US Nuclear Propulsion - Archived 8/2001

Outlook

Orientation

US Department of Energy

US Navy

Bechtel Bettis Inc

Bechtel Plant Machinery Inc

General Dynamics Corp

General Electric Co

L-3 Communications

Newport News Shipbuilding & Drydock Co

Pennsylvania State University

Technical Data

Variants/Upgrades

US nuclear reactor nomenclature began by using specific names for types of reactors and acronyms based on those names. The growing numbers of reactor types in service led to the introduction of a systematic nomenclature system in 1955. Under this system, an initial letter indicated the type of ship for which that reactor was intended (A for Aircraft carrier, C for Cruiser, D for Destroyer and S for Submarine). This was followed by a serial number, then a final letter indicating the producer (G for General Electric, W for Westinghouse, C for Combustion Engineering).

The CVN-77 is still believed to feature the same A4W/A1G pressurized water reactors as the Nimitzes, with the two reactors providing a pressure of 42.3 kg/cm². However, the subsequent carriers (CVX) are likely to have a new propulsion system still based on a nuclear reactor but with a new-design reactor and possibly electric drive. Depending on the availability of funding, their configuration may differ substantially from the preceding carriers of this series.

Nautilus in which the heat exchangers were carried low, aft of the reactor, the whole assembly being covered by a thick horizontal deck. Both systems worked well, but the S3W arrangement was much more efficient and was adopted for all subsequent reactor designs.

Program Review

The goal of the DoE program is to design, develop, and test improved nuclear propulsion plants and reactor cores having long fuel life, increased reliability, improved performance, and simplified operation and maintenance requirements. The ultimate goal is to develop reactor cores that will last the life of a ship. Special emphasis is placed on obtaining advanced long-life cores needed for increased ship performance and availability. The DoE also seeks ways to safely dispose of used reactors from decommissioned submarines.

The Department of the Navy, through the Naval Nuclear Propulsion Office, is responsible for the military application of nuclear propulsion, including constructing, operating, and maintaining nuclear-powered ships, and for developing the non-reactor portions of the nuclear propulsion plants.

This office has, by nature of its work, very close ties to the DoE while maintaining a great deal of independence. The office has been traditionally led by four-star generals (admirals) with eight-year tenures.

The office is the successor to the nuclear program office founded in the late 1940s by Admiral Hyman Rickover for the development of nuclear submarine propulsion. He was able to run the office single-handedly, thanks to the total secrecy of the program funded officially by the DoE. Many of the office’s independent practices developed in that era, occasionally leading to heightened conflicts with other parts of the Navy.

The development of US nuclear propulsion technologies continued throughout the Cold War. These efforts culminated in the development of a nuclear-powered submarine, the Nautilus, in the mid-1950s. From this ship onward, the US Navy had entered into a new era in its power projection capability thanks to nuclear power, which offered a virtually unlimited range of operation with no need for refueling while under way.

The size of the submarines grew progressively larger through the 1950s, ‘60s, and ‘70s, the largest ever submarine for the US Navy being the 560-foot-long Ohio class ballistic-missile launch platforms. They were designed in the 1970s and began entering service from the early 1980s onward. Meanwhile, attack submarines were being built with smaller hulls but higher top speeds for patrolling and reconnaissance missions. The Los Angeles class SSNs, which came into service in 1976, were fitted with one GE PWR S6G reactor and two turbines each, producing a top speed of more than 30 knots. The same propulsion arrangement was installed on the Ohios, but due to their massive size, their top speed was less than 30 knots.

At the individual program level, major RDT&E goals in 1982 included advanced reactors for future submarines and surface ships with the potential to put a higher power reactor in a given hull size, a submarine test core with better performance and longer core life, an advanced design propulsion plant for the ballistic missile submarines and guided missile cruisers, an advanced fleet core to extend fuel life, and materials and corrosion testing aimed at extending reactor plant life beyond 20 years.

