Long-time anti-nuclear campaigner and writer Dr Helen Caldicott believes the risks of nuclear power outweigh the benefits.
AS AUSTRALIA grapples with the notion of introducing nuclear power as an energy source, it is imperative that people understand the intricacies of these new technologies including small modular reactors (SMR) and thorium reactors.
There are basically three types of SMRs which generate less than 300 megawatts of electricity compared to current 1000 megawatt reactors.
Light water reactors designs – smaller versions of present-day pressurised water reactors – will be built underground but with the same attendant problems as those at Fukushima and Three Mile Island.
They will be mass-produced, so large numbers must be sold yearly to make a profit, and should a safety problem arise like the Boeing Dreamliner plane, they all will have to be shut down interfering substantially with electricity supply.
SMRs will be expensive because the cost of unit capacity increases with decrease in the size of the reactor. To alleviate costs, it is suggested that safety rules be relaxed including reducing security requirements and a reduction in the 10-mile emergency planning zone to 1000 feet.
High-temperature gas-cooled reactors (HTGR) or pebble bed reactors
Five billion tiny fuel kernels of high-enriched uranium or plutonium will be encased in tennis-ball-sized graphite spheres which must be made without cracks or imperfections, or else they could lead to an accident. A total of 450,000 such spheres will slowly be released continuously from a fuel silo, passing through the reactor core, and then re-circulated ten times. These reactors will be cooled by helium gas operating at high very temperatures (900 C).
The plans are to construct a reactor complex consisting of four HTGR modules located underground to be run by only two operators in a central control room. It is claimed that HTGRs will be so safe that a containment building will be unnecessary and operators can even leave the site – “walk away safe” reactors.
However, should temperatures unexpectedly exceed 1600 degrees, the carbon coating will release dangerous radioactive isotopes into the helium gas, and at 2000 degrees, the carbon would ignite creating a fierce graphite Chernobyl-type fire.
If a crack develops in the piping or building, radioactive helium would escape and air would rush in igniting the graphite.
Although HTGRs produce small amounts of low-level waste, they create larger volumes of high-level waste than conventional reactors.
Liquid metal fast reactors (PRISM)
It is claimed by the proponents that fast reactors will be safe, economically competitive, proliferation-resistant and sustainable.
They are to be fueled by plutonium or highly enriched uranium, and cooled by either liquid sodium or a lead-bismuth molten coolant creating a potentially explosive situation. Liquid sodium burns or explodes when exposed to air or water and lead-bismuth is extremely corrosive producing very volatile radioactive elements when irradiated.
There are two types of fast reactors: a simple plutonium fueled reactor and a “breeder". The plutonium reactor core can be surrounded by a blanket of uranium 238, the uranium captures neutrons and converts to plutonium creating ever more plutonium.
Three small plutonium fast reactors will be arranged together forming a module. Three of these modules will be buried underground and all nine reactors will connect to a fully automated central control room.
Only three reactor operators situated in one control room will be in control of nine reactors. Potentially, one operator could simultaneously face a catastrophic situation triggered by the loss of offsite power to one unit at full power, in another shut down for refuelling and in one in start-up mode. There is to be no emergency core cooling systems.
Fast reactors will require a massive infrastructure including a reprocessing plant to dissolve radioactive waste fuel rods in nitric acid, chemically removing the plutonium and a fuel fabrication facility to create new fuel rods. A total of 15,000 to 25,000 kilos of plutonium are required to operate a fuel cycle at a fast reactor and just 2.5 kilos is fuel for a nuclear weapon.
Thorium itself is not a naturally fissionable material and requires a two-step process to produce fissionable fuel. It is mixed with either 20% enriched uranium 235 or plutonium, to initiate the process to produce fissionable uranium 233. Uranium 233, like plutonium, is fuel for nuclear weapons.
Thorium reactors also produces uranium 232, which decays to an extremely potent high-energy gamma emitter which can penetrate one meter of concrete, making the handling of spent nuclear fuel extraordinarily dangerous.
Thorium advocates say that thorium reactors produce little radioactive waste, however, they simply produce a different spectrum of waste from traditional reactors, including many dangerous isotopes with extremely long half-lives. Technetium 99 has a half-life of 300,000 years and iodine 129 a half-life of 15.7 million years.
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