Nuclear fusion is expected as a main energy source in the future. D-³He nuclear fusion has some better characteristics such as low neutron emission and capability of direct energy conversion than D-T or D-D nuclear fusion. The present paper studies effects of secondary electrons produced at grids of TWDEC by the high-energy protons. It is found that the loss caused by the acceleration of electrons is about 1% of the input kinetic energy of protons, and effects of the electrical charge and the radiation are small. Therefore, all the effects are much smaller than the input power of protons.