Patent Application
20120163526
As shown in
Fuel bundles may be aligned and supported by fuel supports 48 located on a core plate 49 at the base of core 36. Fuel supports 48 may receive individual fuel bundles or groups of bundles and permit coolant flow through the same. Fuel supports 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 36 and core plate 48, 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 RPV 12 through a main steam nozzle 3 near a top of RPV 12. Other fluid coolant/moderators may be used in other reactor designs, with or without phase change.
Example embodiments are directed to fuel supports and reactor cores including the same. Example embodiment fuel supports include an inlet orifice that permits a coolant/moderator to flow through the support into an associated fuel bundle seated into the support, and the inlet orifice is specially designed to achieve a desired fluid flow characteristic, such as coolant/moderator flow rate through the associated fuel bundle. The desired fluid flow characteristic may be determined based on a position of a bundle associated with the inlet orifice within a core of the nuclear reactor. Any number of differently-configured inlet orifices, having different associated fluid flow characteristics, may be used throughout the core and in individual supports. Example embodiment fuel support configurations may include different inlet orifice diameters or use of flow blockages such as filters, venturis, choke plates, etc., to achieve a desired flow loss coefficient or flow rate under known conditions, for example. Example embodiment fuel support may be positioned within a core plate in the nuclear reactor, permitting coolant/moderator flow and potentially a control blade and instrumentation tubes to pass through or between the fuel supports. Several example embodiment fuel supports may be placed at the base of the reactor core, each support having physical configuration to achieve a desired flow characteristic at the associated fuel bundle position. For example, three different configurations may be used at outer core periphery, inner core periphery, and central portions of the core. The configuration at the outer periphery—those positions at the edge of the core and not surrounded by fuel bundles on each side—may have a highest flow loss coefficient so as to limit coolant/moderator flow to periphery bundles requiring less moderation and heat transfer. The configuration at an inner periphery, defined herein as the two or three bundle positions immediately inside the outer periphery, may have intermediate flow loss coefficients, and the configuration in the central portion may have the lowest flow loss coefficients, providing the highest levels of coolant/moderator flow to central bundles at higher power levels.
Example methods configure flow path characteristics of fuel supports in a nuclear core. Example methods may include modifying flow loss coefficients at particular bundle locations, simulating core performance with the modified flow loss coefficients, analyzing the simulated core performance, and/or configuring at least one fuel support to achieve the modified flow loss coefficients. Analyzing may be performed by comparing simulated core performance against desired performance characteristics or comparing simulated core performance against a previously simulated core performance with different flow loss coefficients, in an iterative manner.
Hereinafter, example embodiments will be described in detail with reference to the attached drawings. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. For example, although example embodiments and methods are described in connection with a Boiling Water Reactor (BWR), it is understood that example embodiments and methods are useable with several other reactor types, including PWRs, ESBWRs, heavy-water reactors, breeder reactors, etc. all using a fluid coolant and/or moderator. The example embodiments 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.).
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the language explicitly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures or described in the specification. For example, two figures or steps shown in succession may in fact be executed in parallel and concurrently or may sometimes be executed in the reverse order or repetitively, depending upon the functionality/acts involved.
Inlet orifices 195 of example embodiment fuel supports 148 are physically configured to provide a desired flow level of fluid coolant/moderator through an associated bundle during plant operation. The configuration may be achieved in several ways. For example, diameter da of inlet orifice 195a may be set during fabrication of fuel support 148 to permit a desired level of coolant flow 180a therethrough. Similarly, diameter da may be achieved or adjusted following fabrication through machining or remolding, for example. Or, for example, diameter db of inlet orifice 195b may be achieved or adjusted through addition of an insert, such as an annular choke plate, that reduces diameter db and achieves a desired lower flow rate 180b therethrough. Additionally, inserts, baffles, filters and/or any other structure may be used in example embodiment fuel support 148, on either side of inlet orifices 195, to affect fluid flow loss coefficients of, and a resulting amount of fluid flow through, a given inlet orifice 195 to a desired level during plant operation. For example, a flow restrictor or blockage may be placed in a flow path prior to or in opening 190 to adjust an amount of coolant/moderator flowing into an associated inlet orifice 195 and ultimately through the fuel bundle seated into the associated opening 190.
