The MAPLE 1 and 2 reactors are 10 MW(t), pool type, light water moderated and cooled radioisotope production reactors that are housed in reactor halls within the reactor buildings. The effluent air from the reactor halls is exhausted to an existing stack via dedicated ducts and air filtration systems.

MAPLE 1 Reactor at 8 MWt

The MAPLE reactor core is located above a grid plate and inlet plenum structure at the base of the pool. The core is about 0.4 m in diameter by about 0.6 m in height and consists of low enrichment uranium (LEU) driver fuel bundles and high enrichment uranium (HEU) ⁹⁹Mo target assemblies arranged in a close-packed array. Each fuel bundle and target assembly is in a vertical coolant flow tube that is connected to the grid plate at the base of the core and is open at the top. The core is surrounded by an annular reflector tank filled with heavy water that also contains a number of vertical tubes for isotope irradiation. A large upright structure, called a chimney, is attached to the top of the reflector tank and is open to the pool at its top. It acts as an outlet coolant plenum, collecting water leaving the core.

The core is cooled by low-temperature and low-pressure (~30°C and <0.4 MPa) light water pumped through the core. The primary coolant is piped from a heat exchanger located outside the pool, down to the inlet plenum, where it is directed upward through the grid plate, the flow tubes and the fuel, and exits into the chimney. Two nozzles attached to opposite sides of the chimney conduct the coolant into the core outlet piping leading to the pump inlet. Approximately 10% of the primary flow is released from the core inlet piping at the bottom of the pool. This bypass flow returns down the chimney to provide suppression of the core outlet flow to the lower part of the chimney. Decay heat removal is by natural circulation of the pool water through the core.

Heat is removed from the heavy water in the reflector tank via the Reflector Cooling System, which also rejects its heat to the Process Water System. The Pool Purification and the Skimming Systems control pool water chemistry and purity. The reactor power level is controlled with three Control Absorber Rods (CARs), consisting of annular hafnium absorbers, which slide over the extended flow tubes in the outer ring of the core. Each CAR is connected by a rod and an electromagnetic coupling to a computer-controlled motor drive above the pool.

There are two separate, independent and diverse shutdown systems. One shutdown system uses three absorbers, similar in design to the control rods, which drop around the three remaining extended flow tubes in the outer ring of the core. The second shutdown system employs electromagnet disconnects on the drives of the CARs which, when de-energized, allow the CARs to drop into the core. This second shutdown system also partially drains the heavy water reflector tank.

The MAPLE 1 reactor building also contains the ¹²⁵I Production Facility. The MAPLE 2 reactor serves as backup for the MAPLE 1 reactor for production of ⁹⁹Mo, ¹³¹I and ¹³³Xe, but currently does not include an ¹²⁵I Production Facility. However, provisions have been made to install an ¹²⁵I Production Facility in the MAPLE 2 reactor building at a later date. Four In-Reactor Vessels and the in-pool piping for the ¹²⁵I Production Facility are installed in the MAPLE 2 reactor because these components would be more difficult to install at a later date. Both reactors have a number of vertical tubes in the D₂O filled reflector tank that could be used for isotope irradiation. With the exception of the In-Reactor Vessel for ¹²⁵I production mentioned above, there are presently no plans for using these sites and they will remain empty and capped.