Investigation of nonrecoil fission-product release phenomena using multifrequency source-perturbation experiments in EBR-II

Abstract

A widely-accepted theory that was proposed to explain nonrecoil fission-product release phenomena in LMRs postulated that isotopic transport kinetics are attributable to liquid-state diffusion across a viscous sublayer of Na near the surface of the fuel. A series of multifrequency source-perturbation experiments was recently performed in EBR-II to isolate and quantitatively explore the boundary-layer diffusion mechanism while separating out all other physical variables that affect the isotopic transport kinetics. Detailed analyses of the results using bivariate spectral decomposition and cross-correlation techniques are presented. Results of the analyses provide incontrovertible experimental evidence that boundary-layer diffusion in fact plays no part in the release of short-lived fission products in LMRs. A major conclusion of this investigation is that all nonrecoil fission-product release phenomena originate from mechanisms acting inside the breached element itself. Implications of this and other findings made during this investigation are discussed, and recommendations are made for extending the techniques introduced here in future experiments involving actual breached pins.