Fuel Element Gas Plenum Segmentation for Void Reactivity Control

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Solution Overview

Problem

Fast neutron reactors using metal fuel face increased void reactivity when the coolant boils, which can compromise safety, particularly during anticipated transients without scram or unprotected loss of flow events.

Innovation Solution

A fuel element design with a cladding tube containing metal fuel and a gas plenum region above the fuel, featuring a small-diameter portion within the plenum to increase coolant area and reduce void reactivity, while maintaining compactness and preventing cladding damage from fuel swelling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a gas plenum region is formed above the metal fuel to accommodate fuel swelling, then the fuel element can handle fuel expansion, but the void reactivity increases when coolant boils

Engineering Contradiction:

Improvefuel swelling accommodationVSAvoidsafety during coolant void

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The gas plenum region is divided into a large-diameter portion (adjacent to metal fuel) and a small-diameter portion (above the large-diameter portion). This segmentation allows the plenum to accommodate fuel swelling in the large-diameter region while the small-diameter region reduces the void volume above the fuel, thereby reducing void reactivity and improving safety during coolant void events.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the gas plenum region have different diameters to serve different functions. The large-diameter portion provides space for fuel swelling accommodation, while the small-diameter portion minimizes void reactivity. This local variation in geometric quality optimizes both fuel swelling handling and safety characteristics.

Inventive Principle:

Principle #3Local quality

2Stability of the object's composition

If the gas plenum region has a uniform large diameter to accommodate fuel swelling, then fuel expansion is managed, but the void reactivity is increased

Engineering Contradiction:

Improvefuel swelling accommodationVSAvoidvoid reactivity

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The gas plenum region is segmented into portions with different diameters. The large-diameter portion accommodates fuel swelling while the small-diameter portion reduces void reactivity, resolving the contradiction between fuel swelling accommodation and void reactivity reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The solution addresses the contradiction by introducing a dimensional variation (diameter change) within the gas plenum region. By varying the diameter along the axial direction, the design simultaneously achieves adequate swelling space and reduced void volume for lower reactivity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If the gas plenum region is made compact to reduce void reactivity, then safety is improved, but the space for fuel swelling is reduced

Engineering Contradiction:

Improvesafety during coolant voidVSAvoidfuel swelling accommodation

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The gas plenum region is segmented into a large-diameter portion for swelling accommodation and a small-diameter portion for void reactivity reduction. This segmentation allows the system to achieve both compactness (for safety) and adequate swelling space simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different local portions of the gas plenum have different qualities (diameters) optimized for their specific functions. The large-diameter region provides swelling space while the small-diameter region provides compactness for safety, resolving the contradiction between these two requirements.

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

The design effectively reduces void reactivity and enhances safety by injecting negative reactivity during coolant density changes, improving nuclear characteristics and economic efficiency while preventing cladding tube damage.

Implementation Method 1

a small-diameter portion (12) is formed in the gas plenum region (6). By forming the small-diameter portion (12) in the gas plenum region (6), the area of the coolant material can be increased

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 2

a coolant material passage (11) is formed between the fuel element (1) and the fuel element (1)

Methodology Applied

Scientific EffectConvection cooling: Convection

Data Source

PatentUS11398315B2Fuel element, fuel assembly, and core

Publication Date: 2022.07.26 HITACHI GE NUCLEAR ENERGY LTD

AI summary

The fuel element of the present invention includes a cladding tube and a metal fuel contained in the cladding tube, in which a gas plenum region is formed above the metal fuel and inside the cladding tube and has a small-diameter portion in the gas plenum region. Further, the fuel assembly of the present invention includes the fuel element of the present invention and a wrapper tube surrounding the fuel element, in which a coolant material passage is formed between the fuel element and the fuel element. Further, the core of the present invention includes an inner core fuel region loaded with the fuel assembly according to the present invention, and an outer core fuel region loaded with the fuel assembly of the present invention.