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Experiments in the controlled melting of irradiated fuel speciman, particularly of the APPR, STR, and MTR types, have confirmed that prolonged heating in air at temperatures in excess of the melting point results in the release of a large portion of the radioactivity. On the other hand, a moderate amount of heating in air or steam sufficient only to melt a specimen results mainly in the partial volatilization of rare gases, iodine, bromine, cesium, and rubidium. In the presence of air or water vapor, strontium and other fission products are not released. At trace concentration of fission products, slow melting of the APPR plate at 1525 d C in air or steam effected the release of 50% of the rare gases, 33% of the iodine, 9% of ihe cesium, and traces of strontiuun. After 25% burn-up, the cesiuun value increased to about 60%. Aluminum alloy of the MTR type, also at trace concentration, upon melting at 700 d C released up to 2% of the iodine, 10% of the rare gases, and negligible portions of other fission products. Zirconium alloy of the STR type after 15% burn-up, when melted at 1850 d C, released up to 95% of the rare gases, 90% of the cesium, 60% of the iodine, and only a trace of strontiuun. (auth).
0bservations are reported on the behavior of several fission product elements in molten NaF- ZrF/sub 4/-UF/sub 4/ fuels, irradiated in capsule experiments, forcedconvection in-pile loop experiments, and in the Aircraft Reactor Experiment (ARE). The rare gases have been observed to escape readily from the fuels in dynamic tests, although in static tests the rate of escape is very low. Rutbenium and niobium deposit on the Iaconel walls of the fuel container. probably as metals. Other fission products studied (Sr, Zr, La, Ce) appear to remain in the fuel. The results obtain are entirely consistent with theoretical productions. It is suggested that the observed noble metal deposit map serve to reduce corrosion of methls by molten floride fuels. The unsatisfactory nature of Cs/sup 137/ as a fission monitor in such fuels is reported. and the use of Zr/sup 95/ substitute is discussed. (auth) l6536 In order to evaluate the irradiation stability of the APPR-1 type Fe-B cored, stainless steel clad control rod configuration, a test program consisting of the irradiation of both minature absorber plates and an APPR-1 type full size control rod was initiated. The purpose of these irradiations was to determine toe dimensional stability and structural integrity of this type of absorber material throughout a relatively wide range of B burnups. Results obtained from the post- irradiational examination are summarized. (W.L.H.)).
Essentially all the fission product data for numerous and varied samples taken during operation of the Molten Salt Reactor Experiment or as part of the examination of specimens removed after particular phases of operation are reported, together with the appropriate inventory or other basis of comparison, and relevant reactor parameters and conditions. Fission product behavior fell into distinct chemical groups. Evidence for fission product behavior during operation over a period of 26 months with $sup 235$U fuel (more than 9000 effective full-power hours) was consistent with behavior during operation using $sup 233$U fuel over a period of about 15 months (more than 5100 effective full- power hours). (auth).
This book discusses the technical alternatives for cleanup of radioactive fluoride salts that were the fuel for the Molten Salt Reactor Experiment, a novel nuclear reactor design that was tested in the 1960s at the Oak Ridge National Laboratory in Tennessee. These fluoride salts pose an unusual cleanup challenge. The book discusses alternatives for processing and removing the salts based on present knowledge of fluoride salt chemistry and nuclear reactions of the radioactive constituents.