scholarly journals Delayed Station Blackout Event and Nuclear Safety

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Andrija Volkanovski ◽  
Andrej Prošek
Keyword(s):  
Time Delay ◽  
Time Delays ◽  
Nuclear Power ◽  
Electrical Power ◽  
Event Tree ◽  
Power Sources ◽  
Ac Power ◽  
Complete Failure ◽  
Station Blackout ◽  
Safety Systems

The loss of off-site power (LOOP) event occurs when all electrical power to the nuclear power plant from the power grid is lost. Complete failure of both off-site and on-site alternating current (AC) power sources is referred to as a station blackout (SBO). Combined LOOP and SBO events are analyzed in this paper. The analysis is done for different time delays between the LOOP and SBO events. Deterministic safety analysis is utilized for the assessment of the plant parameters for different time delays of the SBO event. Obtained plant parameters are used for the assessment of the probabilities of the functional events in the SBO event tree. The results show that the time delay of the SBO after the LOOP leads to a decrease of the core damage frequency (CDF) from the SBO event tree. The reduction of the CDF depends on the time delay of the SBO after the LOOP event. The results show the importance of the safety systems to operate after the plant shutdown when the decay heat is large. Small changes of the basic events importance measures are identified with the introduction of the delay of the SBO event.

Station Blackout Analysis of Lungmen ABWR Using TRACE

2012 ◽  
Author(s):  
Jong-Rong Wang ◽  
Hao-Tzu Lin ◽  
Hsiung-Chih Chen ◽  
Wei-Chen Wang ◽  
Chunkuan Shih
Keyword(s):  
Nuclear Power ◽  
Thermal Power ◽  
Electrical Power ◽  
Heat Removal ◽  
Fuel Temperature ◽  
Core Flow ◽  
The Core ◽  
Ac Power ◽  
Station Blackout ◽  
Core Cooling

The Lungmen NPP is the first ABWR (Advanced Boiling Water Reactor) nuclear power plant in Taiwan, consisting of two identical units with 3,926 MWt rated thermal power each and 52.2×106 kg/h rated core flow. The core of Lungmen NPP has 872 bundles of GE14 fuel. There are 10 reactor internal pumps (RIP) in the reactor vessel, providing 111% rated core flow at the nominal operating speed of 151.84 rad/sec. A station blackout (SBO) is defined as the loss of offsite electrical power concurrent with turbine trip and unavailability of the onsite emergency AC power. These result in the loss of core cooling and heat removal systems that rely on the above AC power for their operation. In this research, the TRACE SBO model of Lungmen ABWR has been developed in order for the analysis of SBO transient. The initial condition of SBO transient is 100% rated power/100% rated core flow. The TRACE’s results show that the reactor fuel temperature has been reached 1088.71 K (the zirconium-water reaction may generate) at about 3200 sec. It indicates that the fuels might be damaged after 3200 sec if the RCIC and ACIWA failed to activate in this transient.

scholarly journals Application of MELCOR to Westinghouse 4-loop PWR severe accident and evaluation of RPV lower head performance

2014 ◽  
Vol 4 (3) ◽  
pp. 1-6
Author(s):  
Dai Dien Le ◽  
Thi Hoa Bui ◽  
Thi Huong Vo
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Computer Code ◽  
Severe Accident ◽  
Ac Power ◽  
Lower Head ◽  
Active Safety Systems ◽  
Station Blackout ◽  
Control Volumes ◽  
Safety Systems

In this study, MELCOR computer code is used to simulate the progression of a severe accident initiated from station blackout (SBO) accident for a Westinghouse 4-loop PWR. The hydraulic system is modeled using control volumes and flow paths. The reactor pressure vessel and internals, the primary loops with a pressurizer, steam generators, containment and accumulators are simulated for steady state in a good agreement with reference data. The two scenarios concerning SBO are investigated. The first scenario simulates RCP seal leakage during SBO and the other is SBLOCA to highlight an effectiveness of accumulators as well as to compare with the first simulation. All active safety systems which depend on AC power are assumed to be unavailable in this analysis. The main result of the study is an evaluation of RPV lower head integrity during severe accidents. This is preliminary work and expected to give the experience for further studies in the severe accident in nuclear power plants.

scholarly journals Application of MELCOR to Westinghouse 4-loop PWR severe accident and evaluation of RPV lower head performance

