ML20132C780
| ML20132C780 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 03/06/1985 |
| From: | Johnston W Office of Nuclear Reactor Regulation |
| To: | Lainas G Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19264D658 | List:
|
| References | |
| FOIA-85-353 NUDOCS 8503130528 | |
| Download: ML20132C780 (9) | |
Text
.L a-la EL L.lS - = =
.~
jf. G;c, tw
,,,d-U.R 6 YS5 0'
-~h k{!
g/f.
}
Docket No. 50-344 4g,gg
}
m Macl.Il M5 j
N.
d
~
i MEMORANDUM FOR: Gus G. Lainas, Assistant Director q
for Operating Reactors, DL p
FROM:
William V. Johnston, Assistant Director Lt Materials, Chemical & Environmental Technolmy. OF
SUBJECT:
SPIRIT LAKE / TROJAN PLANT FLOODING SER Attached is our SER addressing the effects of a breakout of Spirit Lake on the Trojan Plant.
-,:j l
Our conclusion that a breakout of Spirit Lake will not affect the safety
- )
of Trojan is based on an unpublished USGS study report and thus may be subject to change. We inquired about the status of the USGS report on ij February 21, 1985, and were advised by W. G. Sikonia of the USGS Tacoma
?)
office that the report is now at the USGS federal headquarters in Reston, 1
Virginia, undergoing final review. He would not speculate as to when the final report will be published. The USGS completed its study over seven months ago and the report has been undergoing review ever since then.
Since our conclusions are based on the USGS study, it would be desirable to have a final report before we furnish our SER.
However, judging from the USGS. review delays, it is doubtful that the final report will be published in time to meet our concerns.
A permanent Spirit Lake outlet tunnel currently under construction will be completed by April 1985. This tunnel will lower the lake level and thus remove the threat of a potential breakout of Spirit Lake and the concern about potential flooding of the Trojan Plant.
Althoughthe?SGSreportisunpublished,weareconfidentthatthe technical findings will remain the same through the review process.
Thus the conclusions in this SER are based on the unpublished report.
1 p
3 William V. Johnston, Assutant Director 1
Materials, Chemical & Environmental Technology Division of Engineering cc.
S.. _ 1 page TwwWS p 1
9po A,'vu, NL m
c.
~.:; y 1
..c...x, wr:. r.
, a;- - -
a~w-.. r..
- .... -...- ~....
>.. -...=..~i
=
=
,j lh
...c'.ts.
R T,C C w
- 1 Gus G. Lainas.
cc: w/o attachment J. Knight s
I t
w/ attachment l
J. Miller l}
C. Trammell R. Ballard D. Chery 1
R. Gonzales j-1 DISTRIBUTION:
Dockets l
j EHEB Rdg.
1 3
6 Li.
O l
J i
.i.
t-r-
Y J
FC
- DE:EHEP
- DE:EHEB EH
_ _ _ :. _ _ _ _ _ _ _ _ _ _ _'Mc. :
DE:ADMCET :
____r___7_/__.____________.:
t s
',AME':RGonzqes:ws DLChery RLBalla
- WJohnston :
4 ATE :3/5 /85
- 3/S/85 3/6785
- 3/J./85 I
0FFICIAL RECORD COPY t
L
_w J a_..uw...... a.....m.
..._..__w_-
d w
I l
HYDROLOGIC ENGINEERING SAFETY EVALUATION REPORT CONCERNING A POSTULATED BREAK 0UT OF SFIRIT LAKE AND ITS IMPACTS ON THE TROJAN PLANT 4
1 i
1.
Purpose of Report On May 18, 1980, Mount St. Helens erupted and caused a massive mudflow flood that deposited a large amount of sediment and debris in the j
Columbia River near the mouth of the Cow'litz River.
The Trojan Nuclear Plant which is located on the west bank of the Columbia River about 4.5 miles upstream of the mout'h of the Cowlitz River (See Figure 1) was not 1
directly affected by the sediment deposited in the Columbia River,
' although large deposits were measured near the intake structure.
In addition to the mudflow flood, the eruption also resulted in an avalanche of rock, mud and ice that swept down the slopes of Mount St. Helens into Spirit Lake and the Upper Toutle River Valley.
