Following 8.9 intensity Earth Quake under sea bed in North Japan yesterday , 11th March 2011 at 2.46 pm local time, disaster hit Sendai most ferociously compared to land mass located far away in Tokyo. We all saw on BBC / CNN some live clips that numbed my senses and made me feel so sorry for the people there who were totally hapless against the speed with which it all happened. Many would have perished as Tsunami sent a thick waft of water with in minutes to the shores .
Along with it came the news that 5 nuclear reactors in Fukushima were shut down. This is keeping in view the automatic triggers that discontinue the nuclear fission process by inserting poison rods inside the reactor core. It is mandatory for nuclear reactors, however the degree of earth quake intensity varies from location to location in order to set this Trigger Quake level. In India we have Five categories of earth quake Zones. Some of Indian reactors are located in Zone IV where the plants can perhaps withstand quake with intensity of 7 on Richter scale. The highest is quake prone is categorized as Zone V , mainly covering the Himalayan region. Himalaya is fragile and Young Mountain compared to many old geological formations in North America and Europe.
Let us come back to Fukushima events that do not portend well for Nuclear Industry, worldwide. The Daiichi site here is located in Onahama city, about 170 miles (270 kilometres) northeast of Tokyo. The 460-megawatt Unit 1 began operating in 1971 and is the oldest at the site. There are five units here and three of them are above 1100 MW installed capacity each (BWR Type) . It is in a boiling water reactor that turbine are driven by radioactive water – steam cycle, unlike pressurized water reactors (PWR) usually found in many other sites in Japan. Any breach in steam circuit in BWR type will allow radioactive material straight into the containment building. Japanese regulators decided in February to allow this plant to run another 10 years. We have in India 2×210 MW capacity reactors supplied of this type by GE, Bechtel and Combustion Engineering, in operation since October 1969. It is still operating with the permission of Atomic Energy Regulatory Board (AERB), a semi – independent nuclear regulatory body in India.
I am guessing in the context of limited information in public domain, the accident in Fukushima, 470 MW, Boiling Water Reactor (BWR) is indeed serious one. It is derived from single fact publicly admitted so far that the radioactivity inside the reactor building has risen by 1000 times the normal level. Vicinity is experiencing over 8 times radiation levels than what is permitted.
In the Loss of Cooling Accident (LOCA) in BWR we know that fuel cladding will give way ( practically rupture) allowing most of the gaseous elements released into the surroundings. Since there is suppression water pool outside of the Dry Well but inside of Reactor containment building it could at best reduce the Iodine by dissolving it water. However still some amount will escape into the containment building air environment. The bigger challenge is that Krypton 87 with 76 Minutes Half life and Xenon 137 with 4 minutes half life cannot be absorbed by water. These are inert gases that do not react with any other element and will eventually escape into the environment. Only anti dote is to stop it from running away from nuclear power plant buildings for many hours and only allow very controlled release. This is almost impossible if the Back Up power is disabled. Only gravity operated ones will do some natural work as barrier. They have their limitations and they are more like natural defence and not serious engineered defence against surging volume of Iodine and highly radioactive inert gases build up.
It is clear that plant authorities are rushing power supplies from external, perhaps mobile DG sets to the site. Batteries, the final recourse when all power fail, will be dead by few hours but can be replaced. There will be chemical emergency team as well at site and evacuation must have planned or put in place.
If the levels are 1000 times high than normal, it is clear case of Fuel rupture, the worst nightmare for power plant manager. They can face Hydrogen build up. Should this exceeds 4% by volume, and we have explosive mixture like a Bomb ticking in the Dry Well containment. The Hydrogen comes from fuel cladding of Zirconium reacting above 1204 Degrees C with water inside the core of BWR and generating this un-cappable gas.
This old reactor BWR type was built in late 60’s based on GE Design. The safety features are still the same that were prevalent in those times. Nothing can be done to change them irrespective of state of art technology prevalent in USA, Japan or Europe today. Even the Control & Instrumentation systems will be old, except the panels in Control Room due to modernization, sensors will be same old ones.
Fukushima 470 MW capacity reactor uses direct Steam cycle which means steam is highly radioactive. This steam goes through reactor core and also Steam Turbine that produces power. Even the PWR type where the secondary steam circuit generates power can face fuel rupture as possible accident scenario.
Release of radioactivity though extremely un-likely in most of the circumstances, such as the one obtained where EQ 8.9 + DG set failure led to core of the reactor overheating, is still puzzling. It must have coincided with other system failures as well. All these elements would have been taken into account ( I do hope) when the 10 year extension was given to the Fukushima plant authorities to operate this unit in its 40th year.
Well we have terrible nuclear power plants in Eastern Europe, poorly maintained that gives nightmares to Western European countries. Finally for nuclear industry it is said “Accident any where is an Accident everywhere”.
Whatever it is, it is going to put Global nuclear industry under severe strain and public conviction will be hard to come by. I would like the Fukushima to come out with faster information dissemination, through its own mechanism or by voluminous information supply to IAEA. Delays will make people around the world very suspicious that industry has habit of suppressing the bad news, worst even delaying and distorting when under public scrutiny.
People will be very averse now to live next to Nuclear Power Plants and face the radioactive release burden and its brunt when there is accident, while others living 100s of kilometers away were enjoying power supply from such facilities. And if this reactor accident happens coincidence with a natrual disaster like Earth Quake, there is wider question. How many countries can deal with it?
As I have been writing about this event based on inputs from TV and websites, the Fukushima suffers a blast at about 2.15 hrs India time. We see that on screen as live coverage . It is time for Camera crew to run away from this place before the radioactive cloud spreads and starts settling down. Fukushima nuclear accident is indeed a bad news for already Quake battered Japan and particularly for people around the plant. With this set back Nuclear industry is in for terrible times.