INTRODUCTION TO NUCLEAR TECHNOLOGY MEHB513 SEM 2,2014/2015 GROUP PROJECT : EVALUATE THE IMPACTS OF THE FUKUSHIMA NUCLEAR ACCIDENT ON THE TECHNOLOGY DEVELOPMENT OF NEW NUCLEAR PLANT MOHD FAIZ BIN ABDUL AZIZ ME MUHAMMAD ASYRAF BIN HAMDAN ME WAN ZUL IZZE IRFE BIN WAN AZMI ME087978

INTRODUCTION The Fukushima Daiichi Nuclear Power Plant is a disabled Boiling Water Reactor (BWR) nuclear power plant. First commissioned in 1971, the plant consists of six boiling water reactor (BWR) Fukushima was the first nuclear plant to be designed, constructed and run in conjunction with General Electric, Boise, and Tokyo Electric Power Company (TEPCO) The plant suffered major damaged from the magnitude 9.0 tsunami and earthquake that hit Japan on March 11, 2011 The sister plant Fukushima II Nuclear Power Plant, or Fukushima Dai- ni (“number two”), is located to the south and also run by TEPCO. It did not suffer a serious accident during the tsunami as cooling continued uninterrupted after the disaster.

PLANT SITTING & PLANT LAYOUT Originally, the plant was to be placed on the top of a hill 35 meters above sea level but was instead dug in just 10 meters above sea level, vulnerable to the 13 meter tall tsunami. By contrast, the nuclear plant in Onagawa was built on an embankment 14 meters above sea level and was able to escape the disaster relatively unscathed, despite being closer to the earthquake’s epicentre

EARTHQUAKE ON large scale tsunami, followed after strong earthquake of M=9 overflow nuclear power plant Fukushima Daiichi. The earthquake occurred under the sea about 70 km eastern of Oshika peninsula at the depth of about 32 km. It was the most powerful earthquake that had ever hit Japan, and fifth the strongest in the world since official modern record began in This earthquake triggered big tsunami which wave reach up to 40 m in Iwate prefecture. The wave height was smaller on another locations, being about 8 m in Fukushima area.

TSUNAMI The plant was protected by a seawall protection designed to withstand a 5.7 m tsunami. However, the 8-14 meters tsunami wave arrived 15 minutes after the earthquake. Obviously this was not enough high to protect against tsunami on The entire plant was flooded, including low-lying generators and electrical devices in reactor basements. Connection to the electrical grid was broken.

Figure 1-The schematic diagram for unit 1 of Fukushima Daiichi plant

Reactor Service Floor (Steel Construction) Concrete Reactor Building (Secondary Containment) Reactor Core Reactor Pressure Vessel Containment (Dry well) Containment (Wet Well) / Condensation Chamber Spent Fuel Pool Fresh Steam line Main Feedwater Plant Reactor and Design

Table 1- The description of each unit reactor in the Fukushima Daiichi reactor

SITUATION AT THE TIME OF THE QUAKE At the time of the quake, reactor 4 had been de-fueled while 5 and 6 were in cold shutdown for planned regular maintenance (refueling). Reactors 1,2 and 3 were operating. At the moment of the quake, reactors were shut down automatically. Emergency generators started to run to pump the water needed to cool the reactors. OVERHEATING OF REACTORS AND SPENT FUEL POOL There were three independent cooling systems. All three cooling systems failed; some of them because connection to the electricity was interrupted. Independent cooling based on generators was also broken, because they were flooded by tsunami. Without any cooling, reactors and spent fuel pool started to heat due to the radioactive decay of fission products. Soon after the tsunami, evidence arose of partial core meltdown in reactors 1, 2, and 3.

MIGITATION STRATEGIES Active core debris cooling is required Core debris cooling is an important element of a robust strategy for mitigating releases. If debris cooling is not provided through water injection or spray into the drywell, containment failure or bypass is likely. Without core debris cooling, the containment can be challenged in several ways

Spraying the containment atmosphere is beneficial. Spraying the drywell atmosphere reduces the airborne fission products in containment. Research had confirmed that the amount of fission products removed using a particular strategy (as measured by the decontamination factor [DF]) is higher when sprays are used. Research also had confirmed that an effective spray pattern can increase the overall containment DF by a factor of two, as compared to a containment flooding case.

Venting prevents uncontrolled release and manages hydrogen. Helps manage the buildup of hydrogen and other no condensable gases generated during the core melting process. Venting maintains the containment pressure below the design pressure and removes hydrogen and other gases from containment Low-efficiency filters can further reduce radionuclide releases The research indicate that several of the combined strategies could reduce radiological releases significantly, with DFs greater than These combined strategies could potentially be enhanced by adding a low- efficiency filter to the vent path to provide additional fission product capture

SAFETY FACTOR The safety factor that improved after the tsunami hit Fukushima : Significant case that have been stress out by researchers and expertise were about the safety problems that occurred inside the NPP itself The accident cause severe damages on that cooling system

1.On 1967, layout of the emergency-cooling system have been addressed. On 27 February 2012, NISA ordered TEPCO to report by 12 March 2012 regarding its reasoning in changing the piping layout for the emergency cooling system 2.Separated the piping systems for two reactors in the isolation condenser from each other 3.The isolation condenser should have taken over the function of the cooling pumps, by condensing the steam from the pressure vessel into water to be used for cooling the reactor 4.TEPCO installed doors to prevent water from leaking into the generator rooms 5.A key Near-Term Task Force (NTTF) recommendation was that such a “risk-informed” approach to safety be installed as the basis for regulation, and need to concur 6.Government issued notices for mandatory evacuation of residents within 12 miles of the site and voluntary evacuation within 18 miles of the site immediately following the declaration of a site emergency