Finer gradations of radioactivity

Make the "radioactive" group value be the safe distance in millimeters
rather than meters, to allow for intermediate values.  Use such
intermediate values for the uranium blocks, using the existing formula
with this finer quantisation.  All other radioactive nodes retain their
existing radioactivity exactly.
Rebalance radiation shielding

Squeeze the range of material shielding values.  The strongest shielding
materials get weaker, and weaker shielding materials, especially low-end
ones such as dirt, get stronger.  The radioactivity of the active
reactor core is increased so that the standard shielding is (still)
only narrowly sufficient.
Update wrench's metadata for technic machines

The changes that this covers are that the alloy furnaces now have one
"src" inventory instead of a "src" and "src2"; that the tool workshop
is now MV; and the existence of MV compressor, extractor, and centrifuge.
Make wrench available in creative mode only

The wrench is far too powerful to be available to survival-mode players
via a cheap recipe.
Make tree tap respect item_drop