IC2 Experimental, which also exists for 1.7.10 builds of MC, got rid of CASUC coolants (ice blocks, snow blocks, water buckets etc) to cool down your reactor, so that won't work.
There are two/three options that may work:
1. setting the profile to CLASSIC in your IC2.ini
2. Installing IC2 Classic instead of IC2 (Experimental). Do note that some addons for IC2 do not work with IC2 Classic.
3. Use RSH/LZH condensators and Reactor Coolant Injectors (RSH/LZH). These two would let you cool down a reactor with redstone dust or lapis lazuli. They can easily be automated with the reactor coolant injectors, but this is very inefficient, so it's advised that you try to automate refilling them with other methods.
I am not sure if there's a specific build in 1.7.10 that still has casuc coolants.
May you look for me please 
_/-><-\_
