Advanced pebble bed modular reactor, SMRs (James Conca)

Link: https://www.forbes.com/sites/jamesconca/2017/03/27/x-energy-steps-into-thering-with-its-advanced-pebble-bed-modular-nuclear-reactor/#49a3d94d745d Please see link above for original article, embedded hot links and comments.

X-Energy Steps Into The Ring With Its Advanced Pebble Bed Modular Nuclear Reactor James Conca, Contributor March 27, 2017 I have been a scientist in the field of the earth and environmental sciences for 33 years, specializing in geologic disposal of nuclear waste, energy-related research, planetary surface processes, radiobiology and shielding for space colonies, subsurface transport and environmental clean-up of heavy metals. I am a Trustee of the Herbert M. Parker Foundation and consult on strategic planning for the DOE, EPA/State environmental agencies, and industry including companies that own nuclear, hydro, wind farms, large solar arrays, coal and gas plants. I also consult for EPA/State environmental agencies and industry on clean-up of heavy metals from soil and water. For over 25 years I have been a member of Sierra Club, Greenpeace, the NRDC, the Environmental Defense Fund and many others, as well as professional societies including the America Nuclear Society, the American Chemical Society, the Geological Society of America and the American Association of Petroleum Geologists.

Contributor I write about nuclear, energy and the environment Opinions expressed by Forbes Contributors are their own.

X-energy, LLC has pebbles to burn. Last week, the company announced that it has started the conceptual design phase for its Xe-100 high temperature gas-cooled (HTGR) pebble bed modular reactor.

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Source: X-energy The Xe-100 high temperature gas-cooled pebble bed modular nuclear power plant has a small physical footprint, only 200 meters by 100 meters with a small emergency planning zone, and a reduced water requirement which means it can be installed in a much wider range of potential locations compared to other clean energy solutions.

The Xe-100 is an innovative advanced nuclear power plant design, that uses its own made-inthe-USA proliferation-resistant spherical nuclear fuel elements, called pebbles. The Xe-100 is a 200MWt (75MWe) reactor that takes less time to construct because of factory-produced components. It cannot meltdown and is walk-away safe under any accident scenario without the need for human intervention.

Partnering with Southern Nuclear to provide some heavy nuclear lifting, X-energy held a Conceptual Design Readiness Review on March 8 to validate the design, provide preparatory documentation, analysis tools, scope, management processes and overall team readiness. All the things needed to prepare for future licensing engagement with the Nuclear Regulatory Commission (NRC).

This reactor is ideal for high-temperature industrial processes such as metal and non-metal melting and smelting, calcining and coking, and is modular for flexibility in power needs and applications like load-following renewables, since it can ramp up and down quickly.

The complete Xe-100 power plant has a small physical footprint, only 200 meters by 100 meters with a small emergency planning zone essentially within its own gates, and a reduced water Page 2

requirement which means it can be installed in a much wider range of potential locations compared to other clean energy systems.

But the real innovation is its nuclear fuel – the pebbles.

X-energy’s Xe-100 reactor uses tennis ball-sized pebbles (see figure) made of thousands of TRISO micro-fuel particles which consist of fissile U-235 surrounded by pyrolytic graphite, which acts as the moderator - slowing down fast neutrons so they more efficiently split the U235 nucleus. The graphite is further surrounded by a coated ceramic layer of silicon carbide for strength and containment of the fission products.

X-energy X-energy’s Xe-100 reactor uses spherical fuel elements, tennis ball-sized pebbles made of thousands of TRISO micro-fuel particles. Thousands of pebbles are amassed to create the reactor core, and are cooled by a gas, such as helium, nitrogen or carbon dioxide. Along with other design features, this reactor cannot melt down. Correction – the size of the TRISO particles are 0.85 mm not 0.5 mm.

Thousands of pebbles are amassed to create the reactor core, and are cooled by a gas, such as helium, nitrogen or carbon dioxide, that doesn’t chemically react with the fuel pebbles. As the pebbles become used, they drop out of the bottom of the core, and are replaced from above, such that the reactor does not need to shut down to refuel.

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Because the reactor is designed to handle high temperatures like 1,600°C, it can cool by natural circulation and still survive any accident. High temperatures provide higher thermal efficiencies and up to 50% more power per unit of fuel than traditional reactors that don’t get much above 400°C. This reactor has the additional feature that the gases do not dissolve contaminants or absorb neutrons as water does, so the core has almost no radioactive fluids.

Last year, the United States Department of Energy awarded X-energy a five-year $53 million Advanced Reactor Concept Cooperative Agreement to move the Xe-100 development forward.

“This is an important and wonderful milestone. Since being founded in 2009, our goal has been to be the world leader in HTGR design as well as the fuel to power these reactors,” said Xenergy founder and CEO Dr. Kam Ghaffarian. “Moving our Xe-100 puts us well on the way to meeting our goal of deployment within 10 years.”

Southern Nuclear, a subsidiary of Southern Company (NYSE: SO), brings a long history of nuclear capabilities and operations to the table. Southern Nuclear operates a total of six nuclear reactors for Alabama Power and Georgia Power, and has two new nuclear units under construction at Plant Vogtle.

“Southern Nuclear and X-energy are well-aligned to allow advanced nuclear capabilities to be a viable part of energy solutions,” said Southern Nuclear Regulatory Affairs Director Brian Whitley.

New reactor designs are pretty advanced and ready to be rolled out. Whether they’re variations on the traditional light-water reactor (NuScale), new molten salt designs (IMSR), air-cooled, liquid metal, or advanced fast-reactors that burn everything from spent fuel from old reactors to Iraqi tank armor (TerraPower; General Atomics), SMRs like the Xe-100 build on the successful experience of previous designs and the redundant safety systems developed over the last 60 years.

These are not your father’s reactors.

But small modular reactors must get over the initial market humps that plague all new technologies, and must quickly become cost-competitive. This hurdle is something a new organization called SMR Start is trying to address by using proven public-private partnerships that have succeeded with other technologies like renewables.

Today’s energy markets are characterized by low natural gas prices, heavily subsidized renewable generation and low growth in electricity demand. American vendors also compete in the international markets for the deployment of SMRs and other advanced nuclear reactor designs. Unfortunately, most countries like Russia and China directly subsidize their nation’s nuclear technologies in order to penetrate global markets.

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The low price of natural gas poses a challenge to low-carbon technology deployment, and a production tax credit (PTC) for nuclear would help to value the carbon-free benefits of SMRs and close this price gap as it has for renewables. Power purchase agreements would help to create demand for new, low-carbon technologies in an era of slower demand growth.

PPAs between SMR operators and federal facilities would align with the directive to support low-carbon technologies codified in Executive Order 13693 from 2015 that recognizes SMRs as a source of clean energy.

But what really matters to the public is safety. The small size and large surface area-to-volume ratio of SMRs, make the plant size very small, and along with other innovative designs like the Xe-100, allows natural processes to cool it indefinitely in the case of a complete power blackout, with no humans needed to intervene, no AC or DC power, no pumps, and no additional water for cooling.

Translation – no meltdowns!

And that is why we need to move forward fast on these new nuclear reactors.

Dr. James Conca is an expert on energy, nuclear and dirty bombs, a planetary geologist, and a professional speaker. Follow him on Twitter @jimconca and see his book at Amazon.com

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