Per F. Peterson

Molten-salt-cooled advanced high-temperature reactor for production of hydrogen and electricity

Abstract The molten-salt-cooled Advanced High-Temperature Reactor (AHTR) is a new reactor concept designed to provide very high-temperature (750 to 1000°C) heat to enable efficient low-cost thermochemical production of hydrogen (H2) or production of electricity. This paper provides an initial description and technical analysis of its key features. The proposed AHTR uses coated-particle graphite-matrix fuel similar to that used in high-temperature gas-cooled reactors (HTGRs), such as the General Atomics gas turbine-modular helium reactor. However, unlike the HTGRs, the AHTR uses a molten-salt coolant and a pool configuration, similar to that of the General Electric Super Power Reactor Inherently Safe Module (S-PRISM) liquid-metal reactor. Because the boiling points for molten fluoride salts are near ~1400°C, the reactor can operate at very high temperatures and atmospheric pressure. For thermochemical H2 production, the heat is delivered at the required near-constant high temperature and low pressure. For electricity production, a multireheat helium Brayton (gas-turbine) cycle, with efficiencies >50%, is used. The low-pressure molten-salt coolant, with its high heat capacity and natural circulation heat transfer capability, creates the potential for robust safety (including fully passive decay-heat removal) and improved economics with passive safety systems that allow higher power densities and scaling to large reactor sizes [>1000 MW(electric)].

High-Temperature Liquid-Fluoride-Salt Closed-Brayton-Cycle Solar Power Towers

Liquid-fluoride-salt heat transfer fluids are proposed to raise the heat-to-electricity efficiencies of solar power towers to about 50%. The liquid salt would deliver heat from the solar furnace at temperatures between 700°C and 850°C to a closed multireheat Brayton power cycle using nitrogen or helium as the working fluid. During the daytime, hot salt may also be used to heat graphite, which would then be used as a heat storage medium to make night-time operations possible. Graphite is a low-cost high-heat-capacity solid that is chemically compatible with liquid fluoride salts at high temperatures. About half the cost of a solar power tower is associated with the mirrors that focus light on the receiver, and less than one-third is associated with the power cycle and heat storage. Consequently, increasing the efficiency by 20–30% has the potential for major reductions in the cost of electricity. Peak temperatures and efficiencies of current designs of power towers are restricted by (1) the use of liquid nitrate salts that decompose at high temperatures and (2) steam cycles in which corrosion limits peak temperature. The liquid-fluoride-salt technology and closed Brayton power cycles are being developed for high-temperature nuclear reactors. These developments may provide the technology and industrial basis for an advanced solar power tower.

Diffusion Layer Theory for Turbulent Vapor Condensation With Noncondensable Gases

In turbulent condensation with noncondensable gas, a thin noncondensable layer accumulated and generates a diffusional resistance to condensation and sensible heat transfer. By expressing the driving potential for mass transfer as a difference in saturation temperatures and using appropriate thermodynamic relationships, here an effective condensation thermal conductivity is derived. With this formulation, experimental results for vertical tubes and plates demonstrate that condensation obeys the heat and mass transfer analogy, when condensation and sensible heat tranfer are considered simultaneously

An investigation of condensation from steam–gas mixtures flowing downward inside a vertical tube

Abstract This research investigates experimentally local heat transfer from condensation in the presence of noncondensable gases inside a vertical tube. Using a novel experimental apparatus for accurately measuring local heat fluxes, an extensive data base has been obtained for the condensation of pure steam, steam–air mixtures and steam–helium mixtures. Three different correlations, implementing the degradation factor method, diffusion layer theory, and mass transfer conductance model, are presented. The correlation using the simple degradation factor method has been shown to give satisfactory engineering accuracy. However, this method is based on very simplified arguments that do not fully represent the complex physical phenomena involved. Based on diffusion layer theory and a mass transfer conductance model, more physically based correlations were developed for the heat transfer of vapor-gas side. The total heat transfer coefficient predicted by the correlations from these two mechanistic models are in close agreement with experimental values.

Multiple-Reheat Brayton Cycles for Nuclear Power Conversion with Molten Coolants

Abstract Gas-turbine power conversion systems can have lower capital costs than comparable steam-turbine systems due to their higher power density. The recent commercialization of magnetic bearing systems for large turbomachinery now makes direct recuperated Brayton cycles the preferred power conversion choice for gas-cooled reactors. This paper presents a multiple-reheat closed gas cycle optimized to use energy input from liquid-metal or molten-salt coolants with temperatures as low as 550 to 650°C. By utilizing reheat, these molten coolant gas cycles (MCGCs) have the potential for substantially higher thermal efficiency than current gas-cooled reactors if used with comparable turbine inlet temperatures. The MCGC system also eliminates the need for steam generators, which removes the potential for chemical reactions between the molten coolant and steam, and greatly simplifies the control of tritium for fusion energy systems.

