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Fire-Safety Neutron-Capture Materials

#2929


Improving Methods of Radioactive Waste Storage with Advanced Fire-Safety Neutron-Capture Materials on the Basis of Light Elements

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment
  • CHE-SYN/Basic and Synthetic Chemistry/Chemistry
  • MAT-COM/Composites/Materials

Status
3 Approved without Funding

Registration date
18.11.2003

Leading Institute
VNIITF, Russia, Chelyabinsk reg., Snezhinsk

Supporting institutes

  • Institute of General and Inorganic Chemistry (IONKh), Russia, Moscow

Collaborators

  • Camozzi, Italy, Brescia

Project summary

The main goal of the project is development of novel means of neutron protection. Primarily, it is planned to use the results of the project for improvement of technology of radioactive wastes storage. The goals and the main tasks determine the key feature of the project, namely its multi-task and complex character as well as wide range of possible applications. Basic tasks of the project are development of boron-containing materials with complex of needed properties, choosing materials with optimal parameters from developed “library”, after this optimization of technological processes of boron-containing compounds synthesis, and finally choice of the optimal way of utilizing these compounds as the neutron-protective materials, including determination of thickness (and other key parameters) of coatings and content of “working” components.

One of the key problems, which it is necessary to solve for positive achievement of project goals, is development of new streamlined production methods of synthesis of solid-state, resistant to atmospheric moisture, chemically and thermally stable materials with excellent neutron-protective properties.

The most promising precursors for these materials are compounds based on polyhedral anions BnHn2- (n = 10, 12). During the last 40 years numerous compounds, which cage consists solely of boron atoms or also include atoms of carbon, silicon, nitrogen, phosphorus, sulfur, transition metals etc., were an object of particular interest for theoreticians and experimentalists.

Peculiarity of compounds on a basis of boron-hydrogen fragments and their derivatives consists in a variety of versions of localization of atoms and their coordination; this peculiarity is closely connected with electron-deficient character of chemical bonds and high values of coordination numbers of atoms, comprising polyhedral cages, cluster character of bonding and high degree of electron delocalization in the cage. In the last years chemistry of BnHn2- cluster anions (n = 6-12) has been investigated very thoroughly. Numerous articles devoted to this theme evidence that this field of boron chemistry is quite complicated and should be judged as inpidual scientific discipline. Boron anions BnHn2- (n=6-12) as well as recently discovered fullerene molecules are among few examples of completely “non-metal” clusters. Theoretical studies of the electron structure of these compounds were conducted nearly simultaneously with the first experimental works and, in some cases, even earlier.

It was the quantum-chemical calculations made by Longe-Higgins and Roberts that demonstrate the possibility of cluster boron polyhedra existence in the form of doubly charged ions and becomes the basis for the experimental studies.

Stability of these compounds and their chemical properties are predefined by the presence of delocalized electrons and space-aromatic character of the chemical bonds. Aromatic nature of polyhedral boron anions governs their properties namely thermal and kinetic stability of boron cage, tendency for substitution reactions etc., which differ significantly from the properties of the most of hydrogen-boron compounds.

Combination of such important properties as well as a wide range of possible compositions makes these compounds promising precursors for neutron-protective materials.

Especial attention will be paid to development of adaptable to streamlined production methods of synthesis, as well as investigation of thermal stability, neutron-protective properties and other special properties (adhesion to the surface of vessels, density, chemical composition, linear expansion coefficient, ionizing radiation resistance) of three following groups of boron-containing compounds:

1. Salts of closo-deca- and closo-dodecaborate anions with alkaline and alkaline-earth metals cations; novel methods of synthesis of these compounds will be developed.

2. Coordination compounds of closo-deca- and closo-dodecaborate anions and their substituted derivatives with 3d- and 4f-elements. These compounds will be used as precursors for synthesis of materials with various radiation-protective properties.

3. Substituted derivatives of cluster BnHn-xYx2- cluster boron anions (where Y – functional groups capable of polymerization). These compounds are promising precursors for synthesis of materials with neutron-protective properties and boron-containing polymer composites possessing highly selective sorption ability towards ions of transition metals.

These three types of boron-containing compounds could be used as “working components” of neutron-protective materials in following versions.

Firstly, it is possible to develop thin films, which could be used as a basis for complex multi-layered protective constructions;

Secondly, project includes investigations for development of “thick” thermally stable neutron-protective coatings films.

These compounds could be also utilized in the powdered (fine-crystalline) form as filling neutron-protective materials for hollow constructions.

Besides this, some of the inert fillers could be used for manufacturing neutron-protective composite blocks.

The project includes following basic stages:

1. Synthesis of salts of closo-deca- and closo-dodecaborate anions with alkaline and alkaline-earth metal cations.


2. Synthesis of coordination compounds of closo-deca- and closo-dodecaborate anions and their substituted derivatives with 3d- and 4f-elements.
3. Synthesis and physico-chemical investigation of substituted derivatives of cluster BnHn-xYx2- boron anions (where Y – functional groups capable of polymerization).
4. Investigation of the possible ways of utilization of synthesized compounds as precursors for synthesis of materials with radiation-protective properties.
5. Development of new technologies allowing to form thick layers of synthesized materials.
6. Study of technological properties of developed materials.
7. Study of nuclear-physical, thermo-physical and thermo-mechanical properties of developed materials.
8. Manufacturing of pilot batch of novel non-flammable neutron-capturing materials.

The following results will be obtained as result of the project implementation.

1. Development of novel efficient non-flammable neutron-capturing materials including:

1.1. Salts of closo-deca- and closo-dodecaborate anions with alkaline and alkaline-earth metal cations.
1.2. Coordination compounds of closo-deca- and closo-dodecaborate anions and their substituted derivatives with 3d- and 4f-elements.
1.3. Substituted derivatives of cluster BnHn-xYx2- boron anions (where Y – functional groups capable of polymerization).


2. Development of new materials with increased working temperatures (up to 600 °C, 150-250 °C higher than the working temperatures of existing analogs).

3. Development of novel methods of boron-containing materials synthesis.

4. Development of new technologies allowing to form thick layers of new non-flammable neutron-capturing materials.

5. Preparation of database including information on physico-chemical properties of synthesized materials.

6. Development of technologies allowing placement of developed materials in the containers’ frame.


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