Japanese Earthquake and Tsunami: Fukushima - Research Paper Example

Japanese Earthquake and Tsunami: Fukushima Introduction The nuclear plants at Fukushima are Boiling Water Reactors (BWR), and they generate electricity through boiling water and rotating a turbine with steam from the boiling water. As explained by Okimoto et al. (2011) the nuclear fuel is used to heat the water to create steam, and the steam drives turbines, which generate the electricity. The steam is later cooled and condensed again to water; the process starts again as the water heated by the nuclear fuel to generate steam. The reactor works at nearly 285 Celsius degrees. This paper will briefly examine the terribly Fukushima accident and examine three aspects of that accident on how they relate to the UK’s nuclear safety measures and regulations. One of the aspect will be further be examined. Analysis of events at Fukushima on March 12, 2011 This section gives an overview of the main facts of Fukushima incident. The earthquake that occurred in Japan on that date was more times greater than the worst earthquake the nuclear plant was prepared for. For instance, the earthquake was 8.9 on Richter scale, while the nuclear plant was built to sustain a maximum of 8.2; this means that the earthquake was 5 times more of what was prepared for (Okimoto et al., 2011). When the earthquake happened, all the nuclear reactors at the Fukushima plant automatically went off. Within a few second following the earthquake, the control rods were inserted in the core, which stopped the nuclear chain reaction. At this moment, the NISA (2011) notes that cooling system was to take away the residual heat; this is about 7% of total power heat load on normal operation. However, this was not a normal operation. The earthquake damaged the external power supply of the Fukushima nuclear reactor. This was a difficult accident for any nuclear plant, and such incident is referred as “loss of offsite power.” A nuclear reactor and its backup system is built to manage this kind of an accident by using the backup power system to maintain the operations of the coolant pumps. More so, because the plant went off, it could not generate any electricity. For a period of one hour, the several installed emergency diesel power generators went on and provided the required electricity. Nonetheless, when the tsunami (a rare and larger one) happened, it caused floods to the diesel generators and made them to fail (TEPCO press release (2011). A fundamental aspect of all nuclear power plant structure is “defense in depth.” This aspect results in engineers designing nuclear plants that can resist harsh disasters, even in case of various systems failing. A big tsunami that damages all diesel generators at the same time is also anticipated; however the tsunami that happened that day was not expected at all. Upon the failure of diesel generators, the operators switched on emergency battery powers. However the battery power was designed to last for only 8 hours and after this, the plant operators began emergency operations (TEPCO press release, 2011). The emergency measures taken included starting water injection, they started with seawater and the freshwater that was injected into reactor main circuits. This was meant to stop the fuel melt down that could occur in such a case. Owing to the fact that the plant had lost most of its cooling capabilities the operators had to employ whatever cooling option they had to stop the heat. Though, we may not know every aspect of the accident, there is enough information to determine three aspects in nuclear Safety case being used in UK. The following section will discuss these three aspects. 1. Control and containment of combustible gases As a requirement for design, the production of combustible gases in a nuclear plant has to be reduced in normal operations and even during fault situations. Though high radiation fields’ produces hydrogen from radiolysis of water, the amounts are normally small and under ordinary conditions, the levels of the gases released are comparatively safely managed within the plant. But, very high amounts can be generated during an accident, for example zirconium fuel generation and steam on loss cooling in BWR nuclear cores. According to World Nuclear Association (2011) provision for such case should be developed in BWR, as designed in the PWR. However, gas-cooled nuclear reactors do not generate hydrogen in this manner. In the situation of the Fukushima, there are some arguments that the paths for ventilation of gases from the reactor, maybe, were not updated in accordance to increase global knowledge regarding the possible outcomes of venting in BWR accident situations. Though, not all is known about the specific design aspect of Fukushima-1 reactor, it is possible that shortcomings in venting paths could have worsened the situation, particularly in the destructive explosions that occurred in reactor I and 3. More so it seems that an explosion happened in the suppression pool of reactor 2, probably infringing the primary containment. This could show that a lot of attention ought to be been focused more on the design as well as safety evaluation of the safety of Fukushima reactors. 2. Spent fuel strategies A complicating aspect in the Fukushima incident was the spent fuel kept on the site, specifically in fuel pond in the reactor buildings. for example in reactor unit 4 pond, it is said that there were more than two and half cores that were more than 1,331 of spent fuel kept in the pond that were built close to the reactor. More so, about 6,000 spent fuel elements were kept in the in the main storage pond located on the site, additional quantities of the fuel elements were put in dry storage casks. However, according to Office for Nuclear Regulation (2011), these facilities on the site do not seem to have worsened or contributed to the problems that occurred in Fukushima nuclear plant. Spent fuel ponds in the reactor building forced the operators to employ increased packing density of spent fuel elements because of reduced spare capability in the ponds. Prior to the operators increasing the packing density in the spent fuel pond, they made a lot of consideration regarding the accident as well as the cooling abilities of fuel ponds. This is because increased packing density shortens the available time following the loss of cooling accident, before the boiling of the fuel pond. This thus puts a lot of onus on the dependability of the cooling systems of the reactor and on operator corrective action. 