ML19340E502
| ML19340E502 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 12/03/1980 |
| From: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Magnuson W SENATE |
| References | |
| TAC-41023, NUDOCS 8101140762 | |
| Download: ML19340E502 (4) | |
Text
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UNITED STATES
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%, v.....f The Honorable Warren G. Magnuson United States Senate Washington, DC 20510 Tj
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Dear Senator Magnuson:
This is in response to your letter of October 16, 1980 regarding Carol A.
Snow's letter to you of October 7,1980, which expressed additional concerns about Mount St. Helens and the Trojan Nuclear Plant. Ms. Snow expressed concern that the report which we provided her, in response to her previous letter, was incorrect and does not adequately reflect existing conditions.
She cites as her basis the volcanic debris which moved from Mount St. Helens to the Trojan site.
She notes that this was not predicted by the report.
Our letter to you of Septenter 29, 1980 (which was in response to Ms. Snow's first letter of August 8,1980) did point out three areas wherein the report we furnished with the letter required revision. One of these was an underestimation of the volume of debris associated with mudflows, an item of concern to her in her recent letter. She is correct that no detailed discussion uf dredging in the Columbia River following the eruption of May 18 was contained in our first letter. However, the Mount St. Helens enaption produced debris which approached the plant from a less critical direction than we had assumed in our studies of volcanic hazards, and was therefore a nuch less severe event, as explained below.
In the staff's assessment of the safety of the Trojan Nuclear Plant, we hypothesized the eruption of Mount St. Helens and analyzed a number of physical effects that might occur. One potential effect was a nud flow into the upper reservoir of the Lewis River, an upstream tributary of the Columbia. Overtopping and subsequent failure of Swift Dam was postulated, resulting in a hypothetical domino-type failure of the lower dams (Yale and Merwin) producing a significant flood in the Columbia River Valley. This hypothetical flood would not have inundated the Trojan plant.
In fact, the plant is designed to withstand a nuch larger flood which again would not flood the Trojan plant. We recognized at the licensing review stage the potential for a flood-transported nud flow into the vicinity of the Trojan Nuclear Plant cooling water intake structure. No direct estimates of the amount of material necessary to block the intake were made.
However, it was assumed that the intake was totally blocked by whatever cause.
Trojan Nuclear Plant has alternate sources and methods of obtaining cooling water which can enable the plant to be placed in a shutdown condition and be so maintained without use of the intake structure. Thus, we continue to conclude that the Trojan Nuclear Plant is adequately designed and protected from volcanic-hydrologic activity resulting from eruptions of Mount St. Helens.
Further, the eruption at Mount St. Helens did not produce conditions at the plant approaching the severity of the design bases used for the plant in our original analysis.
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Senator Magnuson Ms. Snow's concern over the dredging near the site is related to a U.S. Army Corps of Ergineers project to remove approximately 55 million cubic yards of volcanic ash and debris from the Columbia River Navigation project. This "nud" entered the Columbia River via the Toutle/Cowlit: Rivers. Mud flowed both downstream and upstream beneath the water surf ace and towards the Trojan pl ant. The effect of the mud flow terminated just upstream of the Trojan plant.
Much more significant nud deposits occurred near the mouth of the Cowlitz River and downstream from that point. The utility has reported that a diver sent into the intake structure found very little nud.
This is consistent with the fact that the rtd flow was losing its momentum and in fact terminated near the plant.
As noted above, should the nud flow have been even more massive than experienced, the Trojan Nuclear Plant could have shut down safely and maintained a safe shutdown condition.
Sincerely,
? Signed)T. A.Rehm William J. Dircks Executive Director for Operations
Enclosure:
Letter, Carol A. Snow to Senator Magnuson dated October 7,1980 l
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