Abstract: A method and device is claimed for preventing reverse coolant flow in a BWR Power Reactor. The device comprises a screen that is free to move between a top plate and a bottom plate in a fuel assembly lower tie plate box. Flow holes are formed and aligned in the top plate and in the bottom plate, creating a path for reactor coolant. Disks at a bottom of the screen are aligned with the flow holes in the bottom plate, and are shaped and formed to cover flow holes in the bottom plate. When flow stagnates or reverses, the screen drops causing the disks to rest on the bottom plate blocking downward flow. Upstanding tabs at the top surface of the screen contact the top plate when normal coolant flow is in the upward direction, allowing flow through the flow holes in the top plate.

Abstract: A method of stabilizing density wave oscillations in boiling water reactor cores is disclosed. The invention introduced a thin metallic fuel element made of fissile isotope baring metal encased and bonded with metallic cladding. The thin construction and the metallic material guarantee very short thermal time constant compared with the oscillation period. Although the feedback of the processes involved in density waves are negative, i.e. oppose any initial perturbation, sufficiently strong feedback may result in unstable behavior because of the time delay inherent in the propagation of the density wave and the heat conduction delay in the traditional fuel rods made of ceramic pellets encased in zircaloy tubes. The new fuel element of this invention introduces fast, not delayed, thermal energy to the coolant in response of any neutron flux perturbation, and thus introduces a stabilizing feedback.

Abstract: This invention introduces a new method for detecting power oscillations that may occur in Boiling Water Reactor (BWR) cores. According to this invention, the Average Power Range Monitor (APRM) is enabled to detect power oscillations even when the signals from the Local Power Range Monitors (LPRMs) that make up the APRM signal are not in-phase and tend to cancel out. The asymmetric filtering algorithm that is the core of this invention is applied to the individual LPRM signals before they are summed up to make a new APRM signal. The new APRM signal will increase when oscillations occur, regardless of the instability type, and can thus be used for detecting reactor instability and enable the operator or automatic reactor protection systems to actuate and prevent reactor fuel damage.

Abstract: The present invention relates to boiling water reactors (BWR) disclosing a new method and device for preventing the flow and power oscillations from growing to severely large amplitudes thus protecting the reactor from the consequences of instabilities associated with the so-called anticipated transients without scram (ATWS). This invention introduces a new method for preventing boiling water reactor fuel damage due to the growth of unstable density wave oscillations to severely large magnitudes. The method limits the growth of the density waves by limiting the magnitude of the oscillation of the coolant mass flow rate at the inlet of the fuel bundle such that only upward flow is permitted.

Abstract: The present invention provides a method of operating a Boiling Water Reactor, having the steps of analyzing LPRM signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals; initiating a reactor protective corrective action if the oscilliatory behavior is determined, and in addition, initiating corrective actions if neutron uncoupled oscillations are possible. Detecting the later is performed through analytically determined exclusion zone on the power flow map or by on-line stability calculations for several high power channels.

Abstract: The present invention provides a method of operating a Boiling Water Reactor, having the steps of analyzing LPRM signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals; initiating a reactor protective corrective action if the oscilliatory behavior is determined, and in addition, initiating corrective actions if neutron uncoupled oscillations are possible. Detecting the later is performed through analytically determined exclusion zone on the power flow map or by on-line stability calculations for several high power channels.

Abstract: The present invention provides a method of operating a Boiling Water Reactor, having the steps of analyzing LPRM signals for oscilliatory behavior indicative of neutron-flux-coupled density wave oscillations, determining if oscilliatory behavior is present in the signals; initiating a reactor protective corrective action if the oscilliatory behavior is determined, and in addition, initiating corrective actions if neutron uncoupled oscillations are possible. Detecting the later is performed through analytically determined exclusion zone on the power flow map or by on-line stability calculations for several high power channels.

Abstract: A new design concept of boiling water reactor fuel assembly water channels is disclosed. The new design utilizes parallel flow paths guided inside an outer conduit without reversing flow. The different flow paths discharge water into the coolant stream, which is the objective of this invention, and resulting in improvements in thermal efficiency and stability of the fuel assembly. The thus diverted flow paths discharge water evenly into the coolant stream, which is the objective of this invention, with the result of improving the thermal efficiency and stability of the fuel assembly.

Abstract: A new design concept of boiling water reactor fuel rod is disclosed. The new design is characterized by an upward shift in the location of the fuel pellet stack inside the fuel cladding. The resulting axial power shift upward decreases two-phase and total pressure drop and has a stabilizing effect. A device for affecting such fuel pellet displacement is a crushable tube placed under the fuel pellet stack, which also helps to mitigate fuel-clad mechanical interaction and reduces the likelihood of clad failure.