Material marvels: Hanford B nuclear reactor

Materials World magazine
1 Aug 2017

On 26 September 1944, a first sustained nuclear chain reaction at a new reactor began. Its purpose was not to prove whether fission could be achieved or sustained, but to explore its weaponised potential. Khai Trung Le looks at Hanford B, the world’s first full-scale nuclear reactor.

The Hanford B nuclear reactor has a complex legacy. Created in wartime secrecy, the world’s first full-scale nuclear reactor is undoubtedly one of humanity’s greatest engineering accomplishments. It was paramount to the success of the Manhattan Project, producing the plutonium used in the 1945 Trinity atomic tests and the ‘Fat Man’ atomic weapon dropped on Nagasaki, Japan, and its rapid design and construction is a testament to the collaborative spirit of the engineering community.

But the Historic American Engineering Record is unremittingly direct about the sole purpose of Hanford B – ‘Its mission was to transmute uranium into plutonium, which could then be fashioned into an atomic bomb’. Within two years from the beginning of construction, the plutonium produced at Hanford B resulted in the deaths of between 70,000 and 80,000 people, and it is impossible to escape this context when discussing the B reactor.

The Greater Manhattan Love Song

Hanford B was created as part of the secretive Manhattan Project, which sought to exploit the newly recognised fission process for military purposes. The project, which began with a modest US$6,000 budget before escalating to US$2 billion, has its roots in the Advisory Committee on Uranium (ACU), formed in October 1939 by President Franklin Roosevelt to investigate the feasibility of atomic weapons, as encouraged in a letter by physicists Leo Szilard and Eugene Wigner and signed by Albert Einstein, in response to known similar efforts from Germany. Soon after, in April 1940, Germany invaded Denmark and Norway, capturing a plant in Vemork, Norway, that specialised in heavy water, at the time suspected to be a key ingredient in generating nuclear power. 

The ACU was focused on the highly fissionable isotope uranium-235 until a research group under Dr Glenn Seaborg at the University of California, USA, succeeded in creating and isolating the first submicroscopic amount of plutonium-239 on 6 March 1941, and just 22 days later demonstrated that 239Pu would fission when bombarded with slow thermal neutrons. In December 1941, the ACU sponsored a research programme on plutonium, designing, constructing and operating a plant for the conversion of uranium into plutonium, led by Dr Vannevar Bush.

Shortly after the USA entered the Second World War in 1942, Bush declared that an atomic weapon was feasible and could be developed in time to influence the war, and Brigadier General Leslie Groves took charge of all Army activities related to the Manhattan Project. As the Army Corp of Engineers began exploring possible plutonium production sites, Professor Enrico Fermi and his University of Chicago, USA, team successfully created the world’s first controlled, self-sustaining nuclear chain reaction in December 1942. His pioneering work provided the framework for Hanford B as Fermi was chosen to supervise the design of the reactor. While the Chicago pile (as reactors were referred to at the time) did not produce more than 200W, the B Reactor operated at 250MW, and in later years exceeded 2,000MW.

Bring your B game

The site of the Hanford Engineering Works, the earliest name of the Hanford site, was approved in January 1943. It was located on the banks of the Columbia River, and excavation for the 105-B building, which would house the nuclear pile, began in October 1943. Shortly after the site was chosen, all 300 residents from the nearby town of Richland were evicted in the spring of 1943 to facilitate the influx of staff that would construct and work on Hanford. Throughout the reactor’s life, the plant hired 94,307 people, with over 45,000 workers on the payroll during its peak in mid-1944.

Hanford B was one of eight planned reactors, and three constructed under the Manhattan Project – B, D and F, and for the first nine months, all construction at Hanford was performed under a letter of agreement, awaiting a formal contract between the US Government and a principle contractor. The DuPont Corporation was chosen as the principle contractor for the project due to the company’s experience in designing, building and operating large manufacturing plants. DuPont’s involvement has been celebrated, with construction of Hanford B essentially complete by September 1944. However, Hanford B did not escape a number of problems, not least the hardship of reactor construction being an unknown quality and the secretive nature meant workers were told little of the purpose of the project.

John Fox, President of the B Reactor Museum Association, told Materials World, ‘DuPont faced designing reactors and remotely operated chemical processing plants without knowing enough about them to be sure they would work, and thus built flexibility and contingencies using rigorous project management and safety methodologies. Of course, a blank cheque and top wartime priorities helped.’

The 105-B reactor building housed the 8.5 x 11m graphite pile, weighing 1,200 tonnes and penetrated with 2,004 aluminium process tubes that would shuttle uranium fuel slugs and water from the nearby Columbia River to keep it cool. A water treatment plant was constructed nearby to help provide high-purity water. Suspended above the pile were 29 vertical safety rods that could be dropped to scram the pile – stop the nuclear chain reaction and shut down – a term originating from Fermi’s original work with the Chicago reactor.

