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DECONTAMINATION OF LARGE-VOLUME NUCLEAR COMPONENTS USING FOAMS

Ziel

There are only a few methods for in situ decontamination of very large components usually in complex forms, such as large valves, reservoirs, heat exchangers, turbines, vessels, boilers.

The foam application processes have the major advantage of using only small quantities of liquid and being able to penetrate forcefully everywhere. Suitable chemical reagents are added to the foam, which acts a dynamic carrier.

In this contract, a technique of permanent foam circulation will be sought, so that decontamination can last for several hours in order to be as effective as possible and to use only a minimum amount of liquid. Decontamination factors of over 100 are expected.

The objectives of the programme are to:
develop and demonstrate an effective in situ decontamination technique for large-volume components using chemical foams containing decontamination reagents;
minimize the volume of secondary wastes produced and demonstrate a treatment and disposal route, eg, electrolytic processes, wet oxidation.
The objectives of the programme are to:
develop and demonstrate an effective in situ decontamination technique for large volume components using chemical foams containing decontamination reagents; minimise the volume of secondary wastes produced and demonstrate a treatment and disposal route, eg electrolytic processes, wet oxidation.

The first specimens taken from the carbon steel deaerator storage vessel of the Winfrith team generating heavy water reactor (SGHWR) allowed:
characterization of the oxide deposit and its contamination; selection of the reagents with which the component could be treated and specification of their formulation; application of foam decontamination at laboratory level.

The first analyses carried out at Winfrith on the component in feritic steel revealed the presence of an oxide layer (150 to 350 um) made of 40 per cent haematite and 60 per cent magnetite. The presence of 10 per cent chromium oxide and 5 per cent nickel oxide is also noted in the surface oxide layer (5 to 10 um). The radiochemical activity of the oxide layer is due to cobalt-60 (420 KBq/m{2} and to manganese-54 (2 KBq/m{2}. The selction of reagents was nade at Cadarache floowing a series of tests carried out on test specimens from Winfrith in a liquid medium. The treatment which proved the most effective is applied at ambient temperature in 2 stages: a 2 hour degreasing process, and oxide etching process. In these conditions, the residual activity obtained varies from 0.5 to 1.5 Bq/cm{2}.

The results obtained on the Winfrith test samples allow the following remarks to be noted:
decontamination by foam loaded with chemical reagents requires a longer treatment period than by a liquid medium (8 instead of 4 to 5 hour); it is easier to embrittle the oxide in one step than to carry out the rinsing over several steps.

Studies on vessel with a capacity of 2.5 m{3} have been undertaken, with the aim of demonstrating the decontamination of test pieces, taken from the W infrith deaerator storage vessel, using rotating nozzles to spray foam.

Tests have been carried out at Winfrith, to investigate the destruction of the surface active agents and alcohols present using the WETOX process (catalytic oxidation using hydrogen peroxide) and the Ag II oxidation process. Initial results indicate that both processes will effectively destroy the organic components.
WORK PROGRAMME

1.Chemical foam formulation containing decontamination reagents (AEA and CEA)
2.Foam production and development of a circulation system (AEA and CEA)
3.Small pilot tests to qualify the decontamination method (CEA)
4.Secondary wastes treatment (AEA)
5.Design construction and operation of a prototype foam production and circulation rig; nonradioactive demonstration (AEA and CEA)
6.Industrial application by radioactive tests on a 25 m cubic contaminated vessel from Winfrith Steam Generating Heavy Water Reactor (AEA)

Aufforderung zur Vorschlagseinreichung

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Koordinator

Commissariat à l'Energie Atomique (CEA)
EU-Beitrag
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Adresse
Centre d'Études de Cadarache Sere-Ders
13113 SAINT-PAUL-LEZ-DURANCE
Frankreich

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