ML19253B657
| ML19253B657 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/14/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19253B655 | List: |
| References | |
| NUDOCS 7910160743 | |
| Download: ML19253B657 (2) | |
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SUPPLEMENT TO THE DRAFT SAFETY EVALUATION (C0i4TAINMENT S(STEMS THREE MILE ISLAND STATION UNIT 1 DOCKET NO.:
50-289 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 from the primary reactor system into the containment atmosphere. After initial blowdown, heat flow from the core, primary metal structures, and steam generators to the ECCS water, will produce additional steam. This steam together with any ECCS water spilled from the primary system will flow through the postulated break into the contai nment. 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 sinks 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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_2 The ECCS containment pressure calculations for Three Mile Island Unit 1 were done generically by B&W for rearicrs of this type as described in RAW-10103, "ECCS Evaluation of B&W's 1/7-FA Lcwered Loop NSSS." 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 o# the plant-dependent input parameters used in the analysis be submitted fo. our review of each plant.
Justification for the containment input data were submitted for Three Mile Island Unit 1 dated October 2L 1975. This justification includes a comparison of the actual containment parameters for Three Mile Island with those assumed by B&W in BAW-10103. Metropolitan Edison has re-evaluated 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 as-built drawings. The containment heat removal systems were assumed ta operate at their maximum capacities, and minimum operation values for the spray water and service water temperatures were assumed. The containment pressure analysis by B&W in 8AW-10103 was demonstated to be conservative for Three Mile Island Unit 1.
We have concluded that the plant-dependent information used for the ECCS containment pressure analysis for Three Mile Island Unit 1 is reasonably conservative, and therefore, the calculated containment pressures are in accordance with Appendix K to 10 CFR 50 of the Cormiission's regulations.
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