More
than a dozen advanced reactor designs are in various stages of development.
Some are evolutionary from the PWR, BWR and PHWR designs above, some are more
radical departures. The former include the Advanced Boiling Water Reactor
(ABWR), two of which are now operating with others under construction, and the
planned passively safe ESBWR and AP1000 units (see Nuclear Power 2010 Program).
● The Integral Fast Reactor (IFR) was built, tested and
evaluated during the 1980s and then retired under the Clinton administration in
the 1990s due to nuclear non-proliferation policies of the administration.
Recycling spent fuel is the core of its design and it therefore produces only a
fraction of the waste of current reactors.
● The Pebble Bed Reactor, a High Temperature Gas Cooled
Reactor (HTGCR), is designed so high temperatures reduce power output by
doppler broadening of the fuel's neutron cross-section. It uses ceramic fuels
so its safe operating temperatures exceed the power-reduction temperature range.
Most designs are cooled by inert helium. Helium is not subject to steam
explosions, resists neutron absorption leading to radioactivity, and does not
dissolve contaminants that can become radioactive. Typical designs have more
layers (up to 7) of passive containment than light water reactors (usually 3).
A unique feature that may aid safety is that the fuel-balls actually form the
core's mechanism, and are replaced one-by-one as they age. The design of the
fuel makes fuel reprocessing expensive.
● The Small Sealed Transportable Autonomous Reactor
(SSTAR) is being primarily researched and developed in the US, intended as a
fast breeder reactor that is passively safe and could be remotely shut down in
case the suspicion arises that it is being tampered with.
● The Clean And Environmentally Safe Advanced Reactor
(CAESAR) is a nuclear reactor concept that uses steam as a moderator — this
design is still in development.
● The Hydrogen Moderated Self-regulating Nuclear Power
Module (HPM) is a reactor design emanating from the Los Alamos National
Laboratory that uses uranium hydride as fuel.
● Subcritical reactors are designed to be safer and more
stable, but pose a number of engineering and economic difficulties. One example
is the Energy amplifier.
● Thorium based reactors. It is possible to convert
Thorium-232 into U-233 in reactors specially designed for the purpose. In this
way, thorium, which is more plentiful than uranium, can be used to breed U-233
nuclear fuel. U-233 is also believed to have favourable nuclear properties as
compared to traditionally used U-235, including better neutron economy and
lower production of long lived transuranic waste.
○ Advanced Heavy Water Reactor (AHWR)— A proposed heavy
water moderated nuclear power reactor that will be the next generation design
of the PHWR type. Under development in the Bhabha Atomic Research Centre
(BARC), India.
○ KAMINI — A unique reactor using Uranium-233 isotope
for fuel. Built in India by BARC and Indira Gandhi Center for Atomic Research
(IGCAR).
○ India is also planning to build fast breeder reactors
using the thorium – Uranium-233 fuel cycle. The FBTR (Fast Breeder Test
Reactor) in operation at Kalpakkam (India) uses Plutonium as a fuel and liquid
sodium as a coolant.