High Temperature Reactors (HTR - HTGR). Hydrogen production for future transport, electricity generation and burning weapons fuel. Graphite moderated helium cooled. (See generation four designs below.)

High Temperature reactor basic diagram

Fuel is in the form of particles under 1 mm dia. Each has a kernal of oxycarbide with Uranium enriched to 17% U235 surrounded by layers of carbon and silicon carbide to contain the fission products. These are arranged in blocks, or hexagonal prisms of graphite, or in pebbles of graphite encased in silicon carbide each with 15000 fuel particles and 9g uranium.

This is stable to 1600 C and the coolant, helium, will be heated to 950 C and used to produce hydrogen for transport etc and to drive gas turbines for electricity generation. The thermal efficiency will be up to 48% and there is a strong negative temperature coefficient. (See also CCGT on electrical page)

HTR developments (ref 6)

Eskom and Westinghouse are developing a 285 MWe Pebble bed Modular Reactor (PBMR) for South Africa with fuel in the form of billiard ball size pebbles of graphite encased in silicon carbide, 42% thermal efficiency, to drive direct cycle gas turbines.

A 285 MWe Modular Helium Reactor (GT-MHR) is being developed by General Atomics (USA) Minatom (Russia) - Franatom ANP - Fuji (Japan), initially to burn ex -weapons plutonium at Tomsk.

China is developing a 200 MWe HTR-PM l pebble bed reactor at Weihei in Shandong. 60 year life & 85% load factor expected. One objective is thermo chemical hydrogen production (with a helium output temperature of 850 to 1000 C.)

Japan plans a 600MW GTHTR300C unit for electricity and hydrogen production by the IS process (see transport page on hydrogen) (p96 ref 6).

General atomics forecast that the cost of producing hydrogen thermo chemically from a 2400MW HTR operating at 850 C would be $1.53/kg or at 950 C $1.42/kg (2003) which is competitive with steam reforming.

Advanced reactors or new 'Generation Three' designs; safety improvements, simpler to build, operate, inspect and maintain.

Advanced reactors will supersede the generation one and two designs that have been built and operated over the last 60 years and discussed on the Nuclear page and the advanced types are developments of them. Features are:-

An Advanced Boiling water reactor (ABWR 1300) has been in operation since 1996 in Japan, more are under construction, with a life expectancy of 60 years.

Advanced PWR's in design and construction

Advanced pressurized water reactors: APWR1500 for Tsuruga Japan and APR1450 South Korea). the Westinghouse standardized AP 600 and AP1000 designs (projected core damage frequency is 1000 times less than NRC requirements), the French standard EPR 1600, also in Germany, Gidropress 1000 Novovoronezh Russia and India, in Canada the advanced CANDU Reactor ACR 1000.

Westinghouse AP600 and AP1000 standardized PWR designs

Westinghouse say that "The features of the AP600 passive safety systems include passive safety injection, passive residual heat removal, passive containment cooling, and passive main control room habitability maintenance. All of these passive systems have been designed to meet the NRC single failure criteria, and probabilistic risk analyses have also been used to verify their reliability. These passive systems employ natural forces and stored energy to operate. They are highly reliable because in the unlikely event of an accident, with an assumed unavailability of non-safety systems, they do not require the starting of auxiliary motors, pumps, or diesel generators."

Generation four plans. year 2020 to 2030 (Ref 165)

The Generation four International Forum (GIF), including USA, EU, Russia, China and other major countries, is committed to joint development of six new reactor designs and applications for deployment between 2020 and 2030, calling on relevant experience in the past over many years:-

1) High Temperature thermal reactors (HTR HGTR etc) graphite moderated and Helium cooled. Fuel UO2 pebbles or prisms. up to 1000 C output for hydrogen production and electrical power. (See description at top of this page.)

2) Sodium cooled fast reactors. Fuel U238 & MOX. 550 C. Based on experience in US, UK & 6 other countries (see description of fast neutron reactor on nuclear page with diagram.)

3) Lead (Pb or Pb-Bi) cooled fast reactors. Fuel depleted uranium or nitride. 550 - 800 C. Natural convection cooling. Based on experience of the Russian BREST fast reactor over 40 years in submarines. Modular 300-400 MW Units; OR 1400 MW units for hydrogen production and electrical power.

4)Gas (Helium) cooled fast reactors. Fuel U238 plus other materials, fissile or fertile. 850 C. Hydrogen production and electrical power.

5) Supercritical water cooled (thermal or fast) reactors. Fuel UO2. 510 to 550 C. Operates above the thermodynamic critical point of water to directly drive a turbine. Based on research in Japan.

6) Molten fluoride salts reactor. Epithermal. Fuel UF in salt circulating through graphite channels. 700 to 800 C for hydrogen and electrical production via a secondary coolant circuit. Based on the US experience with their alternative (to sodium cooled) breeder fast reactor.

Near Breeder Reactor India.

India is developing the Advanced Heavy Water (thermal) Reactor (AHWR) to use its large amounts of Thorium 232 which are placed around the core to breed U233 as in a fast reactor. This will require some U235 and Pu239 in the fuel as there is not quite enough U233 to sustain the reaction.