Safety Engineering for the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory
Abstract The Relativistic Heavy Ion Collider (RHIC) is a high energy particle accelerator built to study basic nuclear physics. It consists of two counter-rotating beams of fully stripped gold ions that are accelerated in two rings to an energy of 100 GeV/nucleon. The rings consist of a circular lattice of superconducting magnets, 3.8 km in circumference. The beams can be stored for a period of five to ten hours and brought into collision for experiments during that time. The first major physics objective when the facility goes into operation is to recreate a state of matter, the quark-gluon plasma, that has been predicted to have existed at a short time after the creation of the universe. There are only a few other high energy particle accelerators like RHIC in the world. Each one is unique in design and contains systems and hazards that are not commonly found in general industry. Therefore, the designers of the machine do not always have consensus design standards and regulatory guidance available to establish the engineering parameters for safety. Some of the areas where standards are not available relate to the cryogenic system, containment of large volumes of flammable gas in fragile vessels in the experimental apparatus and mitigation of a Design Basis Accident with a stored particle beam. The ASME Code requires Charpy testing of welds at cryogenic temperature, but testing at 4 K is nearly impossible to conduct. Engineered welds were used to provide an equivalent level of safety. A cryogenic system is a process system. The RHIC system was designed first by selecting a safe operating mode, then analyzing to ensure this mode was preserved. Cryogenic systems have unique processes, and the safe mode will surprise most process engineers. The experimentalists require detectors to be designed to meet the need of the physics objectives, but the application of standard construction techniques would make research mission impossible. Unique but equivalent safety engineering must be determined. The rules promulgated in the Code of Federal Regulations under the Atomic Energy Act do not cover prompt radiation from accelerators, nor are there any State regulations that govern the design and operation of a large superconducting collider. Special design criteria for prompt radiation were developed to provide guidance for the design of radiation shielding.
