Safety of Nuclear Power Plant

Topics: Nuclear fission, Nuclear power, Electricity generation Pages: 5 (1794 words) Published: June 17, 2013
Question 3
A nuclear power plant (NPP) make used of its nuclear power to generate electricity. The expression “nuclear power” is defined as a controlled release of energy by nuclear fission or nuclear fusion reactions (Nuclear Power, 2004, p. 2809). The world’s first exposure to nuclear power came with the detonation of two atomic bombs over the Japanese cities of Hiroshima and Nagasaki in 1945 by the army of the United State of America (Nuclear Power, 2004, p. 2809). At that time, scientists believed that the power of nuclear energy can be harnessed for effective use such as the generation of electricity instead of weapons. Currently, there are approximately 430 nuclear reactors devoted to the generation of electricity operating worldwide (Nuclear Power, 2004, p. 2809). In general, NPP consists of a reactor, coolant system, electrical power generation unit, and safety system (The Nuclear Power Plant, 2004, p. 2810). The main source of energy created for the generation of electricity happens in a nuclear reactor in which neutrons are collided with uranium-235 or plutonium-239 (fuel) to create a nuclear fission reaction (The Nuclear Power Plant, 2004, p. 2810). Products of energy, fission products and free neutrons are released (The Nuclear Power Plant, 2004, p. 2810). Therefore, chain reactions will continue to occur. To obtain a controlled release of energy, there must be a constant reliable flow of neutrons (The Nuclear Power Plant, 2004, p. 2810). A moderator and control rods are used to reduce the speed and number of neutrons respectively (The Nuclear Power Plant, 2004, p. 2810). “Coolant such as pressurized water, liquid sodium, or carbon dioxide gas” is used to absorb the heat energy produced in the reactor to allow it to boil or the heat absorbed is used to boil water (The Nuclear Power Plant, 2004, p. 2810). The steam produced is used to turn the turbine which in turn, turns the generator to produce electricity (The Nuclear Power Plant, 2004, p. 2810). Although NPP has the advantage over coal power plant when it comes to electrical generation in terms of reducing the air pollution, however, the process of nuclear fission in the NPP produces unstable isotope which emits high level of radioactive material. If the government were to build a NPP, an appropriate safety system must be incorporated into the NPP in order to ensure the safety of workers and general public in the area. One common type of nuclear reactor is the pressurized water reactor (PWRs). Its reactor pressure vessel (RPVs) is where the nuclear fission will occur. Therefore, “it is the penultimate barrier to the release of radioactivity from the nuclear reactor core to the environment” if the containment is destroyed. It must be a tough RPV to withstand the impact of nuclear fission (Tipping, 2010, p. 614). The vessel is built using tough low alloy ferritic steel by heat treatment, forging and welding (Tipping, 2010). In order to prevent steel corrosion, the steel is internally coated with austenitic stainless steel or zirconium alloy (Tipping, 2010, p. 614,615). However, the RPV especially the core beltline area might result in neutron embrittlement issues due to high neutron fluence (Tipping, 2010, p.615). Particularly, during a large loss-of-coolant-accident (LOCA), the RPV will undergo pressurized thermal shock (PTS) which causes rapid cooling of the RPV inner wall (Tipping, 2010). The rapid cooling with the combination of high internal pressure causes large thermal stress, hence, potential embrittlement. A method called thermal annealing is used to “heal” neutron-induced microstructural damage to the RPV whereby it is heated to 4750C and remain constant for 150 hours before the RPV is slowly cooled down (Tipping, 2010, p.617). A RPV has a control rod drive mechanisms (CRDMs) located at the upper closure head (Tipping, 2010, p.618). CRDMs allow control rod assemblies (CRAs) to be inserted into the core to absorb the excess neutrons. Without the...

References: 1. Nuclear Power. (2004, February). Gale Encyclopedia of Science 3, p. 2809.
2. The Nuclear Power Plant. (2004, February). Gale Encyclopedia of Science 3, p. 2810.
3. Tipping, Philip G. (2010). Understanding and Mitigating Ageing in Nuclear Power Plants - Materials and Operational Aspects of Plant Life Management (PLiM). (pp: 614-624). Woodhead Publishing.
4. Nuclear Waste Management. (2004, February). Gale Encyclopedia of Science 3, p. 2811.
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