DEUT with gray fireworks. To do so, you put deut into #1 first, and before putting gray fireworks in #2, you activate the engines, so that there are already neutrons that the fireworks can use. the pressure goes up a little higher that 256
I think PLUT works just fine though. +1 this is an amazing save.
fireworks (the orange one) and gunpowder work the best, in my eyes.