Safety Analysis: the Chernobyl Accident - Case Study Example

1 Introduction An accident is an occurrence which is usually caused by human error, or a mechanical malfunction. The consequences of which may affect only the environment or its inhabitants. The effects of which can be short lived or long term. Some of the most infamous accidents which have besieged mankind have assumed a number of different causative classifications. Some of the most infamous accidents which have affected mankind are: “The failure of the Banqiao Dam (Henan, China, 1975) – where an estimated 26,000 people died from flooding and another 145,000 died from subsequent epidemics and famine” (Wikipedia). “The Bhopal disaster (India, 1984) – the death toll was nearly 3,000 deaths initially, and at least another 15,000 have died from related illnesses” (BBC) “…On the morning of December 3, 1984, a holding tank with 43 tonnes of stored MIC from the Union Carbide factory, overheated and released toxic MIC gas mixture, which, being heavier than air, rolled along the ground through the surrounding streets. The transportation system in the city collapsed and many people were trampled trying to escape”(BBC). “…The chemical accident was caused by the leakage of water into methyl isocyanate holding tank E610, due to slip-blind water isolation plates being excluded from an adjacent tank's maintenance procedure. The resulting reaction generated a major increase in the temperature of liquid inside the tank (to over 200°C). The MIC holding 2 tank then gave off a large volume of toxic gas, forcing the emergency release of pressure”(Wikipedia) According to the Bhopal Medical Appeal, “around 500,000 people were exposed to the leaking gas. Approximately 20,000 to this date are believed to have died as a result; on average, roughly one person dies every day from the effects”(BMA). Hundreds of thousands continue to suffer the effects of the disaster, such as breathing difficulties, cancer, serious birth-defects, blindness, gynecological complications and other related problems. “The Jilin chemical plant explosions in Jilin City, Jilin Province, China, were a series of explosions which occurred over the period of an hour on November 13, 2005 in the No.101 Petrochemical Plant..The blasts created an 80 km long toxic slick in the Songhua River, a tributary of the Amur. The slick, predominantly made up of benzene and nitrobenzene, passed through the Amur River over subsequent weeks. The explosions killed six, injured dozens, and caused the evacuation of tens of thousands of residents”(Wikipedia). “The cause of the blasts was initially determined two days after the blast: the accident site is a nitration unit for aniline equipment. T-102 tower jammed up but was not handled properly, hence the blasts” (PeoplesDaily) “…The blasts were so powerful that they shattered windows at least 100 to 200 meters away from the scene of the explosions. At least 70 people have been injured and six were killed”(Pravada 2000) The city of Chernobyl was evacuated in 1986 due to its namesake disaster. The 3 nuclear power plant is located nine miles north – northwest, which places it in the Chernobyl Raion district. The city today is mostly uninhabited, there remains a small number of persons who reside in houses which bear signs that state, “owner if this house lives here”. Before the city was evacuated, there were approximately 55,000, who called this place home. There were a number of ordinary workers and administrative personnel Who were stationed in what has become to be known as the Zone of Alienation. All of these persons have since been evacuated due to increasing radiation levels, which has rendered the area unsafe. The contamination of milk was subsequently associated with the illness of babies across Europe. The City of Chernobyl and its surrounds are now the domain of nuclear scientists and as assortment of radiation experts, physicists, and other types looking for present and long term affects of the nuclear disaster. Through a controlled renovation process, Chernobyl presently has 500 residents. The curiosity of prospective visitors has prompted the construction of a lodge to accommodate visitors to the Zone of Alienation. “…Scientist report mammals experiencing heavy doses from internally deposited Caesium – 137 and strontium – 90 radioactive fallout”(Vidal) “… One study has found mutations in 18 generations of birds, another that radioactivity levels are still rising”(Vidal. “Levels of Caesium – 137 are expected to remain high all over Europe for decades, says the United Nations. “Everyone who helped in the clean-up is now ill”, “the situation is worsening. In 1985 we had four lymph cancers a year. Now we have seven times that many, we have 4 between five and eight people a year with