RU2451704C1 - Polydimethylsiloxane based neutron shield composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to design of materials having neutron-absorbing properties, and can be used as a protective layer in making transportation and packaging structures for transportation and storage of spent nuclear fuel, as well as biological protection from other neutron radiation cases. The filling compound contains polydimethylsiloxane with terminal hydroxyl groups, low-molecular weight polydimethylsiloxane with terminal trimethylsilyl groups, a boron compound, ethyl silicate, an organotin curing agent.

EFFECT: obtaining a composition having high fluidity under normal conditions, which can be used as a protective layer for transportation and packaging structures and high thermal stability (prolonged operation at temperature of up to 22°C).

1 tbl

Description

The invention relates to the field of development of materials with neutron-absorbing properties, and can be used, for example, as a protective layer in the manufacture of transport packaging structures (TUK) for transportation or storage of spent nuclear fuel, as well as for biological protection against other cases of neutron radiation.

A known composition used for the manufacture of neutron-absorbing products, consisting of a polymer base - polyethylene with a molecular weight according to viscometric measurements of 2.5 · 10 ⁶ ÷ 1,0 · 10 ⁷ g / mol, and boron or

boron-containing compounds (boric acid, boron nitride, boron carbide or a mixture thereof). It is most preferable to use finely divided boron carbide, which prevents the separation of components during the mining process. The content of boron carbide in a mixture with polyethylene is 5-50% of the mass, most preferably 20-30% of the mass. The polyethylene used must not contain impurities. To increase its stability to light, heat and oxidation, a stabilizer is introduced into the composition in the amount of 0.1 ÷ 0.2% of the mass. As a stabilizer, for example, 4,4'-thio bis- (3-methyl-6-tert-butyl-1-phenol), dilauryl-thiopropionate, etc. can be used.

Neutron-absorbing material is obtained by homogeneous mixing of the starting components in an appropriate mixer, followed by heating the mixture at a temperature of 180-250 ° C under a pressure of 10-15 MPa and subsequent cooling also under a pressure of 3-5 MPa (US Pat. No. 5,221,646, C03C 4/08, prior . 06.22.93).

Due to the fact that such a composition is able to acquire fluidity, it can be technologically acceptable methods placed in the cavity of the TUK as a neutron-protective layer.

The disadvantage of the composition is its low heat resistance and relatively low thermo-oxidative stability, which does not allow its long-term use at temperatures of 150-200 ° C even in the presence of stabilizers proposed in the patent. According to well-known data, products based on polyethylene in contact with metal are not operable at temperatures above 70 ° C (Reference "Electrical Cables, Wires and Cords" Belorussov NI, Saakyan AE, Yakovleva AM, Energoatomizdat, 1988 g.), while the walls of the TUK are always made of metal.

The closest analogue is a neutron-absorbing composition consisting of a polymer base - polydimethylsiloxane with terminal hydroxyl groups, which has satisfactory thermal stability and can be used as a protective layer in TUKs.

The composition of the composition includes, in addition to the polymer base, a boron-containing compound, low molecular weight polydiethylsiloxane, ethyl silicate and an organotin hardening catalyst in the following ratio of ingredients, parts by weight:

Polymer one hundred Polydiethylsiloxane 8-12 Boron compound 4-30 Ethyl silicate 0.1-0.2 Catalyst 0.5-1.0

As the basis of the composition using dimethylsiloxane rubbers type SKTN (GOST 13635-73). As boron compounds can be used, for example, boric acid, boron nitride (TU 2036-1045-88).

As organotin curing catalysts, for example, dibutyltin caprylate, dibutyltin laurinate, tin octoate, etc. can be used. Tin octoate is most preferred; due to the lowest toxicity.

As low molecular weight polydiethylsiloxane, for example, PES-5 polydiethylsiloxane liquid is used (Pat. RF 2373587 C1 of 06/18/2008).

However, this composition has insufficient heat resistance. The term of its use at 200 ° C is limited to 25 days. It should also be noted that the process of obtaining the polydiethylsiloxane oligomer (PES-5) used in the composition is multistage in nature, which determines its high cost, which affects the cost of the composition as a whole. In addition, due to the relatively high viscosity of PES-5 (200-500 mm ² / s), such a composition can only be loaded into a TUK tank using a pump, which complicates the process of its use for the above purpose.

