Subcritical core reactivity bias projection technique
A method to determine a global core reactivity bias and the corresponding estimated critical conditions of a nuclear reactor core prior to achieving reactor criticality. The method first requires collection and evaluation of the inverse count rate ratio (ICRR) data; specifically, fitting measured ICRR vs. predicted ICRR data. The global core reactivity bias is then determined as the amount of uniform reactivity adjustment to the prediction that produces an ideal comparison between the measurement and the prediction.
1. A method of determining a global core reactivity bias for a nuclear reactor core and bringing the nuclear reactor core to a critical reactor state, the method comprising:
predicting a combination of parameters expected to yield the critical reactor state of the nuclear reactor core, wherein the parameters comprise control rod position, soluble boron concentration, and coolant temperature;
operating a nuclear reactor at a first subcritical state;
measuring, using a source range detector, a first measured neutron flux value while the nuclear reactor is operating at the first subcritical state;
adjusting the nuclear reactor to operate at a second subcritical state by repositioning at least one control rod of the nuclear reactor;
measuring, using the source range detector, a second measured neutron flux value while the nuclear reactor is operating at the second subcritical state;
predicting a first spatially-corrected neutron flux value for the first subcritical state and a second spatially-corrected neutron flux value for the second subcritical state;
comparing each of the measured neutron flux values with the corresponding spatially-corrected neutron flux values to determine the global reactivity bias;
wherein a spatial correction factor is not applied to the measured neutron flux values;
updating the predicted combination of parameters by adjusting at least one of the parameters according to the global reactivity bias; and
bringing the nuclear reactor core to the critical reactor state using the updated combination of parameters.
2. The method of claim 1 , further comprising performing a regression analysis to determine a relationship between the measured neutron flux values and the corresponding spatially-corrected neutron flux values to determine the global reactivity bias;
wherein the determined global reactivity bias is used to detect an anomaly associated with the nuclear reactor core without operating the reactor at a critical state.
3. The method of claim 1 , wherein the first subcritical state and the second subcritical state are steady-state conditions.
4. The method of claim 1 wherein the predicted combination of parameters are updated without operating the nuclear reactor at the critical reactor state.
5. The method of claim 1 , wherein operating the reactor at the first subcritical state occurs after an initial construction of the nuclear reactor.
6. The method of claim 1 , wherein operating the nuclear reactor at the first subcritical state occurs after a refueling of the nuclear reactor.
7. The method of claim 2 , wherein the anomaly associated with the nuclear reactor core is an anomalous reactivity behavior.
8. A processing device programmed to carry out the method of claim 1 .
9. A machine readable medium comprising instructions for carrying out the method of claim 1 .