rare bone cancers, when previously, we never had any. We expect more cancers and ill health. One in three pregnancies are malformed. We are overwhelmed”(Titiana) A doctor in the local regional hospital says; …“The children born to people who cleaned up Chernobyl are dying very young. We are finding Caesium and strontium in breast milk and placenta. More children now have leukemia’s, and there has been a quadrupling of Spina bifida cases. There are more clusters of cancers. Children are being born with stunted growth and dwarf torsos, without thighs. I would expect more of this over the years”(Hell on Earth) Description of Accident During the nights of April 25 – 26,1986, the Chernobyl reactor explosion released 100 times more radiation than the atom bombs which were dropped by the United States over Nagasake and Hiroshima. This unfortunate accident provided the Chernobyl occurrence with the distinction as being “the greatest industrial disaster in the history of human kind. At 1:23 on April 26, 1986: A test of the cooling system began in unit no.4 of the Chernobyl power plant. At 1:23:40: The engineering shut down failed. The unstable state of the reactor did not show on the control panel, and it appeared that none of the members or the reactors crew were cognizant of the impending dangers. “…The steam to the turbines was shut off and, as the momentum of the turbine generator drove the water pumps, the water flow decreased, decreasing the absorption of the neutrons by the coolant. The turbine was disconnected from the reactor, 5 increasing the level of the steam in the reactor core. As the coolant heated, pockets of the steam found voids in the coolant lines. Due to the RBMK reactor-type’s large positive void coefficient, the steam bubbles increased the power of the reactor. As soon as the reactor power increased, the positive feedback that had acted to drive reactor power down, now acted to increase it further. As power increased, the Xe – 135 poison began to be burned faster than it was being produced by I -135 decay, which increased power, resulting in a faster Xe – 135 burn, and so on. With the manual and automatic control rods removed, nothing prevented a runaway reaction”(CNPP) Reactor diagram. Source: OECD NEA 6 “…At 1:23:40 the 4th reactor exploded, as the workers attempted to perform a test on the reactors safety systems, and in the process the computer controlled safety systems were disabled”(Wikipedia) the operators pressed the AZ-5 (Rapid Emergency Defense 5”) button that ordered a “scram” – a shutdown of the reactor, fully inserting control rods, including the manual control rods that had been incautiously withdrawn earlier. It is unclear whether it was done as an emergency measure, or simply as a routine method of shutting down the reactor upon the completion of the experiment (the reactor was scheduled to be shut down for routine maintenance). It is usually suggested that the Scram was ordered as a response to the unexpected power increase”(Wikipedia). Engineering Failure According to Anatoly Dyatlov in Chernobyl How Did It Happen, the occurrence took the following course: “…The slow speed of the control rod insertion mechanism (18–20 seconds to complete), and the flawed rod design which initially reduces the amount of coolant present, meant that the SCRAM actually increased the reaction rate. At this point an energy spike occurred and some of the fuel rods began to fracture, placing fragments of the fuel rods in line with the control rod columns. The rods became stuck after being inserted only one-third of the way, and were therefore unable to stop the reaction. At this point nothing could be done to stop the disaster. By 1:23:47 the reactor jumped to around 30 GW thermal, ten times the normal operational output. The fuel rods began to melt and the steam pressure rapidly increased, causing a large 7 steam explosion. Generated steam traveled vertically along the rod channels in the reactor, displacing and destroying the reactor lid, rupturing the coolant tubes and then blowing the lid off the reactor”(Dyatlov). Additionally the Nuclear Energy Authority (2002), offered the affect of the continuation of the engineering breakdown described by Dyatlov; “…After part of the roof blew off, the inrush of oxygen combined with the extremely high temperature of the reactor fuel and graphite moderator, started a graphite fire. This fire greatly contributed to the spread of radioactive material and the contamination of outlying areas”(NEA 2002). An assessment of the incident According to the CNPP states that: “…the reactor had a dangerously large positive void coefficient. The void coefficient is a measurement of how the reactor responds to increased steam formation in the water coolant. Most other reactor designs produce