DE3739720A1 - Eliminating hydrogen from a post-accident atmosphere of a nuclear power station - Google Patents

Abstract

In the reactor accidents in Three Mile Island and in Chernobyl, explosive hydrogen-oxygen reactions occurred prematurely. During accidents of this type ionising beams dissociate from the fission products molecular hydrogen, which collects in the gas space as a result of metal-water reactions, to give highly-reactive atomic hydrogen, which can directly react explosively with oxygen, whereby the safety container can fail prematurely. Previously known hydrogen recombiners - for example contact catalysts or sparking plugs - reduce the hydrogen concentration in the safety container only very slowly and are only effective in their direct vicinity. Furthermore, these recombiners, instead of recombining the hydrogen as planned, can actually unintentionally trigger a premature hydrogen explosion or detonation. In the case of contact catalysts it can occur that the finest particles of catalyst material can be detached from the actual catalyst by mechanical or thermal loadings. A sufficient heat dissipation is then not present. At high hydrogen throughputs these particles can be heated to red-hot temperature (as in the historic Döbereiner firework) and unintentionally trigger hydrogen explosions just like the sparking of the sparking plugs. The invention presented here allows the hydrogen concentration already to be reduced rapidly in the gas space. For this purpose the hydrogen is fed specially to ... Original abstract incomplete.

Description

The invention relates to a method for elimination of hydrogen from an after-accident atmosphere of a core power plant using mild hydrogen reactions organic substances (hydrogenation, hydrogenolysis).

It is known that after a serious accident in a core Hydropower generated by metal-water reactions must be removed from the gas phase to be explosive Hydrogen-oxygen reactions with high pressure peaks to prevent; otherwise there is an early failure of the Security container cannot be excluded. Various recombination methods have been around for a long time known from hydrogen and oxygen z. B .:

• - thermal recombination
  After an accident, thermal recombiners are to be connected externally to the safety container in order to free the post-accident atmosphere to be pumped out by means of controlled thermal recombination, if necessary with the addition of oxygen, and hydrogen. The recombination throughput, which is ultimately limited by the connection cross section, only allows a local long-term reduction in the hydrogen concentration, which, however, increases very rapidly in a short time in the event of an accident in the containment and is also not homogeneously distributed. The high radiation intensity in this case makes it even more difficult to connect and operate this recombination.
• - catalytic recombination
  Catalytic recombiners are contact catalysts, at the boundary layers of which hydrogen and oxygen recombine with the release of heat. Experience with conventional catalyst material such as platinum has shown that, due to thermal and / or mechanical loads, the finest particles can detach from the actual catalyst material and lack adequate heat dissipation. With high hydrogen conversions, these particles (historical Döbereiner lighter) can heat up to the glow temperature and trigger local explosions, which can lead to premature failure of the containment. In addition, an after-accident atmosphere contains a wide variety of elements and compounds, the effects of which have not been investigated as possible catalyst poisons. In an emergency, contact catalytic recombination can be severely impaired or impossible.
• - spark recombination
  Spark plugs for hydrogen oxidation require a constant supply of electrical energy. In addition to unwanted ignitions of locally increased hydrogen concentrations with the consequences already mentioned, major corrosion problems can occur in the post-accident atmosphere of the spark electrodes in continuous operation.
• - Recombination on CuO₂
  Baukal et al / BMI-1984-033 "Possibilities for removing hydrogen" / propose to vacuum the post-accident atmosphere outside the containment and to thermally oxidize the hydrogen via CuO₂. The resulting Cu must be constantly regenerated or exchanged for unused CuO₂. This solution, too, only allows long-term removal of the large quantities of hydrogen from the containment and is therefore to be assessed like thermal recombination.

A serious disadvantage of all previous solutions is the limitation of the recombiner effect to once selected installation locations or their immediate vicinity, the the hydrogen slowly over turbulent and / or molecular Diffusion can achieve.

