TECHNICAL FIELD

This document relates to systems and methods for controlling a nuclear reaction in a nuclear reactor power system.

BACKGROUND

In nuclear reactors designed with passive operating systems, the laws of physics are employed to ensure that safe operation of the nuclear reactor is maintained during normal operation or even in an emergency condition without operator intervention or supervision, at least for some predefined period of time.

SUMMARY

In an example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a boron injection system positioned in the open volume of the containment vessel and including an amount of boron sufficient to stop the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state.

In an aspect combinable with the example implementation, the boron injection system includes a boron container sized to hold or enclose the amount of boron.

In another aspect combinable with any of the previous aspects, the boron container includes a openable enclosure that includes a latch actuatable by at least one of a temperature or a pressure.

In another aspect combinable with any of the previous aspects, the boron container includes a meltable or dissolvable member that encloses or surrounds the amount of boron.

In another aspect combinable with any of the previous aspects, the reactor vessel further includes at least one valve openable to fluidly couple the volume of the reactor vessel with the open volume of the containment vessel.

In another aspect combinable with any of the previous aspects, the at least one valve includes a reactor vent valve configured to vent a vaporized primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; and a reactor recirculation valve configured to circulate a mixture of the vented primary coolant and at least a portion of the amount of boron to the reactor core.

In another aspect combinable with any of the previous aspects, the amount of boron is in solution with a condensed form of the vented primary coolant.

In another aspect combinable with any of the previous aspects, the vaporized primary coolant is at at least one of a pressure or temperature sufficient to actuate the latch to release the amount of boron from the boron container into the open volume, or the vaporized primary coolant is at a temperature sufficient to melt or dissolve the member to release the amount of boron into the open volume.

In another aspect combinable with any of the previous aspects, the boron is solid boron in granular form.

In another aspect combinable with any of the previous aspects, the reactor vessel excludes control rod assemblies.

In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to generate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate the nuclear fission reaction, a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel, and a boron injection system positioned in the open volume of the containment vessel and including an amount of boron; initiating an emergency operation of the nuclear power system based on a loss of a primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; based on the emergency operation, releasing the amount of boron into the open volume of the containment vessel; circulating the amount of boron from the open volume of the containment vessel to the reactor core; and with the amount of boron, stopping the nuclear fission reaction or maintaining the nuclear fission reaction at a sub-critical state.

In an aspect combinable with the example implementation, releasing the amount of boron includes releasing the amount of boron from a boron container positioned in the open volume and sized to hold or enclose the amount of boron.

In another aspect combinable with any of the previous aspects, releasing the amount of boron from the boron container includes actuating a latch on the boron by at least one of a temperature or a pressure in the open volume of the containment vessel.

In another aspect combinable with any of the previous aspects, releasing the amount of boron from the boron container includes melting or dissolving at least a portion of the boron container based on a temperature in the open volume of the containment vessel.

Another aspect combinable with any of the previous aspects further includes, based on the emergency event, opening at least one valve on the reactor vessel to fluidly couple the volume of the reactor vessel with the open volume of the containment vessel.

In another aspect combinable with any of the previous aspects, opening at least one valve on the reactor vessel includes opening a reactor vent valve to vent a vaporized primary coolant from the volume of the reactor vessel to the open volume of the containment vessel; and opening a reactor recirculation valve to circulate a mixture of the vented primary coolant and at least a portion of the amount of boron to the reactor core.

In another aspect combinable with any of the previous aspects, the amount of boron is in solution with a condensed form of the vented primary coolant.

In another aspect combinable with any of the previous aspects, the vaporized primary coolant is at at least one of a pressure or temperature sufficient to actuate the latch to release the amount of boron from the boron container into the open volume, or the vaporized primary coolant is at a temperature sufficient to melt or dissolve the member to release the amount of boron into the open volume.

In another aspect combinable with any of the previous aspects, the boron is solid boron in granular form.

Another aspect combinable with any of the previous aspects further includes operating the nuclear power system to generate the nuclear fission reaction without any operation of control rod assemblies.

In another example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control rod assembly system positioned in the reactor vessel and configured to position a plurality of control rods in only two discrete positions, such that the plurality of control rods are fully withdrawn from the reactor core in a first discrete position of the only two discrete positions and the plurality of control rods are fully inserted into the reactor core in a second discrete position of the only two discrete positions.

In an aspect combinable with the example implementation, the control rod assembly is configured to adjust the plurality of control rods from the first discrete position to the second discrete position by at least one of releasing the plurality of control rods to fall to the second discrete position from the first discrete position; or forcibly urging the plurality of control rods from the first discrete position to the second discrete position.

