That really doesn't seem to be it. Here I've got something like 250 infinite water reservoirs supplying the same setup - that's more than 10
per boiler - with exactly the same end result.
Spamming one of the boilers with an angular transducer reports that the internal tank always has either 11,800 or occasionally 11,600 mB of water, never any less, and yet the neutron absorbers are still heating up to 1500 C or something and melting quite rapidly. I've tried breaking every absorber, steam line and boiler and replacing them to see if it's some obscure tile entity thing without any luck.
At least the boilers themselves aren't quick to go, I only ever had one of those explode once (taking the entire pipe network with it, that was irritating to clean up).
If the boilers are, in fact, using this much water... I'm really not sure how to run one of these, like, ever. Even in creative. Reservoirs and liquid pipes seem to be able to move several buckets per tick if there's ample draw, and with over 250 of them? I can't think of any non-server-killingy way to supply anywhere near even that much water, especially without infinite sources like magic reservoirs.