Aerial of the Hanford Site's 100K Area from October 2022.
Hanford’s 100 Area is the part of the Hanford Site located along the banks of the Columbia River. It is where Hanford’s nine former plutonium production reactors are found. The nine reactors (B Reactor, C Reactor, D Reactor, DR Reactor, F Reactor, H Reactor, K East Reactor, K West Reactor, and N Reactor) were built between 1943 and 1965. They were constructed next to the river because of the availability of hydroelectric power and cooling water needed to operate them.
These reactors were needed to facilitate the process by which the natural element uranium was changed into the man-made element plutonium, which was the critical substance required for atomic weapons to be produced. The Hanford reactors used a process called a chain reaction to change uranium into plutonium. During Hanford’s plutonium production mission from 1943 through 1987, tons of plutonium were produced by hundreds of thousands of tons of uranium fuel rods being subjected to the chain reactions inside the reactors.
This process of producing plutonium was extremely inefficient. The years of plutonium production generated millions of tons of solid waste and billions of gallons of liquid waste. Cleaning up those wastes constitutes Hanford’s current mission for the Department of Energy.
The last operating reactor, the N Reactor, was shut down in 1988. Beginning in the 1990’s, workers began the process of “cocooning” the reactors. When a reactor is cocooned, about 80% of the buildings and auxiliary structures needed to support the reactor during its operating days are demolished. The remaining 20% of the reactor complex, including the core of the reactor itself, is enclosed in a cement-and-steel, airtight and watertight structure called a cocoon. This prevents any radiation or contamination left over from the nuclear operations from escaping into the environment. Ultimately, eight of the nine reactors at Hanford will be cocooned. C, D, DR, F, H, K East, and N Reactors are already cocooned, with K West next in line. The ninth, B Reactor, has been preserved as the B Reactor National Historic Landmark and is part of the Manhattan Project National Historical Park.
Every five years Hanford crews enter these cocooned reactors to ensure the structures remain airtight and watertight. These cocoons will be in place over the reactors for approximately 75 years, allowing the radiation within the deactivated reactors to safely decay to levels where it doesn’t pose a threat to the environment or workers performing final demolition. Hanford engineers and scientists are already working on plans to demolish the reactors following the 75-year life spans of the cocoons.