FI118444B - Oxide material trapped in the melted core of a nuclear reactor - Google Patents

Description

118444

OXIDE MATERIAL TO TREATED NUCLEAR REACTOR

FIELD OF THE INVENTION

The invention relates to the nuclear industry, in particular so-called sacrificial materials, i.e. materials for the trapped fusion reactor core, intended to localize the fused nucleus in sealed water-cooled nuclear reactors, in the event of an on-10 incident. In the event of such an accident, this material, interacting with the high-temperature melted core of the nuclear reactor, binds (lyxes) the molten trap and cools it, providing subcritical conditions and thus preventing the formation of a self-sustaining chain reaction, i.e., nuclear reactor. In doing so, the sacrificial material itself is gradually decomposed due to complex physico-chemical processes and ceases to be in its original form.

DESCRIPTION OF PRIOR ART

* m m • * · ***. The importance of developing sacrificial materials for devices used to localize the fused nuclear Φ · · 25 generated by a nuclear accident became evident in the large-scale accident at the Fourth Reactor at the Ternobyl Nuclear Power Plant, and the Nuclear Power Plant at Nuclear Power Station, . · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·. creating, in many respects, reliable systems for localizing the fused core of a nuclear reactor, and creating efficient sacrificial materials for nuclear reactors.

35 There is little research and development on sacrificial materials that are essentially new types of materials, and because direct large-scale tests are not feasible, they are based on system design methods using theoretical calculations and model tests.

It is known that the fused core 5 of a nuclear reactor consists of two phases: metallic (lighter) and oxide (heavier). To effectively lower the temperature of the molten overheated metal component, it is possible to use steel or iron as a refrigerant, which, however, cannot affect the oxy-10 portion of the molten, where most of the radioactive components are located and where a nuclear chain reaction can occur. Further, such an agent does not cause combustion and explosion of zirconium dissolved in the molten oxide moiety and partially migrated to its metallic moiety, which can cause the hydrogen formed as a result of the interaction of unoxidized zirconium and water vapor.

Ke-20 incorporation of gaseous substances formed when zirconium is oxidized with silicon or aluminum oxides results in a sharp increase in the release of radionuclides in the form of aerosols which pass through the containment (i.e., the space where the nuclear reactor is located and closed). t '*: occurring in a nuclear power plant) and penetrates gaps in the surrounding shell of the said space, causing radioactive contamination of the environment.

• · ·

Radionuclides are radioactive isotopes of various chemical elements, which occur in a molten nucleus and are produced by the radioactive decay of the nuclei of radioactive elements. The degree of environmental contamination caused by the radioactive isotope depends ***. which passes from the molten to the gas phase which, in turn, ···. depends on its amount (concentration) in the melt and its evaporation • · * · * 35. The higher the concentration and volatility of the radioactive isotope, the greater the amount of * · ** · that leaves the molten and finds its way around the work. The detrimental effect of radioactive contamination of the environment by the action of a particular isotope, i.e. the danger it poses to living nature, and in particular to man, depends to a large extent on its half-life and its ability to accumulate in the human body, particularly bone marrow and lungs. The longer the half-life of an isotope, the longer it is harmful to the environment. The more isotope is removed from the body, the longer it has a deleterious effect that can cause many diseases, especially cancer.

An oxide material for the trap of a nuclear reactor molten core containing silica or alumina as a cooling and oxidizing agent is known (see RU2165106, See G21C 9/016, 12/10, 10.04.2001). These oxides are mixed with uranium dioxide, which is present in large quantities in the molten and lowers its concentration, thereby reducing the possibility of a nuclear reaction in the molten state, which enters an over-20 critical state; also, due to their relatively high heat capacity, they facilitate the cooling and localization of the molten trap.

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In addition, when such a material is used, oxidation of the zirconium occurs by means of silicon and aluminum oxides. This oxidation occurs, however,: ***: only at high temperature, i.e., for a short time · «*.:. until the temperature of the molten has fallen as a result of contact with the sacrificial material. For example, oxidation of zirconium by alumina occurs only at temperatures above 2300 ° C. When ··· *** j is lowered, some fused zirconium remains in the molten core to release hydrogen: as a result of the interaction of zirconium and water vapor, · ** · ***. as mentioned above.

