FR2527376A1 - PROCESS FOR IMPROVING THE PROPERTIES OF RADIOACTIVE SOLID WASTE INCORPORATED IN A MATRIX AND SOLIDIFIED - Google Patents

Abstract

A. THE PROCESS IS INTENDED TO IMPROVE THE PROPERTIES, NECESSARY FOR LONG-TERM STORAGE, OF RADIOACTIVE WASTE SOLIDIFIED BY INCORPORATION IN A MATERIAL TAKING UP BY ADDITION OF WATER. B. A MATERIAL CONSTITUTED OF A SODIUM AND POLYMERIC ALUMINUM SILICATE IS USED AS THE MATERIAL FOR THE MATRIX, THE VOLUME OF WATER NECESSARY FOR THE TAKING INCORPORATED IN THIS MATRIX BEING 10 TO 20 BY VOLUME. C. THIS KIND OF MATRIX INCREASES THE RESISTANCE OF THE BLOCKS AGAINST CORROSION, AND AGAINST CONCENTRATED ACIDS AND CONCENTRATED SALINE SOLUTIONS.

Description

Process for improving the properties of solid waste

  radioactive material incorporated in a matrix and

".

  the invention relates to a process for improving the properties necessary for the long-term storage of solidified radioactive waste, which are incorporated in

  a matrix material hardening by the addition of water.

  Radioactive waste means: solid waste, in pieces such as for example

  sheaths of fuel elements or

  key, etc., solid waste sludge in fine particles, such as cleaning sludge from reprocessing

  nuclear fuel and / or iron

irradiated tiles,

  ash containing c-ray sources, and

  very residues of combustion, etc. To solidify this solid waste, in pieces or also granules, it has often been used until now cement-water suspensions The disadvantage of bulk products of cement and waste thus obtained is that because of the relatively high content of water, it is formed under the effect of radioactive radiation emitted by waste, -by the radiochemical decomposition of water, high amounts of hydrogen and oxygen It can

  resulting in disadvantages to the safety of

  If high temperatures prevail in the final storage, water is released from the product, causing considerable pressure to be created within the plant. In the case of barrel corrosion, it may be possible, if the drum corrodes, to release radioactivity in the environment. It has further been found that the products solidified with cement,

  16 obtained until now, lose, after

  lined with salt solutions, their properties are sufficient

  previously well, such as resistance

with pressure.

  The object of the invention is to improve the

  properties necessary for long-term storage of solidification blocks containing solid radioactive waste such as pieces of

  sheath of combustible elements, other metallic wastes

  radioactive sources, ashes containing radiation sources ", and other

  cleaning sludge from the reprocessing of

  irradiated materials and / or nuclear fuels, incorporated in a matrix made with water, and to propose a method for achieving this objective. In particular, solidified blocks should be

  present in comparison with those prepared according to the previous

  of the technique, high resistance to radia-

  and reduced formation of radiolysis gas, an increase in corrosion resistance, even towards concentrated acids and concentrated salt solutions,

  for example with regard to quinary solutions (ie

  say an aqueous solution with a composition in% by weight of: 24.7% Mg C 12; 2.3% Mg 504; 1.9% of

  NaCl; 3.3% KC 1; 67.9% of H 20), and good resistance

thermal shock.

-27,376

  For this purpose, the invention proposes a process characterized

  in that, as a material for the matrix, it is

  a substantially heat-shrinkable, acid-proof, amorphous, non-hydrate-phase, amorphous material consisting of sodium silicate and polymeric aluminum, and

  solid waste is either put in contact with a suspension

  of the material to form the matrix, containing

  10 and 20% by volume of water, either incorporated under stirring

  in a suspension of this type prepared in advance,

  and then allowing the waste / matrix mixture to cure.

  The materials usable for the matrix according to

  the invention are known in the field of

  fund for natural gas and oil, under which

  "Hydrothermal Cements". A Mallow, J K Dean Transactions of the ASME Journal of Pressure Vessel Technology, Paper No. 77 / Pet-27, pp. 1-5 (1977).

  Materials are marketed by different manufacturers.

  Despite the name of hydrothermal cements, these materials have nothing to do with cements used in construction, and this partly because of their

  on the other hand because of their composition.

  They consist mainly of sand Si O 2,

  SiO 2 powder, sodium silicate and AI (OH) 3.

  sorption of water during hardening amounts to the maximum

to 20% by volume.

