A nuclear reactor is any class of devices that can generate and control a self-sustaining series of nucleus split, of a heavy atom into two smaller units which will eventually lead to a chain reaction. Nuclear reactors are mainly used in nuclear power plants as a source of energy. There have been developments in nuclear power industries for some decades now, and a new generation of nuclear reactors is being created to fill in new orders and to enhance safer and reliable operating units. This papers reviews a newer generation nuclear reactor, Gen IV Nuclear Reactor regarding its safety improvements assured soon.
The safety of nuclear reactors relies mainly on the control of nuclear reactivity of which is a measure of a state in which a reactor would be in if it were in a critical state. Subcritical is when the reactor is negative, zero at critically and supercritical when the reactivity is positive. There are various ways of ensuring that reactivity is in control namely, altering the amount of absorber that contends with the neutrons’ fuel, by changing the ratio of neutrons leaking out the system with those that are in the system and lastly by removal or addition of fuel. There are both manual and automatic ways of performing this task.
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The Neutron leakage changes are automatic for instance a power increase will result in a decrease in density of a reactor’s coolant and eventually causing it to boil. This density decrease will result in a system leakage of the neutrons and thus a reduction in reactivity. The control of the neutron population by varying the absorbers can be done manually whereby an operator can change the change the absorbers’ concentration in the coolant (Mahaffy et al., 2015).
Fission takes place at a rapid rate which that does not allow an operator efficient time to observe the state that the system is in and respond appropriately. Luckily, delayed neutrons released by fission products are of great help to the reactor control, a however small percentage compared to the actual neutrons in the reactor it is very much sufficient in facilitating the control and monitoring of the changes occurring in the system and the safe regulation of an operating reactor.
Four distinct Nuclear Reactor Generations include Generation I reactors that were the very first to develop civilian nuclear power, later in the 1960s a better version of it was innovated which is a generation II design or a commercial power reactor. It is the most widely used nuclear reactor in the world today. In its design, quite many elements were incorporated to ensure the safety of the reactor and to minimize potential accidents in case of a malfunction. However, it requires electric power to run and a human controller to activate hence the operating personnel is at significant risk of being hurt or killed in case something goes wrong.
A nuclear reactor of class generation III is the current functioning design; it is a design rendered safe and reliable which was initially developed for naval use. The generation IV design is on a concept stage that will not be operational, not until the 2020s. It will be able to incorporate inherent or passive safety features that do not require operational interventional or active controls to prevent accidents in case of a malfunction and may rely on natural convection, gravitational force, and high-temperature resistance. It is unlike traditional reactors that involve mechanical or electrical operation on command that depend on functioning and engineered components.
Some countries are planning on using Generation IV power which is also known as the next generation of nuclear plants (NGNPs) in their nuclear industries. For a reactor to be classified as an NGNP it has to satisfy some requirements, it should be highly economical, should incorporate enhanced safety, minimal waste is the climax for waste production, and lastly, it should be proliferation resistant.
There is much hope for the Generation IV reactors regarding safety; it will be an opportunity to create a sustainable nuclear reactor for a long term future. A hierarchy of safety standards has been established, to begin with, Safety Fundamentals to Safety Design Criteria and Guidelines and finally Technical Codes & Standards. The Safety Criteria has been explored for a variety of dissimilar systems that are already prototyped (Kok, 2016).
Generation IV systems will mainly involve fast reactors that are going rely on numerous recycling and reprocessing of fuel which will address the proliferation resistance of the fuel cycle. This will result in the unsuitability of nuclear material in making nuclear weapons or other related products. The radiological intensity of the material will be increased; as a result, it will be controlled without any special shielding equipment. Secondly, there will be an assurance that at no point during the fuel cycle will there be a suitable isotopic composition of fuel for the manufacture of the nuclear explosive device and lastly by limiting opportunities for alteration during transportation, intermediate storage and reprocessing.
The system uses sodium as a reactor coolant, the advantage of this is that is that it can function under high temperature and low pressure. Sodium cooled is far much better compared to water since it has demonstrated inherent safety features which would eliminate potential threat like catastrophic accidents. Sodium is also highly compatible with reactor materials, hence the ruling out of corrosion of the nuclear plant. Also, the molten lead can also be used as a coolant as it plays a significant role in heat removal, radiation shielding and relatively compatible with a steam system. It improves the overall operability and makes the system easier for designing.
Contrary to the sodium coolant, a molten salt coolant provides the transparency that enables easier maintenance and inspection of components hence safety is improved. Also, salt can be dissolved in the reactor fuel to facilitate elimination of impurities and cooling of solid fuel.
Gas is also is also advanced to be a reactor coolant in this system whereby Helium is the preferred gas as it shows some special properties. It remains a gas at any temperature; it is entirely inert and very much transparent. It operates under high pressure but lower than water coolant. However this gas coolant is the weakest, this disadvantage is alleviated by it producing a large heat buffer in the form of the graphite structure. The graphite structure is a necessity in these industries as the pressurized gas flow at any given condition ensures safety.
Generation IV is all about modifications from earlier generations whereby safety designs being explored will allow reactors to minimize or completely avoid pressurized operations by using appropriate coolants like sodium cooled to prevent accidents related to this, for example, the Fukushima accident. Automatic reactant shutdowns will also be fitted in these systems in case of an accident. These designs are avoiding the use of water as a coolant to minimize risks situations where there is water leakage (Kim, 2016).
As the General IV development and research are ongoing, a few Gen IV types are already under consideration as a result of multinational interest in these reactors. Industries, governments, and environmentalists are fully supporting Nuclear Energy due to reliable zero emissions electricity (Mahaffy et al., 2015). From the advancements being done, employees working a nuclear plant specifically the Gen IV are being assured of zero accidents with the current strategies being put in place in ensuring that their safety is significantly upheld.
References
Kim, T. K. (2016). Gen-IV Reactors. Encyclopedia of Sustainability Science and Technology , 1-21.
Kok, K. D. (Ed.). (2016). Nuclear engineering handbook . CRC Press.
Mahaffy, J., Chung, B., Song, C., Dubois, F., Graffard, E., Ducros, F., & Moretti, F. (2015). Best practice guidelines for the use of CFD in nuclear reactor safety applications-revision (No. NEA-CSNI-R--2014-11). Organisation for Economic Co-Operation and Development.
