Core, nuclear reactor

The thermal rockets, other than chemical rockets,. currently at the furthest state of development are surface heat transfer rockets. The term surface heat transfer is used to imply that thermal energy is transferred to the propellant through a material wall. Many sources of the thermal energy are possible and include solid core nuclear reactors, radioisotopes, electrical resistance heaters, and solar heaters. 

SEFIDVASH, F. Fixed bed suspended core nuclear reactor concept, Kerntechnik, 68 56-59 (February 2003),... 

Many of the HEAs contain cobalt, which is not a desirable material for in-core nuclear reactor applications due to the neutron-induced transmutation to produce °Co that can make some plant maintenance activities more difficult (due to normal corrosion processes that cause atomic deposition of core materials throughout the primary coolant loop, particularly in the cooler regions). Some single-phase HEAs with attractive mechanical properties that do not contain cobalt have been manufactured [116]. Tensile properties for a single-phase fee high-entropy alloy are summarized in Fig. 16.6. 

Energy Use and Conservation. A variety of materials are needed for high performance thermal insulation, particularly as components of nuclear reactors. Replacements for asbestos fibers are needed for components such as reactor core flooring, plumbing, and packaging. The fibers must be very resistant to high temperatures with outstanding dimensional stabiHty and resistance to compression. 

Most nuclear reactors use a heat exchanger to transfer heat from a primary coolant loop through the reactor core to a secondary loop that suppHes steam (qv) to a turbine (see HeaT-EXCHANGETECHNOLOGy). The pressurized water reactor is the most common example. The boiling water reactor, however, generates steam in the core. 

A number of pool, also called swimming pool, reactors have been built at educational institutions and research laboratories. The core in these reactors is located at the bottom of a large pool of water, 6 m deep, suspended from a bridge. The water serves as moderator, coolant, and shield. An example is the Lord nuclear reactor at the University of Michigan, started in 1957. The core is composed of fuel elements, each having 18 aluminum-clad plates of 20% enriched uranium. It operates at 2 MW, giving a thermal flux of 3 x 10 (cm -s). The reactor operates almost continuously, using a variety of beam tubes, for research purposes. 

Because of their low thermal conductivity, high temperature capability, low cost, and neutron tolerance, carbon materials make ideal thermal insulators in nuclear reactor environments. For example, the HTTR currently under construction in Japan, uses a baked carbon material (Sigri, Germany grade ASR-ORB) as a thermal insulator layer at the base of the core, between the lower plenum graphite blocks and the bottom floor graphite blocks [47]. 

T. D. Burchell, M. O. Tucker and B. McEnaney. Qualitative and Quantitative Studies of Fracture in Nuclear Graphites, Materials for nuclear reactor core applications. BNES, London, 1987, pp. 95-103. 

Chapter 6 was concerned, with determining the probability of various failures leading to insufficient core cooling of a nuclear reactor. This chapter describes how the accident effects are calculated as the accident progresses from radionuclide release, radionuclide migration within the plant, escape from retaining structures, atmospheric radionuclide transport and the public health effects. 

The heart of the nuclear reactor boiler plant system is the reactor core, in which the nuclear fission process takes place. Nuclear fission is the splitting of a nucleus into two or more separate nuclei. Fission is usually by neutron particle bombardment and is accompanied by the release of a very large amount of energy, plus additional neutrons, other particles, and radioactive material. The generation of new neutrons during fission makes possible a chain reaction process and the subsequent... 

Nuclear reactor boiler plants consist essentially of a central reactor core providing controlled energy that is transferred via a pressurized cooling system to one or more steam generators. These in turn provide superheated steam for delivery to a turbine. 

Boric acid [B(OH)3] is employed in primary coolant systems as a soluble, core reactivity controlling agent (moderator). It has a high capture cross-section for neutrons and is typically present to the extent of perhaps 300 to 1,000 ppm (down from perhaps 500 to 2,500 ppm 25 years ago), depending on nuclear reactor plant design and the equilibrium concentration reached with lithium hydroxide. However, boric acid may be present to a maximum extent of 1,200 ppm product in hot power nuclear operations. 

The turbine and generator components of a nuclear power plant have exact counterparts in power plants fueled by fossil fuels. The uniqueness of the nuclear power plant lies in its core. The core is a nuclear reactor where fission takes place under conditions that keep the reactor operating just below the critical level. The core contains three parts fuel rods, moderators, and control rods. These components act on the flow of neutrons within the core, as shown in Figure 22-13. The fate of neutrons must be controlled carefully. Fission must be sustained at a steady rate that produces sufficient energy to mn a generator, but the rate must not be allowed to increase and destroy the reactor. 

The main danger in the operation of a nuclear power plant is potential loss of control over the nuclear reaction. If the core overheats, it may either explode or melt down. In either event, radioactive materials escape Irom the reactor to contaminate the environment. Designers attempt to make nuclear reactors fail-safe by providing mechanisms that automatically shut the core down on overheating. One way this has been done is to design the control rods to fall into the core if their control mechanism fails. 

There are many advantages of using metal chlorides as interprocess intermediates. One of the most important advantages is that the metal chlorides could be readily purified. In other words, co-occurring metals could be more readily separated from one another as chlorides. This is particularly important when the co-occurring metals have very different technological properties and the presence of one in another in the final product is detrimental to the intended commercial application. A famous example of such co-occurrence is that of zirconium and hafnium in the mineral zircon. Not more than 100 ppm hafnium should be present in the zirconium intended for use in the nuclear reactor core. The hafnium content of zircon is about 2.5%. 

The past safety record of nuclear reactors, other than the Soviet Chernobyl-type RBMK reactors, is excellent Excluding RBMK reactors, there had been about 9000 reactor-years of operation in the world by the end of 1999, including about 2450 in the United States.1 In this time there was only one accident involving damage to the reactor core, the 1979 Three Mile Island accident, and even at TMI there was very little release of radionuclides to the outside environment. 

Toxitolerant an organism able to withstand high levels of damaging agents. For example, living in water saturated with benzene or in the water-core of a nuclear reactor. 

Puska, Eija Karita. Nuclear reactor core modelling in multifunctional simulators. 1999. 67 p. + app. 73 p. 

Zirconium is used for structural parts in the core of water moderated nuclear reactors to this end Zr has several good properties and especially it has low thermal neutron cross-section. Hf, on the contrary, has a high thermal neutron absorption coefficient, so it is necessary to be able to prepare Hf-free zirconium. On the other hand, in some cases the Hf properties too may be useful in nuclear technology, in the control rods of submarine reactors. 

Beryllium carbide (Be C) is used for the cores in nuclear reactors. 

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