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QUANTIFICATION OF ACTIVITY LEVELS AND OPTIMIZATION OF DOSE RATE MANAGEMENT TO PREPARE STAGE 3 DECOMMISSIONING OF GAS-COOLED REACTORS

Obiettivo

As part of the preparatory work for Stage 3 decommissioning of the G2/G3 gas-cooled reactors at Marcoule, the project involves:

quantifying the activity levels of complex core structures based on theoretical analysis and on a large number of dose rate measurements;
design of a software package to optimize the dismantling and related operations and best minimizing of the dose rates incurred by the personnel.

It is important to determine the dose rates and time necessary on each manual dismantling operation, and to assess the material activity levels for optimum waste conditioning and disposal.

The development of suitable software tools and thorough examination of all the possible scenarios are very time-consuming undertakings requiring aid beyond national boundaries.
The project involves:
quantifying the activity levels of complex core structures based on theoretical analysis and on a large number of dose rate measurements;
design of a software package to optimise the dismantling and related operations and minimise the dose rate measurements;
design of a software package incurred by the personnel.

Among the various elements, the graphite stock composing the central part of the core is the one that is best known. During reactor operation, graphite was under close monitoring by means of numerous samplings. The recent radial drillings right across the core improved the radiological knowledge of graphite, both in the nature of radioelements present as well as their absolute quantity and their distribution. A few samples used to quantify graphite were taken from a vertical diameter of the vessel equidistant to the graphite rear and front faces. The results of the tritium analyses show that this hydrogen isotope is largely preponderant (from 51.4 per cent to 96.3 per cent).

Samples were taken of the specific activity of carbon-14 in graphite to give the axial and radial distribution of this radioelement.

The nature of the different isotopes and the value of the specific activity present in the concrete upper part of the reactor vessel were defined thanks to results obtained during the horizontal drilling carried out in a region close to the maximum flux region.

The physical or geometrical inventory of the core constituents was carried out.

The EVODIF computer program was developed to calculate gamma activity levels in the entire core.
WORK PROGRAMME

1. Dose rate measurements and analyses of core samples after a literature review (CEA).

2. Analyses of geometric, physical and radiological data (Radia)

3. Development of a computer programme to calculate gamma-activity levels in the entire core (Radia)

4. Development of a computer programme to minimize dose rates during human interventions (CEA)

5. Comparison of calculated and measured results (CEA).

6. Examination of dismantling scenarios (CEA).

7. Revision of expert software considering decommissioning time and doses (CEA).

8. Evaluation of costs, radioactive job doses, working time and secondary waste arisings (All).

Invito a presentare proposte

Data not available

Meccanismo di finanziamento

CSC - Cost-sharing contracts

Coordinatore

Commissariat à l'Energie Atomique (CEA)
Contributo UE
Nessun dato
Indirizzo
Centre d'Études Nucléaires de la Vallée du Rhône Cité de Marcoule
30205 Bagnols-sur-Cèze
Francia

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Costo totale
Nessun dato

Partecipanti (1)