• · • · »*. 35 In order to achieve a more efficient oxidation of zirconium, oxide material has been proposed to trap the fused core of the nuclear reactor (see Markus Nie. Ap-118444 4 plication of Sacrificial Concrete for Retention and Conditioning of Molten Corium in EPR Core Melt Retention Concept. OECD Workshop is Ex-Vessel Debris Coolability Karlsruhe, Germany, 15-18 November 5, 1999) using a mixture of iron oxide, silica and alumina as well as boron, calcium, magnesium and chromium oxides, as a cooling and oxidizing agent . The iron oxide content of such material is about 22-45%, the silica content 10 is about 25% and the alumina content is about 2%.

Although the use of iron oxide improves the oxidation of the zirconium because it occurs at lower temperatures than the oxidation of the zirconium by alumina, the presence of iron oxide in the known sacrificial materials in the above amounts does not result in complete oxidation of the zirconium The use of silica also promotes the formation of gaseous products due to its interaction with zirconium during which gaseous silicon oxide is formed. As a result, the emission of radionuclides increases.

The main object of the present invention is to create a * oxide material in the nucleation site of a molten core reactor which can reduce the emission of radionuclides from the melt, in its localization. radionuclides contaminate the environment badly and • · · ·. ···. are very harmful to living nature and especially to humans, and thus reduce both pollution levels. 30 and its harmful after-effects.

· * ·· ···

SUMMARY OF THE INVENTION

:; *; In view of the above-mentioned main objective, · * ·. ···, an oxide material is proposed for the trap of a melted nuclear reactor • · "* 35 nucleus containing a cooling and oxidizing agent to cool the melted nucleus and oxidize its more active components. 118444 5, which material, according to the invention, further comprises a target excipient consisting of at least one oxide selected from the group consisting of SrO, CeO2, BaO, Y2O3 and La2O3.

5 The introduction of such a target adjuvant allows, due to the dilution of radioactive isotope oxides present in the molten, by stable isotope oxides of the same elements, and by the deviation of in more detail, are among the most damaging to the environment and to living nature, especially humans.

As noted by the present inventors, the partial pressure of the vapors of Sr, Ce, Ba, La, and Y oxides, unlike known Henry's law, depends on the non-linearity of the concentration of the corresponding oxides in the liquid phase (molten). This non-linearity dependency represents a graph of a rapidly decreasing derivative of the oxide concentration in the gas phase relative to the concentration of the same oxide in the liquid phase. "**! As a result, dilution of radioactive isotope oxides in the liquid phase by the introduction of anti-*** stable agents (natural non-radioactive)

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isotope oxides in the sacrificial material, substantially decreases the concentration of radioactive isotopes in the gas phase.

. The concentration of said target excipient may be up to 15% by weight, preferably 2-5% by weight, more preferably 3-15% by weight.

*: Coolant and • · ·. *** for core trap oxide material. the oxidizing agent preferably contains Fe 2 O 3 and / or 35 Fe 3 O 4 and Al 2 O 3, wherein the concentration of Fe 2 O 3 and / or Fe 3 O 4 is between 46 and 80% by weight, the concentration is between 16 and 50% by weight.

118444 6

The inventors have found that the use of such a cooling and oxidizing agent, due to the high content of iron oxides, results in more complete oxidation of the zirconium in the molten, reducing the formation of hydrogen. Further, iron oxide does not form gaseous products when it interacts with zirconium which reduces the release of radionuclides.

Due to the good mixing of iron and alumina with uranium in the molten state, the density of the molten oxide moiety is substantially reduced to cause inversion, i.e., the rise of the oxide moiety on the surface of the metallic component. It also prevents the formation of hydrogen caused by contact of water or water vapor with metals present in the metallic component but absent from the molten oxide moiety.

