Abstract
In short, the events that culminated to result in the Fukushima Daachi disaster in 2001 were largely unavoidable, but as with most situations of this nature sometimes the event itself is not the issue, but how it is handled. A high-caliber tsunami and earthquake created the perfect storm for a nuclear accident, with widespread damage that continues to be noticeable today. In short, the plant lost AC and DC power, and the plant operators used improper readings to falsely assume the situation was managable, when in actuality it was a very critical situation that should have been met with more force in hindsight. In addition, when it comes to Fukushima, TEPCO employees, as well as the employees of the auditing company, were immoral and dishonest in terms of divulging the errors made by the company. These factors came together to result in contamination that is found in the air and water nearby, making the impact very intense locally, and on a level of contamination that can be found globally. This report will touch on the background information that lead up to the events that took place at the plants, as well as the key decisions that were made by TEPCO before and after the accident took place. It will also look into how these decisions impacted the local Japanese culture as well. Lastly, it will be discussed how if the plant had been outfitted with a different selection of core materials as well as a passive core cooling system, this accident may have resulted in a much less severe impact.
I. BACKGROUND INFORMATION ON THE FUKUSHIMA ACCIDENT
In March of 2011, a 9.0 earthquake caused a significant amount of damage to the Japanese coast of Daaichi. Down the coast, several sets of Reactor plants were shut down due to the loss of power. Fukushima Daaichi was the most affected by this loss of power. When the reactor plant was originally designed, the engineers only accounted for a 7m high wave, The height of the tsunami was approximately 13m*. The whole area surrounding the major buildings of Units 1 to 4 was flooded to a depth of approximately 1.5m to 5.5m. (Fukushima Nuclear Accident Analysis Report (Interim Report)). Due to poor designing of the layouts of the reactor plants, the emergency generators were installed below the water level that the tsunami reached instead of above. Although the earthquake caused a loss of power, causing the reactor plants to shutdown, the tsunami had effects that were much more severe. When a reactor plant that has been operated for a long time at high powers is shutdown, decay heat is created. This decay heat caused a rise in temperature and subsequently the explosion of the 1, 2, 3, and 4 reactor plants.
II. INITIAL CONDITIONS AND EVENTS AFTER THE EARTHQUAKE
Before the earthquake occurred, Fukushima Daachi Units 1-3 were operating at power producing electric power for the grid while Units 4-6 were shutdown. Unit 4 was depressurized and undergoing a refueling overhaul with its contents removed from the core. Units 5 and 6 were also undergoing specific inspection, but still had their contents within the core.
Due to the seismic acceleration caused from the earthquake, Units 1-3 were shut down after operating at full power. Within minutes, the Emergency Diesel Generators were started up automatically due to the loss of the off-site power supply. All was occurring as expected with a loss of power: the EDGs had started up and were supplying emergency power to the decay heat removal systems within each plant. Roughly 45 minutes after the onset of the earthquake, the tsunami arrived with an estimated 15m, which was much larger than the sea wall of 5m. (FUKUSHIMA DAIICHI: ANS Committee Report.)
FIG 1 – The Epicenter of the Great East Japan Earthquake, IAEA (2015)
This caused the loss of all but one EDG operating at plant number 6. This caused the loss of all AC power generation for cooling components at units 1-5 due to the electrical connections being submerged in water. Unit 6 emergency AC power generation continued due to Unit 6 having air cooled components within it instead of water like the others.
The shutdown of the operating reactor plants was necessary to minimize the amount of heat that was built up in the reactor plant. This shutdown of each of the reactor plants was caused by the response acceleration in the ground caused by the earthquake. Concurrently, the transmission lines for off-site emergency power distribution were damaged by the earthquake. The effects of this earthquake, and the resulting response accelerations can be seen below.
FIG 2 – Observed and Design Basis Seismic Data, INPO (2011)
Before 2011, the probability for exceeding the design basis acceleration was in the range of 10-4 to 10-6 per reactor-year (INPO, 2011). As can be seen from the above table, the largest horizontal acceleration seen was 550 gal in Unit 2, and 302 gal in the vertical direction. Not only were several design basis accelerations exceeded with the earthquake, each of the plants scram set points for the plants were also exceeded during the earthquake. Once the scram had occurred at each of the operating plants, operators began attempting to operate within protocol.
