Totally passive, totally unavoidable shutdown and cooling. ThorCon combines a strongly negative temperature coefficient with a massive margin between the operating temperature of 700C and the fuelsalt’s boiling temperature (1430C). As the reactor temperature rises, ThorCon’s power output drops. This is an intrinsic, immutable property of the reactor physics. In any casualty that raises the temperature of the salt much above operating level, ThorCon will shut itself down.
If the high temperature persists, the freeze valve will thaw and drain the fuel from the primary loop to the drain tank, where the silo cold-wall will passively handle the decay heat.
There is no need for any operator intervention. Not in 3 days, not in 300 days, not in 3000 days. Nor are there any valves that must be realigned by either system or operator control as in some so called passive systems. In fact there is nothing the operators can do to prevent the shutdown, drain, and cooling.
Release resistance. ThorCon has three gas tight barriers between the fuelsalt and the atmosphere. Here is a sectional view of the hull in way of the fission island. The structure is similar to the cargo hold section of a large tanker with a 3 meter wide double bottom and double sides. In addition, a 3m deep double roof is provided in way of the fission island. The double sides and roof are filled with sand or concrete. This is an extremely strong structure. It will not be penetrated by a Boeing 777 engine in a perpendicular impact at 400 knots. The hull, which is a double barrier, is only one of at least three gas tight barriers between the the fuel salt and the atmosphere. The Can silo is a gas tight structure; and the Can itself is a gas tight structure. All these must be breached to allow a release.
But even if they were, there is no internal dispersal mechanism. The ThorCon reactor operates at near-ambient pressure. In the event of a primary loop rupture, there is little pressure energy and no phase change. The spilled fuelsalt merely flows to the drain tank where it is passively cooled.
Moreover, the most troublesome fission products, including iodine-131, strontium-90 and cesium-137, are chemically bound to the salt. They will end up in the drain tank as well.
ThorCon does no chemical processing online to remove fission products or to isolate fissile materials or their precursors. Noble xenon and krypton gases bubble out of the fuelsalt and pass through holding tanks as they decay to harmless radiation levels, then are cooled, compressed, and bottled.