Daya Bay Nuclear Power Plant Research Articles

A CFD study on radionuclides diffusion and dose assessment in Daya Bay nuclear power plant

Computational fluid dynamics (CFD) is used to simulate the short-range dispersion of radionuclides in a real nuclear power plant site. Firstly, the results of the validation case showed that the wind speed and concentration distribution were consistent with the measured data. Then, the potential consequences of radionuclide diffusion within the Daya Bay Nuclear Power Plant (DBNPP) were evaluated. Based on the wind direction and speed data from DBNNP over a 30-year period, the prevailing wind is northeasterly and southwesterly. The simulation results show that northeasterly and southwesterly winds dominate the diffusion direction of radionuclides, which mainly accumulate near nuclear reactor containment vessels. However, radionuclides cover most areas of DBNPP under a tailwind condition, causing severe contamination. Finally, it is necessary to pay attention to the accumulation of I-131 and Cs-137, and corresponding actions should be taken for regions of different radiation doses.

Development of modular dynamic code for steam power conversion system in sodium-cooled fast reactor

Sodium-cooled fast reactor (SFR) is one of the most promising Generation IV reactor types. To improve operational safety and economy, SFR requires accurate prediction of the steam power conversion system. Therefore, a one-dimensional thermal-hydraulic analysis code of the steam power conversion system of SFR is developed in this study where each equipment is packaged as a separate module with modular modeling method. JFNK is adopted to solve ODE in this code, which expand the universality of the code. The model is validated by comparing with design results from the Daya Bay nuclear power plant and the BN-600 steam generator. The maximum relative errors for pressure and temperature are 5.44% and 2.40%, respectively. After validation of the code, the steady-state analysis of the SFR steam power conversion circuit is carried out where the flow and heat transfer process of key equipment can be accurately simulated considering a complete steam power conversion cycle. This work provides reference value for the thermal-hydraulic characteristics of steam power conversion system in SFR.

Inverse method study based on Characteristic Statistic Algorithm (CSA) with application in estimating core states parameters

In reactor-related scenarios, inverse methods utilizing monitoring data are frequently employed to address issues such as state estimation, accident analysis, and power reconfiguration. These problem-solving approaches can entail converting the original problem into a parameter estimation problem. This paper presents a versatile and scalable framework for solving inverse problems by iterative optimization. To address intricate core parameter problems effectively, we incorporate the CPACT program, a physical thermal engineering solution program. Additionally, we employ the global optimization algorithm known as CSA (Characteristic Statistic Algorithm) to tackle specific challenges associated with nonlinear global optimization. To evaluate the performance of our framework, a numerical simulation model based on the Daya Bay Nuclear Power Plant was used as the test object design as our test subject.

Spatial and temporal distribution of fish egg communities in the adjacent waters of Daya Bay nuclear power plant and their relationship with environmental factors

The thermal discharge of Daya Bay Nuclear Power Plant has a certain impact on the ecological environment of the adjacent waters. In order to understand and evaluate changes in the fish egg community structure in the adjacent waters of Daya Bay Nuclear Power Plant and their relationship with environmental factors, four surveys were conducted to investigate fish eggs in January (winter), March (spring), August (summer) and November (autumn) of 2020. A total of 100,985 fish eggs were collected and 17 taxa were identified, belonging to five orders, 14 families and 17 genera. Among them, Perciformes and Clupeiformes were the main contributing taxa to fish egg species and abundance in the waters adjacent to Daya Bay Nuclear Power Plant. The number of fish egg species ranged from high to low was summer, spring, autumn and winter; the average abundance ranged from high to low was spring, summer, winter and autumn. The results showed that except in winter, the average abundance of fish eggs was greater in northeast area than in southwest area. The Shannon-Weiner species diversity index (H’), Pielou evenness index (J’) and Margalef richness index (d) were significantly different between seasons, but none were significantly different between areas. The results of NMDS analysis showed that there were significant differences in fish egg communities between seasons. Surface seawater temperature the average abundance of fish eggs was positively correlated in the results of all four seasons. Although the entrainment effect of nuclear power plant water intake and thermal pollution of partial waters owing to thermal discharge can cause some loss of fish eggs, fish resources can still be effectively maintained.

