The alloy chosen for the Nautilus reactor was Zircaloy-1, which was a binary alloy of zirconium and tin (Zr-2.5%Sn). While pure zirconium was used for the Mark I cladding, it was understood that an alloy was needed to improve yields and reliability in performance. The much lower neutron cross section of zirconium compared to stainless steel, however, offered long-term economic advantages that outweighed these short-term risks. There also were many risks regarding zirconium’s performance and the ability to manufacture enough of it for the needed supply. It was a bold decision because there was no industrial source of zirconium.

In 1949, Rickover chose to use zirconium as the cladding for the Mark I prototype for the Nautilus over the more practical choice of stainless steel. The story of the development of zirconium alloy cladding sticks out in this regard. As I have read what others have written about him and what he has written himself, I have come to understand that a key reason for his ability to take risks was that he knew what the risks would be and that he could course correct or cancel a project. Reactor safety was always paramount to Rickover. While that created flexibility in decision-making, it also came with much responsibility. He was not only the designer, but essentially the regulator as well. Rickover had autonomy over the design requirements that current reactor vendors do not have. There are obvious differences between today and the 1950s. There has never been a shortage of big, innovative ideas in the nuclear power industry, but there has been a shortage of realizing them. How Rickover did it is still worth understanding today as the nuclear power industry begins what I hope is a new era of innovation. Then when I think about the new materials that had to be developed to ensure success, such as zirconium alloys manufactured on an industrial scale, I marvel again. Whenever I think about Rickover’s accomplishment in designing, building, and operating the first pressurized water reactor in a matter of five years, I marvel at it.

Rickover’s influence: Like the trip under the ice cap to the North Pole, Rickover’s development of nuclear power for the Navy was filled with risks. While Rickover wasn’t on the Nautilus when it made the trip under the North Pole, his inclusion as an honoree that day in New York City was a recognition that such a trip was only possible because of his development of nuclear power for the Navy and the country. Rickover were honored with a ticker tape parade in New York City to commemorate this incredible journey. President Eisenhower presented Commander Anderson with the Legion of Merit on August 8, and the entire crew received a special Presidential Unit Citation for its bravery in the face of danger, the first such citation ever issued in peace time. The country cheered the Nautilus’s accomplishment. Rickover pictured in 1955 as a rear admiral.

Nautilus submarine north pole