Electromagnetic Testing of Rod Cluster Control Assemblies in Pressured-Water Reactor Power Plants

Minhhuy Le,Sunbo Sim,Jinyi Lee

doi:10.3390/app9194013

Minhhuy Le, Sunbo Sim + Show 1 more

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https://doi.org/10.3390/app9194013

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Abstract

This paper presents an electromagnetic testing system for rod cluster control assemblies used in pressurized-water reactors. The system uses several encircling-type magnetic cameras equivalent to a number of the control rods; each sensor probe composes of an encircling Hall sensor array (EHaS) and a bobbin coil. The EHaS has 16 Hall sensor elements that measure the electromagnetic field distribution in the radial direction of the control rod induced by the bobbin coil for defects. Experiments are performed on artificial defects on the cladding tube of real control rods to simulate short-circumferential grooves (SCGs), sliding wears (SWs), and circumferential cracks (CCs). The system can inspect the artificial SCGs, SWs, and CCs with depths up to 20%, 30%, and 40% of the cladding tube thickness (0.47 mm), respectively. Furthermore, the shape and depth of the defects could be estimated. The standard deviations of depth estimation are 18%, 5.8%, and 6.0% for CCs, SCGs, and SWs. The SCGs and SWs have a small and similar estimation error, but the CCs have the highest error of estimation, and have a small width of 0.2 mm.

Highlights

Rod cluster control assemblies (RCCAs) are used in pressurized-water reactors (PWRs) to control fast reactivity changes and stop the reactor when an accident happens
There are eight guide cards located at the upper side of the reactor core to support the RCCA, which are visible after the nuclear fuel is withdrawn during operation of the nuclear reactor
We propose an integrated system comprising 24 encircling Hall sensor array (EHaS) probes that enable the inspection of a 17×17 type RCCA in a single scan

Summary

Introduction

Rod cluster control assemblies (RCCAs) are used in pressurized-water reactors (PWRs) to control fast reactivity changes and stop the reactor when an accident happens. The RCCA usually consists of 16 (14×14 type), 20 (16×16 type), or 24 (17×17 type) control rods. Each control rod includes an absorber consisting of Ag (80%)-In (15%)-Cd (5%) in the core and covered with a cladding tube made of stainless steel (STS340) to prevent corrosion and cracking [1]. Wear can occur on the cladding tube due to the up/down movement of the RCCA and vibration of control rods against the guide cards, the vibration of the guide cards themselves, and vibration against the inner walls of the guide tubes on the fuel assemblies [1,2]. Irradiation assisted stress corrosion cracking usually occurs in the cladding tubes and end tips of the control rods [3].

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