Determining the long-term impact area of coastal thermal discharge based on a harmonic model of sea surface temperature

AbstractCoastal nuclear power plants discharge large amounts of warm cooling water, which may have environmental impacts. This study proposes a method for determining the long-term impact area based on the average distribution of sea surface temperate (SST) increases. Taking the Daya Bay Nuclear Power Plant as a case study, 101 TM/ETM+ images acquired from 2000 to 2013 were used to obtain SST products. Cross-validation with NR_2P products showed that the accuracy of the SST products, in terms of the systematic error, root-mean-square error, and mean absolute error of 1,000 randomly selected verification points, was all <0.3°C, while Willmott’s index of agreement values was all >0.7. An annual SST cycle harmonic model was established. The mean difference between the modeled and observed SSTs was −2.1 to 2.5°C with a standard deviation range of 0–1°C. The long-term impact area was extracted by the harmonic analysis method and multi-year average method for comparison. The following conclusions can be drawn: 1) with sufficient SST samples, the temperature distributions of the two methods are similar, with the multi-year average method giving less noise and clearer boundaries. 2) When SST data are lacking for some months, the mean and standard deviation of the percentage of pixels belonging to areas of different temperature rise were calculated. The standard deviations of the two methods were both <0.04 in the temperature-rise classes of 1–2, 2–3, 3–4, and 4–5°C, while in the 0–1°C class, the standard deviation of the multi-year average method was 0.461, which is much higher than that of the multi-year average method (0.098). Performing statistical analysis on all pixels of >0°C, the multi-year average method had a standard deviation of 0.506, while the harmonic analysis method had a value of 0.128. Overall, the harmonic analysis method makes it possible to obtain and evaluate the long-term stability impact area of the thermal discharge over a period of time comprehensively and quantitatively. Even though it introduces a small amount of noise, it has less dependence on the input SST products and could improve the stability and reliability of thermal discharge monitoring, providing technical support for precise pollution control.

Research on the spatial distribution of n-γ field outside of the spent fuel cask based on Monte Carlo method

For systematically understanding the spatial distribution of the n-γ field and its dosage level outside of the spent fuel cask, we calculated the initial energy spectrum of both neutron and γ particles first. Then, in the Geant4 framework, we set up the sampling method of n-γ particles and built the physical model of the cask within fully loaded spent fuel modules to simulate the radiation field. Based on the simulation result, we plotted the spectrum of both neutron and γ particles and concluded the characteristics of the spectrum before and after penetrating the cask wall. At the end, we made a comparison of the simulation result with the field measurement data collected from the Daya Bay nuclear power plant (China) to test the validity of our model. The relative error of our simulation result with the field measurement data is 23.8%–33.7%. It is proven that our method can be a useful way to calculate the n-γ mixture field when multiple groups of spent fuel modules need to be transported in the future.

Spatial and seasonal distributions of ten species of benthic macrofauna and twelve water environmental factors in a subtidal zone near the Daya Bay nuclear power plant

In this study, we analyzed the spatial and seasonal distributions of ten species of benthic macrofauna and 12 water environmental parameters at thirty-six sampling stations in the subtidal zone near the Daya Bay Nuclear Power Plant. The results showed that there were four types of distribution characteristics for 10 species of macrobenthic animals and 12 water environmental factors near the Daya Bay nuclear power plant: (1) three species of benthic macrofauna, namely Apionsoma (Apionsoma) trichocephalus, Amphioplus (Lymanella) laevis, and P. bidentata, and six water environmental parameters, including water depth, salinity, dissolved oxygen, suspended solids, chromium, and lead increased from inside the bay to outside the bay. (2) Three species of benthic macrofauna, P. cristata, T. lata, and T. scabra, and four water environmental parameters, including oils, arsenic, total phosphorus, and silicate, decreased from inside to outside the bay. (3) Two species of benthic macrofauna, A. dibranchis, and P. undulatus and one water environmental parameter, pH, were higher in the central bay than inside and outside the bay. (4) One species of benthic macrofauna, Sigambra hanaokai, and one water environmental parameter, total nitrogen, were lower in the central bay than inside and outside the bay. Correlation and BIO-ENV analyses confirmed that water depth was the main environmental factor affecting the ten species of benthic macrofauna. Understanding the distributions of the dominant benthic macrofauna could help protect nuclear cold source systems from benthic macrofaunal blockage and explore marine ecosystem connectivity.

