Annular Neutron Stop for Reactor Cavity Shielding
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Solution Overview
Problem
Nuclear reactors generate high neutron fields that escape into reactor cavities, posing risks to radiation-sensitive equipment and personnel located above the reactor core due to neutron reflectivity and cavity design, which channels neutrons upward into potentially hazardous regions.
Innovation Solution
An annular neutron stop comprising neutron-absorbing materials is positioned above the reactor core to block neutrons from escaping into the reactor cavity, using a combination of high-temperature and standard neutron-absorbing materials arranged in rings to effectively reduce neutron leakage, with additional measures like neutron plugs and check valves to prevent leakage through penetrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If neutron reflectors are disposed around the reactor core to retain neutrons, then neutron concentration inside the core is improved, but neutron concentration outside the reactor pressure vessel increases
Solution Approach 1:
The patent introduces an intermediate neutron shielding structure between the reactor pressure vessel and the surrounding environment. This intermediary component absorbs excess neutrons that escape the core, preventing them from reaching external areas while maintaining the reflector's neutron retention function. The shielding acts as a mediator that resolves the contradiction by capturing the harmful neutron leakage without compromising the beneficial neutron retention.
Solution Approach 2:
The patent extracts the harmful neutron flux from the system by introducing a dedicated neutron absorption zone. This extracted region captures the neutrons that would otherwise propagate outward, separating the useful neutron population (inside the core) from the harmful leakage (outside the vessel). The extraction mechanism removes the harmful factor while preserving the beneficial neutron economy within the reactor core.
2Ease of operation
If the reactor cavity design allows for equipment and personnel access above the reactor core, then operational flexibility is improved, but neutron radiation exposure to equipment and personnel increases
Solution Approach 1:
The patent introduces a neutron shielding structure as an intermediary barrier between the high-radiation reactor core region and the equipment/personnel access areas. This intermediary shielding layer allows operational flexibility and access while blocking the harmful neutron radiation, enabling equipment and personnel to function in the upper regions without direct exposure to the intense neutron field generated by the core.
Solution Approach 2:
The patent converts the harmful neutron radiation that would otherwise expose equipment and personnel to a beneficial configuration by directing it into a dedicated absorption zone. The neutron flux that would be a hazard is instead channeled into the shielding structure where it is absorbed, transforming the harmful radiation into a contained phenomenon that protects rather than exposes the surrounding environment.
3Object-affected harmful factors
If neutron-absorbing materials are placed in the reactor cavity to reduce neutron fields, then radiation protection is improved, but the complexity of the reactor structure increases
Solution Approach 1:
The patent merges the neutron shielding function with existing structural components of the reactor cavity. Rather than adding completely separate shielding elements, the neutron-absorbing materials are integrated into the cavity structure itself, combining the protective function with the structural support function. This merging approach reduces overall structural complexity while achieving the desired neutron field reduction.
Solution Approach 2:
The patent designs the reactor cavity structure to serve multiple functions: structural support, neutron shielding, and radiation protection. The cavity structure is made multi-functional by incorporating neutron-absorbing materials that provide both mechanical support and neutron absorption, eliminating the need for separate dedicated shielding components and thereby reducing overall system complexity.
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
Significantly reduces neutron fields in upper regions by a factor of one million, protecting equipment and personnel from harmful radiation exposure while maintaining reactor operation and safety during loss of coolant accidents.
Implementation Method 1
The annular neutron stop comprises neutron absorbing material filling an annular gap between the reactor pressure vessel and the wall of the reactor cavity
Data Source
AI summary
A nuclear reactor includes a reactor pressure vessel and a nuclear reactor core comprising fissile material disposed in a lower portion of the reactor pressure vessel. The lower portion of the reactor pressure vessel is disposed in a reactor cavity. An annular neutron stop is located at an elevation above the uppermost elevation of the nuclear reactor core. The annular neutron stop comprises neutron absorbing material filling an annular gap between the reactor pressure vessel and the wall of the reactor cavity. The annular neutron stop may comprise an outer neutron stop ring attached to the wall of the reactor cavity, and an inner neutron stop ring attached to the reactor pressure vessel. An excore instrument guide tube penetrates through the annular neutron stop, and a neutron plug comprising neutron absorbing material is disposed in the tube at the penetration through the neutron stop.