The Hanford reservation is a remote patch of barren desert on the Columbia River near Richland, Washington yet it houses one of the most important artifacts of the nuclear age: the world’s first plutonium production reactor. Fissile material bred in B-Reactor was used in the first plutonium-based implosion nuclear weapon, known as Fat Man. As part of the Manhattan Project, Hanford’s creation and operations were so secret that most of the scientists and engineers working there didn’t know for what purpose the materials they were breeding were intended. The facility’s secret became public following the bombing of Nagasaki in August 1945, as seen in the headlines of the Richland Villager newspaper. “It’s atomic bombs! News spreads slowly, surprises everyone here,” proclaims the subheadline, illustrating just how carefully the secret was kept.
My visit to Hanford took place in June 2014 with the UW student chapter of Institute of Nuclear Materials Management as part of an internship informational tour to Pacific Northwest National Laboratory. I’ll try to keep the physics of nuclear materials and processes entry-level, enough to understand what it being shown, but not too in depth about any of it.
Hanford is infamous in Washington as an ecological and radiological nightmare: the facility was built rapidly with little environmental concerns during the height of WWII, with the intent of being taken offline soon after the war concluded. The immediate jump into the Cold War kept the reactor online, producing tons of plutonium for thousands of nuclear weapons as the Red Scare and arms race escalated.
When the reactor was decommissioned in 1968, much of the radiological waste (stored in lined clay pits) was bulldozed over and forgotten by the government, at least until the waste pits started to leak and radioactive ants began to roam the desert. Hanford houses 53 million gallons of radioactive waste in 177 underground tanks, 23 million cubic feet of solid waste, and 200 square miles of contaminated ground water underneath the site (and bordering the Columbia River), leading the BBC to label it as America’s most contaminated nuclear site. Significant amounts of radioactive waste was released into the river by leaks over the decades (sorry, Oregon). The site is so polluted that when it came time to dismantle nuclear submarines, the government said “fuck it” and threw the reactors into open aired pits in the Washington desert (for Russian satellites to keep account, by treaty).
Today the reservation is the site of a massively expensive clean-up. The reservation remains off-limits, with the remains of six plutonium reactors encased in concrete sarcophagi, too hot to be dismantled for the next 70 years. The reservation is also home to the only working Washington Public Power Supply System reactor, a failed attempt to bring nuclear power to the masses during the 1970s. Now operated by Energy Northwest, residents refer to the unfortunate acronym as “whoops” (because only one reactor was built for the 7 billion-dollar project). Our group was told that photography is restricted on the reservation due to security concerns, so I wasn’t able to get any decent photos approaching B-Reactor. Of course, I also forgot my camera on the trip (it was part of the PNNL tour, and I didn’t want to drag the camera through the internship meetings), so all my pictures are cellphone snaps.
Just outside the main entrance to the building lies what remains of Hanford’s trains. Trains like these were used to carry radioactive material ten miles to T-Plant, and as such represent the final stage of production at B-Reactor. The fuel plugs that came out of the reactor were incredibly radioactive (and incredibly hot from thermal energy). In the early days fuel plugs were fished out of a large tank of water behind the reactor and placed into containers filled with water in the back of trucks. The trucks would then have to race to T-Plant before the water evaporated. Needless to say, it was a pretty dangerous task. I don’t know when the rail system was built, but the powerful locomotives enabled a much safer system to transport the fuel plugs. The large black coffin (called a ‘cask’) on the flatbed car was a thick-walled lead vessel filled with water. A full reactor load was 60,000 fuel plugs at the height of operation.
The reactor building itself rises out of the desert, an otherwise unremarkable brick of concrete rapidly designed for efficiency rather than aesthetics. The main tour entrance is what used to be a service entrance to the reactor room itself. What really surprised me was how easy the reactor is to access, just down a short hallway from the entrance. Walking the short hall, rounding the corner to be faced with the monster that is the reactor pile was quite an experience: I’ve been reading about B-Reactor, nuclear history, and weapons production for years so to come abruptly face to face with history was startling. Of course when it was designed, the military had the entire reservation locked down tight and intruders weren’t a major concern. Still, it’s jarring in comparison to today’s high-security systems. Our tour was specially arranged by PNNL so the site staff were busy renovating displays and preserving the building when we arrived.
The reactor itself is in the center of the building, an imposing 41 feet tall. Construction began June 7, 1943 under the design and guidance of Enrico Fermi. It was the first full-scale nuclear facility and the first production reactor to operate in the history of the world. The DuPont corporation built the facility in 11 months. Wary of post-war legal issues related to war-profiteering (as happened in WWI), DuPont agreed to build the facility for cost plus $1 with the understanding that the government assumed full responsibility for the site once the contract was completed.
