Abstract: A storage vessel for radioactive material comprising metallic particles that are, preferably but not necessarily spherical, forming a matrix that includes a moderator and absorber of neutrons. The matrix is disposed between an inner vessel and an outer casing having metallic walls. The walls of the inner vessel contains the radioactive materials and shields against photon radiation, and outer the casing, in addition to photon shielding, also serves as a protective layer against physical impact. The metal particles are ideally composed of depleted uranium, however, lead or other high density metals which can attenuate photon radiation can also be utilized. The matrix includes a neutron attenuating and absorbing mixture which fill the interstices between the metallic particles.