Patent Number: 
Section: claims

1. A reactor oscillation power range monitor comprising:a receiving unit which receives local power range monitor (LPRM) signals generated from a plurality of LPRM detectors provided in a reactor core, the LPRM detectors distributed over the entire reactor core into several groups in a regular manner, each group classified as a cell and each of the LPRM signals allocated to a specified cell;an exclusion processing unit which searches the LPRM signals allocated to each cell for an LPRM signal corresponding to an exceptional condition, wherein the exceptional condition determines a LPRM signal unsuitable for a power oscillation monitoring;an averaging unit which averages the allocated LPRM signals for each of the cells by excluding the LPRM signals corresponding to the exceptional condition and outputs an average flux value;a time averaging unit which calculates a time average of the average flux value and outputs a time averaged flux value;a normalized value calculation unit which divides the average flux value by the time averaged flux value and outputs a normalized value;an initialization unit which outputs an initialization signal when a value of an LPRM signal changes to correspond or not correspond to the exceptional condition, the initialization signal identifying the cell allocated to the LPRM signal;a determination unit which derives at least one of amplitude and cycle of the power oscillation from the normalized value and performs determination of nuclear thermal hydraulic instability based on a predetermined algorithm; andin response to the initialization signal, the normalized value calculation unit outputs a constant value instead of the normalized value of the cell identified by the initialization signal. 2. The reactor oscillation power range monitor according to claim 1, wherein the determination unit is configured to initialize the predetermined algorithm in response to the initialization signal. 3. The reactor oscillation power range monitor according to claim 1, wherein the normalized value calculation unit is configured to continue outputting the constant outputted in response to the initialization signal until at least all LPRM signals subjected to calculation of the normalized value become the same. 4. The reactor oscillation power range monitor according to claim 1, further comprising a timing control unit which causes the determination unit to initialize the algorithm during a period in which the constant continues to be outputted from the normalized value calculation unit. 5. The reactor oscillation power range monitor according to claim 4, whereinthe timing control unit sets the period in which the constant continues to be outputted from the normalized value calculation unit. 6. A reactor power oscillation monitoring method comprising the steps of:receiving local power range monitor (LPRM) signals generated from a plurality of LPRM detectors provided in a reactor core, the LPRM detectors distributed over the entire reactor core into several groups in a regular manner, each group classified as a cell and each of the LPRM signals allocated to a specified cell;searching the LPRM signals allocated to each cell for an LPRM signal corresponding to an exceptional condition;outputting an average flux value by averaging the allocated LPRM signals for each of the cells by excluding the LPRM signals corresponding to the exceptional condition, wherein the exceptional condition determines a LPRM signal unsuitable for a power oscillation monitoring;outputting a time averaged flux value by calculating a time average of the average flux value;outputting a normalized value by dividing the average flux value by the time averaged flux value;outputting an initialization signal identifying the cell allocated to an LPRM signal having a value which changes to correspond or not correspond to the exceptional condition; andperforming determination based on a predetermined algorithm by deriving at least one of amplitude and cycle of the power oscillation from the normalized value of nuclear thermal hydraulic instability.