Host matrices for actinide immobilization will undergo the formation of large He quantities due to α-decay. The He diffusion rate had to be known in order to predict the long-term behaviour of the material, and particularly, the influence of He accumulation on mechanical properties. A nuclear reaction analysis method, namely the 3He(d,p)4He reaction, was used to analyze the evolution of 3He profiles after ion implantations at 1 and 3MeV in two materials, monoclinic ZrO2 (as a test material) and Ca9Nd(PO4)5(SiO4)F1.5(OH)0.5 britholite (envisaged for Am and Pu long-term storage). Two data processing methods were used: the classical excitation curve (proton yields versus deuteron energy) and second, the proton energy spectrum for a given deuteron energy. The characteristics of the 3He profiles (depth, width) obtained by both methods, during subsequent annealing, indicated that the He diffusion rate in the britholite could be described by:

D (cm2/s) = 2.5 x 10-4 exp[-1.07(eV)/kT]

at 200 to 400C, in agreement with previous results on similar materials. Moreover, the shape of the proton energy spectra suggested channeling effects in britholite.

Determination of the Helium Diffusion Coefficient in Nuclear Waste Storage Ceramics by a Nuclear Reaction Analysis Method. D.Gosset, P.Trocellier, Y.Serruys: Journal of Nuclear Materials, 2002, 303[2-3], 115-24