These efforts continued in 1983. A major change was reorienting the Nuclear Propulsion Technology Program to better reflect the actual objectives of the program in reactor development. In 1984, nuclear reactor development and procurement programs saw a modest growth in RDT&E funding and more substantial growth in procurement funding. The Navy has funded up to seven major development programs for reactor RDT&E, but from 1984 through 1986, only four were active.

The S6G reactor program for the SSN-688 class submarines was absorbed into the Operational Reactor Development Program (PE#0205675N), as was the D2W reactor program. The three programs are examined in detail below.

The Nuclear Propulsion Technology Program (PE#0602324N) continued developing and qualifying advanced nuclear physics methods for improved plant performance and safety. Nuclear physics methods also were qualified to enhance design capability. The Navy qualified a vectorized three-dimensional diffusion theory to optimize nuclear design programs.

A vectorized two-dimensional theory with depletion capability also was developed. Surveys were held on cores installed in prototype plants to provide physics and mechanical data. The service also continued development of structural computer program capabilities with nonlinear time-dependent response. Tests were carried out on various materials to determine their corrosion resistance, and alloys with improved corrosion resistance were developed.

In 1987 this program investigated the long-term effects of radiation, heat, and operational loads on reactor materials to ensure continued safe operation of existing plants and that developmental plants use the safest materials available. Advanced instrumentation, control and electronic technologies were developed to improve reactor plant reliability, while improved thermal and fluid transfer technology was developed to improve efficiency. New physics methods also were developed. These efforts continued in 1988, as did the development and analysis of new plant materials. New microprocessor and graphic display technology was developed for possible use in plant instrumentation and control systems.

The Advanced Nuclear Reactor Components and Systems Development Program (PE#0603570N) gained a new project in 1986, when the S6W Nuclear Propulsion Plant Project (S1914) was established. This project was to develop the nuclear reactor for the SSN-21 Seawolf class attack sub. The program was expected to see major advances in noise reduction. The Navy was developing new pumps, instrumentation and control equipment, valves, heat transfer equipment, shielding and component systems in 1985 and 1986. Other developments included testing main coolant pump subsystems, designing microprocessor-controlled instrumentation and developing new propulsion plant shielding systems. A full-scale mockup of the reactor plant was built to determine optimum system location.

During 1987 and 1988, this program continued to develop heat transfer components using stronger materials. Fluid transfer and control equipment also was developed. Shock tests were held on portions of the reactor in 1988, valves were developed for the plant and instrumentation test units were fabricated. The Navy also analyzed reactor plant foundations and piping to assess structural and acoustic adequacy, and built a plant mockup to establish arrangement details.

The second project in PE#0603570N is Advanced Nuclear Reactor Components and Systems Development (S1258), which is an integrated research project including both Department of the Navy and Department of Energy funding, with most of the funding coming from the latter. In 1985 and 1986, heat transfer technology research was conducted to improve steam generator and pressurizer performance. Steam generator shock test data were evaluated, as was the material, chemical, and radiological behavior of reactor plant components. New shielding designs were developed to assure safe radiation exposure levels for operating personnel. Another major effort involved the development of lead unit refueling equipment and shipping containers for irradiated structural components.

Year 1987 efforts in this program included the design of new and improved heat transfer equipment for greater reliability and performance. Fluid transfer material was designed and tested, as was better instrumentation and control equipment. In 1988, new concept steam generator material structures were developed, small-scale heat transfer units were fabricated and tested and the design of a large-scale unit was begun. The Navy determined the feasibility of various manufacturing methods for a new steam generator. The service also developed remote robotic steam generator inspection equipment to reduce the amount of exposure to personnel during inspections. It began designing advanced diagnostic equipment and developed and tested alternative bearing material.