In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state in the second discrete position.

Another aspect combinable with any of the previous aspects further includes a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of the control rod assembly system during a normal operation of the nuclear power system.

In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the power generation system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values.

In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust at least one of the turbine inlet steam valve or the feed water pump to adjust the power output of the nuclear fission reaction includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction, or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction; or decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction, or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction.

In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the chemical injection system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values

In another aspect combinable with any of the previous aspects, the operation of adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction.

In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to initiate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to initiate and maintain the nuclear fission reaction during a normal operation, a riser positioned above the reactor core, and a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction; transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power; and operating a control rod assembly system positioned in the reactor vessel to adjust a position of a plurality of control rods from a first discrete position of only two discrete positions to a second discrete position of the only two discrete positions, such that the plurality of control rods are fully withdrawn from the reactor core in the first discrete position and the plurality of control rods are fully inserted into the reactor core in the second discrete position.

In an aspect combinable with the example implementation, adjusting the plurality of control rods from the first discrete position to the second discrete position includes at least one of releasing the plurality of control rods to fall to the second discrete position from the first discrete position; or forcibly urging the plurality of control rods from the first discrete position to the second discrete position.

In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state in the second discrete position.

Another aspect combinable with any of the previous aspects further includes controlling a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

In another aspect combinable with any of the previous aspects, the nuclear power system further includes a chemical injection system in fluid communication with the primary coolant flow path.

Another aspect combinable with any of the previous aspects further includes controlling the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation.

Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values.

In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust at least one of the turbine inlet steam valve or the feed water pump to adjust the power output of the nuclear fission reaction includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction, or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction; or decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction, or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction.

Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values

In another aspect combinable with any of the previous aspects, adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction.

In another example implementation, a pressurized water reactor (PWR) includes a reactor module that includes a reactor vessel including a volume sized to enclose a reactor core, a riser, and a steam generator, and a containment vessel including a volume sized to enclose the reactor vessel; and a plurality of control rods mounted in the reactor vessel above the reactor core on a control rod manifold, the control rod manifold attached to a control rod actuator operable to release the control rod manifold to drop the plurality of control rods from a first position above the reactor core to a second position within the reactor core.

In an aspect combinable with the example implementation, the control rod actuator is inoperable to move the control rod manifold to move the plurality of control rods from the second position to the first position.

In another aspect combinable with any of the previous aspects, the plurality of control rods are sufficient to shut down a nuclear fission reaction or maintain the nuclear fission reaction generated by one or more nuclear fuel assemblies in the reactor core at a sub-critical state in the second position.

In another example implementation, a nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a riser positioned above the reactor core; a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; a primary coolant that circulates through the primary coolant flow path to receive heat from the nuclear fission reaction and release the received heat to generate electric power in a power generation system fluidly or thermally coupled to the primary coolant flow path; and a control system communicably coupled to the power generation system and configured to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

An aspect combinable with the example implementation further includes a chemical injection system in fluid communication with the primary coolant flow path, wherein the control system is communicably coupled to the chemical injection system and configured to control the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation.

In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the power generation system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values.

In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust the turbine inlet steam valve includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction; or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction.

In another aspect combinable with any of the previous aspects, the operation of controlling the power generation system to adjust the feed water pump includes at least one of decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction.

In another aspect combinable with any of the previous aspects, the control system is configured to perform operations to control one or more parameters of the chemical injection system including determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values

In another aspect combinable with any of the previous aspects, the operation of adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction.

In another example implementation, a method for controlling a nuclear fission reaction includes operating a nuclear power system to initiate a nuclear fission reaction, the nuclear power system including a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel, the reactor core including one or more nuclear fuel assemblies configured to initiate and maintain the nuclear fission reaction during a normal operation, a riser positioned above the reactor core, and a primary coolant flow path that extends from a bottom portion of the volume below the reactor core, through the reactor core, within the riser, and through an annulus between the riser and the reactor vessel back to the bottom portion of the volume; circulating a primary coolant through the primary coolant flow path to receive heat from the nuclear fission reaction; transferring the received heat into a power generation system fluidly or thermally coupled to the primary coolant flow path to generate electric power; and controlling a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation.

In an aspect combinable with the example implementation, the nuclear power system further includes a chemical injection system in fluid communication with the primary coolant flow path.

