Complex sentence: A few months later, Portal, who had not been appointed when this decision was taken, began to have doubts about it as word reached him of problems with the Hanford Site reactors, which had been all but completely shut down due to Wigner's disease.
Split into simpler sentences: A few months later, Portal, who had not been appointed when this decision was taken, began to have doubts. Word reached him of problems with the Hanford Site reactors, which had been all but completely shut down due to Wigner's disease.