Laser Intertial Fusion Energy: Neutronic Design Aspects of a Hybrid Fusion-Fission Nuclear Energy System

Abstract

This study investigates the neutronics design aspects of a hybrid fusion-fission energy system called the Laser Fusion-Fission Hybrid (LFFH). A LFFH combines current Laser Inertial Confinement fusion technology with that of advanced fission reactor technology to produce a system that eliminates many of the negative aspects of pure fusion or pure fission systems. When examining the LFFH energy mission, a significant portion of the United States and world energy production could be supplied by LFFH plants.The LFFH engine described utilizes a central fusion chamber surrounded by multiple layers of multiplying and moderating media. These layers, or blankets, include coolant plenums, a beryllium (Be) multiplier layer, a fertile fission blanket and a graphite-pebble reflector. Each layer is separated by perforated oxide dispersion strengthened (ODS) ferritic steel walls. The central fusion chamber is surrounded by an ODS ferritic steel first wall. The first wall is coated with 250-500 µm of tungsten to mitigate x-ray damage. The first wall is cooled by Li 17 Pb 83 eutectic, chosen for its neutron multiplication and good heat transfer properties. The Li 17 Pb 83 flows in a jacket around the first wall to an extraction plenum. The main coolant injection plenum is immediately behind the Li 17 Pb 83 , separated from the Li 17 Pb 83 by a solid ODS wall. This main system coolant is the molten salt flibe (2LiF-BeF 2 ), chosen for beneficial neutronics and heat transfer properties. The use of flibe enables both fusion fuel production (tritium) and neutron moderation and multiplication for the fission blanket. A Be pebble (1 cm diameter) multiplier layer surrounds the coolant injection plenum and the coolant flows radially through perforated walls across the bed. Outside the Be layer, a fission fuel layer comprised of depleted uranium contained in Tristructural-isotropic (TRISO) fuel particles having a packing fraction of 20% in 2 cm 1 diameter fuel pebbles. The fission blanket is cooled by the same radial flibe flow that travels through perforated ODS walls to the reflector blanket. This reflector blanket is 75 cm thick comprised of 2 cm diameter graphite pebbles cooled by flibe. The flibe extraction plenum surrounds the reflector bed. Detailed neutronics designs studies are performed to arrive at the described design.The LFFH engine thermal power is controlled using a technique of adjusting the 6 Li/ 7 Li enrichment in the primary and secondary coolants. The enrichment adjusts system thermal power in the design by increasing tritium production while reducing fission. To perform the simulations and design of the LFFH engine, a new software program named LFFH Nuclear Control (LNC) was developed in C++ to extend the functionality of existing neutron transport and depletion software programs. Neutron transport calculations are performed with MCNP5. Depletion calculations are performed using Monteburns 2.0, which utilizes ORIGEN 2.0 and MCNP5 to perform a burnup calculation. LNC supports many design parameters and is capable of p...

Evaluation of subcritical hybrid systems loaded with reprocessed fuel

“…The majority of them were based on (Kramer, 2010). The mass of actinides is about 7.18E + 08 out of 8.19 E + 08 (total mass).…”

“…2 was based on concentrically spheres as purposed by Kramer (2010). Nevertheless, some modifications were made to achieve a source multiplication factor around k src % 0.95.…”

“…Therefore, in this study, two different systems are proposed. One based on a system designed to an ADS (Barros et al, 2012) called system 1 and another designed to a Fusion-Fission system based on inertial confinement (Kramer, 2010) called system 2. Each system has their particular characteristics such as materials, geometries, volume of fuel, fission power and neutron source.…”

Fusion-Fission Blanket Options for the LIFE Engine

“…9 The requirement to operate at constant thermal power is such that early in the cycle excess tritium is produced (TBR > 1) and stored for later use when TBR falls below 1. The cycle ends when the full tritium inventory is exhausted or the system cannot sustain the prescribed power level.…”

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“…The depleted uranium hybrid LIFE blanket strives to close the fission fuel cycle without enrichment or reprocessing, while simultaneously achieving high discharge burnups with reduced proliferation concerns [Moses et al, 2009;Seifried, 2009;Kramer, 2010;. Tritium and deuterium fuel the engine's DT fusion reaction.…”