Another aspect combinable with any of the previous aspects further includes controlling the power output of the nuclear fission reaction independent of any control rod assemblies by controlling one or more parameters of at least one of the power generation system or the chemical injection system during normal operation.

Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, controlling the power generation system to adjust at least one of a turbine inlet steam valve or a feed water pump to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values.

In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust the turbine inlet steam valve includes at least one of adjusting the turbine inlet steam valve toward a fully closed position to decrease the power output of the nuclear fission reaction; or adjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction.

In another aspect combinable with any of the previous aspects, controlling the power generation system to adjust the feed water pump includes at least one of decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; or increasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction.

Another aspect combinable with any of the previous aspects further includes determining that the power output of the nuclear fission reaction is greater than an upper value or less than a lower value; based on the determination, adjusting an amount of a chemical injected into the reactor core from the chemical injection system to adjust the power output of the nuclear fission reaction; and subsequent to the adjustment, determining that the power output is within a range between the upper and lower values

In another aspect combinable with any of the previous aspects, adjusting the amount of the chemical injected into the reactor core from the chemical injection system includes at least one of increasing the amount of the chemical injected into the reactor core from the chemical injection system to decrease the power output of the nuclear fission reaction; or decreasing the amount of the chemical injected into the reactor core from the chemical injection system to increase the power output of the nuclear fission reaction.

In another example implementation, a pressurized water reactor (PWR) includes a control rod assembly-less reactor module that includes a reactor vessel including a volume sized to enclose a reactor core, a riser, and a steam generator without enclosing a control rod assembly system, and a containment vessel including a volume sized to enclose the reactor vessel; and a power generation system including a steam conduit in fluid communication with the steam generator, a steam turbine-generator, and a steam condenser.

In an aspect combinable with the example implementation, the volume of the reactor vessel is less than a volume of a conventional reactor vessel sized to enclose a control rod assembly system.

Another aspect combinable with any of the previous aspects further includes a control system communicably coupled to the reactor module and the power generation system, the control system configured to adjust a power output of one or more nuclear fuel assemblies in the reactor core by controlling at least one of a flowrate or pressure of a steam supply to the steam turbine generator or a flowrate or temperature of a feed water circulated from the steam condenser to the steam generator.

Another aspect combinable with any of the previous aspects further includes a passive boron injection system electrically decoupled from a Class1E power source that is electrically coupled to the reactor module.

In another aspect combinable with any of the previous aspects, the passive boron injection system is positioned in the volume of the containment vessel and fluidly isolated from the volume of the reactor vessel during normal operation of the reactor module.

In another aspect combinable with any of the previous aspects, the passive boron injection system is configured to release an amount of solid boron sufficient to shut down a nuclear fission reaction of the reactor module during an emergency core cooling system (ECCS) event.

Various implementations according to the present disclosure may include one, some, or all of the following features. For example, implementations of a nuclear power system according to the present disclosure eliminate control rod assemblies and associated systems in a reactor module, thereby eliminating cost and space associated with installing such systems in the reactor module (e.g., lower material and installation costs in money and time). Further, potential nuisance trips and safety related concerns associated with control rod assemblies need not be accounted for in a nuclear power system with no control rod assemblies and systems. As another example, reactor start-up and shutdown procedures may be more efficiently performed in a nuclear power system that includes no control rod assemblies. As yet another example, operating costs of the reactor module may be reduced for a reactor module with no control rod assemblies compared to convention reactor systems with control rod assemblies. As yet another example, normal operational power output adjustment of the reactor module may more efficiently rely on control of one or more components of a power generation system thermally coupled to the reactor module and/or one or more components of a chemical injection system of a reactor module.

The present disclosure also describes implementations of a nuclear power system that includes a binary position control rod assembly system. In some aspects, such a nuclear power system may have lower manufacturing and installation costs in money and time, because the binary position control rod assembly system may include less complex control and installation designs.

The present disclosure also describes implementations of a nuclear power system that includes a passive boron injection system. In some aspects, such a system may allow for and facilitate the elimination of control rod assemblies from a reactor module. In some aspects, such a system may allow for and facilitate the use of a binary position control rod assembly system within a reactor module. As another example, such a system may allow for a shutdown of the reactor module (e.g., of the nuclear fission reaction) even with a loss of power (e.g., Class 1E power). As another example, such a system may allow for and facilitate the elimination of active boron systems, including liquid holding tanks, piping, and associated controls, thereby reducing time and cost in manufacturing and commissioning the reactor module.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

