Preserving the Hanford B-Reactor: A Monument to the Dawn of the Nuclear Age

Robert F. Potter

September 2009 marked the 65th anniversary of the startup of the world’s first industrial-scale nuclear reactor, the Hanford B Reactor. Designed and constructed within 22 months of Enrico Fermi’s first demonstration of a self-sustaining chain reaction, B Reactor produced plutonium for the Trinity Test and for the “Fat Man” nuclear weapon dropped on Nagasaki.

Cutaway diagram of a Hanford reactor

Cutaway diagram of a Hanford reactor. Illustration supplied by the author.

Unfortunately, as many of the facilities constructed for the Manhattan Project have been demolished or are off-limits to the general public, subsequent generations have lost valuable opportunities for learning about the history and impact of the Project. Since 1991, an all-volunteer group, the B Reactor Museum Association (BRMA), has worked with local and federal authorities to preserve B Reactor as a public museum. The reactor building and its contents are being restored to reflect their appearance as they were during operation, and exhibits reflecting the history of the Hanford site are being added. In this article I describe the history of B Reactor and BRMA’s preservation efforts.

B Reactor Construction and Operation

Based on the success of Fermi’s CP-1 pile, General Leslie Groves approved the Hanford Engineer Works site in southeastern Washington state for plutonium production in January 1943. Under design, engineering, construction and operations supervision of the DuPont corporation, a massive construction project promptly began on that remote 670-square mile reservation. The accompanying photograph, which shows just one of three wartime reactor sites at Hanford, gives an idea of the immensity of the project.

With its 250 MW thermal power output, B reactor was designed to produce sufficient plutonium for a nuclear weapons arsenal by itself, but duplicate D and F Reactors were also authorized to provide additional production capacity. [Editor’s note: At a power output of 250 MW thermal, a reactor fueled with natural uranium produces about 190 grams of Pu per day; the bare critical mass of Pu-239 is about 15 kg.] B reactor was constructed between October 1943 and September 1944.

The reactor buildings were 120 feet wide by 150 feet long and 120 feet tall. They were built on 23-foot thick concrete foundations, with quarter-inch steel plate set into the concrete and later welded to the outside walls of the reactor to form a gas-tight enclosure to keep circulating helium gas in. Helium was chosen for the reactor atmosphere because it was chemically inert and did not absorb neutrons [See Ref. 1 for a detailed description of the construction and engineering of the reactor.] The core of each reactor comprised more than 75,000 individually-machined graphite moderator blocks measuring approximately 4 inches square by 48 inches long and weighing 50 to 60 pounds each. The finished graphite pile was 36 feet wide by 36 feet tall by 28 feet front to back. As shown in the accompanying cutaway diagram, the core was surrounded by thermal and biological shields; the former comprised 10-inch interlocking cast iron blocks on all sides of the reactor to capture much of the radiation which escaped from the core, and the latter was a 50-inch thick sandwich of alternating layers of steel and Masonite designed to further reduce radiation to acceptable operating levels.

The core contained 2004 aluminum process tubes to hold the reactor fuel. These tubes ran from front to rear through the thermal and biological shields and the core. Each tube held 32 aluminum-clad cylindrical fuel elements, each approximately 1.5 inches in diameter by 8 inches long. A full fuel load was 64,000 elements. Each process tube had removable end-cap assemblies at the front and rear faces of the reactor to provide access for refueling and connection to the cooling system. Cooling water was taken from the Columbia river, purified, and pumped in a single pass through the tubes. Nine control rods entered from the left side of the reactor. Operators in the control room (to the lower left of the reactor in the cutaway diagram) could adjust these rods remotely to start the reactor and subsequently increase, decrease, or stabilize the reaction rate or shut the reactor down altogether if necessary. Twenty-nine vertical safety rods entered from the top of the reactor. Each of these was suspended above the reactor to a winch that was locked by an electromagnetic clutch. In the event of a power failure or other emergency, the clutch would release and the rods would drop into the core to shut down the reactor.