The invention has for its object from a post-accident atmosphere of a nuclear power plant quickly and to be eliminated primarily in the gas space, with the serious Disadvantages of previous solutions can be avoided. Hydrogen- Oxygen reactions, as in Chernobyl and in weakened form occurred in Three Mile Island do not repeat themselves

This object is achieved in that the hydrogen with additionally supplied unsaturated organic substances Contact catalysts or on organometallic catalysts or by chemical activation of the reactants in the beam field of ionizing radiation in mild reactions (i.e. under low energy release) and reacts to the organic Substances is bound. The substances necessary for this can also be supplied in gas, vapor or aerosol form. When using the droplet aerosol, you can use it earlier Proven hydrogenation reactions in the liquid phase also in the gas space expire. The substances and materials required for this can be tested from a variety of known Possibilities / z. B. Ullmann vol. 13 p. 546; 16 p. 602; 24 p. 328ff / can be selected; Droplet aerosols can be for example with known liquid atomizers - if necessary under Use of pressure differences - generate in the containment.  

The present invention therefore does not relate to space redundant insertion devices but the use of such Reactions that lead to an accumulation of hydrogen cause unsaturated organic substances in mild reactions, as well as the use of the necessary materials.

Important advantages of the invention are that

• - Already everywhere in the gas room, d. H. especially in critical Areas, using a quick elimination of hydrogen mild reactions occur and with it
• - a previously unavoidable restriction on hydrogen removal to locally defined reaction areas on contact catalysts or attached to the outside of the containment Systems eliminated and
• - The enthalpies of the mild reactions are significantly lower than with previously proposed hydrogen oxidations, so that on the one hand a generally reduced temperature rise occurs due to hydrogen removal and on the other hand
• - unwanted local ignitions by heating up particles Catalyst material can be avoided and
• - catalyst poisoning in the gas space must be excluded, if organometallic catalyst material in aerosol form with an extremely enlarged surface is constantly supplied.

In summary it can be said that with this invention a early containment failure due to hydrogen Explosions or detonations can be prevented. Mild reactions due to low energy releases also an improvement of known contact catalytic processes for removing hydrogen from gas phases (e.g. OS DE 36 04 416 Chakroborty et al) possible. But it would have to be checked whether at high Hydrogen sales on the very thin catalyst layers this OS is too high even with mild reactions gradients occur due to different expansion coefficients of the different layer materials local peeling or cause particle detachment from catalyst material can. But should such particles occur, then that would be an early explosion due to the presence of these particles mild reactions are much less likely than in the oxidation reactions provided by the OS mentioned.  

Another major innovation is the mild reactions of the Hydrogen with the organic substances on organometallic Catalysts (OMC) are presented, mostly made of organic Metal complexes exist, with transition metals such as the precious metals prove to be particularly suitable. At a The proposed solution to the problem, the hydrogen already The reactants can eliminate from the gas space (OMC and organic substances) as aerosols in the gas space be effective. Expected aerosol losses from the gas space through effects such as deposition, condensation, diffusion and therm mophoresis and possible catalyst poisoning by delivering fresh, unused reaction partners be compensated in aerosol form (possibly with sump circulation). High temperatures occur near the meltdown and therefore associated metal-hydrogen reactions as well as high intensities ionizing rays. Successful dissociation of hydrogen and chemical activation of the gas, vapor or aerosol organic substances already ionizing in the field Radiate, so mild reactions of the reactants in the Drain the gas space even without a catalytic effect.

Catalytic hydrogenation

Catalytic hydrogenation (hydrogenation) means the addition of hydrogen to compounds in the presence a catalyst. In general, these additions take place reactions as molecular reactions exothermic according to the following Gross equation:

A + n H₂ ⇄ B - Δ H

A = starting molecule
B = hydrogenation product
n 1
H₂ = molecular hydrogen
H = enthalpy