The A4W/A1G Nuclear Propulsion Plant Program (PE#603578N), which developed the reactor for the CVN-68 Nimitz class aircraft carriers, saw several milestones between 1985 and 1987. In 1985 this program evaluated basic circuitry, and tested and evaluated new instrumentation and control system technologies. The Navy also tested systems for the first CVN-68 refueling. Due to the expanded operating cycles of the nuclear carriers in the early 1980s, the Navy also analyzed reactor core lifetime performance versus original core objectives. This program ended in 1987.

The Operational Reactor Development Program (PE#0205675N) developed modifications and improvements to existing naval nuclear reactors, while testing and evaluating new systems. In 1985 and 1986, reactor plant engineering, thermal and hydraulic studies were conducted, and the development of systems to ensure safe reactor operation continued. Stress, vibration and brittle fracture analysis studies were conducted, as were stress corrosion tests.

The 1987 and 1988 program plans called for continuing development and testing of reactor servicing and refueling equipment and methods to evaluate corrosion. Efforts continued to resolve design issues and evaluate engineering tests, and thermal and hydraulic analyses were conducted of operating reactor plants. Also, the service investigated ways to operate reactor plants beyond their original design lifetimes, while continuing to evaluate new prototype propulsion systems and designs to determine deficiencies.

Year 1989 efforts in PE#0602324N included the continuation of reactor materials work. Irradiation, corrosion and mechanical property were tested, and technology was further developed for cutting and welding such materials.

New technologies to be developed and tested included graphic display technology for use in advanced systems; fiber-optics; high-power semi-conductors; and microprocessor-based power conversion techniques for use in power generation, control and distribution systems. Work on improved thermal and fluid transfer systems was to continue, with major efforts emphasizing new thermal transfer technology to maximize heat exchange. Improved water chemistries to reduce corrosion were to be developed. Finally, the effects of shock vibration and high temperature on plant equipment were to be investigated.

Under the Advanced Reactor Components and Systems Program small- and large-scale tests were to be conducted to determine the optimum design features for new steam generators. Remote robotic steam generator inspection system development was to proceed, as was the design of equipment using microprocessor and graphic display technology. Also, new pumps and valves were to be developed. S6W reactor efforts were to include the development and qualification of improved heat exchanger components, including steam generator and moisture separators. Pumps, charging pumps, and charging valves were to be developed and qualified. Furthermore, new plant protection monitoring and control equipment were to be developed. Plant components and systems were to be tested to confirm designs and plant operating procedures and guidelines were to be developed.

Operational Reactor Development work was to include the design, development, test and evaluation of reactor refueling equipment and methods to support the initial SSBN-726 Ohio class refueling, the defueling of power units aboard CVN-65 USS Enterprise and the continued CVN-68 Nimitz class refueling. The Nimitz class equipment would provide the capability to disassemble and reuse core components. The initial refueling of the NR-1 deep submergence vehicle was to be provided for, along with the shipment of nuclear fuel and irradiated core components. Methods to avoid the need for premature component replacements were to be analyzed. Thermal, hydraulic and mechanical analyses were to continue. Finally, diagnostic test results were to be evaluated to determine plant noise performance and to improve quieting.

Under the AFR program, the US Navy is developing the reactor for the Virginia class next-generation SSN, developing advanced propulsion technology, improving existing reactors, and ensuring continued safe operation. The Virginia class submarine is the follow-on/ replacement type for the SSN-21, which was limited to three units. The reactor type used on this new submarine is designated S9G, and made by General Electric.

Under reactor development, the Navy will direct several key elements. It plans to develop and qualify high-integrity nuclear fuel. The focus will be on how to extend the life of existing reactors and their cores. Additionally, work will be conducted on heat and fluid transfer to reduce size, enhance efficiency, and reduce corrosion. Work will also be performed in the area of instrumentation and controls to improve the system by incorporating microprocessors and fiber optics. Construction will be completed on the new stationary neutron radiography system. While the new facility will be strictly for research and development, it will enter operation in later in the decade. Little information is being made public.

