If you’ve ever pulled a building permit, you know the approval is rarely the last piece of paper. There’s almost always one more inspection before anyone lets you move in.<\/p>\n
Radiant is in pretty much that spot right now. The El Segundo, California, startup sent its Kaleidos microreactor up to Idaho National Laboratory in August, which we covered when it left Los Angeles on a flatbed<\/a>. On October 29, the company announced that the Department of Energy had approved the reactor’s Documented Safety Analysis, the safety paperwork behind a test campaign that’s supposed to end with 60 effective days at full power.<\/p>\n It still doesn’t have any fuel in it, though. Before that changes, DOE has one more review to finish.<\/p>\n A Documented Safety Analysis is basically the reactor’s rulebook. It lays out what could go wrong, how the reactor and the building around it are supposed to handle it, and which limits the operators have to stay inside. DOE accepted a preliminary version from Radiant back in February. This is the final one. Radiant says it covers running the reactor at power as well as getting it to its first chain reaction.<\/p>\n That distinction matters more than you’d think. Criticality is the moment a reactor’s chain reaction keeps itself going, and you can reach it at what’s called zero power, where the core makes basically no useful heat. A handful of other startups have taken reactors critical this year, but those were zero-power tests. Radiant wants to go a lot further with the same unit.<\/p>\n The company’s chief nuclear officer, Rita Baranwal, said in Radiant’s announcement<\/a> that “this approval for full-power demonstration is a first within the microreactor industry.”<\/p>\n So is it really a first?<\/p>\n That’s Radiant’s claim, and it’s a fairly narrow one. Radiant billed its February approval as a first for a full-power test too. DOE also signed off on a final safety analysis for Last Energy’s pilot reactor in Texas earlier in October, but according to the American Nuclear Society that pilot starts with low-power criticality. So as far as I can tell, Radiant’s first only works because the claim says full power.<\/p>\n The plan has five phases. It starts with first criticality, then steps the reactor up through higher and higher power levels so Radiant and the lab can check the core, the instruments and the whole system working together.<\/p>\n Radiant’s headline target is 60 effective full-power days, spread across several months. Those days don’t have to come in a row. Radiant keeps a running total, so it works more like an odometer than a calendar. Run the reactor at half power for two days and you’ve banked one full-power day, which means Radiant can stop, check things and pick back up without resetting the count.<\/p>\n Then there’s the 150-hour run. Radiant wants at least 150 hours straight at full power without an operator stepping in, which works out to a little over six days. Frankly, I think that’s the most interesting number in the whole plan. The pitch for Kaleidos is a reactor that gets dropped off at a military base and runs for years, and a reactor that needs someone hovering over the controls doesn’t really fit that pitch.<\/p>\n From the looks of things, the fuel itself isn’t the hold-up. Radiant’s TRISO fuel started arriving at the lab back in July<\/a>. TRISO is uranium broken into particles about the size of a poppy seed, each one wrapped in layers of carbon and ceramic. Each particle basically carries its own little containment shell, so the fuel holds on to what it makes even when things get very hot.<\/p>\n What’s missing is DOE’s Readiness Review. That review checks whether the reactor, the systems around it and the people who’ll run it are actually ready to start nuclear operations. Only after it’s done can Radiant load fuel and kick off phase one, as Interesting Engineering reported<\/a> when the approval came out.<\/p>\n Radiant hasn’t said when that review will happen, and I couldn’t find a date from DOE either. We also don’t know which day DOE actually signed the approval. All we’ve got is the day Radiant announced it.<\/p>\n It’s fair to say the schedule has slipped a bit. When Kaleidos left El Segundo, Radiant was aiming to wrap up all five phases by the end of September. It’s now November, and phase one hasn’t started. Admittedly, a startup’s timeline for a first-of-its-kind nuclear test was always going to be on the optimistic side.<\/p>\n Kaleidos itself is a helium-cooled reactor rated at 1 megawatt of electricity. It’s packed into a 35-foot container that comes in at north of 70 tons by Radiant’s own figures, as we noted when the Navy picked it for an Indiana base<\/a>. Radiant plans to build the commercial versions at its R-50 factory in Oak Ridge, Tennessee.<\/p>\n The first commercial units are due in 2028, headed for Colorado’s Buckley Space Force Base and the Army’s Fort Benning in Georgia. The Navy picked Radiant in October, too, for a Kaleidos at Naval Weapons Station Crane in Indiana. That’s three military bases for a reactor that hasn’t made a single watt yet, which is arguably a pretty big bet on the Idaho test going to plan.<\/p>\n So as of Radiant’s October 29 announcement, the reactor that rode a flatbed to Idaho in August is sitting in the dome waiting on DOE’s Readiness Review, and it still hasn’t been fueled.<\/p>\n","protected":false},"excerpt":{"rendered":" If you’ve ever pulled a building permit, you know the approval is rarely the last piece of paper. There’s almost … <\/p>\nSo what did the Energy Department actually approve?<\/h2>\n
So what does 60 days at full power actually mean?<\/h2>\n
The fuel is already in Idaho<\/h2>\n
The customers are already lined up<\/h2>\n