The equilibrium is usually at temperatures <400 ° C Sides of the hydrogenation products B. back reactions, dehydrations, often occur above 400 ° C. In contrast to ion reactions Molecular reactions are significantly slower because in tramolecular bonds are released to activate the molecules Need to become. The thermal energy is sufficient in a homogeneous phase at temperatures <500 ° C the threshold of the Ak  overcoming activation energy. With suitable hydrogenation catalysts the activation energy of the hydrogenation reactions reduce to the extent that mild reactions already at temperatures <100 ° C occur / Ullmann vol. 13 p. 136 /. For contact catalysts Hydrogen molecules dissociate at the interfaces through chemisorption in monoatomic layers. There are highly active ones Hydrogen atoms with low space exchange energy and associated great mobility on the catalyst surface in front. The likelihood of desorption of the water is because of the relatively large activation energy very low. The chemisorption of the organic to be hydrogenated Substance (s) on the same catalyst surface also leads to activate the substance (s) so that hydrogenation, a mild reaction occurs.

In particular, the transition metals, e.g. B. precious metals are for Dissociation and activation of hydrogen are suitable as they their incompletely occupied, inner electron shells with the Electrons of the adsorbed molecules or atoms (H⁺) to the noble gas configuration can fill. Platinum (Pt) or palladium (Pd) Contacts show highly active catalyst properties, with Pt has a slightly higher hydrogenation activity than Pd. At Pt- In addition to hydrogenation, contacts also occur hydrogenolysis reactions on.

At OMK in a homogeneous phase instead of the boundary surfaces with chemisorption individual molecules (metal complexes) with anla processes are catalytically active. The hydration properties At OMK, not only the type of metal atoms in the Complex but also strong on the nature of the other ligands influenced. OMK reactions e.g. B. are in the liquid phase e.g. B. in / Ullmann vol. 13 p. 137 /:

There is also a clear presentation of hydrogenations various unsaturated hydrocarbons under mild conditions using, for example, the most universal usable OMK ClRh [P (C₆H₅) ₃] ₃ - chloro-tris- tri phenylphosphane -rhodium - in / B.R. James: Homogeneous hydrogenation J. Wiley New York 1973; F. M. Jardine: Prog. Inorg. Chem. 28 64 (1981) /.

Paint over the boundary conditions of the hydrogenation reactions on OMK  very large bandwidths, e.g. B.

• - a wide partial pressure range of hydrogen 48 kPa (480 mbar) / G. Platbrood: J. Mol Catal. 1 265 (1965/76) / up to 1.6 · 10⁷ Pa (160 bar) / N. Nakamura et al. S. Otsuka: Tetrahedron Lett. 1973 4529 /
• - a wide temperature range of 20 ° C / M. Cais et al. D. Fraenkel: Coord. Chem. Rev. 16 27 (1975) / up to 200 ° C / A. Futura: Agric. Biol. Chem. 46 1757 (1982) /
• - in addition to common organic solvents Water (H₂O) / Y. Dror u. J. Manassen: J. Mol. Catal. 2nd 219 (1977) and A.F. Borowski et al: Nouv. J. Chim. 2nd 137 (1987) /.

Claims (7)

1. Process for the removal of hydrogen from a hydrogen-containing accident atmosphere inside a nuclear power plant, characterized in that such unsaturated organic substances are introduced into containers or rooms with a hydrogen-containing gas mixture, are produced or released there, to which hydrogen can be added in mild reactions. 2. The method according to claim 1, characterized in that that additionally introduced contact catalysts and exposed to the gas phase. 3. The method according to claim 1, characterized in that additionally organometallic catalyst materials introduced, created there or to be released. 4. The method according to any one of the preceding claims, characterized in that the organic Substances and / or the organometallic kata lysatormaterials supplied in the liquid phase will. 5. The method according to claim 4, characterized in that the organic substances and / or the organometallic catalyst materials in one Solvents are dissolved. 6. The method according to any one of the preceding claims, characterized in that the organic Substances and the organometallic catalytic converter door materials in gas, vapor or aerosol form introduced, generated and released there will. 7. The method according to any one of the preceding claims, characterized in that the supply of to be introduced, generated or released there Substances in the gas space of the container or Spaces are made redundant, with one back management of substances to which hydrogen is not yet available was deposited from the swamp solution into the gas space can be provided.