Past experience has shown that nuclear power has limited benefits for surface ships besides aircraft carriers. For those ships, it gives a great deal of propulsion power without the need for refueling, and the size of these vessels can support the existence of a nuclear infrastructure aboard. It is very unlikely, though, that more nuclear-powered surface combatants will be ordered. They are difficult and expensive to design, their deployment carries major political costs, and the environmental effects of one hitting a mine are catastrophic.

The Naval Nuclear Propulsion Office itself is also undergoing major turmoil in its mission and leadership structure. In 1996, when the tenure of Admiral Bruce DeMars was coming to an end, a great deal of debate centered on the need to have a four-star general with an eight-year tenure in charge of the office. Furthermore, his senior position in the Department of Energy, on top of his defense duties, was also being questioned, since it may represent a compromise in the oversight of the Propulsion Office’s operations.

The Navy has been critical of suggestions to reform the office leadership structure and function, citing the technological complexity of the issues involved and the necessity to maintain the office’s current authority, linking those issues ultimately to nuclear safety overall. One solution may be to separate the technology development of nuclear reactors from safety issues, which would be handled by the propulsion office only. No decision has yet been made on the issues of reducing the tenure to six or even four years and having the head being of a lower rank, or of stripping the office of its Department of Energy functions and responsibilities.

The Department of Energy is also under fire and much public scrutiny these days for apparent oversights in security concerning access to sensitive nuclear weapons data by nationals of other countries, particularly China. It is highly probable that changes will be made in the organization of the DoE as a result of these lapses in security, but a definition of an exact relationship between that agency and the Defense Department on issues such as nuclear propulsion is likely to be a long, time-consuming process that evolves with the political realities of the time.

On the other hand, the issues concerning the safety of Russian submarines and their nuclear fuels being an environmental hazard may have an impact on the general perception of nuclear power’s "cleanliness" and safety. In that regard, tolerance for nuclear power in general is much lower in the environmentally sensitive Europe and Japan. Consequently, the issue of ships with nuclear power or with nuclear weapons on board visiting such ports will need to be considered as well. It has already been discussed in the context of Japan not allowing nuclear-powered aircraft carriers at its ports, while the Seventh Fleet plays an important role for the US Navy’s Pacific theater defense strategy.

The US Navy nuclear power program has been cut back from its heydays in the 1970s and 1980s, now comprising the completion of the last of the SSN-21 Seawolf class submarine plus one more Nimitz class aircraft carrier (CVN-77). The follow-on program to the Seawolf class, the SSN-774 Virginia class New Attack Submarine program (originally referred to as Centurion and at a time also known as the NSSN), will be nuclear powered, as will the next-generation carriers, now only referred to as the CVX class. The Virginia class development program was expanded to allow the participation of both Electric Boat and Newport News from early on, thus – at least theoretically – somewhat spreading the knowledge base of the US nuclear propulsion technology.

Some concern with the application of nuclear power even on aircraft carriers has been expressed occasionally. Although the advantages of a nuclear-powered carrier are significant and undeniable (operating range, endurance, speed and acceleration), so are the costs involved. This applies both to the procurement cost of the ship itself and to the cost of each refueling it will undertake during its operational life. A conventionally powered carrier would cost less to buy and could be built at many other yards besides Newport News. The financial savings, the argument goes, could be used for purchasing a larger ship instead. Diversifying carriers away from Newport News would entail a valuable broadening of the existing shipbuilding infrastructure.

However, as the debate surrounding the construction of both CVN-77 and the more futuristic CVX carrier concept indicates, the Navy is reluctant to abandon nuclear propulsion as the power source of these very large ocean-going vessels. Nuclear power offers the range and power sources needed by carriers which are, for all intents and purposes, miniature cities on water. Nuclear power therefore ensures extended operating times and continued power delivery, regardless of political turmoil in the oil-producing world. The operating freedom of the ships is limited only by the amount of supplies carried on board and the comfort of the crew.

