The S8G reactor was designed by General Electric for use on the Ohio Class (SSGN/SSBN-726) submarines. It is a natural circulation reactor, capable of operating at a significant fraction of full power without reactor coolant pumps. The S stands for submarine, 8 for 8th reactor design, and G for General Electric. The S8G reactor provides nuclear power for operating the Ohio-class (SSGN/SSBN-726 Class) submarines in the US Navy. The eighth generation S8G reactor was capable of operating at a significant fraction of full power without reactor coolant pumps.
TRIDENT originated in the Strat-X planning exercise, a paper competition conducted in 1966-67. At the conclusion of Strat-X, Rear Admiral Levering Smith was named the Project Manager for TRIDENT, the role that SPO had played in the development of POLARIS and POSEIDON. With that mandate, the office pursued on a low-priority basis in 1967-69 various technical designs and gradually evolved its preferred design along the line of the Strat-X conception, i.e. a big boat that carried large missiles and was relatively slow. The TRIDENT program attracted the attention of Vice Admiral Hyman G. Rickover, who challenged Smith's conception of TRIDENT.
Smith thought that the 17,000 shp Narwhal design provided adequate power for TRIDENT. Rickover, however, proposed to develop a far larger natural circulation reactor which would offer not only the increased quietness, but also greater top speed. The analytic trade-off was that a boat using Rickover's reactor would have to be far larger - and more expensive - than the SPO design. It is always better to go faster, Rickover argued, even if the systems analysts could not imagine why. The commanders of operational submarines, always reliable advocates of speed, agreed. Behind the argument, however, lay a critical fact: if the new reactor were used, Rickover would have substantial authority in the TRIDENT program. On the other hand, if an existing reactor design like the Narwhal's were used, SPO would have maximum control over the entire boat, including the engine room, as it had in the POLARIS program.
The S8G is used operationally on all Ohio-class SSBNs and SSGN-conversions. The 1 x S8G PWR rated at 312 MWt (est.), 2 x main steam turbines with a combined rating of 60,000 hp (45 MW) driving a single shaft. Some sources cite a reactor power rating of 220 MWt, but this seems too low to deliver the cited 60,000 shp propulsion power. The S8G reactor compartment for the Ohio submarines is 42 feet (13 m) in diameter, 55 feet (17 m) long and weights 2,750 tons.
Fuel life spans depend on how much the ship is operatee, and how accurately one can predict reactor performance. Current cores for the NIMITZ Class aircraft carrier, LOS ANGELES Class SSN, and OHIO Class SSBN last on average about 20 years. Efforts to extend the lives of operating reactor plants resulted in longer ship lifetimes; NIMITZ-Class carriers are now expected to last 50 years, and OHIO-Class submarines 40 years, versus their original design lifetimes of 30 years.
A land based prototype of the reactor plant was built at Knolls Atomic Power Laboratory at Ballston Spa, New York. The S8G prototype was built at the Kesselring Site in West Milton, NY. The prototype is equipped with an automatic reactor fill system that can flood the reactor with borated water in the event of a loss of coolant accident. The prototype started operation some time around 1980. In 1994, the original S8G core was replaced with an S6W core to be used on the Seawolf-class SSNs
In 2018, the S8G prototype was scheduled to start a 3-year refueling and overhaul outage intended to support the Ohio-replacement reactor design. The S6W Seawolf core will be replaced with the “Technology Demonstration Core” (TDC) and other changes will be made to update the facility.
The prototype was used for testing and crew training throughout the 1980s. Located at the Kesselring site in New York, the S8G prototype plant was overhauled in the early 1990s, and in 1994 it was refueled with the Westinghouse S6W Advanced Fleet Reactor core intended for use on the Seawolf attack submarine. The prototype is equipped with an automatic reactor fill system that can flood the reactor with borated water in the event of a loss of coolant accident.
The Prototype reactor plant has served Naval Reactors’ needs for research, development, and training since 1978, and the reactor provides a cost-effective testing platform for new technologies and components before they are introduced to the Fleet. Equally important, it provides an essential, hands-on training platform for the fleet’s reactor plant operators, every one of whom qualifies on an operating reactor before their assignment to a submarine or aircraft carrier.
By 2018, Naval Reactors will begin to refuel and overhaul the S8G land-based prototype, which will preserve a critical research and development asset that provides a cost-efective test and evaluation platform for new technologies, materials, and components before introduction into the fleet. Naval Reactors has embarked on an important projects, namely, the refueling overhaul for the S8G Land-Based Prototype reactor. The refueling of the S86 Prototype includes removing the naval spent nuclear fuel assemblies and other supporting equipment from inside and outside the reactor vessel. Once the existing core is removed, it will be replaced with a new core and supporting equipment.
The core to be installed in the S86 Prototype has been designated as the Technology Demonstration Core (TDC). The TDC will be designed and built using established Naval Nuclear Propulsion Program (NNPP) processes. The spent nuclear fuel removed from the S86 Prototype will be placed into an M-140 shipping container and shipped off site; therefore, there will be no spent nuclear fuel stored at the Kesselring Site. The refueling work will be conducted in accordance with stringent NNPP requirements for controlling refueling work, handling radioactive materials and ensuring compliance with applicable environmental, safety and health standards.
The Budget Control Act of 2011 established discretionary caps, which are delaying several of the Administration’s nuclear modernization initiatives. Of the three new projects, only the S8G Land-Based Prototype Refueling Overhaul remained on the originally envisioned schedule that was presented to Congress in 2011. To continue vital research capabilities, as well as train sufficient operators to man the Fleet, the S8G Land-Based Prototype Refueling Overhaul must begin in 2018. This budget fully funds the FY13 effort required for the upcoming refueling overhaul of the S8G Land-Based Prototype. The new prototype reactor core work will be used to test the manufacturability of new core materials required for the OHIO Replacement submarine.
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