After roughly 45 minutes on emergency power, the tsunami that struck the coast caused a loss of all the operating EDGs in reactors plants 1-5, and all but one EDG in reactor plant 6. Not only did the tsunami cause a loss of power, it caused a significant amount of damage to operating sea water pumps in the plants as well.
The emergency diesel generators produce 3 phase alternating current to be used by the emergency cooling systems. In order for 3 phase Alternating Current to be produced, there are three things that are required for inducing a voltage: current carrying conductor, magnetic field, and relative motion between the two. The electricity for the plant is produced by the interactions between the three and can be seen below.
In order for 3 phase AC voltage to be generated, 3 assumptions need to be made:
- What the north pole is under any unprimed winding, the output is max (+)
- The RHR for coils must be used for rotor flux
- The rotation of the rotor is in the clockwise direction
As the rotor spins around, voltage is induced in the armature 3 phase generation is produced. Frequency of the 3 phase sine wave can be calculated by multiplying the number of poles and speed of the rotor and dividing that by 120. For example, if a generator spins at 3600 revolutions per minute, and contains 2 poles, the frequency can be calculated as follows:
=> Where F= frequency, N= speed of the rotor
=>
Emergency generation of power is achieved by attaching a diesel engine to the other end of the rotor field. In the case of the reactor plants in Fukushima, the time emergency generation of power was available was cut short due to the tsunami that struck shortly after the earthquake.
ATTEMPTING A RECOVERY
With Unit 6 being the only unit with emergency power, operators began to attempt to recover power by cross connecting power in units 5 and 6. When all emergency power was lost to the plants, TEPCO personnel began informing the government of the emergency conditions that existed. The problem was that the roads on the path to the plants were damaged by the flooding from the tsunami. After the first plant was scrammed, operators began frantically trying to remove decay heat in accordance with written procedures. The problem with the first 3 reactors was that the off-site power was lost due to the damage of transmission lines as well. This loss of off-site power resulted in the loss of normal systems used in the event of a reactor scram to control pressure and temperature.
In addition, the steam stops for plant 1 were shut as well. This resulted in the ability to remove decay heat, and subsequently pressure began to rise in plant 1. Because unit 1 was an older model, operators were forced to utilize the plant isolation condensers. When operators utilized the plant isolation condensers, they felt that it lowered plant pressure and temperature too rapidly. Instead, the operators began to cycle the system as necessary to lower pressure to prevent core damage and minimize the chance of exceeding plant design pressure changes.
Units 2-6 were designed after 1 and as a result, did not utilize the isolation condensers to remove heat and pressure from the RPV.
Units 2 and 3 had their steam stops shut as well, however, the steam reliefs that were designed to prevent RPV from overpressure lifted. This sent steam from the RPV into the suppression pools, and allowed operators to lower pressure within the plants. Due to the loss of AC and DC power in all plants except plant 6, the operators were at a loss for deciding the next actions to take to control plant temperature and pressure. It took roughly nine days to return power to units 1 and 2 after the tsunami and took over 2 weeks to restore power to units 3 and 4. Unit 5 was able to receive power from the operating EDG at unit 6.
DECAY HEAT REMOVAL (Program Outcome 1)
Although it proved futile in the end, the amount of decay heat that was removed from the plants was crucial in allowing more time to save the plants. The decay heat that was produced in the reactor plants was brought on by two major factors, power history and the time since the shutdown. This power history can be calculated by using the number of days the reactor has been operating and the levels it had been operating at. The following equation can be used to calculate beta and gamma decay heat generation:
Where P is the decay power, P0 is the nominal reactor power; τ is the time since reactor startup and τs is the time of reactor shutdown measured from the time of startup.
Formula 1 (Decay Heat Estimate for MNR)
Using the following information containing the plant history and time since shutdown, decay
heat can be calculated:
Power At Shutdown (%)
Duration at Power (days)
Duration Shutdown (days)
Thermal Power (MWth)
Core Decay Heat Generation at Time of Earthquake (MWth)
Unit 1
100
140.0
1380
83.52
Unit 2
100
80.0
2381
143.42
Unit 3
100
130.0
2381
144.01
Unit 4
0.0
No Fuel In RPV
2381
0.00
Unit 5
100
395.4
67
2381
2.13
Unit 6
100
395.4
209
3293
1.40
(Program Outcome 6)
Units 1 and 3 had the highest amount of decay heat generation produced in their plants. Using the information above, the curves can be generated showing their decay heat generation by entering the information into Microsoft Excel and producing the following graph. It’s important to note that the left side of the graph is the decay heat, and the bottom is the time since shutdown:
The most important time for decay heat removal in a plant is the period immediately following a SCRAM. When there is a reactor SCRAM, a condition where all the control rods are inserted causing the reactor to shutdown, the amount of fission reactions in the core almost reach a standstill lowering power to about 7% of full power in 1 second. The power doesn’t fully die off to zero simply because of the radioactive isotopes that remain from the prior fission events in the fuel. These fission products go on to create the different types of radiation as they decay, such as alphas, betas, and gamma rays particles. The formation of decay heat results when the radiation energy is deposited in the fuel.