The levels of fluid coolant/moderator flow permitted by various diameters and/or other configurations of inlet orifices 195 in example embodiment fuel supports 148 may be set at any desired level. Local flow loss coefficients caused by these configurations on a given fluid may provide a universal metric to compare individual inlet orifice 195 functionality in an operating nuclear plant. For a universal inlet pressure and fluid, a higher loss coefficient correlates with less fluid moderator/coolant flow through an orifice and associated fuel bundle, resulting in less moderation and fuel usage while directing more flow to other bundles. Higher loss coefficients may be achieved in example embodiment fuel supports 148 by decreasing inlet orifice 195 diameter and/or providing other flow-interrupting structures within inlet orifice 195 or fuel support 148, as discussed above. Under the same universal inlet pressure and coolant/moderator fluid, a lower loss coefficient correlates with increased fluid moderator/coolant flow through an orifice and associated fuel bundle, resulting in greater moderation and fission energy generation while decreasing flow available to other bundles. Lower loss coefficients may be achieved in example embodiment fuel supports 148 by increasing inlet orifice 195 diameter and/or removing flow-interrupting structures in example embodiment fuel supports 148. Several different types of orifice configurations may be used together on a same fuel support 148 or even on a same inlet orifice 195, based on the flow characteristics desired of that orifice.
As shown in
In this way, example embodiment core 236 includes example embodiment fuel supports having several types of orifices with intermediate variations of loss coefficients, from outer periphery orifices with the highest loss coefficients to inner central orifices with the lowest loss coefficients. The quadrant shown in
Bundles at peripheral and intermediate positions “2,” “3,” and “4” in example embodiment core 236 may possess lower fuel enrichment (through age or initial enrichment) and suffer from increased neutron loss at core boundaries, resulting in lower fission energy production. Due to the lower power levels at peripheral and inner peripheral positions, less moderator/coolant flow may be required to maintain bundles at these positions at operating temperature and maximum power production. Example embodiment core 236 provides higher loss coefficients, and thus less flow, for fluid moderator/coolant through intermediate bundles with orifices at “3” and “4” locations, compared to conventional cores, such as the core shown in FIG. 3, which provide full, central orifices for the same bundles at intermediate, inner periphery locations. In this way, example embodiment core 236 may direct more moderator/coolant to bundles at central locations “1,” while directing less moderator/coolant to bundles at intermediate peripheral locations “3” or “4,” with the same whole-core flow rates, compared to conventional cores such as those shown in
Further, near end of operating cycles, bundles in a given core are more depleted in fissionable material, and bundles at peripheral and intermediate positions “2,” “3,” and “4” in example embodiment core 236 may possess especially low fuel enrichment due to age and lower initial enrichment. Operators in end of cycle conditions may increase total core flow so as to provide additional moderator to the depleted bundles, sustaining a fission chain reaction for several more days beyond what typical or rated core flow would be able to sustain. However, due to the lower power levels from low enrichment and neutron loss at peripheral and inner peripheral positions, the increased moderator/coolant flow in end of cycle conditions may be wasted on peripheral and inner peripheral positions and result in wet moderator with high moisture carryover to pass through the core through these positions. Example embodiment core 236 provides higher loss coefficients for increased core flow, and thus even less flow at end of cycle conditions using increased core flow, for fluid moderator/coolant through intermediate bundles with orifices at “3” and “4” locations, compared to conventional cores. In this way, example embodiment core 236 may further decrease moisture carry-over and increase steam quality and plant efficiency for plants operating with increased core flow to extend cycle life.
Other example embodiment core configurations are achievable with example embodiment fuel supports and individualized orifices therein. For example, as shown in scenarios 1-3 below in
The inventors compared example embodiment fuel supports and cores, with more than two different inlet orifice and thus bundle flow characteristics, with conventional cores having only two, central and peripheral, inlet orifice flow characteristics.
To generate the results of
The simulated channel flow and MCPR values for scenarios 1-5 were compared against the results of the simulated channel flow and MCPR values for the Reference Scenario, and the percentage change or value difference was graphed in
Example methods generate nuclear core configurations having customized fuel supports to achieve several different desired levels of coolant/moderator flow within the core. As shown in
Example methods including S100-S140 may be executed for each bundle location within a core or only a subset of bundle locations of interest. Alternatively, example methods may be executed only with respect to a particular bundle in order to, for example, optimize core operating characteristics or fix a limiting problem with respect to the particular bundle location. Similarly, example methods may be used as an integral part of core design or as a separate step performed alternatively and/or iteratively with other known methods of core design. For example, a known core design program may output a core map using fuel bundle characteristics and core parameters using uniform orifice configuration and associated flow loss coefficients. Example methods including S100-S140 may then be performed on some or all fuel bundle locations involved in the map, changing their operational characteristics including flow loss coefficient. The core design program may then be re-executed with the modified characteristics, and this core configuring involving example and other core optimization methods may continue until no further optimization is possible or desired. Or, example methods may be used as an integral part of otherwise known core design methods, treating flow loss coefficient parameters affected by orifice configuration as additional variables in the core design process. It is also recognized that one or more actions S100-S140 may be executed by different programs or parties in the fuel services and licensee context.
Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied through routine experimentation and without further inventive activity. For example, it is readily appreciated upon reading the above disclosure that other core configurations and fuel support shapes and capacities from the specific example embodiments described may be achieved. Variations are not to be regarded as departure from the spirit and scope of the example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
