Anatomy of a nuclear reactor

An explosion at an earthquake-hit nuclear plant in Japan has sparked fears of a radiation leak and nuclear meltdown. A meltdown occurs when failure of the cooling system leads to fuel rods overheating and melting BOILING WATER REACTOR Water, heated by splitting of uranium atoms, turns to steam and drives turbine-generators to make electricity. Steam condenses back to water and is pumped back into the reactor to continue cycle. There are multiple barriers to prevent release of radiation. 1. METAL CLADDING Encases uranium fuel rods in reactor. 2. REACTOR PRESSURE VESSEL 3. CONTAINMENT BUILDING 4. CONTROL RODS Hydraulically driven into core within seven seconds. 5. EMERGENCY COOLING Diesel generators power emergency cooling. Failure produces more heat, increases STEAM WATER pressure. 6. WET WELL Pressure-relief systems active at about 1,000 psi. If reactor pressure gets too high, relief valves open and discharge steam to water-filled pool inside containment building. 7. MELTDOWN Above 1,200°C fuel-rod cladding melts, releasing radioactive isotopes of caesium and iodine into containment building. Radiation escapes into environment, if containment fails. THE GLOBE AND MAIL » SOURCE: GRAPHIC NEWS