Reactor Core Materials

Determination of the neutron fluence in reactor core materials... 

Andresen, P. L., Ford, F. P., Murphy, S. M., and Perks, J. M., State of Knowledge of Radiation Effects on Environmental Cracking in Light Water Reactor Core Materials, Proceedings of 4th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems—Water Reactors, D. Cubicciotti, Ed., NACE, Houston, TX, 1990. 

Hoffman, et al. "Reactor Core Materials Interactions." Nuclear Technology Volume 87, August 1989, 147. 

P. HOFMANN and al. "Reactor core materials interaction at very high temperatures". Nuclear Technology, Vol. 87 (August 1989) -146-186. 

Technical Progress Review, Reactor Core Materials 1 18, 1958. 

Zircon is a potential source of yttrium and heavy lanthanides. However, the present demand for zirconium is not great nor is it expected to be in the intermediate future. The principal use for zirconium is in nuclear reactor core material and refractories. 

The following Space Nuclear Reactor technologies shall be developed for Lunar and Mars surface power reactors 1) Nuclear fuel, 2) Reactor core materials and coolants, and 3) Instrumentation and Control. (This item was indicated as an objective - minimum requirement not yet defined.)... 

There were two different liner material classes under consideration a refractory metal alloy and a Ni-base superalloy. The refractory options consist of niobium, tantalum, or molybdenum alloys. The Ni-base superalloy options are the same as those for the outer pipe Inconel 617, Haynes 230, and Nimonic PE-16. -Considerations that would have affected liner selection include the performance of the material at high temperatures, material compatibility with the insulation, reactor core materials, and turbine, as well as the interface with the reactor and turbine. 

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. 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

The fifth component is the stmcture, a material selected for weak absorption for neutrons, and having adequate strength and resistance to corrosion. In thermal reactors, uranium oxide pellets are held and supported by metal tubes, called the cladding. The cladding is composed of zirconium, in the form of an alloy called Zircaloy. Some early reactors used aluminum fast reactors use stainless steel. Additional hardware is required to hold the bundles of fuel rods within a fuel assembly and to support the assembhes that are inserted and removed from the reactor core. Stainless steel is commonly used for such hardware. If the reactor is operated at high temperature and pressure, a thick-walled steel reactor vessel is needed. 

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. 

A critical assembly is a split bed on which fissionable material used to mock up up a separated reactor core that is stacked half on each half. One half is on roller guides so that the two halves may be quickly pulled apart if the neutron multiplication gets too high. Use the Preliminary Hazards Analysis method described in section 3,2.1 to identify the possible accidents that may occur and the qualitative probabilities and consequences. List the initiators in a matrix to systematically investigate the whole process. Don t forget human error. 

Any release of radioactive material affecting the public requires temperature above the melting point of the materials to deform the reactor core and confining structures This section lists the barriers preventing release, presents scoping calculations that illustrate the conditions and time scale of concern. Conjectures are presented as to how core melt might happen. The section concludes with information about the partial core melt that occurred at TMI-2. 

The most serious accident tliat Ciui occur in a nuclear plant is a reactor core meltdown. In a core meltdown, the enclosed gases physically melt through tlie reactor vessel, and once contacting with cooler liquids or vapors either in a cooling jacket or in the outer enviromnent, cause a physical e. plosion to occur. However, tlie hazard caused by the e. plosion itself is minimal and more localized compared with the release of radioactive material that accompanies such an accident. 

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... 

While nuclear power plants use multiple layers of protection from the radioactive particles inside the reactor core, a serious accident can cause the release of radioactive material into the environment. It is not a nuclear explosion, because the uranium fuel used in a nuclear power plant does not contain a high enough concentration of U-235. For an explosion to occur, the uranium fuel inside the reactor would have to be enriched to about 90% U-235, but it is only enriched to about 3.5%. 

We regard the essential aspects of chemical reaction engineering to include multiple reactions, energy management, and catalytic processes so we regard the first seven chapters as the core material in a course. Then the final five chapters consider topics such as environmental, polymer, sohds, biological, and combustion reactions and reactors, subjects that may be considered optional in an introductory course. We recommend that an instmctor attempt to complete the first seven chapters within perhaps 3/4 of a term to allow time to select from these topics and chapters. The final chapter on multiphase reactors is of course very important, but our intent is only to introduce some of the ideas that are important in its design. 

---