ML19276H134

Applicants' Prepared Testimony Re Flood Protection for Public Hearing in Harrisburg,Pa

ML19276H134
Person / Time
Site:	Three Mile Island
Issue date:	10/25/1973
From:	METROPOLITAN EDISON CO.
To:
Shared Package
ML19276H123	List: ML19276H122 ML19276H124 ML19276H125 ML19276H127 ML19276H128 ML19276H130 ML19276H131 ML19276H132 ML19276H133 ML19276H134 ML19276H135
References
NUDOCS 7910100570
Download: ML19276H134 (4)

Text

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October 25, 1973 UNITED STATEi OF AMERICA ATOMIC ENERGY COMMISSION Before the Atomic Safetv and Licensing Board In the Matter of METROPOLITAN EDISON ) Occket No. 50-289 COMPANY, et al. )

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(Three Mile Island Nuclear )

Station, Unit 1) )

APPLICANTS' PREPARED TESTIMONY RELATED TO FLOOD PROTECTICN Three Mile Island's (TMI ' s ) dike design (1,100,000 cfs) is greater than the maximum floods of record, including Agnes in 1972 (1,000,000 cfs) . For floods up to the Probable Maximum Flood (1,625,000 cfs) , TMI is provided with additional protection by flood gates, inflatable door seals, watertight doors and manway covers , assuring the ability to shutdown and cooldown the plant and maintain it in a safe shutdown condition.

A summary of the flow characteristics of the Susquehanna River as evidenced by data recorded at Harrisburg through 1965 revealed a river average flow of 34,000 c.'z, a mean annual flood of 300,000 cfs, and a maximum flood on March 19, 1936 of 740,000 cfs. Based upon this 1391-1965 1A17 1<7 7910100 7O data, the Corps of Engineers' estimate in 1965 was that the Probable Maximum Flood (PMF) for the Susquehanna River would produce a flow rate of 1,083,000 cfs (150% of the 1936 maximum flood of record) . This flood, upon which TMI's dike design was based, corresponded to a flow rate of 1,100,000 cfs of the Susquehanna River at TMI.

During the five years since TMI's dike design was finalized, there have been two related developments. Based upon revised criteria, the Corps of Engineers in 1970, estimated PMF for the Susquehanna River would produce a flow rate of 1,625,000 cfs at TMI. On June 24, 1972, rains from tropical storm Agnes resulted in a flood volume of 1,000,000 cfs. Thus, while the Corps of Engineers' PMF has been revised to a value above the cri: n11 design flood, neither the 1936 flood of record nor the 1972 flood were in excess of the design flood of 1,100,000 cfs.

The dikes around TMI are earth embankments, constructed of clay and silt and designed in accordance with sound Civil Engineering practices. The dike at the north end of the island has a top elevation of 310'. The dikes on the east and west sides of the island start at a top elevation of 310' at the north end and steadily decline to 305 ' at the south end.

The dikes are protected by a layer of dumped rip rap of sufficient size and thickness to withstand wave action of 1A17 158 2 1/2 feet and a selocity in excess of 12 fps. The rip rap continues downward into natural ground for a minimum depth of 2 feet to provide a cut off against undermining.

To insure that the dikes maintain their integrity, the technical specification will require periodic inspection of the dikes at least every six months and af ter the river returns to normal should the level of the river exceed flood stage.

The dikes were constructed to be capable of providing adequate protection for a design flood in which the flow rate of the Susquehanna River at TMI would reach 1,100,000 cfs.

If this size flood were to occur, the water elevation at the north end of the island would be 304'. This would provide a freeboard of approximately 6' above the design flood. The water level would be 303' at the intake structure while the dike in this area is at 305' leaving about 2 ' of freeboard above the design flood.

In addition to these dikes and because of the difference between the plant design flood and the PMF, a commitment has been made to the AEC that the plant would be provided with component protection to the degree whicT will assure a safe and orderly shutdown for the level of flooding corresponding to the PMF.

In the event of flood flows greater than the design flood up to and including flows of 1,645,000 cfs (PMF) ,

protection of all equipment necessary to shutdown and cool-down of the plant and co maintain it in a shutdown condition

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is provided by flood gates, inflatable door seals, water tight doors and manway covers.

To insure that the TMI commitment to the AEC is mat, an emergency procedure has been written and a Technical Specification has been provided which requires the unit to be brought to the hot shutdown condition if the river stage reaches elevation 302' at the river water intake strucrure, corresponding to 1,000,000 cfs river ficw. There are four (4) action levels prior to the shutdown action level with specific actions taken at each level which will assure proper component protection to the degree a safa and orderly shut-down can be performed if required.

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