On March 11, 2011, an earthquake measuring magnitude 9 struck the power station.The scale of seismic motions was far greater than those used for designing the plant.Yet, the power station withstood the quake.Its three units in operation shut down automatically.The loss of off-site power activated the emergency power system, which began cooling down the reactors to achieve the state of cold shutdown.Everything went as designed.Plant operators must have heaved a sigh of relief after observing the plants through the three bouts of violent tremors.
Then came tsunami waves one hour later. It submerged underground power supplies, rendering all equipment for safe reactor cool-down inoperable.This station blackout lasted for 13 days thereafter, substantially longer than the maximum power loss of 8 hours, which the utilities had insisted to be a sufficient design basis for power stations.
Yet even after the station blackout, safety equipment that does not require electricity continued to work.Unit 1's isolation condenser continued to cool the reactor core for half a day.The steam turbine-driven coolant injection systems at Unit 2 and Unit 3 continued injecting water into the reactor core for approximately 3 days and 1.5 days respectively.These equipment maintained their operation longer than they were designed for and substantially delayed the development of major incidents.However, the failure to recover off-site power eventually led to nuclear accidents.
Decay heat evaporated cooling water to leave the reactor cores exposed.This raised the temperature of fuel cladding, which then chemically reacted with steam to generate a massive amount of hydrogen gas and melted fuel rods in the cores with the heat of the reaction.The hydrogen gas generated subsequently caused the explosions at Unit 1 and Unit 3, to be explained later.
Different people have different views on the current extent of fuel rods melting.I suspect that, if the reactor cores are still contained in the pressure vessels, melted fuel rods are now boiling at over 2,000 degrees Celsius inside an egg-shape crust measuring 4 meters in diameter and 2 meters in height.The crust should be around 20 – 30 centimeters now.Regardless of the degree of speculation and its accuracy, the major problem is the continued discharge of radioactive materials from the melted reactor core.The fact that pressure, water level and other parameters that indicate the condition of the reactor cores have been stable is very reassuring as it indicates the relative stability of the reactor cores.
Since steam escaping from the reactor cores is not much hotter than 100 degrees Celsius, gaseous radioactive materials discharged into the atmosphere are limited to noble gas, iodine, etc., most of which have already been released.Radiation levels at observation points appear to be decreasing according to the decay cycle of iodine 131.It may be time to consider allowing evacuees, who are living a life of inconvenience and hardship, to go home.
At the same time, the level of contamination of water accumulated on the power station premises is rising day by day.This is the main issue that needs to be addressed.Radioactive materials released from molten reactor cores are cooled down with ambient water and steam and build up in water.Its high contamination level denies personnel access and hinders future restoration work.Dumping the water into the sea is irresponsible and out of question.
The current operation to spray water on the plants merely serves to remove generated heat and has no effect toward cooling and solidifying the molten cores.Amidst the protracted battle to control decay heat, the amount of highly contaminated liquid continues to rise.Time is slipping by in the absence of a solution.Each day of inaction adds 100 days of difficulty.Any further procrastination with no concrete action plan will be considered almost criminal in its perceived neglect.We must urgently initiate forcible core cool-down to solidify the molten fuel and terminate any further discharge of radiation.This is the urgent task.Yet, sadly, I do not see any definite moves toward it.
Even worse, they have committed the folly of dumping radioactive liquid waste into the sea without giving much notice to other countries even though the radioactive level is low.It is only natural that the action has invited anger from local fishermen and protests from South Korea.It seems that the government and TEPCO have both become bewildered with the scale of the crisis and lost their mind.I sometimes think they may not actually realize the true reality and gravity of the situation.
The same applies to the Atomic Energy Society of Japan.One month has passed since March 11, and the Society has yet to launch any relief activities in this emergency despite being Japan's only group of nuclear engineers.What good does it do if it does not act?The failure to recognize the reality and gravity of the situation points to the lack of understanding and sense of mission.
The Nuclear Safety Commission of Japan has not even issued a single message to the public.The Nuclear and Industrial Safety Agency spends all their time giving event updates but provides no outlook.We cannot even see what the TEPCO leadership is up to despite their direct involvement.With no end to the current crisis in sight, the sense of frustration and distrust in nuclear-related parties is running high among the general public.The situation is even worse overseas, where accurate information is scarce.The government's failure to make a clear statement of commitment and resolve has led to the perception of Japan's indecisiveness.To break the stalemate, the Japanese government must issue a statement setting out the goal of its countermeasures.
What nuclear professionals should do is to sound a warning to resolve the stalemate, and offer underlining support.There is no shortage of tasks to be handled by the teams of experts, e.g. developing a roadmap for achieving the goal, exploring technologies required and providing cooperation including physical involvement.I expect to see each one of you taking immediate action.
With radiation levels rising, the accident site is now likened to a battleground.A battle against radiation requires a trustworthy general commander, commands issued by the general staff who speaks through a voice of reason, and unreserved government support and backing.It is necessary to define the power station compound and its surrounding sea area as a battle zone and apply emergency rules there.Such type of extra-legal action is under the government's exclusive jurisdiction, but can only be achieved with the help of us experts.
The primary force in this battle zone consists of field engineers who have extensive knowledge of the power station.People with little or no experience of working in a radioactive environment invariably become fearful and nervous and end up becoming a burden to their colleagues.Those who are better at desktop work should concentrate on providing logistics support and raising public awareness rather than interfering with frontline work.This is a lesson learned from the Russo-Japanese War.
