In case of an LMFBR whole-core accident, fuel and fission products may be released instantaneously from the HCDA bubble through vessel head leaks or delayed from hot or boiling sodium pools after vessel melt-through. It is necessary to investigate the radiological source terms for both scenarios. In the paper we present and discuss retention factors for simulated fission products and fuel from FAUST under-sodium rupture disk tests on the instantaneous source term and from NALA tests with hot and boiling sodium pools on the delayed source term.