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.     

Prediction of permanent deformation in asphalt pavements using a novel symbiotic organisms search–least squares support vector regression

Neural Computing and Applications - The prediction of asphalt performance can be very important in terms of increasing service life and performance while saving energy and money. In this study, a...     

Combining machine learning models via adaptive ensemble weighting for prediction of shear capacity of reinforced-concrete deep beams

Engineering with Computers - This study presents a novel artificial intelligence (AI) technique based on two support vector machine (SVM) models and symbiotic organisms search (SOS) algorithm,...     

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.     

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.     

Synthesis,characterization, and gas separation performances of polysulfone and cellulose acetate-based mixed matrix membranes

ABSTRACT

The combination of polymeric and inorganic fillers inside mixed matrix membranes (MMMs) becomes a hot research topic due to the gas permeability-selectivity trade-off in polymeric membranes. Until recently, the problem of voids hampers the real application of MMMs, hence deep understanding on polymer-particle compatibility is required. This study focuses on the synthesis and characterization of polysulfone and cellulose acetate-based MMMs that combined with ZIF-8 and TiO₂ particles. ZIF-8 dispersed more uniform than TiO₂. The crystallinity of MMMs was higher than pure polymeric membrane. In addition, micro voids in MMMs resulted a slight decrease in CO₂/N₂ selectivity (from 15 to 12).     

Nano-silica/polysulfone asymmetric mixed-matrix membranes (MMMs) with high CO2 permeance in the application of CO2/N2 separation

Nano-sized silica/polysulfone (PSf) flat sheet asymmetric MMMs with high CO₂ permeance for CO₂/N₂ separation were fabricated by dry/wet phase inversion method using N, N-dimethylacetamide (DMAc) and tetrahydrofuran (THF) as solvents and ethanol as additives. The results indicated that the addition of nano-silica on the polymer matrix resulted on reduced membrane performance due to void formation and particle agglomeration. Optimum membrane performance was obtained at the following fabrication parameters: 22 wt.% PSf, 31.8 wt.% DMAc, 31.8 wt.% THF, 14.4 wt.% ethanol, 20 s evaporation time, and 0 wt.% silica loading, with CO₂/N₂ selectivity of 15.6 and CO₂ permeance of 14.2 GPU.     

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.     

Cognitive consequences of subcortical magnetic resonance imaging changes in Alzheimer''s disease: comparison to small vessel ischemic vascular dementia

When an elderly patient with Alzheimer's disease or other form of dementia exhibits agitated behavior, the caregiver often wants the physician to "do something"--i.e., give a neuroleptic drug. Yet, an individualized, rational approach to identify and treat the cause of the agitation is more effective. We present an algorithm that emphasizes environmental and behavioral therapy.     

Intranasal Administration of Undifferentiated Oligodendrocyte Lineage Cells as a Potential Approach to Deliver Oligodendrocyte Precursor Cells into Brain

Oligodendrocyte precursor cell (OPC) migration is a mechanism involved in remyelination; these cells migrate from niches in the adult CNS. However, age and disease reduce the pool of OPCs; as a result, the remyelination capacity of the CNS decreases over time. Several experimental studies have introduced OPCs to the brain via direct injection or intrathecal administration. In this study, we used the nose-to brain pathway to deliver oligodendrocyte lineage cells (human oligodendroglioma (HOG) cells), which behave similarly to OPCs in vitro. To this end, we administered GFP-labelled HOG cells intranasally to experimental animals, which were subsequently euthanised at 30 or 60 days. Our results show that the intranasal route is a viable route to the CNS and that HOG cells administered intranasally migrate preferentially to niches of OPCs (clusters created during embryonic development and adult life). Our study provides evidence, albeit limited, that HOG cells either form clusters or adhere to clusters of OPCs in the brains of experimental animals.