ACOUSTIC MONITORING TECHNIQUES FOR CORROSION DEGRADATION IN CEMENTED WASTE CANISTERS

Obiettivo

THERE IS A REQUIREMENT ON RADIOACTIVE WASTE PRODUCERS TO ENSURE THE INTEGRITY OF THE CEMENTED WASTEFORMS THAT THEY PRODUCE. PRESENTLY AVAILABLE CORROSION MONITORING AND NDT TECHNIQUES ARE NOT READILY APPLICABLE TO WASTE CANISTERS.
A TECHNIQUE THAT OFFERS PROMISE IN MONITORING THE CORROSION-INDUCED DEGRADATION OF CEMENTED WASTEFORMS FROM OUTSIDE OF THE DRUM IS ACOUSTIC EMISSION.
THIS PROGRAMME AIMS TO INVESTIGATE THE FEASIBILITY OF USING ACOUSTIC EMISSION MONITORING AS A QUANTIFIABLE MEASURE OF CORROSION-INDUCED DEGRADATION AND DEVELOP PROTOTYPE EQUIPMENT FOR MONITORING A NUMBER OF CANISTERS SIMULTANEOUSLY.
A technique that offers promise in monitoring degradation of a cemented metal containing wasteform from the outside of a canister is acoustic emission. This report describes work carried out to investigate the use of acoustic emission to monitor corrosion and degradation of such wasteforms where the waste is a potentially reactive metal.
Electronic monitoring equipment has been designed, built and tested to allow long term monitoring of a number of waste packages simultaneously. Acoustic monitoring experiments were made, on a range of 1 litre cemented Magnox and aluminium samples cast into canisters, comparing the acoustic events with hydrogen gas evolution rates and electrochemical corrosion rates. The attenuation of the acoustic signals by the cement grout under a range of conditions has been studied to determine the volume of wasteform that can be satisfactorily monitored by 1 transducer. The final phase of the programme monitored the acoustic events from full size (200 litre) cemented, inactive, simulated aluminium swarf waste packages.
It is concluded that the technique offers good potential for monitoring cemented containers of the more reactive metals, for example Magnox and aluminium.
THE PROGRAMME WILL MEASURE ACOUSTIC EMISSIONS FROM A TYPICAL CEMENTED WASTEFORM EG MAGNOX, STEEL OR ALUMINIUM IN A 3:1 BLAST FURNACE SLAG (BFS)/ORDINARY PORTLAND CEMENT (OPC) GROUT AND COMPARE THE RESULTS WITH CORROSION RATES MEASURED BY ELECTROCHEMICAL TECHNIQUES AND, IN THE CASE OF MAGNOX AND ALUMINIUM, HYDROGEN GAS EVOLUTION. THE ACOUSTIC EMISSION TECHNIQUE HAS THE POTENTIAL TO DISTINGUISH "CRITICAL" CORROSION, IE THE CORROSION THAT STRESSES THE CEMENT MATRIX FROM CORROSION OCCURING INTO VOIDS IN THE CEMENT MATRIX WHEREAS OTHER TECHNIQUES INDICATE THE TOTAL AMOUNT OF CORROSION, INCLUDING THAT INTO VOIDS, WHICH WILL CARRY NO THREAT TO WASTEFORM INTEGRITY. IT IS HOPED THEREFORE THAT ACOUSTIC EMISSION WILL PROVE TO BE A SENSITIVE MONITOR OF DEGRADATION PROCESSES WHICH THREATEN THE MONOLITHIC NATURE OF A CEMENTED WASTE FORM.

1. SAMPLE PREPARATION AND CURING
LABORATORY SCALE SAMPLES WILL BE PREPARED, CURED AND CONDITIONED TO SIMULATE CEMENTED METAL WASTESTREAMS. THESE WILL BE CAST AS CYLINDERS WITH LOADINGS OF TYPICAL METAL E.G. MAGNOX. THE SAMPLES FOR ELECTROCHEMICAL TESTS WILL REQUIRE METAL COUPONS TO ALLOW AN ELECTRICAL CONNECTION TO BE MADE. THE CEMENT GROUT USED WILL BE 3:1 BFS/OPC. IF NECESSARY CORROSION WILL BE INDUCED AND ACCELERATED BY ADDITIONS OF CHLORIDE IN THE GROUT MIX.

2. MEASUREMENT OF CORROSION RATES
THE ACOUSTIC EMISSIONS, ELECTROCHEMICAL CORROSION RATE AND HYDROGEN GAS EVOLUTION RATES WILL BE RECORDED WITH TIME EITHER ON THE SAME SAMPLES OR ON IDENTICAL DUPLICATES. THIS WILL ALLOW A COMPARISON OF THE RATES OF DEGRADATION INDICATED BY THE TWO RECOGNISED TECHNIQUES COMPARED WITH THE ACOUSTIC MEASUREMENTS. THIS DATA COMBINED WITH DESTRUCTIVE EXAMINATION OF THE SAMPLES POST-TEST SHOULD ALLOW CALIBRATION OF THE ACOUSTIC SIGNALS WITH OTHER MEASURES OF CORROSION RATE. THE ELECTROCHEMICAL CORROSION RATE WILL BE MEASURED USING AC IMPEDANCE OR THE COULOSTATIC PULSE TECHNIQUE TO OBTAIN THE MINIMUM PERTURBATION OF THE CORRODING SYSTEM. THE HYDROGEN GAS WILL BE COLLECTED OVER WATER AND ITS VOLUME MEASURED.

3. CRITICAL VERSUS NON-CRITICAL CORROSION
TO DETERMINE THE SENSITIVITY OF THE ACOUSTIC MEASUREMENT TO CORROSION THAT STRESSES THE CEMENT COMPARED TO CORROSION THAT OCCURS INTO VOIDS SAMPLES WILL BE PREPARED THAT ARE IDENTICAL IN ALL RESPECTS APART FROM THE DEGREE OF CEMENT VOIDAGE THEY CONTAIN. IN THIS WAY IT IS HOPED TO DEMONSTRATE THAT ACOUSTIC SIGNALS ARE A SENSITIVE GAUGE OF THE CORROSION WHICH THREATENS THE INTEGRITY OF THE WASTEFORM.

4. PORTABLE MEASURING AND RECORDING EQUIPMENT
PARALLEL TO THE ABOVE TASKS THE PRESENTLY AVAILABLE EQUIPMENT AND MICROCOMPUTER RECORDING EQUIPMENT WILL BE FURTHER DEVELOPED TO MAKE IT ADAPTABLE TO USE IN A WASTE DRUM STORE.

5. TESTS ON FULL SIZE WASTE PACKAGES
THE EFFECTS OF SIGNAL ATTENUATION BY THE WASTEFORM AND THE OPTIMUM NUMBER OF ACOUSTIC TRANSDUCERS FOR A STANDARD 200 OR 500 LITRE WASTE CANISTER WILL BE INVESTIGATED. THIS WOULD INVOLVE MEASUREMENTS BEING MADE ON SUCH A STANDARD PACKAGE PREPARED AT THE UKAEA'S PILOT CEMENTATION PLANT AT WINFRITH.

Campo scientifico

Programma(i)

FP1-RADWASTOM 3C - Research and development programme (Euratom) on the management and storage of radioactive waste, 1985-1989

Argomento(i)

Data not available

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

CSC - Cost-sharing contracts

Coordinatore

United Kingdom Atomic Energy Authority

Contributo UE

Nessun dato

Indirizzo

353,Harwell
OX11 0RA Didcot - Oxfordshire
Regno Unito

Costo totale