Kupfuura: Most fission reactors are thermal-neutron reactors that use a neutron moderator to slow down ("thermalize") the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239. Uyezve, uranium-238 has a much lower capture cross section for thermal neutrons, allowing more neutrons to cause fission of fissile nuclei and propagate the chain reaction, rather than being captured by 238U. The combination of these effects allows light water reactors to use low-enriched uranium. Heavy water reactors and graphite-moderated reactors can use natural uranium even as these moderators have much lower neutron cross capture sections than water. Kuwedzera kwekupisa kwemafuta kunowedzerawo chikamu chemuchinjikwa cheU-238 nekutambanudza kupisa kwemafuta kweiyo nyukireya dzinoputika dzakadai se uranium-235 kana plutonium-239.
thermal-neutron reactors anoshandisa neutron moderator kunonoka