Gravity-Driven Boric Acid Injection for BWR Core Cooling
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Solution Overview
Problem
In boiling water nuclear reactors, the gravity-driven emergency core cooling system (ECCS) faces challenges in maintaining a subcritical state during anticipated transients without scram (ATWS) incidents, where the boric acid aqueous solution injection is diluted by the large volume of water from the gravity-driven ECCS, potentially leading to core re-criticality and increased reactor pressure.
Innovation Solution
A boiling water nuclear reactor design incorporating a gravity-driven water injection pool holding boric acid aqueous solution at a higher position, with an emergency core water-injection piping system allowing the boric acid solution to fall and inject into the reactor pressure vessel, combined with a static containment vessel cooling system and gas vent pipe to manage pressure and prevent core re-criticality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a large volume of water is injected by the gravity-driven ECCS to cool the core, then the cooling effect is improved, but the boric acid aqueous solution is diluted and the core may become re-critical
Solution Approach 1:
The invention divides the water injection function into two separate systems: (1) the gravity-driven ECCS for emergency core cooling, and (2) the boric acid injection system for maintaining subcritical state. This segmentation allows each system to perform its specific function independently without interfering with the other, thus resolving the contradiction between cooling effectiveness and boric acid concentration maintenance.
Solution Approach 2:
The invention introduces a separate boric acid injection system as an intermediary mechanism that specifically addresses the neutron absorption requirement. This intermediary system ensures that boric acid is injected independently of the cooling water injection, maintaining the subcritical state while the ECCS performs its cooling function without dilution concerns.
2Device complexity
If the gravity-driven ECCS is used to maintain subcritical state, then the simplicity of the system is improved, but the boric acid concentration cannot be maintained during ATWS incidents
Solution Approach 1:
The invention segments the safety systems into distinct functional units: the gravity-driven ECCS for cooling and the separate boric acid injection system for reactivity control. This segmentation maintains overall system simplicity while ensuring that each subsystem can independently fulfill its specific safety function without compromise.
Solution Approach 2:
The invention creates a multi-functional safety system where the boric acid injection system serves the universal purpose of maintaining subcritical state across all accident scenarios (LOCA, ATWS, etc.), while the gravity-driven ECCS provides universal cooling capability. This multi-functionality approach ensures comprehensive safety coverage without requiring complex integrated control mechanisms.
3Temperature
If water is injected to raise the water level in the reactor pressure vessel, then the core cooling is improved, but the internal pressure of the reactor containment vessel increases
Solution Approach 1:
The invention changes the physical parameters of the injected substance from pure water to boric acid aqueous solution. This parameter change serves dual purposes: the water component provides the necessary cooling effect by raising the water level, while the boric acid component maintains neutron absorption capability. Additionally, the system controls the injection rate and timing to manage pressure rise within acceptable limits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively maintains the reactor in a subcritical state during ATWS and LOCA events, preventing core damage and excessive pressure rises by ensuring high boric acid concentration and efficient cooling, thus enhancing reactor safety.
Implementation Method 1
a gravity-driven water injection pool holding boric acid aqueous solution arranged at a position higher than the core to cause the boric acid aqueous solution to fall by gravity
Implementation Method 2
a static containment vessel cooling system heat exchanger arranged in the static containment vessel cooling system pool
Data Source
AI summary
A boiling water nuclear reactor comprises: a reactor containment vessel including a dry well and a wet well; a vent pipe connecting the dry well and the pressure suppression pool; a gravity-driven water injection pool to hold boric acid aqueous solution; an emergency core water-injection piping system for causing the boric acid aqueous solution in the gravity-driven water injection pool to fall so as to be injected into the reactor pressure vessel in case of reactor accident; a static containment vessel cooling system pool; a static containment vessel cooling system heat exchanger; a dry well connection pipe connecting an upper part of the static containment vessel cooling system heat exchanger and the dry well; and a gas vent pipe for discharging noncondensible gas in the static containment vessel cooling system heat exchanger into the inside of the pressure suppression pool.