I'm just finishing the Rhodes history, "The Making of the ..." , and am curious about the resolution of the Xenon poisoning problem after it was first discovered in the first production reactor at Hanford, the 100-B pile. According to Rhodes, shortly after starting the reactor for the first time they discovered the reactor dropping sub-critical every few hours due to Xenon poisoning, and the power up again as the Xenon decayed. The problem was resolved by adding another ~500 Uranium slugs, which overcame the neutron losses. My question is, with the additional U slugs, I assume power levels would still cycle up and down with Xenon production while staying critical, so how was control accomplished at that time with the B-pile? Apparently Fermi used Cadium rods in the Chicago experimental pile. Were these also used with the B-pile, and would they then need to be constantly pushed and pulled in and out of the pile, manually, to maintain constant power?