2014 ◽  
Vol 4 (3) ◽  
pp. 19-28
Author(s):  
Dai Dien Le ◽  
Thi Hoa Bui ◽  
Thi Huong Vo
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Computer Code ◽  
Severe Accident ◽  
Ac Power ◽  
Lower Head ◽  
Active Safety Systems ◽  
Station Blackout ◽  
Control Volumes ◽  
Safety Systems

In this study, MELCOR computer code is used to simulate the progression of a severe accident initiated from station blackout (SBO) accident for a Westinghouse 4-loop PWR. The hydraulic system is modeled using control volumes and flow paths. The reactor pressure vessel and internals, the primary loops with a pressurizer, steam generators, containment and accumulators are simulated for steady state in a good agreement with reference data. The two scenarios concerning SBO are investigated. The first scenario simulates RCP seal leakage during SBO and the other is SBLOCA to highlight an effectiveness of accumulators as well as to compare with the first simulation. All active safety systems which depend on AC power are assumed to be unavailable in this analysis. The main result of the study is an evaluation of RPV lower head integrity during severe accidents. This is preliminary work and expected to give the experience for further studies in the severe accident in nuclear power plants.

Passive Safety Systems of Advanced Nuclear Power Plant: AP1000

2010 ◽  
Author(s):  
Guohua Yan ◽  
Chen Ye
Keyword(s):  
Nuclear Power ◽  
Human Error ◽  
Cooling System ◽  
Heat Removal ◽  
Injection System ◽  
Passive Safety ◽  
Human Errors ◽  
Power Sources ◽  
Passive Safety Systems ◽  
Safety Systems

In the entire history of commercial nuclear power so far, only two major accidents leading to damage of reactor core have taken place. One is Three Mile Island (TMT) accident (1979), which is caused by a series of human error, and the other is Chernobyl accident (1986), which is due to the combined reason of design defects and human errors. After TMI and Chernobyl accidents, in order to reduce manpower in operation and maintenance and influence of human errors on reactor safety, consideration is given to utilization of passive safety systems. According to the IAEA definition, passive safety systems are based on natural forces, such as convection and gravity, and stored energy, making safety functions less dependent on active systems and operators’ action. Recently, the technology of passive safety has been adopted in many reactor designs, such as AP1000, developed by Westinghouse and EP1000 developed by European vendor, and so on. AP1000 as the first so-called Generation III+ has received the final design approval from US NRC in September 2004, and now being under construction in Sanmen, China. In this paper, the major passive safety systems of AP1000, including passive safety injection system, automatic depressurization system passive residual heat removal system and passive containment cooling system, are described and their responses to a break loss-of-coolant accident (LOCA) are given. Just due to these passive systems’ adoption, the nuclear plant can be able to require no operator action and offsite or onsite AC power sources for at least 72h when one accident occurs, and the core melt and large release frequencies are significantly below the requirement of operating plants and the NRC safety goals.

The Application of Time-Related Event Tree During the HTR-PM Design Phase

2006 ◽  
Author(s):  
Ping Min ◽  
Jiejuan Tong ◽  
Xuhong He
Keyword(s):  
Nuclear Power ◽  
Safety Assessment ◽  
Reactor Design ◽  
Design Phase ◽  
Event Tree ◽  
Insufficient Information ◽  
Related Event ◽  
Efficient Information ◽  
Safety Systems ◽  
Tree Approach

The Probabilistic Safety Assessment of HTR-PM, the demonstration nuclear power plant of High-Temperature Gas-Cooled Reactor in P.R. China, started in 2005, in order to offer supplementary support to the reactor design. Four critical initiating events families such as water-ingress, primary depressurization, loss of primary cooling etc. have been selected for the accident sequence analysis during the preliminary reactor design phase. Due to the special characteristics of doing PSA in the new reactor design phase, such as insufficient information, unavoidable iterations, complicated communications among multiple specialties and so on, efficient measures shall be developed to further the projects. A time-related Event Tree approach presented in this paper is one of them. Compared with ordinary event tree, the time-related event tree intends to illustrate not only the accident propagation processes, but also the key time points when safety systems, signals and operator actions are challenged and the durations. It seems to be a good bridge between designers and PSA engineers for the consistent understanding and more efficient information exchanging.

