Stability of I-125 and C-14 labelled boom clay organic matter

The candidate host formation for the disposal of radioactive waste in Belgi um is Boom Clay which may contain up to 4% organic matter (OM) [1]. A limit ed fraction (less than 0.05%) of this OM is mobile. OM can complex radionuc lides and so influence their migration. The migration behaviour of the OM i tself has been extensively studied but to date such studies have used absor bancy measurements to quantify the OM. Unfortunately various problems accom pany the use of absorbancy measurements. The particular problems may be ove rcome by using radiolabelled OM. Accordingly as a precursor to planned in situ migration experiments in Boom Clay (BC) using radiolabelled OM, stability studies on I-125 and C-14 labe lled materials have been conducted. The I-125 containing solutions were ana lysed using Gel Permeation Chromatography (GPC) and the C-14 solutions usin g High Performance Size Exclusion Chromatography (HPSEC). Dissappointingly at the relevant pH of 8.5, even in the absence of the clay, the I-125 label was found to be unstable. However the C-14 labelled OM (C-14-BC-OM) was st able under the mild conditions employed in the test, so its stability was i nvestigated in the presence of Boom Clay. The results were compared with th at of C-14 labelled humic acids (C-14-HA), treated similarly. Unexpectedly the C-14 labelled material was found to be partially unstable in the presen ce of Boom Clay. However the instability has not hampered the laboratory co lumn experiments and should not hamper the proposed in situ experiments wit h this material.