Subcritical Reactivity Monitor Utilizing Prompt Self-Powered Incore Detectors

Abstract

A subcritical reactivity monitor that utilizes one or more primarily gamma sensitive (prompt responding) self-powered detector style radiation measurement devices located within the core of a nuclear reactor to determine the amount that the reactor multiplication factor (Keff) is below the reactivity required to achieve or maintain a self-sustaining nuclear chain reaction. This invention utilizes measured changes in the self-powered detectors' current(s) to allow a reactor operator to measure the value of Keff at essentially any desired interval while the reactor is shutdown with a Keff value less than the critical value of 1.0. This invention will enable integration of the output of the value of Keff directly into the Reactor Protection System, which will enable the elimination of the operational and core design analysis constraint costs associated with the current Boron Dilution Accident prevention methodology and enable automatic control of the Chemical Volume Control System.

Description

BACKGROUND1. Field[0001]This invention relates to conditions in a nuclear-fueled power-generating unit, and more particularly, to methods and apparatus for determining the effective neutron multiplication factor in a nuclear reactor.2. Related Art[0002]The primary side of nuclear power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are conne...

AI Technical Summary

Benefits of technology

The invention describes a nuclear reactor system with a pressure vessel housing a nuclear core and coolant. The system includes fuel assemblies with gamma sensitive, self-powered neutron detectors that respond to the fission reaction activity in the core and generate an output indicative of it. A subcritical reactivity monitor receives the output and calculates a core average value of gamma radiation distribution. A processing system receives the core average value and calculates a value of Keff based on a specific equation. A chemical volume control system receives the value of Keff and triggers a signal to add Boron to the coolant in the event of a predetermined, undesirable change in Keff. The system also includes a source range detector for monitoring fission events in the core when the reactor is below criticality. The chemical volume control system automatically adds Boron to the coolant in the event of a predetermined, undesirable change in Keff. Overall, the invention provides improved monitoring and control of the nuclear reactor system.

Problems solved by technology

This support column arrangement assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability.

Such fission and ionization chambers are capable of operation at all normal power levels, however, they are generally not sensitive enough to accurately detect low level neutron flux emitted in the source range.

However, that patent does not address the approach to criticality when a reactor approaches criticality due to withdrawal of control rods.

Currently, there is no direct method for measuring when criticality will occur from the source range ex-core detectors.

Therefore, estimating the conditions under which the plant will go critical from the ICRR curve is subject to much uncertainty, but also subject to considerable scrutiny by the Nuclear Regulatory Commission and International Nuclear Power Organization.

This behavior makes it difficult for the reactor operator to use the source range detector information properly.

However, this solution is still an estimate and does not raise confidence as to the estimate of the closeness to criticality which can be used to establish automatic control of the reactor's Chemical Volume Control System that will assure the reactor system remains below criticality.

While such detector elements provide a direct measure of neutron flux, which in turn is directly related to core power, the materials of this type which are more responsive to neutrons are fairly rapidly depleted.

While the gamma sensitive elements are not depleted by the neutron flux, they require complex electronics or reactor physics methods to provide a measure of reactor power distribution.

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