Restarting a shut-down reactor

The word “restart” covers two very different situations. In one, a unit has been idle for years but its owner never declared the closure permanent: it is still a licensed power reactor waiting on an approval, a regulatory reform or a commercial decision. In the other, the owner has already certified to the regulator that operation ceased for good and has begun taking the plant apart. What separates them is not engineering. It is the legal state of the licence, and it decides whether a restart is measured in months or in years.

In the United States that boundary is written into 10 CFR 50.82(a)(1), which asks the licensee for two written certifications: one that operation has permanently ceased, and one that fuel has been permanently removed from the reactor vessel. The next paragraph, (a)(2), sets out the effect: once those certifications are docketed, the Part 50 licence no longer authorizes operation of the reactor or emplacement or retention of fuel in the vessel. The plant keeps its licence, but only to possess and safeguard the material. The permission to switch it back on is gone, and the rule provides no route for handing it back.

Palisades, an 805 MWe Combustion Engineering PWR in Michigan, was the first to walk that road in reverse, and its dates show how much of the job is paperwork. The unit permanently ceased operation on 20 May 2022; Entergy certified on 13 June that the fuel had gone to the spent fuel pool on the 10th, and with that the licence lost its authority to operate. Holtec, the new owner, applied on 28 September 2023 for an exemption from 50.82(a)(2) allowing a one-time rescission of those certifications. The NRC approved it on 24 July 2025, effective 25 August, alongside the licence transfer and four licence amendments tied to resuming power operations. A year later, on 31 August 2026, the plant began loading the first 8 of its 204 fuel assemblies.

The docket is half the problem; the machine is the other half. A reactor that has sat cold for years does not start with the turn of a key. At Palisades the two steam generators needed their tubes reinforced, accumulated corrosion products had to be removed, and the control rod drive mechanism nozzles were replaced, on top of buying fresh fuel and licensing operators again. Duane Arnold, a BWR-4 with a Mark I containment rated at 601 MWe net and 624 gross, permanently ceased operation on 10 August 2020 after a derecho damaged its cooling towers, and filed its two 50.82(a)(1) certifications on 27 August and 12 October of that year, which leaves it facing exactly the same paperwork as Palisades. It received a $1.9 billion Department of Energy loan on 8 September 2026 and is scheduled to restart in 2029. Three Mile Island 1, closed in 2019, is aiming at 2027 under the name Crane Clean Energy Center.

None of this is entirely new outside the United States. In Canada, Bruce A units 3 and 4 were laid up in early 1998 and came back in October 2003 and January 2004; units 1 and 2, shut in 1997 and 1995 —the latter after a lead blanket left inside a steam generator contaminated the circuit— returned in 2012 after a major refurbishment. What had no precedent in 2022 was not bringing an old, laid-up reactor back into service. It was doing so after the owner had certified the closure as permanent.

Japan belongs to the first category, which is why restart counts do not compare cleanly across countries. After 2011 the Japanese fleet stood idle awaiting new regulatory standards, but almost no unit was declared permanently closed: they stayed on the books as suspended, and since Sendai 1 restarted in 2015 fifteen of them have returned to operation while eighteen remain suspended. In Germany, by contrast, the last three plants —Emsland, Isar 2 and Neckarwestheim 2— closed on 15 April 2023 and hold dismantling permits, with the work under way. Why a restart moves in one country and not in another is almost always answered by looking at the state of the licence, not the state of the reactor.