Chapter 2: Advanced Nuclear Energy, High Temperature Gas Reactors
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TRISO Fueled, Helium Gas Cooled, High Temperature Reactors
High Temperature Gas-cooled Reactors (HTGR)
The Chinese are building 40 for the Rongcheng Power Complex: 
HTR-PM Pebble Bed Reactor Progress - 01-China-DONG_V2 .pdf

HTR-PM Pebble Bed Reactor Progress - Photos - 01-China-DONG_V2. pdf

The Little Reactor That Could. 
It's hot enough to power Skyscrubbers and Hydrogen Generators.

About TRISO nuclear fuels
This is the helium gas cooled reactor that will eventually replace today's outmoded water cooled nuclear reactors.

Both of these reactors use prisms made of poppy-seed size TRISO particles. 
(Below) Major components.  Similar design: The AREVA Antares.

Good Description of a TRISO reactor  General Atomics GT-MHR Conceptual Design Description Report - gtmhr-preapp1.pdf

At first, TRISO is mysterious. 
It has almost nothing in common with your grandfather's nuclear reactors.

Unlike your grandfather's reactor which, at 550°F, can only boil water to make electricity,
TRISO reactors can push 2,000°F, run bright red, which is hotter than most fires, and is intended to replace fire in many applications.
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear.
The major downside of the 2,000°F version is how hard they push the refractory metals that make up their parts.
The TRISO fuel is ceramic so the reactor's heat is not a problem for the fuels.

A 2011 NRC evaluation of this technology: 

"Current interest expressed by industry in HTGR plants, particularly modular plants with power up to about 600 MW(e) per unit, has prompted NRC to task PNNL with assessing the currently available literature related to codes and standards applicable to HTGR plants, the operating history of past and present HTGR plants, and with evaluating the proposed designs of RPV and associated piping for future plants.

Considering these topics in the order they are arranged in the text, first the operational histories of five shut-down and two currently operating HTGR plants are reviewed, leading the authors to conclude that while small, simple prototype HTGR plants operated reliably, some of the larger plants, particularly Fort St. Vrain, had poor availability. Safety and radiological performance of these plants has been considerably better than LWR plants. Petroleum processing plants provide some applicable experience with materials similar to those proposed for HTGR piping and vessels.  [ Highlight added by site author. ]

At least one currently operating plant – HTR-10 – has performed and documented a leak before break analysis that appears to be applicable to proposed future US HTGR designs.

Current codes and standards cover some HTGR materials, but not all materials are covered to the high temperatures envisioned for HTGR use. Codes and standards, particularly ASME Codes, are under development for proposed future US HTGR designs. A ―roadmap‖ document has been prepared for ASME Code development; a new subsection to section III of the ASME Code, ASME BPVC III-5, is scheduled to be published in October 2011.

The question of terminology for the cross-duct structure between the RPV and power conversion vessel is discussed, considering the differences in regulatory requirements that apply depending on whether this structure is designated as a ―vessel‖ or as a ―pipe‖. We conclude that designing this component as a ―pipe‖ is the more appropriate choice, but that the ASME BPVC allows the owner of the facility to select the preferred designation, and that either designation can be acceptable. " - - - (Summary) High Temperature Gas Reactors:  Assessment of Applicable Codes and Standards   PNNL-20869
Prepared for the U.S. Nuclear Regulatory Commission under an Interagency Agreement with the U.S. Department of Energy Contract DE-AC05-76RL01830

China, Saudi Arabia agree to build HTGR -  Posted on

(WNA) An MOU for cooperation in building the high-temperature gas-cooled reactor (HTGR) was signed by King Abdullah City for Atomic and Renewable Energy (KA-CARE) president Hashim bin Abdullah Yamani and China Nuclear Engineering Corporation (CNEC) chairman Wang Shu Jin. No details of the size of the plant or the project timeline were disclosed.

A demonstration HTR-PM unit under construction at Shidaowan near Weihai city in China’s Shandong province. That plant will initially comprise twin HTR-PM reactor modules driving a single 210 MWe steam turbine. Construction started in late 2012 and it is scheduled to start commercial operation in late 2017.