UNIT 1
After the shutdown, Unit 1 used a cooldown system where the heat and steam from the reactor was transferred to a condensing pool that was vented to atmosphere. While the steam from the reactor was allowed to enter the condenser pool, the heat was removed by a heat sink created from the ocean. Eventually, this condenser pool boiled away, resulting in the loss of the only heat sink cooling the reactor plant. This system when used properly had enough water to cool the RPV for eight hours. This method of core cooling is advantageous because it requires less power supplies due to being driven by gravity and thermal driving head.
FIG 3: Diagram of Reactor Core Isolation Cooling active system (IAEA, 2015).
UNITS 2-6 COOLING METHOD
Due to units 2-6 being newer models than unit 1, the decay heat was attempted to be removed by a reactor core isolation cooling system (RCIC). This system takes cool, borated water and injects it into the core. This system would seemingly continue for days if the RCIC pump began pulling from the suppression pool once the condensate storage tank ran out.
FIG 4: Diagram of Reactor Core Isolation Cooling active system (IAEA, 2015).
In unit 2, the RCIC system was working as planned until it shut down on high level in the RPV. Due to the isolation of the main steam stops on loss of power, pressure and temperature began to rise. This rise in pressure eventually caused the steam reliefs to lift, sending steam into the suppression pool. The problem with all of the plants was the loss of power caused a loss in the monitoring systems for the plant as well. Once the operators determined that the pressure lowered, they reinitiated RCIC manually. Once DC power was lost, operators no longer had indication that water was being injected into the core.
In unit 3, the DC busses were not completely lost and allowed operators to maintain some plant indications but because of the loss of all AC, the main steam stops remained shut and plant pressure was unable to be relieved. Once the RCIC system failed on March 12th, core cooling was lost in plant 3. Once the reactor core began to boil off due to the buildup of decay heat, the high pressure coolant injection system initiated and began to cool the reactor using a steam driven pump. After roughly 8 hours, core cooling was lost due to the low steam pressure in the RPV. The choice was made to use a fire pump at a lower pressure, and attempts to change the outcome of the incident were futile, much due to the low discharge pressure of the system.
(Program Outcome 2)
Once DC power was lost, operators were forced to use disconnected car batteries to return limited plant indications and more importantly, the water level in reactor 1. This information seemed to give the operators a false sense of security. The gauge registered a water level of 550 millimeters above the top of the fuel assembly, which, while far below normal safety standards, was enough to assure the operators that no fuel had melted yet. (Strickland 2011)
It was found later that the gauges TEPCO used were wrong. Calculations would later reveal that the superheated water inside the reactor pressure vessel had dropped all the way below the bottom of the uranium fuel rods shortly before operators checked the gauge, leaving the reactor core completely uncovered.
DISCUSSION ABOUT RADIATION EFFECTS
One of the biggest issues with the Fukushima accident was the fact that the operators did not understand the severity of the conditions in the plant. Due to the loss of AC and DC power early on, the operators lost indication of key reactor plant indications. Plant operators were wise to not use seawater until all other means had failed. This causes the operating life of the reactor plant to deplete due to the damage from the corrosive products. However, the heat transfer in the core was the biggest issue that needed to be resolved due to the decay heat being built up. In order for the decay heat to be removed a large enough heat transfer must occur. There are several different forms of heat transfer: conduction, convection, and radiation. Convection happens when the fuel interacts with the coolant. This relationship can be described as the relationship between the mass flow rate in the primary, and the specific heat capacity of water, followed by the difference in temperature:
(Program Outcome 9)
Formula 2: Heat Transfer Equation (U.S. Department Of Energy, 1992).