Iron and aluminum oxides form solid solutions during the interaction. Alumina, which in its free state oxidizes zirconium to form gaseous Al 2 O, in solution with iron oxide does not react with zirconium and thus forms gaseous products, which also reduces the release of radionuclides.

The proposed oxide sacrifice material may further contain: SiO 2 in an amount up to 4% by weight, preferably · · · ·; *** · 1-4% by weight.

· · ·

Because high iron oxide content results in virtually complete oxidation of the zirconium, · · *** does not, when used in small amounts, react with zirconium and form gaseous products. you (silica). At the same time, adding even small amounts of silica produces a result of 40-. 50% increase in the durability of sacrificial material due to · · · · · · · · · · · · · · · · · · · · · · · · ·

• · 118444 7

BRIEF DESCRIPTION OF THE IMAGES

The figure below is an experimental curve showing the strontium oxide concentration (partial pressure) in the Psro (r > gaseous phase) plotted against the strontium oxide concentration in Csro = n after interaction with the sacrificial material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The sintered oxide sacrifice material proposed in accordance with the invention was obtained by a double calcination process which provides stable dimensions of the sheets formed. Initially, the starting components were prepared for subsequent mixing in the required ratios. Thereafter, the components were blended and dry vibratory grinding of the target material (Gd203, Eu203 and / or Sm203) representing the cooling and oxidizing agent, and separately, was performed to obtain powders having particle sizes did not exceed 63 μτη. When the particle size of 63 μπΐ: η was reached, the milling was stopped. The target excipient oxide powders were mixed with a portion of the stock material in a ratio of 1 2V to 1/10 to 1/5 (25 control excipients were not used in the control example). The resulting mixture was homogenized and this; after that was introduced for the remaining basic material. After mixing was repeated, • 1 · ·. ···. a homogeneous distribution of the fine powder of the target excipient was obtained in a powder containing the base material, 30 components. The plates were then pressed using 5% aqueous polyvinyl alcohol to remove

'·· .1 mail as burning fence and burned at 1280-1300 ° C

at 2 hours. The plates are then crushed

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3. ···. were cured, ground, sorted into fractions, mixed with • 1 "13 35 temporary adjuvant (5% v / v aqueous solution of polyvinyl alcohol) and pressed. The remainder were burned in air at 1320 ° C 6 for an hour.

During use, the proposed oxide sacrifice material is trapped, e.g., located underneath the nuclear reactor, preferably together with the metal sacrifice material. In the unlikely event of an accident and melting through the reactor wall, the molten core at about 2700 ° C flows down into the trap and interacts with the sacrificial material. In such a case, the sacrificial material is thawed and agitated with the molten core, first, to cool the molten to about 2000 ° C to avoid melting of the trap wall and thereby localize the molten, and second, to dilute the uranium dioxide present in the molten, . In addition, the sacrificial material oxidizes the zirconium in the molten core, reducing the amount of hydrogen released as a result of the interaction between the zirconium and the water.

When the molten core is cooled, the radionuclides, i.e. the radioactive isotopes of the various chemical elements, are released from the melt, which radiates into the outside of the containment, contaminating the environment.

• · '· 25 Radioactive isoforms released from the melt

. ***. among the tops are 90Sr, 144Ce, 140Ba, 140La and 90Y

most harmful. All of these isotopes are * 1 ”related to those that accumulate at relatively high levels in the nuclear reactor fuel during its operation. In addition, 90Sr, which has a very long half-life (28.6 years), remains long-lived in the environment, ··· · ... · has high volatility and can accumulate in bone. . ·. to the core and lungs in large quantities. 144Ce retains ···, ·· ». also in the environment over a long period (with a half-life of • m *** 35 284.9 days) and demonstrates the greatest potential for accumulation in the lungs. 140Ba is one of the most volatile isotopes remaining in the environment for several days over a period of 1,1844,49 (with a half-life of 12.75 days); it can accumulate in the bone marrow and lungs. 140La can accumulate to a very large extent in the bone marrow and especially in the lungs. 90Y can accumulate to lung-5 up to 140La.