Three-dimensional numerical study of cooling water discharge of Daya Bay Nuclear Power Plant in southern coast of China during summer

The impact of thermal pollution caused by cooling water discharge of power plant on the surrounding marine ecology has been a hot issue in oceanographic research. To reveal the distribution pattern of cooling water discharge of Daya Bay Nuclear Power Plant in summer and the impact on the surrounding marine environment, this research established a high-resolution three-dimensional (3D) numerical model based on ECOMSED in the Daya Bay. The model results are consistent with the observations on the distribution of tide level and temperature. The simulated horizontal distribution of temperature rise is consistent with the distribution trend of remote sensing images. The study showed that the stratification of the Daya Bay water is stronger in summer. The cooling water mainly spreads in the surface layer, and the temperature rise in the bottom layer is not apparent. Quantitative analysis showed that around 18.8-21.6 km2 of the area has 1°C surface temperature rises. The area of temperature rises that exceeds 2 °C is between 6.2 and 8.1 km2. The area of temperature rises that exceeds 4 °C is between no more than 1.2 km2. The area with a bottom temperature rises of 1 °C does not exceed 2.2 km2, and there is no area that has a bottom temperature rise over 1 °C. The tidal dynamics process influences on the dispersion of cooling water discharge from Daya Bay Nuclear Power Plant, where the influence is more significant in the spring tide period than in the neap tide period. Our findings are consistent with previous researches.

Study on the Dispersion of Radionuclides under Different Hydrological Conditions of Spent Fuel Shipping in Daya Bay

The radionuclide dispersion in coastal water is mainly controlled by the water flow and tidal effect. Tracing and analysis of radioactive pollutant dispersion in coastal water can predict distribution of radionuclide under marine transportation accident of spent fuel. In this work, factors such as continuous emission, radioactive decay, and water depth are considered, and a hydrodynamic model of radionuclide dispersion based on shallow water equations is established to simulate the dispersion of the radioactive pollutant in coastal waters under different hydrological conditions. As far as the characteristics of the radionuclide dispersion in coastal water are concerned, the simulation of pollutants by the hydrodynamic model is in good agreement with the work of Bailly du Bois et al., which validated the correctness of this model. The model has been applied to simulate the distribution of radionuclides in coastal water following a marine transport accident of spent fuel near Daya Bay Nuclear Power Plant in China. The simulation reveals that the distribution features are significantly affected by different hydrological conditions. In addition to limiting the diffusion range, the vortex effect can also cause the accumulation of radionuclides near the vortex, which helps to provide more practical information for nuclear emergency decision makers.

Rising temperature contributed to the outbreak of a macrozooplankton Creseis acicula by enhancing its feeding and assimilation for algal food nearby the coastal Daya Bay Nuclear Power Plant

An outbreak of a macrozooplankton Creseis acicula occurred in the summer of 2020 nearby the Daya Bay Nuclear Power Plant located on the coast of the Daya Bay in the South China Sea. The outbreaks of C. acicula often threaten human health, the marine environment, and other human activities including the safe operation of coastal nuclear power plants. Seawater temperature has been suggested as an important factor influencing such outbreaks. However, the underlying mechanisms through which temperature influences C. acicula remains unknown. Here, we studied the effects of temperature on the ingestion and assimilation of algal food by feeding radiocarbon-labeled algae Chlorella sp. at simulated field temperatures (19–31 °C) to C. acicula collected during the outbreak in the Daya Bay. We also quantified the allocation of the food carbon to dissolved organic carbon (DOC), CO2, and fecal pellets. The results showed that the zooplankton during the same feeding time ingested doubled or tripled algal food at higher temperatures, and it produced and released significantly more DOC, CO2, and fecal pellets with more ingested food carbon. Meanwhile, the assimilation efficiency for the ingested food carbon slightly increased from 48% to 54% with rising temperature. As a result, higher assimilation rates indicating faster growth of C. acicula were observed at higher temperatures. In addition, the high activation energy of 0.908 eV indicated that the assimilation rate was very sensitive to temperature rising. Our results show that relatively rising temperature can enhance C. acicula’s ingestion and assimilation rates for algal food, benefit its growth and metabolism, and contribute to its outbreak. This study provides a mechanistic interpretation for the relationship between rising temperature and the outbreaks of C. acicula and suggests that such outbreaks may occur more frequently and widely in the warming ocean.

