Isolation condenser systems for nuclear reactor commercial electricity generation

Nuclear reactors include isolation condenser systems that can be selectively connected with the reactor to provide desired cooling and pressure relief. Isolation condensers are immersed in a separate chamber holding coolant to which the condenser can transfer heat from the nuclear reactor. The chamber may selectively connect to an adjacent coolant reservoir for multiple isolation condensers. A check valve may permit coolant to flow only from the reservoir to the isolation condenser. A passive switch can operate the check valve and other isolating components. Isolation condensers can be activated by opening an inlet and outlet to/from the reactor for coolant flow. Fluidic controls and/or a pressure pulse transmitter may monitor reactor conditions and selectively activate individual isolation condensers by opening such flows. Isolation condenser systems may be positioned outside of containment in an underground silo with the containment, which may not have any other coolant source.

BACKGROUND

FIG. 1is a schematic of a containment building36that houses a reactor pressure vessel42with various configurations of fuel41and reactor internals for producing nuclear power in a related art economic simplified boiling water reactor (ESBWR). Reactor42is conventionally capable of producing and approved to produce several thousand megawatts of thermal energy through nuclear fission. Reactor42sits in a drywell51, including upper drywell54and a lower drywell3that provides space surrounding and under reactor42for external components and personnel. Reactor42is typically several dozen meters high, and containment building36even higher above ground elevation, to facilitate natural circulation cooling and construction from ground level. A sacrificial melt layer1, called a basemat-internal melt arrest and coolability device, is positioned directly below reactor42to cool potential falling debris, melted reactor structures, and/or coolant and prevent their progression into a ground below containment36.

Several different pools and flowpaths constitute an emergency core coolant system inside containment36to provide fluid coolant to reactor42in the case of a transient involving loss of cooling capacity in the plant. For example, containment36may include a pressure suppression chamber58surrounding reactor42in an annular or other fashion and holding suppression pool59. Suppression pool59may include an emergency steam vent used to divert steam from a main steam line into suppression pool59for condensation and heat sinking, to prevent over-heating and over-pressurization of containment36. Suppression pool59may also include flow paths that allow fluid flowing into drywell54to drain, or be pumped, into suppression pool59. Suppression pool59may further include other heat-exchangers or drains configured to remove heat or pressure from containment36following a loss of coolant accident. An emergency core cooling system line and pump10may inject coolant from suppression pool59into reactor42to make up lost feedwater and/or other emergency coolant supply.

As shown inFIG. 1, a gravity-driven cooling system (GDCS) pool37can further provide coolant to reactor42via piping57. A passive containment cooling system (PCCS) pool65may condense any steam inside containment36, such as steam created through reactor depressurization to lower containment pressure or a main steam line break, and feed the condensed fluid back into GDCS pool37. An isolation cooling system (ICS) pool66may take steam directly at pressure from reactor42and condense the same for recirculation back into rector42. These safety systems may be used in any combination in various reactor designs, each to the effect of preventing overheating and damage of core41, reactor42and all other structures within containment36by supplying necessary coolant, removing heat, and/or reducing pressure. Several additional systems are typically present inside containment36, and several other auxiliary systems are used in related art ESBWR. Such ESBWRs are described in “The ESBWR Plant General Description” by GE Hitachi Nuclear Energy, Jun. 1, 2011, incorporated herein by refence in its entirety, hereinafter referred to as “ESBWR.”

SUMMARY

Example embodiments include simplified nuclear reactors with an isolation condenser system connecting to the nuclear reactor through integrally isolatable connections that have a minimal risk of leakage or failure. In this way, example nuclear reactors may be effectively completely isolated from the isolation condenser system. Example embodiment isolation condenser systems include one or more isolation condensers immersed in a segregated coolant such that the condenser can transfer heat to the immersive coolant when receiving a working coolant or moderator from the nuclear reactor. The immersive coolant can be drawn from a separate coolant reservoir that supplies one or more separate isolation condensers. Barriers may prevent flow between the various isolation condensers; for example, a check valve may permit coolant to flow only from the reservoir to the isolation condenser and separate the two if the immersive coolant level becomes too high, too hot, too radioactive, etc. about the isolation condenser. A switch can passively monitor coolant level between the isolation condenser and reservoir, selectively permitting flow based on relative elevation of floats in the reservoir and coolant surrounding the isolation condenser. Movement of the floats may actuate the check valve and/or the isolation condenser itself. Isolation condensers in example systems can be activated by opening a fluid loop through the condenser to/from the reactor. For example, fluidic controls and/or a pressure pulse transmitter may monitor reactor conditions and selectively activate individual isolation condensers, trip and/or isolate the reactor, and/or trip the rest of the plant based on detected reactor pressures, coolant levels, etc. Such passive and reliable sensors may place the plant in a safe shutdown condition with indefinite cooling capacity if operations divert from design bases. Example embodiment isolation condenser systems may be positioned outside of containment in an underground silo with the containment, which may not have any other coolant source.

