Pickering Compared to the other major Canadian nuclear power plant built earlier, Pickering station, the Bruce reactors have higher power output, achieved by: increasing the number of fuel channels, increasing the number of bundles per channel, and a change in the fuel bundle itself. At Bruce, the fuelling equipment is shared by the four reactors of each plant, while at Pickering each reactor had a fuelling machine. The Bruce fuelling machine and fuel channel end fitting design (mostly by Canadian General Electric) is based on the Nuclear Power Demonstration design. The Pickering design by AECL was based on Douglas Point. The building design of the reactor differs: Bruce uses a squarish "close-in" design, in which as much of the equipment as possible is arranged outside the main containment envelope for easier access during maintenance and emergencies. The steam generators penetrate the containment. The primary coolant pumps and primary piping systems are inside the containment enclosure, but the pump motors are outside containment and the drive shaft seals form the containment boundary. Pickering has round domes which enclose much of the secondary cooling equipment. The Pickering A system did not originally have a second independent shutdown system. The Bruce containment concept differs: the reactor's reactivity mechanism deck serves as a part of the containment boundary, is closer to the reactor, and more prone to damage in the event of an accident ("accidental physical disassembly"). The designers therefore foresaw the need for a second safety system to reduce the risk of an accident. Bruce received a second, fully independent Safety Shutdown System (SDS2) which uses a liquid neutron poison injection method. The Bruce system also has a high-pressure Emergency Coolant Injection System (ECIS). Each Bruce "4 pack" has its own Vacuum Building, while Pickering has one per eight reactors. At Pickering, the vacuum duct was closed by nonreturn valves, to prevent flow of the steam/air mixture from the duct to a non-accident reactor unit following a LOCA. In the Bruce concept, there is no such non-return valve; the reactor buildings are all interconnected during normal operation. Bruce uses single-circuit heat transport system, while Pickering had two circuits. The first two reactor units of Pickering A originally used Zircaloy-2 pressure tubes. All subsequent CANDU units use a zirconium – 2.5% niobium alloy. Bruce uses a pressurizer to maintain coolant pressure, Pickering a different system. The Pickering design utilized 12 small steam generators operated