WO2014018127A1

WO2014018127A1 - Hydrogen recombiner

Info

Publication number: WO2014018127A1
Application number: PCT/US2013/034422
Authority: WO
Inventors: Seyed M. AZIZI; David Grimmett
Original assignee: Aerojet Rocketdyne Of De, Inc.
Priority date: 2012-07-24
Filing date: 2013-03-28
Publication date: 2014-01-30
Also published as: JP2015529806A; KR20150046005A; CN104470848A

Abstract

A hydrogen recombiner includes a series of catalyst stages, each of the series of catalyst stages define a catalyst activity that increase as a function of a flowpath.

Description

HYDROGEN RECOMBINER

BACKGROUND

[0001] The present disclosure claims priority to United States Provisional Patent Disclosure Serial No. 61/675,155, filed 24 July 2012.

[0002] The present disclosure relates to an advanced auto-catalytic hydrogen recombination to passively remove hydrogen from inside a containment vessel of a nuclear reactor in the event of a loss of coolant.

[0003] Nuclear power plants facilitate very efficient electric power production. Light Water-cooled nuclear reactors (LWRs) are designed to minimize the threat to the integrity of containment due to a loss-of-coolant accident ("LOCA"). A LOCA may result in the ejection of hot water and steam into the containment atmosphere. Unless systems are employed to remove heat from containment, the pressure and temperature within containment may rise beyond design limits.

[0004] Furthermore, a LOCA may also lead to uncovering of the core and consequently an increase in fuel temperature that may lead to oxidation of zirconium alloy when reacting with residual steam. The reaction is exothermic and produces hydrogen that may escape along with steam into the containment atmosphere. The mass release rate of hydrogen can be in the order of a kilogram per second. Unless systems are employed to maintain hydrogen activity below self-ignition limits, a potentially ignitable gas mixture can be created in the reactor containment.

[0005] Current LWRs are exceedingly safe and provide fail-safe operations with minimal reliance on electrical supplies, service water and operator action to mitigate the effects of a LOCA. In addition to various active cooling options, many LWRs employ passive systems to transfer heat from the containment atmosphere. For example, some reactors utilize steel containment vessels and external water cooling from elevated tanks to promote heat transfer. Heat from the containment atmosphere is transferred to the containment vessels by natural convection. Hot steam from the break mixes with air and rises to the top of containment and then is cooled by contact with the cold containment vessel. The cooler denser mixture falls and a process of natural circulation is begun wherein flow near the walls is down and flow in the central area is up. After the initial blow-down period, the pressure and temperature within containment increases until the rate of condensation of steam on the cold containment vessel, and other cool surfaces, equals the rate of steam discharge from the break.

[0006] Nuclear reactors also utilize various passive systems to mitigate hydrogen build-up. Pre-inerting, for example, generates an oxygen-depleted atmosphere in containment before or during start-up. An inert gas (usually nitrogen) is injected into containment to substitute for air to reduce the oxygen activity below the level needed for hydrogen combustion.

[0007] Yet another passive system is a hydrogen recombiner. A hydrogen recombiner combines hydrogen and oxygen to produce water to reduce the hydrogen activity in containment. Auto-catalytic recombiners, as opposed to thermal recombiners, are self-starting and do not require external power and are accordingly passive.

[0008] To operate effectively, hydrogen recombiners require a relatively high flow rate of air. The conventional use of natural circulation of containment atmosphere to effect containment cooling typically does not produce sufficiently high flow rates to render effective passive hydrogen recombiners to deal with large containment volumes. The elevated temperatures generated in catalytic recombiners from the reaction between hydrogen and oxygen promotes local convection. This may generate convection flows within the recombiner greater than those from natural circulation alone.

BRIEF DESCRIPTION OF THE DRAWINGS

10009] Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

[0010] Figure 1 is a schematic view of a hydrogen recombiner according to one disclosed non-limiting embodiment;

[0011] Figure 2 is a schematic view of a hydrogen recombiner according to another disclosed non-limiting embodiment;

[0012] Figure 3 is a schematic view of a hydrogen recombiner according to another disclosed non-limiting embodiment;

[0013] Figure 4 is a schematic view of a hydrogen recombiner according to another disclosed non-limiting embodiment;

[0014] Figure 5 is a schematic view of a hydrogen recombiner according to another disclosed non-limiting embodiment; and

[0015] Figure 6 is a schematic view of a hydrogen recombiner according to another disclosed non-limiting embodiment.

