The United States should plan to store spent nuclear fuel in cooling pools and concrete-and-steel casks for 100 years as it sorts out what should be done with it in the long term, according to a new study from MIT. Storing spent fuel temporarily, the study argues, is in some ways better than immediately transferring it into permanent underground storage at facilities like the proposed one at Yucca Mountain.

The report comes in the aftermath of the Fukushima nuclear-power-plant disaster in Japan, where stored fuel was a major source of radioactive material that escaped into the surrounding area. And it comes at a time when many are again worried about the vast amounts of nuclear waste piling up at power plants around the country.

When most nuclear plants were built in the United States, the plan was to reprocess the fuel, retrieving material that could be used to generate more electricity. As a result, plant designers included only enough storage space to deal with about a 10 years' worth of fuel. When, for multiple reasons, the idea of reprocessing was abandoned, the federal government took on the obligation to dispose of the fuel itself—but so far it hasn't done so. The question of what to do with spent fuel before sending it to permanent storage "has frankly been an afterthought," says Ernest Moniz, director of MIT's Energy Initiative and an author of the report. After decades of operation, many power plants have run out of room and are resorting to ad hoc approaches to deal with the spent fuel.