Why can't nuclear fusion be used in nuclear power plants?

Nuclear fusion cannot be used in nuclear power plants because it cannot be controlled. Once it is started, it cannot be stopped till the reactants are finished. Moreover, tremendous amount of energy is released during the nuclear fusion and it is very difficult to use the energy efficiently. If in the future, it may be controlled then it could be used in nuclear power plants.

Nuclear fusion has not yet been successfully harnessed for widespread use in nuclear power plants due to technical challenges in achieving sustained fusion reactions at a scale and efficiency necessary for commercial energy production. Despite significant research efforts, scientists have yet to develop a practical and economically viable fusion reactor design that can reliably generate more energy output than the input required to initiate and sustain the fusion process. Additionally, the extreme temperatures and pressures required to initiate and contain fusion reactions present engineering hurdles that have yet to be fully overcome. While progress continues to be made in fusion research, practical fusion power plants remain a goal for the future rather than a current reality.