  An advantageous embodiment of the invention is characterized in that the waste / matrix mixture is

  after curing, to remove non-water

  heat treatment at a temperature

  between room temperature and 100% C.

  Although the process according to the invention makes it possible to produce solidified blocks of waste presenting the

  required properties, the preparation of these blocks is

  kills in a simple way with a minimum of expense for

a process of this kind.

  The invention will be better understood from the examples

ples below:

Example 1

  Compressive Strength Testing of Inactive Hydrothermal Cement Products from Swindell Rust Company, USA (The Rust Engineering Company):

  A characteristic composition of hydrogen cement

  This type of thermal energy is, for example: (data in% by weight) Quartz sand 37.5 Quartz powder 18.8 Na silicate, anhydrous 7.5 Na silicate, aqueous 7.5

A 1 (OH) 3

H 20 13.7

  a) product prepared with water from the distribution network

tion,

  (shake or mix vigorously the cement hydrother-

  with H 20 in the appropriate proportion at room temperature, and cure for 24 hours): Proportion Porosity Water / Solid Resistance (%) Compression (N / mm 2)

0.15 19.3 25.0

0.13 15.1 32.3

0.10 14.7 35.0

  (b) product containing simulated MAW (= inactive salt solution, the composition of which is essentially that of a medium-release wastewater):

0, 15 14, 2 15.05

0.15 14.2 15.0

0.13 14.2 15.0

0.1 16.1 22.5

0.1 X) 7.1 32.3

  x) compacted, pouring with stirring the mixture not

still hardened, in a drum.

  The pressure resistance of these products is

  the order of magnitude of that of the solidified prepa-

according to the state of the art.

Example 2

  Comparison of the corrosion resistance of an inactive product according to the invention and of inactive products

  prepared according to the state of the art.

  a) hydrothermal cement products (described in Example 1) prepared with a water / solid ratio of the order of 0.10 to 0.15 (pressure resistance N / mm 2) were stored under various conditions under

  corrosive medium, in order to test the corrosion resistance

if we.

  The storage was carried out: in dilute solution of HC 1 (1: 10) at room temperature; in quinary saline solution at 90 ° C, under 1 bar; in saline solution

 C, under 100 bars.

  To determine the corrosion resistance, weight loss and modulus of elasticity were determined

dynamic test pieces.

  Results: In HC 1 solution storage, there was no change even after 12 months; In storage in quinary salt solution at 90 C and under 1 bar, there was no modification even after 12 months In quinary solution storage at? 000 C under 100 bar,

  there was no change after 4 months.

  The specimens retained their dimensional stability

  no bursting or cracking, the test specimens were not swollen, their weight was

remained constant.

Example:

  Starting weight 64.3 g Dynamic modulus of elasticity 19.9 after 228 days 64, lg (N / mm 2) 19.9 after 331 days 64.3 g 20.3 The modulus of elasticity (modulus E> dynamic , which can be an indicator of mechanical strength

  specimens, did not change either.

  (b) By way of comparison, the test-pieces of cement Port-

  land (PZ 35) (water / cement = 0.45) corresponding to

  state of the art, led to the following results:

  (under the same storage conditions as under 'a'):

  In storage in HC 1 (1 in 10 solution) at room temperature

  the test tubes were completely decompo-

  in 1 to 2 days; In quenched solution storage at 90% C at 1 bar, the test pieces showed, after 2 months, obvious signs of corrosion (cracks, swelling, weight gain, decrease in the dynamic E-module) and after 3 months, they were destroyed; In storage in quinary solution at 2000 C at 100 bar, the scrapers were completely decomposed after

7 days.

  These results show that the process according to the invention

  tion provides products with resistance

  significantly improved corrosion.

Example 3

  Search for the release of radiolysis gas.

  A hydrothermal cement product (as described in Example 1) prepared with a water / solid ratio of the order of 0.1 to 0.15 was subjected after curing (1 week) to 55 C (2 days) and

 C (1 day).

  The H 2 content was reduced here to 1% by weight, the pressure resistance remained unchanged

35 N / mm 2.

  The product was then irradiated with 10 Me V electrons at a P / I dose of 108 rad, and the amount produced of radiolysis gas (essentially H 2) was measured. - A value of 1.5 to 4 ml of H 2 / g Mrad was obtained, which is a factor of 10 less than that

  an untreated irradiated test piece.

Example 4

  Comparative tests of thermal shock resistance.