less energy as they get hotter, because if the coolant contains steam bubbles, fewer neutrons are slowed down. Faster neutrons are less likely to split uranium atoms, so the reactor produces less power. Chernobyl’s RBMK reactor, however, used solid graphite as a neutron moderator to slowdown neutrons, and neutron-absorbing light water to cool the core. Thus neutrons are slowed down even if steam bubbles form in the water, increasing an RBMK (1000) reactors temperature means that more neutrons are able to split uranium atoms, increasing the reactors power output. This makes the RBMK (1000) design very unstable at low power levels, and prone to suddenly increasing energy production to dangerous levels if the temperature rises. This was counter-intuitive and unknown to 8 the crew”(CNPP) Analysis of Cause and Circumstances Critical to the process, the operators disabled all of the safety systems down to the generators, this prevented the main process computer (S.K.A.L.A.), from being able to shut down the reactor or reduce the power. Under normal circumstances or conditions the reactor would have commenced to position the control rods. Additionally the computer would have started the “Emergency Core Protection System”. The time lapse would have consumed 2-5 seconds and 24 control rods would have been inserted in the active zone. It should be noted, that even by 1986 standards, this time line would be characterized as a bit retarded. The human operators were taking their cues from the process computer, which essentially malfunctioned, coupled with the fact that the human operators were not highly skilled or experienced with nuclear reactors. It is alleged that the plant operators violated plant procedures and were deficient in their knowledge of the necessary safety requirements which the RBMK 1000 design required. They did not have a thorough knowledge of the reactors design and they also lacked the necessary experience and were not sufficiently trained. Additionally the management team at the plant was comprised of personnel who were not qualified RBMK personnel. The director of the management team did have experience and training in a cold-fired power plant. The chief engineer, was also a veteran from a conventional plant, the deputy engineer of reactors 3 and 4, had only limited experience, and that experience was with nuclear reactors much smaller than Chernobyl. 9 There were a number of procedural shortcomings which were attributed to the cause of the accident. Primary was the lack of communication between the operators in charge of the experiment and the safety officers. “…To reduce costs, and because of its large size, the reactor had been constructed with only partial containment. This allowed the radioactive containments to escape into the atmosphere after the steam explosion burst the primary vessel”(Wikipedia) “…The reactor had also been running for over one year, and was storing fusion by products, these by products pushed the reactor towards disaster”(Wikipedia). “…AS the reactor heated up, design flaws caused the reactor vessel to wrap and break up, making further insertion of control rods impossible”(Wikipedia). Summary of findings “Chernobyl was a human-caused power excursion causing a steam explosion resulting in a graphite fire, uncontained, which lofted radioactive smoke high into the atmosphere – TMI was a slow, undetected leak that lowered the water level around the nuclear fuel, resulting in over a third of it melting”(Wikipedia) Chernobyl, was the worst nuclear power plant accident in history and the only instance so far of level 7 on the International Nuclear Event Scale, resulting in a severe nuclear meltdown. “Far fewer people died as an immediate result of the Chernobyl event than died at Hiroshima, and the eventual total is also significantly less when including those predicted by the World Health Organization to die in the future. Due to the differences in half life the different radioactivity fission products undergo exponential decay at different rates. Hence the isotopic signature of an event where more than one radioisotope is involved will change with time”(Wikipedia) “Some simplistic comments have been made in which the radioactive release of the Chernobyl event is claimed to be 300”(CDAS) or 400 (Guardian 2006) times that of the bomb dropped on Hiroshima . The work of SCOPE suggests that,” the two events can not be simply compared with a number suggesting that one was XX times larger than the other. The radioactivity released at Chernobyl tended to be more long lived than that released by a bomb detonation hence it is not possible to draw a simple comparison between the two events”(SCOPE). “There are two official theories about the main cause of the accident. The first was published in August 