The first fuel was loaded into B Reactor by Enrico Fermi on September 13, 1944. Criticality was achieved with only 1,500 tubes loaded on the evening of September 26. As is well-known, the reactor shut itself down within a few hours due to Xenon poisoning, a situation which necessitated a significant delay in order to add fuel to the additional process tubes and to plumb the tubes into the cooling system. Full 2,004-tube criticality was achieved on December 28, 1944. The first “official” shipment of irradiated fuel elements from B Reactor was processed on December 26, 1944, and the first small batch of plutonium nitrate was transferred by DuPont to the Corps of Engineers on February 5, 1945. This plutonium was taken to Los Alamos and used in the Trinity Test. In the months that followed, the B, D, and F Reactors produced the plutonium that was used in the “Fat Man” bomb. In describing the pioneering nature of the plutonium project, General Groves wrote that “It was a phenomenal achievement; an even greater venture into the unknown than the first voyage of Columbus.” [2]

B Reactor in the Cold War and Beyond

Front face of B-reactor.

Front face of B-reactor. Photo supplied by Ruth Howes.

After World War II, six more reactors were built and operated at Hanford to produce materials for America’s nuclear weapons program. B Reactor operated for more than 20 years, finally being shut down for good in February 1968. While designed to operate at 250 MW, B Reactor was operated at levels that exceeded 2000 MW, with the only major modification being an increase in the cooling water capacity from 30,000 to 70,000 gallons per minute – a stunning tribute to the strength of the original design.

All nine of the reactors at Hanford were shut down by October 1989. That year, the primary mission of Hanford was changed from producing weapons material to cleanup of the waste that was the legacy of more than 40 years of material production. The new cleanup mission has two regulatory drivers: the U.S. Environmental Protection Agency (EPA)’s Superfund National Priorities List (NPL) and the Tri-Party Agreement between the EPA, the U.S. Department of Energy (DOE), and the State of Washington Department of Ecology. The NPL requires compliance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). CERCLA established regulatory requirements for cleanup of the site, including the decommissioning of the Hanford reactors, but it also provided a possible regulatory path for preserving B Reactor. The Tri-Party Agreement includes legally binding milestones for the cleanup of the site over the next few decades.

The possibility of B Reactor being decommissioned and demolished became the catalyst that focused the community on preserving B Reactor. In 1991, a small band of local supporters organized the B Reactor Museum Association (BRMA), a non-profit corporation dedicated to educating the public about the historical and technological significance of B Reactor by working to ensure its preservation and making it available to the public as a museum. Many of the more than 100 BRMA members spent their careers at Hanford; some helped to build and operate B Reactor and were present when Fermi directed its start-up.

BRMA’s initial activities included amateur lobbying, letter-writing, disseminating information, making presentations to civic and social organizations, participating in community activities, and establishing a working relationship with DOE to become a stakeholder in the future of the Hanford Site. Since the mid-1990’s BRMA has provided tour guide services for DOE visitors and for DOE-approved escorted public tours of the reactor. In 1999, BRMA was contracted to prepare the Historic American Engineering Record (HAER) for B Reactor, an in-depth look at the design, construction, and operation of the reactor. This document was submitted to the National Park Service to be included in the HAER archives in the Library of Congress and is available online [1].

In, 1993, DOE issued a Record of Decision (ROD) for the final Environmental Impact Statement for the decommissioning of the shut-down Hanford reactors. The ROD directs that the reactors will be placed in interim safe storage for up to 75 years, during which time monitoring, surveillance, and minimum maintenance will be performed. The 75-year safe-storage period would be followed by final demolition and disposal of the reactor blocks. Interim safe storage for the reactors, called “cocooning,” includes demolition of the reactor building down to the shield walls and installation of a safe storage enclosure roof; the remaining shield wall becomes part of the enclosure. Cocooning of the first of the reactors began in 1995; to date, five have been cocooned, with the other three scheduled to be completed by 2015.

In response to community interest in preserving B Reactor, DOE delayed the decision on the final interim safe storage option for B Reactor. In 1999, DOE issued the ROD for the Final Hanford Comprehensive Land-Use Plan, with a preferred alternative that includes B Reactor as a possible museum and the surrounding area available for recreational support activities. To address the museum alternative and to meet CERCLA requirements, DOE conducted an Engineering Evaluation/Cost Analysis (EE/CA) for an interim removal action for B Reactor to support escorted public access. The result of the EE/CA was an Action Memorandum issued in 2001 by the EPA that authorized DOE to perform hazards mitigation within the reactor and to provide for public access to the reactor along a tour route designated in the EE/CA for up to 10 years. DOE subsequently invested more than $3 million for hazard mitigation, including monitoring to ensure safe radiation levels. All work on the reactor must be done in compliance with the National Historic Preservation Act of 1966 and the approval of the Washington State Historical Preservation Office. With the upgrades complete, DOE increased the number of scheduled escorted public tours of the reactor. More than 8000 visitors have toured B Reactor since 2001; at this writing, an additional 5000 visitors are scheduled to visit during 2009.

