ML19319C512
| ML19319C512 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/19/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319C507 | List: |
| References | |
| NUDOCS 8002190945 | |
| Download: ML19319C512 (2) | |
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SUPPLEMENT TO THE DRAFT SAFETY EVALUATION REPORT (CONTAINMENT SYSTEMS)
DAVIS-BESSE UNIT 1 DOCKET NO.
50-346 ECCS Containment Pressure Evaluation Appendix K to 10 CFR 50 of the Commission's regulations requires that the effect of operation of all the installed pressure reducing systems and processes be included in the ECCS evaluation. For the evaluation it is conservative to minimize the containment pressure since this will increase the resistance to steam flow in the reactor coolant loops and reduce the reflood rate in the core. Following a loss-of-coolant accident, the pressure in the containment building will be increased by the addition of steam and water rom the primary reactor system into the containment a tmosphere. After initial blowdown, heat flow from the core, primary metal structures, and steam generators to the ECCS water, will produce add' inal steam. This steam together with any ECCS water spilled from the primary system will flow through the postulated break into the containment.
This energy will be released to the containment during both the blowdown and later ECCS operation phases; i.e., reflood and post-reflood phases.
Energy' removal occurs within the containment by several means.
Steam condensation on the containment walls and internal structures serves as a passive energy heat sink that becomes effective early in the blowdown transient. Subsequently, the operation of the containment heat removal systems such as containment sprays and fan coolers will remove energy from the containment atmosphere. When the energy removal rate exceeds the rate of energy addition from the primary system, the containment pressure will decrease from its maximum value.
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.. The ECCS containment pressure calculations for Davis-Besse Unit I were done generically by B&W for reactors of this type as described in BAW-10105, "2CCS Evaluation of B&W's 177-FA Raised Loop NSS." The NRC staff reviewed B&W's ECCS evaluation model and published a Status Report on October 15, 1974, which was amended November 13, 1974. We concluded that B&W's containment pressure model was acceptable for ECCS evaluation. We required, however, that justification of the plant-dependent input parameters used in the analysis be submitted for our review of each plant.
Justification for the containment input data were submitted for Davis-Besse Unit 1 dated September 5,1975. This justification includes a comparison of the actual containment parameters for Davis-Besse with those assumed by B&W in BAW-10105. Toledo Edison Company has reevaluated the containment net-free volume, the passive heat sinks, and operation of the containment heat-removal systems with regard to the conservatism for the ECCS analysis.
This evaluation was based on measurements within the containment and from as-built drawings to which a margin was added. The containment heat removal' systems were assumed to operate at their maximum capacities, and minimum operational values for the spray water and service water temperatures were assumed. The containment p,ressure analysis by B&W in BAW-10105 was demonstrated to be conservative for Davis-Besse Unit 1.
We have concluded that the plant-dependent information used for the ECCS containment pressure analysis for Davis-Besse is reasonably conservative and, therefore, the calculated containment pressures are in accordance with 1
Appendix K to 10 CFR Part 50 of the Commission's regulations.
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