Single event upsets (SEUs) are becoming increasingly problematic for VLSI circuits due to device scaling, decreasing supply voltages and increasing operating frequencies. To deal with SEUs, radiation hardening is often employed to increase the reliability of VLSI systems. Most existing radiation hardening approaches focus on the combinational or sequential part of the design. Little or no attention has been paid to the impact of radiation particle strikes on the clock network of an IC. Recently, it has been shown that in the deep submicron regime, radiation particle strikes on clock networks can prove to be catastrophic. As a result, the clock network contributes significantly to the chip level Soft Error Rate (SER). In this paper, we present two SEU hardened clock regenerator designs which are immune to radiation particle strikes. The new designs result in a significant reduction in SEU induced clock jitter. Experimental results demonstrate that our clock regenerator hardening approaches reduce the radiation induced jitter to around 30ps and completely eliminates radiation induced voltage glitches, for radiation strikes with a deposited charge of up to 150fC.