DETAILED DESCRIPTION

Because this is a patent document, general, broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may 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 examples set forth herein.

It will be understood that, although the ordinal terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship. 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 or methods. As used herein, the term “and/or” includes all combinations of one or more of the associated listed items. The use of “etc.” is defined as “et cetera” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s).

It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. 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 and routing between two electronic 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. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, characteristics, steps, operations, elements, and/or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and/or groups thereof.

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 single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments.

The inventors have recognized that conventional auxiliary or emergency coolant systems typically require powered, digital controls to activate and operate in nuclear reactors. Such emergency systems typically require pumps and/or active valves and monitors for proper operation. With several, diverse coolant systems, complex logic and controls may be required to achieve activation protocols and selectively activate individual safety systems. These systems are typically positioned inside containment for immediate reactor access, requiring a large and complex containment. To overcome these newly-recognized problems as well as others, the inventors have developed example embodiments and methods described below to address these and other problems recognized by the inventors with unique solutions enabled by example embodiments.

The present invention is isolation cooling systems, plants containing the same, and methods of operating such systems and plants. 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.

FIG. 2is a schematic of an example embodiment reactor system100including example embodiment reactor142, example embodiment containment136, and related cooling and power generation systems. System100is similarly described in co-owned application Ser. No. 15/585,162 to Hunt, Dahlgren, and Marquino, filed May 2, 2017 for VERY SIMPLIFIED BOILING WATER REACTORS FOR COMMERCIAL ELECTRICITY GENERATION and incorporated by reference herein in its entirety. Although not shown inFIG. 2, example embodiment system100is useable with conventional and known power generating equipment such as high- and low-pressure turbines, electrical generators, switchyards, condensers, cooling towers or heat sinks, etc., which may connect, for example to main feedwater line120and main steam line125in a similar fashion to any power generation facility. Example embodiment containment136is composed of resilient, impermeable material for limiting migration of radioactive material and plant components in the case of a transient or accident scenario. For example, containment136may be an integrally-formed concrete structure, potentially with reinforcing internal steel or rebar skeleton, several inches or feet thick. Or, for example, as discussed below, because containment136may be relatively smaller, an all-steel body may be used without being prohibitively expensive or complexly-fabricated, to enhance strength, radiation shielding, and lifespan of containment136.

As shown inFIG. 2, example embodiment containment136may be underground, potentially housed in a reactor silo190. A concrete lid191or other surface shield level with, or below, ground90may enclose silo190housing example embodiment reactor142and containment136. Silo190and lid191may be seismically isolated or hardened to minimize any shock wave encountered from the ground and thus minimize impact of seismic events on reactor142and systems in silo190such as example ICS300and/or control system165. If underground as shown inFIG. 2, example embodiment system100may present an exceedingly small strike target and/or be hardened against surface impacts and explosions. Further, if underground, example embodiment system100may have additional containment against radioactive release and enable easier flooding in the case of emergency cooling. Although not shown, any electricity-generating equipment may be connected above ground without loss of these benefits, and/or such equipment may also be placed below ground.

Based on the smaller size of example embodiment reactor142discussed below, example embodiment containment136may be compact and simplified relative to existing nuclear power plants, including the ESBWR. Conventional operating and emergency equipment, including a GDCS, PCCS, suppression pools, Bimacs, backup batteries, wetwells, torii, etc. may be wholly omitted from containment136. Containment136may be accessible through fewer access points as well, such as a single top access point under shield191that permits access to reactor142for refueling and maintenance. The relatively small volume of example embodiment reactor142and core141may not require a bimac for floor arrest and cooling, because no realistic scenario exists for fuel relocation into containment136; nonetheless, example embodiment containment136may have sufficient floor thickness and spread area to accommodate and cool any relocated core in its entirety, as shown inFIG. 2. Moreover, total penetrations through containment136may be minimized and or isolated to reduce or effectively eliminate risk of leakage from containment136.

