Author Archives: Carel Neffenger

Plutonium Scale

Seederer-Kohlbush scale @ Hanford B Reactor

This Seederer-Kohlbusch scale, circa 1944, is found in a side room of the B Reactor at Hanford along with displays of other artifacts and mementos of the Manhattan Project. This is the original scale used to weigh the first milligrams of plutonium (Pu) produced at the facility.

Hanford B Reactor

In October 1943, construction began on the B Reactor at the Hanford Site in Washington, with the purpose of producing plutonium. Fuel slugs — uranium billets extruded into slugs and sealed in aluminum jackets — were then placed in the reactor for several weeks to a year. The reactor went critical on September 26, 1944. The first irradiated slugs were discharged from the reactor on December 25, 1944.

T Plant located in 200 West Area of Hanford. (T Plant @

Fuel slugs were then removed from the reactor and placed in a 90-day underwater cooling off period before being transported by train to the Hanford T Plant, which began operations on December 26, 1944. Next, the bismuth phosphate process was used on the fuel slugs to separate the plutonium from uranium and other fission products. The final processed product was plutonium nitrate, which made for safer shipping to Los Alamos.

In late January, 1945, the first milligrams of plutonium produced at Hanford were weighed on this scale then sent by courier to Los Alamos for testing. Los Alamos received its first plutonium from Hanford on February 2, 1945.

Building D, Tech Area, Los Alamos (Tech Area Gallery @

Subsequently, Building D in the Tech Area at Los Alamos would purify and fabricate the plutonium nitrate received from Hanford into the highly purified metallic hemispheres used in the Trinity and Nagasaki devices.

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SL-1 Memorial Plaque

SL-1 Memorial Plaque at the EBR-1 Atomic Museum

New this year at the EBR-1 on U.S. 20/26 between Arco and Idaho Falls, ID, is a memorial plaque to honor the three men who died in January 1961 at the Stationary Low Power Reactor (SL-1).

Thanks to Joe Tokarz for sending us these pictures of the new memorial during his visit on May 15. In Joe’s words:

Thank you to the DOE & INL for their support in making the SL-1 Memorial a reality. Bring a chair. It is a perfect location for quiet contemplation of the sacrifices made by Byrnes, McKinley, and Legg and the lessons we learned. All gave some. Some gave all.

The EBR-1 Atomic Museum is open from Friday, May 27, through Labor Day, September 5, for the 2022 season. It’s open every day, and the museum is open from 9am-5pm for self-guided tours. The new memorial plaque is in the parking lot between the transport train and the aircraft engines.

For more information on the SL-1 accident, visit: SL-1 Accident Briefing Report 1961, SL-1 at Wikipedia, CE1 Richard Carlton Legg, SP5 John Arthur Byrnes III, and SP4 Richard Leroy McKinley.

The Atomic Age

On January 26, 1939, Niels Bohr publicly announced the splitting of the uranium atom. A plaque outside the entrance to Corcoran Hall at The George Washington University commemorates this.

The Fifth Washington Conference on Theoretical Physics, organized by George Gamow and Edward Teller, was held to discuss low-temperature physics and superconductivity.

However, the most famous event at the conference came from Niels Bohr with the public announcement that the nucleus of uranium had been split by bombardment with neutrons, with significant energy release. This was the dawn of the atomic age.

The announcement occurred in the Hall of Government, Room 209, which is located across 21st Street from Corcoran Hall.

Another plaque was placed inside Room 209 of the Hall of Government commemorating the announcement along with a list of the physicists present.