The series of Control Tests has been completed. These tests were conducted to evaluate the suitability of the apparatus design, to test the various fission product characterization devices and methods, and to establish the behavior of known chemical species which are expected to be encountered in the latter phases of the program. Those tests which utilized either CsI or Cs/sub 2/O were found to yield deposits of hydrated CsOH in the moist environment. With the completion of the Control Test Series, attention has been turned to the development of an acceptable method of implanting selected fission product forms into the fuel-cladding gap, and to studies of the release of such implanted species from subsequently ruptured capsules. The method of implantation which has been employed in the tests conducted thus far involves application of CsI and CsOH on UO/sub 2/ pellet surfaces from aqueous solution, and implantation of TeO/sub 2/ on the fuel pellet ends from an aqueous slurry. The tests conducted to date indicate some decomposition of CsI to yield elemental iodine, stabilization of the CsOH, probably through reaction with UO/sub 2/, migration of the tellurium to the cladding, and transport of the CsI down temperature gradients within the fuel …