Small modular reactor

Small modular reactors (SMRs) are a type of nuclear fission reactor which are smaller than conventional reactors, and manufactured at a plant and brought to a site to be assembled. Modular reactors allow for less on-site construction, increased containment efficiency, and heightened nuclear materials security. SMRs have been proposed as a way to bypass financial barriers that have plagued conventional nuclear reactors. Small modular reactors (SMRs) are a type of nuclear fission reactor which are smaller than conventional reactors, and manufactured at a plant and brought to a site to be assembled. Modular reactors allow for less on-site construction, increased containment efficiency, and heightened nuclear materials security. SMRs have been proposed as a way to bypass financial barriers that have plagued conventional nuclear reactors. Several designs exist for SMR, ranging from scaled down versions of existing nuclear reactor designs, to entirely new generation IV designs. Both thermal-neutron reactors and fast-neutron reactors have been proposed. The main advantage of small modular reactors is that they could be manufactured and assembled at a central factory location. They can then be sent to their new location where they can be installed with very little difficulty. SMRs are particularly useful in remote locations where there is usually a deficiency of trained workers and a higher cost of shipping. Containment is more efficient, and proliferation concerns could be lowered. SMRs are also more flexible in that they do not necessarily need to be hooked into a large power grid, and can generally be attached to other modules to provide increased power supplies if necessary. The electricity needs in remote locations are usually small and highly variable. Large nuclear power plants are generally rather inflexible in their power generation capabilities. SMRs have a load-following design so that when electricity demands are low they will produce a lower amount of electricity. Many SMRs are designed to use new fuel ideas that allow for higher burnup and longer fuel cycles. Longer refueling intervals can decrease proliferation risks and lower chances of radiation escaping containment. For reactors in remote areas, accessibility can be troublesome, so longer fuel life can be very helpful. SMRs could be used to power significant users of energy, such as large vessels or production facilities (e.g. water treatment/purification, or mines). Remote locations often have difficulty finding economically efficient, reliable energy sources. Small nuclear reactors have been considered as solutions to many energy problems in these hard-to-reach places. Cogeneration options are also possible. Because of the lack of trained personnel available in remote areas, SMRs have to be inherently safe. Many larger plants have active safety features that require 'intelligent input', or human controls. Many of these SMRs are being made using passive or inherent safety features. Passive safety features are engineered, but do not require outside input to work. A pressure release valve may have a spring that can be pushed back when the pressure gets too high. Inherent safety features require no engineered moving parts to work. They only depend on physical laws. There are a variety of different types of SMR. Some are simplified versions of current reactors, others involve entirely new technologies.All current small modular reactors use nuclear fission. When an unstable nucleus (such as 235U) absorbs an extra neutron, the atom will split, releasing large quantities of energy in the form of heat and radiation. The split atom will also release neutrons, which can then be absorbed by other unstable nuclei, causing a chain reaction. A sustained fission chain is necessary to generate nuclear power.SMR designs include thermal-neutron reactors and fast-neutron reactors. Thermal-neutron reactors rely on a moderator to slow neutrons and generally use 235U as fissile material. Most currently operating nuclear reactors are of this type.Fast reactors don’t use moderators to slow down the neutrons, therefore they rely on the nuclear fuel being able to absorb neutrons travelling at higher speeds. This usually means changing the fuel arrangement within the core, or using different fuel types. 239Pu is more likely to absorb a high-speed neutron than 235U.