Long-lived activation products in light-water reactor construction materials: implications for decommissioning

An experimental program assessed the problems posed to reactor decommissioning by long-lived isotopes produced by direct activation of major construction materials in the reactor internals, vessel, and bioshield. The materials were analyzed for up to 52 elements to develop a data base of activable major, minor, and trace elements. A thorough evaluation was made of all possible nuclear reactions that could lead to long-lived activation products. A detailed series of calculations was carried out using average values of the measured compositions for the appropriate materials to predict the levels of activation products expected for PWR and BWR geometries. A comparison was made between calculated activation levels and regulatory guidelines for shallow-land disposal according to 10 CFR 61. The analysis showed that PWR and BWR shroud material may exceed Class C limits, potentially unsuitable for near-surface disposal. The PWR core barrel material can also approach the Class C limits, if feasible, this can be circumvented by single-piece removal of the vessel and internals during decommissioning. Most of the remaining massive components should qualify as either Class A or B waste. A limited radiochemical analysis verified the computer model. In particular, the presence of /sup 94/Nb in activated stainless steel and Inconel at or above expected levels was confirmed. 14 refs.; 7 figs.; 11 tabs.