Westinghouse Electric Corporation

Westinghouse Electric Company LLC

Toshio Morita

Albert J Impink, Jr

Michael D Heibel

Raymond Calvo

Louis R Grobmyer

Charles L Beard, Jr

Robert E Sariscak

R Wade Miller

John L Duryea

A method is provided for evaluating pellet-cladding interaction (PCI) in a nuclear core having a reactor protection system and a plurality of elongated fuel rods each having fuel surrounded by cladding with a gap therebetween. The method includes: selecting a number of core parameters to be analyzed; evaluating the selected parameters at a plurality of statepoints; generating a model of an operating space of the core based, at least in part, upon the statepoints; selecting a subset or loci of statepoints from the model wherein each of the statepoints of the loci of statepoints, when subjected to a predetermined transient, falls within the operational limits of the reactor protection system; and evaluating the loci of statepoints for PCI in response to the transient. In this manner, the potential for PCI can be accurately determined without requiring every statepoint for every fuel rod in the core to be individually analyzed.

Method for analysis of pellet-cladding interaction

A safety system grade dropped rod detection system for a pressurized water reactor (PWR) utilizes core exit thermocouples arranged in multiple trains and hot and cold leg RTDs to generate a safety system grade rod stop signal. The system generates from the temperature signals a relative power deviation (RD) and a curvature index (CI), which is the spatial second derivative of RD for each fuel assembly. The CI signatures not only provide rapid, reliable detection of dropped control rods, but also clearly identify failed and failing thermocouples.

Safety system grade apparatus and method for detecting a dropped control

The present invention is a system that updates a pressurized water reactor core model, or data file describing the core, periodically using measured values determinable from core instrumentation. The system starts with a calibrated model calibrated from a flux map and a boron concentration measurement both determined monthly. Reactor system measurements are performed and the model is updated from the measurements using a standard depletion calculation. Some of the measured values are also used to determine measured actual values of axial offset and pinch. Standard neutronics equations are used to calculate analytical values of axial offset and pinch from the model, and the measured and calculated values are compared. If a deviation beyond a certain magnitude is detected, buckling coefficients in the model are adjusted to compensate for model drift. The updated model is stored and a time-out period is entered until it is time for another drift compensation cycle to start. The adjustment overcompensates the coefficients until the difference between the measured values and calculated values is slightly less in magnitude than the deviation but of an opposite sign. The adjusted and updated model can be used for accurate initial values of a core predictor or for display to the operator.

Reactor core model update system

A nuclear fuel rod cladding having a burnable absorber integrally incorporated therein has an outer tubular layer of a zirconium alloy; an intermediate layer, of a thickness less than the outer tubular layer, of a zirconium alloy containing a boron-containing burnable absorber; and an inner layer, of a thickness less than the intermediate layer, of zirconium metal. The layers are bonded together to form a cladding for the containment of nuclear fuel.

Nuclear fuel cladding containing a burnable absorber

This invention provides a method of operating a nuclear reactor with the object of maintaining a substantially symmetric axial xenon distribution during normal power operation including load follow. Variations in the xenon distribution are controlled by maintaining a substantially symmetric axial power distribution. Procedures are described for maintaining the axial offset value of the core, as an indicia of the axial power distribution, substantially equal to a target value, which is modified periodically to account for core burnup. In one embodiment a neutron absorbing element within the core coolant, or moderator, is employed to assist control of reactivity changes associated with changes in power with the full length control rods mainly employed to adjust variations in the axial power distribution, while the part length rods remain completely withdrawn from the fuel region of the core. In a second embodiment reactivity changes associated with changes in power are controlled by the full length rods, while the part length rods are used to adjust the axial power distribution and the neutron absorbing element within the core coolant or moderator is used to compensate for xenon buildup or depletion.

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Wilkinsburg, PA, United States of America

Toshio Morita