Chernobyl Accident (Case Study Sample)

Chernobyl Accident
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Introduction
According to the world nuclear association, a German scientist named Martin Klaproth, discovered uranium in the year 1789. However, it was not until 1895 that Wilhelm Rontgen started working with uranium in ionizing chambers. Over the period of 1895 and 1945, much of the nuclear technology was developed, with some of the resultant technologies and applications filtering to today. Majority of the countries across the globe now use the technology to produce much of their electricity. This has been a viable option as most of the petroleum reserves are now getting depleted and nuclear energy acts as the alternative energy source. However, even with these developments in energy technology, on the 26 April 1986, the world woke up to dreadful catastrophes that took place at Chernobyl nuclear plant near the city of Prypiat in Ukraine. The accidents resulted from a flaw in the designs of the reactors and operated by poorly skilled staffs. Rated as one of the most catastrophic accidents, it claimed two staffs on that days at the firm and later more than 28 over several weeks that followed. Over more than 20 years that followed, the people that were exposed to the radiation from the plant have developed thyroid cancer among other complications other than dying. However in 2011 the Chernobyl site was declared by the Ukrainian government a tourist site following resettlement of the people that lived around the site and restoration of the area.
Technological and Engineering Failures That Led To the Disaster
The nuclear power station was known as V.I. Lenin, and consisted of four reactors, which were of the type commonly referred to as the RBMK-1000. These were huge reactors as they were capable of producing around 1000 megawatts of electric power and 3200 megawatts of thermal power. While the designs of the rectors used after the accident have been modified a little to fit in within the safety standards, a lot has not changed. Currently it is estimated that half of the power that is produced from nuclear sources in Russia and what was previously Soviet Union comes from reactors with the same design as the one that blew up in the early morning of April 26th 1986. This translates to more than 5% of the total power production capacity in the region. As such the influence of these reactors is felt to date. Much of the changes that have been made to the reactors include the lengthening of the rods. At the same time the number of the rods has also been increased to reduce the amount of compromise on the reactivity at the cores. This means that that the reactors now have some form improved ability to control and easily monitor the systems. Other than the rods the systems have been improved through boosting the capabilities of the cooling pumps to handle the level of reactivity and the thermal energy generated at any given time. Previously the cooling systems were complicated and they failed in the events leading to the accident. To deliver more power, the fuel has also been enriched further, by increasing the amount of Uranium 235 within the fuel that can actually fission. Using these improvements, the engineers have been in apposition to limit the type of responses from the system. Ideally, the systems are now less reactive to the kind of mistakes that took place on the night of the accident. In an example the changes to the fuel through further enrichment using Uranium 235, to the tune of about 2.4% has increased safety of the system. The safety of the system has increased in the sense that, power bursts like the one that caused the explosion at Chernobyl are now limited. This is because; power surges do not take place in the presence of the water/steam bubbles as previously experienced.
Much of the reason as to why the accident took place has been attributed to the human error element, as most of the staff at the plant did not follow the proper guidelines as most of them were poorly trained on the severity of the system. However, there are some very crucial technological and engineering flaws in the design of the reactors that also complicated the human errors and possibly fired the disaster even further (Engineeringfailures.org, 2011).
One of the flaws that have been noted in the design of the reactors at the time was the fact that, the neutron fields were too sensitive to the control rods movement. Ideally, in the design of the reactors, there are quite a big number of the absorbers which are basically introduced in the reactor due to the fact that there is a lot of surplus reactivity. This means that the large numbers of absorbers are brought in as a way of compensating the high level of reactivity in the reactor. Moving some of the absorbers especially in the peripheral zones could easily have led to criticality locally (Lallanilla, 2013). At the same time there were more than 15 channels that were actually loaded with fuel; however there were no absorbers in the zone. With these kinds of features it is very hard to control the direction of the reactions. By reducing the number of absorbing rods within the core this increases the steam void coefficient. Due to the large reactivity bouts created, the stability of the power generation is destabilized, with the power stability going down to three minutes. With this kind of spikes in power and poor control, the event of an explosion is practically unavoidable. This is further spiked by the fact that the people in control do not have much of the know how to keep the reactors within their limits without increasing the risk of destabilizing the system.
By the early 70s, engineers understood how to control the steam void coefficient by increasing the number of additional absorbing rods within the core. However, if there were going to be permanently positioned within the core, there was a need to feed the system with much higher enriched fuels. Before the 70s the RBMK reactors used fuel that was enriched up to 1.8%, however now they had to enrich the fuels up to 2%. However, later on the reactors still the problem related to steam void increases. This meant that the engineers had to enrich the fuels even further, which led to the introduction of enriched fuels up to 2.4%. These developments came in later after the accidents to make sure that the engineers had more control of the reactivity (Engineeringfailures.org, 2011).
One other technological failure which aggravated the situation at Chernobyl, was the design used for the various absorbers; that is the ER, SAR and the MR absorbers. According to the design of the absorbers, the displacers on the RBMK are around 4.5 meters in length. When the absorbers are drawn to their top most position well above the core of the reactor, the displacers come to the mid sections of the cores of the reactor. The cores in the RBMK reactors are about 7 meters in height which explains the mid level rise of the displacers as they bring up the absorbers. Water columns in these reactors tend to form above and below the displacers at a height of about 1.25 meters. As such, during the lowering of the absorbers by the displacers back into the core, the water columns are displaced as well from the bottom of the core. The aspect of lowering the absorbers back into the core creates some for of spiked reactivity.
This basically due to the fact that the displacers are made of graphite, at it tends to absorb neutrons at a much slower pace that the water in columns at the base of the cores. However this flaw in design only takes it effects when the absorbers are lowered back to the core after having been raised to the top most position of the reactor (Engineeringfailures.org, 2011). The cooling systems of the reactors were also found to be very complicated. At the same time the speed of lowering the emergency rod into the core was also flawed. Given the reactivity spikes that may take place from time to time, there are emergency and control rods that help with stabilizing the system. In this case, the time it took the rods to reach the core and regulate the power spikes was too long if they had been raised to the top most position. Given that the rods would lower in to the cores at the rate of 0.4 meters per second, relative to the height of the rods, it would take roughly 20 second for the rods to be fully inserted into the cores. This is awfully a lot of time wasted by a mechanism that is supposed to bring control to power spikes that only take second to spiral out of control. For a system that had these many flaws, it did not help that the cooling system is also complicated. This is so, considering that the staffs at the plant were also compromised by the fact that some of them did not have right skill level, other that the fact that those that were skilled also contributed to the disaster, as they had such high levels of negligence. At the same time the coolant used in the cooling system can change its physical state within the core which can be catastrophic.
Sequence of Failures (Test)
On the 25th of April in 1986, the crew was planning to shut down the reactor 4 for maintenance. At the time the crew also decided to test if the slowing turbine had enough capabilities to still produce power for the circulating pumps of the cooling system. This power was to assist to drive the pumps until the diesel power system kicked in, if the power at the station went out. Largely the cause of the accident rests on the miscommunication of the staffs that were coordinating the test and those at the ground carrying out the tests. There were quite a number of safety measures that were by-passed before the total failure of the system which brought about disastrous results.
As part of the program the emergency core cooling system was to be shut down at 1400hr. Even though much of the processes that followed were not affected greatly by this shut down, it goes on to the laxity...