The task of immediate urgency is the sorting and organization of the battle zone.The use of high-tech remote-control devices and radiation shields is essential in a battle against radiation.It is also necessary to install temporary equipment for cooling down the molten cores.To do this, the work environment must be prepared including the lowering of radiation levels.The battle must start with bringing in heavy machinery to remove unnecessary equipment and debris, as well as removing contaminated water and decontaminating floor surfaces.In preparation, workers must clear the ground and arrange transportation routes to enable the assembling of machinery.The April 11 morning edition of Yomiuri Newspaper reported that this work has finally begun, which is good news.
The future outlook can be established once we clear the battle zone and cool down the molten reactor cores.The next step is to inspect the location and condition of the solidified cores.This should be undertaken under international cooperation.In declaring support and cooperation for Japan, foreign governments are trying to acquire valuable lessons on nuclear disasters.The Japanese Foreign Ministry must be aware of this in handling the matter.
Once the conditions of the reactor cores are identified, the roadmap for their removal and dismantlement can be drawn.Then, we only need to make a decision and put it into action.There could be thousands of different approaches, but now is not the time to discuss it any further.
Let us look back on how the incident unfolded, and examine what was lacking in our plant considerations.What immediately come to mind in engineering terms are the scale of tsunami that outstripped our design-basis assumption and the protracted loss of power, as clearly seen in the aforementioned development of events.All equipment that is supposed to have brought the units to cold shutdown withstood the earthquake itself.Even with tsunami, some of the emergency safety and core cooling equipment operated as designed to continue cooling the reactor cores.Safety equipment served their intended roles until their last breath.Safety design is not to blame.
Except for aspects of any personnel responses to be investigated in the future, accountability lies in design assumptions made regarding tsunami and the duration of power loss.There was a blind faith in figures based on past historical examples, and their application to plant designs.
Figures taught in complex geophysics are based on events that occur very rarely and therefore have a large margin of error.Incorporating such figures to nuclear plant design, which requires precision to the tune of millimeters, was the starting point of this disaster.The lack of consistency is evident in the fact that the section on design-basis considerations against natural phenomena in the Seismic Safety Design Review Guide is divided into two subsections, one for earthquakes and the other for other types of natural disasters.Latest engineering insight should be applied to examine the effects of tsunami, floods, typhoons, tornadoes, rainstorms, snowfalls and any other natural phenomena to the same extent as the examination on the effects of earthquakes.
The recovery of power was the absolute expertise of electric utilities who are also plant licensees.This was a pitfall.Their judgment was flawed when they trusted past figures and wrongly ruled out the possibility of a tsunami on that scale and subsequent loss of power.Future safety designs must encompass countermeasures based on the assumption that such abnormal events "could happen".Based on lessons learned in this incident, a countermeasure for tsunami could be the restoration of power supply within a set period of time, and a countermeasure for the total power loss could be the preparation of diverse power supplies to withstand a variety of natural disasters.The fact that a temporary power supply is currently used in Fukushima to restore power is a valuable lesson.
Another development that requires our attention is a series of hydrogen explosions.While they may not have directly affected the melting of the reactor cores, the blasts caused public anxiety and the resulting debris is still hampering restoration efforts.We should highlight the fact that Unit 2 did not experience a hydrogen explosion when Unit 1 and Unit 3 did, along with Unit 4.Some speculate that the blowout panels on Unit 2's reactor building became dislodged (due to the explosion at Unit 3), allowing hydrogen gas to escape and preventing its buildup in the building.Further studies must be conducted for clarification.
Until now, we believed in containing radiation and put priority on achieving it.However, the hydrogen explosions cast a doubt on this approach.Releasing hydrogen gas and other gasses in the containment vessel before the reactor core begins to melt, turns out to be far safer in terms of radiation exposure control and explosion prevention.This is a new insight that should be examined closely.Incidentally, in the TMI accident, an evacuation order was issued due to concerns that a hydrogen explosion might damage the containment vessel.Ironically, even before such concerns were voiced, a hydrogen explosion had already occurred inside the containment vessel.
I have outlined the current status, concerns and reflections surrounding the nuclear power station based on information updates of this incident.Scrutinizing the incident in further detail is the task of you juniors.Engage in active discussions to draw up rational actions to take.This exercise will eventually expand into international debate without a doubt.
Let us acknowledge the fact that there is public debate on whether the incident has been handled correctly.Political dickering was behind the issue of Prime MinisterKan's inspection of affected areas, and there is no need for us to concern ourselves on the matter.For the sake of future prevention of nuclear disasters, accurate data must be submitted to scientific and technological debate in the international arena.Our tasks include the tough job of laying out mistakes in the open for scrutiny.
However tough it may be, as an old saying goes, "family must be sacrificed for the greater good".After such a major disaster, it is the credibility of Japan that is at stake.TEPCO has separated itself from the negative legacy of data tampering and cover-up.We expect the company to compile and present true and honest accounts of the incident to the rest of the world.That is the lofty mission that TEPCO must accomplish.
Finally, I wish to express my profound gratitude and respect to TEPCO workers on the site and personnel of the Self Defense Forces, police and fire department for their on-going efforts in the tough environment.We must not forget the contribution of the U.S. military, which has even mobilized a nuclear-powered aircraft carrier to engage in relief operations.Let me express my sincere gratitude for the support from our ally, the United States, in concluding this emergency proposal.