Patent Number: 
Section: claims

1. A nuclear power system, comprising:a reactor vessel that comprises a reactor core mounted within a volume of the reactor vessel, wherein the reactor core comprises one or more nuclear fuel assemblies configured to generate a nuclear fission reaction, and wherein the reactor vessel does not include any control rod assemblies therein;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 coupled to the primary coolant flow path;a chemical injection system in fluid communication with the primary coolant flow path; anda control system communicably coupled to the power generation system and the chemical injection system, wherein the control system is configured to control a 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, and wherein the control system is configured to perform operations to control one or more parameters of the chemical injection system, the operations comprising: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; andsubsequent to the adjustment, determining that the power output is within a range. 2. The nuclear power system of claim 1, wherein the control system is further configured to perform operations to control one or more parameters of the power generation system comprising: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. 3. The nuclear power system of claim 2, wherein the operation of controlling the power generation system to adjust the turbine inlet steam valve comprises 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; oradjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction. 4. The nuclear power system of claim 2, wherein the operation of controlling the power generation system to adjust the feed water pump comprises at least one of:decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; orincreasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. 5. The nuclear power system of claim 1, further comprising:a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; anda boron injection system positioned in the open volume and comprising an amount of boron sufficient to stop the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state. 6. The nuclear power system of claim 5 wherein the boron injection system comprises a boron container sized to hold or enclose the amount boron, and wherein the boron container is configured to release the amount of boron directly into the open volume in response to at least one of a predetermined temperature and pressure within the open volume such that the amount of boron is in fluid communication with an inner surface of the containment vessel. 7. A nuclear power system, comprising:a reactor vessel that comprises a reactor core mounted within a volume of the reactor vessel, the reactor core comprising 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;a chemical injection system in fluid communication with the primary coolant flow path; anda control system communicably coupled to the chemical injection system, wherein the control system is configured to perform operations to control one or more parameters of the chemical injection system to control a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation, the operations comprising: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, wherein the operation of adjusting the amount of the chemical injected into the reactor core from the chemical injection system comprises 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; ordecreasing 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; andsubsequent to the adjustment, determining that the power output is within a range between the upper and lower values. 8. A method for controlling a nuclear fission reaction, comprising:operating a nuclear power system to initiate a nuclear fission reaction, the nuclear power system comprising:a reactor vessel that comprises a reactor core mounted within a volume of the reactor vessel, the reactor core comprising one or more nuclear fuel assemblies configured to initiate and maintain the nuclear fission reaction during a normal operation, wherein the reactor vessel does not include any control rod assemblies therein,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; anda chemical injection system in fluid communication with the primary coolant flow path;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; andcontrolling a power output of the nuclear fission reaction independent of any control rod assemblies during the normal operation by: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; andsubsequent to the adjustment, determining that the power output is within a range between the upper and lower values. 9. The method of claim 8, wherein adjusting the amount of the chemical injected into the reactor core from the chemical injection system comprises 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; ordecreasing 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. 10. The method of claim 8, wherein controlling the power output of the nuclear fission reaction further comprises: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. 11. The method of claim 10, wherein controlling the power generation system to adjust the turbine inlet steam valve comprises 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; oradjusting the turbine inlet steam valve toward a fully open position to increase the power output of the nuclear fission reaction. 12. The method of claim 10, wherein controlling the power generation system to adjust the feed water pump comprises at least one of:decreasing an output flowrate of the feed water pump to decrease the power output of the nuclear fission reaction; orincreasing the output flowrate of the feed water pump to increase the power output of the nuclear fission reaction. 13. A pressurized water reactor (PWR), comprising:a control rod assembly-less reactor module that comprises:a reactor vessel comprising a volume sized to enclose a reactor core, a riser, and a steam generator without enclosing a control rod assembly system, wherein the reactor core comprises one or more nuclear fuel assemblies configured to generate a nuclear fission reaction, and wherein the reactor vessel includes 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 chemical injection system in fluid communication with the primary coolant flow path; anda containment vessel comprising a volume sized to enclose the reactor vessel and the chemical injection system;a power generation system comprising a steam conduit in fluid communication with the steam generator, a steam turbine-generator, and a steam condenser; anda control system communicably coupled to the power generation system and the chemical injection system, wherein the control system is configured to control a 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, and wherein the control system is configured to perform operations to control one or more parameters of the chemical injection system, the operations comprising: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; andsubsequent to the adjustment, determining that the power output is within a range between the upper and lower values. 14. The PWR of claim 13, wherein the volume of the reactor vessel is less than a volume of a conventional reactor vessel sized to enclose a control rod assembly system. 15. The PWR of claim 13, wherein the control system is further configured to adjust the power output of the nuclear fission reaction 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. 16. The PWR of claim 15, further comprising a passive boron injection system electrically decoupled from a Class 1E power source that is electrically coupled to the reactor module. 17. The PWR of claim 16, wherein 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. 18. The PWR of claim 17, wherein 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.