BRMA was a principal driver in establishing a local Coalition for B Reactor Preservation in 2005. The Coalition includes representatives from BRMA; the Tri-Cities Economic Developmental Council and Visitor and Convention Bureau, the Columbia River Exhibition of History, Science and Technology, and the Hanford Reach National Monument Heritage and Visitor Center. The Coalition has significantly increased the effectiveness of the grassroots effort to preserve B Reactor with the local DOE Office, DOE headquarters, and Congressional delegations.

The Coalition has received significant support from the Atomic Heritage Foundation (AHF), a Washington-based nonprofit organization dedicated to preserving the history of the Manhattan Project and its legacy. The Coalition joined with AHF to obtain a $350,000 grant from the M.J. Murdock Charitable Trust of Vancouver, Washington, to fund multimedia interpretive exhibits that were installed in B Reactor in 2007. These include audio-video vignettes accompanied by a computer-generated model of the reactor, archival photos, movie footage, filmed statements by Manhattan Project veterans, and a cutaway scale model of the reactor. Also located throughout the tour route are self-standing storyboard panels that describe the operation of various reactor systems.

A further initiative that may significantly impact the future of B Reactor is the “Manhattan Project Special Resources Study” currently being conducted by the National Park Service (NPS). This study was authorized by an act of Congress in 2003 which directed the NPS to evaluate the creation of a multi-site unit of the National Park System at Manhattan Project sites in Oak Ridge, Los Alamos and Hanford. BRMA has been working closely with the NPS Seattle Regional Office on the study, providing input for evaluating the suitability, feasibility, and possible management options for B Reactor to be included in the National Park System. The report on the results of the study is scheduled to be submitted to Congress by the Secretary of the Interior by the end of this year (2009), and will recommend how to preserve Manhattan Project facilities and identify the management resources necessary to make them available to the public. Follow-on Congressional action will presumably provide the direction and means necessary to preserve these facilities.

Finally, B Reactor was placed on the National Register of Historic Places by the NPS in 1992. In 2005, BRMA submitted a draft application to the NPS Seattle Office for B Reactor to receive the nation’s highest designation for a historic property, that of a National Historic Landmark. Following receipt of review comments from the NPS Program Office of National Register of Historic Places and National Historic Landmarks, the NPS Seattle Office took the lead in preparing and submitting the final application and sponsoring the nomination before the Landmark Committee. After more than two years of reviews and hearings, the Secretary of the Interior designated B Reactor as a National Historic Landmark in August 2008. This is a significant achievement: less than 3% of sites on the National Register ever get elevated to Landmark status.

BRMA and the Coalition for B Reactor Preservation feel that we are close to reaching our goals of preserving this historic marvel of science and making it available to the public. While there is still work to be done, there are lessons that have been learned that will continue to serve us well as we go forward and can serve as guides for others involved in similar projects:

  • Clearly define and stay focused on your objective. Plan and execute actions that directly address your objective – don’t waste time and resources doing things that don’t advance your cause.
  • Know and understand the regulatory requirements that impact your project, and use them to your advantage.
  • Maintain effective and open communications with all levels of local, state and federal governments and the regulatory agencies that are involved in your project. Find and work with at least one advocate for your project within each of those organizations.
  • Build a broad base of community and political support.
  • For projects that involve Federal agencies, involve support from your Congressional delegation and their staff.
  • Don’t lose patience – the wheels of government grind slowly and are largely beyond your control.


[1]B Reactor Museum Association, Historic American Engineering Record B Reactor (105-B Building) HAER No. WA-164, (Richland: U.S. Department of Energy, 2001) Available online.

[2]Leslie R. Groves, Now It can Be Told (1962; reprint DeCapo Press, Inc., 1983), p. 38.

Robert Potter is a retired Project Manager with Bechtel Corporation with 30 years of experience in the nuclear industry, including more than 15 years at the Hanford Site. While at Hanford, Potter’s responsibilities included surveillance and maintenance of retired plutonium production reactors (including B Reactor) and management oversight for the decommissioning of five of those reactors. Mr. Potter is a member of the BRMA and is Co-chair for Public Relations. Further information on BRMA’s activities can be found at

This contribution has not been peer refereed. It represents solely the view(s) of the author(s) and not necessarily the views of APS.