Pressurized Water Reactor Control Rod Segmentation for Power Modulation
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Solution Overview
Problem
Existing methods for regulating the operating parameters of pressurized water nuclear reactors, such as temperature and axial power distribution, are limited in their ability to automatically control these parameters across a wide range of reactor power levels, especially when operating at high power, leading to constraints in power modulation and frequency adjustment.
Innovation Solution
A method that calculates and adjusts the average temperature setpoint of the primary coolant and axial power distribution by dividing control rods into sub-assemblies, using two control laws to manage boron concentration and rod positions, allowing for automatic regulation of temperature, axial power distribution, and ramp-up capacity across a broader power range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If control rods are permanently inserted in the lower part of the core to ensure control of axial power distribution, then axial power distribution control is improved, but the ability to automatically vary turbine power and operate in frequency adjustment is lost at high power levels
Solution Approach 1:
The control rod groups are divided into two distinct sub-assemblies: a control sub-assembly with groups that can be fully inserted and extracted for power modulation, and a heavy sub-assembly with groups permanently positioned in the lower core for axial power distribution control. This segmentation allows each sub-assembly to perform its specialized function independently, resolving the contradiction between maintaining axial control and enabling power modulation.
Solution Approach 2:
The function of axial power distribution control is extracted from the mobile control rod groups and assigned to a dedicated heavy sub-assembly with groups permanently positioned in the lower core. This extraction allows the main control sub-assembly to focus solely on power modulation and temperature control without the constraint of needing to maintain axial distribution control through permanent insertions.
2Power
If control rods are kept in the upper part of the core at high power, then power level operation is maintained, but automatic regulation of temperature and axial power distribution cannot be performed
Solution Approach 1:
By segmenting control rods into control sub-assembly groups (mobile) and heavy sub-assembly groups (permanently positioned), the system enables automatic regulation at high power through coordinated control of these sub-assemblies, eliminating the need to switch to manual operation modes.
Solution Approach 2:
The heavy sub-assembly acts as an intermediary that provides the necessary lower core control presence even when operating at high power with all control rods in the upper position. This intermediary structure enables automatic regulation functionality to be maintained across the full power range.
3Device complexity
If a single control law is used for regulation, then system simplicity is maintained, but effective control across the full power range including switchover zones is not achieved
Solution Approach 1:
The control system dynamically adapts by selecting between two control laws based on operating conditions. The first control law is used when control sub-assembly groups are inserted in the lower core, and the second control law is used when they are in the upper core. This dynamic adaptation enables effective automatic regulation across the entire power range, including the previously problematic switchover zones.
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
Enables efficient and automatic control of the reactor's operating parameters, including temperature, axial power distribution, and ramp-up capacity, even at high power levels, facilitating seamless power modulation and frequency adjustment without excessive stress on control rods.
Implementation Method 1
groups of control rods capable of being inserted into the core of the reactor... essentially comprising water and dissolved boron... The boron in solution in the primary liquid absorbs the neutrons emitted by the nuclear fuel assemblies
Implementation Method 2
The boron in solution in the primary liquid absorbs the neutrons emitted by the nuclear fuel assemblies, so that the reactivity of the core 10 drops when the boron concentration increases
Implementation Method 3
a core 10 producing a variable thermal power... nuclear fuel assemblies each comprise a bundle of very long tubes containing pellets of fissile material
Data Source
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Figure 3A~3C
AI summary
The method for controlling operating parameters of a nuclear reactor core (10) in pressurized water, comprises evaluating the actual values of operating parameters according to the acquired quantities of operating conditions of the reactor core, selecting a control law of an absorbent compound concentration and insertion positions of rods between first and second control laws, and controlling operating parameters using control laws according to a record regarding the parameters and actual evaluated values of the operating parameters. The method for controlling operating parameters of a nuclear reactor core (10) in pressurized water, comprises evaluating the actual values of operating parameters according to the acquired quantities of operating conditions of the reactor core, selecting a control law of an absorbent compound concentration and insertion positions of rods between first and second control laws, controlling operating parameters using control laws according to a record regarding the parameters and actual evaluated values of the operating parameters, calculating an average temperature record of a primary cooling of liquid in the core from a quantity of a power supplied to an electrical network through the reactor, distributing the rods in a sub-set for controlling the primary cooling of the liquid average temperature in the core and in a heavy subset, which ensures the control of the axial distribution of power, calculating displacements of the rods in a control sub-set according to a record and an actual value of the average temperature of primary cooling of the liquid in the core, modifying the insertion position of the rods in control sub-set according to the calculated displacements of the rod for regulating the average temperature of primary cooling of the liquid in the core, calculating displacements of the rods in a heavy sub-set according to a record and an actual value of the axial distribution of thermal power, and modifying the insertion position of the rods in heavy sub-set according to the calculated displacements for regulating the axial distribution of thermal output. The nuclear reactor comprises a reactor core divided into an upper and a lower zone and producing a thermal power, control rods of the core to immerse a multiple racked insertion positions vertically from a higher position in the core, unit for inserting rods in the core vertically, a primary circuit (30) ensuring a circulation of a liquid for primary cooling through the core, unit for adjusting a concentration of a neutron absorbing compound in the primary cooling, and unit for acquiring representative quantities of operating conditions of the reactor core. The controlled operating parameters comprise an average temperature of primary cooling of the liquid in the core, an axial distribution of thermal power between upper and lower zones of the core, and a parameter represents a reactor power increasing capacity, which is corresponds to a thermal power to be produced by the core. The first law is selected when a group of rods is in an insertion position, which is lower than a predetermined position of the rods, and the second law is selected reversely. The reactor power increasing capacity is determined from insertion positions of rods of the control sub-set. The controlling stage using the second control law comprises calculating a concentration of absorbent compound depending on the record value of operating parameters and the actual value of the axial distribution of thermal power, adjusting the concentration of absorbent compound in the primary cooling of the liquid to the calculated concentration for regulating the axial distribution of thermal power as the record value of the operating parameters, calculating the displacement to be performed for the rods of control subset and heavy subset according to the record and the actual value of insertion positions of the rods of control subset, and modifying the insertion positions of the rods of control subset and/or heavy subset according to the calculated displacement to maintain the rods of control subset in a deadband around the insertion position. The rods of control sub-set are sequentially inserted or extracted when a heating power produced by the core varies.