Nuclear Reactor Depressurization Blocking Device
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Solution Overview
Problem
The automatic depressurization system in pressurized water nuclear reactors can be spuriouly actuated under normal conditions, leading to unnecessary flooding of the reactor containment and potential severe accidents, as it lacks a mechanism to differentiate between normal and accident scenarios.
Innovation Solution
A blocking device is integrated into the depressurization system that prevents automatic depressurization when the core makeup tanks are full, using sensors to monitor tank levels and only allow depressurization when the tanks are drained, ensuring that the system acts only during critical loss of coolant events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the automatic depressurization system is activated to remove decay heat during shutdown, then the reactor core cooling capability is improved, but the system may be spuriouly actuated under normal conditions causing unnecessary flooding and potential severe accidents
Solution Approach 1:
The patent applies preliminary action by pre-positioning blocking devices in the depressurization system that automatically prevent actuation unless specific accident conditions are met. The blocking devices are installed in advance to block normal depressurization paths, and only when coolant level sensors detect actual loss of coolant conditions do the blocks remove, allowing depressurization to proceed. This preliminary blocking mechanism ensures the system remains inert under normal conditions while being ready to activate during true accidents.
Solution Approach 2:
The patent uses blocking devices as intermediary elements between the coolant loss detection system and the depressurization system. These blocking devices act as mediators that translate sensor signals into appropriate system responses - remaining in place during normal operation to prevent spurious actuation, and removing only when genuine accident conditions are detected, thereby controlling the flow of activation signals through the safety system.
2Device complexity
If the depressurization system uses passive gravity-driven water injection, then the system complexity and pump requirements are reduced, but the system requires substantial pressure reduction to enable gravity flow from the water storage tank
Solution Approach 1:
The patent applies segmentation by dividing the depressurization process into multiple staged steps with different pressure thresholds. Rather than requiring complete depressurization to atmospheric pressure before gravity flow can begin, the system is segmented into stages: first stage depressurization to an intermediate pressure level, then activation of gravity-driven injection, with additional depressurization stages following. This segmentation allows gravity injection to commence at higher pressures than full atmospheric pressure would require.
Solution Approach 2:
The patent applies preliminary action by pre-establishing gravity-driven flow paths and positioning water storage tanks at elevated locations before accidents occur. The passive injection system is pre-configured with tanks positioned to provide sufficient gravitational head pressure, and blocking devices are pre-positioned to control when these pre-established paths become active. This preliminary preparation allows the system to transition to passive gravity-driven operation without requiring active pumping during the actual accident response.
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
This solution reduces the frequency of spurious actuations of the automatic depressurization system, minimizing the risk of unnecessary flooding and ensuring the system remains operational during true accident scenarios by preventing actuation under normal conditions.
Implementation Method 1
A blocking device is connected to the depressurization system for preventing the depressurization system from activating when coolant within the core makeup tank is above a preselected level
Implementation Method 2
A series of valves 72 couple the reactor outlet 56 to the inside of the containment shell 54. When initially commencing the pressurization, the coolant circuit 46 and the containment structure 54 are coupled by the depressurization valve 72 through one or more small conduits 76 along a flow path with not insubstantial back pressure
Implementation Method 3
Inasmuch as the in-containment refueling water storage tank drains by gravity, no pumps are required. Draining the water into the bottom of the containment building where the reactor vessel is located, develops a fluid pressure head of water in the containment sufficient to force water into the depressurized coolant circuit
Implementation Method 4
Water in the form of steam escaping from the reactor coolant circuit is condensed on the inside walls of the containment shell, and drained back to be injected again into the reactor coolant circuit
Data Source
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AI summary
A blocking device for preventing the actuation of an automatic depressurization system in a pressurized nuclear reactor system due to spurious signals resulting from a software failure. The blocking signal is removed when the coolant level within the core makeup tanks drop below a predetermined level.