Unique Aspects Associated Witb tbe Design and Certification of a Radioisotope Thermoelectric Generator Transportation Package

Radioisotope Thermoelectric Generators (RTGs) are used as power or heat sources for space applications such as the Cassini Mission scheduled for 1997. Due to the radioactive material content of the RTGs, a certified, Type B(U) packaging is required for ground transportation. In addition, the RTGs typically contain plutonium in sufficient quantities to dictate the use of double containment per the requirements of 1 0 CFR 71.63(b) (10 CFR 71 1994). When this double containment requirement is coupled with a relatively high RTG internal heat load of up to 4,500 watts and a very demanding set of normal operating temperature limits for the RTG itself, a significant thermal design challenge exists. In addition to the thermal design challenge, with the catastrophic impact of a malfunctioning RTG on a program such as the Cassini Mission, several other design constraints not commonly imposed on a radioactive materials transportation package development effort come into play. These added constraints are primarily directed at ensuring the operational integrity of the RTGs under all normal handling and transport conditions, thus ensuring proper function of the RTG once deployed in space. Included are rather restrictive normal operating condition shock and vibration limits and a requirement for continuous monitoring of the RTGs via electrical feed-through devices which penetrate both levels of containm~nt. Structural design challenges are also created by rather restrictive, facility imposed size and weight constraints. The weight efficient nature of certain RTG payload designs also inherently leads to a potential for payload reconfiguration and payload/package interactions in the event of 10 CFR 71. 73-defined accident conditions. Such reconfiguration also presents thermal and, to a lesser extent, shielding design challenges for the packaging subsequent to the accident sequence.