ML16340C032
| ML16340C032 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/09/1981 |
| From: | NRC |
| To: | |
| References | |
| NUDOCS 8110020087 | |
| Download: ML16340C032 (6) | |
Text
September 9, 1981 Floodplain Aspects of Diablo Canyon Nuclear Power Plant, Units 1 and 2
Docket Numbers 50-275/323 All major plant structures were substantially complete at the time Executive Order 11988, Floodplain Hanagement, was signed by President Carter in Piay 1977.
This includes the intake and discharge structures, the breakwaters and the switchyards.
It is our conslusion that consideration of alternate locations for those structures identified as being in the floodplain is neither required nor practicable.
There are two water bodies within or adjacent to the site; Diablo Canyon Creek to the north and the Pacific Ocean to the west.
Neither of these two water bodies have a distinct and well defined lowland floodplain.
The channel of the creek is a steep, narrow and deep canyon.
Both the 1 percent chance (100-year) flood, which was estimated by the applicant to be 1093 cubic feet per second (cfs) at the mouth of the creek, and the 0.2 percent (500) flood, estimated to be 1900 cfs, would be well contained within the canyon.
During construction, two sections of the canyon were filled in and culverts were installed in order to pass creek flow.
A section of the canyon was filled in to accommodate the 500 kV and 230 kV switchyards.
A 10 foot diameter culvert passes creek flow under the switchyards.
Ponding of water behind the switchyards during a flood event exceeding the culvert's capacity would be confined to the creek canyon offsite.
The local topography is such that if, during a Probable Paximum Flood (an event which is considerably
( 81i0020087 Bi0909 PDR ADOCK 05000275 A
~y more severe than the 0.2 percent chance flood), the culvert were blocked. the plant would not be flooded.
The second section of the canyon was filled in for a road.
There is an 8 foot diameter culvert where the road embankment
'pans the creek near its mouth.
Floods exceeding this culvert's capacity would not endanger the plant rior offsite areas.
Me conclude that neither the 1 percent chance flood nor 0.2 percent chance flood will constitute a
hazard to the nuclear plant.
The Pacific Ocean coastline near the plant is characterized by steep bluffs rising to about 50 feet above mean sea level (msl).
The 1 percent chance flood and 0.2 percent chance flood would result from tsunamis combined with high tides.
The only structures that could be effected by high ocean levels are the intake and discharge structures and the breakwaters which extend offshore.
All these structures have been designed to withstand and remain functional during the Probable maximum Tsunami which is a more severe flood event than either of the above mentioned events.
Because of tsunamis'ong wave lengths the breakwaters will have relatively little effect on them, while the intake and discharge structures should not influence them at all.
No offsite flood effects would result from interactions of tsunamis with these structures.
Me therefore conclude that because of the lack of plant induced offsite flood hazards and because the plant itself is designed to withstand the effects of flood events more sever'e than those considered in the Executive Order, the operation of the Diablo Canyon plant will comply with the intent of Executive Order 11988.
A r
t
9/16/81 DISTRIBUTION:
NRC PDR LPDR TERA gWRs~eFiles (5O-27+
5O-~PS'SIC
0
%=i,
'" Nr
,/
sl i
gt il t+
1 I
r gW I
L b l I
J~l