Nuclear waste may rise from the grave

 作者:火娅     |      日期:2019-03-02 03:05:01
By ROGER MILNE Late changes to the design of Britain’s first underground nuclear waste repository increase the risk of radioactivity escaping back to the surface, government advisers warn. In a report published this week, the Radioactive Waste Management Advisory Committee (RWMAC), headed by geologist John Knill, raises a number of questions about the technical feasibility and the safety of the new proposals. The repository will be an underground labyrinth excavated beneath the nuclear complex at Sellafield in Cumbria. UK Nirex, the agency responsible for the country’s growing stockpile of low and intermediate level nuclear waste, wants to commission the dump by 2006. The main sticking point is Nirex’s decision to backfill the storage vaults with a permeable and friable cement grout. Because the grout can be ‘cut with a knife’, it would allow waste packages to be retrieved if necessary. The original plan was to use a much harder material. But the RWMAC says although the friable grout would form a long-term chemical barrier to radionuclides escaping from waste containers, it would also let water and gas migrate from the vaults into the surrounding rock. With time, gas generated in the repository and water flowing through would transport radionuclides from the waste and eventually reach the surface. The original design was intended to provide a series of barriers to prevent radioactivity escaping from the repository, beginning with the waste containers and finishing with the harder form of backfill. Nirex maintains that the physical barriers will last hundreds of years, and the chemical ones thousands. But the RWMAC is concerned that the friable grout will undermine this ‘multi-barrier’ effect. The material puts at risk the ‘long-term structural integrity of the vaults’, it says. The RWMAC is also worried that as vaults are progressively sealed with the grout and further caverns are excavated,