As the debris avalanche slid into Spirit Lake, it displaced the lake level upward by more than 200 feet. The avalanche also deposited an estimated 3.9 billion cubic yards (bcy) of sediment in the upper 17 miles of the North Fork Toutle River Valley and blocked the outlet channel of Spirit Lake with debris rangingindE?thto500 feet. This debris-blockage, which is a massive and unstable deposit, caused a dramatic increase in the volume of water stored in Spirit Lake.
Because of the unstable nature of the debris blockage, there was a concern that Spirit Lake could breach the blockace and cause a mudflow flood that could possibly affect the safe operation of the Trojan Plant. This report addresses the potential effects of such a mudflow flood at the Trojan Plant.
n
-4 S
r--
~
a a.:..:.. ~.a
-a
- - ~ ~. - -
--~<
" - - - =
2.
Introduction i
Mudflows associated with the Mey 1980 eruption moved down the Toutte River and carried more than 50 million cubic yards (mcy) of material 5
into the Cowlitz River and its overbank areas. An additional 45 mcy were deposited in the Columbia River, mostly in a nine mile reach of
'the river extending from about 5 miles downstream of the mouth of the Cowlitz River to 4 miles upstream.
In the fall of 1981, a task force organi' zed by the U.S. National Forest Service determined that the effective crest of the debris blocking the Spirit Lake outlet would deteriorate from elevation of 3490 ft to 3475 ft l
during the. winter of 1982-83 because of subsidence and erosion.
It was estimated that Spirit Lake would fill to elevation 3475 ft (314,000 acre-feet) sometime in March 1983 assuming that no action was taken to reduce the level and volume of the lake and that the annual inflow was average. Were this to happen, there would be a very high potential for failure of the blockage and catastrophic flooding downstream.
To reduce 7
the potential for failure, the Corps of Engineers, as an interim measure, constructed a pumping facility at Spirit Lake and pumping began on November 5, 1982 (see Figure 2). The goal of the pumping operation was to stabilize the lake level at an elevation of about 3,462 ft, which corre-spends to a lake volume of ebout 275,000 acre-feet.
However, greater-than-normal rainfall, failure or disruption of the pumping system and/or addition of debris into Spirit Lake from a subsequent eruption could cause the lake level to rise excessively.
In an extreme case the debris blockage could fail.
Because of the potential public safety hazard as'sociated with a breakout of Spirit Lake, the Corps of Engineers has developed a plan to permanently lower the level of Spirit Lake. This plan consists of drilling a tunnel from Spirit Lake to South Coldwater Creek (See Figure 2).
This will allov Spirit Lake to drain so that the i
lake level can be maintained at an elevation low enough to remove the I
w\\
~\\
1 4
y vm-
~~. --
~'
+1;:- zw..
. :n
.-a..
)
4'.
ij -
?
threat of a Spirit Lake debris dam failure and consequent mudflow flood.
1 1
Construction of the tunnel was initiated in July 1984. It is expected
. that the tunnel will be completed by April 1985.
3 1.
1 3.
Analys'is t
- t 4
A potential breakout of Spirit Lake was also of concern to the U.S.
Federal Emergency Management Agency (FEMA) becaese flooding from a breakout could have a severe impact on public safety and on the regional economy. To enable it to' plan' for such 'an event, FEMA requested the USGS to study-the impacts of a Spirit Lake breakout on the entire lower 4
The USGS has completed its study and its report is now (February 1985) being reviewed by the USGS Federal Headquarters in Reston, Virginia. The study addresses the impacts of a postulated breakout of Spirit Lake on the Columbia River from Bonneville Dam to the mouth. The Trojan Plant is located within this stretch of the river.
The USGS, using a sediment transport computer model, concluded that T.
-following a postulated breakout of Spirit Lake, a large sediment blockage would form in the Columbia ' River at the confluence of the l
Cowlitz, with subsequent impoundment of water upstream of the blockage.
This blockag(*would result in a slowly rising water level at the Trojan Plant which would continue for 16 days after the blockage formed.
