A unique and critically important feature of ThorCon is the membrane wall. Each silo is fitted with a membrane tube wall, shown in blue in this view. The membrane wall is made up of vertical steel tubes connected by strips of steel plate which are welded to the tubes. These tubes are filled with water and connected by circular headers, top and bottom. The top header is connected by a riser to a heat exchanger in the pond as shown in the second figure. The outlet of the heat exchanger is connected to the membrane wall bottom header by a downcomer.
The Can is cooled by thermal radiation to the silo membrane wall. This heat converts a portion of the water in the wall tubes to steam. This steam/water mixture rises by natural circulation to the cooling pond, where the steam is condensed, and returned to the bottom of the membrane wall. The pond in turn is cooled by either wet (shown) or dry cooling towers. Even if the less expensive wet alternative is chosen, Can cooling requires less than 1 m3 per day of pond make up water per module.
The silo membrane wall also cools the Fuelsalt Drain Tank (FDT) after a drain. The FDT is made of low cobalt Haynes 230. This is the only place where ThorCon uses a superalloy. The FDT is located directly below the Can. The drain tank is tall, thin rectangular trough that has been wrapped into a circle. It is shown in green in the 3D view. This arrangement provides sufficient radiating area to keep the peak tank temperature after a drain well within the limits of the Haynes 230. After a full power drain, the decay heat that is transferred to the membrane wall peaks at 4.7 MW about 2 hours after the drain. At that point, the FDT temperature is about 960C. Then a slow cooling process begins.
This entire process is totally passive, requiring no operator intervention, no valve realignment, nor any outside power.
The Silo Membrane Wall is What Makes the ThorCon Can Work.
- The membrane wall allows us to keep the Can interior below 300C during normal operation. The fact that the membrane wall is always operating is an important safety feature. If a problem develops in the membrane wall loop, we will find out before a casualty occurs rather than during.
- The membrane wall allows us to capture any tritium permeating through the Can or drain tank in the inert gas in the annulus between the Can/FDT and the silo wall.
- The wall cools more rapidly as the Can/FDT heats up, but more slowly as the Can/drain tank cools down, which is exactly what we want to handle both emergencies and avoid salt freeze ups.
- The wall maintains a double barrier between the fuelsalt and the membrane wall water, even if the primary loop is breached.
- The membrane wall protects the silo’s concrete lining.
- The membrane wall does all this without any penetrations into the Can or the Fuelsalt Drain Tank.