How is Pu-239 produced in a typical reactor?

How is Pu-239 produced in a typical reactor?

• A. Direct fission of U-238
• B. Neutron capture by U-235 followed by alpha decay
• C. Neutron capture by U-238 followed by beta decay to Pu-239
• D. Spontaneous transmutation during cooling

Answer: (C)

Pu-239 is produced in a reactor by neutron capture on U-238, forming U-239, which then beta decays to Np-239 and subsequently to Pu-239. This sequence happens under continuous neutron exposure, so Pu-239 builds up over time as the reactor operates. The timescales—U-239 decays in about 23.5 minutes to Np-239, and Np-239 decays in a few days to Pu-239—allow Pu-239 to accumulate alongside the fission products. Direct fission of U-238 or spontaneous transmutation during cooling do not produce Pu-239, and neutron capture by U-235 doesn’t yield Pu-239 through a simple, immediate path.

Pu-239 is produced in a reactor by neutron capture on U-238, forming U-239, which then beta decays to Np-239 and subsequently to Pu-239. This sequence happens under continuous neutron exposure, so Pu-239 builds up over time as the reactor operates. The timescales—U-239 decays in about 23.5 minutes to Np-239, and Np-239 decays in a few days to Pu-239—allow Pu-239 to accumulate alongside the fission products. Direct fission of U-238 or spontaneous transmutation during cooling do not produce Pu-239, and neutron capture by U-235 doesn’t yield Pu-239 through a simple, immediate path.