A 238Pu heat source in marine coastal sediment: formation of a protective concretion

The effect of the marine environment upon a vented Ir-encapsulated 238Pu heat source was investigated. The heat source was emplaced in coastal submarine feldspathic sediment. In less than a month it became encased in a rock-like concretion. The capsule was cemented initially with a white deposit of anhydrite, a mineral identified with high temperature deep-sea springs. As the concentration increased in thickness sedimentary particles were incorporated by the cementing agent. A non-porous barrier was formed such that decay product He was impeded from escape. This property protected the heat source against intrusion by the corrosive marine waters. As determined by neutron activation, the major and minor elements within the coastal sediment, various fractions of the concretion, and certain discrete entities within or on the surface of the concretion, are included.