Background on ITER

The fuels needed for fusion are deuterium, plentiful in ordinary water, and tritium, which can be produced from the abundant element, lithium. Only five percent or less of this deuterium-tritium (DT) fuel is consumed (fused) as it passes through the ITER plasma chamber. Because the unburned DT fuel is both hazardous and expensive, it can’t be merely discarded. Instead, it must be processed and prepared for re-injection into the reactor together with make-up DT fuel. This process requires a tritium plant like the one Los Alamos operated for 21 years.

From 1982 to 2003, Los Alamos ran a fusion fuel processing pilot plant called the Tritium Systems Test Assembly (TSTA). It included all tritium plant subsystems in an interconnected loop and demonstrated that DT fuel could be effectively and safely recycled as needed for fusion. Los Alamos’ TSTA, which was recently decommissioned, was approximately one tenth the scale of ITER. Los Alamos National Laboratory was a key developer of the specialized technologies needed for the tritium plant. The technology developed at TSTA was successfully fielded in the 1990’s at the Princeton Plasma Physics Laboratory which for a time held the world record for magnetically confined fusion power. Based on this experience, the U.S. has been assigned responsibility for supplying the Tokamak Exhaust Processing (TEP) system for the ITER Tritium Plant. (“Tokamak” is a Russian acronym which refers to the magnetic, torus-shaped chamber in which the plasma is generated). The TEP system must accept gases from the tokamak exhaust and from other sources and remove impurities. In general, these gases will consist mostly of DT. The TEP must purify this DT, but it must also recover the DT from impurities that grow into the gas during its journey through the fusion reactor’s thermonuclear environment. Such impurities include water and methane.

Savannah River National Laboratory (together with Washington Savannah River Company) recently constructed large, weapons-related tritium processing facilities. Since Savannah River’s fabrication and procurement capabilities complement Los Alamos’ experience with R&D, design, and testing of fusion tritium processing systems, the two labs will work together to provide ITER’s exhaust processing system. The system must be finished, tested, and delivered to Cadarache by 2014.

While considerable tritium processing technology is available, delivery of a successful TEP system will be a challenge. Compared to current and previously operated systems, ITER’s TEP will have to operate with a flow rate and tritium inventory increased by a factor of 10, and it will have to deliver a specified product about 10 times faster. These scale-up considerations are perhaps the largest technical risks associated with the project. These risks will be addressed with state-of-the-art computer modeling and system testing at the end of the project.

— Craig Taylor

Information released under LAUR 06-044

Reviewed for accuracy Nov. 2011