Nuclear power plant explosion safety method

Abstract

A method of improving explosion safety in closed spaces by attenuating the effect of a combustion wave or shock wave on a protected surface consists in placing obstructions before the protected surface in the form of elastic membranes filled with a flame-retardant substance. A non-flammable gas is used as the substance filling the membranes; the membranes themselves are made of a material that disintegrates during, and under the action of, displacement of the front of a combustion wave or shock wave along the surface of the membranes. The membranes are filled with a non-flammable gas immediately after flammable gas is detected at a dangerous concentration in the space in front of the protected object.

Description

NUCLEAR POWER PLANT EXPLOSION SAFETY METHOD The invention relates to methods of decreasing the effect of blast loads on industrial spaces relating to, inter alia, nuclear power plant and large chemical manufacturing facilities. Methods and devices for mitigating a shock wave using foam or porous materials but without use of any additional damping mechanisms are known [1. V.M. Kudinov, B.I. Palamarchuk, B.Ye. Gelfand, S.A. Gubin Shock wave parameters during explosive charge explosion in foam / / "Reports of the Academy of Sciences of the USSR". Vol.228, 1974, 4. - P. 555-558. 2. B.Ye. Gelfand, A.V. Gubanov, Ye.I. Timofeev Interaction of shock air waves with a porous screen / / "Izvestiya of the Academy of Sciences of the USSR, MZhG", 1983, 4. - P. 79-84.]. However, such devices are characterized by low efficiency and high consumption of consumables, which significantly limits the possibilities of their practical application. In order to reduce the intensity of shock waves, screens from a porous material with an open cell structure (for example, polyurethane foam) filled with a non-flammable liquid are also used [RU 2150669, F 42 V 33 / 00, F 42 D 5 / 04, 15.03.1999.]. However, the use of such an approach in industrial spaces is not effective, since the presence of liquid in the porous screen leads to formation of high humidity and, accordingly, corrosion, as well as to an increased weight load on the walls and floors of the protected room. Prior art methods include placing obstructions in front of the protected surface, in the form of elastic membranes filled with a flame-retardant liquid, the obstructions are dedicated for attenuating the blast wave. [RU 2125232, F 42 V 39 / 00, F 42 V 33 / 00, 23.09.1997]. The closest prior art prototype is a blast effects suppression device used to limit the damage associated with explosions, specifically, to reduction of impulse and overpressure of compression waves in order to minimize the damages in area being protected. The prior art prototype device consists of a cylindrical container placed between an object to be protected and a potential source of compression wave. The container has elastic walls designed to collapse or rupture. The internals of the container are filled with a non-flammable substance at a low pressure (for example, with air, nitrogen or carbon dioxide). The walls of the container are designed to collapse or rupture during and under action of the shock wavefront or combustion wavefront propagating along the surfaces of the containers. If the peak pressure or the impulse of the compression wave exceeds predetermined level, the pressure detector changes its output (electrical current or voltage). As a result, amplifier generates an electrical signal sufficient to activate the igniter. The activated igniter provides a detonating electrical impulse and initiates an explosion of pyrotechnic charge to rupture the diaphragm, connecting internals of the container with atmosphere and generating the negative pressure wave. The generated negative pressure wave propagates outside and interferes with moving compression wave and reduces the peak pressure in the space around the containers (see US 2066 / 0027419A1, B64F 1 / 26, 09.02.2006). The disadvantages of the prior art prototype are that the device contains a pressure sensor, while the negative gas pressure in the container internals relative to the ambient pressure does not allow using elastic, rapidly destructible walls for the container, which complicates the device. In addition, protection depends on the operation of the pressure sensor, which reduces the reliability of the device as a whole and the effectiveness of the method, since the sensor is activated after the explosion. The objective of the claimed invention is to improve explosion safety. The technical result of the present invention is decrease in the effect that an explosive wave formed in an accidental explosion of fuel-air mixtures has on the walls and floors of protected spaces. In order to achieve the said technical result, the known method providing explosion safety, comprising placing obstructions before the protected surface in the form of membranes filled with a flame-retardant gas it is proposed to make the membranes from an elastic material filled with non-flammable gas, capable to disintegrate during, and under the action of, displacement of the front of a combustion wave or shock wave along the surface of the membranes, wherein the membranes are filled with a non-flammable gas immediately after flammable gas is detected at a unacceptable concentration in the space in front of the protected object, wherein the elastic membranes are placed before the protected surface in at least two layers. Helium is used to fill the elastic membranes as a non-flammable substance. Each subsequent layer of the elastic membranes is located in depressions of the previous one. To fill the elastic membranes, an air / helium mixture with a helium content of at least 50 vol.