Patent Application
20160379722
As shown in
Fuel bundles may be aligned and supported by fuel support castings 48 located on a core plate 49 at the base of core 36. Castings 48 may receive individual fuel bundles or groups of bundles and permit coolant flow through the same. Fuel support castings 48 may further permit instrumentation tubes 50, control blades 20, and/or other components to pass into core 36 through or between fuel supports 48. A fluid, such as light or heavy water, is circulated up through core plate 49 and core 36, and in a BWR, is at least partially converted to steam by the heat generated by fission in the fuel elements. The steam is separated and dried in separator tube assembly and steam dryer structures 15 and exits vessel 12 through a main steam line 3 near a top of vessel 12. Other fluid coolants and/or moderators may be used in other reactor designs, with or without phase change.
A cruciform or other opening 21 may permit a control blade 20 (
Example embodiments include castings for supporting and directing fluid flow through nuclear fuel assemblies. Example castings define four open ends connected by a channel, with a fuel assembly configured to seat into the topmost open end. The channel is elongated to increase fluid flow inertia, in excess of the conventional 0.3 meter fuel casting. For example, the channel may be over about 0.8 meters long or more. In boiling water reactor designs, channels having lengths of several meters can be used. The channel may be effectively straight and vertical to enhance inertial fluid flow. The channel may be any shape, including a circular or ellipsoid shape that matches the open ends. Example embodiment castings may specifically dimension the channel to achieve a desired pressure drop and/or use a side or bottom entry orifice to reduce pressure. Example embodiment castings may accommodate any number of fuel assemblies with a proper number of associated channels with openings for each fuel assembly, as well as other core structures such as control blades, instrumentation tubes, etc. Example castings are useable in any number of different nuclear reactors, including BWR, ABWR, and ESBWR designs having hundreds or thousands of fuel assemblies seating into example embodiment fuel castings.
Example embodiments will become more apparent by describing, in detail, the attached drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus do not limit the terms which they depict.
Because this is a patent document, general broad rules of construction should be applied when reading and understanding it. Everything described and shown in this document is an example of subject matter falling within the scope of the appended claims. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use example embodiments or methods. Several different embodiments not specifically disclosed herein fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only example embodiments set forth herein.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” or “fixed” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange routes between two devices, including intermediary devices, networks, etc., connected wirelessly or not.
As used herein, the singular forms “a”, “an” and “the” are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise with words like “only,” “single,” and/or “one.” It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, steps, operations, elements, ideas, and/or components, but do not themselves preclude the presence or addition of one or more other features, steps, operations, elements, components, ideas, and/or groups thereof.
It should also be noted that the structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, so as to provide looping or other series of operations aside from the single operations described below. It should be presumed that any embodiment having features and functionality described below, in any workable combination, falls within the scope of example embodiments.
The inventors have recognized that existing flow structures in nuclear cores that create desired flow direction may have relatively high instability in the instance of thermo-hydraulic perturbation, such as when the inlet temperature or pumped flow is reduced. Boiling two-phase flow in a fueled region of a fuel assembly is sensitive to power and flow perturbations, which can create oscillatory behavior in the flow. Such instability is described in the April 1992 publication, “Coupled Thermohydraulic-Neutronic Instabilities in Boiling Water Nuclear Reactors: A Review of the State of the Art” by March-Leuba et al., incorporated by reference herein in its entirety. This phenomenon may be addressed with an inlet orifice that presents a single, liquid-phase flow path to dampen these oscillations, depending on the magnitude of pressure loss at the inlet orifice relative to two-phase pressure loss in the fuel. This dampening of the oscillatory effect of the two-phase response is required, and existing flow structures at the inlet like inlet orifices are typically retained to achieve this dampening and because modifying the inlet may complicate removal during shutdown maintenance, increase fabrication cost, have negative impacts on overall flow rate, and affect compatibility with existing core component.
However, the inventors have recognized that increasing pressure loss in the fuel support casting to correct such oscillations with an inlet orifice may detrimentally increase overall pressure loss, and reduce flow through the fuel assembly. To overcome these newly-recognized problems as well as others, the inventors have developed systems that reduce or eliminate pressure and flow oscillations in fluid coolant or moderator flowing through fuel assemblies in a nuclear fuel core, while preserving fuel compatibility with core components and placement and desired core flow.
The present invention is fuel castings and methods of using the same in nuclear reactors. In contrast to the present invention, the few example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention.
As shown in
Example embodiment fuel support casting 148 may further include a lower opening 194 that is relatively less or non-orificed. For example, lower opening 194 may be circular or otherwise matching a perimeter of flow passage 196 at a bottom end of example embodiment casting 148. Lower opening 194 may provide a vertical entry into flow passage 196 for coolant flow 80, such that coolant flow 80 through example embodiment casting 148 is substantially vertical and straight, such as being no more than a few degrees from vertical and not including several bends or flow path deviations. Flow passage 196 being continuous and straight may enhance flow inertia in the vertical direction. Similarly, because a ratio of passage length to area is a stabilizing term in flow momentum, a longer passage 196 creates a more stable flow condition for a same flow area.
In order to replicate the pressure drop caused by a conventional orifice, flow passage 196 may have a smaller inner diameter to mimic pressure drop through frictional losses in flow 80 through flow passage 196. Additionally or alternatively, an orifice 195 may be included in example embodiment casting 148 as an opening into flow passage 196. Any orifice 195 may be side-entry, as shown in
Although shown with an up-down-up flow path in
Example embodiment fuel castings 148 and 248 may otherwise be shaped and sized to replace conventional fuel castings or to be placed in new plant types. Of course, example embodiment fuel castings may also be easily re-sized to accommodate new reactor and core designs. Example embodiment fuel castings 148 and 248 may be fabricated of materials compatible with operating nuclear reactor environments and for contacting fuel assemblies seating in openings 190/290. It is further possible to retrofit existing fuel castings as example embodiment fuel castings by extending a lower portion to form longer internal flow passages 196 and potentially further remove or relocate a side-entry orifice in such existing castings. In such a retrofit, a lower opening for may be drilled in a control rod guide tube to accommodate longer flow passages.
The inventors have discovered that a longer vertical flow path versus flow path area, such as the vertical longer flow path 196 provided by example embodiment fuel support casting 148, beneficially reduces power and flow disruption to a significant degree following a flow disruption through a nuclear fuel core. The longer flow path, such as a path 0.8 meters or longer for flow rates in most light water reactor designs, greatly enhances vertical flow inertia, thereby combating pressure shock waves and resulting self-reinforcing flow oscillations following a flow disruption. A longer flow path may further maintain an equivalent pressure loss as existing flow structures, while providing a beneficial time shift in pressure loss response relative to two-phase response in the fuel assembly; this time shift may additionally dampen oscillatory flow behavior through fuel assemblies by changing the phase relationship. A lower, open entry for the flow path, such as lower opening 194 in example embodiment fuel support casting 148 may further enhance inertia and permit quicker decay of power oscillations.
As shown in
Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied and substituted through routine experimentation while still falling within the scope of the following claims. For example, a variety of different available source holder locations, in several different types of reactor designs, are compatible with example embodiments and methods simply through proper dimensioning of example embodiments—and fall within the scope of the claims. Such variations are not to be regarded as departure from the scope of these claims.
