Regional Overpower Protection Systems Research Articles

Incorporating single detector failure into the ROP detector layout optimization for CANDU reactors

In CANDU® reactors, the regional overpower protection (ROP) systems are designed to protect the reactor against overpower in the fuel which could reduce the safety margin-to-dryout. In the CANDU® 600MW (CANDU 6) design, there are two ROP systems in the core, each of which is connected to a fast-acting shutdown system. Each ROP system consists of a number of fast-responding, self-powered flux detectors suitably distributed throughout the core within vertical and horizontal flux detector assemblies. The placement of these ROP detectors is a challenging discrete optimization problem. In the past few years, two algorithms, DETPLASA and ADORE, have been developed to optimize the detector layout for the ROP systems in CANDU reactors. These algorithms utilize the simulated annealing (SA) technique to optimize the placement of the detectors in the core. The objective of the optimization process is typically either to maximize the TSP value for a given number of detectors in the system or to minimize the number of detectors in the system to obtain a target TSP value. One measure to determine the robustness of the optimized detector layout is to evaluate the maximum decrease (penalty) in TSP value when any single detector in the system fails. The smaller the penalty, the more robust the design is. Therefore, in order to ensure that the optimized detector layout is robust, the single detector failure (SDF) criterion has been incorporated as an additional constraint into the ADORE algorithm. Results from this study indicate that there is a significant reduction in the TSP penalty value of the optimized solution, as a result of incorporating SDF criterion during the optimization process.

IMPROVING REGIONAL OVERPOWER PROTECTION TRIP SET POINT VIA CHANNEL OPTIMIZATION

In recent years, a new algorithm has been introduced to perform the regional overpower protection (ROP) detector layout optimization for CANDU ® reactors. This algorithm is called DETPLASA. This algorithm has been shown to successfully come up with a detector layout which meets the target trip set point (TSP) value. Knowing that these ROP detectors are placed in a number of safety channels, one expects that there is an optimal placement of the candidate detectors into these channels. The objective of the present paper is to show that a slight improvement to the TSP value can be realized by optimizing the channelization of these ROP detectors. Depending on the size of the ROP system, based on numerical experiments performed in this study, the range of additional TSP improvement is from 0.16%FP (full power) to 0.56%FP.

ADORE-GA: Genetic algorithm variant of the ADORE algorithm for ROP detector layout optimization in CANDU reactors

The regional overpower protection (ROP) systems protect CANDU® reactors against overpower in the fuel that could reduce the safety margin-to-dryout. The overpower could originate from a localized power peaking within the core or a general increase in the global core power level. The design of the detector layout for ROP systems is a challenging discrete optimization problem. In recent years, two algorithms have been developed to find a quasi optimal solution to this detector layout optimization problem. Both of these algorithms utilize the simulated annealing (SA) algorithm as their optimization engine. In the present paper, an alternative optimization algorithm, namely the genetic algorithm (GA), has been implemented as the optimization engine. The implementation is done within the ADORE algorithm. Results from evaluating the effects of using various mutation rates and crossover parameters are presented in this paper. It has been demonstrated that the algorithm is sufficiently robust in producing similar quality solutions.

Utilization of reduced fuelling ripple set in ROP detector layout optimization

The ADORE (Alternative Detector layout Optimization for REgional overpower protection system) algorithm for performing the optimization of regional overpower protection (ROP) for CANDU® reactors has been recently developed. This algorithm utilizes the simulated annealing (SA) stochastic optimization technique to come up with an optimized detector layout for the ROP systems. For each history in the SA iteration where a particular detector layout is evaluated, the goodness of this detector layout is measured in terms of its trip set point value which is obtained by performing a probabilistic trip set point calculation using the ROVER-F code. Since during each optimization execution thousands of candidate detector layouts are evaluated, the overall optimization process is time consuming. Since for each ROVER-F evaluation the number of fuelling ripples controls the execution time, reducing the number of fuelling ripples will reduce the overall execution time. This approach has been investigated and the results are presented in this paper. The challenge is to construct a set of representative fuelling ripples which will significantly speedup the optimization process while guaranteeing that the resulting detector layout has similar quality to the ones produced when the complete set of fuelling ripples is employed.

Evaluating the robustness of the ADORE algorithm for ROP Detector Layout Optimization

The ADORE (Alternative Detector layout Optimization for REgional overpower protection system) algorithm for performing the optimization of regional overpower protection (ROP) systems for CANDU® reactors has been recently developed. The simulated annealing (SA) stochastic optimization technique is utilized within this algorithm to come up with an optimized detector layout for the ROP systems. In the implementation of the SA algorithm, there are several SA-related parameters which can be varied to assist the optimization process toward the desired solution. However, it is required that the algorithm be independent of these parameters and be able to consistently produce solutions with similar qualities. Only then can the algorithm be considered robust. The robustness of the ADORE algorithm has been evaluated and the results are presented in this paper.

