Robert Petroski’s research while affiliated with TerraPower and other places

New designs of advanced nuclear power plants have been proposed that may allow nuclear power to be less expensive and more flexible than conventional nuclear. It is unclear how and whether such a system would complement variable renewables in decarbonized electricity systems. Here we modelled stylized electricity systems under a least-cost optimization framework taking into account technoeconomic factors only, considering electricity demand and renewable potential in 42 country-level regions. In our model, in moderate decarbonization scenarios, solar and wind can provide less costly electricity when competing against nuclear at near-current US Energy Information Administration (US$6,317 per kilowatt-electric (kWe)) and at US$4,000 kWe−1 cost levels. In contrast, in deeply decarbonized systems (for example, beyond ~80% emissions reduction) and in the absence of low-cost grid-flexibility mechanisms, nuclear can be competitive with solar and wind. High-quality wind resources can make it difficult for nuclear to compete. Thermal heat storage coupled to nuclear power can, in some cases, promote wind and solar. Advanced nuclear reactors may lead to a significant reduction in the cost of nuclear energy. Duan et al. incorporate a wide range of potential advanced nuclear costs in their assessment of future decarbonization options and find areas where nuclear can support wind and solar.

A new reactor concept is described that directly couples a supercritical CO2 (sCO2) power cycle with a CO2-cooled, heavy water moderated pressure tube core. This configuration attains the simplification and economic potential of past direct-cycle sCO2 concepts, while also providing safety and power density benefits by using the moderator as a heat sink for decay heat removal. A 200 MWe design is described that heavily leverages existing commercial nuclear technologies, including reactor and moderator systems from Canadian CANDU reactors and fuels and materials from UK Advanced Gas-cooled Reactors (AGRs). Descriptions are provided of the power cycle, nuclear island systems, reactor core, and safety systems, and the results of safety analyses are shown illustrating the ability of the design to withstand large-break loss of coolant accidents. The resulting design attains high efficiency while employing considerably fewer systems than current light water reactors and advanced reactor technologies, illustrating its economic promise. Prospects for the design are discussed, including the ability to demonstrate its technologies in a small (∼20 MWe) initial system, and avenues for further improvement of the design using advanced technologies.

Energy security, reducing air pollution, and carbon emissions are topics of high importance to many countries throughout the world, particularly in Asia where energy use is expected to grow at 3.7 % per year, the highest growth rate in the world. According to the International Energy Agency (IEA), China alone is expected to account for almost one-fourth of world energy demand in the next 20 years. Although low-carbon options like wind and solar have seen large strides in deployment, growing by double and triple digits, the building of new coal plants still outpaces them all by orders of magnitude. In addition, most intermittent sources currently use fossil fuel generators as back up, lowering the potential gains that can be made in emission/carbon reduction goals. To further exacerbate this issue, worldwide electricity production is expected to double by 2040 to meet global needs, where coal is expected to play a major role in supplying that electricity unless an alternative can be found. Given the need to reduce the use of fossil fuels due to emissions/pollution/carbon concerns, and a desire for sustainable and globally scalable energy sources, an “all of the above” strategy for electricity generation has become an imperative. Nuclear power meets the requirements of a non-emitting source, and thus will need to be considered as part of the global energy strategy. However, nuclear energy in its current form has limitations, both perceived and real, regarding economics, waste, proliferation, and safety. In order to further improve on the current generation of reactors, TerraPower has developed the Traveling Wave Reactor (TWR), a near-term deployable and truly sustainable energy solution that is globally scalable for the indefinite future. As a fast reactor, the TWR allows up to a ~35-fold gain in uranium utilization when compared to conventional light water reactors (LWRs) using enriched fuel. Compared to other fast reactors, TWRs represent the lowest cost and lowest risk alternative: (1) they provide the energy security benefits of an advanced nuclear fuel cycle without the associated proliferation and cost concerns of fuel reprocessing; (2) they require less lifetime enrichment than LWRs, translating to a reduced number of enrichment plants that need to be built; (3) they produce less waste by volume than an LWR, resulting in less needed waste capacity requirements and reduced waste transportation costs; and (4) they require less uranium ore to be mined or purchased since natural or depleted uranium can be used directly as fuel. In addition to the benefits described above, the paper also describes the origins and current status of the TWR engineering, design, development, and test programs at TerraPower. Areas covered include the key TWR design challenges, and brief a description of the TWR-Prototype (TWR-P) reactor.

