Fukushima Nuclear Accident
A nearly 9.0 magnitude Tohoku Earthquake and tsunami hit Japan on March 11, 2011. This is considered to be the most powerful known earthquake that has hit Japan till date. Apart from the huge death toll rate and devastation of the Japanese infrastructure, the tsunami also resulted in a series of nuclear accidents. The most serious nuclear accident was witnessed at the Fukushima Nuclear Power Plant. The total cost involved in the entire accident is expected to be more than USD 300 billion.
This is the most expensive natural disaster recorded till date. At Fukushima I and II nuclear plants tsunami waves crossed the seawalls destroying the diesel backup power systems. This lead to massive complications at Fukushima, including three large explosions and radioactive leakage. Sooner the Fukushima Nuclear Power Plant witnessed a series of equipment failures and venting of radioactive gases. This nuclear failure is considered to be the most disastrous of the nuclear accidents in Japan due to the Tohoku earthquake and tsunami.
Further, the experts also stated it to be the second most massive nuclear accident just behind the Chernobyl disaster, however, was more complex since all reactors were involved. The nuclear plant comprised of six different boiling water reactors managed by the Tokyo Electric Power Company (TEPCO). As a result of the Tohoku earthquake and tsunami the nuclear reaction had to be brought to a standstill. However, cooling system was required to remove the residual heat which required 7% of the total power load in case of normal conditions.
Due to the earthquake, there was no power supply from the external sources. At the initial stages, for some hours multiple emergency diesel power generators were used to provide the required electricity. However, the generators failed when the tsunami hit Fukushima. Then, the operators at the reactor moved to power through emergency batteries. This provided power backup only for 8 hours for cooling of the core. After 8 hours, the emergency batteries became non-functional and hence, the left over heat could not be carried away. Hence, operators at the plant persuaded emergency procedures that were required to be followed in an event of loss of cooling.
Now, if the cooling process was not continued, there would have been the melting of the core or better termed as “Fuel failure”. This situation was to arrive even before the fuel started melting and would have lead to mechanical, thermal, or chemical failures i.e. excessive pressure, high oxidation, or extreme temperature. Even before melting, the primary aim of the operators was to control the core while it was getting heated as well as also to ascertain that the fuel cladding remains functional as long as it can. As almost all resources to bring about cooling was already exhausted, the reactor operators had no choice than to use whatever cooling system capacity was available to carry away maximum of the heat.
However, till the time heat production was more that the capacity to remove the heat, more of the water boiled to form steam and hence, the pressure kept increasing proportionately. Hence, now the operators’ priority was to maintain the temperature lower than the 1200°C mark. Now, for maintaining the pressure levels of the system at the controllable level, steam which had several other gases that were there in the reactor, had to be vented out at regular time interval. The prime aim of this measure was that the pressure should not exceed what could be handled by the components. Thus, the containment structure and the reactor pressure vessel had a number of relief valves to release the reactor pressure.
So, the operators of the reactor started removing the steam gradually for pressure management. When the steam was vented out, it had some of the gases which were radioactive fission in nature. However, they existed in quite small amount. Thus, as the operators started venting the system, some radioactive gases also got released in to the environment in a restricted and controlled manner via scrubbers and filters.
Though some of the released gases were radioactive, there was not significant threat to public safety as well as to the workers at the reactor site as the radioactive substances were present in very small quantities. Hence, the entire procedure is acceptable and justified as its results were of very low intensity, especially as compared to the consequences that could have occurred if removal of the steam and gases was not performed at the right time.
Followed with the onset of the accident, when the cooling system failed at the nuclear plant, thousands of people living within a 20km radius of the Fukushima I Nuclear Power Plant and 10 km radius of the Fukushima II Nuclear Power Plant were evacuated from the region immediately. As a precautionary measure, a state of emergency was also declared around the Fukushima power plant No 1.
Further, the Japanese ministry banned the sale of food cultivated near the nuclear plant area. They also advised not to temporarily use the tap water for preparing food for infants. It was stated that the worldwide measurements of caesium-137 and iodine-131 stated that the radioactive releases from Fukushima were of the same magnitude as that of the isotopes released during the 1986 Chernobyl disaster. At the starting, officials at Japan ranked the fukushima nuclear plant incident at level 4 of the International Nuclear Event Scale (INES). Afterwards, it upgraded the accident INES level to 5 and later to the maximum level of 7. According to the experts, it would require a huge workforce, may be in the hundreds or even thousands, and would take years or could be decades to sanitize the area.
It’s a fact, everyone should add a Geiger counter to their list of essential survival tools.