On Tuesday, October 27, three leaders from X-Energy spoke to the Virginia ANS chapter about their company and the Xe-100, the high temperature, pebble bed gas reactor power system that they are designing.

During the presentation, meeting attendees learned that X-Energy is an early phase start-up with a total staff of a few dozen people, most of whom share one of three backgrounds. Some are former NASA engineering contractors, some come from the U.S. DOE’s Next Generation Reactor Program (NGNP) and some come from South Africa’s Pebble Bed Modular Reactor (PBMR) program.

The founder, CEO and primary funding source is Dr. Kam Ghaffarian, who cofounded Stinger Ghaffarian Technologies (SGT) Inc. in his basement in December 1994. He’s now the sole owner of that company, having bought out his cofounder about seven years ago. SGT is one of the largest engineering services contractors for NASA, with an annual revenue of $400 million and a backlog in excess of $3 billion.

Here is his explanation for founding X-Energy:

I began X-energy because the world needs energy solutions that are clean, safe, secure, and affordable. With so much at stake, we cannot continue down the same path.

Dr. Pete Pappano provided most of the technical portion of the talk. He described himself as a “graphite guy” who has worked for SGL Group (The Carbon Company) and at Oak Ridge National Laboratory in the group that produced the fuel compacts used for performing qualification irradiations for the highly successful TRISO fuel that has been manufactured on a testing scale for the NGNP.

Meeting attendees could feel his passion for his favorite material as he provided a synopsis of the reactor grade graphite production process; even though that was peripheral to the X-Energy talk, it was fascinating information.

Xe-100 side view

Pappano provided an overview of the Xe-100 which is a 125 MWth helium-cooled, graphite-moderated, once-through-then-out, passively-safe, pebble-bed reactor. The helium is pumped through the reactor and then through a steam generator that produces superheated steam sent to a standard Siemens steam turbine to produce 50 MW of electric power.

Each reactor contains about 170,000 pebbles. The pebbles are 60 mm in diameter with 5 mm thick unfueled layer of graphite on the outer part of the pebble. Inside the unfueled shell, there is a mix of about 25,000 tiny particles with a graphite binder. The particles are less than a mm in diameter; the fuel kernel in the center is about 475 microns in diameter. It is surrounded by four layers; a porous layer of pyrolytic graphite, a dense layer of pyrolytic graphite, a layer of silicon carbide and a final layer of dense pyrolytic graphite.

X-Energy fuel form

Each pebble contains about 9 grams of heavy metal enriched to about 10% fissile concentration. TRISO particles have been tested with various combinations of uranium, thorium and plutonium. X-Energy is aiming to initially use enriched uranium in the form of UCO.

Even in the case when all coolant stops flowing and coolant pressure falls to atmospheric, the reactor system cannot overheat because there is sufficient heat transfer through conduction to the surrounding environment to keep the hottest places inside the reactor below 1600 C. The TRISO fuel tested for NGNP has been shown to be able to maintain its integrity even when heated to 1800 C for lengthy periods of time.

The graphite reflector that surrounds the pebble bed container is designed to last for the life of the system. X-Energy currently envisions that the reactor will never need to be shut down because new fuel can be continuously added while depleted fuel is dropped out of the bottom into a container.

The proposed installation calls for four reactor/steam generator systems with a single used fuel storage vault in the center of the associated silos. That vault will be sized to hold a lifetime of used fuel. There will be an automated system that moves filled containers from below the reactors and replaces those containers with empty ones as needed. The containers will be moved into the central storage vault.

X-Energy has not yet begun its interaction with the U.S. Nuclear Regulatory Commission. Ralph Loretta, the Chief Financial Officer, explained that the company would like to be further along in its design process before it begins paying NRC professional staff-hour fees.

Following the meeting, I spent some time talking to the X-Energy executives and exchanging business cards. I’m in contact with X-Energy’s public relations office and will be arranging a discussion for the Atomic Show sometime in the near future. Feel free to pose questions here; I might use them during that interview.