The Explosion at the Fukushima Nuclear Power Plant - Case Study Example

The explosion at the Fukushima Nuclear Power Plant The Fukushima Daiichi nuclear disaster occurred at the Fukushima I Nuclear Power Plant on 11th March 2011 as a consequence of the Tohoku earthquake and tsunami. The disaster involved “a series of equipment failures, nuclear meltdowns, and releases of radioactive materials” (IGEM Osaka, 2011). The strong tsunami interrupted the power supply to reactors and led to damage of generators because of uncontrollable flooding of rooms. The damage of generators ceased the circulation of coolant water in the reactor, and this, in turn, resulted in the overheating of reactors. Despite intensive efforts to cool and shut down the reactors, a number of hydrogen explosions occurred. In addition, many workers were exposed to radiation during the course of emergency responsive activities. Although Japanese officials initially estimated the disaster as Level 4 on the International Nuclear Event Scale (INES), the intensity of the accident eventually rose to Level 5 and 6 (World News Inc, 2012). Analysis of the disaster Evidently, tsunami was the main cause of Fukushima nuclear plant disaster. Japanese government argued that the 13-metre high devastating tsunami waves were higher than the Tokyo Electric Power which supplies electricity to run the plant. As a result, authorities could not take any effective measure to prevent the catastrophe or to protect the reactor cores from sustaining extreme damage. Although the magnitude 9 earthquake did not damage the key facilities at the plant, the resulted flooding caused “simultaneous loss of multiple safety functions” (Times Live, 2011). In order to get a detailed view of the underlying causes of the disaster, it is necessary to describe the accident in all the 6 Units in Fukushima nuclear plant. The Unit 1 of the Fukushima nuclear power plant is a “General Electric BWR 3 rated 460 MW electric (1380 MW thermal)” (Nuclear Engineering International, 2011). At the time of the earthquake, the Unit 1 was generating electricity and the earthquake caused automatic shutdown of the Unit. However, the resulted tsunami damaged the emergency core cooling system. As Holt et al (2012) reported, the reactor vessel’s water levels drastically dropped and reached a level below the top of the hot fuel. Similarly, steam reacted with zirconium fuel cladding and produced huge amounts of hydrogen. It is the main cause of the hydrogen explosion that occurred at the upper part of the reactor building (ibid). Nearly after 12 hours, pressure inside the primary containment doubled to the designed level. At the same time, radiation from the plant increased sharply. Scientists believe that overpressurisation might have led to leaking of hydrogen from the primary containment into the upper building structure. TEPCO estimated that whole nuclear fuel in Unit had melted during the disaster because of the massive rise in temperature (25,000o C) and this process caused the damage of reactor pressure vessel (ibid). Venting of the RPV led to an increase in the hydrogen concentration inside the primary containment vessel. Like Unit 1, Unit 2 was also generating electricity at the event of earthquake and gradually it went into an automatic shut down. The 13 metre high tsunami waves flooded a backup diesel generator. Even though the air-cooled generator continued to operate, its electrical switchroom suffered water damaged and subsequently failed to continue its operations (Contents of Summary, n.d). Plant operators tried to fix the problem by bringing a portable generator in Unit 2. However, the hydrogen explosion in the Unit 1 caused the propelling of debris into the portable generator and ultimately the efforts for the restoration of power failed. The breach of the primary containment caused the containment pressure to drop. The breakage of blowout panel in the Unit 2’s outer wall allowed hydrogen to escape from the reactor setting. Since the functioning of all core cooling was halted for over six hours, the hot reactor core became uncovered by water and eventually began to melt. According to TEPCT reports, dysfunction of core cooling system caused the melting of nearly 57% of the fuel in Unit 2. It is suspected that some amount of melted fuel might have fallen to bottom of the RPV. Like the first two cases, the earthquake caused the automatic shut down of the Unit 3 and it lost AC power during the resulted tsunami. As an impact of the disaster, forceful injection of water into the vessels was halted for nearly 36 hours and the cooling system was still at dysfunction when the seawater injection started. The fault of the cooling system led to extreme fuel damage and generation of huge volume hydrogen gas because the reactor core was kept uncovered by water. The level of pressure inside the primary containment structure increased sharply and subsequently plant operators worked hard to vent the