Radiation damage neutron

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

SiHcon carbide s relatively low neutron cross section and good resistance to radiation damage make it useful in some of its new forms in nuclear reactors (qv). SiHcon carbide temperature-sensing devices and stmctural shapes fabricated from the new dense types are expected to have increased stabiHty. SiHcon carbide coatings (qv) may be appHed to nuclear fuel elements, especially those of pebble-bed reactors, or siHcon carbide may be incorporated as a matrix in these elements (153,154). 

Fig. 6. Radiation damage in graphite showing the induced crystal dimensional strains. Impinging fast neutrons displace carbon atoms from their equilibrium lattice positions, producing an interstitial and vacancy. The coalescence of vacancies causes contraction in the a-direction, whereas interstitials may coalesce to form dislocation loops (essentially new graphite planes) causing c-direction expansion.

Simmons, J.H.W., Radiation Damage in Graphite, Pergamon Press, Oxford, 1965. Kelly, B.T. and Burchell, T.D., Structure-related property changes in polycrystallinc graphite under neutron irradiation, Carbon, 1994, 32, 499 505. 

Since this change in distribution of the radioactive iron occurs most strongly in samples which have suffered a heavy fast neutron bombardment, one surmises that there must be a reaction with the products of bulk radiation damage. The products have not been identified. 

As with other radioactive substances, exposure to its ionizing radiation can cause cancer. When ingested it tends to accumulate in the liver, kidney, and spleen causing radiation damage from the alpha particles. All operations and handling must be carried out in leak-proof boxes by mechanical means behind thick neutron shields. 

In the work reported here, which was directed toward the attainment of an isotopic enrichment of the trivalent actinide and lanthanide elements, the problem was compounded by the fact that these elements do not readily form appropriate compounds, like iodine in ethyl iodide. They do form some stable organic chelates, and, indeed, it is possible to obtain a Szilard-Chalmers reaction with such compounds. However, their radiation damage resistance does not appear adequate to permit useful production of an isotope like 247Cm, which requires a thermal neutron exposure ap-... 

It has been reported that Linde X maintains its crystallinity, gas absorption, and ion-exchange properties up to about 1019 fast neutrons cm-2, but these properties were rapidly lost at higher exposures (9). Since radiation damage is predominantly caused by fast neutrons, it would be advantageous to use a neutron source with a substantially smaller fast component. Such facilities can be built, and experiments in this direction are planned. 

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