A SUSTAINABLE NUCLEAR FUEL CYCLE BASED ON LASER INERTIAL FUSION ENERGY

Abstract The National Ignition Facility (NIF), a laser-based Inertial Confinement Fusion (ICF) experiment designed to achieve thermonuclear fusion ignition and burn in the laboratory, will soon be completed at the Lawrence Livermore National Laboratory. Experiments designed to accomplish the NIF’s goal will commence in 2010, using laser energies of 1 to 1.3 MJ. Fusion yields of the order of 10 to 35 MJ are expected soon thereafter. We propose that a laser system capable of generating fusion yields of 35 to 75 MJ at 10 to 15 Hz (i.e., ≈ 350- to 1000-MW fusion and ≈ 1.3 to 3.6 x 1020 n/s), coupled to a compact subcritical fission blanket, could be used to generate several GW of thermal power (GWth) while avoiding carbon dioxide emissions, mitigating nuclear proliferation concerns and minimizing the concerns associated with nuclear safety and long-term nuclear waste disposition. This Laser Inertial Fusion Energy (LIFE) based system is a logical extension of the NIF laser and the yields expected from the early ignition experiments on NIF. The LIFE concept is a once-through, self-contained closed fuel cycle and would have the following characteristics: (1) eliminate the need for uranium enrichment; (2) utilize over 90% of the energy content of the nuclear fuel; (3) eliminate the need for spent fuel chemical separation facilities; (4) maintain the fission blanket subcritical at all times (keff <0.90); and (5) minimize future requirements for deep underground geological waste repositories and minimize actinide content in the end-of-life nuclear waste below the (the lowest). Options to burn natural or depleted U, Th, U/Th mixtures, Spent Nuclear Fuel (SNF) without chemical separations of weapons-attractive actinide streams, and excess weapons Pu or highly enriched U (HEU) are possible and under consideration. Because the fission blanket is always subcritical and decay heat removal is possible via passive mechanisms, the technology is inherently safe. Many technical challenges must be met, but a LIFE solution could provide a sustainable path for worldwide growth of nuclear power for electricity production and hydrogen generation.

Theoretical basis for the Uchida correlation for condensation in reactor containments

Correlations of data presented by Uchida et al. (1965) have been used extensively in the nuclear industry to predict condensation rates inside containment structures, where non-condensable gas effects are important. This work presents a theoretical basis for the form of the Uchida correlation. The good performance of this correlation is found to be an artifact of the method used to perform that and subsequent experiments. In the experiments, the initial inventory of non-condensable gas remained constant as the steam mass fraction was increased, so that the bulk non-condensable gas density remained constant. The theory presented here shows that the Uchida correlation can produce substantial error at other bulk gas densities, raising concern in situations in which non-condensable gas may be sequestered in subvolumes of a containment and for subatmospheric containments.

Diffusion layer modeling for condensation in vertical tubes with noncondensable gases

Abstract Noncondensable gases significantly modify the mechanism of condensation for cocurrent downward flow in vertical tubes. Two-dimensional experimental measurements presented here show similarity between gas concentration distributions and the temperature distributions encountered in laminar and turbulent heat transfer. Thus the analogy between heat and mass transfer, coupled with a reasonable condensate film model, can provide predictions of the local condensation rate. This work presents a simple 9-step iterative calculation procedure for calculating the local heat flux. The empirical model, based on a modified Dittus-Boelter formulation and utilizing an effective condensation thermal conductivity, converges with 2 to 10 iterations at each axial location. Experimental results from several investigators are compared with the predictions of the model, with good agreement.

Pressure suppression pool mixing in passive advanced BWR plants

In the SBWR passive boiling water reactor, the long-term post-accident containment pressure is determined by the combination of noncondensible gas pressure and steam pressure in the wetwell gas space. The suppression pool (SP) surface temperature, which determines the vapor partial pressure, is very important to overall containment performance. Therefore, the thermal stratification of the SP due to blowdown is of primary importance. This work looks at the various phases and phenomena present during the blowdown event and identifies those that are important to thermal stratification, and the scaling necessary to model them in reduced size tests. This is important in determining which of the large body of blowdown to SP data is adequate for application to the stratification problem. The mixing by jets from the main vents is identified as the key phenomena influencing the thermal response of the suppression pool and analytical models are developed to predict the jet influence on thermal stratification. The analytical models are implemented into a system simulation code, TRACG, and used to model thermal stratification behavior in a scaled test facility. The results show good general agreement with the test data.

Options for Scaled Experiments for High Temperature Liquid Salt and Helium Fluid Mechanics and Convective Heat Transfer

Abstract Liquid fluoride salts and helium have desirable properties for use as working fluids for high-temperature (500 to 1000°C) heat transport in fission and fusion applications. This paper presents recent progress in the design and analysis of scaled thermal-hydraulic experiments for fluid mechanics and convective heat transfer in liquid salt and helium systems. It presents a category of heat transfer fluids and a category of light mineral oils that can be used for scaled experiments simulating convective heat transfer in liquid salts. By optimally selecting the length, velocity, average temperature, and temperature difference scales of the experiment, it is possible to simultaneously match the Reynolds, Froude, Prandtl, and Grashof numbers in geometrically scaled experiments operating at low-temperature, reduced length, and velocity scales. Mechanical pumping power and heat input are reduced to ~1 to 2% of the prototype power inputs. Helium fluid mechanics and heat transfer likewise can be simulated by nitrogen following the same procedure. The resulting length, velocity, temperature, and power scales for simulating helium are quite similar to those for the liquid salts, and the pressure scale is reduced greatly compared to the prototypical pressure scale. Steady state and transient heat transfer to a steel and graphite structure can be reproduced with moderate distortion using Pyrex and high-thermal-conductivity epoxies, respectively. Thermal radiation heat transfer cannot be reproduced, so the use of these simulant fluids is limited to those cases where radiation heat transport is small compared to convective heat transport, or where corrections for thermal radiation heat transfer can be introduced in models using convective heat transfer data from the simulant fluids. Likewise for helium flows, compressibility effects are not reproduced.