primary containment. The secondary containment was destroyed by a severe hydrogen explosion at 11 a.m. on March 14 and this explosion allowed hydrogen to escape from the primary containment (American Nuclear Society, 2012). In addition, the explosion caused widespread damages including destruction of portable generators, hoses, fire engines, and temporary power cables (ibid). Hence, it is clear the hydrogen explosions resulted from the disaster worsened the situation at the plant because this issue prevented plant workers from fixing the technical damages (Micro-Simulation Technology, 2011). In addition, melting of fuel due to the dysfunction of the cooling system also greatly contributed to the severity of the catastrophe. TEPCO officials point that “much of the reactor core of Unit 3 melted but was retained in the reactor vessel.” (cited in Holt et al, 2012). Unlike first three Units, the Unit 4 was not operating when the earthquake occurred. Since the all nuclear fuel of the Unit 4 had been transferred to the spent fuel pool, the cooling system damage did not much affect the reactor core. However, the disaster significantly increased the heat load of the spent fuel pool. A severe hydrogen explosion in the absence of fuel in the reactor pointed towards the spent fuel pool. Early reports reflected that loss of majority of the water in the Unit 4 spent fuel pool resulted in overheating and which in turn led to hydrogen generation. However, later on it was discovered that water in the spent fuel pool had not dropped below the minimum level and hence there was no issue of overheating. TEPCO analysts argue that the hydrogen gas that caused explosion at the Unit 4 came from Unit 3 during the venting process conducted on the precious day. While analysing the design of the Unit 3 & 4, it seems that both these Units share a common exhaust stack. The loss of power during the earthquake and tsunami left Unit 4’s exhaust gas valves left opened. “As a result, when the Unit 3 primary containment was vented, hydrogen and other gases were able to flow backward from the common exhaust stack into Unit 4 and eventually into the reactor building’s air duct system” (Holt et al, 2012). The Unit 4’s exhaust gas filters radiation samples also supported this activity because they showed “higher contamination levels in the filters closest to the common stack” (ibid). Units 5 & 6 are located away from the Units 1-4 and they were not functioning at the time of the earthquake. Tsunami caused the breakdown of four emergency diesel generators at Units 5 and 6; but, air-cooled generator successfully continued its operation (American Nuclear Society, 2012).The working generator was capable of providing uninterrupted flow of power to Unit 6 and later to Unit 5. Holes at the reactor roof were opened to check hydrogen build up. In short, Units 5 and 6 escaped almost undamaged. In total, the damage of core cooling system can be considered as the major cause of Fukushima Daiichi nuclear disaster. In my opinion, tsunami was the major underlying cause of the disaster. The tsunami flooded generator rooms and resulted in power failure, which in turn caused the damage of core cooling systems. As discussed earlier, breakdown of core cooling systems led to melting of fuel and a series of hydrogen explosions. In addition, the Fukushima Nuclear Plant had not taken adequate protective measures to prevent such a huge earthquake and tsunami. Many of the plant’s protective facilities had been imported from the United States. Since they were designed to suit the US conditions where the possibility of ‘Great’ earthquakes is relatively less, they were not recommendable for the Japan’s territory where probability of ‘Great’ earthquakes is high. Japanese government’s negligence also increased the intensity of the catastrophe. The government greatly depended on nuclear power, and on the other hand, it neglected potential risk factors. References American Nuclear Society., 2012. Fukushima Daiichi: ANS committee report, ANS: Special Committee on Fukushima, pp. 1-40, [Online] Available at: Contents of Summary., n.d, pp. 1-47, [Online] Available at: [Accessed 14 April 2012]. Holt, M, Campbell, RJ & Nikitin,, MB., 2012. Fukushima nuclear disaster, Congressional Research Service, pp. 1-12, [Online] Available at: [Accessed 14 April 2012]. IGEM Osaka., 2011. Bio-dosimeter, [Online] Available at: [Accessed 14 April 2012]. Micro-Simulation Technology., 2011. Fukushima event PCTRAN analysis, [Online] Available at: [Accessed 14 April 2012]. Nuclear Engineering International., 2011. Events at unit 1, Fukushima Daiichi Crisis: Simulation, [Online] Available at: [Accessed 14 April 2012]. Times Live., 02 December 2011. Tsunami was a direct cause of Fukushima disaster: Operator, [Online] Available at: [Accessed 14 April 2012]. World News Inc., 2012. Fukushima nuclear plant two flyovers shot In high definition, [Online] Available at: [Accessed 14 April 2012]. Read More