Antinuclear

HELEN CALDICOTT: Small modular reactors — same nuclear disasters 

Now that the “nuclear renaissance” seems dead and buried following the Fukushima catastrophe (one-sixth of the world’s nuclear reactors were closed after the accident), the corporations invested in making nuclear plants and radioactive waste –including Toshiba, Nu-Scale, Babcock and Wilcox, GE Hitachi, General Atomics and the Tennessee Valley Authority – are not to be defeated.

Their new strategy is to develop small modular reactors (SMR), which can be sold around the world without, they say, the dangers inherent in large reactors — safety, cost, proliferation risks and radioactive waste.

There are basically three types of SMRs which generate less than 300 megawatts of electricity compared to the current 1,000-megawatt reactors.

Light water reactor designs

These will be smaller versions of present-day pressurised water reactors using water as the moderator and coolant but with the same attendant problems as Fukushima and Three Mile Island. They are to be built underground, which obviously makes them dangerous to access in the event of an accident or malfunction.

They will be mass-produced (turnkey production) and large numbers must be sold yearly to make a profit. This is an unlikely prospect because major markets – China and India – will be uninterested in buying U.S. reactors when they can make their own.

If a safety problem arises, such as with the Dreamliner plane, all of them 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. Billions of dollars of government subsidies will be required because Wall Street will not touch nuclear power. To alleviate costs, it is suggested that safety rules be relaxed — including reducing security requirements and a reduction in the ten-mile emergency planning zone to 1,000 feet.

Non-light water designs

These are 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 very high 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 Celsius, the carbon coating will release dangerous radioactive isotopes into the helium gas and at 2000 C, 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.

Despite these obvious safety problems and despite the fact that South Africa has abandoned plans for HTGRs, the U.S. Department of Energy has unwisely chosen the HTGR as the “Next Generation Nuclear Plant”.

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.

Should a crack occur in the reactor complex, liquid sodium would escape burning or exploding. Without coolant, the plutonium fuel would melt and reach critical mass, inciting a massive nuclear explosion. One-millionth of a gram of plutonium induces cancer and it lasts for 500,000 years. Yet it is claimed that fast reactors will be so safe that no emergency sirens will be required and emergency planning zones can be decreased from ten miles to 1,300 feet.

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.

Some are keen about fast reactors because plutonium waste from other reactors can be fissioned converting it to shorter-lived isotopes like caesium and strontium which last “only” 600 years instead of 500,000. But this is fallacious thinking because only ten per cent is fissioned leaving 90 per cent of the plutonium for bomb-making and so on.

Construction

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 off-site power to one unit at full power, in another shut down for refuelling and in one in start-up mode.

There are 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.

Thus, fast reactors and breeders will provide the perfect plan for nuclear weapons proliferation and despite this danger, the industry plans to sell them to many countries.