The Design of Thermodynamic System Instrument & Control for the Daya Bay Turbine High Pressure Cylinder Retrofit

Before the retrofit, the equipments of the turbine high pressure cylinder of the Daya Bay Nuclear Power Plant is of the old technology. The design of the leaf shape and the steam runner is not advanced, and the equipments are aged after more than 20 years’ operation. From the point of increasing the power and improving the reliability of the equipments, it’s decided to retrofit the turbine high pressure cylinder of Daya Bay Nuclear Power Plant unit 1 and unit 2. The retrofit relates to the design and modification of many secondary loop thermodynamic systems’ instrument & control parameters, in order to match with the first loop reactor control systems, and also the mechanism and electric systems, it’s necessary to verify and optimize these designed parameters of the units after the retrofit. This design and analysis method and experience of the secondary loop thermodynamic systems’ instrument & control parameters can be referred by the similar retrofit of other nuclear power plants.

Effects of Seawater Temperature and Salinity on Physiological Performances of Swimming Shelled Pteropod Creseis acicula During a Bloom Period

Creseis acicula is a swimming shelled pteropod species, widely distributed in the world’s oceans. In 2020, an unprecedented bloom of C. acicula was observed in Daya Bay, and lasted from June to July. To date, there is very limited information on the physiological characteristics of this species, which is essential to understand bloom dynamics. In the present study, the physiological performances of C. acicula in response to temperature (17–35°C) and salinity (18–38 ppt) were investigated. The oxygen consumption (OCR) and calcification rates (CR) of C. acicula peaked at 32 and 26°C, respectively, while ammonia excretion rate (AER) significantly increased with increasing temperature. The thermal coefficient Q10 (respiration) of C. acicula dropped to a minimum value between 32 and 35°C, suggesting that they were in a stressful status. The O:N ratio ranged from 3.24 to 5.13, indicating that protein was the major catabolism substrate. Temperature exerted a stronger effect on the OCR and AER of C. acicula. Salinity has a more influence on CR. The preferable temperature for C. acicula ranges from 29 to 32°C, and the preferable salinity ranges from 28 to 33 ppt. Based on a comprehensive consideration, we presumed that the warmer seawater temperature around the thermal discharge area of Daya Bay nuclear power plant is a possible cause for the bloom of C. acicula.

Validation of PWR Neutronics Code Package TORCH V2.0 With Nuclear Power Plant Measurements

This article presents the verification and validation (V and V) of PWR neutronics code package TORCH V2.0 with nuclear power plant (NPP) measurements. The advanced nuclear power engineering design software, TORCH V2.0, was developed by the Nuclear Power Institute of China (NPIC), China National Nuclear Corporation (CNNC). Based on the two-step calculation scheme, TORCH V2.0 mainly contains lattice physics code for assembly homogenization, link calculation code for few-group constant parameterization, and core simulation code for few-group core calculation. The calculation modules of each code were already verified against various benchmark problems, whereas this article focuses on the V and V of linked code system. The measured values of the reactor startup physics test and NPP operation from six PWR NPPs (Daya Bay NPP, Ling Ao NPP, Fangjiashan NPP, Qinshan NPP, Hainan Changjiang NPP, and Fuqing NPP) were utilized to perform the comparison and analysis of V and V. Compared parameters of the reactor startup physics test include critical boron concentration, control rod integral value, boron differential value, and isothermal temperature coefficient. Compared parameters of the NPP operation contain critical boron concentration, assembly-wise power distribution, hot spot factor, and nuclear enthalpy rise factor. The results show that the software TORCH V2.0 has reliable calculation ability and can be applied in the PWR nuclear power engineering design which is based on square fuel assembly.

