To provide a composition for a heat cycle system comprising trifluoroethylene (HFO-1123), which has a low global warming potential and excellent cycle performance of HFO-1123 and which has high durability, and a heat cycle system employing the composition, which has less influence over global warming and has both high cycle performance and durability.
A composition for a heat cycle system, which comprises a working fluid for heat cycle containing trifluoroethylene, and a radical scavenger, and a heat cycle system employing the composition for a heat cycle system.