Decommissioning of Nuclear Submarines: Waste Minimization by Recycling

Abstract

The `'conventional'' method of decommissioning nuclear submarines is to cut out the compartment enclosing the reactor and primary system, seal it and dispose of it as a whole as radioactive waste. Normally, this requires about 800-1000 m(3) of final repository space. Recycling of the contaminated primary system by decontamination and melting can reduce the required repository space by up to 90%. Only the reactor vessel and the secondary waste from decontamination needs to be stored permanently. The secondary waste will concentrate and contain the radioactivity from the contaminated surfaces. Recycling will also allow the reclamation of valuable strategic materials. Studsvik RadWaste, Sweden, has developed a one-step, room temperature decontamination process SODP, based on nitric acid, cerium nitrate and ozone. The method has been tested on contaminated material from steam generators from France, USA and Sweden, achieving residual activity levels of under 1 Bq/g. Studsvik RadWaste also operates a melter for low-contaminated metals. The company has melted over 2300 t of steel, over 610 t of which have been released for remelting at commercial foundries. The remaining ingots are being stored for decay to releasable levels. This recycling approach to decommissioning has been demonstrated on steam generators of a submarine sized reactor, the 80 MW Agesta PHWR, which operated outside Stockholm from 1964-74. Another demonstration has been done on two 330-tube sections of a steam generator removed from the Dampierre 900 MWe PWR in France, in an EU-supported project. This approach is now considered mature for demonstration on the primary system of a submarine reactor.