-The depth of flooding in the Columbia River would be dependent on the
[.
coincident discharge in the river at the timehthe breakout flood peak 3
arrived at the mouth of the Cowlitz River. The USGS determined surface
[
water. elevations corresponding to various coinc} dent discharges in the
(-
Results of their study were as follows:
,r
't I
l t
-p 4%
g 2,m=
y me-en6+Md6bh m
(
g E..p wh eMbO e'Ne Y
GO**
4 l
l Resultant Water Surface Elevations in the Columbia River at the Trojan Plant due to ai postulated breakout of Spirit Lake Coincident Columbia River Discharge in cfs
~ 233,000 410,000 610,000 750,000 820,000 Recurrence Interval in years (average) (2 year) (10 year) (50 year) (100 year)
Columbia River Water Surface 32 38 41 43 44 Elevation in feet at the' Trojan Plant This table shows that a postulated breakout of Spirit Lake occurring coincident with a flood in.t'he Columbia River as severe as a 100 year event will not affect the safe operation of the Trojan Plant because the plant grade elevation is higher at 45 ft than the flood level would be.
4.
Summary and Conclusion By pumping water out of Spirit Lake the Corps of Engineers has been i
successful in maintaining the Lake level at an elevation that has I
minimized the chances for a breakout and the potential threat to the Trojan Plant. The staff however, remained concerned because it was uncertain about whether or not a lake breakout and the ensuing flood could affect the safe operation of the plant.
The USGS study, however, provides information that indicates that even if Spirit Lake did break out, the result (( flood level in the Columbia River at the Trojan Plant would not rise as high as plant grade even if the breakout occurred coincident with a 100 year flood discharge in the Columbia River.
The tunnel being constructed between Spirit Lake and South Coldwater Creek (See Figure 2) will provide a permanent outlet for Spirit Lake.
This.lunnel will permanently
- lower the level of Spirit Lake and remove the threat of a breakout and the potential for high water in the Cc'umbia River at the Trojan Plant.
6
.. = _. -...
- a.u.=.l:L.
-- : ~ ~ -
-The staff concludes that a breakout of Spirit Lake will not affect the i
safe operation of the Trojan Plant.
Furthermore, once the Spirit Lake cutlet tunnel is completed, there will be na safety concern regarding a breakout as far as the Trojan Plant is concerned.
m l
e 96 r
i w
J e
I
. _,, - - - ~,,
' ' * ~ ^
' ' ~ ' ' ~ ~ ' ~ ' "
J
_..s..'__...-
8 123 00' 45' 30*
I S' 122'00*
e i
'?
O 5
to 15 MAES O
6 10 15 20 KROMETERS T
t J WASHINGTON
.9tudy jg
area i
Mayfield Reservoir p;4, O'
gget c,c2 wa ta o
Toledo
[
N O
h n
j Creen Riv er y
'+
creek Hottstadt
,get o
camp g 3 creek Baker Oo bpITht g
g Castle Silver e%th Vj]
Rock Lake
- e Cr * %
n 15'
~
k
&*1 o t
Q Ct og r
Toutte e,
River 1
Q f
Mourit 7
S d
Lexington cowem,
St. Heier's f
a 4
t,ngvi.,
. k el$o
'g k
y [I
=
a G
T m
S C a o
t n
4*
'o44 O
e 4
g 4
ye, rill]
LBk*
4, Cs 4
4Marna Swift Reservoir TROJAN NPP e 4eo Yale 00' Lake bO' Merwin t
p
4 s
- e 2
t LEGEND I
Extent of Debris Deposited by the May 1980 Eruption I
FIGURE 1 GENERAL AREA MAP - TROJAN / SPIRIT LAKE / MOUNT ST. HELENS
-b
J,..-..'.
_.. _
- da'..s. ;
,, g,,4 l
g,, = g
=.-
emew.ame km
,.e,,...
TROJAN NPP, guy 9
'W
./
+,
/
Q Y
d J.J COLDwATER LAN WS EL 2472 li
.N.
%g,%
Permanent Spirit Lake
,1(. s/
IS Outlet v ~4
%q%...
~
- ~,
,e N
JossNSTON'55 MARRY'S
,, f -
"g.
- iDGE
~
- RIDGE
~
[
Spinst LAwE V '-
LlueTS DE GRi$ AvaL ANCE AND hPJ0 FLOE d
no E con E
INT t wiu OUTLET wo#F S w (COUPLE TED, NOV 1982)
, k.,
A. ALAN..,
.A.
's\\,'
N
/
f
-/
/
\\
{
\\
-c.
L f:
i.
FIGURE 2 LOCATION OF SPIRIT LAKE OUTLET 2-