In order for an analysis of the Fukushima accident to be performed, certain equations must be used. The first, is the equation above in order to understand the heat transfer that happens inside the reactor. The following equation can be used in order to understand heat transfer between the RCIC or IC condenser and the reactor plant when emergency cooling is initiated. It shows the realationship between U or overall heat capacity, A or the Area of the thickness in the condenser tubes, and the difference between the seawater and the steam exhaust, or:
(Program Outcome 9)
Formula 3: Overall Heat Transfer Equation (U.S. Department Of Energy, 1992).
The difference in temperature between the heat sink and the heat source is what determines the amount of cooling a system delivers. The different emergency cooling systems were able to maintain cooling to the core for a certain period of time. In the case of the first plant, operators were afraid of exceeding brittle fracture limits of the plant materials, so they isolated the emergency cooling system. As temperature in the core began to rise after cooling was isolated, heat transfer rate dropped. The conditions in the core became worse and worse as time went on, and eventually the fluid that the rods were cooled by began to boil away. As the level in the reactor core became lower and lower, the risk of exposure to the public, the radiation levels, and the hydrogen produced in the plant rose.
Once the temperature in a plant rises above saturation temperature, the water begins to enter the vaporization phase. The latent heat of vaporization is the energy that must be added to a liquid in order to transform it into a gas. Using the above heat up rate, and another listed below, it can be determined just how much energy is needed to raise temperature one degree, and how much energy is needed to boil water, or transform it into steam. In order for boiling to be understood, the heat of vaporization equation needs to be utilized because the plant is no longer at saturation.
(Program Outcome 9)
Formula 4: Heat of Vaporization (U.S. Department Of Energy, 1992).
As the temperature and pressure continues to rise in the core and water is boiled off, a steam void is produced around the fuel cells. Once the steam void is created around the fuel, heat transfer is lost. Temperature continues to rise until
In order for us to use the equations above, some assumptions must be made. First, mass flow rate needs to be assumed constant in order to calculate the energy necessary for temperature rise in a saturated temperature. Also, it must be assumed that the temperature from the bottom of the RPV to the top. The different cooling means were also maintained at different pressures, which causes different saturation conditions for each. Within the core, there is a difference in the specific heat capacity of water normally due to the boric acid.
As the water in the core continued to boil off, the heat transfer rate drops and continues to raise temperature of the fuel. Centerline temperature continues to rise until heat transfer rate goes p as a result of the exceedingly high temperatures in the core. This heat transfer can be seen in the figure below.
The point between the nucleate boiling and the partial film boiling, or departure from nucleate boiling (DNB), is when the boiling in the core causes steam bubbles to gather on the walls, significantly reducing heat flux until temperature gets high enough. This temperature difference between saturation temperature and the boiling fluid must be greater than 120 degrees Celsius for DNB to occur.
FIG 5: The Boiling Heat Transfer Curve (U.S. Department of Energy, 1992, pg. 42).
Due to the properties of zirconium alloys, an exothermic oxidation reaction occurs as follows:
(Program Outcome 9)
Formula 7: Steam Zirconium Alloy Exothermic Reaction (U.S. Department Of Energy, 1993).
This heat continues to transfer to the fuel, and the hydrogen production due to the reaction goes up. The rising hydrogen levels in the reactor plant continually raised the risk for the operators of the Fukushima plants and ultimately the public. Eventually these hydrogen gas buildups caused explosions and ultimately damage to the reactor buildings, releasing fission products to the environment.
RADIATION EFFECTS (Program Outcome 7)
Before the reactor plant even ruptured due to the buildup of hydrogen, radiation levels were rising in the plant. This can be seen from the following equation for calculating DR. One of the shielding materials considered when deciding how to minimize the exposure that operators will receive is actually water. In this case, the water in the core not only acts as a moderator, but also as a shielding material from the fuel rod exposure. Using the equation below, the amount that DR goes up for each inch of water lost in the core can be calculated as follows:
(Program Outcome 7)
where N is the thickness of the shield divided by its tenth thickness value (x/x1/10).
Where DRs is Dose rate calculated with the shielding added in, and DRu is the Dose rate prior to adding in the shielding.
Assuming for the purpose of this calculation, the dose rate was 50 rem, and for the sake of making the math easier, there was initially 24 inches of water shielding. Knowing this, and the tenth thickness of water (24 inches), dose rate can be calculated before and after as follows:
(Program Outcome 3)
However, it must be understood that the change in dose rate is logarithmic. It is also important to note that the density of the fluid is going to change as temperature continues to rise. The density of steam is much less than that of water as well, approximately 0.037 lbm/ft3 versus 59.838 lbm/ft3. This is important to note because of how much the radiation levels are going to rise when the water boils off. This is what caused the accident to become more dangerous for emergency workers, exposing them to higher radiation levels as a result of the radiation levels.
