Richard L. Moore

THE ARIES-CS COMPACT STELLARATOR FUSION POWER PLANT

Abstract An integrated study of compact stellarator power plants, ARIES-CS, has been conducted to explore attractive compact stellarator configurations and to define key research and development (R&D) areas. The large size and mass predicted by earlier stellarator power plant studies had led to cost projections much higher than those of the advanced tokamak power plant. As such, the first major goal of the ARIES-CS research was to investigate if stellarator power plants can be made to be comparable in size to advanced tokamak variants while maintaining desirable stellarator properties. As stellarator fusion core components would have complex shapes and geometry, the second major goal of the ARIES-CS study was to understand and quantify, as much as possible, the impact of the complex shape and geometry of fusion core components. This paper focuses on the directions we pursued to optimize the compact stellarator as a fusion power plant, summarizes the major findings from the study, highlights the key design aspects and constraints associated with a compact stellarator, and identifies the major issues to help guide future R&D.

Modifications to the MELCOR code for application in fusion accident analyses

For the past several years, the Fusion Safety Program at the Idaho National Engineering and Environmental Laboratory (INEEL) has modified the MELCOR code in order to assess safety issues associated with loss-of-cooling accidents (LOCAs) and loss-of-vacuum accidents (LOVAs) in the international thermonuclear experimental reactor (ITER) engineering design activity (EDA). MELCOR is a thermal hydraulics computer code developed by the Sandia National Laboratory for analyzing severe accidents in fission power plants. This paper describes these modifications and the role they played in LOVA and LOCA analyses performed for the non-site specific safety report (NSSR) for the ITER EDA.

SAFETY ASSESSMENT OF THE ARIES COMPACT STELLARATOR DESIGN

Abstract ARIES-CS is a 1000 MW(electric) compact stellarator conceptual fusion power plant design. This power plant design contains many innovative features to improve the physics, engineering, and safety performance of the stellarator concept. ARIES-CS utilizes a dual-cooled lead lithium blanket that employs low-activation ferritic steel as a structural material, with the first wall cooled by helium and the breeding zone self-cooled by flowing lead lithium. In this paper we examine the safety and environmental performance of ARIES-CS by reporting radiological inventories, decay heat, and radioactive waste management options and by examining the response of ARIES-CS to accident conditions. These accidents include conventional loss of coolant and loss of flow events, an ex-vessel loss of coolant event, and an in-vessel loss of coolant with bypass event that mobilizes in-vessel radioactive inventories (e.g., tritium and erosion dust from plasma-facing components). Our analyses demonstrate that the decay heat can be safely removed from ARIES-CS and the facility can meet the no-evacuation requirement.

OPERATIONAL WINDOWS FOR DRY-WALL AND WETTED-WALL IFE CHAMBERS

Abstract The ARIES-IFE study was an integrated study of inertial fusion energy (IFE) chambers and chamber interfaces with the driver and target systems. Detailed analysis of various subsystems was performed parametrically to uncover key physics/technology uncertainties and to identify constraints imposed by each subsystem. In this paper, these constraints (e.g., target injection and tracking, thermal response of the first wall, and driver propagation and focusing) were combined to understand the trade-offs, to develop operational windows for chamber concepts, and to identify high-leverage research and development directions for IFE research. Some conclusions drawn in this paper are (a) the detailed characterization of the target yield and spectrum has a major impact on the chamber; (b) it is prudent to use a thin armor instead of a monolithic first wall for dry-wall concepts; (c) for dry-wall concepts with direct-drive targets, the most stringent constraint is imposed by target survival during the injection process; (d) for relatively low yield targets (<250 MJ), an operational window with no buffer gas may exist; (e) for dry-wall concepts with indirect-drive targets, a high buffer gas pressure would be necessary that may preclude propagation of the laser driver and require assisted pinch transport for the heavy-ion driver; and (f) generation and transport of aerosols in the chamber is the key feasibility issue for wetted-wall concepts.

