Mechanical properties of blended polyethylene (PE) containing the antioxidant Irganox 1010 and the UV-absorber Tinuvin 326 were studied for future use as radiation capsule material for the TRIGA Mark II research reactor. High density and low density polyethylene were blended with the additives and tested for elongation at break, impact strength and gel content, before and after irradiation inside the nuclear reactor. Characterization via FTIR as well as determination of crystallization and melt transition temperatures through DSC were also conducted. It was found that the addition of the antioxidant at different amounts (from 0 to 4 phr) had various effects on the properties of the blended PE, with 0 phr being the amount at which there was the biggest increase in elongation at break and impact strength, post-irradiation.