It also important to understand the significant effects that the accident had on the radiation levels in the surrounding area. There have been many studies on the exact effect that this accident had on the environment, and the immediate surrounding area. The first effect that was noticed in the surrounding area around the reactor was the elevated dose rates. These rates were so high in fact those operators in the plant were forced to wear respirators with a charcoal filter in order to minimize their internal exposure. In the Unit 3/4 control room, operators were required to relocate to the Unit 4 side of the control room due to dose rates exceeding 1200 mRem/hr on the Unit 3 side. Debris from the explosions resulted in ground material emitting radiation in excess of 1R per hour, further complicating recovery actions. (INPO SOURCE) A photo showing the dose rates seen around the site can be seen below:
FIG 6 – Site Dose Rates (mRem/hr) INPO (2011)
On top of the elevated exposure limits around the site, there was a large amount of fission products released to the environment. The figure below shows just easily the fission products were spread across the world in just a few weeks. This image shows the dispersion of the radionuclide Cs-137. This is a gaseous nuclide, and activity levels due to the dispersion are expected to be low enough to be negligible.
FIG 7 – Global Model of Atmospheric dispersion of Cesium 137, IAEA (2015)
EMERGENCY WORKERS AND SURROUNDING AREA
As of the most recent monitoring period, no observable health effects have been reported in any of the emergency workers. It should be noted that acute health effects are not expected at these doses to workers, although all are being closely monitored. For chronic health effects above 0.1 Sv (100 mSv), the cancer risk can be approximated as increasing by 10%/Sv (using the regulatory accepted linear no-threshold dose model used in radiation protection)( FUKUSHIMA DAIICHI: ANS Committee Report 2012). The highest dose received by one worker was 670 mSv. This means that his chance of cancer was increased by 6.7 percent. The problem with these estimates however, is that the outside risk of cancer due to environmental risks, such as alpha exposure from the sun, is not taken into consideration. This means that already existing chances of cancer are not factored in, resulting in an even higher risk of cancer.
The average dose rate for the 25,000 workers involved, made up of TEPCO employees and contractors/ subcontractors has been estimated to 12mSv or 1.2 rem. Approximately 175 workers received doses in excess of 100mSv or 10 rem, and 8750 workers received doses in excess of 10 mSv or 1 rem. The standard worker dose limit for Japanese workers is 50 mSv/year and 100 mSv over 5 years. Before the accident, the emergency dose limit was set at 100 mSv/year but was raised to 250 mSv/year to allow workers to respond to this serious accident. (FUKUSHIMA DAIICHI: ANS Committee Report 2012) The image below shows the dispersion of Cs-134 radionuclide to surrounding areas around the Fukushima plant which is known to have a half life of approximately 2 years. This image shows rough estimates of expected exposure rates for the towns surrounding the Fukushima plants. These estimates are based on aerial and ground monitoring results.
FIG 8 – Monitoring Results (FUKUSHIMA DAIICHI: ANS Committee Report 2012)
The doses received by members of the public have come from four different pathways: submersion dose from airborne radioactivity, inhalation dose from airborne radioactivity, consumption of contaminated water and foodstuffs, and direct exposure from contaminated surface deposition. (Brock, 2013) Food and water contamination has been documented in the areas surrounding Fukushima as well. Dose rate investigations were taken on areas surround the site associated with high doses. A total of 122 participants—90 residents from Namie Town, 20 residents from Iitate Village, and 12 residents from Kawamata Town—were initially enrolled in the survey, and 109 subjects were surveyed in follow-up examinations. (FUKUSHIMA DAIICHI: ANS Committee Report 2012) 134Cs, 137Cs, and 131I exposure was measured by whole body counters, along with urine tests. Cesium-134 was detected in 52 out of 109 people (47.7%), with the highest value being 3,100 Bq or roughly 310 mrem. Cesium-137 was detected in 32 out of 109 people (29.4%), with the highest value being 3,800 Bq or roughly 38 mrem. Both Cs-134 and Cs-137 were detected in 26 out of 109 people (23.9%).(FUKUSHIMA DAIICHI: ANS Committee Report 2012)
The image below shows the areas that were forced to be evacuated due to high exposure rates. The black mark in the center right part of the image is the Fukushima plant, and as the image explains, red indicates areas that were controlled as exclusion zones.
