Published on July 3rd, 2008 | by Rod Adams15
China's Second Pebble Bed Reactor Steam Plant; World's Third Commercial HTGR
There is some excitement in the nuclear focused blog world about “The World’s First Commercial High Temperature Nuclear Reactor” based partly on a recent article in Power Engineering by Jana Miller titled “Powering Up A Growing Nation”. This project in Shandong Province will be a unique plant whose reactor heat source is two containers full of spherical fuel elements, each one of which is about the size of a billiard ball.
I am a bit reluctant to call this plant a “first”, but I can get just as excited about the third, 10th or 100th plant in a progressive series of improved plants that should number 1000 reactors or more.
The plant, designated as HTR-PM, will be a 200 MWe pebble bed reactor heated steam plant with two reactors, each with a single steam generator (boiler) feeding a single turbine. The plant will be built in Rongchen City on a site large enough to host series of perhaps 10-12 similar plants. In that area of China, there are hundreds of older coal fired power plants generating 50-300 MWe each.
The HTR-PM is a carefully watched project that uses technology old enough to be new again. The concept was introduced in the late 1940s by Farrington Daniels who suggested the idea of combining uranium with graphite, which is a high temperature substance that also moderates neutrons, into small, discrete units that could be piled into a simple, shielded container.
This concept, known as the Daniels’ Pile, was a bit before its time. The material science available in the late 1940s could not provide the tight, vapor-proof coatings needed to ensure that all fission by-products remained sealed in the pebbles in all core conditions. That problem was addressed and overcome by the German project known as the Arbeitsgemeinschaft Versuchsreaktor (AVR) run in Julich from 1959-1988.
The first commercial high temperature reactors
The AVR did not operate in isolation; during the same time there was a high temperature gas cooled reactor, built by Gulf General Atomics (now just General Atomics) and operated in the US at Fort St. Vrain. That HTGR was based on fuel in a different form, but it used fuel particles surrounded by layers of graphite and silicon carbide to provide the capability of operating at a significantly higher temperature and thermal efficiency than the conventional light water reactors.
I had the opportunity to visit General Atomics in 1994, before they decommissioned the fuel manufacturing facility that produced the Ft. St. Vrain fuel, and they gave me the pebble that you see here as a keep sake. It has been on my desk ever since.
The German group operating the AVR also built a commercial unit – Thorium High Temperature Reactor (THTR) – using fuel pebbles where some pebbles contained uranium-235 and others contained thorium-232. This fuel combination intrigued the designers because thorium is about 3-4 times as abundant as uranium, but it needs to be exposed to neutrons in a reactor before it can be used as fuel.
Unfortunately, though they were both commercial reactors, neither the Ft. St. Vrain HTGR nor the THTR operated for very long and neither led to any immediate successors. Good ideas, however, often incubate in the minds of problem solvers that see all of the potential and determine ways to solve the problems for another try.
China’s New High Temperature Reactors (HTR)
In 2000, the AVR rose up like a Phoenix in a new location at Tsinghua University with a new name – HTR-10. The Chinese had recognized the potential of the design and purchased essentially all of the makings including technical drawings, machinery, and consulting engineering services from the German owners. In January 2003, the HTR-10 began critical operations and testing. I have a number of friends and colleagues who have visited the facility and have been impressed. You can have a similar experience by watching a video produced by the Australian Broadcasting System titled Nuclear China.
There are many things about pebble bed reactors that fascinate me, but one of them is the fact that they can be configured to be able to withstand a complete loss of cooling without causing any core damage. As long as each reactor unit produces less than 400 MW of thermal energy, operators can turn off the cooling circulators and walk away knowing that the plant will heat up a bit, shut itself down, and never exceed a temperature at which any fuel damage will occur. Now that is a hot idea whose time has come!
The HTR-PM is capable of providing very high quality steam, identical to the steam produced in the most efficient coal fired power plants. In fact, Jim Holm has suggested that we could short cut the lengthy nuclear plant construction process by replacing boilers in existing steam plants with high temperature pebble beds.
It is one hell of a way to help solve the world’s most pressing energy challenge – how do we replace the low cost heat that coal provides to enable our modern economy without creating emissions that may overheat our planet?
Photo credits HTR-10 Schematic and simulated pebble fuel element from Rod Adams archives under creative commons.
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