PSA study of the effect of extreme snowfall on a floating nuclear power plant:case study in the Bohai Sea

This study presents a probabilistic safety analysis(PSA)method for the external event of extreme snowfall on a floating nuclear power plant(FNPP)deployed in the Bohai Sea.We utilized the Weibull and Gumbel extreme value distributions to fit the collected meteorological data and obtained a hazard curve for the event of an extreme snowfall where the FNPP is located,providing a basis for the frequency of extreme snowfall-initiating events.Our analysis indicates that extreme snowfall primarily affects the ventilation openings of the equipment,leading to the failure of devices such as the diesel generators.Additionally,extreme snowfall can result in a loss of off-site power(LOOP).Therefore,the developed extreme snowfall PSA model is mainly based on the LOOP event tree,considering responses such as snowfall removal by personnel.Our calculations indicate a core damage frequency(CDF)of 1.13×10^(-10) owing to extreme snowfall,which is relatively low.The results of the cut-set analysis indicate that valve failures in the core makeup tank(CMT),passive residual heat removal system(PRS),and in-containment refueling water storage tank(IRWST)significantly contribute to the CDF.

Control Effect of Floating Plants Constructed Wetland to Nitrogen and Phosphorus Pollution from Rice Field Drainage

[Objective] The control effect of floating plants constructed wetland to nitrogen and phosphorus pollution from rice field drainage was studied.[Method] Firstly,the characteristic of floating plants and the purification principle of pollutants were introduced,and then purification effect was analyzed through controlling nitrogen and phosphorus pollution from rice field drainage by floating plants constructed wetland.[Result] By means of floating plants constructed wetland,the average removal rate of total nitrogen(TN) from double-season early and late rice field drainage reached 52.17% and 62.23%,respectively,while that of total phosphorus(TP) was 45.69% and 74.37%,respectively,with better removal effect.Meanwhile,floating plants have ecological and ornamental value to some extent.[Conclusion] Floating plants constructed wetland could not only control nitrogen and phosphorus pollution in field drainage effectively but also keep farmland ecosystem in healthy state.

Floating plants reduced methane fluxes from wetlands by creating a habitat conducive to methane oxidation

Wetlands are one of the important natural sources of atmospheric methane (CH_4),as an important part of wetlands,floating plants can be expected to affect methane release.However,the effects of floating plants on methane release are limited.In this study,methane fluxes,physiochemical properties of the overlying water,methane oxidation potential and rhizospheric bacterial community were investigated in simulated wetlands with floating plants Eichhornia crassipes,Hydrocharis dubia,and Trapa natans.We found that E.crassipes,H.dubia,and T.natans plants could inhibit 84.31%-97.31%,4.98%-88.91%and 43.62%-92.51%of methane fluxes at interface of water-atmosphere compared to Control,respectively.Methane fluxes were negatively related to nutrients concentration in water column but positively related to the aerenchyma proportions of roots,stems,and leaves.At the same biomass,root of E.crassipes (36.44%) had the highest methane oxidation potential,followed by H.dubia (12.99%) and T.natans (11.23%).Forty-five bacterial phyla in total were identified on roots of three plants and 7 bacterial genera (2.10%-3.33%) were known methanotrophs.Type I methanotrophs accounted for 95.07%of total methanotrophs.The pmoA gene abundances ranged from 1.90×10^(16)to 2.30×10^(18)copies/g fresh weight of root biofilms.Abundances of pmoA gene was significantly positively correlated with environmental parameters.Methylotrophy (5.40%) and methanotrophy (3.75%) function were closely related to methane oxidation.This study highlights that floating plant restoration can purify water and promote carbon neutrality partially by reducing methane fluxes through methane oxidation in wetlands.

