20) A white powder is analyzed and found to contain 43.64% phosphorous and 56.36% oxygen by mass. The compound has a molar mass of 283.88 g/mol. What are the compound's empirical and molecular formulas?
31) A topic not covered by the final exam review is how a nuclear reactor works:
A nuclear reactor is basically a system of recycled water. The water is heated and is turned into steam which travels down a steam line to spin the blades of a turbine. The turbine then turns the shaft of a huge generator, where electricity is produced. The steam then cools down back into water and the cycle repeats. Control rods prevent the reactor from overheating and when they and the fuel rods are spent they are placed in a cooling tank called a "swimming pool".
Thursday, April 7, 2011
April 7, 2011
The Accident at Chernobyl
Nuclear power plants produce electricity when the reactors split atoms of an element. The heat that the nuclear reaction emits creates steam. The steam then powers the reactor’s generator, which in turn creates electricity. The water in the reactor serves as a coolant that prevents the plant and reactor from overheating. The generator ignites the spark while the turbines turn it. Meanwhile, radioactive material heats water into the system in the reactor’s core.
In 1986, an accidental nuclear reaction occurred in Chernobyl, Ukraine due to a poor reactor design and ill-trained employees. Chernobyl lies just about one hundred miles north of Kiev on the border of Belarus and is situated near an artificial lake that once provided cooling water to the reactors. In the Chernobyl Power Complex there were four nuclear reactors of RBMK-1000 design. The Chernobyl 4 Reactor was built by 1983. At the end of a normal workday on April 25, the nuclear power plant was going to run a test involving the plant’s turbines. They wanted to find the amount of time that the turbines would spin to supply power to circulating pumps in case there were to be a loss of “main electrical power supply”. The operators on the night before April 26 were to disable automatic shutdown mechanisms along with the emergency core cooling system that provides water for cooling the core in case there was an emergency. When an operator attempted to shut down the reactor, they noticed that it was unstable. The control rods’ design had caused a huge power surge when they were inserted into the Chernobyl 4 reactor. The reactor’s power was decreasing at a rate much quicker than planned for by the test operators because it was so late at night and they felt pressed for time. In result, fuel elements busted and fission built up in the core, which increased the generation of steam and pressure in the Chernobyl 4 Reactor. The water coolant could not work quickly enough and the increased pressure detached the reactor’s support plate, which in turn, jammed the control rods. To add to the chaos, the control rod tips were made of graphite and just added to the reaction. The reactor lost its coolant and became progressively hotter. The steam and the heat caused two explosions early in the morning of April 26, 1986. The explosions and fires lasted for ten days after the initial explosions, but radiation is still among the Ukrainian town today, as well as its surrounding lands. In the burning Chernobyl 4 Reactor, iodine-131 and cesium-137 were released. Luckily, iodine-131 has a half-life of eight days, so the radioactive isotope disintegrated shortly after the tragic accident. Unfortunately, however, cesium-137 has a half-life of thirty years and is still found in items such as food and soil today. The heavier debris rose up to about one kilometer in the air before settling near the nuclear power plant, but the lighter materials such as fission products were taken away and scattered by the wind. Hundreds of firemen arrived on the scene, but the first ones to arrive received the worst from the radiation. Within the first three months, thirty firemen and operators had died. There were 134 confirmed cases of acute radiation syndrome, which eventually killed 47 of the affected people.
Parts of modern-day Belarus, Russia, and Ukraine were greatly affected by the radiation. Five million people were in contaminated areas and unluckily, there are many ways in which a human being may be affected by the toxic radiation. First of all, the steam can scald someone. Also, radioactive fallout can cause thyroid cancer, mainly found in children. Surprisingly, just simply the fear of radiation can cause severe cases of stress. Another effect of the Chernobyl radiation is the contamination of locally grown food. To prevent inhalation of the contamination, local food is often thrown out in a fallout area, which decreases the amount of nutrients citizens have each day. Also, during the time of the Chernobyl tragedy, many women decided to have abortions due to the fear of having radiated contaminated fetuses. Symptoms of radiation poisoning may include nausea, vomiting, a brief appearance of no illness, headache, and fever. Late symptoms may include dizziness, weakness, fatigue, hair loss, low blood pressure, and the coughing up of blood. At the time of the incident, more than 100,000 people were evacuated from surrounding areas and some of the land today is still contaminated.
Fukushima, today however, in Japan has had more explosions in their nuclear reactors than Chernobyl did almost twenty-five years ago. Chernobyl’s RMBK reactors were Russian models (reaktor bolshoy moshchnosty kanalny) with the coolant of water, similar to Japan’s Light Water Reactors. However, Chernobyl it has been learned from the Chernobyl incident in places such as Japan to not use graphite as a moderator. Also unlike Chernobyl, Japan’s incident was cause by a natural disaster, a tsunami, whereas Chernobyl’s tragedy was a result of employee error and unstable reactor models. Also, the workers at the power plants at Fukushima did as instructed in case of an earthquake emergency, so they are not at fault. In Japan, the power that kept the cooling system running was shut off by the tsunami; therefore, the reactor overheated and caused explosion. Whereas Chernobyl was a badly executed safety test, Japan was simply a freak accident.
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Chernobyl 4 Reactor's control room