McMaster University has a comprehensive radiation safety program that is implemented and overseen by the Health Physics Department and the university’s Senior Health Physicist. The program covers the extensive nuclear infrastructure on campus, including the nuclear medicine department at the hospital, licensed radioisotope laboratories in nearly a dozen buildings, X-ray sources and instruments, sealed sources of radioactivity, an extensive High Level Laboratory Facility for work with large quantities of radioisotopes, a 3 MV Van De Graaff Accelerator, a 1.25 MV tandem accelerator, two cyclotrons, and, of course, the nuclear reactor. The objectives of the radiation safety program are both to ensure that nuclear scientists and technicians are exposed to a minimum of ionizing radiation, and to protect McMaster students, employees, and residents in the surrounding community from any potentially harmful effects of the nuclear infrastructure on campus. The watchword for the radiation protection program is “ALARA”, meaning that work with nuclear materials is planned and carried out in such a way that exposure to ionizing radiation is kept As Low As Reasonably Achievable.
Radiation Safety & MNR’s Nuclear Energy Workers
Routine tasks at MNR are carried out according to standard procedures that have been approved by the Health Physics Department: any changes to existing procedures must be approved in advance. Radiation exposure to MNR staff is kept to a minimum by careful design of procedures and implementation of good work practices, such as recalling the principles of radiation protection: time, distance, and shielding. The time spent handling nuclear materials is kept to a minimum by the highly trained staff members; the distance between the worker and the nuclear material is maximized using remote handling tools; and radioactive materials are encased in lead or dense plastic containers to provide shielding from radioactive samples by attenuating the radiation they emit. Highly radioactive samples are handled in specially designed facilities such as MNR’s industrial hot cell, which is constructed of thick lead, to prevent radiation exposure to the worker.
A technician uses forceps to handle a stock solution of Iodine-125. The radioactive material is in a lead container that provides local shielding, with additional shielding and containment provided by the plexiglass window of the glovebox in which the assembly is contained.
A lead-shielded work area or “hot cell” with a leaded glass window and mechanical manipulators for remote handling of highly radioactive materials.
Reactor Operations staff maintain a safe distance from a sample while using a hand-held radiation survey meter (yellow, left) to measure the radiation field emanating from it prior to deciding if it can safely be removed from the shielding of the reactor pool water.
Staff members conducting work with radioactive materials at MNR have Nuclear Energy Worker status, meaning that they have received instruction in the effects of ionizing radiation and both acknowledge and accept the potential hazards of their work. Each staff member who works with nuclear materials within the reactor containment building is issued an Electronic Personal Dosimeter (EPD), a device that provides real-time monitoring of the radiation dose the worker has sustained, and the rate at which dose is being accrued. The device “chirps” when the dose rate is above a prescribed threshold, providing an auditory indication to the wearer to step back and reassess the situation. Radiation doses to personnel are reviewed regularly for trending and analysis purposes and to ensure that they are within both the legal limits set by the CNSC and the far more stringent Administrative Control Levels set by the Health Physics Department.
(Images courtesy of www.mirion.com)
L: An Electronic Personal Dosimeter (EPD).
R: Example of an EPD display screen indicating dose rate and accumulated dose.
In addition to personal dosimeters, the reactor containment building is equipped with thirteen area monitors that provide local, real-time measurements of radiation dose rates so that any minor increases in radiation levels can be detected and addressed promptly. There are also two continuous air samplers fitted with filtration assemblies in place to record levels of radioactivity in airborne particulate matter; radioactivity in the air inside the containment building is also examined in order to detect and quantify the gaseous fission product argon-41. Because one of the major commercial activities at MNR is the production of iodine-125, a potentially volatile radioisotope, four additional continuous air monitors equipped with charcoal filters that absorb iodine are in place to collect and quantify this species. The data produced by these monitoring devices are used to ensure that the levels of radioactivity inside the containment building are below both the legal (? permissible?)release limits set by the Canadian Nuclear Safety Commission (CNSC) and the Administrative Control Levels set by the Health Physics Department, which are approximately 100 times lower than the levels permitted by the CNSC.
The dedication of MNR personnel to radiation safety was recognized in 2003, when the “MNR I-125 ALARA Team” was named a recipient of the President's Award for Outstanding Service to McMaster University. The team was composed of members of the Health Physics Department and MNR staff members involved with the production of the medical radioisotope Iodine-125: the team’s objective was to reduce radiation doses to Iodine-125 production technicians to As Low As Reasonably Achievable (ALARA) levels. The team undertook a comprehensive and systematic review of the Iodine-125 production process, and several procedural modifications were implemented in consequence. The ultimate result of this study was a 93% reduction of the radiation doses sustained by the Iodine-125 production staff, which has allowed them to continue producing this cancer-treating radioisotope safely.
The “MNR I-125 ALARA Team”
Back row (L-R): Stan Spina, Steve Staniek, Jim McAndrew. Middle (L-R): John Avelar, Brad Trushinski, Djorde Bijelic, Rose Nielson, Peter George. Front: Alice Pidruczny, Heinz Schlicting , Ursula Walker. Absent: Shen Pang, Patti Smith, Richard Tomlinson.
The McMaster Daily News article describing the 2003 President’s Award ceremony, including recognition of the “MNR I-125 ALARA Team” can be accessed here.
For more detailed information about this joint Health Physics/McMaster Nuclear Reactor initiative, please visit the Health Physics webpage.