Saturday, March 12, 2011

Concern Over Nuclear Radiation Leak in Japan

The Devastation in Japan caused by the earthquake and the tsunami defies imagination. To the loss of lives, displacement of people and damages to property and infrastructure, the possibility of radiation leak from an explosion in the Fukushima Daiichi Nuclear Power Station (about 150 miles north of Tokyo) has added a sinister dimension. If exposed to lethal ionizing radiation, and the Japanese have a visceral reaction to it from Hiroshima and Nagasaki, the effect of this natural disaster can take decades to heal.

Of course, it is only human nature to consider the darkest possibilities in the wake of something as catastrophic as this. Japanese engineers and experts are crippling the affected nuclear reactors by flooding them with seawater to minimize any radiation leak. Japan is better off anyway without these aging reactors that sit atop the “Ring of Fire,” the earthquake hotbed along the Pacific Rim.

Dr. C. S. Karim, a nuclear physicist, explains the radiation leak: “Japan has six reactors of the Boiling Water type (BWR) at the Daiichi plant and five at Daini. Any reactor has multiple systems that can shut down nuclear chain reaction during emergencies. The technical term is SCRAM. This is what ought to happen during earthquakes and tsunamis and other extreme natural events. Unfortunately, the speed and force with which these events can occur may not allow enough time for SCRAM to go into effect. In any case, the residual heat inside the reactor core continues for days, starting from seconds after the nuclear chain reaction ceases.

“The Emergency Core Cooling System is provided to take care of cooling during this period. As a backup to electricity, which may not have been available after the tsunami, there are other procedures such as immediate injection of borated water from an accumulator. The problem arises when there is damage to the reactor cooling system. Pipes in the system may be broken due to strong vibrations from an earthquake. Then, even if there is coolant available and pumps are operating, the water may not reach the reactor core to remove the residual heat.

“Any reactor design uses a concept called ‘defense in depth,’ that is, providing multiple barriers between the source of radiation and the environment. Most of the radiation is contained in the nuclear fuel element, comprising Uranium Oxide pellets shrouded in Zircaloy cladding.

“The reactor cooling system has two loops. Heat that is carried by water from the reactor core is transferred indirectly to another cooling loop. Steam, thus produced, flows through the turbine to produce electricity. If, as the reports are suggesting, there were explosions inside the reactor, they could have been due to the loss of coolant.”

Radiation dosage is measured in rem, short for "roentgen equivalent in man." It measures the amount of radiation that produces a specific amount of damage to living issues. At Hiroshima and Nagasaki, for instance, people received a dose of rems at the instant of the explosions, then more from the surroundings and from fallout when the "mushroom" descended to earth. Doses above 100 rems can cause nausea, vomiting and headache. Doses of 300 rems can cause hair loss and more sever internal damages. 50% of people exposed to 450 rems die while 800 rems are always fatal.

We do not yet know the exact level of radiation leak in northeastern Japan, other than that some leaks have occurred. The effect may turn out to be harmless to humans and other living species. Then again, it may not. What is clear is that, as life returns to normal, the Japanese will undoubtedly question the safety of their nuclear plants and perhaps even demand that the government either close most of them or make them more fail-safe. No advances in nuclear engineering and reactor design can match the ferocious power unleashed when tectonic plates shift violently beneath our feet or beneath our oceans.

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