ML17325B355
| ML17325B355 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/21/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17325B354 | List: |
| References | |
| NUDOCS 8912060166 | |
| Download: ML17325B355 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.'C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 129 TO FACILITY OPERATING LICENSE NO.
DPR-58 AND AMENDMENT NO. 114 TO FACILITY OPERATING LICENSE NO.
DPR-74 INDIANA MICHIGAN POWER COMPANY DONALD C.
COOK UNIT NOS.
1 AND 2 DOCKET NOS.
50-315 AND 50-316
- 1. 0 INTRODUCTION In a letter dated January 27,
change to the TS for the Donald C.
Cook Nuclear Plant, Units 1 and 2 that would allow a portion of the Waste Gas Holdup Explosive Monitoring System to be inoperable (on a one time basis) for up to 160 days while the system is modified.
The modificati on involves replacing the existing analysis system (tlC-31) used to continuously monitor oxygen and hydrogen in the gas decay tanks with a more reliable oxygen and hydrogen analysis system.
Another oxygen monitor (gC-370) would remain in service.
gC-370 monitors the line from the operating waste gas compressor and automatically isolates the gas decay tank being filled (while placing the standby tank in service) if the oxygen content reaches three percent.
To further augment hydrogen and oxygen detection capability, the licensee has proposed to collect and analyze grab samples every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> while gC-31 is out of service.
The proposed amendments would also make some minor editorial changes to increase clarity and consistency.
- 2. 0 EVALUATION Per 10 CFR 50.92, the licensee's submittal addressed why the proposed amendments would not involve a significant hazards consideration.
The staff s evaluation of the licensee's no significant hazards assessment is discussed in this section.
Need for H dro en and Ox en Waste Gas S stem Monitors As discussed previously, the proposed amendment would allow the gas decay tank hydrogen and oxygen analysis system (gC-31) to be out of service for up to 160 days.
The purpose of the hydrogen and oxygen analyzers is to alert operators to a potentially combustible mixture of hydrogen and oxygen in the waste gas system.
During power operation, hydrogen gas is stripped from the reactor coolant and discharged to the CVCS holdup tanks during boron dilution.
However, the highest volume of hydrogen gas is generated during the process of plant shutdown when the reactor coolant system is degassed.
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pDR Since combustible concentrations of hydrogen are possible during these evolutions, the waste gas system is designed to minimize oxygen concentrations.
This is accomplished by (1) the use of a nitrogen cover gas, (2) restricting components that discharge to the waste gas vent header to those containing no air or no aerated fluids, and (3) maintaining the vent header at a positive pressure to prevent in-leakage.
Despite the design considerations, oxygen ingress into the waste gas system is possible.
This could occur, for example, following a seal failure on the suction side of the waste gas compressor.
Thus, it is essential for operators to be promptly aware of oxygen concentrations that would support combustion of hydrogen.
Potential for Not Detectin Combustible H dro en/Ox en Concentration Figure 1 (attached) shows the minimum concentration of oxygen and hydrogen required for combustion in a nitrogen environment which is about 5X and 4X, respectively.
(It is assumed that an ignition source will be available. )
The licensee has stated that the hydrogen level will be assumed to be higher than the 4X minimum flammable concentration during the hydrogen monitor replacement.
- Thus, the lack of information provided by the hydrogen analyzer should not increase the probability of combustion during the replacement period.
While the unavailability of the gC-31 oxygen monitor during the replacement period does eliminate the redundancy in the capability to continuously monitor oxygen concentration, the prompt automatic actions that may be required in response to oxygen in-leakage into the waste gas system would remain unchanged (i.e.,
gC-370 would initiate a switching of the waste gas holdup tanks to prevent the oxygen level from reaching the point where it could ignite with the hydrogen).
In
- addition, oxygen concentrations based on grab sample analysis would be available every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The current D.
C.
Cook TS action statement for the oxygen monitors allows operation of the waste gas holdup system for 30 days with one oxygen monitor inoperable with no compensatory requirement for obtaining grab samples.
Grab samples are only required if both oxygen monitors are inoperable.
Thus, the licensee's proposal to take grab samples every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (even when gC-370 is in service) constitutes a level of compensatory action equivalent to the existing TS.
If gC-370 were to become unavailable during the replacement period,'he licensee would follow the existing TS requirement (i.e., operation of the waste gas system would be discontinued if gC-370 could not be repaired within 30 days).
In a teleconference between the Project Manager and licensee representatives on September 15, 1989, the licensee agreed to increase the sampling frequency to every eight hours during plant shutdown evolutions involving reactor coolant system degassing and during periods of gC-370 unavailability.
The licensee also provided rationale for the duration of the requested 160 day replacement period.
The licensee fully expects that the modifications will require the 0
and H
monitor system (gC-31) to be out of service for about 80 days.
The 163 days 5as conservatively selected to ensure that unanticipated complications in the installation or testing of the explosive monitoring system would not necessitate an additional TS amendment request.
Conse uences of Not Detectin Combustible H dro en/Ox en Concentration 3.0 The worst case scenario involving the inoperability of oxygen and hydrogen monitors would be that a highly explosive mixture of hydrogen and oxygen ignites and causes the failure of a gas decay tank.
Section 14.2.3 of D. C. Cook' Updated Safety Analysis Report (USAR) summarizes the analysis of a gas decay tank rupture.
In the analysis, it was assumed that the entire equilibrium inventory of KR-85 and Xe'-133 in the reactor coolant system and volume control tank space is contained in a single gas decay tank at the time of rupture.
Assuming the incident occurred immediately after a refueling shutdown following operation with 1% fuel cladding defects, the maximum two-hour integrated whole body dose at the site boundary would be 1.26 rem.
The consequences of this design basis event would not be changed by the proposed modification.
Based on the above, the staff has determined that the extended interval of time in which the oxygen and hydrogen monitor will be out of service for the replacement effort does not involve a significant increase in the probability or consequences of an accident previously evaluated.
In addition, the extended interval of time in which the oxygen and hydrogen monitor will be out of service for the replacement effort will not create the possibility of a new or different kind of accident.
As discussed previously, the worst case scenario is bounded by USAR accident analysis.
Finally, in consideration of the automatic isolation function provided by gC-370, the requirement to sample for hydrogen and oxygen every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and the increased sampling frequency during RCS degassing evolutions and during periods of gC-370 unavailability; the proposed change does not involve a significant reduction of a safety margin.
The proposed editorial changes are also acceptable to the staff ENVIRONf'lENTAL CONSIDERATION Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no significant impact was published in the Federal Re ister on November 16, 1989 (54 FR 47742).
Accordingly, based upon t e environmental assessment, the Commission has determined that issuance of this amendment will not have a significant effect on the quality of the human environment.
4.0 CONCLUSION
We have 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 these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Dated:
September 18, 1989 Principal Contributor:
J.
G. Giitter
COIINUSTISLE NON F LANI AIL'IR Figure 1.
CONCENTRATION OF H2 AND 02 REQUIRED FOR COMBUSTION IN A NITROGEN ENVIRONMENT