It is essential in commercial reactors that the safety limits imposed on the fuel pellets and fuel clad barriers, such as the linear power density (LPD) and the departure from nucleate boiling ratio (DNBR), are not violated during reactor operations. In order to accurately monitor the safety limits...
It is essential in commercial reactors that the safety limits imposed on the fuel pellets and fuel clad barriers, such as the linear power density (LPD) and the departure from nucleate boiling ratio (DNBR), are not violated during reactor operations. In order to accurately monitor the safety limits of current reactor states, a detailed three-dimensional (3D) core power distribution should be estimated from the in-core detector signals. In this paper, we propose a calculation methodology for detailed 3D core power distribution, using in-core detector signals and core monitoring constants such as the 3D Coupling Coefficients (3DCC), node power fraction, and pin-to-node factors. Also, the calculation method for several core safety parameters is introduced. The core monitoring constants for the real core state are promptly provided by the core design code and on-line MASTER (Multi-purpose Analyzer for Static and Transient Effects of Reactors), coupled with the core monitoring program. through the plant computer, core state variables, which include reactor thermal power, control rod bank position, boron concentration, inlet moderator temperature, and flow rate, are supplied as input data for MASTER. MASTER performs the core calculation based on the neutron balance equation and generates several core monitoring constants corresponding to the real core state in addition to the expected core power distribution. The accuracy of the developed method is verified through a comparison with the current CECOR method. Because in all the verification calculation cases the proposed method shows a more conservative value than the best estimated value and a less conservative one than the current CECOR and COLSS methods, it is also confirmed that this method secures a greater operating margin through the simulation of the YGN-3 Cycle-1 core from the viewpoint of the power peaking factor for the LPD and the pseudo hot pin axial power distribution for the DNBR calculation.
It is essential in commercial reactors that the safety limits imposed on the fuel pellets and fuel clad barriers, such as the linear power density (LPD) and the departure from nucleate boiling ratio (DNBR), are not violated during reactor operations. In order to accurately monitor the safety limits of current reactor states, a detailed three-dimensional (3D) core power distribution should be estimated from the in-core detector signals. In this paper, we propose a calculation methodology for detailed 3D core power distribution, using in-core detector signals and core monitoring constants such as the 3D Coupling Coefficients (3DCC), node power fraction, and pin-to-node factors. Also, the calculation method for several core safety parameters is introduced. The core monitoring constants for the real core state are promptly provided by the core design code and on-line MASTER (Multi-purpose Analyzer for Static and Transient Effects of Reactors), coupled with the core monitoring program. through the plant computer, core state variables, which include reactor thermal power, control rod bank position, boron concentration, inlet moderator temperature, and flow rate, are supplied as input data for MASTER. MASTER performs the core calculation based on the neutron balance equation and generates several core monitoring constants corresponding to the real core state in addition to the expected core power distribution. The accuracy of the developed method is verified through a comparison with the current CECOR method. Because in all the verification calculation cases the proposed method shows a more conservative value than the best estimated value and a less conservative one than the current CECOR and COLSS methods, it is also confirmed that this method secures a greater operating margin through the simulation of the YGN-3 Cycle-1 core from the viewpoint of the power peaking factor for the LPD and the pseudo hot pin axial power distribution for the DNBR calculation.
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제안 방법
cases without signal errors. Also, the values of the proposed method are a little more conservative than the reference values but are less conservative than the COLSS values when the random normal distribution signal errors are applied. Thus, the proposed method secures a larger operating margin than the current COLSS and CECOR methods.
Most commercial power reactors have some type of fixed or movable in-core detectors and ex-core detectors. Also, these facilities are equipped w辻h an on-line or off-line core power or flux distribution monitoring program to estimate the 3D power distribution by a combined use of detector signals and pre-calculated monitoring constants. For example, the YGN-3 pressurized water reactor (PWR) [1], 卄le first ABB Combustion Engineering (ABB-CE) PWR in Korea, has self powered rhodium fixed in-core neutron detectors installed at 45 fuel assem비y (FA) sites on five axial levels.
The four cases are: the YGN-3 Cycle-1 all rod out (ARO) cores at the beginning of the cycle (BOC) at 100 % power; the mid이e of the cycle (MOC) at 100 % power; the end of the cycle (EOC) at 100 % power; and a case in which control rods were inserted at EOC at 70 % power with axially skewed power distribution. As such, we calculated 3D power distribution using the 4 nodes-per-fuel assembly (N/A) nonlinear Analytical Nodal Method (ANM) and assumed it to be the true 3D power distribution. We used the nodal powers at the instrumented nodes to simulate the 225 detector box powers from the 4 N/A reference calculations.
ECOMS calculates the Limiting Conditions for Operation (LCOs) in이uding the LPD, DNBR, power of the whole core, the quadrant power tilt, the axial power deviation, and so forth. It compares the calculated values and the limiting ones, and provides alarms so that a plant operator can effectively monitor the operating states of the core and can maintain the core states within a range of limited operating conditions.
Then, the simulated detector box signals are constructed using the 3D nodal powers at the instrumented nodes from the reference 3D power distribution. Finally, a comparison of the monitored 3D power distribution and the reference is made to establish the prediction accuracy of the proposed method. To validate the proposed method, one may 니se the detector measurements instead of the simulated detector box signals.