A proposal to construct two 600 MWe HTRs at Ruijin city in China’s Jiangxi province passed a preliminary feasibility review in early 2015. The design of the Ruijin HTRs is based on the smaller Shidaowan demonstration HTR-PM. Construction of the Ruijin reactors is expected to start next year, with grid connection in 2021.

CNEC said it is actively promoting its HTR technology overseas and has already signed MOUs with Saudi Arabia, Dubai, South Africa “and other countries and regions” to consider the construction of HTGR plants.

Like all such agreements in principle, they only become realized when followed by construction contracts. Often years of negotiations take place before that happens.



(Above) General Atomics' new EM2 fast reactor that can run 30 years on a single load of thorium. 
(Fast reactors are the "Camels" of the reactor world.)


Like charcoal briquettes, TRISO nuclear pebbles and prisms glow red hot.
The TRISO Nuclear Reactor
Why? Much safer, and, at 1,740F, hot enough to power a Skyscrubber
(The above reactor is a NGNP proposal by General Atomics publically posted on the IAEA web site.  It is used as much as possible on this web site as a generic prismatic reactor.)

How safe is it?  The NRC does not require this type of reactor to be in an explosion containment building.

Industrial quantities of nuclear heat are cheaper than heat from fossil fuels.  A TRISO helium reactor could supply heat hot enough to "fire" a CO2 extraction kiln.

Water and nuclear reactor cores do not mix.  This web site opposes building any more hazardous water-cooled reactors such as Three Mile Island, Chernobyl, and Fukushima, but is suggesting a far safer reactor design - the helium cooled TRISO reactor.

The General Atomics' EM2 TRISO reactor can run 30 years on a single fill-up of thorium or nuclear waste and does not use potentially dangerous water in it's core. 

The TRISO reactor General Atomics built for the Ft St Vrain, Colorado, nuclear plant was considered to be so safe the NRC did not require it to be housed in an explosion containment building. Containment vs Confinement .pdf      Introduction to TRISO nuclear fuel reactors.      Our energy reserves.

For a variety of reasons, the thorium-uranium blends used in TRISO reactor fuels appear to be the best combination of safety, temperature, efficiency, and high proliferation resistance.

Other TRISOs


          AREVA Antares Steam           GA EM2 Fast Neutron TRISO             EM2 on truck                 GA GT-MHR Generator                  GA Steam Boiler 
 (Image: Idaho National Laboratories.) Technical Evaluation Study Project No. 23843 - Assessment of High Temperature Gas Cooled Reactor (HTGR) Capital and Operating Costs
(Notice TRISO reactors can be easily teamed up like multiple engines on an airplane.)


While it may distress you that our most powerful energy option is nuclear, please bear in mind we are very fortunate to HAVE ANY OPTIONS.
Everything most people know about radioactivity and nuclear energy is incorrect.   Hormesis, Radiation's Healthy Surprise
This web site advocates mass-produced TRISO thorium nuclear power plant barges along with using the Woods Hole undersea option
along with the idea of a repository in the ice-free land part of the Antarctic  are advocated for their waste disposal.  This provides inexpensive nuclear energy and leaves no radioactivity behind at the power plant site.



Skyscrubbers need massive amounts of very hot heat
and TRISOs really deliver.

(Below) The dramatic differences in temperature and operating pressures between different modern nuclear reactors.

Using a power plant's unneeded nighttime energy to power a Skyscrubber's kiln
(There is a useful property in the Skyscrubber's chemical reaction (above) that makes this possible.)

(Above)  Already built and running, most power plants can use their available nighttime power to run a million ton per year CO2 air scrubber.