The objective of the proposed technical solution is to develop a casting composition based on polydimethylsiloxane for neutron protection, which can be used as a protective layer of TUK and has increased thermal stability and increased fluidity under normal conditions.

This object is achieved in that the composition for neutron protection based on polydimethylsiloxane with terminal hydroxyl groups, including a boron compound, ethyl silicate, an organotin curing catalyst and a low molecular weight polydialkylsiloxane, contains as the low molecular weight polydialkylsiloxane the following components:

end polydimethylsiloxane hydroxyl groups one hundred end polydimethylsiloxane trimethylsilyl groups 6-14 boron compound 3-30 ethyl silicate 0.1-0.2 catalyst 0.5-1.0

As boron compounds can be used, for example, boric acid, boron nitride (TU 2036-1045-88).

As the basis of the composition using polydimethylsiloxane, type SKTN (GOST 13835-73).

As organotin curing catalysts, for example, dibutyltin caprylate, dibutyltin laurinate, tin octoate, etc. can be used. Tin octoate is most preferred as the least toxic.

As a low molecular weight polydimethylsiloxane with trimethylsilyl terminal groups, for example, PMS-5, PMS-10 grade polydimethylsiloxane liquid is used.

The proposed composition is prepared as follows: In a device equipped with a stirrer, first dimethylsiloxane polymer and low molecular weight polydimethylsiloxane are mixed for 0.5-2.0 hours, then a boron-containing compound, ethyl silicate and an organotin catalyst are introduced. Further, the mixture is homogenized in a rotary pulsation apparatus (RPA) and, after passing twice through the RPA by gravity, is fed into the protective cavity of the TUK.

Examples illustrating the proposed technical solution with a description of the composition and properties of the composition for ease of consideration are summarized in table.

The composition and properties of the proposed compositions according to examples 1-7 Composition No. of examples one 2 3 four 5 6 7 Structure, % SKTN, MM = 100000 one hundred one hundred SKTN, MM = 90000 one hundred one hundred one hundred one hundred SKTN, MM = 70,000 one hundred PMS-5 6 fourteen 8 10 6 6 PMS-10 8 boron nitride 3 thirty 6 3 5 3 boric acid 5 ethyl silicate 0.2 0.2 0.2 0.2 0.1 0.2 0.2 tin octoate 1,0 1,0 1,0 0.8 0.5 1,0 dibutyltin caprylate 1,0 Property Vitality, hour 16 eleven 8 16 eighteen 12 16 Dynamic viscosity, m · Pa · 10 ⁴ 1.8 1.4 1,2 1.8 1,5 1,6 2.0

The possibility of long-term use of the composition when exposed to temperatures up to 220 ° C is determined by the method of predicting changes in properties during thermal aging in accordance with GOST 9.713-86. Since, during operation, the composition in the cured state is inside the sealed TUK shell, which may be accompanied by destructive changes in the polymer, the change in time of the conditional hardness at temperatures of 180, 200, and 220 ° C is chosen as a characteristic indicator of aging.

The obtained test results for a long exposure (40 days) of the vulcanizate samples showed that the hardness of the samples practically did not change, which in turn allowed extrapolating the performance of the composition to 50 years at a temperature of 200-220 ° C.

When the above compositions are irradiated with a neutron flux up to a fluence of 4 · 10 ¹⁴ neutrons / cm ² and gamma radiation up to an absorbed dose of 1 MGy, the material retains its properties unchanged.

Thus, the proposed composition has good fluidity under normal conditions and can easily be poured into the cavity of the TUK. The composition has good thermal stability, is operable for a long time at temperatures up to 220 ° C and can be used as a protective layer in TUKs from neutron radiation.

Claims (1)

A hydroxyl-terminated polydimethylsiloxane-based neutron-shielding filling composition comprising a boron compound, ethyl silicate, an organotin curing catalyst, and a low molecular weight trimethylsilyl-terminated polydimethylsiloxane in the following ratio of parts by weight:
end polydimethylsiloxane hydroxyl groups one hundred end polydimethylsiloxane trimethylsilyl groups 6-14 boron compound 3-30 ethyl silicate 0.1-0.2 catalyst 0.5-1.0