3. Cooling supplies The situations that resulted in this accident were such that new and untested way of supplying coolant in the reactors and the affected fuel ponds were necessary for a number of weeks. According to Office for Nuclear Regualtion (2011a) this led in numerous of tones of contaminated water being amassed on the site with some water leaking into the sea, while some of the water were discharged by the operators to the sea to free tank capacity. In the duration some other cooling could be employed at the Fukushima- 1 reactor, steam pressures went up in the reactors that were affected since the level of water reduced, making the hot fuel to be exposed. This exposure resulting in temperatures that led to zirconium fuel cladding reacting with steam and producing a hydrogen-enriched atmosphere. Accordingly, when the operators in the reactor vented the vessels to reduce steam pressure in the reactor, the vented gases coming from the reactor finally went to other sections of the reactor building, and mixed with air in this building resulting in explosive mixtures. When fresh water supplies were finished, the operators opted to use sea water that they injected in the pressure vessels to ensure fuel cooling. Though this seems a logical measure, it did result to some concerns regarding its long use owing to the possibility for pressure vessel corrosion and probable impairment and heat transfer together with salt deposition occurring on the fuel. An important aspect of most of the nuclear reactors is their ability to “natural” has a cooling capacity in a situation of forced circulation. Further analysis of cooling supplies Though, in UK there we have gas-cooled nuclear rectors and not BWR, the safety rules on regarding the design of the nuclear plant and particularly regarding cooling supplies is one area that can be improved (Waker, 2005). It would be very prudent to reexamine the capability for the coolant replenishment, n case extreme conditions like that happened in Japan occurs to the plants in the UK, when extra supplies on the nuclear plants may be hindered for some duration. Safety plans could thereafter be revised where necessary. At the same time, safety plans on design the motor driven auxiliary of a nuclear plant has to be reexamined. According to the Office for Nuclear Regulation (2011) heat sink normally built for post trip cooling system has to be provided for the essential services water system. This will provide an effective cooling system. According to Office for Nuclear Regulation (2011) the UK gas cooled nuclear reactors have got lower power densities, though they have bigger thermal capacities compared to water cooled nuclear reactors which have a natural cooling capacities that give longer durations for correction action. More so, the Health Safety Executive (2003) report shows that, they have a lower requirement for venting when loss of cooling occurs, and do not generate concentrations of hydrogen that is supposed to come from fuel cladding overheating. Owing to this observation, the UK nuclear plants should reexamine the need for, and where required the capability to provide a long withstanding coolant supplies to the nuclear plants in the country, in case a harsh off-site disruption happens. This is particularly true in a case where an on-site supplies or bigger off-site capacity is required. Conclusion From the discussion in this paper, it has to be understood that to attain sustained high standards of nuclear safety, countries have to follow the principle of “continuous improvement.” Indeed, this principle is outlined in the UK nuclear regulations, whereby there is constant requirement for the nuclear designers as well as the operators so as to reduce nuclear risks as much as practicable possible. This is outlined by the need for detailed regular appraisals of safety to look for more improvements. The Fukushima accident underlines the fact the no matter how good the levels of nuclear design and successive operations are, need for improvement should not stop. Endeavoring to learn from accidents and new knowledge both national and international has to be a basic aspect of safety practices of the UK nuclear industry. Bibliography Health Safety Executive (2003): Literature Review on the Perceived Benefits and Disadvnages of UK safety Case Regimes: Retrieved on 18/9/2011 from: http://www.hse.gov.uk/research/misc/sc402083.pdf NISA (2011): NISA briefing, Seismic Damage Information (12th Release), 12 March 2011, Retrieved on 18/9/2011 from: http://www.nisa.meti.go.jp/english/. Office for Nuclear Regulation (2011): Japanese earthquake and tsunami: Implications for the UK Nuclear Industry, Interim Report: HM Chief Inspector of Nuclear Installations: Retrieved on 18/9/2011 from: http://www.hse.gov.uk/nuclear/fukushima/interim-report.pdf Office for Nuclear Regualtion (2011a): European Council “Stress Tests” for UK Nuclear Power Plants National Progress Report:http://www.hse.gov.uk/nuclear/fukushima/stress-tests.pdf Okimoto, D , Hanson, A, Marvel, A (2011): The nuclear crisis in Japan. (March 2011). Retrieved on 18/9/2011 from: http://iis-db.stanford.edu/evnts/6615/March21_JapanSeminar.pdf. TEPCO press release (2011): Results of the investigation regarding tsunami arrived in Fukushima Dai-ichi Nuclear Power Station and Fukushima Power Station. Waker , C (2005): Nuclear Safety Directorate-Business Management system:http://www.hse.gov.uk/foi/internalops/nsd/tech_asst_guides/tast051.pdf World Nuclear Association (2011): Safety of Nuclear Power Reactors: Retrieved on 18/9/2011 from: http://www.world-nuclear.org/info/inf06.html Read More