Carbon-14 and Iodine-129 Migration in Cement (CIM) Introduction

Carbon-14 and Iodine-129 released from repositories of L/ILW and TRU wastes typically contribute most to dose rates over the long-term (i.e. 10 ka to 100 ka) according to performance assessment (PA) calculations. This is primarily due to the combination of (i) high solubility and (ii) low sorption properties of the chemical forms that the two radionuclides are expected to exist in. In the case of C-14, experimental work on the speciation of carbon during corrosion of activated and un-activated steel under anoxic conditions similar to that of an emplacement tunnel showed the formation of oxygenated and reduced hydrocarbons, including carboxylic acids and CH4.

Methane is not expected to react with cementitious material or with the host rock. Uncertainties remain, however, on the retardation of carboxylic acids in clay and cementitious materials. In the case of formic acid, so far no retardation was expected in near-neutral environments; however laboratory experiments at PSI showed evidence of weak sorption of formic acid on cementitious material.

I-129 originates largely from reprocessed waste and is expected to occur mostly as iodide. Although it is planned that large amounts of cementitious material will be used in L/ILW and TRU waste repositories, there remains much uncertainty on both the release and in-situ retardation of I-129 as well as C-14 species in cementitious materials, especially in naturally aged cement on the field scale.

 

Aims of the experiment

The following aims were developed based on the wishes from the current partners (NUMO, RWM, SURAO and Nagra):

  • Simulate the transport of C-14 and I-129 through aged cementitious backfill of a L/ILW or TRU waste repository and into the saturated host rock
  • Provide confirmation on the effect of cementitious on material retarding C-14 and I-129
  • Further improve the process understanding of the behaviour of C-14 and I-129 under real in-situ conditions
  • Develop a method to upscale the results obtained from extensive laboratory based migration studies to the field/disposal tunnel scale.
The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.