Answer is: b. safe disposal of hlrw.
HLRW is High-level radioactive waste.
Nuclear (radioactive) waste is hazardous to all forms of life and the environment.
Long term storage of radioactive waste is needed. It is important the stabilization of the waste into a form which will neither react nor degrade over many years.
If nuclear waste is wasted in atmosphere or into oceans and lagre lakes, eventually it will come in contact with living organisms.
Nuclear fission is a nuclear reaction or a radioactive decay where nucleus of atom split into smaller ligher nuclei.