Conversion and verification of proportional–integral​ controller parameter in Daya Bay distributed control system modification project

The nuclear island analog system in the Daya Bay Nuclear Power Plant is made up of discrete analog boards. Owing to the difficulties in purchasing spare parts and maintaining systems, the overall digital upgrade and modification shall be carried out during the 30-year overhaul period. In view of the difference between analog and digital systems in expressing and processing process signals, this paper proposed the proportional–integral (PI) controller parameter conversion method for digital modification, highlighting the importance of controller input/output range matching in the process of parameter conversion. The Daya Bay process simulation model, minimum digital system, and minimum analog system are built into a system verification platform through a programmable logic controller (PLC). Taking primary single-phase pressure control loop system and downflow pressure control loop system as research objects, the disturbance was introduced through the step of the primary pressure setting value and opening/closing of the second downflow orifice plate respectively, and the adjustment time、 overshoot and other adjustment quality differences in different systems are compared. The correctness of the parameter conversion method is verified through the system verification platform, which not only ensures the correct input of controller parameters of the Daya Bay DCS modification project but also provides invaluable experience for other digital modification projects of analog systems.

Kinetics of low radioactive wastewater imbibition and radionuclides sorption in partially saturated ternary-binder mortar

This study seeks to assess the imbibition kinetics of low radioactive wastewater (from the DayaBay nuclear power plant) into a partially saturated ternary-binder mortar, as well as the sorption kinetics of 60Co and 137Cs from the water. Mortar samples with the initial saturation degrees of 0, 0.4, 0.6, 0.8 and 1.0 were prepared for the wastewater treatment. Pore structure of the mortar was characterized using water vapor sorption isotherm and mercury intrusion porosimetry tests interpreted by the Guggenheim-Anderson-de Boer isothermal equilibrium, and volume- and energy-based fractal models. Results show that the mortar has consistent fractal pore structure between the models, and the liquid imbibitions follow the fractal imbibition kinetics, in which the parameters are non-linearly impacted by the initial saturation degrees. The sorption rate and retention capacity of 137Cs are much lower than those of 60Co, and both follow the Brouers–Sotolongo fractional kinetics. The findings uncover the complex liquid imbibition and radionuclides sorption kinetics in cement-based porous materials, and the in-situ data would contribute to the material designs and sorption controls for large scale in-situ treatments of wastewater from nuclear power plant.

Acoustic study on the outbreak of Creseise acicula nearby the Daya Bay Nuclear Power Plant Base during the summer of 2020

From the mid-June to mid-July 2020, there was a massive bloom of Creseise acicula nearby the waters of Daya Bay Nuclear Power Plant Base (DNPP base). In order to find out the spatiotemporal dynamic characteristics of C. acicula and the main factors related to its outbreak and extinction, acoustic surveys and in-situ observations were performed. The results showed that the average abundance of C. acicula at the in-situ observation site fluctuated with the tidal rhythm. Furthermore, a horizontal migration pattern during ebb tide and a vertical subsidence trend of C. acicula was found. The outbreak of C. acicula bloom nearby the waters of DNPP base was the result of the joint action of water temperature, salinity and food availability etc. The extinction of C. acicula was mainly related to the adhesion of Licmophora, predation pressure from phytoplanktivorous fishes (such as Sardinella lemuru and Dussumieria elopsoides) and human intervention.

Study on Life Cycle Management System for Main condensers in Nuclear Power Plant

Daya Bay Nuclear Power Plant has been running for above 20 years. main condensers have begun to run during the commissioning phase before the official commercial operation, so it is imminent to carry out the life cycle management of main condensers combined with demonstration of the operation license extended to 60 years. A life cycle management system for main condensers in nuclear power plant is established in this paper, which is applied to management practices of Daya Bay Nuclear Power Plant.

