``Maximal credible accident`` simulation studies at the storage ring of the APS

This study was aimed at determining the adequacy of the storage ring bulk shielding for reducing the radiation hazard outside of secured areas, due to errant particle beam losses. The hazard class (Low, Medium or High) of an accelerator is determined by the onsite and offsite effective dose equivalent under the assumption of a maximal credible accident occurring. The credible maximal accident condition is that which produces at the weakest part of the shielding at full power the greatest amount of radiation at the subject position outside the secured area during one hour. For the hazard class to be Low, the onsite radiation level must be between 1 and 25 rem in the one hour duration of the maximal credible accident. The safety envelope defines the bounding conditions for the safe operation of a DOE accelerator facility. The measured dose rate results at each location showed wide variations, which tends to indicate that the missteered beam may not have hit at the same point for each repeat of a given loss scenario. However, all measured results were comfortably below the calculated values. It appears the use of semi-empirical calculational methods are generally quite conservative, which is desirable for perceived beam loss accidents at the safety envelope. With respect to the disagreement between the calculated dose rates and the measured values for the maximal credible accident, the authors suspect that the actual showering which takes place is more distributed along the beamline than the 4-m-long beam spill assumed in the calculations. Since the distribution is not known this adds further to the difficulty in correlating the measured results with the calculated values. In all controlled loss studies, it appears that the measured results were obtained for showers that may not have been fully developed