  (Below) As the evening progresses, a power plant's daily electricity load becomes lighter. 
This enables the Skyscrubber kiln to be speeded up to absorb the increasing amounts of available heat, thus extracting more CO





Authoritative web sites about TRISO fueled, helium gas cooled, nuclear reactors
(Click to enlarge images)

   TRISO fueled, helium cooled?
The Department of Energy quickly realized the value of coated uranium dioxide particles and on March 14, 1972, was issued U.S. Patent No. 3,649,452, which describes the TRISO fuel particle and its use in nuclear reactors.  The NGNP reactor, now being developed at Idaho National Labs, uses the most advanced TRISO fuel particle, the uranium oxycarbide (UCO) - a mix of uranium dioxide (UO2) and uranium carbide (UC). 
   Idaho National Laboratories.  Home of the US TRISO Very High Temperature Reactor

   NRC Nuclear Regulatory Commission NGNP page 

   The Next Generation Nuclear Plant (NGNP) Industry Alliance Limited
   DOE Department of Energy Small Modular Reactor (SMR) page 

   The NGNP reactor   
   Download a pdf
   General Atomics, USA GT-MHR reactor  All the TRISO reactor we need for now.
   General Atomics, USA
EM2 Energy Multiplier Module  A thorium burner.  Perhaps the ultimate TRISO reactor.
   At the moment, there are 1,384 combined cycle power plants in the world.
   George Andrew Olah got the 1994 Nobel Prize for his work in vehicle fuels.

According to my Nuclear Engineering textbook "Nuclear Engineering", by Ronald Allen Knief, Second Edition, there are 44 of these critters - either in prismatic or pebble fuel configurations - around the world.  That's news to me.  The only one I had heard of was the prismatic at Colorado's Fort St Vrain.  The author comments that "safety features" of the prismatic may serve as the basis for a "next generation" reactor.  See INL's NGNP, above.  China has 40 more pebble beds in the works for their Rongcheng site.



(Below) General Atomics' current GT-MHR offering.   TRISO reactors produce power in the 600 megaWatt (thermal) range.


From the World Nuclear Association:


In the 1970s General Atomics developed an HTR with prismatic fuel blocks based on those in the 842 MWt Fort St Vrain reactor, which ran 1976-89 in the USA. Licensing review by the NRC was under way until the projects were cancelled in the late 1970s.

Evolved from this in the 1980s, General Atomics' Gas Turbine - Modular Helium Reactor (GT-MHR), would be built as modules of up to 600 MWt, but typically 350 MWt, 150 MWe. In its electrical application each would directly drive a gas turbine at 47% thermal efficiency. It can also be used for hydrogen production (100,000 t/yr claimed) and other high temperature process heat applications. The annular core, allowing passive decay heat removal, consists of 102 hexagonal fuel element columns of graphite blocks with channels for helium coolant and control rods. Graphite reflector blocks are both inside and around the core. Half the core is replaced every 18 months. Enrichment is about 15.5%, burn-up is up to 220 GWd/t, and coolant outlet temperature is 750°C with a target of 1000°C.

The GT-MHR is being developed by General Atomics in partnership with Russia's OKBM Afrikantov, supported by Fuji (Japan). Areva was formerly involved, but it has developed the basic design itself as Antares.  Initially the GT-MHR was to be used to burn pure ex-weapons plutonium at Seversk (Tomsk) in Russia. A burnable poison such as Er-167 is needed for this fuel. The preliminary design stage was completed in 2001, but the program to construct a prototype in Russia has languished since.

General Atomics says that the GT-MHR neutron spectrum is such, and the TRISO fuel is so stable, that the reactor can be powered fully with separated transuranic wastes (neptunium, plutonium, americium and curium) from light water reactor used fuel. The fertile actinides would enable reactivity control and very high burn-up could be achieved with it – over 500 GWd/t – the 'Deep Burn' concept. Over 95% of the Pu-239 and 60% of other actinides would be destroyed in a single pass.

A smaller version of the GT-MHR, the Remote-Site Modular Helium Reactor (RS-MHR) of 10-25 MWe has been proposed by General Atomics. The fuel would be 20% enriched and refueling interval would be 6-8 years.


