Parametric analyses for a radioisotope heat source for an artificial heart device

Abstract

Parametric analyses were performed to determine the optimum heat source configuration relative to previously determined selection criteria. Heat source sizes, weights, volumes, material interaction depths, and thermal expansion differentials between the various components were calculated for all candidate designs. These analyses included single-layer, two-layer, and three-layer designs of flat-ended and hemispherically-ended configurations of all material combinations under consideration. Selective and nonselective vent systems were designed to vent the fuel-generated helium from the heat source to retain and/or decay the Radon-220 to levels below the maximum allowable body burdens. The capsule wall thickness required to survive bullet impact, granite impact, and crushing was determined for the various configurations, and the thickness of a selectively-vented capsule required to survive creep due to the internal helium pressure was also determined. Based on these analyses, minimum required wall thicknesses were determined and an optimum design of each material configuration was generated. Forty-three candidate designs were scored against the selection criteria. The recommended system, which is currently being fabricated, is a rightcircular cylinder consisting of a Pt-20Rh liner, a T-111 strength member, a Pt-20Rh clad and a nonselective pressure relief device/capillary tube assembly. The liner and clad are interconnected to seal off the strength member from external contamination.