by Roberta Velyn

Created on: December 03, 2010

Modern science has developed several different types of nuclear reactors to produce electrical power. Most of these produce energy when a critical mass of highly radioactive enriched uranium is accumulated. Within the reaction chamber nuclear particles fly about, striking each other to break apart the nuclei of the atoms, producing a chain reaction that releases immense energy. Uncontrolled this would be a nuclear explosion. To control the reaction, carbon rods are raised and lowered into the containment chamber, running interference between the nuclear particles and preventing them striking each other too quickly. So long as the carbon rods can be operated, the reaction can be controlled, producing heat that is used to turn water into steam which turns turbines that transform the energy into electricity. Water circulating around the containment chamber also helps to moderate the temperature of the vessel.

But things happen. At Chernobyl, a mechanical malfunction prevented manipulation of the carbon rods, which then melted and fell into the reaction chamber, where they lay useless at the bottom of the chamber. Without rods the reaction could not be controlled. Other interventions prevented an all-out explosion, but a large amount of radioactivity escaped and incalculable damage occurred. At Three Mile Island, a malfunction in the cooling mechanism allowed water to escape so that the reaction overheated and melted the core. Some radioactivity was released in the course of the meltdown, and the reactor was destroyed.

The CANDU ("CANada Deuterium Uranium") reactor employs a less dramatic mechanism. It is fuelled by natural uranium, which cannot, in any amount, achieve a sustained chain reaction. Instead of one large containment chamber, the CANDU reactor has bundles of smaller reaction tubes cooled by unpressurized heavy water (D2O instead of H2O) which is capable of absorbing more heat than ordinary (“light”) water. If the reaction were to heat up, the pressure chamber would deform, causing greater heat transfer to the moderating heavy water and bringing the reaction below the temperature required to maintain the chain reaction. Accordingly, the very physics of the reactor prevent overheating. Another benefit of the CANDU reactor is that it's less particular about the fuel it uses: depleted uranium from fission reactors (nuclear waste), weapons-grade plutonium from dismantled warheads, and radioactive by-products from the production of medical isotopes can all serve as fuel. A third benefit of the CANDU is that it can be refueled while operating whereas other nuclear reactors have to be shut down in order to remove spent fuel and replace it with fresh material.

Most of the nuclear power plants around the world carry with them unwarranted risks. CANDU reactors are a safer technology. Solar power, geothermal energy, wind power, and wave energy all carry great promise for the move away from the burning of hydrocarbon fuels, but they will never meet the world’s ever-increasing demand for more and more energy. CANDU reactors can.

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