I promise to keep this as short as possible. There are several radioactive isotopes that are fissile, meaning you can split them into smaller components. One byproduct of splitting the atoms is the release of the energy that was holding the components together (known as binding-energy). Although small, this energy multiplied millions or billions of times results in the massive explosion for which nuclear weapons are infamous. two of the isotopes most suited for use in weapons are uranium 235 and plutonium 239.Uranium occurs naturally, however most uranium ore is 99.3% 238U (stable) and only .07% 235U. Plutonium does not naturally occur, but can be created by bombarding 238U with neutrons until something sticks in a process called ‘breeding’. The resulting isotope is unstable and over time decays into 239Pu. The process of one element changing to another is called transmutation.
B-Reactor was designed to breed plutonium by bombarding uranium fuel plugs with neutrons until they transmuted into plutonium isotopes. The fuel plugs would then need to be chemically processed to separate the isotopes, which happened at T-Plant. The process is by no means efficient, producing a lot of waste for a little plutonium.
Nuclear fission happens when an atom is split into various component pieces, as already covered. Along with releasing binding energy, the component pieces of the atom which was split (usually a neutron) can strike other atoms and cause them to split as well. This is literally a crap-shoot in the hope that a chain of subsequent atom-splitting will be initiated. Radioactive isotopes are decaying all the time, however the chances of the product of atomic decay striking another atom’s nucleus in such a way to initiate a split is extremely unlikely. Ways to make the odds better of causing a chain of fission is to make your material more dense, or to have more material. Density makes it more likely that a stray neutron will strike another atomic nucleus while amount of material means there are more atoms within range of the neutron that could be potentially hit. Once this chain becomes self-sustaining it is said to be in a critical state, with no increase of decrease in reactions. A critical mass is the amount of fissile material needed to sustain a critical state.
Criticality is important for both nuclear reactors and weapons. When the reaction is self-sustaining, it is known as k=1. This is considered a controlled state, similar to feeding just enough fuel to a gas flame to keep it at a set size and temperature. If an atom splits and produces more than one subsequent split, the chain is said to be supercritical. This state is known as k>1 and is what drives nuclear weapons. A supercritical chain reaction can build on itself and go wildly out of control, resulting in massive releases of energy. This is how a nuclear weapon works. Imagine the gas flame, but this time simply feeding it as much gas as it can burn.
Nuclear reactors seek to control the chain of fission at k=1 through neutron moderators (absorbent materials that soak up excess neutrons). Nuclear weapons foster k>1 with special focusing mirrors and tampered casings. Fortunately, the design of reactors and weapons are so different and specific that even if a reactor were to become supercritical, it would not result in a nuclear explosion. Explosions at nuclear power plants have occurred, however it was due to release of flammable gasses such as hydrogen, not from atomic fission.
B-Reactor is a water-cooled, graphite moderated, single-pass reactor meaning the fuel plugs were only passed through the center of the reactor once. Nuclear reactors in electrical power stations are used as a source of thermal energy to heat water into steam, which turns a turbine, generating electricity. As a breeder reactor, the B-Reactor was not tuned for thermal energy output. Rather it was intended to produce neutrons which transmuted uranium atoms into neptunium, which later decays into plutonium. Water was used for cooling, however the excess heat was not used to produce electricity.
Fuel plugs were inserted into channels on the face of the reactor by a working crew. As one plug as inserted, an irradiated plug was pushed out the rear. Freshly irradiated fuel plugs were too radioactive for handling, instead falling directly from the reactor into a storage room filled with water 20′ deep where it sat “cooling” for 90 days. Workers used 20′ tongs to lift plugs into baskets underwater, which were then transferred to casks for transport to T-Plant.
The reactor pile was built of a core with 2, 004 aluminum tubes that served to house the fuel plugs. Vertical channels housed control rods, which prevent criticality by absorbing neutrons when lowered. They control both the heat/neutron production of the reactor as well as acting as emergency shutoff system (scram).
Surrounding the core is an 8-10″ thick cast iron thermal shield. Layered masonite and steel plates surround the thermal shield to protect operators from radiation. Bricks of ultra-pure graphite moderate the reactions. Fuel plugs consisted of uranium pellets 1″x3″ encased in aluminum. Cool Columbia River water was then piped through the fuel tubes at high pressure.
Bear in mind that B-Reactor was designed with 1943 technology: pre-transistor, pre-modern plastics, pre-automation. Most functions were monitored on simple coil gauges, controlled, and logged by hand. The task inspired creative solutions: an automatic electric typewriter was designed here in 1948 when an operator and mechanic wired an Underwood typewriter with solenoids connected to temperature recorders. The keys corresponded to specific temperatures, and eventually it was expanded to include red ink ribbons for numbers falling outside of specifications.
As the earlier diagram showed, fuel plugs that went into the reactor came out the rear side highly irradiated. They were pushed out into a discharge chute set in thick concrete, falling into a deep pool of water. Every 90 days the plugs were removed for reprocessing. The water moderated both heat and radioactivity, and workers never directly handled the plugs. This was as far as our tour was allowed to go, but there is a lot more history for those interested. I would recommend the B-Reactor tour for anyone interested in history, nuclear industry, or science. Or perhaps even just for creepy places– B-Reactor was a marvel of science and engineering, however it was also a radioactive nightmare producing components for the scariest weapons humans have ever developed… and at least one of those weapons was used.