Walter Zinn
1907 - 2000

Walter Zinn as a Queen’s University senior in 1927. [Photo, courtesy Queen’s University Archives]

Walter Zinn, born in Berlin (now Kitchener), Ontario, in 1907, graduated from Queen’s University and received his Ph.D. in nuclear physics from Columbia University in 1934.   Recruited by Enrico Fermi to work on the Manhattan Project, Zinn released the world’s first self-sustaining nuclear reaction by withdrawing a control rod from the world’s first nuclear reactor in 1942 at the University of Chicago.   This view depicts "Wally" Zinn as a Queen’s University senior in 1927. [Photo, courtesy Queen’s University Archives]

When the Columbia nuclear physics research group moved to the University of Chicago early in World War II, Zinn supervised all phases of the construction of the first experimental nuclear reactor, or "atomic pile" as it was then called.   On December 2, 1942 he pulled out the emergency control rod from the reactor that released the world’s first self-sustaining nuclear reaction and reinserted it to terminate the chain reaction after 28 minutes of operation.   Later Zinn designed the first experimental fast breeder reactor and also provided key scientific advice in the design of the first United States nuclear-powered submarine.
- from Releasing the Power of the Atom - Early Canadian Connections by D. McCormack Smyth.

Originally attracted by the opportunity to conduct laboratory experiments, the Canadian-born scientist, who had acquired a mathematics degree in 1927 from Queen's University in Kingston, Ontario, left the actuarial department of an insurance company to study physics.   His graduate work led to a Ph.D. from Columbia University in 1934, and he then assumed a faculty position at the City College of New York, subsequently collaborating with Leo Szilard and Enrico Fermi to investigate chain reactions.
- from "Argonne National Laboratory 1946-96" by Jack M. Holl, p.47

From the Argonne National Laboratory website at
"Logos", Spring 2000 -- vol. 18, no. 1
Corrections and comments in italics

Nuclear pioneer Walter Zinn dies

by Dave Jacqué

Walter Zinn, Argonne’s first director and a pioneer in nuclear physics and reactor development, died Feb. 14, 2000, of a stroke in Clearwater, Fla.   He was 93.

Walter Zinn (standing) presses a button to shut down the Chicago Pile-3 research reactor.
HISTORIC SHUTDOWN -- Walter Zinn (standing) presses a button to shut down the Chicago Pile-3 research reactor.   He was responsible for building CP-3 [world's first working D2O moderated pile] and many other early reactors.   Argonne National Laboratory photo.

Zinn was a part of the team who designed and witnessed the world’s first self-sustaining nuclear reaction December 2, 1942. His breeder reactor design became common in U.S. nuclear submarines [not true - the PWR is the predominant type], and the boiling water reactor he developed served as the prototype for commercial nuclear reactors all over the world.

He served as the first director of Argonne National Laboratory from 1946-1956.   After leaving Argonne, Zinn formed a nuclear engineering consulting company, from which he retired in 1970.   He served as an advisor on nuclear energy for presidents from Dwight D. Eisenhower through Richard Nixon.

Zinn’s background of academic and practical experience, combined with a hard-driving personality, helped the fledgling laboratory off to a strong start.

Under his direction, the nation’s first national laboratory grew from a reactor research group housed at several sites to a world center for both reactor design and development and basic science, including environmental studies, biology, chemistry, physics, computers and metallurgy.

During Zinn’s tenure, the laboratory developed and built several new reactor designs including Experimental Breeder Reactor-I and CP-5.

Zinn designed the Experimental Breeder Reactor-I - the first nuclear reactor to produce electric power (Dec. 20, 1951) -- in Idaho at the National Reactor Testing Site.   EBR-I [aka CP-4] is a National Historic Landmark for its many achievements.

In 1953 it was the first nuclear reactor to demonstrate the breeding principle - that reactors can generate more nuclear fuel than they consume.   In November 1963, EBR-I became the first nuclear reactor to achieve a chain reaction with plutonium and the first to demonstrate the feasibility of using liquid metals at high temperatures as a reactor coolant.   EBR-I was nicknamed ZIP - for Zinn’s Infernal Pile.

CP-5, the fifth reactor in the Chicago Pile series, operated at Argonne from 1954 to 1979, providing neutrons for experiments that probed the structure of solids and liquids.   CP-5 was a heavy-water-moderated, highly enriched uranium-fueled thermal reactor.

Nuclear power beginnings

Zinn worked with Leo Szilard at Columbia University on the Manhattan Project, then moved with the project to the University of Chicago.   A principal assistant to Enrico Fermi, he oversaw the construction of Chicago Pile-1 in a squash court at the university.   Zinn devised a weighted safety rod monikered ZIP that would automatically trip if the reactor core became too energetic.   Zinn stood by with an emergency ZIP, tied to the balcony rail, ready to operate it by hand if needed.   It was not.

Zinn received a special commendation from the U.S. Atomic Energy Commission in 1956.   He received the Atoms for Peace Award in 1960 and the Enrico Fermi Award in 1969.

[Canadian Nuclear Society home page]