Example embodiment reactor142may be a boiling-water type reactor, similar to approved ESBWR designs in reactor internals and height. Reactor142may be smaller than, such as one-fifth the volume of, ESBWRs, producing only up to 600 megawatts of electricity for example, with a proportionally smaller core141, for example operating at less than 1000 megawatt-thermal. For example, example embodiment reactor142may be almost 28 meters in height and slightly over 3 meters in diameter, with internals matching ESBWR internals but scaled down proportionally in the transverse direction to operate at approximately 900 megawatt-thermal and 300 megawatt-electric ratings. Or, for example, reactor142may be a same proportion as an ESBWR, with an approximate 3.9 height-to-width ratio, scaled down to a smaller volume. Of course, other dimensions are useable with example embodiment reactor142, with smaller height-to-width ratios such as 2.7, or 2.0, that may enable natural circulation at smaller sizes or proper flow path configuration inside the reactor.

Keeping a relatively larger height of example embodiment reactor142may preserve natural circulation effects achieved by known ESBWRs in example embodiment reactor142. Similarly, smaller reactor142may more easily be positioned underground with associated cooling equipment and/or possess less overheating and damage risk due to smaller fuel inventory in core141. Even further, smaller example embodiment reactor142with lower power rating may more readily satisfy modular power or peaking power demands, with easier startup, shutdown, and/or reduced power operations to better match energy demand.

A coolant loop, such as main feedwater line120and main steam line125, may flow into reactor142to provide moderator, coolant, and/or heat transfer fluid for electricity generation. An emergency coolant source, such as one or more example embodiment isolation condenser systems (ICS)300, may further provide emergency cooling to reactor142in the instance of loss of feedwater from line120. Example embodiment ICS300may include steam inlet162from example embodiment reactor142and condensate return163to reactor142. Each of these connections to reactor142may use isolation valves200that are integrally connected to reactor142inside containment136and represent negligible failure risk.

Aside from valves200, example embodiment containment136may be sealed about any other valve or penetration, such as power systems, instrumentation, coolant cleanup lines, etc. The fewer penetrations, smaller size, lack of systems inside, and/or underground placement of containment136may permit a higher operating pressure, potentially up to near reactor pressures of several hundred, such as 300, psig without any leakage potential.

As seen in example embodiment reactor system100, several different features permit significantly decreased loss of coolant probability, enable responsive and flexible power generation, reduce plant footprint and above-ground strike target, and/or simplify nuclear plant construction and operation. Especially by using known and approved ESBWR design elements with smaller volumes and core sizes, example embodiment reactor142may still benefit from passive safety features such as natural circulation inherent in the ESBWR design, while allowing a significantly smaller and simplified example embodiment containment136and reliance on passive isolation condensers166for emergency heat removal.

FIG. 3is an illustration of an example embodiment ICS300useable in example embodiment plant100. As shown inFIG. 3, example embodiment ICS300may include multiple isolation condensers310,320, etc. in fluid connection with a large reservoir or ICS pool301. Although only a first isolation condenser310and a second isolation condenser320are shown inFIG. 3, it is understood that any number of isolation condenser(s) may feed from ICS pool301. Each isolation condenser310and320may include its own ICS chambers311and321with independent coolant control and levels that may be replenished by ICS pool301. Because ICS300may be outside of any containment, ICS pool301, isolation condensers310and320, and any other component of ICS300may be easily reached for maintenance, inspection, emergency refill, and/or operation, regardless of plant state.

As shown inFIG. 3, each isolation condenser310and320may be fed by steam inlet162providing steam produced in the nuclear reactor. The steam may pass down through heat exchanger312in isolation condenser310transferring heat to a fluid, such as water, in chamber311that condenses the steam back to liquid water. Condensate return line163then allows this condensed water to flow back into the reactor, driven by gravity, steam inertia, and density gradient between the steam and condensed water. Isolation condensers310and320may use a double, split loop through two, multi-channel heat exchangers312as shown inFIG. 3, or use other known designs, such as ICS designs from approved ESBWR plants or others.