As shown in Fig. 1, the partial pressure of the strontium gas depends essentially nonlinearly on its concentration in the molten liquid, namely, the rate of growth of the partial pressure drops rapidly as the concentration increases. The curves showing the partial pressure dependence of the Ce, Ba, La and Y oxides on their concentrations in the melt have a similar appearance. From the curves, it can be seen that said non-linear dependency provides the possibility of lowering the concentration of radioactive isotope oxides of the aforementioned metals in the gas phase by adding the same oxides but containing non-radioactive isotopes. For oxides of non-radioactive isotopes added, if the total concentration of the given metal oxide in the salt increases, the partial pressure of this oxide sometimes increases to a lesser extent, thereby providing a lower partial pressure of the radioactive isotope oxide. For example, if the radioactive strontium oxide has a concentration of 0.2% by weight, its partial pressure is about 0.3 X 10'4 atm.

I. ·. 25 Adding 2% non-radioactive strontium oxy- • * * • · · ·, ···. dia, the partial pressure of the strontium oxide (radioactive and • radioactive), due to deviation from Henry's law, will be "" 0.9 x 10'4 atm, i.e. not 11 but only 3 times higher. Since radioactive strontium oxide represents 9% of its total amount, the partial pressure of radioactive strontium oxide will be 9% · * · of the total strontium oxide pressure, i.e. 0.08 χ 10χ4. ·, Atm, or almost 4 times lower than the starting value. Mi- • · · .m, Potassium added with 15% strontium oxide to the starting melt will * · * "35 have a total strontium oxide pressure of 1.9 · 10 · 4 * · ** · atm, while the radioactive strontium correspondingly to be 0.025 x 10'4 atm, i.e.

12 times lower than starting pressure.

The introduction of stable isotopes in the form of oxides, together with the oxide sacrifice material, into the molten core can often reduce the concentration of the respective radioactive isotopes in the gas phase. In such a case, SrO is selective for 90Sr, CeO2 is selectively for 144Ce, BaO is selectively for 140Ba, La2O3 is selectively for 140La, and Y203 is selectively for 90Y. The present inventors have found that the introduction of SrO, CeO 2, BaO, Y 2 O 3, La 2 O 3 in amounts up to 15% by weight in sacrificial material-15 provides the potential to reduce 90Sr, 144Ce, 140Ba: n, 90Y and 140La to such an extent that their risk is commensurate with that of less dangerous isotopes.

The upper limit of the target excipient is preferably 15% by weight to 20% by weight. When the concentration of the target excipient is greater than 15% by weight, the efficiency of the leaching of the nuclear reactor molten core begins to decrease. It is preferred that the concentration of each of these oxides (or a combination thereof) is less than 2% by weight, more preferably less than 3% by weight. 25 so that the impact of their introduction would not be too great. weak, because for the lower concentration of said oxides, the dependence of the gas phase partial pressure on their concentration in the molten approximates the theoretical curve (i.e. becomes linear) of Henry's law.

30 When the molten material reaches the sacrificial material, ·· * ···· causes the sacrificial material to melt and the molten to cool.

* · .. * When using a preferred material composition wherein ϊ; * · the cooling and oxidizing agent contains 46 to 80% by weight M · · ***. Fe 2 O 3 and / or Fe 3 O 4 and 16 to 50% by weight Al 2 O 3,

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*, 35 undergoes a high-power exothermic reaction with heat generation at the forefront of the interaction of molten and relatively large amounts of iron oxide 118444 11 contained in such oxide sacrificial material, due to the intense oxidation of the zirconium, leaving the molten with liquid for some time effective dilution with this material. The high activity of said interaction results in rapid formation of sacrificial material components and molten core and faster cooling of the molten due to vigorous heat removal through the trap walls from the liquid in the trap. Said release of heat at the boundary between the sacrificial material and the molten core prevents melt crystallization at said boundary and, as a result, the conversion of the sacrificial material to the molten core from a high speed liquid phase reaction to a slow speed solid phase reaction. This, in turn, prevents the formation of a solid shell of unreacted sacrificial material near the trap wall and, as a result, reduces heat dissipation through said walls, which reduction slows down cooling.

