James R. Powell

Design of particle bed reactors for the space nuclear thermal propulsion program

Abstract This paper describes the design for the Particle Bed Reactor (PBR) that we considered for the Space Nuclear Thermal Propulsion (SNTP) Program. The methods of analysis and their validation are outlined first. Monte Carlo methods were used for the physics analysis, several new algorithms were developed for the fluid dynamics, heat transfer and transient analysis; and commercial codes were used for the stress analysis. We carried out a critical experiment, prototypic of the PBR to validate the reactor physics; blowdown experiments with beds of prototypic dimensions were undertaken to validate the power-extraction capabilities from particle beds. In addition, materials and mechanical design concepts for the fuel elements were experimentally validated. Four PBR rocket reactor designs were investigated parametrically. They varied in power from 400 MW to 2000 MW, depending on the missions goals. These designs all were characterized by a negative prompt coefficient, due to Doppler feedback, and a moderator feedback coefficient which varied from slightly positive to slightly negative. In all practical designs, we found that the coolant worth was positive, and the thrust/weight ratio was greater than 20.

The Linear Accelerator Fuel Enricher Regenerator (LAFER) and Fission Product Transmutor (APEX)

Two major problems face the nuclear industry today; first is the long-term supply of fissile material and second is the disposal of long-lived fission product waste. The high energy proton linear accelerator can assist in the solution of each of these problems. High energy protons from the linear accelerator can interact with a molten lead target to produce spallation and evaporation neutrons. The neutrons can be absorbed in surrounding light water power reactor (LWR) fuel elements to produce fissile Pu-239 or U-233 fuel from fertile U-238 or Th-232 in-situ. A schematic of the target assembly for enriching PWR fuel elements is shown in Figure 1. The enriched fuel element is used in the LWR power reactor until reactivity is lost after which the element is regenerated in the linear accelerator target blanket assembly and then the element is once again fissioned in the power LWR. In this manner the natural uranium fuel resource can supply an expanded nuclear power reactor economy without the need for fuel reprocessing, which satisfies the administrations policy of non-proliferation. Furthermore, the amount of spent fuel elements for long-term disposal is reduced in proportion to the number of fuel regeneration cycles. The limiting factor is the burnup damage to the fuel cladding. A 300 ma-1.5 GeV (450 MW) proton linear accelerator can produce approximately one ton of fissile (Pu-239) material annually which is enough to supply fuel to three 1000 MW(e) LWR power reactors.

High-Performance Ultra-light Nuclear Rockets for Near-Earth Objects Interaction Missionsa

ABSTRACT: The performance capabilities and technology features of ultra compact nuclear thermal rockets based on very high power density (30 Megawatts per liter) fuel elements are described. Nuclear rockets appear particularly attractive for carrying out missions to investigate or intercept near‐Earth objects (NEOs) that potentially could impact on the Earth. Many of these NEO threats, whether asteroids or comets, have extremely high closing velocities, i.e., tens of kilometers per second relative to the Earth. Nuclear rockets using hydrogen propellant enable flight velocities 2 to 3 times those achievable with chemical rockets, allowing interaction with a potential NEO threat at a much shorter time, and at much greater range. Two versions of an ultra compact nuclear rocket based on very high heat transfer rates are described: the PBR (Particle Bed Reactor), which has undergone substantial hardware development effort, and MITEE (MIniature ReacTor EnginE) which is a design derivative of the PBR. Nominal performance capabilities for the PBR are: thermal power ≃1000 MW thrust ≃45,000 lbsf, and weight ≃500 kg. For MITEE, nominal capabilities are: thermal power 100 MW; thrust ≃4500 lbsf, and weight ≃50 kg. Development of operational PBR/MITEE systems would enable spacecraft launched from LEO (low‐Earth orbit) to investigate intercept NEOs at a range of ∼100 million kilometers in times of ∼30 days.