1986 and effectively placed the blame solely on the power plant operators. This is known as the flawed operators theory”(Wikipedia) “The second theory, proposed by Valeri Legasov and published in 1991, attributed the accident to flaws in the RBMK reactor design, specifically the control rods. This theory is called the flawed design theory”(Wikipedia) Changes in Design, Operating Procedures The trouble at the Chernobyl plant did not end with the disaster in reactor 4. The damaged reactor was sealed off and 200 metres (660 ft) of concrete was placed between the disaster site and the operational buildings . “A more significant flaw was in the design of the control rods that are inserted into the reactor to slow down the reaction. In the RBMK reactor design, the control rod end tips were made of graphite and the extenders (the end areas of the control rods above the end tips, measuring 1-metre (3 ft) in length) were hollow and filled with water, while the rest of the rod – the truly functional part which absorbs the neutrons and thereby halts the 11 reaction – was made of boron carbide. With this design, when the rods are initially inserted into the reactor, the graphite ends displace some coolant. This greatly increases the rate of the fission reaction, since graphite is a more potent neutron moderator (a material that enables a nuclear reaction) and also absorbs far fewer neutrons than the boiling light water. Thus for the first few seconds of control rod activation, reactor power output is increased, rather than reduced as desired”(Wikipedia) “A fire broke out in reactor 2 in 1991; the authorities subsequently declared the reactor damaged beyond repair and had it taken offline. Reactor 1 was decommissioned in November 1996 as part of a deal between the Ukrainian government and international organizations such as the IAEA to end operations at the plant. On December 15, 2000, then-President Leonid Kuchma personally turned off Reactor 3 in an official ceremony, effectively shutting down the entire plant”(Wikipedia) “In September 2007, Ukraine approved the building of a steel casing over the reactor. The casing, to be built by the French firm Novarka, will be at a cost of $1.4bn. The arch shaped structure, which will measure 190 m (623 ft) wide and 200 m (660 ft) long, is scheduled to take 5 years to complete. Once the structure is complete, dismantling of Reactor 4 will begin”(BBC News) Conclusion It is probably now clear to all parties that there are basic things which must be done, whenever any entity is contemplating the establishment of a nuclear power plant. Since the affects and impact of a mishap can affect not only the local environment where an accident might take place, but an accident can represent a major and life threatening 12 impact on an international level. The design of a nuclear plant should be subject to the approval of an international commission of experts. Additionally, the phases of construction; material quality and the integrity of the construction, should be monitored by an impartial international consortium. This is to assure that no short cuts are taken, and that the most appropriate equipment and materials are selected. When it comes to staffing the plant, there must be specific mechanisms which guarantee that the personnel is trained in every aspect of the operation of the plant and is professionally aware of the function of its components. It is also critical for management to create an environment which is open to there should under no circumstances be situations where personnel is hired if they are not qualified. Particularly, if the organization does not have a bona fida training program in place. Given the sensitivity of the work, all personnel should be required to undergo periodic reviews. These reviews should be both job specific and general knowledge of the entire operation. Communication between all levels of the operation, and the placement of safety regulations, which should be monitored by management on a weekly basis if not daily.It is imperative for every employee to be aware of what needs to be done, if any scenario arises. Bibliography British Broadcasting Company News, Chernobyl to be covered in steel Chernobyl Nuclear Power Plant Comparison of damage among hiroshama/Nagasaki, Chernobyl and Semipalatinsk,retrieved on line on April 14, 2008, from http://www.hiroshima-cdas.orjp Dyatlov, A. Chernobyl How did it happen Nuclear Energy Authority Peoples Daily on line, (2005), Five dear, one missing, nearly 70 injured after chemical plant blasts, November 15, 2005 Pravda, (2005) Chemical plant explosion in China, one confirmed dead, November 15, 2005 Vidal, J., Hell on Earth, Guardian Wednesday April 26, 2006, retrieved on line on April 12, 2008, from www.society.guardian.co.uk Read More