Sodium-Cooled Fast Reactor Fuel Assembly MA Transmutation

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Solution Overview

Problem

Conventional techniques for sodium-cooled metal fuel fast reactors do not effectively increase the nuclear transmutation of minor actinides (MA) within the reactor core, limiting the reduction of radioactive waste toxicity and rationalization of geological disposal sites.

Innovation Solution

The use of a U—Pu-MA-Zr alloy with low Pu enrichment in axial and radial blanket fuel regions, where the MA enrichment is less than or equal to the Pu enrichment, to increase the weight of MA loaded in the reactor core, thereby enhancing nuclear transmutation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional fuel assembly configurations are used, then the reactor core structure is simple and easy to manufacture, but the nuclear transmutation amount of minor actinides is insufficient

Engineering Contradiction:

Improvenuclear transmutation amount of MAVSAvoidfuel assembly structure complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The fuel assembly is divided into multiple fuel rod types: first fuel rods containing MA and second fuel rods containing no MA. This segmentation allows selective placement of MA-containing fuel rods in specific positions (inner core region and outer core region) to optimize transmutation efficiency while managing overall complexity through standardized rod designs

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different fuel rod types are strategically distributed throughout the reactor core according to spatial requirements. MA-containing fuel rods are positioned in regions requiring enhanced transmutation, while MA-free fuel rods are placed in regions needing structural simplicity or different functional characteristics, creating local optimization without requiring complete redesign of the entire core

Inventive Principle:

Principle #3Local quality

2Productivity

If MA content in fuel rods is increased, then nuclear transmutation of MA is enhanced, but void reactivity increases exceeding safety limits

Engineering Contradiction:

Improvenuclear transmutation amount of MAVSAvoidvoid reactivity control

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention changes the compositional parameters of the fuel rods by controlling the enrichment levels of fissile materials. First fuel rods have a first enrichment level optimized for transmutation, while second fuel rods have a second enrichment level (lower than the first) that provides negative reactivity feedback. This parameter differentiation allows the core to achieve high MA transmutation while keeping void reactivity within safe limits through the balancing effect of mixed enrichment levels

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If uniform Pu enrichment is used in all fuel assemblies, then manufacturing is simplified, but power distribution in the radial direction cannot be flattened

Engineering Contradiction:

Improvefuel assembly manufacturing simplicityVSAvoidpower distribution in radial direction

Core Design Contradiction:

Ease of manufactureVSPower

Solution Approach 1:

Fuel assemblies are differentiated by their radial position in the reactor core. Inner core fuel assemblies contain first fuel rods with higher enrichment, while outer core fuel assemblies contain second fuel rods with lower enrichment. This local differentiation of enrichment levels naturally flattens the radial power distribution by reducing power density in the outer regions, achieving both manufacturing feasibility through standardized processes and optimal power distribution through strategic material placement

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach increases the nuclear transmutation amount of MA by 1.8 times compared to conventional methods, allowing for more effective reduction of radioactive waste toxicity and improved reactor performance within the void reactivity limits.

Implementation Method 1

Fuel assemblies loaded in the core each have a plurality of fuel rods with plutonium-enriched depleted uranium (U-238) encased therein

Methodology Applied

Scientific EffectNuclear fission: Nuclear Fission

Implementation Method 2

The fuel assembly and the reactor core increase the nuclear transmutation amount of minor actinides (MA)

Methodology Applied

Scientific EffectNuclear transmutation:

Implementation Method 3

liquid sodium as a coolant is filled in the reactor vessel

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS20240355487A1Fuel Assembly for Sodium-Cooled Metal Fuel Fast Reactor, Reactor Core, and Manufacturing Method of Fuel Assembly

Publication Date: 2024.10.24 HITACHI GE NUCLEAR ENERGY LTD

AI summary

Provided are a fuel assembly for a sodium-cooled metal fuel fast reactor, a reactor core, and a manufacturing method of the fuel assembly. Compared with conventional techniques, the fuel assembly and the reactor core can subject more MA to nuclear transmutation by allowing to increase the weight of MA to be loaded in the reactor core. One or more of an upper axial blanket fuel or lower axial blanket fuel in an inner core fuel assembly or outer core fuel assembly, or a radial blanket fuel in a radial blanket fuel assembly is a U—Pu-MA-Zr alloy of a low Pu enrichment lower in Pu enrichment than a core fuel, and has a MA enrichment and a Pu enrichment satisfying a relationship of 0 wt %<MA enrichment≤Pu enrichment.