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Power Fast Reactor Radioactive Sodium

#2911


Development of Technology of Conversion to the Safe Condition of Non-Drained Residues of Sodium Radwaste in Fast Reactors

Tech Area / Field

  • FIR-DEC/Decommissioning/Fission Reactors

Status
8 Project completed

Registration date
29.10.2003

Completion date
22.11.2007

Senior Project Manager
Tocheny L V

Leading Institute
FEI (IPPE), Russia, Kaluga reg., Obninsk

Collaborators

  • CEA Commissariat a l'Energia Atomique, Cadarache, France, Saint-Paul-lez-Durance

Project summary

At the SSC RF IPPE, it was proposed to use N2O gas for neutralization of Na residues in the primary and secondary circuits (vessels, cold traps, piping, etc.) of NPP with fast reactors. Preliminary laboratory studies were carried out on N2O-Na interaction. Chemical process is characterized by the high activation energy causing reaction start at the temperature T > 200 °C and gas pressure 0.51 bar, 250-300 °С temperature range being optimum. It was shown by the experiments that using nitrous oxide for a long time, all nitrogen can be converted into sodium nitrate NaNO3, which is chemically neutral composite. The rate of sodium layer thickness decrease is within 1.5-2.5 mm/hour range. It was determined that no gas impermeable layer was formed on the interaction surface, since reaction caused permanent release of nitrogen, which loosened intermediate reaction products and assured access of fresh N2O portions to Na.

Feasibility of method of neutralization of alkali metal (AM) residues was demonstrated experimentally, when 2 kg of AM residues was treated in transport vessel, initial layer thickness being equal to about 40 mm. During 1.5 days of treatment by nitrous oxide, AM was almost completely converted into the mixture of AM salts and oxides.

Demonstration experiment was successfully performed on neutralization of AM residues in the spent hot oxide trap having complicated internal geometry with dead-end areas and narrow (1.0-1.5 mm) gaps.

The most significant advantages of this method are as follows


- no hydrogen release in the process;
- high solubility of reaction products in water without any undesirable effects;
- relatively high rate of sodium layer conversion (at least, 1.5 mm/hour) into the safe composites;
- possibility of AM treatment in the slots and complicated configuration structural elements.

Laboratory studies will be completed within the framework of existing ISTC # 1767 Project.

Work contents in the proposed ISTC Project

- Development of technological documents and construction of test facility with mockups simulating the following real structures:

- bottom sections of vessels: non-drained cavity volume is up to 10 L, layer thickness – 10 cm;
- complicated structural units of the cold traps;
- sodium valves;
- piping;
- bellows corrugations.


- Tests and experimental studies of technological features as applied to various conditions and designs.

- Development of recommendations on the modes of removal of AM residues for various designs.


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