RCCA Clad Strain Mitigation via Powder Collection and Plenum Expansion

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Solution Overview

Problem

Nuclear reactor Rod Cluster Control Assemblies (RCCAs) and Control Element Assemblies (CEAs) face clad strain issues due to powder accumulation from ceramic absorber materials like boron carbide (B4C) in high fluence regions, which restricts thermal and irradiation expansion gaps, leading to potential cracking during normal and accident conditions.

Innovation Solution

Incorporating a powder collection and blockage device between upper and lower absorber materials, featuring a spacer, garter spring, and fine mesh screen to prevent powder accumulation while allowing gas passage, and increasing plenum volume by adding axial holes to end plugs with optional radial grooves for gas expansion channels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If ceramic absorber material is used in high fluence region, then neutron absorption performance is improved, but powder accumulation occurs which restricts expansion gaps and causes clad strain

Engineering Contradiction:

Improveneutron absorption performanceVSAvoidclad strain and cracking risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The control rod is divided into upper and lower absorber material sections separated by a spacer. The spacer segments the continuous absorber material into discrete sections, preventing powder from the upper section from accumulating in the lower high fluence region while maintaining neutron absorption capability in both sections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A garter spring is introduced as an intermediary component between the upper and lower absorber materials. The garter spring acts as a mediator that physically blocks powder accumulation in the lower section while allowing thermal expansion, and provides mechanical support to maintain the spacer position and expansion gaps.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If absorber material expansion space is increased, then thermal and irradiation expansion is accommodated, but plenum volume is reduced

Engineering Contradiction:

Improveexpansion gap maintenanceVSAvoidplenum volume

Core Design Contradiction:

Stability of the object's compositionVSVolume of stationary object

Solution Approach 1:

Axial holes are added to the end plugs, creating additional volume in the axial dimension. This dimensional addition to the plenum volume compensates for the space required by the spacer and maintains adequate plenum volume for absorber material expansion during normal and accident conditions.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If lower absorber material is positioned at bottom, then neutron absorption in high fluence region is improved, but powder accumulation blocks expansion gaps

Engineering Contradiction:

Improveneutron absorption in high fluence regionVSAvoidexpansion gap accessibility

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The spacer and garter spring are pre-installed in the control rod assembly before operation. This preliminary action prevents powder accumulation in the lower section from the beginning of the rod's service life, ensuring expansion gaps remain accessible throughout the operational cycle.

Inventive Principle:

Principle #10Preliminary action

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

Prevents powder accumulation in high fluence regions, ensuring sufficient expansion gaps for thermal and irradiation growth, reducing clad strain and the risk of cracking, and providing additional plenum volume for absorber material expansion during accidents.

Implementation Method 1

The garter spring prevents the powder from passing down the clad, but does not prevent backfill gases and gases generated during irradiation from moving through the control rod

Methodology Applied

Scientific EffectMechanical blocking:

Implementation Method 2

The spacer provides enough room for thermal and irradiation expansion of the absorber materials

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

The spacer provides enough room for thermal and irradiation expansion of the absorber materials

Methodology Applied

Scientific EffectIrradiation expansion:

Implementation Method 4

incorporating an axial hole into a top end plug... increasing the plenum volume... providing additional plenum volume for absorber material expansion during accidents

Methodology Applied

Scientific EffectVolume expansion:

Implementation Method 5

incorporating radial grooves in the bottom of the lower absorber material to provide a flow channel for gas expansion or generation

Methodology Applied

Scientific EffectGas flow:

Data Source

PatentUS12046381B2Methods and devices to improve performances of RCCA and CEA to mitigate clad strain in the high fluence region

Publication Date: 2024.07.23 WESTINGHOUSE ELECTRIC CORP

AI summary

The present disclosure is generally related to methods, devices and systems for improving the performances of a Rod Cluster Control Assembly (RCCA) and/or a Control Element Assembly (CEA) to mitigate clad strain, especially in the high fluence region, during normal operation conditions and accident conditions. One method may include incorporating a device such as a powder collection and blockage device between the ceramic upper and ceramic lower absorber materials of the RCCA and/or CEA. Another method may include increasing the plenum volume by incorporating an axial hole into the top end plug extension. Another method may include increasing the plenum volume by incorporating an axial hole into the bottom end plug and optionally incorporating radial grooves in the bottom of the lower absorber material to provide a flow channel for gas expansion or generation to ensure that the lower absorber does not block the opening in the bottom end plug.