Pedestrian Choice Modeling and Simulation of Staged Evacuation Strategies in Daya Bay Nuclear Power Plant

Considering the distances to exits, exits’ capacities, the sizes of queues at exits, distances to the nuclear power plant, as well as individual characteristics, the exit choice model for pedestrians in the plume planning area is established based on a random forest model. This model is trained and verified with the survey data of residents around the Daya Bay Nuclear Power Plant collected from a serious game-based questionnaire system. Combining the pedestrian choice with the agent-based pedestrian behavior simulation model, the evacuation process of a nuclear accident is simulated. Based on the detailed evacuation simulation model, a comparative experiment is performed to evaluate the staged evacuation strategy in such scenarios. Simulation results indicate that staged evacuation may not be the best strategy all the time, and the number of groups highly impacts its performance.

Flexible feeding patterns of copepod Centropages tenuiremis in fluctuating conditions: a possible survival strategy to cope with disturbance

Centropages tenuiremis is a species with a wide distribution range in disturbed coastal waters. However, due to a lack of dietary information, it remains unclear as to how they maintain such dominance in fluctuating conditions. In this study, C. tenuiremis was collected from the Daya Bay Nuclear Power Plant both in inlet and outfall regions at 06:00, 12:00 and 18:00 on April 27, 2011 and their in situ diet was analyzed using a PCR protocol targeting 18S ribosomal genes. Thirty-four species of prey organisms were identified totally, including Dinophyta, Baciliariophyta, Viridiplantae, Rhizaria, Apicomplexa, Chordata, Mollusca, Arthropoda and Fungi, indicating an obvious omnivorous feeding habit of C. tenuiremis. Centropages tenuiremis obviously exhibited spatial and temporal variations in diet composition. More plant prey (land plants and phytoplankton) were consumed in the morning (~50%), while more animal prey (metazoans and protozoans) were ingested at midday and night (60%–70%). Furthermore, a more diverse diet was detected in the outfall region (10–11 taxa), where the temperatures were relatively higher and more fluctuating, than in the control region (5–10 taxa). This finding indicated that C. tenuiremis could potentially expand its food spectrum under stressful condition. Specifically, C. tenuiremis exhibited phytoplankton preference (58.62%–67.64%) in the outfall region with a lower omnivory index (0.27–0.35) than in the control region (0.51–0.95). However, phytoplankton density was lower than that in the control region, suggesting a possible herbivorous tendency of C. tenuiremis under elevated temperatures to balance the energy acquirement and feeding effort. The flexible food choices of C. tenuiremis observed here could effectively buffer environmental fluctuations and might be an important survival strategy in coastal ecosystems.

Feasibility analysis of 60Co production in pressurized water reactors

The radioactive isotope 60Co is used in many applications and is typically produced in heavy water reactors. As most of the commercial reactors in operation are pressurized light water reactors (PWRs), the world supply of high level radioactive cobalt would be greatly increased if 60Co could be produced in them. Currently, 60Co production in PWRs has not been extensively studied; for the 59Co (n, γ) 60Co reaction, the positioning of 59Co rods in the reactor determines the rate of production. This article primarily uses the models of 60Co production in Canadian CANDU power reactors and American boiling water reactors; based on relevant data from the pressurized water Daya Bay nuclear power plant, a PWR core model is constructed with the Monte Carlo N-Particle Transport Code; this model suggests changes to existing fuel assemblies to enhance 60Co production. In addition, the plug rods are replaced with 59Co rods in the improved fuel assemblies in the simulation model to calculate critical parameters including the effective multiplication factor, neutron flux density, and distribution of energy deposition. By considering different numbers of 59Co rods, the simulation indicates that different layout schemes have different impact levels, but the impact is not large. As a whole, the components with four 59Co rods have a small impact, and the parameters of the reactor remain almost unchanged when four 59Co rods replace the secondary neutron source. Therefore, in theory, the use of a PWR to produce 60Co is feasible.