There were few issues surrounding the B reactor, but Fox noted that ‘the first metallurgical issue was the process for canning the roughly 10 x 2cm diameter natural uranium “slugs” in aluminium cans with assured thermal bonding.’ This was ultimately resolved ‘at nearly the last minute’ in 1944 with a process based on submerging the steel-sleeved cans in a pot of molten aluminium-silicon alloy and manually inserting the slugs into the cans. The yield of serviceable canned slugs gradually reached acceptable levels for the required large throughput, but the process was never successfully automated, despite later attempts during the Cold War.


The secrecy of the project meant progress could continue unabated – essentially suspending the practice of a democracy. Groves’ involvement and position of authority insulated the Manhattan Project from multiple agencies, eliminating the need for discussion and compromise. Vice President Truman only learnt of the project upon being made President following Roosevelt’s death. This secrecy persisted as Hanford B was operational – very few staff knew the purpose of the reactor and fewer still of the wider Manhattan Project.

On 16 July 1945, a 13.5-pound plutonium core produced at Hanford B was used in the world’s first nuclear explosion, the Trinity test. The resulting explosion released as much energy as 21,000 tonnes of TNT and, to the observers situated six miles away, was deemed a success.

Less than one month later, on the evening of 8 August 1945, the B-29, Bockscar, flew towards Nagasaki with the nuclear implosion device, ‘Fat Man’, powered by Hanford plutonium. At 11:02 local time on 9 August, the bomb was dropped, exploding at a force equivalent to 22,000 tonnes of TNT – 40% greater than the ‘Little Boy’ bomb dropped on Hiroshima. 30% of the city was destroyed, including most of the city’s industrial district, with a death toll by the end of 1945 between 70,000 and 80,000, and increasing to more than 140,000 within five years.

In Richmond, the atmosphere was markedly different. On 6 August, after the attack on Hiroshima, the local newspaper, The Villager, ran the headline, ‘IT’S ATOMIC BOMBS’, as the secrecy surrounding the Manhattan Project and role of Hanford B began to dissipate. The Historic American Engineering Record notes a jubilant mood across the town – to the vast majority of Hanford workers, it was the first indication of their role in the war effort, and a source of great pride. On 14 August 1945, Japan formally surrendered and the Second World War was over, with many historians attributing this decision to the severity of the USA nuclear attacks. To this day, ‘Fat Man’ and ‘Little Boy’ are the only two atomic bombs ever used in combat.

Cold legacy

Hanford B was planned and built to fulfil a very short-term desire. With the end of the Second World War the need for plutonium began to vanish, and the contract between the US Government and DuPont was terminated in September 1946. General Electric took control of the site and Hanford B was initially closed, but as tension between the USA and the country’s primary nuclear rival, the Soviet Union, flared, Hanford B was restarted in 1948 to support plutonium production until 1967.

The reactor produced numerous forms of plutonium in its lifespan. Hanford B initially made plutonium nitrate, until the early 1950s when the conversion to metal was added, looking to exploit the relatively low melting point and complex metallurgy of metallic plutonium. Fox said, ‘In the 1960s, the Hanford R&D laboratory built a heavy water moderated reactor (PRTR) and produced mixed uranium-plutonium oxide ceramic fuel elements for its operation as part of a programme to develop plutonium fuels suitable for nuclear power reactors. In the late 1960s and beyond, a molten sodium-cooled fast reactor was built and operated as a pilot-scale fast breeder plant, until the US Government dropped the programme.’

In total, Hanford produced more than 67 tonnes of plutonium, enough for the manufacture of 13,000 atomic bombs. Former USA energy secretary, John Herrington, remarked that the country was ‘awash with plutonium’, and with the dissolution of the Soviet Union, 55 tonnes of plutonium was declared excess. Similarly, Hanford was reaching the end of its useful economic life, and on 12 February 1968 was finally deactivated.

The Hanford site consisted of more than 30 buildings and 20 facilities, and many have been dismantled and removed since. But the B reactor has been honoured and preserved by many organisations, including being named a National Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers in 1976, listed in the National Register of Historic Places in 1992 and declared a National Historic Landmark in 2008.

The Hanford B nuclear reactor’s role in history is undeniable, and rightly celebrated as a feat of wartime engineering and in asserting the feasibility of nuclear power. But the B reactor also helped demonstrate the awesome destructive force of nuclear energy. Now, nine countries – China, the USA, Russia, the UK, India, Pakistan, France, Israel and North Korea – collectively possess around 16,300 nuclear weapons. Some held under the promise of mutually assured destruction, more than enough to eliminate the human race, and all of which trace their origins to that first sustained chain reaction on 26 September 1944.