The proposed ultrasonic Reactor water Level Monitoring system is intended for monitoring water level in the hot leg of a nuclear reactor during Operation at Reduced Inventory (ORI) with the core in place as may be needed for certain maintenance activities. Since the existing fuel bundles continue the production of heat thorough the decay process, it is critical to maintain a certain water flow rate through the reactor. The Residual Heat Removal System (RHRS) handles this task during the reactor shutdown. The free water surface during ORI subjects the RHRS to the risk of air intake. Such an event would trigger a set of emergency procedures for priming the RHRS and bringing it back online. Some of the possible outcomes of such an event are: extension of outage, handling of the extra regulatory reporting tasks, potential requirements for extra testing after system recovery, possible damage to RHR pump, boiling of reactor water, generation of airborne contamination, and fuel damage. Another risk during ORI is reactor overflow. The major immediate concern is the safety of personnel in case of accidental overflow. This event could result in contamination and the related outage delays. The previously existing systems have always had problems with transducer reliability. This has lead to the need for removal and re-installation of their transducers from outage to outage. However, the proposed system uses a redundant design with permanently mounted transducers. The system uses advanced digital signal processing techniques to determine the water level.

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