  A hydrothermal cement product (as described in Example 1), prepared with a water / material ratio

  solid, of the order of 0.1 to 0.15, was

  curing (1 week) at a temperature of 500 C, then

suddenly cooled in water.

  As a result of this treatment, the test pieces remained intact, no macro-cracking appeared,

  and the mechanical strength was not diminished.

  When submitting concrete specimens from Port-

  In a treatment of this kind, the test specimens

  macro-cracks and decompose.

Example 5

  Solidification of sheaths of inactive fuel elements

with hydrothermal cement.

  In a mixture prepared according to Example 1 from "Swindress Bond 100", a Hydrothermic L hydrolithic from the Swindell Rust Company, USA, and water, with a ratio of

  water / solids in the range of 0.1 to 0.15, it was

  stirring slightly, pieces of sheaths of

  combustible materials (diameter 1 cm, length 5 cm).

  After curing, a product was obtained which completely filled the voids and interstices between the sheath pieces. The weight proportion of the sheath pieces in the final product was 25% by weight. After curing at room temperature (1 week), it was possible to lower the H 2 content of the product to

  1% by weight, by drying at 50-900 C (1 to 2 days).

  The reduction in the content of H 20 necessarily reduces the possibility of emission of the radiolysis gases of solidified radioactive waste in comparison with the quantity

  formed with the products according to the state of the art.

  Water needed for solidification with cement

  Hydrothermal is only used to mobilize

  reactants, or for the reaction, that is to say

  for the formation of polymeric Na-Al silicates, which can

  may also contain multiple valence cations,

  and does not take part in the development of the structure.

  On the contrary, when solidified with the usual cements

  In addition, water (for example, Portland cement, etc.) is used for the hydration of the compounds formed during curing. The residual H 2 content after thorough drying (2 to 3 days at a

  at 2500 C) is assembled, with cement blocks hydrother-

  (water / cement = 0.13) at 0.2% by weight, and with Portland cement blocks (PZ 35) (water / cement = 0.4) at

  -8.7% by weight, that is to say more than 40 times more.

  An important advantage of the invention is that the solidification of the radioactive waste with hydrothermal cement leads to a better adhesion of the cured mass to the metal and concrete surfaces, than if using construction cement, which takes Moreover, the products containing waste, obtained according to the invention, are also less subject, in their container (for example drums) in the event of leakage (for example in case of local corrosion). ) to a leaching medium than the usual products containing waste, in

their own containers.

  The water / solid mixtures according to the invention can have their composition modified so that high temperatures (from, for example, the heat of decomposition of the radionuclide waste)

  not a negative influence on the hardening

is lying.

Example 6

  Fixing of dissolution residues (cleaning sludge)

  reprocessing of irradiated nuclear fuels.

  In a mixture produced according to Example 1, from

  of "Swindress Bond 100" and water, with a water-to-water

  solid material of 0.1 to 0.15, a simulated dissolution residue (composition: see Table 1) is incorporated in

  proportion such as the proportion of residue of dissolu-

  The final product is 1 to 5% by weight.

  After curing at room temperature (1 week)

  it was possible to determine a compressive strength of

  Viron 20 N / mm By drying at 901 C (1 day), the water content in the final product was lowered to 1% by weight, and the

  pressure resistance remained unchanged.

  Table 1 To Composition of Dissolved Dissolving Residue: Ruthenium Compound Ruthenium Dioxide Pd (Pd + Rh) Mo O 3

M 4 OO 3

  11 n O 2 Sb 203 Ce 203 Chips of Zr Steel chips 1 4541 Steel chips 1 4568 Inconel chips 718 g / 1000 g

Claims (1)

R E V E N D I C A T IO N S   ) A method of improving the properties, necessary   for long-term storage, radioactive waste   solidified actives which are incorporated in a water-hardening matrix material, which process is   in that, as a material for the matrix, it is   reads a material with little or no   heat and acid resistant, amorphous vis-   of the hydrate-free phase, consisting of sodium silicate and polymeric aluminum, and that solid waste is either brought into contact with   suspension of the material to form the matrix, containing   10 to 20% by volume of water, either incorporated with stirring in a suspension of this type prepared in advance, and then allowed to cure the waste / matrix mixture. 2) Process according to claim 1, characterized in that the waste / matrix mixture is subjected after curing, to remove uncombined water, to a heat treatment at a temperature between room temperature and 1000 C.