I'll get some pics up once I firm up some ideas and make it a bit prettier. I am trying an inner ring now as well, so I will have absorbers and boilers both inside and outside the toroids.
Here are some pics:
http://imgur.com/a/AIYKm
I've been trying different things in different quadrants. I also added an inner ring, which works quite well, it runs hot, but stable so far. I'll let it awhile to see if any bit melts.
The outer quadrant with the boilers arranged to form a right angle performs the worst. The corner does not get hot enough to make steam, and very few neutrons go there.
The thicker outer arc seems a bit overkill. The other thin ones seem to work fine with fewer boilers and absorbers.
In all cases on the outer parts, the first five blocks or so out from each plasma injector are quite cool, very few neutrons stray there. I put absorbers there anyway to catch strays.
I've noticed that placing absorbers higher up, above the other ones, also get hot. Seems some neutrons may be going up, I may try another ring up a bit and see if gets warm enough.