The complete Russian thesaurus is available as a single file (in UTF-8 encoding).
The calculation of semantic classes uses the Singular Value Decomposition method (it is based on a database computation procedure developed by Reinhard Rapp) and finds a cluster (i.e. words which semantic classes also contain words similar to the original word). You can control the size of intersection between semantic classes of the two words to consider them as belonging to the same cluster.
The interface was developed by Serge Sharoff; contact me at s.sharoffleeds.ac.uk, if you have further queries.