Brief descriptions of the NS Savannah nuclear plant and other concepts which have been offered by reactor plant suppliers follow:

EXISTING (LIGHT WATER)

NS "SAVANNAH" REACTOR

The NS Savannah is powered by a pressurized water type of reactor. The reactor core is 62 inches in diameter and 66 inches high. Within the honeycomb-like structure are 32 fuel elements, each containing a bundle of 164 stainless steel-clad fuel rods arranged in four bundles of 41 rods each. The fuel in these rods is slightly enriched (4.4 percent uranium oxide. The fission process is controlled by 21 boron stainless steel control rods. Ordinary water circulated in a closed loop called the "primary system" flows through the elements under a pressure of 1,750 pounds per square inch to remove the heat generated by atomic fission. Entering the reactor vessel at the bottom it heats up as it flows through the hot core and emerges from the top of the vessel at approximately 521° F. It then circulates through two heat exchangers which remove enough heat to keep the reactor at an aver age temperature of 508° F. Secondary water flows at a lower temperature around the heat exchanger tubes and being at a much lower pres sure boils as it is heated by the primary water.

The pressure vessel enclosing the core, measure 25 feet 10%1⁄2 inches in height, 8 feet 2 inches inside diameter and has a primary shield of steel and lead tank of water. The containment vessel of steel plate is 50.5 feet long and 35 feet diameter. The gross weight of the reactor system, containment, and shielding is 2,500 tons.

CANDIDATE CONCEPTS (LIGHT WATER)

BABCOCK AND WILCOX CO. (CNSG CONSOLIDATED NUCLEAR STEAM

GENERATOR)

The CNSG concept has been specifically designed for marine application. The plant consists of a pressurized water reactor, a steam: generator, and a pressurizer combined in a single pressure vessel. The reactor core, located near the bottom of the pressure vessel, has fue elements comprised of pins loaded with low enriched UO, clad in zircaloy tubes. The once-through steam generator is located concentric to the pressure vessel wall in the space between the core and the reactor vessel wall. Here the heat energy of the primary water is transferred to the steam generator fluid to produce superheated steam. Forced circulation of the primary coolant is achieved by axial flow pumps located on pump stalks at the periphery of the vessel near the vessel head. The reactor vessel is housed in a pressure suppression containment to reduce further the space requirements of the reactor system. The CNSG core is designed for a long life to give low fuel cycle costs. Long core life requires a large amount of reactivity and, therefore, a large amount of reactivity holddown. Holddown is achieved by use of movable cluster control rods and fixed lumped burnable poisons. The lumped burnable poison rods are made of an inert material containing boron or boron compounds inside of a zircaloy tube. The burnable poison rods are dimensionally identical to the fuel rods and are interchangeable in the fuel element lattice.

GENERAL ELECTRIC CO. (630A MARK III, IV, V)

The General Electric Co. proposed an air-cooled beryllium reflected light water moderated calandria reactor concept for the maritime application (630A Mark III). Investigations were made of improvements in the Mark III, resulting in Mark IV and Mark V concepts. Consideration of comparative costs, technical uncertainties, and the absence of significant improvements offered over pressurized water designs led to the conclusion that there were insufficient incentives to warrant further development of these concepts by the Atomic Energy Commission.

COMBUSTION ENGINEERING (UNIMOD)

The proposed unified modular plant is a compact water cooled and moderated steam supply system for a ship propulsion plant. Plant compaction is achieved by employing a self-pressurized light water reactor with the heat exchanger located within the reactor containment vessel. The elimination of the external primary loop components reduces the radioactive volume requiring shielding, and hence, the shield size and weight. The reactor vessel with surrounding shielding is completely encapsulated by the containment vessel. Water within the containment vessel provides a reservoir for vapor suppression as well as providing part of the shielding.

he once-through heat exchanger is arranged along the inside periy of the reactor vessel. It is comprised of six independent circumatial segments, any five of which will provide full steam flow. The can be refueled without removal of the heat exchangers.

imary water leaving the core flows upward to the steam dome, ally into the six heat exchanger segments where it makes a downI pass followed by an upward pass over the total length of the anger, into three down-comers located between each pair of heat anger segments, out through the three pumps, back into the reactor 1, and down to the core inlet.

e reactor vessel is insulated inside the coaming which extends nd the vessel, pumps, and the cold shutdown mechanisms. The

space between the canned vessel assembly and the containment wall is filled with borated water to a level above the reactor vessel head. The principal radiation shielding is provided by iron and water with lead added in local areas for additional gamma attenuation. The reactor vessel, heat exchanger and vessel internals provide a measurable contribution to the shielding. Steel slabs are employed in the annular region between the pressure vessel and containment vessel for the additional attenuation.

The Unimod concept is designed to deliver 600 pounds per square inch steam from zero to full load during the entire core life with the nuclear steam generator output controlled solely by the demand at the turbine.

Plant control is achieved by utilizing the inherent load following characteristics of water cooled reactors to a greater degree than is usually done. By allowing the negative moderator temperature coefficient to compensate entirely for any changes in operating conditions, no external reactivity control is required. As the load on the heat exchanger increases, the core inlet temperature falls, increasing the reac tivity and the reactor power level. Under such conditions, outlet coolant temperature rises and since this determines the operating pressure, this also rises.

WESTINGHOUSE

The Westinghouse nuclear propulsion plant consists of a single pressurized water reactor furnishing power to two shafts.

Connected in parallel to the reactor are two essentially identical heat transfer loops; each containing a reactor coolant pump, a steam generator, isolation valves and instrumentation. A single pressurizer is provided to control the system pressure.

Auxiliary systems are provided to charge the reactor coolant system and add makeup water, purify reactor coolant water, provide chemicals for corrosion inhibition and reactor control, cool system components, remove decay heat when the reactor is shut down, sample reactor coolant water, provide for emergency safety injection, and dispose of liquid wastes from the reactor systems.

Reactor coolant water enters the reactor vessel through nozzles located above the core, flows downward around the outer periphery of the reactor core, reverses direction near the bottom of the vessel, flows upward through the reactor core to remove heat generated by the nuclear chain reactor, and then leaves the vessel through nozzles located above the core.

The reactor coolant system is located inside the plant container, a vertical cylindrical structure that forms an integral part of the ship's structure. It consists of an inner and an outer shell. The inner shell is reinforced concrete which acts as radiation shielding, and also protects the outer shell from thermal and mechanical shock.

The condensate and feed water cycle contains three stages of feed water heating and conventional deaeration. Each condenser has two main condensate pumps, with the second serving as a complete spare. There are three feed booster pumps and three main boiler feed pumps: the third pump, in both cases serving as a spare.