FIG 9 – Status of exclusion zones as of September 2013 (Brock, 2013)
Finally, because of the accident, Cs-137 was dispersed into the Pacific Ocean. The image below shows the release of this radionuclide to the environment, and the contamination of water. It can be seen that the dispersion of Cs-137 was diluted as it spread across the ocean by currents to roughly minute levels.
FIG 10 – Oceanic Model of Dispersion, IAEA (2015)
ETHICAL AND SOCIETAL IMPACT (Program Outcome 12)
Warren Buffet once said, “It takes twenty years to build a reputation and only five minutes to ruin it”. In order for a nuclear program to maintain freedom of operation, the company has an obligation to the public to maintain safety. This obligation comes with countless requirements as well. One of our biggest requirements in our Naval Nuclear community is ethics. The code of ethics mostly applies to operation of the plants in order to maintain ourselves invisible from the public. The core values of the nuclear program are integrity, knowledge, and excellence. In the case of the Japanese company TEPCO, it seemed that many issues with the tsunami occurrence and the lack of preparation surrounding the accident was attributed to a poor management culture in the company.
Safety officials investigating TEPCO stated that common cause failures in equipment were not documented properly. The company chose to correct these issues without having any record of them occurring. This was brought to light when surrounding facilities experienced the same issues and went about correcting them the right way. This involved logging the issues and reporting them to the proper officials. This choice to fix minor problems without reporting them undermined the entire process of quality assurance for the company. They should have obtained the proper permission after it was realized that plant safety was not an issue. In the case of the TEPCO leak tightness test, there was no correction to a small problem. TEPCO staff manipulated main steam valves to reduce leak rates during containment testing in 1991 and 1992, the company has admitted. (NEI Magazine) While government officials conducted the leak test, staff chose to inject air into the system through the main steam stop valves. This lead to a leak rate of <0.45%, although the actual leak rate was much higher at 2%.
As time continued on, additional violations of plant safety protocols were reported, such as cases involving flaws found in the recirculation pumps and piping connected to the primary circuit in the Fukushima, and surrounding reactor plants. The problem with these types of inspections was that they were carried out by an outside agency, Hitachi. In one of the cases conducted by Hitachi, it was discovered that problems arose with the neutron measuring equipment at one of the BWRs at Fukushima. Hitachi officials admitted to having fudged the numbers due to a request from one of their major clients, TEPCO.
In addition to the problems covered up, it seemed that the risk research funding arrangements were skewed in the nuclear community. One official from NISA stated that more of the funding was directed towards researching the protection against earthquakes and not towards tsunami prediction and preparation. This can be seen by more of the Japanese power plants being prepared for earthquakes and less prepared for the more devastating of the two events that occurred. In 2005, The Japan Atomic Energy Agency was formed by combining the Power Reactor and Nuclear Fuel Development Corporation and Japan Atomic Energy Research. As one government official said, “there are many tsunami experts in Japan,” but their findings as a rule have “not been taken seriously” by industry and government agencies responsible for making rules on nuclear safety issues. (Why Fukushima was Preventable)
Another issue that was brought to light was the failure of officials at TEPCO to utilize the Network System for Prediction of Environmental Emergency Dose Information (SPEEDI). SPEEDI is expected to play an important role in protecting local population from radiation exposure and the planning of evacuation. (Executive Summary of the Interim Report) Without SPEEDI being operational at the time, government officials were making on the fly decisions with regards to public safety and evacuation. The government instruction on evacuation for the public did not reach all local governments and subsequently did not reach the public promptly. Due to this lack of communication, the local governments were forced to make decisions for evacuation without proper information. Part of the cause for such disarray after the accident was the lack of instruction from government officials on actions to be taken after a disaster.
Many people wonder why the members of both companies chose to act the way they did, but I think a lot of it had to do with the Japanese culture and it’s reflections on company culture. When a man decides to graduate from college and enter a company, it is assumed by that man that he will have no other job until he retires at 65. A Japanese man and his family are often socially ranked by the reputation of the company he works for and the position and prospects he has there. These types of long term relationships are what create very strong bonds between the employer and the employees. In a typical Japanese office the words used to informally refer to senior and junior employees are often the same words used to describe the hierarchy of a human family. These business men have been known to be willing to move mountains if for the good of their company. Knowing this, it’s no surprise that there were actions taken by the employees of TEPCO to protect their company.
