Pure nickel and Ni-2wt%Si doped with several levels of boron- 10 (¹⁰B) and natural boron(ⁿB) were irradiated in FFTF at 679, 793 and 873 K and 40 dpa, for the purpose of examining the applicability of. boron addition to the study of helium effects. The comparison of B and ⁿB doped specimens showed that boron addition enhances cavity nucleation and growth via its transmutation effect and suppresses the nucleation via its chemical effect. Generally the transmutation effect was dominant at higher temperatures. In Ni-Si alloys, boron's chemical effect in suppressing the cavity density was stronger than that in pure nickel. Ni³Si precipitates were observed at 679 K but not at 793 and 873 K. Radiation-induced segregation of silicon at grain boundaries was most prominent at 793 K. The influence of boron addition on Ni³Si precipitation or the segregation of silicon is not yet clear.