The intense oxidation of the zirconium prevents its interaction with water vapor in the containment and with water provided to cool the molten, and thus hydrogen formation and accumulation, which can lead to combustion and explosion.

Due to the good dilution of uranium oxide · »· in the molten aluminum and iron oxides, the molten ·· *. • lighter than the oxide moiety and rising to the surface above the · · metal part of the molten, i.e. inverting the molten one. 30 siots. The downward movement of the metal components prevents the formation of hydrogen, which is caused by a metal component such as chromium,; oxidation of iron and nickel with water vapor.

* · · These metals do not oxidize with the oxides of the sacrificial material · ♦ •, 35 until all zirconium is oxidized. Because zirconium is highly soluble in the oxide moiety of the molten, it * * continues to oxidize even after inversion of the molten.

12 1 18444 In this case, despite the high content of alumina in the sacrificial material, the zirconium molten does not react with the alumina to form gaseous products that facilitate the release of radionuclides. This is due to the fact that iron and aluminum oxides together form compounds (solid solutions). Aluminum oxide in such a solid solution, when melted, does not oxidize the zirconium in the molten, thus preventing the formation of caustic products.

Preferably, the proposed oxide sacrificial material has a composition in which iron and aluminum contents are balanced to achieve complete oxidation of the zirconium in the molten core to prevent the formation of hydrogen whose accumulation can lead to its combustion and explosion, and formation of volatile substances and thus release of harmful radionuclides into the environment.

20 If the Fe203 and / or Fe304 content in the material is less than 46% by weight, complete oxidation of the zirconium due to lack of oxygen, which can lead to hydrogen and other dangerous gaseous and volatile substances, is not achieved. formation of products and thus • * · .: j 25 increases the release of radionuclides. If Fe 2 O 3 and / or

The Fe3C> 4 content exceeds 80% by weight, the total ·· «interaction becomes exothermic and occurs remarkably. **. • · «* release of gaseous and volatile products, and thus radionuclides.

3 0 If the Ai203 content is less than 16% by weight, "I * the non-exothermic reaction will not be a hazard of the oxidative effect of the trap's heating of the trap and the resulting exothermic effect will result in self-warming of the melt melting device. · · · 35 Al20Oittää content greater than 50% by weight, no oxidation of zirconium due to the absence of Fe20O3 and / or Fe3O>, elevated melt liquefaction temperature and formation of 118444 13 hydrogen in non-oxidized zirconium and water vapor. resulting in substantially increased likelihood of hydrogen combustion and explosion.

Addition of small amounts of SiO 2 to the proposed material, as indicated above, substantially increases its durability without causing deposition of the system including the trapped oxide material and the molten core of the reactor.

If the SiO 2 content exceeds 4% by weight, gas evolution increases and the likelihood of melt deposition increases due to the smelting process, with the result that radionuclide release is also increased. If the SiO 2 content is less than 1% by weight, no significant increase in the durability of the sacrificial material is achieved.

The ability of the proposed material to provide efficient localization of the fused core of the nuclear reactor was evaluated by model tests and thermodynamic calculations.

The following values were determined for experimental equipment designed to perform high-frequency induction melting techniques in a cold crucible, in particular during the model experiments, specifically * ':: · · 25: the rate of interaction of the proposed material with the core. ··· with the molten core of the actor, the beginning of the interaction »II ·; · **. temperature and temperature of the liquefaction mixture containing • · · and the sacrificial material. A sample of the proposed sacrificial substance 30 was placed in the bottom of a cold crucible. Screening of the unit from the inductor was done by means of a water-cooled screen. Door, ί, · .: with openings for mounting the pyrometer cavity, measuring the rinsing depth, and monitoring the molten surface. 35, was placed in a sealed quartz oven oven | above the cold crucible. Prior to this, the melted core was prepared from non-irradiated reactor fuel 118444 14 by inductive melting in a cold crucible, which resulted in the molten being brought into contact with the sacrificial material body by moving it into the contact zone with the molten material. The molten crucible was placed on a desk provided with means for moving the crucible in a vertical relationship with the inductor and display. The rate of transition of the interaction edge was determined at the time points in which the melt touched the hot 10 ends of the thermocouples placed in the sacrificial material. The partial pressure of the isotopes was determined by high temperature mass spectrometry of the gas phase above the respective feathers.