Rather than hiding the mistakes in the company, employees should realize that in the long run, it will help develop trust between the company and the public to be honest. The first thing that government officials should do is raise awareness in the public by providing basic knowledge of radioactive substances. This can include how they are released, how they are spread in the event of an accident like a tsunami, and what kind of negative effects they can have on human health. Had the government officials been better prepared with an evacuation plan for the public in the event of a major accident, there would not have been as much confusion. This preparation can include drills for the reactor plant members, and even members of the public.
Due to the poor preparation by the government initially, there was widespread confusion and officials began to scramble to recover. About a month after the disaster, on April 19, 2011, Japan chose to drastically increase its official “safe” radiation exposure levels from 1 mSv to 20 mSv per year – 20 times higher than the US exposure limit. This allowed the Japanese government to downplay the dangers of the fallout and avoid evacuation of many badly contaminated areas. (Starr) Exclusion zones were created around the nuclear plants where the public was prohibited to enter for fear of radiation poisoning. 12 miles (20 km) of the destroyed nuclear power plant, encompassing an area of about 230 square miles (600 sq km), and an additional 80 square miles (200 sq km) located northwest of the plant, were declared too radioactive for human habitation. (World Nuclear News)
It was estimated that roughly 12,000 miles were contaminated by long lived Cesium dispersed from the reactor plants. Fukushima officials estimated that approximately 160 thousand people were forced from their homes due to radiation levels being too high. Not only did the Cesium become dispersed in the atmosphere, but it also contaminated the soil, crops, animals, and water in surrounding areas. Due to the long half-life of Cesium, the people forced from their homes, might not ever return again. Fishing of the coast of Fukushima has been banned and continues to be today due to higher levels of Cesium found in the fish surrounding the coast.
Money is still being spent on cleanup efforts for the reactor plants. Fukushima Reactors 1-3 are constantly emitting gasses that produce more and more radiation. The uranium cores of reactors 1, 2 and 3, which completely melted down and then melted through the bottom of the steel reactor vessel, will continue to produce enormous amounts of radiation and heat for many years. (Nuclear Information & Resource Service) Meanwhile, seawater is constantly being poured into the reactor plants to provide cooling and then drained into the containment system where it is collected and filtered. This accumulation of radioactive water creates more and more of a risk should another earthquake strike the area. While the scientists can’t predict when an earthquake in Fukushima Daiichi will occur, they state that the ascending fluids observed in the area indicate that such an event is likely to occur in the near future. They warn that more attention should be paid to the site’s ability to withstand strong earthquakes, and reduce the risk of another nuclear disaster. (European Geosciences Union)
Changes in the Nuclear Community (Program Outcome 8)
Choices made by TEPCO and the results of the accident have had lasting effects on the nuclear community. I was stationed onboard the USS Pennsylvania when the accident happened in March of 2011. The results of this accident cause a major change to the requirements for Decay Heat Removal while in port. When we returned from our deployment, Naval Reactors had issued a design restriction that required an independent source of power be installed, in the form of an off hull shore diesel. There was an order from our Immediate Superior in Command (ISIC) that designated that the ship’s battery no longer counted as an independent source of power, and we needed to hook up a shore diesel. This was required because the Reactor Plant Manual we operate by states that in order to operate our reactors in port; we need to have two independent sources of “infinite” power. Due to the loss of electrical power in the plants in Fukushima, the nuclear community needed a change in decay heat removal requirements.
As a result of the accident, Emergency Control Centers were required to be manned all across the United States. These included San Diego, Bangor, and several others including the one here in South Carolina prototype. The ECC here was manned for 3 months after the accident. As soon as the accident was called away and news reached the command, crews were working in shifts to analyze and give action recommendations in effort to aid the actions in Japan. Despite the efforts to lower the decay heat in the reactor plant, the explosion occurred just days later.
DESIGN IMPROVEMENT
In order for improvements to the design of the reactor plant to made, it must be understood what the root causes of the accident were. The largest struggle leading up to any one of the buildings exploding was the hydrogen buildup in the primary caused by the loss of core cooling. A much better solution and one that is required in many operating reactors as a result of the accident is a passive core cooling system that doesn’t rely on power to operate valves. Much of what caused the explosion in the previously operating reactor plants was due to the loss of all power. The backup EDGs were damaged in the tsunami after the loss of AC power caused by the earthquake.