In February 2010, General Atomics announced a modified version of its GT-MHR design – the Energy Multiplier Module (EM2). The EM2 is a 500 MWt, 240 MWe helium-cooled fast-neutron HTR operating at 850°C and fuelled with 20 tonnes of used PWR fuel or depleted uranium, plus 22 tonnes of low-enriched uranium (~12% U-235) as starter. Used fuel from this is processed to remove fission products (about 4 tonnes) and the balance is recycled as fuel for subsequent rounds, each time topped up with 4 tonnes of further used PWR fuel. (The means of reprocessing to remove fission products is not specified.) Each refueling cycle may be as long as 30 years. With repeated recycling the amount of original natural uranium (before use by PWR) used goes up from 0.5% to 50% at about cycle 12. High-level wastes are about 4% of those from PWR on open fuel cycle. A 48% thermal efficiency is claimed, using Brayton cycle. EM2 would also be suitable for process heat applications. The main pressure vessel can be trucked or railed to the site, and installed below ground level.

The company anticipates a 12-year development and licensing period, which is in line with the 80 MWt experimental technology demonstration gas-cooled fast reactor (GFR) in the Generation IV programl."


From "Steam Cycle Modular Helium Reactor", Arkal Shenoy, John Saurwein, Malcolm Labar, Hankwon Choi, John Cosmopoulos Nuclear Technology / Volume 178 / Number 2 / Pages 170-185 May 2012

"The HTGR design option being advanced by General Atomics for the NGNP demonstration plant, and for follow-on commercial deployment, is the Steam Cycle Modular Helium Reactor (SC-MHR). The SC-MHR, which is the subject of this paper, uses fuel elements in the form of hexagonal blocks, which are stacked together to form the reactor core. This type of HTGR is referred to as a prismatic HTGR, as opposed to a pebble bed HTGR, which uses billiard ball-size spherical fuel elements. The above-noted generic features of HTGRs coupled with the modular helium reactor design features of the SC-MHR allow for adequate removal of residual heat from the reactor by completely passive means in the event of a loss of forced cooling or loss of coolant pressure. This ensures that the fuel remains below time-at-temperature limits at which fuel damage could occur during such events, thereby ensuring radionuclide retention within the fuel particles. Thus, the safety of the SC-MHR (as well as other modular HTGR designs) is inherent to the design, and the rare, but severe, accidents postulated for light water reactors and other advanced nuclear concepts are not possible with the SC-MHR."

First HTR-PM construction progresses

04 April 2014

CORRECTED - An earlier version of this story incorrectly said that the basemat for the first CAP1400 unit at Shidaowan had been completed. It was in fact for the first HTR-PM unit being built at the same site. 

The pouring of concrete for the basemat of the first HTR-PM unit - a demonstration high-temperature gas-cooled reactor - at Shidaowan in China's Shandong province was recently completed. Another 19 of the small modular reactors could follow.

Shidaowan 1 first concrete 460 (CNEC)

The construction site of the first HTR-PM at Shidaowan (Image: CNEC)


Plant constructor China Nuclear Engineering Corporation (CNEC) announced that the pouring of first concrete, marking the official start of construction of the HTR-PM, began on 28 March and took 20 hours to complete. Construction of the reactor building itself will now begin.

The demonstration plant's twin HTR-PM units will drive a single 210 MWe turbine. It is expected to begin operating around 2017. Eighteen further units are proposed for the Shidaowan site, near Rongcheng in Weihai city.

Work began on two demonstration HTR-PM units at China Huaneng Group's Shidaowan site in December 2012. China Huaneng is the lead organization in the consortium to build the demonstration units with CNEC and Tsinghua University's Institute of Nuclear and New Energy Technology (INET), which is the research and development leader. Chinergy, a joint venture of Tsinghua and CNEC, is the main contractor for the nuclear island.

Two demonstration CAP1400 units - scaled up versions of Westinghouse's AP1000 - are also planned for the Shidaowan site. About 80% of components for these will be made in China. The Shidaowan site is part of the larger Rongcheng Nuclear Power Industrial Park.

Researched and written by World Nuclear News


TRISO Summary Image




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