Breeder nuclear reactor is a reactor in which nonfissile u-238 is converted into fissile pu-239. the process involves bombardment of u-238 by neutrons to form u-239 which then undergoes two sequential beta decays.

Nuclear reaction 1: ²³⁸U + n⁰ → ²³⁹U.
Nuclear reaction 2: ²³⁹U → ²³⁹Np + e⁻ + electron antineutrino.
Nuclear reaction 3: ²³⁹Np → ²³⁹Pu + e⁻ + electron antineutrino.
Beta decay is radioactive decay in which a beta ray and a neutrino are emitted from an atomic nucleus.
There are two types of beta decay: beta minus and beta plus. In beta minus decay, neutron is converted to a proton and an electron and an electron antineutrino. 

The total number of nucleons

The ground state electron configuration of a phosphorous atom has  three unpaired electrons. they're in the 3p sublevel. the electron configuration is: , for a total of  15 electrons.