Experimental Research on the Application of Water Hyacinths to the Ecological Restoration of Water Bodies with Eutrophication

[Objective] The study aims to discuss the application of water hyacinths to the ecological restoration of water bodies with eutrophication through simulation experiments. [Method] In this study, water hyacinths were used to restore the simulated eutrophic water with green algae as the dominant algae species, and then the restoration effect of the simulated eutrophic water by water hyacinths was analyzed. [Result] In the simulation test without sediment, the peak chlorophyll concentration was 434.6 mg/m3 in the tank without water hyacinths, which decreased to 285 and 119 mg/m3 respectively in the tanks with 1 and 4 water hyacinths. In the experiment with sediment, compared with the control tank without water hyacinths, a 58% reduction in chlorophyll concentration could be observed in the tank with 4 water hyacinths planted (with a coverage of 51%). The results showed that water hyacinths could inhibit alga growth notably, but there was likely a density threshold (51% coverage), and no significant eco-restoration effect was observed in the simulated eutrophic water with too few water hyacinths planted. [Conclusion] The research could provide scientific references for the ecological restoration of eutrophic water bodies.

Fault line selection in cooperation with multi-mode grounding control for the floating nuclear power plant grid

The Floating nuclear power plant grid is composed of power generation,in-station power supply and external power delivery.To ensure the safety of the nuclear island,the in-station system adopts a special power supply mode,while the external power supply needs to be adapted to different types of external systems.Because of frequent single phase-ground faults and various fault forms,the fault line selection protection should be accurate,sensitive and adaptive.This paper presents a fault line selection method in cooperation with multi-mode grounding control.Based on the maximum united energy entropy ratio(MUEER),the optimal wavelet basis function and decomposition scale are adaptively chosen,while the fault line is selected by wavelet transform modulus maxima(WTMM).For high-impedance faults(HIFs),to enlarge the fault feature,the system grounding mode can be switched by the multi-mode grounding control.Based on the characteristic of HIFs,the fault line can be selected by comparing phase differences of zero-sequence current mutation and fault phase voltage mutation before and after the fault.Simulation results using MATLAB/Simulink show the effectiveness of the proposed method in solving the protection problems.

Investment risk evaluation of inland floating photovoltaic power plants in China using the HFLTS-TFN method

Inland floating photovoltaic power plants(IFPPPs)are the key to making full use of water advantages to develop solar resources in the future.Identifying the investment risk is an important prerequisite for promoting the projects on a large scale.This paper proposes a model to assess the investment risk of IFPPPs in China.First,this paper identifies the investment risk factors and establishes an evaluation indicator system from four aspects.Second,the indicator data are collected and described by adopting hesitant fuzzy linguistic term sets and triangular fuzzy numbers to ensure soundness and completeness.Third,a weighted method combining the best-worst method and the entropy method are utilized to determine the indicator weights under the consideration of the impact of subjective preferences and objective fairness.Fourth,the results show that the overall risk level of China’s IFPPPs is‘medium low’.Fifth,sensitivity analysis and comparative analysis are implemented to examine the stability of the evaluation results.Finally,this paper also provides some risk-response strategies for the development of China’s IFPPPs from economy,society,technology and environment.

Effects of clonal integration, nutrients and cadmium on growth of the aquatic macrophyte Pistia stratiotes

Aims Many wetlands are polluted with both nutrients and toxic metals and vegetated largely by clonal plants.We hypothesized that eutrophication and clonal integration can increase phytoremediation of toxic metal pollution by increasing plant growth,even under the stress imposed by toxicity.Methods To test this hypothesis,single ramets of the common,widespread,floating,stoloniferous plant Pistia stratiotes L.,were grown for 42 days at two levels of nutrient availability with and without 0.6 mg L^(-1) cadmium.Ramets were either severed from their vegetative offspring to prevent clonal integration or left connected,and severed offspring were either removed to eliminate intraclonal competition or left in place.Important Findings Plants subjected to cadmium addition accumulated almost twice as much dry mass if given the higher nutrient level,due mainly to a doubling of the number of clonal offspring.Severance had little effect on the final mass of the parent plus offspring ramets.Removing offspring following severance had no effect on the final mass of the parental ramet in the presence of added cadmium,but it did increase the final mass of the parent in the absence of cadmium.These results support the hypothesis that eutrophication can increase remediation of toxic metal pollution by aquatic macrophytes but provided no evidence that clonal integration can affect remediation.Species such as P.stratiotes may help remediate co-pollution of wetlands with toxic metals and nutrients,and fragmentation of clones may not affect their remediation capacity.