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Nuclear Power
Published in Robert Ehrlich, Harold A. Geller, John R. Cressman, Renewable Energy, 2023
Robert Ehrlich, Harold A. Geller, John R. Cressman
Nuclear reactor designers also need to decide what fuel to use. The most common choice is uranium, which has been enriched to around 3%–5% of the fissionable isotope 235U. A noteworthy exception is the Canadian Canada deuterium uranium (CANDU) reactor, which was originally designed to use natural (unenriched) uranium, since Canada at the time lacked enrichment facilities. CANDU is a trademarked abbreviation standing for “CANada Deuterium Uranium,” and unlike most reactors, it uses heavy water as its moderator and coolant. The reason for the heavy water is that in a normal light water reactor, while the water may be a very effective moderator in slowing neutrons to energies where they cause fission, it also has the unfortunate side effect of sometimes absorbing neutrons and decreasing the probability that they will reach 235U nuclei and cause fissions. Heavy water—a much poorer neutron absorber, but still an excellent moderator—avoids this problem and allows a reactor to operate at the enrichment level of 0.7% found in nature. Despite its capability, however, CANDU reactors now do operate using enriched uranium, which allows them to operate at higher power levels.
Preliminary considerations: reactor types and characteristics
Published in Peter R. Mounfield, World Nuclear Power, 2017
The CANDU reactor offers a number of advantages: on-load refuelling at full power has enabled the design to lead the world in terms of load factor and reliability; the use of natural uranium results in lower fuel fabrication costs than for PWRs, BWRs and AGRs, which require expensive fuel enrichment facilities. The use of natural uranium makes CANDU reactors virtually inflation proof once they are built. More parts, more processing, more tubing, more pellet-grinding, more hardware and more labour are involved in producing a tonne of LWR fuel than in producing a tonne of CANDU fuel. The use of pressure tubes for fuel in the reactor core allows the coolant to be pressurized without the need for a large steel or reinforced concrete pressure vessel; it is economically competitive with most other proven reactor types for plants of about 500 MWe and over; it is an efficient producer of plutonium; it does not have a high excess of reactivity as do reactors using enriched fuel, and this helps to reduce the likelihood of a major power excursion.
Uranium Enrichment, Nuclear Fuels, and Fuel Cycles
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
The CANDU reactor has a very simple fuel cycle, and because it can run on natural uranium alone, it does not require a gaseous or centrifugal enrichment plant to increase the concentration of U-235 beyond about 0.7%. This means that the fuel from a CANDU reactor is rarely recycled, and the national strategy within Canada as a whole has been to simply dispose of the waste and mine additional natural uranium ore. One advantage of the CANDU reactor is that it can be refueled online (e.g., without shutting down), and the uranium dioxide fuel is exceptionally stable in this environment because the burnup rarely exceeds 10,000 or 20,000 MW days per metric ton. The fuel cycle for a CANDU reactor is shown in Figure 10.45. CANDU reactors can also run on a combination of uranium and plutonium dioxide, which means that they can accommodate a variety of mixed oxide fuels. We will explore the pros and cons of the CANDU design in more detail in Chapter 12.
Mechanism of the Initial States of a Bubble Formation and Departure from a Heated Surface in a Subcooled Flow
Published in Nuclear Science and Engineering, 2021
Maryam Medghalchi, Nasser Ashgriz
The CANada Deuterium Uranium (CANDU) reactor is a Canadian-developed pressurized heavy water nuclear reactor. CANDU reactors comprise a series of horizontal fuel rods inside a high-pressure subcooled flow. The ability to model the nucleation and heat transfer processes in such reactors is essential for their safety as well as for their efficiency. Since full computational simulation of the whole reactor is not feasible, the reactor is simulated using subchannel models, which basically lump certain physics into one large grid. This type of simulation may not be able to realize certain important heat transfer processes that occur, especially during the initial periods of the bubble nucleation.
Of fission and fallout: New Zealand in the nuclear age
Published in Journal of the Royal Society of New Zealand, 2021
The most common design of plant in operation around the world is the PWR, and France and Japan both developed large nuclear programmes in the 1970s and constructed more than 50 operating reactors each. In France more than 75% of electrical power is supplied by nuclear stations. In Canada the natural uranium deuterium-moderated reactor (CANDU) was developed, and some plants built in other countries. While in much of Europe and the US there has been little or no recent construction, more advanced designs with greater ‘fail-safe’ systems have been developed, and more advanced features have been incorporated in recent construction as in South Korea.
Data-Driven Analysis of Ultrasonic Inspection Data of Pressure Tubes
Published in Nuclear Technology, 2018
Panagiotis Zacharis, Graeme West, Gordon Dobie, Timothy Lardner, Anthony Gachagan
CANDU is a type of pressurized heavy water reactor (PHWR) that uses natural uranium as fuel and heavy water [deuterium oxide (D2O)] as both coolant and moderator. The core structural components consist of low neutron absorbing materials (zirconium alloys), and its design enables high neutron economy, which is critical for achieving fission through a sustained chain reaction given that natural uranium has a low fissile content. The core consists of a low-pressure steel tank called the calandria, which contains the moderator and around 480 fuel channels that run across the length of the calandria tank.