WR-1 DESIGN DETAILS
The calandria contains the heavy water moderator, space for heavy water dump, and provision for alignment, support, and cooling of the coolant tubes.
Internally, the calandria is divided into two major compartments by a flanged head which is part of the dump port assembly (dump slot). The upper or core region contains the fuel, and during operation the moderator. Aluminum calandria tubes are rolled into internal bosses at each end of the region, providing separation of the moderator from the fuel channel assemblies. The lower or dump space region has sufficient volume to allow rapid lowering of the moderator to below the critical level. Stainless steel dump tubes welded to the lower vessel head and dump floor separate the pressurized helium gas in the dump space from the fuel channels, and support the dump floor.
Extension tubes rolled into bosses in the top and bottom heads penetrate completely through the top and bottom shields. They form an extension of the calandria pressure boundary, providing support for the fuel channel assemblies. Closures on the channel assemblies and the shield plugs complete the pressure boundary.
Heavy water is fed to the vessel by two inlet lines in the top. A second dished head, mounted two inches below the main top head forms an inlet head for D2O, providing a mounting for the 97 nozzles which distribute incoming moderator. This moderator flows from the core region into the dump space over the dump ring crest, through annuli surrounding each dump space tube, and through an annulus between the dump ring and the wall. Outflow of heavy water from the vessel takes place through an eight-inch return (drain line) connecting the dump space to the dump tank. The whole calandria assembly is supported by three adjustable rods mounted on the side thermal shield.
Since the calandria provides support and location for the fuel channels, the dimensional limits for each site are identical in order to have the same capacity for taking different types of channels and calandria tubes. Calandria tubes up to a maximum outside diameter of 4.875 in. can be accepted. Insulated coolant tubes can be accomodated up to a maximum of 4.750 in. Fifty-four of the possible 55 sites are fitted with calandria tubes. Of these 24 are 3.9 in. inside diameter and the remaining 30 are 4.75 i.d.
The calandria tubes are partly cooled by direct immersion in the moderator, and partly by the incoming heavy water spray. The proportion in each cooling region varies with the moderator level.
The action of the heavy water sprays, and the splashing of falling water in the dump space release dissociated deuterium gas and oxygen into the system. To prevent the concentration from exceeding three percent by volume, a sweep flow of pure helium gas is maintained in both regions by separate gas lines. A recombination unit in the system controls deuterium concentration.
The reactor does not use conventional control rods, but relies on control of the heavy water moderator to give the required power output. The reactor is shut down by rapid dumping of the moderator. In an emergency, the reactor is automatically tripped by gas pressure equalization, releasing the moderator into the dump space. The dump port consists of an annular ring placed outside the fuel site cluster, near the periphery of the vessel.
The reactor is cooled by three independent systems, each with approximately 20 thermal megawatts capability. Each system is connected to fuel channels by means of separate inlet and outlet feeders and headers. Four independent loops, three organic cooled and one cooled by light water, are also in operation.
Coolant circulation and heat removal is provided by a separate pump and heat exchanger in each loop.
To permit experiments in any site of the reactor core, facilities exist for connections of other test circuits to the existing feeders.
Pressure control in each primary system is achieved by modulating the flow of organic fluid to separate degasification systems to provide a back pressure against separate charging pumps. The make-up flow is measured and controlled to a selected value. Attenuation of pressure surges is achieved by a surge tank in each heat transport system. A pressurized nitrogen blanket maintains the required liquid level.
Two dump tanks in the heat transport system permit drainage of the total system fluid content. Individual fuel channels drain into the tanks.
A 20 thermal megawatt capacity water-cooled heat exchanger removes the heat from each system. Untreated process water is used for normal cooling but in the event of a loss of process water, standby cooling water from the elevated tank is available immediately for safe shut down.
Each system is provided with one pump of sufficient capacity to provide 100 percent of the maximum flow.
The coolant inlet and outlet headers for two coolant circuits are located in the header room adjacent to the reactor. For the third circuit the headers and other major pieces of equipment are in an extension on the east side of the reactor building. Individual feeder pipes run from the inlet headers in each system into the lower reactor service space to connect to the bottom ends of each coolant tube. Individual outlet feeders connect each coolant tube in the top service space to the outlet headers of each system. Each site in the reactor has its own flow measurement nozzle, activity monitoring element and temperature sensing element, located in the feeders.
Gas is continuously generated in the coolant as it passes through the high radiation field in the core. Each primary system is complemented by a separate degassing and particulate removal system which includes two absorption columns and two back-up filters in addition to the degassing tank and vapour condensers.
To provide cooling in the unlikely event of a pipe rupture in the main heat transport circuits, the inlet headers of each system are connected to common pressurized injection tanks containing relatively cold organic (200oF, 93oC) of sufficient quantity to prevent overheating of the fuel elements during the initial shutdown period.
Revised March 1982
Fact Sheet: WR-1 Reactor
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