Degraded Power Supplies

2016 ◽  
Author(s):  
Maja Lundbäck ◽  
Mattias Karlsson
Keyword(s):  
Power System ◽  
Power Supply ◽  
Nuclear Power ◽  
Electrical Power ◽  
Power Supplies ◽  
Operational Experience ◽  
Electrical Power System ◽  
Best Available Technology ◽  
Available Technology ◽  
Safety Systems

The electrical disturbance in Forsmark 2006 [3] led to increased attention being paid to the power supplies of nuclear power plants and their role in safety system reliability, both nationally and internationally. Since then numerous disturbances similar in nature have occurred in the electrical power supply which raises questions whether best available technology (BAT) has been utilised in the design and analysis of the electrical power supply of the safety functions of nuclear facilities. On repeated occasions this type of disturbances has had an impact on redundant parts of several safety systems due to functional dependencies between these. The frequency of these occurrences has been unexpected. The Swedish Radiation Safety Authority (SSM) has decided to write this document to clarify the regulators position on this issue. The document is also intended to support SSM:s assessments and evaluations of the Licensees efforts regarding degraded power supplies. An assessment of nuclear power plant electrical power systems is necessary in the light of the past years’ operational experience [1–7], where disturbances in the electrical power supply on repeated occasions have caused a power supply with degradation severe enough to challenge plant safety. As the potential consequences of such a degraded power supply can be severe it must be proven that the frequency of such occurrences is tolerably low. Furthermore, it is important to consider experiences from known situations with degraded power supplies, to enable a reasonable approach to identify and take counter-measures based on the root-cause and ensure utilisation of best available technology. A sufficient approach to enable prevention, protection and mitigation against this type of disturbances has been difficult to identify. Actual events and conditions causing a degraded power supply have often been complex in nature and difficult to anticipate, wherefore events and conditions which has not yet occurred are difficult to foresee. For this reason it is deemed most effective to identify and implement proportional measures that enhances the independence of the power supplies, such that a degraded power supply with a higher reliability is prevented from propagating to multiple parts of the safety systems. In this memorandum, SSM describes a state-based approach to analysing electrical power system functionality in different states of degraded power supply. The approach is intended to identify potential design weaknesses and measures to enhance robustness. Such an approach is viewed as more favourable in facilitating the identification of such measures, which may otherwise be neglected due to an estimated low frequency of occurrence, or missed due to incomplete identification of possible events and conditions. Furthermore this document describes how an assessment of electrical power system design can be performed, where the lowest common denominator from operational experience e.g. [1–7] is identified and counteracted. Actual occurrences of degraded power supplies, which all have been “unknown during the event identification process” but “well-known electrical phenomena”, can be described as unidentified degrading conductive disturbances.

scholarly journals Modeling of Discrete Networked Control Systems in State Space for Electrical Power System with Time Delays: نمذجة نظم التحكم الشبكية المتقطعة في فضاء الحالة لنظام قدرة كهربائية مع وجود التأخيرات الزمنية

2021 ◽  
Vol 5 (5) ◽  
pp. 50-30
Author(s):  
Mohamad Morhaf Bachar Alnifawi, Bassem Omran, Jomana Mahmoud Mohamad Morhaf Bachar Alnifawi, Bassem Omran, Jomana Mahmoud
Keyword(s):  
Time Delay ◽  
Power System ◽  
Time Delays ◽  
Negative Impact ◽  
Electrical Power ◽  
Linear Quadratic Regulator ◽  
Electrical Power System ◽  
Linear Quadratic ◽  
Lqr Controller ◽  
The Stability

Electrical power systems distributed over wide geographical areas are exposed to a set of factors that affect their stability. The most important factors are the time delays between their subsystems. In this paper, a flexible modeling method was concluded consisting of a set of generalized rules and conditions that apply to any network controlled system to ensure its stability with time delays between the elements of the controlled network. In addition, a linear quadratic regulator (LQR) controller was implemented. The aim of the LQR controller is to reduce the negative impact of the time delay on the stability of the electrical power system. The study was applied to a networked electrical power system consisting of three-generation stations distributed in three separate geographical areas. Computer simulations using MATLAB showed a remarkable improvement in the stability of the discrete networked system through the speed of damping the vibrations in the system, and the system ability to be stable at certain limits of the time delay.

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