When was the first nuclear reactor invented the?

Answer 1

The nuclear reactor (and atomic bomb) were invented in 1933 in London by Leo Szilard. He applied for a patent in 1934, was granted it in 1936, and the British Admiralty (Navy) promptly classified it to prevent the Nazis from learning of it. But no work was done as no material was known to exist that could fuel either.

In 1939 a joint team working in Germany and Sweden discovered that uranium-235 would fission when struck by a neutron and it immediately became obvious (even to scientists that were unaware of Szilard's classified invention) of the possibility of making both nuclear reactors and atomic bombs. But there was still a long way to go before either were practical to build.

The first experimental nuclear reactor (CP-1) was built on December 2, 1942 (less than a year after the Japanese attack on Pearl Harbor) by Enrico Fermi in Chicago as part of the secret Manhattan Project to build the atomic bomb.

The first atomic bomb was tested on July 16, 1945 and the second and third atomic bombs were dropped on Japan on August 6, 1945 and August 9, 1945 resulting in Japan's surrender on August 14, 1945. The fourth atomic bomb (built before the surrender) arrived in San Fransisco on August 18, 1945 to be flown across the Pacific and dropped on Japan in late August was instead ordered by President Truman to be returned to Los Alamos, where it became the first atomic bomb in the US nuclear stockpile. Note: this decision by Truman to stop the atomic bombing of Japan was his first actual decision on the use of nuclear weapons, prior to this he simply continued the policy decisions made by FDR prior to his death (and all final targeting and delivery date decisions for the atomic bomb were delegated to the field military commanders, the authorization to use was simply "as they became available" from Los Alamos and could be shipped to the field).

The first nuclear powerplants had to wait until the early 1950s.