[en] To ensure the safe encapsulation of spent nuclear fuel rods for geological disposal, SKB of Sweden are considering using the Copper-Iron Canister, which consists of an outer copper canister and a cast iron insert. Over the years a programme of laboratory work has been carried out to investigate a range of corrosion issues associated with the canister, including the possibility of expansion of the outer copper canister as a result of the anaerobic corrosion of the cast iron insert. Previous experimental work using stacks of test specimens has not shown any evidence of corrosion-induced expansion. However, as a further step in developing an understanding of the likely performance of the canister in a repository environment, Serco has set up a series of experiments in SKB's Aespoe Hard Rock Laboratory (HRL) using inactive model canisters, in which leaks were deliberately introduced into the outer copper canister while surrounded by bentonite, with the aim of obtaining information about the internal corrosion evolution of the internal environment. The experiments use five small scale model canisters (300 mm long x 150 mm diameter) that simulate the main features of the SKB canister design (hence the project name, 'MiniCan'). The main aim of the work is to examine how corrosion of the cast iron insert will evolve if a leak is present in the outer copper canister. This report describes the progress on the five experiments running at the Aespoe Hard Rock Laboratory and the data obtained from the start of the experiments in late 2006 up to Winter 2011. The full details of the design and installation of the experiments are given in a previous report and this report concentrates on summarising and interpreting the data obtained to date. This report follows the earlier progress reports presenting results up to December 2010. The current document (progress report 4) describes work up to December 2011. The current report presents the results of the water analyses obtained in 2007, 2008 and 2010 including gas composition and microbial activity. These data show an increase in the dissolved iron concentration inside the support cage, together with a decrease in the pH. Both these observations appear to be mainly due to microbial activity, but it is also possible that abiotic processes could have contributed to changes in the local chemistry. Microbial analysis has shown the presence of sulphate-reducing bacteria (SRB) and autotrophic acetogens. The presence of low density bentonite appears to stimulate the growth of SRB, but recent studies reported in the literature indicate that high density fully compacted bentonite inhibits SRB activity. A further set of water samples was taken for analysis at the end of 2010 and these results are also included in this report. These data show a similar trend as before, with increases in the dissolved iron concentration inside the support cage and a decrease in the pH. Further water analysis on Experiment 3 was carried out before it was removed for analysis, but the results from this analysis are presented in a separate report