The same is true for the submarine fleet, where the benefits of nuclear power are being questioned – especially now that the focus of submarine warfare has shifted from the blue oceans to littoral regions. It is possible that the US will drop to a single yard that is capable of building nuclear-powered submarines, plus one for nuclear-powered surface ships and using a single procurement source for their reactors. Trends for such consolidation are already evident in the debate surrounding the construction of the Virginia class SSNs, the future carriers and, most recently, the corporate acquisition plans as suggested by Newport News, Litton, and General Dynamics.

Funding

This program is funded through US Department of Energy and the Department of Navy. In the developmental phase, the funding had been posted mostly under DoE expenditures; when most of the activity becomes development of existing technologies and conversion of existing reactors (refueling and maintenance), much of the funding is listed as Navy expenditures.

During FY82, the total Department of Energy development budget request for naval nuclear reactors was US$361 million, a US$58 million increase over the FY81 budget. The US Navy requested US$95.3 million in FY82 as its share of naval nuclear propulsion development costs and requested $360.8 million for procurement of reactor power units and components. Funding levels declined in the subsequent years and, as stated above, are now mostly in the area of alterations and maintenance.

This activity was awarded US$189.1 million in FY92, dropping to US$139.5 million in the following year and to US$108.6 million in 1994. The next year saw an increase in funding for Nuclear Alterations activity, to US$156.8 million, dropping back to US$120.45 million the following year and even lower, to US$68.5 million, in FY97. For FY98, the President’s Budget Request was US$74.1 million, but the amount bounced back to US$109.8 million in FY99. After that, a steady flow of between US$100 and US$150 million a year has been recorded for the Nuclear Alterations line item in the US national defense budget.

Funding for the development of new reactors themselves or entirely new programs is not widely publicized. The office admits to managing about US$1.6 billion a year in funding, but it is generally believed that hundreds of millions of dollars more goes under classified projects and accounts. As a result, it is very difficult to estimate the total funding made available to the Naval Nuclear Propulsion Office by the Defense and Energy departments. Hence the focus in the above discussion is on information about upgrades and modifications to existing systems.

Recent Contracts

Timetable

Worldwide Distribution

UK (1 S5W plant now decommissioned.)

US (A total of 237 reactors of varying types have been installed on ships. Allowing for shore-based and experimental systems, the total production probably exceeds 250 reactors today.)

Additionally, S5W technology is widely believed to have been used by France for its SSBN program, although no formal technology transfer agreement exists. It is also possible that this technology has found its way to China for the Chinese SSBN program.

Forecast Rationale

Despite all the speculation to the contrary, it is highly probable that the submarines of the US Navy will remain nuclear powered in the foreseeable future. Nuclear power has the same appear for submarines that it has for aircraft carriers: unlimited operational range and power production, low noise level, and no need for en-route refueling. Nuclear power guarantees an operating range restricted only by the amount of supplies carried on board, and the mental well-being of the crew. Even the new Virginia class attack submarine, which will be smaller than the existing submarines of the US Navy fleet, will be powered by nuclear propulsion for those very same reasons.

A return to non-nuclear submarines would be realistic only if a major change in philosophy occurred at decision-making levels. This would have to reflect a perceived need for submarines so much smaller that they physically could not accommodate a nuclear reactor and powerplant on board. Such a shift in policy is not presently in sight for the US Navy. Even with the increased emphasis on littoral regions in future naval warfare scenarios, the US Navy is reluctant to go down to the level of the European diesel-electric boats in its submarine size, at least at this conjecture. The coastal areas of the United States to be defended require platforms different in caliber from those suited for operations in the Mediterranean, parts of the Atlantic or the Baltic Sea.

The following forecast is based on the commissioning dates for platforms being procured for the present programs. The numbers provided represent the total number of reactors for those platforms, rather than the number of ships.

Ten-Year Outlook