The continuous advancement of complementary metal-oxide-semiconductor technologies makes flip-flops (FFs) vulnerable to soft errors. Single-node upsets (SNUs), as well as double-node upsets (DNUs), are typical soft errors. This paper proposes two radiation-hardened FF designs, namely DNU-tolerant FF (DUT-FF) and DNU-recoverable FF (DUR-FF). First, the DUT-FF which mainly consists of four dual-interlocked-storage-cells (DICEs) and three 2-input C-elements, is proposed. Then, to provide complete self-recovery from DNUs, the DUR-FF which mainly uses six interlocked DICEs is proposed. They have the following advantages: (1) They can completely protect against SNUs as well as DNUs; (2) the DUT-FF is cost-effective but the DUR-FF can provide complete self-recovery from any DNU. Simulations show the complete SNU/DNU tolerance of DUT-FF and the complete SNU/DNU self-recovery of DUR-FF but at the cost of indispensable area overhead when compared to the SNU hardened FFs. Besides, compared to the FFs of the same-type, the proposed FFs achieve a low delay making them suitable for high-performance applications.