DETAILED DESCRIPTION

[0016] Figure 1 schematically illustrates a hydrogen recombiner 30 that generally includes a housing 31 and a series of catalyst stages 32 A, 32B, 32C, etc. therein. Although three are illustrated it should be appreciated that any number will benefit herefrom. Each of the series of catalyst stages 32A, 32B, 32C define a catalyst activity that increase as a function of fiowpath from an inlet 34 to an outlet 36. Each successive stage of the series of catalyst stages 32A, 32B, 32C reduces the activity of hydrogen such that the output of the hydrogen recombiner 30 has a substantially lower hydrogen activity level.

[0017] The recombination reaction (H2 + 202 = 2H20) generates heat at the catalyst surface. The greater the H2 activity, the greater the heat produced such that the catalyst activity in each of the series of catalyst stages 32A, 32B, 32C may be defined with respect to an operational temperature, such as, for example, a temperature of less than about 932F (500C) to efficiently remove hydrogen yet avoid hydrogen deflagration.

[0018] Although passive in operation, the hydrogen recombiner 30 may additionally include a fan 38 (illustrated schematically; Figure 2) to facilitate flow. That is, even without the fan 38, the hydrogen recombiner 30 operates efficiently, but the fan 38 may be operable by an uninterruptable power supply (UPS) dedicated to the fan 38, or should external power be available, the fan 38 is operable to increase efficiency.

[0019] Generally, the first of the series of catalyst stages 32A is tailored for relatively low catalytic activity as the first of the series of catalyst stages 32A are exposed to a relatively high hydrogen content. That is, the first of the series of catalyst stages 32A has a relatively low catalyst activity so that surface temperatures remain below a predefined temperature. For such a low activity catalyst, materials less expensive than precious metals may be utilized. The intermediate catalyst stage 32B provides relatively intermediate catalyst activity. The final catalyst stage 32C provides for a relatively high catalyst activity for removal of hydrogen at low activities so that surface temperatures remain below a predefined temperature [0020] The catalyst activity in each of the series of catalyst stages 32A, 32B, 32C may be controlled by, for example, partial catalyst coverage on a thermally conductive substrate such that the substrate will convey heat from the catalyst surface and convection will remove heat from the substrate. In another disclosed non-limiting embodiment, a metallic alloy mesh may be located on the catalyst surface or embedded therein to enhance heat transfer. Various catalyst arrangements or combinations thereof may alternatively or additionally be provided.

[0021] Furthermore, various catalyst geometries and orientations may be used individually or in combination within each of the series of catalyst stages 32A, 32B, 32C. In one disclosed non-limiting embodiment, vertically oriented catalyst plates 40 are utilized in each of the series of catalyst stages 32A, 32B, 32C (Figure 3). In another disclosed non-limiting embodiment, vertically oriented rods or tubes 50 are utilized in each of the series of catalyst stages 32A, 32B, 32C (Figure 4). In yet another disclosed non-limiting embodiment, arrays of spheres 60 are utilized in each of the series of catalyst stages 32A, 32B, 32C (Figure 5). In still another disclosed non-limiting embodiment, vertically oriented coiled sheets 70 are utilized in each of the series of catalyst stages 32A, 32B, 32C (Figure 6). Again, it should be realized that various other arrangements and combinations will benefit herefrom.

[0022] The hydrogen recombiner 30 thereby readily removes heat in stages to preclude overheat and failure both without power and when emergency power is available. Furthermore, capital cost reductions are possible as the hydrogen recombiner 30 may reduce the required number of hydrogen recombiners as upwards of 10 times the volume of Hydrogen is readily removed as compared to conventional hydrogen recombiners.

[0023] The use of the terms "a" and "an" and "the" and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

[0024] Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.

[0025] It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

[0026] Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

[0027] The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be appreciated that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.

Claims

CLAIMS What is claimed is:

1. A hydrogen recombiner comprising:

a series of catalyst stages, each of said series of catalyst stages defines a catalyst activity that increases as a function of a flowpath.

2. The hydrogen recombiner as recited in claim 1, wherein said catalyst activity increases from an inlet to an outlet.

3. The hydrogen recombiner as recited in claim 2, further comprising a fan adjacent to said inlet.

4. The hydrogen recombiner as recited in claim 1 , wherein said catalyst activities are defined with respect to an operational temperature.

5. The hydrogen recombiner as recited in claim 4, wherein said operational temperature is less than a hydrogen deflagration temperature.

6. A method of passively removing hydrogen from inside a containment vessel of a nuclear reactor comprising:

locating a series of catalyst stages within the containment vessel, the series of catalyst stages defining a catalyst activity that increase as a function of a flowpath.

7. The method as recited in claim 6, further comprising maintaining an operational temperature less than a hydrogen deflagration temperature within each of the series of catalyst stages.

8. The method as recited in claim 6, further comprising locating a fan upstream of the series of catalyst stages.