CAMBRIDGE — Set back along the railroad tracks that cross Massachusetts Avenue, the featureless, cylindrical structure resembles an ordinary water tank. But inside its steel casing and thick concrete walls is something remarkable: about 100 pounds of uranium, silently fissioning in a bath of warm water illuminated by the characteristic blue glow of radiation.
This is the nuclear reactor the Massachusetts Institute of Technology has been operating as a classroom and research center for more than 40 years. Its engineers conduct cutting-edge science, including developing a cladding for nuclear fuel that could prevent another Fukushima-type disaster and helping China design a new generation of meltdown-proof reactors.
At the heart of this work is the reactor's surprisingly small core, an 18-inch wide, 2-foot-tall hexagon containing thin plates of high-enriched uranium, or HEU. It's one of just eight research and test reactors in the country that still burn HEU, the form of uranium that's easiest to make into an atomic bomb.
Because of the risk that high-enriched uranium could be stolen by terrorists, the US Department of Energy wanted to have MIT and the operators of similar reactors switch to a safer, lower-enriched form of uranium by 2014. But the government effort to develop and manufacture a new fuel for these reactors has been plagued by technical setbacks and poor management.
The difficulties mean MIT will continue to use the weapons-grade uranium until at least 2027, according to a new schedule set by the government.
While federal energy officials debate whether to adopt a controversial interim solution recommended by a group of independent scientists, MIT is left in a frustrating position: staring down another 11 years of potential public relations headaches over the presence of high-enriched uranium on its campus but unable to change anything until the Department of Energy says so. Its confidence in even the new, far-off 2027 deadline is low.
"If your deadline is slipping two days for every day of work, it's a fantasy, not a project," said David Moncton, the head of MIT's Nuclear Research Laboratory, about the latest delay. "They think this deadline is solid, and that I don't believe. Good project management has eluded them."
In the meantime, Moncton stressed the reactor and its fuel are protected by tight physical security. Fresh fuel is loaded into the core almost immediately upon delivery, he said, adding that anyone who stole the uranium once it has been irradiated would essentially be committing a gruesome suicide by acute radiation poisoning.
Still, Moncton and other MIT scientists are eager to show the nuclear industry it's possible to run a high-performance research reactor on low-enriched uranium.
"We want to demonstrate that you can convert a high-performance reactor from HEU and still run it at parameters similar to the ones it ran at before," Moncton said.
With the federal effort dragging, a panel of scientists commissioned by Congress has recommended a temporary solution: switch MIT's and the other US reactors to a type of "medium-enriched" uranium already being made in Europe that could more readily match the performance of the more potent fuel officials want to phase out.
"Given that the timeline has been pushed so far back, why not convert them to this medium grade?" said Gerald Gabrielse, a Harvard University physicist and member of the National Academy of Sciences committee that authored the report. "Then we've made progress as a world towards having less high-enriched uranium around."
Natural uranium needs to be enriched to contain enough fissionable material to generate a nuclear chain reaction. The higher the enrichment, the less material is needed to build a working bomb. For example, fuel made up of more than 90 percent of uranium-235, the material that powers many nuclear reactors, is considered weapons-grade; below 20 percent and it becomes impractical to make into a bomb.
Operators of research reactors such as the one at MIT like high-enriched uranium because of the high rate at which it generates neutrons, useful for imaging and radiation-testing various materials. Commercial power reactor operators have simpler requirements and are able to generate electricity with uranium fuel enriched below 5 percent.
Getting a small reactor like MIT's to run on low-enriched uranium while still generating many neutrons means developing a fuel that's more than five times as dense as its current high-enriched fuel — a steep technical challenge that has slowed the Department of Energy program.
For decades, the US government has helped to close or convert dozens of reactors around the world that use high-enriched uranium, worried terrorists would steal their fuel. The effort, which took on additional urgency after the 9/11 attacks, was especially focused on Russia and other former Soviet-bloc countries where security at reactors can be lax.
Federal officials stressed that the campaign to remove the high-enriched fuel from MIT does not arise from specific security concerns about the Cambridge facility, where the current reactor has operated without serious incident since coming online in 1973.
The medium-grade uranium recommended by the National Academy of Sciences committee, at around 35 percent enrichment, would be above that safer 20 percent threshold. Even so, the committee argued, a terrorist would need hundreds of pounds of medium-enriched fuel to make a primitive atomic weapon with it. So using it at the MIT facility and similar reactors would result in a meaningful safety improvement, the scientists said.
Moncton believes it's feasible to convert MIT's reactor to the medium-enriched fuel. But he's worried implementing the interim effort might take nearly as long as the original low-enriched fuel program.
"There's no timeline, no cost estimate, no details about what has to be done," Moncton said. "Intuitively, I don't feel the practicalities make sense."
The decision ultimately rests with federal energy officials, who said in an interview they're unlikely to make a determination before a new presidential administration takes office in January. They were skeptical of the idea, though, worrying the interim measure would distract from the ultimate goal of developing a form of low-enriched uranium these types of reactors can use.
Officials and specialists also argued that sticking with the program to get low-enriched uranium into MIT's and similar reactors would help give credibility to American efforts to get rid of the more dangerous fuel in reactors in other countries. But others contend that by pursuing the interim conversion as well, the United States would prove it is committed to reducing its use of high-enriched uranium as soon as possible.
Meanwhile, some critics question why MIT is still operating a reactor at all.
"MIT is one of the more questionable ones among the US reactors. Most of the tasks they're doing are not particularly unique," said Miles Pomper, a senior fellow at the Center for Nonproliferation Studies. "As long as the HEU is there, it's something you have to worry about. The question is whether the value of what you're getting out of material is worth the risks."
Moncton disagrees emphatically. The unique design of the MIT reactor, he said, allows operators to simulate the conditions inside commercial power reactors, making it invaluable for training and testing purposes. And indeed, the facility has a reputation within nuclear circles as a serious research center.
Moncton also noted the United States has built few new reactors in recent decades.
"If this reactor was shut down, we'd be even further below the capability of a modern country," he said. "It would be an embarrassment to the United States."