% is used as a non-flammable substance. Membranes filled with air are placed in front of the membranes filled with helium. The total thickness of the elastic membranes filled with non-flammable gas along the normal to the protected surface exceeds two critical detonation diameters in the free space for the mixture of stoichiometric composition. The disclosed set of features allows to achieve high efficiency of the method of reducing highly explosive and thermal effect of a blast wave on spatially extended flat and curved surfaces, which limit the protected space. Description of the drawings: While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numerals, and where: Figure 1 illustrates a system for protecting premises from explosion loads using elastic membranes filled with a non-flammable gas; and Figure 2 shows a schematic diagram of an explosion chamber used for testing the effectiveness of shock wave attenuation. Detailed description of illustrated embodiments: The proposed method for attenuating the effect of a blast wave on the protected surface is explained on Fig. 1 illustrating the system for protecting premises from explosion loads, that uses elastic membranes with non-flammable (inert) gas, and Fig. 2. Fig. 1 shows one possible embodiment of the claimed method, and Fig. 2 shows a schematic diagram of an explosion chamber where the effectiveness of shock wave attenuation was experimentally tested. According to Fig. 1, sensors 2 for determining the concentration of explosive gas; a controller 3 actuating, if necessary, the gas supply mechanism 4; cylinders for storing compressed gases 5; a gas distribution system 6; elastic membranes 7 and a compressor 8 are arranged in the protected room 1. The term "critical detonation diameter" refers to a well-established parameter in explosive physics, widely recognized by those skilled in the art. It denotes the smallest diameter of a cylindrical charge of a high explosive at which the propagation of self-sustaining detonation is still possible. This parameter is crucial in assessing the behavior of combustible gas mixtures, including hydrogen-oxygen mixtures, under specific conditions. For instance, the critical detonation diameter of a stoichiometric hydrogen-oxygen mixture is approximately 0.3 m, as determined through standard experimental procedures. The invention leverages this principle to enhance explosion safety by ensuring that the total thickness of the elastic membranes filled with non- flammable gas exceeds two critical detonation diameters, or approximately 0.6 m, thereby significantly reducing the propagation potential of detonation waves. By designing the protective layers to exceed two critical detonation diameters, the invention effectively prevents the sustenance of detonation within the protected space, ensuring a marked decrease in explosive pressure and thermal effects on the protected surfaces. This feature is a critical element of the disclosed method and contributes to its ability to attenuate the impact of combustion or shock waves on the walls and floors of the protected space. Experimental data, as described herein, demonstrates the efficacy of this design in real-world applications, particularly in mitigating explosion risks in high-stakes environments such as nuclear power plants. The surfaces of NPP spaces are protected from blast loads as follows. Signals related to the concentration of flammable gas, for example, hydrogen, in the protected room of the NPP, are continuously sent from the sensors 2 to the controller 3. When the controller 3 detects an unacceptable concentration of flammable gas (in the event of an emergency), the controller 3 issues a command to the gas supply mechanism 4, and the elastic membranes 7 are filled with non- flammable gas, for example helium, through the distribution system 6 from the containers 5 (on Fig. 1, two layers of the membranes are filled with non-flammable gas). If the flammable gas concentration in the space 1 can be decreased to a safe level (for example, because of operation of the ventilation system and the system of the flammable gas chemical oxidation, not shown on the Figures), the gas from the membranes 7 can be pumped using the corresponding compressors back to the containers 5 for subsequent use. Thus, the explosive load protection system of the spaces, using elastic membranes with non-flammable (inert) gas, can be returned to the original operating state. If explosive combustion occurs in the space 1, the combustion wave (or shock wave), approaching the elastic membranes 7, disintegrates them, and continues its displacement in the environment of non-flammable (inert) gas, which leads to a decrease in its force action on the walls and, in particular, on the dome of the space 1. The effectiveness of shock wave attenuation was tested in the experiments with a large-scale explosion of a local volume of a hydrogen-air mixture in a spherical explosion chamber 9 with a diameter of 12 m, which schematic is shown on Fig. 2. The pre-mixed flammable mixture was pumped into a latex membrane 10 (balloon probe) with a volume of up to 40 m3. The combustion or detonation was initiated in the center by a charge of condensed explosive 11. Pressure sensors <semantics>12D1−4<annotation encoding="application / x-tex">12 D_{1-4}< / annotation>< / semantics> and ionization sensors <semantics>12I1−4<annotation encoding="application / x-tex">12 I_{1-4}< / annotation>< / semantics> were located inside the membrane and partially outside of it. In relation to external objects, which in the simplest case are represented by limiting surfaces, the spherical volume 10 located in the near-wall area simulates the accumulation of a flammable hydrogen-air mixture in the internal space of the nuclear power plant. For recording the explosive load parameters, four pressure sensors 13 were located near the surface of the explosion chamber, shown in the right-hand part of the layout on Fig. 2. As pressure sensors 13, sensors of RSV113 model were used, which were mounted flush to a steel plate of 6 mm thickness and of 0.52x0.65 m2 surface area (not shown on the Figure). Elastic membranes 7 filled with helium or air and having a gas layer thickness of 0.6 m, or filled with a two-layer air-helium gas system with the same total gas layer thickness of 0.6 m and with a layer thickness ratio of 1:1, were installed on a part of the sensors 13. In the experiments, the pressure recorded by the sensors 13 was compared for two variants – with and without local protection membranes 7, as shown on Fig. 2. Differential pressure comparison table [Image disponible dans le document PDF, Image available in the PDF document] [Image disponible dans le document PDF, Image available in the PDF document] 35-40 These tests have shown that elastic membranes filled with helium provide the most effective pressure decrease. The specified gas layer thickness of 0.6 m in the elastic membranes on the blast wave propagation path is at least double critical detonation diameter in the free space for a hydrogen-air mixture with stoichiometric composition.