In order to investigate the effect of the detector reading errors, the normal distribution signal errors, with a zero mean and 10 % three sigma (3(了=10%, RMS = 3%), are randomly applied to the simulated detector signals and are compared to the 3D power distribution based on the proposed method. Because it is known that the uncertainty of the in-core detector readings is about 3.
In this paper, a method of generating 3D power information for core monitoring coupled with the core design code is introduced. The proposed method was examined by purely numerical experiments for the core power distribution calculation in the YGN-3 Cycle-1, the first ABB-CE PWR in Korea.
In this paper, the methodology of generating 3D power information for core monitoring by using detector signals and several core monitoring constants, such as the 3D Coupling Coefficients (3DCC) and the pin-to-node factors, is st나died and the core monitoring program ECOMS is developed. The 3DCC and several core monitoring constants for peak power calculation are provided promptly by the core design code, MASTER (Multi-purpose Analyzer for Static and Transient Effects of Reactors) [14], which is on line and is coupled with the core monitoring program.
The MASTER code calculates the local heterogeneous fuel pin power distrib니tions in each axial segment within a FA. The calculation is performed by modulation of the local homogeneous distrib니tions based on the pin power reconstruction method and heterogeneous power form functions describing the fine structure of the assembly. The form hinctions are prepared from a lattice code while an effective cross section is generated.
Based on the detailed 3D power distribution data, ECOMS also calculates the power peaking factor (Fq) for the LPD, the pseudo hot pin axial power distribution for the DNBR calculation, the quadrant power tilt, the axial power deviation, and so forth. The developed method is verified through a simulation of the YGN-3 Cycle-1 core from the viewpoint of 3D power distribution, the Fq, and the pseudo hot pin axial power distribution.
MASTER analyzes the steady-state and transient core behaviors. The major calculation modules for the design application consist of depletion, steady state flux, transient flux, pin power, pin burnup, xenon dynamics, adjoint flux, thermal hydraulics, and design-specific activities like fuel management. MASTER performs microscopic depletion calculations using microscopic cross sections and also has the pin information reconstruction capability.
The method introduced in this paper was examined by p냐rely numerical experiments for core power distribution calculations in the YGN-3 Cycle-1, the first ABB-CE PWR in Korea with fixed in-core rhodium detectors installed at the 45 FA locations on five axial levels. For the numerical experiment, reference 3D power distributions in the YGN-3 Cycle 1 core are calculated by the MASTER code and are presumed to be the true 3D power distributions.
design code is introduced. The proposed method was examined by purely numerical experiments for the core power distribution calculation in the YGN-3 Cycle-1, the first ABB-CE PWR in Korea. The proposed method exactly reproduces the reference power distribution and the power peaking factors when no signal errors are assumed.
To verify the proposed method, the core 3D power distribution, the core power peaking factor, and the pseudo hot pin axial power distrib니tion for four different core states was conducted. Results were compared with those of MASTER and of ECOMS by using the simulated detector signals.
이론/모형
Based on the MASTER result of 卄le local pin power reconstruction, the peak pin power in each FA is calc니lated using a pin-to-node factor ikz in the proposed method.
MASTER performs microscopic depletion calculations using microscopic cross sections and also has the pin information reconstruction capability. Its neutronics model solves the space time dependent neutron diffusion equations with modern nodal methods. It is a multi-purpose and multi-function integrated code that is designed to provide fuel pin information and detailed T/H conditions.
The 3DCC and several core monitoring constants for peak power calculation are provided promptly by the core design code, MASTER (Multi-purpose Analyzer for Static and Transient Effects of Reactors) [14], which is on line and is coupled with the core monitoring program.
성능/효과
Each signal error is multiplied to the simulated detector signal and the signal value is changed as much as the amount of the error. Although the random normal distribution signal errors with a zero mean and 10 % three sigma are applied, the 3D power distribution of ECOMS is reproduced within the maximum 1.6 % RMS error. The CECOR method, however, shows a maximum error of 5.
A consistent case without signal errors and a case with signal errors are compared for one core state. For all the consistent cases without signal errors, the 3D node power distribution errors are 0 % in the proposed method but the errors in the CECOR method are higher than 2%. These errors for the consistent cases come from the Fourier expansion of axial power distribution.
In all cases, the Fq value and the pseudo hot pin axial power distribution of the proposed method show 이ightly more conservative values than the reference values but they show less conservative values than those of the current CECOR and COLSS methods. Thus, it is confirmed that the developed methodology can secure a greater operating margin than the current CECOR and COLSS methods.
후속연구
To validate the proposed method, one may 니se the detector measurements instead of the simulated detector box signals. However, considering that not only the true power distribution but also the exact core states, such as the isotopic composition and thermal-hydraulic conditions at the time of monitoring, are always unknown, it is exceptionally difficult to isolate the prediction errors of the proposed method and, therefore, it is hard to make a fair evaluation of the validity of the method. For this reason, pure numerical experiments were examined to validate the proposed method.
참고문헌 (14)
Final Safety Analysis Report for YGN Unit 3 & 4, Korea Electric Power Company
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'Overview Description of the Core Operation Limit Supervisory System (COLSS),' CEN-312-P, Revision 01-P, .ABB Combustion Engineering Inc, Nov. 1986
Final Safety Analysis Report for Wolsung Unit 1, Korea Electric Power Company
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