By Edward Lyman
In January, the Defense Department issued a call for information in support of the aptly titled Project Dilithium. It seeks to develop a tiny, readily transportable, yet virtually indestructible nuclear power reactor for use at forward operating bases, the military facilities that provide logistical and troop support to the front-lines of conflict zones.
The Pentagon presumably chose the name to convey a futuristic image—at least, to the Star Trek aficionados among us. Make no mistake, however: The project, with its naïve optimism that such reactors “have the potential to be an across-the-board strategic game changer,” is less Captain James T. Kirk and more Lieutenant General Samuel D. Sturgis, who founded the now-defunct Army Nuclear Power Program more than sixty years ago.
Project Dilithium’s name isn’t its only science fiction-related aspect. To be sure, the type of reactor it is seeking could be a great military asset: all the benefits of nuclear energy with none of the risks. The costly and dangerous process of trucking diesel fuel to bases, sometimes through hostile territory, may eventually be a thing of the past. Unfortunately, the need to store and ship irradiated nuclear fuel in a war zone will introduce different problems. And the odds that a meltdown-proof reactor could be successfully developed any time soon are vanishingly small.
The quest for a safe modular reactor
The Army Nuclear Power Program was initiated in 1954, in the heady early days of the atomic power era, to develop ground-based nuclear power plants for military use—a mission distinct from the Navy’s submarine nuclear propulsion program already well underway. Over two decades, the US Army built and operated eight small power reactors, ranging from less than one megawatt to ten megawatts of electricity, with limited success. The worst outcome was the 1961 core meltdown and explosion at the SL-1 reactor in Idaho, which killed three operators. Five of the reactors were designed to be portable to some degree, and three were deployed at remote military bases in Greenland, Alaska, and Antarctica. Although these reactors didn’t explode, they proved unreliable and expensive to operate. Based on that experience, the program was shut down in 1977. […]
he greater challenges arise in meeting the RFI’s safety criteria: the reactor should have an “inherently safe design” that ensures “a meltdown is physically impossible in various complete failure scenarios;” cause “no net increase in risk to public safety … by contamination with breach of primary core;” and have “minimized consequences to nearby personnel in case of adversary attack.”
These requirements, obviously, are key. Nuclear reactors deployed at forward operating bases or shipped through war zones would be prime targets of the enemy. An Octrober 2018 report commissioned by the army’s Deputy Chief of Staff admits, quite reasonably, that exposed mobile nuclear plants would “not be expected to survive a direct kinetic attack.” If commanders need to expend significant resources to protect the reactors or their support systems from military strikes, such reactors could become burdens rather than assets.
Can one really invent a reactor robust enough to suffer such a strike without causing unacceptable consequences? The “inherently safe reactor” has been a nuclear industry catchphrase for decades, but the reality has never matched the rhetoric. All it really means is that in certain idealized scenarios, a reactor, after shutdown, could be adequately cooled by passive mechanisms, such as convective airflow. But passive safety cannot eliminate every pathway by which the reactor fuel could be damaged and release radioactivity. If a severe accident or sabotage attack were to induce more extreme conditions than the reactor was designed to withstand, all bets are off. How long would passive airflow keep nuclear fuel safely cool if, say, an adversary threw an insulating blanket over a small reactor? Or if the reactor were buried under a pile of debris? […]