If installed in an example embodiment plant system100(FIG. 2) using a lower-thermal-power reactor, such as in the lower hundreds-megawatt-thermal range, a single isolation condenser310may have cooling capacity for the entire reactor. That is, isolation condensers310and320may each be able to condense a full volume of steam produced by an example embodiment lower power reactor to maintain a steady liquid level in the same. Similarly, isolation condensers may have lower and/or varying capacities and be used in any number to provide a margin of safety, such as four total condensers each with a condensing capacity of 75% total core flow for a 3× safety margin.

Although each isolation condenser310and320is shown with its own steam line162and condensate return line163, it is understood that actual supply and return may branch from a shared steam162and condensate return163line, so as to require only a single isolation valve200(FIG. 2) for all of ICS300having multiple isolation condensers310,320. Control of each isolation condenser may be individualized as discussed below through valves on steam line162and/or condensate return line163. Or, first isolation condenser310and second isolation condenser320may each use an individual steam line162and condensate return line163with separate isolation valves200, such as in the example ofFIG. 2.

Because each isolation condenser310and320may use its own chamber311and321, respectively, coolant levels may be maintained for each, despite drawing from a common pool301. For example, check valves340between pool301and chamber311may permit only one-way flow from pool301into chamber311. In this way, evaporation or boil-off from chamber311may be replenished from pool301without necessarily lowering or affecting levels in other chamber321. Similarly, if chamber311is at a higher fill level, check valves340may not allow coolant to flow out into pool301.

Passive switch330may detect when an ICS chamber should be isolated via check valve340or other connections to pool301, without active or DCIS controls. Passive switch330may further indicate when an isolation condenser311,321, etc. should be deactivated. For example, passive switch330may use two floats,331, one in pool301and another in ICS chamber311. As floats move on the surface of the coolant, such as liquid water, they may move a position of switch330when joined on either side of a pivot. If coolant level in ICS chamber311is lower than pool301, this may be reflected in positioning of floats331, and switch330may open (shown by an arrow) check valve340between floats331and keep isolation condenser310active and ICS chamber311replenished. Or for example, as coolant level in ICS chamber321exceeds a level in pool301, this may indicate malfunction or rupture in isolation condenser320where reactor coolant may be entering ICS chamber321. Floats331in an opposite vertical relative positioning in this circumstance may close switch330, which may close check valve340(shown by an X) and potentially deactivate or isolate isolation condenser320to prevent further reactor leakage and/or coolant flow into ICS chamber321and pool301.

Although floats331are used by passive switch330inFIG. 3, it is understood that other passive or low-failure-mode devices can be used to detect abnormal or undesired conditions of isolation condensers and their chambers. For example, relative pressure detectors, radiation detectors, level-based coolant contact actuators, temperature monitors, etc. may all signal that an isolation condenser should be removed from service and/or cut-off from common coolant sources such as pool301. Similarly, passive switch330or another detector may detect additional ICS cooling or condensation is necessary, such as if chamber321has approached boiling, and activate additional isolation condensers. Aside from check valves340, additional isolating structures may be actuated upon detection of undesired operating conditions in example embodiment ICS300, such as inoperable or leaking isolation condenser320requiring isolation of chamber321. Additional modes of activating and deactivating isolation condensers310and320are discussed below in connection withFIG. 4.

FIG. 4is an illustration of an example embodiment selective activation and isolation system165. As seen inFIG. 2, example embodiment system165may connect to or be interfaced with reactor142, valves200, ICS300, and/or containment136to control operation of the same. As seen inFIG. 4, activation and isolation system165may include multiple fluidic controls166A,166B, etc. each interfaced with an isolation condenser310,320, etc. Although only two fluidic controls and two isolation condensers are shown inFIG. 4, it is understood that any number may be used. Fluidic controls166A and166B may connect to reactor142through a shared pressure line143. Pressure line143may extend through containment with appropriate penetration seal or fluidic controls166may be inside containment.

