" and, "Drywell Hydrogen Concentration" to
" Primary Containment Hydrogen Concentration."
2.3 EvaludiDD The primary containment oxygen monitors provide information to the control room operators to ensure the detection of oxygen concentrations in the primary containment so that actions can be initiated, if necessary, to prevent the accumulation of an explosive gas mixture. The monitors are also used to verify the adequacy of mitigating actions. Normally, these monitors are calibrated during plant operation with the containment inerted. However, if the plant is in an outage when the surveillance lapses, these monitors would be calibrated with the containment I
de-inerted. As discuss above, the oxygen monitors would exhibit a zero-shift when calibrated in other than a nitrogen environment. Thus, if the monitor is calibrated while operating in a de-inerted environment during an outage, the monitor would be inaccurate and inoperable as soon as the transition is made to an inerted environment when the containment is inerted on startup. In addition, while it is possible to calibrate the oxygen monitors with the containment de-inert, this method is considered impractical and undesirable.
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Although the hydrogen monitor is unaffected by this zero-shift phenomenon, the hydrogen and oxygen monitors are both part of the PCMS using the same sample loop. The calibrations are l
conducted in parallel by the same surveillance procedure. Separating the calibrations would l
result in the monitors being made inoperable twice, once for each calibration.
Limiting Condition for Operation 3.6.6.2 requires inerting of the primary containment during plant startup be completed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after thermal power is greater than 15 percent rated thermal power (RTP). Since the potential for a LOCA at or below 15 percent RTP wherein l
significant quantities of hydrogen would be generated is relatively small, it is reasonable to allow I
the initial calibration of the containment oxygen and hydrogen monitors during plant startup to be delayed until containment inerting activities have been completed.
Currently, with both channels inoperable, the allowed out-of-service timo for both the oxygen and hydrogen monitors is 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />; and with one channel inoperable, tha allowed out-of-service
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time for the hydrogen and oxygen monitors is 7 days and 30 days, respectively. The licensee proposed that the maximum duration beyond the time when the containment is required to be i.
Inerted be limited to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> for calibration of one channel and 7 days (more restrictive for the l
oxygen monitors) to complete both channels. In addition, the proposed exception b Specification 4.0.4 for the hydrogen and oxygen monitors calibration provision is necessary only l
if the plant is in an extended outage where the surveillance lapses. The licensee expects this to be an infrequent occurrence. Based on the above, the staff finds the proposed Specification 4.0.4 exception that requires the completion of the calibration of one channel within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and the second channel within 7 days after exceeding 15 percent RTP acceptable.
l Table 4.3.7.5-1 currently requires calibration of the primary containment oxygen monitors at 18-month intervals. However, the licensee stated that the vendor recommends quarterly
. calibration. The staff has reviewed the information pc.jed by the licensee and concludes that the proposed surveillance interval change from once every 18 months to quarterly for the primary containment oxygen monitors would not have a significant effect on safety and, therefore, is acceptable.
Currently, TS Tables 3.3.7.5-1 and 4.3.7.5-1 refer to the drywell hydrogen concentration and the drywell oxygen concentration. However, as discussed above, the hydrogen and oxygen monitors continuously sample the containment atmosphere during Operational Conditions 1 and
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2 when required to be operable by the TS. One division is normally aligned to the drywell, with the other division aligned to the torus. To eliminate the potential confusion over number of channels of each instrument and the normal alignment, the licensee proposed to revise the tables to refer to primary containment oxygen concentration and primary containment hydrogen concentration. The staff considers this to be an editorial change and concludes that it is acceptable.
3.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Michigan State official was notified of the proposed issuance of the amendment. The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to the installation or use of a facility l
component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding (63 FR 19968). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(g). Pursuant to 10 CFR 51.22(b),
no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
l PrincipalContributor: A. Kugler Date:
August 20, 1998 L__._______________________________._____.______________.__________
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