Performance of ceramic materials in high temperature steam and hydrogen

Abstract Materials considered for use in fusion blankets for synthetic fuel production were exposed to flowing steam and a combination of steam and hydrogen at temperatures up to 1668 K and flow velocities of 10 meters per second, which are characteristic of blanket design conditions. The penetration rate of 2mm per year on silicon carbide in steam at 1400 K increased to 6mm per year at 1600 K, while alumina, zirconia, and magnesia were below 0.1mm per year. Steam containing 32 to 44 volume percent hydrogen caused a large increase in the erosion rate of alumina, zirconia, and magnesia at elevated temperatures. The temperature above which the erosion rate greatly increased was 1400 K for magnesia, 1550 K for alumina, and 1600 K for zirconia. The penetration rates below these temperatures were less than 0.1 mm per year; however, 100 K above these temperatures, the penetration rate increased four to six times and continued to increase with temperature. The erosion rate on silicon carbide was unaffected by the presence of hydrogen in the steam. Carbon dioxide was substituted for steam and hydrogen in several runs up to 1670 K, and no significant weight losses occurred. The silicon carbide acquired a porous-glassy coating at the highest temperature.

Maglev Launch: Ultra‐low Cost, Ultra‐high Volume Access to Space for Cargo and Humans

Despite decades of efforts to reduce rocket launch costs, improvements are marginal. Launch cost to LEO for cargo is ∼

High flux research reactors based on particulate fuel

10,000 per kg of payload, and to higher orbit and beyond much greater. Human access to the ISS costs

Structure of Ball Llghtning

20 million for a single passenger. Unless launch costs are greatly reduced, large scale commercial use and human exploration of the solar system will not occur. A new approach for ultra low cost access to space—Maglev Launch—magnetically accelerates levitated spacecraft to orbital speeds, 8 km/sec or more, in evacuated tunnels on the surface, using Maglev technology like that operating in Japan for high speed passenger transport. The cost of electric energy to reach orbital speed is less than

StarTram: An Ultra Low Cost Launch System to Enable Large Scale Exploration of the Solar System

1 per kilogram of payload. Two Maglev launch systems are described, the Gen‐1System for unmanned cargo craft to orbit and Gen‐2, for large‐scale access of human to space. Magnetically levitated and propelled Gen‐1 cargo craft accelerate in a 100 kilometer long evacuated tunnel, entering the atmosphere at the tunnel exit, which is located in high altitude terrain (∼5000 meters) through an electrically powered “MHD Window” that prevents outside air from flowing into the tunnel. The Gen‐1 cargo craft then coasts upwards to space where a small rocket burn, ∼0.5 km/sec establishes, the final orbit. The Gen‐1 reference design launches a 40 ton, 2 meter diameter spacecraft with 35 tons of payload. At 12 launches per day, a single Gen‐1 facility could launch 150,000 tons annually. Using present costs for tunneling, superconductors, cryogenic equipment, materials, etc., the projected construction cost for the Gen‐1 facility is 20 billion dollars. Amortization cost, plus Spacecraft and O&M costs, total

A particle bed reactor based NTP in the 112,500 N thrust class

43 per kg of payload. For polar orbit launches, sites exist in Alaska, Russia, and China. For equatorial orbit launches, sites exist in the Andes and Africa. With funding, the Gen‐1 system could operate by 2020 AD. The Gen‐2 system requires more advanced technology. Passenger spacecraft enter the atmosphere at 70,000 feet, where deceleration is acceptable. A levitated evacuated launch tube is used, with the levitation force generated by magnetic interaction between superconducting cables on the levitated launch tube and superconducting cables on the ground beneath. The Gen‐2 system could launch 100’s of thousands of passengers per year, and operate by 2030 AD. Maglev launch will enable large human scale exploration of space, thousands of gigawatts of space solar power satellites for beamed power to Earth, a robust defense against asteroids and comets, and many other applications not possible now.

The Liquid Annular Reactor System (LARS) propulsion

High Flux Particle Bed Reactor (HFPBR) designs based on High Temperature Gas Reactors (HTGR) particular fuel are described. The coated fuel particles, approx.500 microns in diameter, are packed between porous metal frits, and directly cooled by flowing D/sub 2/O. The large heat transfer surface area in the packed bed, approx.100 cm/sup 2//cm/sup 3/ of volume, allows high power densities, typically 10 MW/liter. Peak thermal fluxes in the HFPBR are 1 to 2 x 1/sup 16/ n/c/sup 2/ sec., depending on configuration and moderator choice with beryllium and D/sub 2/O Moderators yielding the best flux performance. Spent fuel particles can be hydraulically unloaded every day or two and fresh fuel reloaded. The short fuel cycle allows HFPBR fuel loading to be very low, approx.2 kg of /sup 235/U, with a fission product inventory one-tenth of that in present high flux research reactors. The HFPBR can use partially enriched fuel, 20% /sup 235/U, without degradation in flux reactivity. 8 refs., 12 figs., 2 tabs.