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SEPARATION OF STAINLESS STEEL CONSTITUENTS, USING TRANSPORT IN THE VAPOUR PHASE

Objective

A FEW DECADES AFTER SHUTDOWN OF A NUCLEAR POWER PLANT, THE STAINLESS STEEL COVERING THE INSIDE OF THE PRESSURE VESSEL IS RADIOACTIVE ONLY DUE TO COBALT-60. THE SEPARATION OF THIS ELEMENT FROM THE OTHER CONSTITUENT ELEMENTS OF THE STEEL WOULD DRASTICALLY REDUCE THE AMOUNT OF RADIOACTIVE WASTE AND WOULD ALLOW THE RECYCLING OF NON-RADIOACTIVE ELEMENTS, I.E. MOST OF THE STEEL.

TO DATE, NO TECHNIQUE IS KNOWN TO LEAD TO AN EFFICIENT SEPARATION OF COBALT AT REASONABLE COST AND WITHOUT INVOLVING, AS INTERMEDIATE STEPS, AN INCREASE OF THE AMOUNT OF WASTE. THE PRESENT RESEARCH CONSISTS IN A FEASIBILITY EVALUATION OF SEPARATING COBALT FROM STAINLESS STEEL USING VAPOUR PHASE TRANSPORT. THIS PROCESS OFFERS THE FOLLOWING ADVANTAGES :

- NO ADDITIONAL AMOUNT OF WASTE, EVEN FOR A TRANSIENT STEP,
- REPEATABILITY ALLOWING HIGH SEPARATION FACTORS TO BE REACHED.

IT HAS NEVER BEEN APPLIED TO ALLOYS SUCH AS STAINLESS STEEL AND THE CONDITIONS OF APPLICATION WOULD HAVE TO BE ASSESSED BY THEORETICAL AND EXPERIMENTAL RESEARCH ENDING WITH A FIRST ESTIMATE OF THE FEASIBILITY OF THE SUGGESTED PROCESS.
A process of cobalt separation from other constituents in radioactive stainless steel is proposed for the conditioning of materials derived from nuclear reactor vats. It is based on vapour phase transport on a thermal gradient, within a watertight wall, in the presence of an appropriate carrier gas. A thermodynamic calculation has been carried out using iodine. These trials, carried out on 200 mg of stainless steel (in the form of a powder or shavings, in a quartz ampoule) have permitted the determination of a number of operating parameters in the process. These are in areas of temperature gradient, pressure and separation, and yield. It has been shown that shavings may be effectively treated.
B.1. PRELIMINARY WORK ON THE VAPOUR PHASE TRANSPORT INCLUDING THERMODYNAMIC MODELLING OF THE PROCESS, SETTING UP OF COMPUTER PROGRAMS, COLLECTION OF DATA AND ESTIMATE OF MISSING DATA.

B.2. CONDITIONING OF THE METAL TO BE TREATED AND SELECTION BY CALCULATION OF APPROPRIATE TRANSPORT GASES.

B.3. EXPERIMENTAL VERIFICATION OF THE SEPARATION EFFECT ON THE SELECTED GASES ON THE STAINLESS STEELS.

B.4. FEASIBILITY EVALUATION ON THE MOST APPROPRIATE SITUATION AND ECONOMIC EVALUATION OF THE PROCEDURE IN CASE OF INDUSTRIAL APPLICATION.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Grenoble Avenue Des Martyrs
38041 Grenoble
France