RPI's linear accelerator is pretty cool

Rensselaer is the proud owner of a linear accelerator. Not many students know about it as it is somewhat off-campus and somewhat restricted. If I hypothetically wanted to walk to the accelerator and associated nuclear labs, then I would need to walk all the way up to and behind Stackwyck by the east edge of campus, through a wooded road, and then I would get stopped by a barbed wire fence which I would then have to walk around. The reason is that experiments are often conducted here by the Naval Nuclear Laboratory, therefore the Department of Energy has invested heavily into the maintenance of the RPI LINAC and wants to keep security tight.

The tour of the linear accelerator started at 1 pm. Since I was a little late, I missed part of the briefing, but I got the gist of it as we went through the facility. We weren't allowed to bring phones or other sorts of cameras into the accelerator facility due to the facility’s occasional use for government purposes. We started by passing through a room with many computers that were used to process data and remote into the computers close to the linear accelerator itself. The accelerator was offline, likely because there were no current experiments and it is costly to run. It was mentioned in the tour that when there were funding issues in the 70s, RPI used the accelerator to re-color gems for commercial purposes.

The tour then went into the neutron building. The linear accelerator worked by accelerating electrons at a target such as tungsten or tantalum to create a blast of neutrons in all directions. Because of this omnidirectional blast and the neutrons’ high penetrating capability, the door to the room where this occurs is roughly 6 feet thick and on wheels. These neutrons are then collimated to mostly fly in a single direction for experiments. Using these “straight” flying neutrons, you can do experiments to see how neutrons react and scatter from various materials; there are various test stands with neutron detectors at different angles around a target. One fun fact about the neutron targets is that many of them are placed on Red Bull cans due to their high strength-to-weight ratio and aluminum’s low neutron interaction rate.

For any nuclear engineer, the last semester includes experiments with the linear accelerator. I do not know the specifics as I am still a junior.

Afterwards, we returned to the main building, where we saw the electron accelerator. Neutrons, being neutrally charged particles, are hard to manipulate and get up to speed, so electrons are accelerated to hit a target instead, which produces the neutrons.

It was mentioned during the tour that the NNL wants access to the LINAC so that they can see how materials act when hit by neutrons and keep the data secure. RPI is an excellent location, especially since it is close to the NNL’s location in Schenectady. This leads to one of the primary considerations when working with nuclear technology: much of it is restricted and shaped due to national security concerns.

Nuclear fuel supply chains were built with military reactors in mind. Military reactors use a light water reactor, which uses light water—a form of water containing hydrogen, not deuterium—as a coolant. These reactors need enriched fuel to work, which has an increased amount of Uranium-235. Due to the low proportion of Uranium-235 in natural uranium, enriched fuel is significantly more expensive than unenriched fuel. Some designs use unenriched fuel, with the most promising ones using liquid sodium as a coolant. The Navy tested them but decided against implementing them due to the nature of being a ship surrounded by water. Due to the military’s need for enriched reactor fuel, a supply chain was created, and when the civilian nuclear sector was made it was designed to use this supply chain for light-water reactors. That is a major part of why nuclear power has high costs and is an example of military policy that continues to affect civilian nuclear policy.