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Rocketry
Published in Jonathan Allday, Apollo in Perspective, 2019
The neutrons produced by the reaction can go on to collide with other uranium nuclei and cause further reactions that will, in turn, produce more neutrons and other particles. This continuing process is called a chain reaction. Once a chain reaction is started, by introducing neutrons into the reactor, the reaction becomes self-sustaining, if the system is engineered correctly. The neutrons produced by the reaction have to have a good chance of colliding with other uranium nuclei, for example. In a practical reactor, the reaction is regulated by control rods – cylinders of a neutron-absorbing material that are lowered into the reactor core. The further inside the core the control rods sit, the greater the number of neutrons that are absorbed and the slower the reaction rate, and vice versa.
Some different kinds of reactors
Published in Kenneth Jay, Nuclear Power, 2019
Ordinary water is a good moderator, except that it absorbs neutrons quite strongly; enriched fuel is therefore necessary. Water is cheap and hence can be used as coolant as well as moderator; its effectiveness in slowing neutrons makes for a small reactor. It has the drawback that, at ordinary pressures, it boils at a low temperature and therefore must be used under considerable pressure if reasonably high steam temperatures are to be achieved. At the desirable higher temperatures it is corrosive. Two types of water-moderated reactor have been widely studied, especially in the U.S.A. In one, the pressurized-water reactor, the water is maintained under high pressure and not allowed to boil but is used to transfer heat to a secondary circuit in which steam is generated. In the other, the boiling-water reactor, the water is allowed to boil in the reactor core and the steam used to drive a turbine directly.
Electric Power Production
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
Two different systems of nuclear steam production are used for commercial electric power generation: boiling water reactors (BWRs) and pressurized water reactors (PWRs). Both the BWR and PWR systems utilize a steel pressure vessel that contains a core of fuel bundles consisting of the fissionable material. Control rods made of neutron-absorbing cadmium are used to control the intensity of the reaction by insertion and extraction from the reactor core. As the control rods are removed, a point will be reached when the reactor goes critical, i.e., a fission chain reaction is sustained. Reinsertion of the control rods slows the reaction. Both the BWR and PWR systems utilize ordinary water (as opposed to heavy water, D2O) as the working fluid and thus are referred to as light water reactors (LWRs). Heat from the fission reaction is transferred to the water as it flows through the reactor core.
Development of the NuScale Power Module in the INL Modelica Ecosystem
Published in Nuclear Technology, 2021
Konor Frick, Shannon Bragg-Sitton
Control rods sit above the reactor core and consist of neutron-absorbing material that is capable of reducing or increasing reactor power by introducing or removing reactivity. Control rods are typically separated into banks whereby clusters of control rods move in unison. This allows for a reduction in individual controllers and allows for simultaneous core-wide control. Further, control banks have a mechanized laddering system, similar to a link in a chain, that ensures they cannot be inserted or removed too quickly from the core, potentially causing a power excursion. These mechanized ladder systems have a set number of steps that a control bank can be inserted or removed, and the control banks cannot be inserted a noninteger number of steps. To compensate for this limitation, control banks are typically inserted one after another with some level of overlap. This overlap helps ensure stability in the core.
Design and Neutronic, Thermal-Hydraulic Analysis of DSCF Assembly for a SMR and Investigation of the Effect on the Thermal Power Uprate
Published in Nuclear Technology, 2023
Hossein Zayermohammadi Rishehri, Majid Zaidabadi Nejad
The NuScale reactor uses a NC system for core cooling during normal operation. Because of the NC, the NuScale does not need pumps to allow coolant to flow in the core. The coolant is heated by passing through the reactor core. Then the density of the coolant decreases due to the heat of the core and rises upward in the closed cycle. As soon as the heated coolant reaches the top of the pressure vessel, it flows into the steam generators and cools there. Then the density of the coolant increases again, and it is pulled down by gravity. Hence, it is important to consider the NC criteria in the design of the new fuel for this reactor.
Techniques to derive additional information of operation actions for computer-based operating procedure
Published in Journal of Nuclear Science and Technology, 2018
Tulis Jojok Suryono, Akio Gofuku
Reactor trip occurs due to low pressurizer pressure level and automatically trips the turbine and main feedwater system. It will decrease the core power to decay the heat levels, terminate the steam flowing through the turbine, and actuate the steam dump (turbine bypass). During an accident, the reactor trip is automatically done by the safety system. Reactor trip is indicated by the insertion of control rods to the reactor core. The control rods will absorb the neutrons for producing fission reaction and stop heat production in the reactor core.