The nuclear plants in Japan are in news for all the wrong reasons. While there are reports of a meltdown and a hydrogen explosion, here are details of what happens in the highly reactive (activists call `dirty’) soul of a nuclear power plant:
Typically, most nuclear reactors use radio-active uranium (usually uranium-235) as fuel. Some plants use plutonium as fuel. Unlike uranium, which is stable to some extent, plutonium is more deadly and volatile.
Uranium pellets are loaded in special seamless tubes (called rods) and arranged in a circular pattern in a thick steel container. This is called the core of the reactor.
Nuclear power plants have a series of protective systems to prevent radiation leaks in the event of an accident. The core is protected by an outer container, again built of special steel and furbished by cement and lead. This is called the reactor pressure vessel that covers the reactor core and is designed to prevent radiation from being released should something go wrong with the nuclear fuel.
The nuclear fuel rods are kept submerged `nose-deep' in water inside reactor's core. This is to prevent the rods from over-heating. But if the water level dips (because of a failure in electricity which maintains a critical level of water and the coolant systems), fuel rods get over-heated resulting in the reactor core's temperature to rise.
If the core's temperature exceeds a critical level, the fuel rods melt. This is called a meltdown occurs. What happened in Fukushima nuclear power plant was a partial meltdown.
In Japan, what happened was that the deadly tsunami knocked out the power systems that run the coolant pumps. In such a situation, the heat in the core would have melted the rods and the steel casing and formed a highly dangerous nuclear soup. Some of the built up heat was released and this contained highly dangerous radioactive material.
Since there is so much heat and radioactive material, how is a meltdown detected?
Nobody can see a meltdown. A meltdown is detected by the presence of a nuclear substance called cesium which is formed after uranium undergoes fission. Cesium can leak from the shell only if the core melts. This happens when the temperature reaches 2,700 C to 2,800 C.
The detection of cesium was a clear indicator that the temperature in the core had reached very high levels.
What is hydrogen explosion?
When the fuel reaches an extremely high temperature, it reacts with the casings and comes into contact with the cooling water that is being pumped in. The special metal's properties then break down the water components and generate hydrogen. The hydrogen can leak from the reactor containment vessel into the outer structure through valves and other gaps.
Neutrons in the reactor's pressure vessel also collide with water molecules and create hydrogen. One section of experts say that it was possible that hydrogen derived from water molecules leaked out of the vessel.
US space shuttles use the hydrogen-oxygen reaction to generate high energy required for outer space travel.
What next?
If the heat is not contained soon, the reactor core's stainless steel cover could melt completely which would result in an explosion. This would be catastrophic not only to Japan, but also to neighbouring countries as the radioactive material can be transported through wind.
The Fukushima Dai-ichi nuclear power plant, located in Okuma in the Futaba district of Fukushima Prefecture, consists of six pressurised boiling water reactors designed by General Electric and generates 4.7 GW power. It is one of the 25 largest nuclear power stations in the world. Fukushima I was the first nuclear plant to be constructed and operated by entirely by Tokyo Electric Power Company (TEPCO).
Fukushima II Nuclear Power Plant is located 11.5 km south. It is also run by TEPCO.
The Indian Scenario
In India, nuclear power stations are operated by the Nuclear Power Corporation of India Ltd (NPCIL) which operates 20 nuclear power reactors (Japan has 54) with an installed capacity of 4,780 MW. This includes two Boiling Water Reactors (BWRs); the rest are Pressurised Heavy Water Reactor (PHWRs).
The PHWRs are designed differently than the BWRs; they have multiple shutdown and cooling water systems.
The Department of Atomic Energy (DAE) constantly monitors the power plants.
A reassessment and audit of safety norms are likely after the Japan episode. NPPCIL is reportedly in touch with the World Association of Nuclear Operators, Tokyo Centre, the Japan Atomic Industrial Forum, World Nuclear Association and the International Atomic Energy Agency for constant inputs.
Source: India Syndicate