Claims

<pat:ClaimStatement>What is claimed is:< / pat:ClaimStatement> <pat:Claims com:id="claims"> <pat:Claim com:id="CLM-00001"> <pat:ClaimNumber>1< / pat:ClaimNumber> <pat:ClaimText>1. A method of providing explosion safety for nuclear power plants, comprising placing obstructions before a protected surface (1) of a protected object in the form of elastic membranes (7) filled with a flame-retardant gas, characterized in that the elastic membranes (7) are made of a material that disintegrates during, and under action of displacement of a front of a combustion wave or shock wave along a surface of the elastic membranes (7), wherein the elastic membranes (7) are filled with a non-flammable gas immediately after flammable gas is detected at a unacceptable concentration in a space in front of the protected object, wherein the elastic membranes (7) are placed before the protected surface (1) in at least two layers. < / pat:ClaimText> < / pat:Claim> <pat:Claim com:id="CLM-00002"> <pat:ClaimNumber>2< / pat:ClaimNumber> <pat:ClaimText>2. The method of claim 1, wherein helium is used as the non-flammable gas filling the elastic membranes (7). < / pat:ClaimText> < / pat:Claim> <pat:Claim com:id="CLM-00003"> <pat:ClaimNumber>3< / pat:ClaimNumber> <pat:ClaimText>3. The method of claim 1, wherein an air / helium mixture with a helium content of at least 50 vol. % is used as the non-flammable gas filling the elastic membranes (7). < / pat:ClaimText> < / pat:Claim> <pat:Claim com:id="CLM-00004"> <pat:ClaimNumber>4< / pat:ClaimNumber> <pat:ClaimText>4. The method of claim 2, wherein further elastic membranes filled with air are placed before the elastic membranes (7) filled with helium. < / pat:ClaimText> < / pat:Claim> <pat:Claim com:id="CLM-00005"> <pat:ClaimNumber>5< / pat:ClaimNumber> <pat:ClaimText>5. The method of claim 1, wherein the total thickness of the elastic membranes (7) filled with non-flammable gas along a normal to the protected surface (1) exceeds two critical detonation diameters in a free space for a stoichiometric mixture. < / pat:ClaimText> < / pat:Claim> < / pat:Claims>