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April 01, 2009

High Temperature Reactor Joint Venture and Potential to Replace Just the Coal Furnace of Coal Plants


Rod Adams at Atomic Insights talks about the joint venture between China and South Africa to develop pebble bed reactor technology

China has started construction of the first of many 210 MWe high temperature reactors which they are targeting to complete in 2013.

The first commercial-scale plant (HTR-PM) in China will make use of indirect cycle, steam turbine systems, while PBMR has been developing a direct cycle gas turbine system. The HTR-PM features two 250 MW (thermal) reactor modules and a 210 MW (electric) steam turbine-generator set.


Towards Deep Burn
Next Generation Nuclear Plant research has already invested about four years in turning the "art" of making TRISO particles into a repeatable process that that can reliably produce fuel that is demonstrating superior results in its test runs in the high flux test facility. Testing has reached the point where fuel particles (TRISO baseball size pellets used for the pebble bed reactors) are achieving 16% burn-up without failure. To provide some perspective, most light water fuels are only licensed to achieve about 5% burn-up.

There is a $7 million project to work on achieving deep burn (60-70% burnup) of TRISO fuel pebbles.

The concept of destruction of spent fuel transuranics in a TRISO-fueled (TRIstructural ISOtropic) gascooled reactor is known as Deep-Burn. The term “Deep-Burn” reflects the large fractional burnup of up to 60-70% fissions per initial metal atoms (FIMA) that can be achieved with a single pass, multi-cycle irradiation in these reactors. The concept is particularly attractive because it employs the same reactor design that is used for the NGNP program, with the same potential for highly efficient electricity and hydrogen production. Spent TRISO fuel from Deep-Burn can be either placed directly into geologic storage to provide long-term containment to the residual radioactivity or recycled for fast reactor fuel.

In parallel to the physics analysis, preliminary work has indicated that, due to the large amount of useful energy that can be extracted from the Deep-Burn TRISO fuel (up to 20 times larger than from mixedoxide (MOX) fuel in LWRs), it may be possible to recover all or part of the costs of reprocessing LWR spent fuel.


A 4 page presentation on project deep burn

Gas reactors have an advantage over light-water reactors in terms of their ability to burn TRU because the use of robust particle fuel, a solid moderator and a neutronically transparent coolant enables the use of fully enriched TRU TRISO fuel, and the attainment of very high burnups (~ 500,000 – 700,000 MWD/tHM). Thus, the overall amount of TRU burned in a single recycle can be much greater in a DB-VHTR than an LWR. In addition, the higher thermal efficiency of the VHTR increases the amount of electricity produced during consumption of the TRU. Preliminary assessments of the DBVHTR indicate that fuel cycle lengths of 1 to 1.5 years are
feasible and that the reactivity swing over the cycle could be managed.

In the early days of VHTR technology, a crush-burn-leach process was proposed to reprocess VHTR fuel. This process produced large quantities of carbon dioxide that needed to be trapped. A new head-end process consistent with the UREX+ separation technologies has been identified and demonstrated at the proof-of-principle level for TRISO fuel in the past few years. The process flow consists of separation of the compacts from the graphite block, disposal of the graphite block as lowlevel waste, grinding and jet-milling of the compact components (matrix, coatings, fuel kernels) into a fine powder to support chemical separation, and leaching, to dissolve the TRU for aqueous separation or a novel electrochemical process termed METROX for the pyroprocessing separation. The project will develop a full flowsheet for TRISO recycling using both aqueous and non-aqueous reprocessing, particularly as it pertains to spent DB-TRISO fuel. The process of crushing the ceramic coatings and exposing the spent-fuel kernels to dissolving agents will be brought up to today’s standards of low secondary waste streams and process losses. The project will study the crush-leach flowsheet to minimize waste, establish and test a laboratory filtering system, and study the suitability of the fuel solution for liquid separation. Lab-scale tests of the equipment for separation of the solid coating and compact material from the fuel solutions will be performed.

The current TRU destruction scenario adopted by GNEP/AFCI is termed the single-tier approach; it is the simplest demonstration of closing the fuel cycle. In this case, spent fuel from LWRs is sent directly to the Advanced Burner Reactor (ABR) for destruction. Our studies suggest that DBVHTRs can have a synergistic relationship with the ABR when operated in dual-tier mode. This synergy allows relaxed operating parameters for the two reactor types and a smaller inventory of recycling TRU relative to the single-tier approach. It would also reduce the number of fast reactors by a factor of 3 as compared to the LWR two-tier scenario. (i.e.,
thermal to fast reactor ratio of 9 to 1 rather than a 3 to 1 ratio).







Details on Using Pebble Beds to Replace Coal Burners from Coal Plants
The principels of converting coal plants has been described in detail at the coal2nuclear site.



HOW the modified power plant would work: The reactor (right) is in a sealed underground silo located in the power plant's coal storage yard. The heat comes from the bed (or pile) of atomic pebbles (the little red dots). The pebbles heat helium gas in the reactor to 1,300°F. The hot helium gas is circulated clockwise to carry the heat from the pebbles to the attached helium-to-water heat exchanger (a "fire-tube" water heater). The heated water (red) that exits through the bottom water pipe of the heat exchanger is supercritically hot (1,150°F), and under about 4,500 pounds per square inch pressure to keep the water from turning into steam. The reactor is rated at about 500 megaWatts thermal so even though the water is carrying almost 1,000°F differential of heat, this will be a large volume of water. In comparison, a conventional PWR reactor's supercritical water undergoes a differential of only about 70°F as it passes through its reactor core - utilizing massive water volume and 6,000 horsepower circulating pumps instead.

NEXT, The heat is carried by the water through new, heavily insulated pipes to a new steam generator located in the power plant. The steam generator is also a type of heat exchanger. This time, the 1,150°F supercritical water is used to make the 1,000°F, 2,400 psi superheated steam needed by the power plant's turbine. The steam generator's steam pipes are connected to the three-stage steam turbine (devices 11, 9, 6) that spins the electricity generator (device 5). The "new" steam is identical to the "old" steam that used to be made by the coal boiler.

Two identical special 200 ton storage vault railroad cars, equipped with with elliptically-keyed wheels, (temporarily removed) would be welded to the ground next to the silo to supply and remove pebbles through pneumatic tubes connected to the car bottoms. The Germans used automated pneumatic transport systems on their pebble bed reactors, the U.S. MIT pebble bed reactor design is even more sophisticated. The pebbles would be held in metal clips on a conveyor belt storage system in the railroad cars. A full load of 450,000 pebbles is about 112 tons containing perhaps 9 tons of uranium.

That's all there is to it folks! What a simple way to end Climate Change. The only new items are the reactor, the two heat exchangers, and a small control and service building located in the now-unneeded coal yard. It should be pointed out that power plant water heaters and steam generators, while not trivial devices, are about 30% the size of conventional nuclear power plant steam equipment so they are much less expensive and can be built in several months almost anywhere.


FURTHER READING
Research on one-pass deep burn of fuel pellets.

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