modern reactive armor that are designed to defeat KE projectiles as well as HEAT technically should work or at the very least diminish the effectiveness of the KE projectile from a railgun.
at the end of the day every single KE projectile be it fired from traditional chemical explosive or a railgun is the same thing, a fast moving solid projectile that transfer their KE into a concentrated spot on the target to pierce and penetrate it and produce damage to the internal either via sheer energy transfer or via spalling.
the reactive armor panel struck would detonate and distort the path and deflect the projectile preventing it from completely transferring the energy onto the same spot, or at the very least reduces it's effectiveness.
this doesn't guarantee it will stop the projectile, but it does increases the likelihood of the projectile failing to penetrate the actual armor.
