Instead of removing it every tick, you could just give the armor a damage resistance of Integer.MAX_VALUE if the DamageSource irs radiation.
I am newbie in mod development, just put some small fixes to existing code before, no serious work.
How should i do that? Maybe i just "subscribe" to some damage event(LivingHurtEvent?) and cancel it if DamageSource is radiation(not sure if it's possible for this type of event, as i said, i am newbie and just began to read Forge docs).
By the way what constant should it be? Should i just compare source with DamageSource("radiation") ?