The traveling wave reactor (TWR) is a once-through reactor that uses in situ breeding to greatly reduce the need for enrichment and reprocessing. Breeding converts incoming subcritical reload fuel into new critical fuel, allowing a breed-burn wave to propagate. The concept works on the basis that breed-burn waves and the fuel move relative to one another. Thus either the fuel or the waves may move relative to the stationary observer. The most practical embodiments of the TWR involve moving the fuel while keeping the nuclear reactions in one place−sometimes referred to as the standing wave reactor (SWR). TWRs can operate with uranium reload fuels including totally depleted uranium, natural uranium, and low-enriched fuel (e.g., 5.5% 235U and below), which ordinarily would not be critical in a fast spectrum. Spent light water reactor (LWR) fuel may also serve as TWR reload fuel. In each of these cases, very efficient fuel usage and significant reduction of waste volumes are achieved without the need for reprocessing. The ultimate advantages of the TWR are realized when the reload fuel is depleted uranium, where after the startup period, no enrichment facilities are needed to sustain the first reactor and a chain of successor reactors. TerraPower's conceptual and engineering design and associated technology development activities have been underway since late 2006, with over 50 institutions working in a highly coordinated effort to place the first unit in operation by 2026. This paper summarizes the TWR technology: its development program, its progress, and an analysis of its social and economic benefits.

Energy security is a topic of high importance to many countries throughout the world. Countries with access to vast energy supplies enjoy all of the economic and political benefits that come with controlling a highly sought after commodity. Given the desire to diversify away from fossil fuels due to rising environmental and economic concerns, there are limited technology options available for baseload electricity generation. Further complicating this issue is the desire for energy sources to be sustainable and globally scalable in addition to being economic and environmentally benign. Nuclear energy in its current form meets many but not all of these attributes. In order to address these limitations, TerraPower, LLC has developed the Traveling Wave Reactor (TWR) which is a near-term deployable and truly sustainable energy solution that is globally scalable for the indefinite future. The fast neutron spectrum allows up to a ~30-fold gain in fuel utilization efficiency when compared to conventional light water reactors utilizing enriched fuel. When compared to other fast reactors, TWRs represent the lowest cost alternative to enjoy the energy security benefits of an advanced nuclear fuel cycle without the associated proliferation concerns of chemical reprocessing. On a country level, this represents a significant savings in the energy generation infrastructure for several reasons 1) no reprocessing plants need to be built, 2) a reduced number of enrichment plants need to be built, 3) reduced waste production results in a lower repository capacity requirement and reduced waste transportation costs and 4) less uranium ore needs to be mined or purchased since natural or depleted uranium can be used directly as fuel. With advanced technological development and added cost, TWRs are also capable of reusing both their own used fuel and used fuel from LWRs, thereby eliminating the need for enrichment in the longer term and reducing the overall societal waste burden. This paper describes the origins and current status of the TWR development program at TerraPower, LLC. Some of the areas covered include the key TWR design challenges and brief descriptions of TWR-Prototype (TWR-P) reactor. Selected information on the TWR-P core designs are also provided in the areas of neutronic, thermal hydraulic and fuel performance. The TWR-P plant design is also described in such areas as; system design descriptions, mechanical design, and safety performance.

The Cheng and Todreas (1986) correlation is widely used for calculation of pressure loss in wire wrapped hexagonal rod bundles. Recent application indicates that the transition region friction factor calculated causes reverse pressure drop as flow rate increases in the vicinity of the transition to turbulent boundary. A modified friction factor formula for the transition region is proposed to avoid this anomalous behavior. The newly introduced exponent in this formula was calibrated by 58 available bundle data sets to be 13. This modified formula not only achieves the original objective but also slightly improves the accuracy of prediction in the transition region.

Proceedings of the 45th Session of the International Seminars on Nuclear War and Planetary EmergenciesErice, Italy, 19 — 24 August 2012Edited by: R Ragaini (Lawrence Livermore National Laboratory, USA)

The Advanced Reactor Modeling Interface (ARMI) code system has been developed at TerraPower to enable rapid and robust core design. ARMI is a modular modeling framework that loosely couples nuclear reactor simulations to provide high-fidelity system analysis in a highly automated fashion. Using a unified description of the reactor as input, a wide variety of independent modules run sequentially within ARMI. Some directly calculate results, while others write inputs for external simulation tools, execute them, and then process the results and update the state of the ARMI model. By using a standardized framework, a single design change, such as the modification of the fuel pin diameter, is seamlessly translated to every module involved in the full analysis; bypassing error-prone multi-analyst, multi-code approaches. Incorporating global flux and depletion solvers, subchannel thermal-hydraulics codes, pin-level power and flux reconstruction methods, detailed fuel cycle and history tracking systems, finite element-based fuel performance coupling, reactivity coefficient generation, SASSYS-1/SAS4A transient modeling, control rod worth routines, and multi-objective optimization engines, ARMI allows “one click” steady-state and transient assessments throughout the reactor lifetime by a single user. This capability allows a user to work on the full-system design iterations required for reactor performance optimizations that has traditionally required the close attention of a multi-disciplinary team. Through the ARMI framework, a single user can quickly explore a design concept and then consult the multi-disciplinary team for model validation and design improvements. This system is in full production use for reactor design at TerraPower, and some of its capabilities are demonstrated in this paper by looking at how design perturbations in fast reactor core assemblies affect steady-state performance at equilibrium as well as transient performance. Additionally, the pin-power profile is examined in the high flux gradient portion of the core to show the impact of the perturbations on pin peaking factors.