CONTROL OF RADIATION EFFECTS IN A GRAPHITE REACTOR STRUCTURE

A procedure was devised for releasing stored energy under controlled operating conditions. This was accomplished in the Broakhaven Reactor's first annealing operation and was accompanied by a fractional reduction of the dimensional growth which had occurred up to that time. Annealing operations are being conducted at more frequent intervals. As the data of these more frequent annealing operations are studied, perhaps a new and more interesting effect is being observed, namely thaat the growth is approaching an equilibrium maximum value, which probably depends on the annealing procedures. This view is confirmed by 4 in. long graphite samples that have been irradiated in the pile and measured within plus or minus 0.00003 in. for growth changes after different annealing treatments. These samples show that the percent contraction or recovery of the graphite on annealing is proportional to its growth since the last anneal. This gross growth value is dependent on the short time temperature history of thae reactor and net thae average temperature. The rate of C-axis increase is approximately ten times the rate of gress growtha after a thermal or pile anneal. The changes in dimensions and C-axis as well as the compressive strenhth and stored energy are discussed. Correlationsmore » between some of these properties are presented. It is concluded that sufficient information is now available on the rates of graphite growth under varying conditions and on methods of controlling growth, that graphite structures might be designed with considerably more assurance than in the past. (auth)« less