Tag: fast reactor

Advanced Burner Reactor with Breed-and-Burn Thorium Blankets for Improved Economics and Resource Utilization

Guanheng Zhang (alumnus), Chris Keckler, Alejandra Jolodosky (former), Massimiliano Fratoni, Jasmina Vujic, Ehud Greenspan

This study assesses the feasibility of designing a Seed and Blanket (S&B) Sodium-cooled Fast Reactor (SFR) to generate a significant fraction of the core power from radial thorium-fueled blankets. The goals of this project support sustainability of the nuclear fuel cycle. The blanket operates in a Breed-and-Burn mode without exceeding currently-verified experimental radiation damage limits. The S&B core is designed to maximize the fraction of neutrons that radially leak into the subcritical blanket. The blanket makes beneficial use of the leaking neutrons for improved economics and resource utilization. Since the blanket fuel requires no reprocessing or remote fuel fabrication, a larger fraction of power from the blanket will result in a lower fuel cycle cost per unit of electricity generated. A unique synergism is found between a low conversion ratio seed and the breed-and-burn thorium blanket. The benefits of this synergism are maximized when using an annular seed surrounded by inner and outer thorium blankets.

Fuel cycle analysis of the S&B design, including basic fuel cycle parameters, nuclear waste characteristics (radioactivity, inhalation/ingestion toxicity), proliferation resistance, fuel cycle cost, and resource utilization, is conducted and compared with a reference Advanced Burner Reactor and Pressurized Water Reactors. The S&B cores can utilize 7% of thorium’s energy value without the need to develop irradiated thorium reprocessing capabilities. This is ~12 times the amount of energy that LWRs generate per unit weight of natural uranium mined, showing vast improvement in resource utilization over current systems.

Preliminary studies have found that the S&B core could establish several new fuel cycle options. Currently under investigation is the option of using the S&B design to burn minor actinides and plutonium from LWR spent fuel, which would greatly benefit the situation for geologic disposition of spent nuclear fuel and increasing the sustainability of nuclear power.

Breed-and-Burn (B&B) reactor design and optimization

Jason Hou (alumnus), Staffan Qvist (alumnus), and Ehud Greenspan

Breed-and-burn (B&B) reactors are a special class of fast reactors that have the potential of significantly improving the sustainability of the nuclear fuel cycle. They are designed to use low grade fuel (e.g. depleted uranium) without fuel reprocessing. One of the most challenging practical design feasibility issues of B&B reactors is the high level of radiation damage their fuel cladding must withstand—more than twice the maximum radiation damage cladding materials in fast reactors have previously been exposed to. This work investigates the feasibility of reducing the peak minimum required radiation damage level by introducing a three-dimensional (3D) in-core fuel management strategy.

A new conceptual design of a B&B core made of axially segmented fuel assemblies was adopted to facilitate the 3D shuffling. The assemblies of the 3D shuffled system are each made of two to four subassemblies that are axially stacked. The subassemblies can be disconnected from one another and then stacked together in a different order and/or combination to constitute new assemblies. Each subassembly is made of short vented fuel pins, requiring a few centimeters of fuel-free space on the top of the pins to accommodate the venting device and the axial fuel swelling.

A combinatorial search methodology has been developed and implemented for 3D shuffling pattern (SP) optimization based on the Simulated Annealing (SA) algorithm. The primary objective of the SA optimization is to minimize the peak radiation damage and its secondary objective is to minimize burnup reactivity swing, the radial power peaking factor, and the variation in power level experienced by a fuel assembly over the cycle.

Compared with the optimal conventional 2D fuel shuffling, the optimal 3D SP offers (1) a 34% reduction of the peak radiation damage level, down to ~350 dpa, (2) a 45% increase in the average fuel discharge burnup, and hence the uranium utilization, and (3) does not violate any major neutronics or thermal-hydraulics constraints. For the same peak dpa level, the average discharge burnup of the 3D shuffled core is 2.23 times that of the 2D shuffled core; this corresponds to a ~120% relative increase in the fuel utilization. These significant improvements may enable nearer-term commercialization of B&B reactors. In the long term, the successful deployment of the B&B core along with optimal 3D shuffling of fuel could provide at least a 30-fold increase in uranium utilization compared to current once-through LWRs, and hence significantly improve the sustainability of the once-through nuclear fuel cycle.