[en] Nuclear fission of uranium releases about 93% of its energy in the form of highly charged (up to 20+) and highly energetic fission fragment (83.5MeV average) and other ionizing radiations, including beta and gamma radiations. Liquid gallium is a semimetal that had been previously explored as a self recovering ionization media for alphavoltiac contact potential cell (CPC), and had been evaluated as a suitable replacement coolant for the next generation of fast reactor. By improving the neutronic aspect of a Liquid Gallium CPC (LGaCPC) with low neutron absorption construction materials, and by using a heterogeneous mixture of CANDU fuel grade uranium oxide powder (provided by CAMECO Inc.) and liquid gallium as its junction material, the direct conversion of fission energy to electricity has been observed when irradiated by the thermal neutron flux of the SLOWPOKE-II Research Reactor at the Saskatchewan Research Council. To further explore the effect of temperature on the operation of the LGaCPC, a High Temperature LGaCPC (HTLGaCPC), and a 6 meter high monolithic Large Volume Submersible Neutron Irradiation Chamber (LVSNIC) have been designed and constructed, which allow high temperature fission experiment up to 623K with a thermal neutron flux of 1.18 x 10"1"0 n/cm"2/s and the result is presented here, along with discussions on the operating principle of the LGaCPC, and on the construction and measurement techniques used in this study. (author)