The evolution of gas was experimentally and theoretically determined as the amount of gaseous products (gases and vapors) above the system consisting of the components of the core molten and sacrificial material at the temperature of molten rinsing using a verified program and the IVTANTHERMO database containing thermodynamic properties.

The thermal effect was calculated as the difference between the system heat contents, i.e. the amount of heat released during cooling of the molten sacrificial material, taking into account all reactions in the system, by thermodynamic calculations using J? 25 of the same program and the IVTANTHERMO database.

; ***; The following table shows an example ···.:. and sacrificial materials created by the inventor ····. ···. and tested by the inventors, where their composition and properties are indicated. Front. 30 mark 1 is for control oxide sacrifice material that did not contain the target excipient; Examples 2-9 are directed to oxide sacrificial materials containing the target excipients of the invention.

• * · # · Table # 35 Table. SrO CeO2, BaO, Y2O3 and? Effect of La203 Deployment on Oxide Sacrifice Material * * Characteristics.

118444 15

Material - Example no.

composition, 123456789% by weight ____________—

Fe203 50 65 - - 26 49, - - 60 ______6____

Fe3Q4 __- _ 79 62 30 _ 52 55 _ A1203 46 23, 16 20 23 31 40 25 17 ___8________

Si02_ 4.0 1.0 1.0 4.0 4.0 4.0 4.0 1.0 4.0

SrO__10 - -_ 10 _

Ce02 __- _3.0 10 5 _

BaO __- __15 _ Y203 __- _ 3,0 15 _

La203 __-__-__-__-_ ~ __15

Oxy- 90Sr 15 3 15 16_3_16 15 15 15_ diosa- 144Ce 31 32__12_5_ 10 32_31 31 31_ pressure, 140Ba 17 18 17 17 18 2_17 16 17 atmxlO 90Y 9 9 9 9__8_ 10 3 1 10 l_140La | l2 fll 13 12 12 11 \ 12 13 [2

From the table it can be seen that the proposed threat • · *. • the carrier material containing the target excipient can · ··· reduce (up to 7-fold) the volatile content of radioactive isotopes, • in particular strontium and cerium, in the gas phase • · * · ”* above the molten core of the actor.

«« ···

INDUSTRIAL USEFULNESS

The proposed material may be used in quarries for the melted core of a nuclear reactor, in particular, in nuclear power reactors and other nuclear reactors, for their safety.

• · · • «· * ·· 15 • * * ·

Claims (7)

An oxide material for a trap for a cored core, said oxide material comprising a coolant and an oxidizing agent for cooling the molten core and for oxidizing its most active components, characterized in that it further contains a melting agent. , which consists of at least one oxide selected from a group containing SrO, CeO2, BaO, Y2 O3 and La2 O3. 10 2. Oxide material according to claim 1, characterized in that the abrasive auxiliary auxiliary is up to 15% by weight. 3. Oxide material according to claim 2, characterized in that the content of milling aids is 2 to 15% by weight. 4. Oxide material according to claim 2 or 3, characterized in that the content of flour auxiliary is 3-15% by weight Oxide material according to any of claims 20 to 4, characterized in that the coolant and the oxidizing agent contain Fe 2 O 3 and / or. Fe304 and Al2O3, where the content of Fe2O3 and / or Fe304 is 46 * ·: · 1 - 80% by weight, the content of Al2O3 is 16 - 50% by weight. * ** 6. Oxide material according to any one of claims 1 to 5, characterized in that it further contains SiO 2 in an amount which is up to and including 4 ···% by weight. ··· 1. ***. 7. Oxide material according to claim 6, characterized in that the content of SiO 2 is 1-4 .. 30% by weight. • · • ·· · ♦ · · · · · ··· · · · 1 · • ♦ · ··· · ·· «• · • ·· 1« · • · · ··· ·