At a pressure setpoint in pressure line143, which reflects pressure in reactor142, fluidic control166A may activate isolation condenser310. The pressure setpoint may be a high pressure associated with reactor overheat or isolation from feedwater or turbine loss, for example. Fluidic control166A may be configured to directly actuate a valve, rupture an accumulator, passively use reactor pressure to open a valve, and/or otherwise reliably open a coolant loop to isolation condenser310at the setpoint. As shown inFIG. 4, the actuated valve may be a valve on the condensate return line163; for example, the valve may be an isolation valve200(FIG. 2) connecting condensate return line163to reactor142or another valve dividing individual isolation condensers from such a line. Fluidic control166A may further actuate a valve on steam inlet162, or it is also possible that steam inlet162is always open to isolation condenser310, such that opening only a single valve for condensate return163causes flow through isolation condenser310, already at reactor pressure to prevent water hammer.

Another fluidic control166B may open a valve associated with another isolation condenser320at the setpoint. Or, for example, fluidic control166B may have a higher pressure activation setpoint, such that isolation condenser320is only activated if the setpoint for activation of fluidic control166A for isolation condenser310has already been activated. For example, isolation condenser310may be leaking or not working, as determined by passive switch330(FIG. 3), which may re-close the valve opened by fluidic control166A, deactivate fluidic control166A, close another valve such as a steam inlet valve for condenser310, or otherwise take isolation condenser310offline. If isolation condenser310is inadequate, inoperable, or deactivated, pressure in reactor142may rise again without any cooling or condensing system, particularly if reactor142(FIG. 2) is isolated by isolation valves200in the event of a transient. Eventually the pressure will rise to the higher setpoint of fluidic control166B, which will activate isolation condenser320and provide pressure relief and cooling. This setup may be repeated for any number or independently-operable fluidic controls166at any number of different, desired pressure setpoints, to provide a throttled and redundant amount of heat removal and condensation to reactor142.

As shown inFIG. 4, pressure pulse transmitter167is interfaced with reactor142through a reactor fluid line144. Pressure pulse transmitter167may similarly activate one or all isolation condensers310,320, etc. Pressure pulse transmitter167may be a passive instrument that detects water level in reactor142and can, through hydraulic pressure, open and/or close any valve, including isolation valves200, to activate isolation condenser310and/or320, isolate reactor142from main steam line125, isolate reactor142from main feedwater line120, etc. Pressure pulse transmitter167may be of a type described in “Passive Pressure Pulse Transmitter” by Areva, incorporated herein by reference in its entirety, or another known type of pressure pulse transmitter.

Pressure pulse transmitter167may actuate valves based on water level in reactor142instead of pressure. As such, pressure pulse transmitter167may offer an alternative and independent metric of reactor functionality and safety on which to trigger safety functions. For example, pressure pulse transmitter167may detect an abnormal water level approaching a top of the reactor core or fuel, at which point all isolation condensers310,320, etc. may be activated by opening valves associated with the same. Or, for example, pressure pulse transmitter167may be configured with several water level setpoints to selectively activate or turn off systems, such as isolation condenser310at a first low reactor coolant level, isolation condenser320at a second lower reactor coolant level, etc. Still further, pressure pulse transmitter167may deactivate isolation condensers310,320, etc. or shut ICS valves on a condensate return line163or steam inlet162at detection of a high reactor coolant level.

As shown inFIG. 4, fluidic controls166and/or pressure pulse transmitter167in example embodiment selective activation and isolation system165may also interface with isolation valves200that isolate reactor142from main feedwater line120and/or main steam line125, in addition to valves associated with isolation condensers310,320. Control connections168are used to illustrate operative control over the various valves controlling flow to isolation condensers, main steam, feedwater, etc.; it is understood that control connections may be contained in a single body with fluidic controls and manipulated valve or may be an actuator line or other powered connection that opens or closes the valve, for example. Similarly, fluidic controls166and/or pressure pulse transmitter167may use control logic to selectively open or close combinations of valves to place a plant in a desired configuration. For example, along with actuation of ICS300, isolation valves200for main feedwater120and main steam outlet125may be closed to isolate reactor142by a single fluidic control166A or transmitter167. Or, different fluidic controls166may place the plant in differing configurations including triggering a reactor scram and/or main turbine trip, based on worsening detected pressure.

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 coolants and fuel types are compatible with example embodiments and methods simply through proper operating and fueling 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.