When a slow neutron goes sufficiently close to a U²³⁵ nucleus, then the process that takes place is

Fission of U²³⁵

Nuclear fission can take place when a heavy nuclide such as ²³⁵U has an interaction with a slow neutron (0.025 eV). If a fission (or breaking apart) takes place, the nuclear breaks into two roughly equal pieces (on average) that move away with kinetic energy, generating heat.