ADORE: Alternative detector layout optimization for ROP system of CANDU reactors

In CANDU ® reactor design, the regional overpower protection (ROP) systems protect the reactor against overpower in the fuel which could reduce the safety margin-to-dryout. Specifically for the CANDU ® 600 MW (CANDU 6) design, there are two ROP systems in the core, one for each fast-acting shutdown systems. Each ROP system includes a number of fast-responding, self-powered flux detectors suitably distributed throughout the core within vertical and horizontal assemblies. The placement of these ROP detectors is a challenging discrete optimization problem. The DLO (detector layout optimization) module of ROVER-F code was used to design the existing ROP detector layout of CANDU 6 reactors. In the past couple of years, a new methodology for designing the detector layout for the ROP system, called DETPLASA algorithm, has been developed. This method utilizes the simulated annealing (SA) technique to optimize the placement of the detectors in the core. This algorithm was developed to overcome the shortcoming of DLO method to produce a detector layout configuration when the size of the problem is large. An alternative method has been recently developed for solving the ROP detector placement problem. This method is called ADORE ( Alternative Detector layout Optimization for REgional overpower protection system). Although technically any stochastic optimization technique can be utilized, presently this method utilizes the SA technique as its optimization engine. This paper presents an overview of ADORE methodology and provides some numerical results from its execution.

The importance of uncertainties in the ROP detector layout design process for CANDU reactors

In CANDU® reactor design, the regional overpower protection (ROP) systems protect the reactor against overpower in the fuel which could reduce the safety margin-to-dryout. The increase in fuel power could be caused by a localized power peaking within the core (for example, as a result of a certain reactivity device configuration) or a general increase in the core power level during a slow-loss-of-regulation (SLOR) event. This overpower could lead to fuel sheath dryout. In the CANDU® 600 MW (CANDU 6) design, there are two ROP systems in the core, one for each fast-acting shutdown system. Each ROP system includes a number of fast-responding, self-powered flux detectors suitably distributed throughout the core within vertical and horizontal assemblies. A new methodology for designing the detector layout for the ROP system, called the DETPLASA algorithm, has been developed recently. This method utilizes the simulated annealing (SA) technique to optimize the placement of the detectors in the core. The evaluation of the trip setpoint (TSP) corresponding to each detector layout configuration ( i.e., each history in the SA algorithm) is performed probabilistically using the ROVER-F code. In this evaluation, there are uncertainties related to both the detector components ( i.e., related to the margin-to-trip) and to the fuel channel components ( i.e., related to the margin-to-dryout). In this paper, the importance of these uncertainties on the outcome of the detector layout optimization process is evaluated. Some parametric studies have been performed to quantify the effect of uncertainties on the resulting detector layout. Two types of investigations have been performed. First, a given detector layout will be used to explicitly determine the effect of changing the uncertainty values. In this study, 343 sets of uncertainty values are used to produce the corresponding TSP values. The variation in the TSP values is analyzed. Second, three sets of uncertainty values (a subset of uncertainties from the first study) are used in independent DETPLASA executions. The resulting detector layout configurations will be examined to observe the effect of these uncertainties on the final design. Results from these investigations are presented in this paper.

Methodologies for optimizing ROP detector layout for CANDU® reactors

The regional overpower protection (ROP) systems protect CANDU® reactors against overpower in the fuel that would reduce the safety margin-to-dryout. Both a localized power peaking within the core (for example, as a result of certain reactivity device configuration) or a general increase in the core power level during a slow-loss-of-regulation (SLOR) event could cause overpower in the fuel. This overpower could lead to fuel sheath dryout. In the CANDU® 600 MW (CANDU 6) design, there are two ROP systems in the core, one for each fast-acting shutdown systems. Each ROP system includes a number of fast-responding, self-powered flux detectors suitably distributed throughout the core within vertical and horizontal assemblies. Traditionally, the placement of these detectors was done using a method called the detector layout optimization (DLO). A new methodology for designing the detector layout for the ROP system has been developed recently. The new method, called the DETPLASA algorithm, utilizes the simulated annealing (SA) technique to optimize the placement of the detectors in the core. Both methodologies will be discussed in detail in this paper. Numerical examples are employed to better illustrate how each method works. Results from some sensitivity studies on three SA parameters are also presented.

Regional overpower protection analysis for CANDU 6 reactors using ROVER-F code

The regional overpower protection (ROP) systems (also known as neutron overpower protection (NOP)) for the CANDU ® 600 MW (CANDU 6) reactors are analyzed using the ROVER-F computer program, developed by Atomic Energy of Canada Limited (AECL). The objective of all such analyses is to ensure that the ROP systems protect the reactor from local overpowers in the fuel, which would reduce the safety margin to fuel dryout. For CANDU 6, the methodology utilized in the ROVER-F code has been used for redesigning the ROP systems and is currently used to perform periodic updates of the ROP trip setpoints of the operating CANDU 6 stations. This paper provides an overview of the methodology used in the ROVER-F code and highlights recent developments in the code.

Regional overpower protection system analysis for the direct use of spent pressurized water reactor fuel in CANDU Reactors (DUPIC)

The regional overpower protection (ROP) system of a Canada deuterium uranium (CANDU) reactor was assessed for the direct use of spent pressurized water reactor fuel in CANDU reactors (DUPIC), including the validation of the Winfrith improved multigroup scheme (WIMS)/reactor fuelling simulation program (RFSP)/reduction power (ROVER) code system used for the calculation of the ROP trip setpoint (TSP). Comparative calculations showed that the WIMS/RFSP/ROVER code system produced results consistent with the current design code system for estimating the ROP TSP of the standard natural uranium CANDU reactor. For the DUPIC fuel CANDU core, the ROP TSP was estimated to be 123.4%, which was almost the same as that of the standard natural uranium core. The extra margin of the ROP TSP for the DUPIC fuel system was enhanced by the flattened axial channel power distribution as well as the reduced refueling ripple of the channel power. This study has shown that the DUPIC fuel does not deteriorate the current ROP TSP designed for the natural uranium CANDU reactor.