Steven J. Piet

Overview of the Blanket Comparison and Selection Study

A comprehensive Blanket Comparison and Selection Study was conducted to evaluate proposed D-T fusion reactor blanket concepts and to identify those concepts that offer the greatest potential for fusion reactor applications. The multilaboratory study was led by Argonne National Laboratory and included support from thirteen industrial, national and university laboratories; six primary subcontractors and seven specialized contributors. The primary objectives of the program were (1) to identify a small number (approx. 3) of the blanket concepts that should be the focus of the blanket R and D program, (2) to define and prioritize the critical issues for the leading blanket concepts, and (3) to provide technical input for development of blanket R and D programs. A blanket concept is generally defined by the selection of the component materials, viz., breeder, coolant, structure, and neutron multiplier, and specification of the geometrical configuration. Blanket concepts were evaluated for both the tokamak and tandem mirror reactor configurations using the STARFIRE and MARS reactor designs as a basis, with appropriate modifications to reflect recent advances in technology.

Approaches to achieving inherently safe fusion power plants

AbstractAchieving inherently safe fusion facilities and conceptual designs is a challenge to the fusion community. Success should provide fusion with important competitive advantages versus other energy technologies. Inherent safety should mean a facility designed with passive safety features such that the public is protected from any acute fatalities under all credible accidental circumstances. A key aspect to inherent safety is demonstrability — the ability to prove that a design is as safe as claimed.Three complementary approaches to achieving inherent safety are examined: toxin inventory reduction, energy source reduction, and design fault tolerance. Four levels of assurance are defined, associated with uncertainty in the words “credible” and “demonstrable.” Sound reasons exist for believing that inherent safety is achievable for fusion. The concept of inherent safety puts a modest upper bound on all accident consequences; it should be considered a part of the collection of safety and environmental is...

Initial Integration of Accident Safety, Waste Management, Recycling, Effluent, and Maintenance Considerations for Low-Activation Materials

A true “low-activation” material should ideally achieve all of the following objectives: The possible prompt dose at the site boundary from 100% release of the inventory should be <2 Sv (200 rem); ...

Implications of Probabilistic Risk Assessment for Fusion Decision Making

AbstractThe potential value of probabilistic risk assessment (PRA) tools to fusion safety and economic issues is discussed. The main results and implications of a systematic examination of these general issues via PRA tools are reported. It is concluded that PRA methodology, tools, and thinking are useful to fusion research in the process of further improving fusion concepts and ideas.The MARS and STARFIRE designs are examined for possible answers to questions posed by using PRA tools. Several general magnetic-fusion design insights result from the study, including the following:1. possible fault interactions must be minimized by decoupling fault conditions2. the reliability of the vacuum boundary appears vital to maximizing facility availability and minimizing safety risk3. economic analyses appear to be incomplete without consideration of potential availability loss from forced outages.A modification to PRA formalism called the “fault interaction matrix” is introduced. The fault interaction matrix conta...

ITER inherent/passive ultimate safety margins

Abstract The self-limiting nature of the fusion reaction, modest mobilizable radioactive inventories, multiple confinement layers, and passive decay heat removal, suggest that ITER will be ‘safe’ with little dependence on engineered ‘safety systems’ for public protection. To assess ITER’s ultimate safety margins, key safety input parameters are varied to study the impact of safety function degradation beyond those explicitly considered in the design process. Typically, the safety consequences from safety function degradation are linear or less than linear, and thus the functions degrade gradually. There are no fusion nuclear process or plasma transients that give safety-related growing non-linearities. Removal of fusion decay heat is robust with multiple processes available: the ultimate being passive natural circulation of the vacuum vessel coolant and gas convection in the cryostat. Using the IAEA dose criterion, the no-evacuation objective is met.

Safety Evaluation of the Blanket Comparison and Selection Study

The results of the safety evaluation of the Blanket Comparison and Selection Study (BCSS) are presented. The safety evaluation measured the relative safety and environmental attractiveness of the final group of BCSS blanket concepts for application with either a tokamak or tandem mirror fusion reactor. Two types of blankets were found to be the most attractive in the safety evaluation. One top-blanket-type is a helium-cooled HT-9 structure with a Li/sub 2/O breeder, which is preferred if tritium effluent control is good; a lithium breeder would be the backup. The other top blanket concept is liquid-metal-cooled V-15 Cr-5 Ti structure with lithium coolant/breeder, preferred if air and water chemical reactions are adequately controlled; 17Li-83Pb would be the backup coolant/breeder material.

An assessment of problems associated with tritium containment

A special task group was established as a part of the Blanket Comparison and Selection Study to investigate the problems associated with tritium containment in blanket systems. The goal of the task group was to review the existing experimental results and to define a set of ground rules that would form a common basis for each design group to resolve this particular problem. The work of the task group is summarized. Due to the scarcity of information, and often contradictory nature of the existing information, note that the conclusions are based on the best judgment of the task group. It is recommended that the conclusions be updated as more experimental results become available.

Identification and Characterization of the Key Issues of Fusion Nuclear Technology

Fusion nuclear technology testing issues are reviewed, covering the technical disciplines of materials science, structural mechanics, MHD, thermal hydraulics, tritium recovery, and others. These issues represent the largest uncertainties whose resolution will require new knowledge through experiments, models, and theory in order to demonstrate the feasibility and attractiveness of the entire fusion nuclear system. Needed tests range in complexity, including basic materials property data, exploration of individual and interactive phenomena, and fully integrated tests. By addressing the complete array of testing issues, this work helps to define needed engineering research which should prove useful in future fusion program planning.

Trends in fusion reactor safety research

Abstract Fusion has the potential to be attractive energy source. From the safety and environmental perspective, fusion must avoid concerns about catastrophic accidents and unsolvable waste disposal. In addition, fusion must achieve an acceptable level of risk from operational accidents that results in public exposure and economic loss. Finally, fusion reactors must control routine radioactive effluent, particularly tritium. Major progress in achieving this potential rests on development of low-activation materials or alternative fuels. The safety and performance of various material choices and fuels for commercial fusion reactors can be investigated relatively inexpensively through reactor design studies. These studies bring together experts in a wide range backgrounds and force the group to either agree on a reactor design or identify areas for further study. Fusion reactors will bistributed radioactive inventories. The next generation of experiments will be critical in demonstrating that acceptable levels of safe operation can be achieved. These machines will use materials which are available today and for which a large database exists (e.g. for 316 stainless steels. Researchers have developed a good understanding of the risks associated with operation of these devices. Specifically, consequences from coolant system failures, loss of vacuum events, tritium releases, and liquid-metal reactions have been studies. Recent studies go beyong next-step designs and investigate commercial reactor concerns including tritium release and liquid metal reactions.

Engineering, safety, and economic evaluations of aspire

A preconceptual design of a Tokamak fusion reactor concept called ASPIRE (Advanced Save Pool Immersed Reactor) has been developed. This concept provides many of the attractive features that are needed to enhance the capability of fusion to become the power generation technology for the 21st century. Specifically, these features are: inherent safety, low pressure, environmental compatibility, moderate unit size, high availability, high thermal efficiency, simplicity, low radioactive inventory, Class C radioactive waste disposal, and low cost of electricity. We have based ASPIRE on a second stability tokamak. However, the concept is equally applicable to a first stability tokamak or to most other magnetic fusion systems.