Improvements on Power Calibration and Core Monitoring at the Penn State Breazeale Reactor
Open Access
- Author:
- Corak, Gokhan
- Graduate Program:
- Nuclear Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 09, 2022
- Committee Members:
- William Walters, Co-Chair & Dissertation Advisor
Marek Flaska, Major Field Member
Kenan Unlu, Co-Chair & Dissertation Advisor
Jeffrey A Geuther, Special Member
Douglas Wolfe, Outside Unit & Field Member
Arthur Motta, Professor in Charge/Director of Graduate Studies - Keywords:
- MCNP
FMESH
PSBR
Penn State Breazeale Reactor
Power Correction
Fission Matrix Method
ADVANTG
Detector Response
Fission Chamber
Gamma Ion Chamber
Compensated Ion Chamber - Abstract:
- Accurate measurements of the power level in a nuclear reactor are important for several reasons. First, the maximum allowable power is limited by regulations for safety reasons, and the reactor should always be maintained below that limit. Second, the power (and thus total neutrons produced by the reactor) is needed to accurately model experiments. Finally, the burnup (energy released per unit mass) of the fuel should be accurately quantified for fuel management purposes. Different detector types measure the reactor power level in Penn State Breazeale Reactor (PSBR), which includes both neutron and gamma-ray measurements which includes fission chambers, gamma ion chamber, and compensated ion chamber and outputs of these detectors are calibrated using PSBR Checks and Calibration Procedures (CCP), specifically thermal power calibration (CCP-2). The power calibration is performed with the reactor operating at the〖 D〗_2 O tank, which should cause a flux tilt away from the detectors, and thus the lowest possible signal. This ensures that the displayed power is never underestimated than the power at other experimental locations. Energy deposition for the above-mentioned detectors is assumed linear during the calibration procedure but detector power levels may show different power outputs in some cases. The first goal of this thesis is to investigate the behavior of the above-mentioned detectors in different temperatures and power levels while incorporating control rod movements, as well as the location of the reactor core near any experimental fixtures (e.g., at the Fast Neutron Irradiator and D2O tank). The effect on the neutron flux shape due to the control rod position is investigated, along with how neutron flux shape affects the behavior of the detectors. Control rod movement significantly affects the neutron flux distribution inside the reactor core, especially in asymmetrical insertion and withdrawal of the control rods. Since these detectors are located at fixed positions outside of the reactor core, Self-Powered Neutron Detectors (SPND) and a miniature fission chamber are investigated computationally to estimate neutron flux in different positions around and within the reactor core due to their small size. The small size is an advantage, allowing them to be placed closer to the reactor core. Later, an experiment conducted with a Westinghouse WL-7186 miniature fission chamber by placing it inside the central thimble at low power and asymmetrical control rod movement was investigated and results showed that asymmetric control rod movement has a significant effect on detectors depending on their location. MCNP 6.2 and Serpent 2 were used in the computational analysis of the behavior of the neutron and gamma transportation as well as the response of the above-mentioned detectors. Detector responses were created for each detector and each core locality incorporating the MCNP FMESH method on various reactor power. The D2O Tank 1000 kW was the case assumed base case for these calculations and a correction is applied for each detector. For non-D2O core locations, the power is overestimated by up to 5.9 %. At lower power, the non-linearity in the detector response due to control rod movement results in up to 7.5 % error. Based on these results, a cubic fitting for the power was made for each core location to correct the observed power. Later, cubic curve fitting was applied to the detector responses to estimate true power in any reactor power for D2O tank, R1 open pool, FNI, and FFT experimental locations. This will allow for more accurate modeling of experiments and better knowledge about fuel utilization. Finally, detector responses were applied to the logbook laptop at PSBR to estimate corrected reactor powers for each case and fuel burnup. In current applications, fuel burnup is calculated by the reactor console. Logbook laptop burnup correction showed that for the core loading 59, a 3.7% difference in burnup was calculated using corrected power. In the future, the power correction method should be applied to the reactor console burnup calculation.