Pedigree Analysis of the MELCOR 1.8.2 Code to be Used for ITER’s Report Preliminary on Safety

This report documents the pedigree analysis of the MELCOR 1.8.2 code to be used for ITER’s Report Preliminary on Safety. To pedigree the code the process involved four steps. First, taking the modified MELCOR 1.8.2 code used by the ITER Joint Central Team (JCT) for analyses in previous ITER Safety Assessments and compared the FORTRAN code of this version line-by-line to the original 1.8.2 version of MELCOR. The second step was a non-regression analysis which involves comparing the results from the pedigreed version against those predicted by the original, unmodified version of MELCOR 1.8.2. The third step involved comparing the pedigreed version results to results from the MELCOR version used by the ITER JCT for the Generic Site Safety Report (GSSR) against a set of accident problems analyzed for the safety report. The fourth and final step involved a comparison between the pedigreed version of the code and the developmental test problems cited in the change documents referenced in this report. The results from the pedigree process are described in this report.

Comparison of athena/relap results against ice experimental data

Abstract In order to demonstrate the adequacy of the International Thermonuclear Experimental Reactor design from a safety stand point as well as investigating the behavior of two-phase flow phenomena during an ingress of coolant event, an integrated ICE test facility was constructed in Japan. The data generated from the ICE facility offers a valuable means to validate computer codes such as athena / relap5 , which is one of the codes used at the Idaho National Engineering And Environmental Laboratory (INEEL) to evaluate the safety of various fusion reactor concepts. In this paper we compared numerical results generated by the athena code with corresponding test data from the ICE facility. Overall we found good agreement between the test data and the predicted results.

Safety issues associated with mobilized activation products in selected APEX designs

In the advanced power extraction (APEX) project, safety and environmental concerns considered up front, as designs evolve, so that the goal of safety and environmental attractiveness is realized. Since the neutron and surface heat loads are higher in APEX designs than those in conventional fusion designs, decay heat and activation are generally higher, presenting an increased challenge when justifying the safety case. Potential first wall materials that can function adequately under higher neutron and heat loads include materials such as tungsten and molybdenum. The activation products of both these materials are radiologically hazardous and mobilizable under accident conditions. We have examined a number of APEX concepts to determine the ability of the design to remove decay heat from the plasma-facing surface during a loss of coolant and air ingress event. In this paper, we concentrate on mobilization of first wall materials during ingress events, and provide guidance to enhance the safety characteristics of APEX designs that utilize tungsten and similar high heat load materials.

SOMBRERO LOVA analysis using CFC NB31 oxidation data

Abstract Carbon fiber composites (CFCs) are often suggested as armor material for the first wall of a fusion plasma chamber because of carbon’s low atomic number, high thermal conductivity, and high melting point. However, carbon is chemically reactive in air and readily absorbs tritium. Accordingly, it is believed that during a loss-of-vacuum accident (LOVA), the CFC armor will react with the air ingress and release its absorbed tritium. The mobilization of this tritium and the carbon monoxide produced by the CFC-air chemical reaction are both safety concerns. This paper discusses the MELCOR thermal-hydraulic analysis of a simulated LOVA for the SOMBRERO fusion design. The MELCOR analysis is important because it included data from recent oxidation experiments that studied the advanced CFC NB31. A previous MELCOR analysis of a simulated SOMBRERO LOVA event suggested that the ingress of air would aggressively oxidize the CFC. While the current analysis revealed initial first-wall temperatures that exceed those of the prior analyses, the trend reversed 10 h after the onset of the LOVA. The calculated wall temperatures at the back of the blanket for the current analysis were consistently lower than those previously calculated using the older data. Accordingly, the conclusion is that a LOVA event for a fusion design similar to SOMBRERO may not be as grave as once predicted.

Modular Pebble-Bed Reactor Project: Laboratory-Directed Research and Development Program FY 2002 Annual Report

This report documents the results of our research in FY-02 on pebble-bed reactor technology under our Laboratory Directed Research and Development (LDRD) project entitled the Modular Pebble-Bed Reactor. The MPBR is an advanced reactor concept that can meet the energy and environmental needs of future generations under DOE’s Generation IV initiative. Our work is focused in three areas: neutronics, core design and fuel cycle; reactor safety and thermal hydraulics; and fuel performance.