Methodology for Calculating Minor Radioactive Releases From VVER 1000 Using TRACE Code

2021 ◽  
Vol 7 (2) ◽  
Author(s):  
M. Ruscak ◽  
G. Mazzini ◽  
A. Dambrosio ◽  
A. Musa
Keyword(s):  
Power Plant ◽  
Severe Accident ◽  
Safety Requirements ◽  
Design Basis ◽  
Long Duration ◽  
Wide Range ◽  
Reduce Risk ◽  
Fukushima Daiichi ◽  
Accident Conditions ◽  
Action Levels

Abstract After the Fukushima DAIICHI accident, new safety requirements were imposed in order to reduce risk of severe accident. One of the principles that have been adopted is the introduction of emergency action levels resulting from the expected consequences. They cover a wide range of component and system malfunctions resulting in emergency, incident, and/or accident conditions. To evaluate those emergency action levels, thermal hydraulic (TH) analyses simulating these malfunction/incident/accident conditions are required. This paper describes the simulation of a real operational incident scenario using a standard thermal hydraulic model of the power plant in the TRACE code that was originally intended for simulation of design basis accidents such as large break coolant accident or loss of flow accident. Special attention was given to the methodology, addressing a long duration of an incident with corrective actions of the operators, and to computational issues leading to model modifications caused by a long duration of the incident along with the necessary conservatisms in the estimated results of the simulated radioactivity release.

A Criticality Evaluation of Fukushima Daiichi Unit 1 Fuel Debris

2018 ◽  
Author(s):  
María Freiría López ◽  
Michael Buck ◽  
Jörg Starflinger
Keyword(s):  
Severe Accident ◽  
Water Density ◽  
Fukushima Accident ◽  
Research Issues ◽  
Wide Range ◽  
Core Meltdown ◽  
Safety Parameter ◽  
Accident Research ◽  
Fukushima Daiichi ◽  
Parameter Ranges

After the Fukushima accident, the interest of the scientific community in severe accident research has been renewed. One of the severe accident research issues that needs to be further investigated is the potential for recriticality of the fuel debris, which is formed after the core meltdown. In this study, a conservative criticality evaluation of the Fukushima Daiichi Unit 1 debris bed has been carried out. Parameters, such as debris size, porosity, particle size, fuel burnup and the coolant conditions, including the water density and the content of boron, were considered. The effect of these parameters on the neutron multiplication factor was analysed and safety parameter ranges, i.e. zones where the recriticality can be totally excluded, have been identified. The content of boron in water required to secure the subcriticality was calculated for those zones with recriticality potential. It was found that recriticality is achievable for a wide range of fuel debris conditions. 1600 ppm B would ensure subcriticality under any conditions.

Design of Severe Accident Management Systems for Beyond Design Basis External Hazards at Paks NPP

2016 ◽  
Author(s):  
Tamás János Katona ◽  
András Vilimi
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Severe Accident ◽  
Management Systems ◽  
Basic Question ◽  
Severe Accidents ◽  
Design Basis ◽  
Accident Management ◽  
External Events

Paks Nuclear Power Plant identified the post-Fukushima actions for mitigation and management of severe accidents caused by external events that include updating of some hazard assessments, evaluation of capacity / margins of existing severe accident management facilities, and construction of some mew systems and facilities. In all cases, the basic question was, what level of margin has to be ensured above design basis external hazard effects, and what level of or hazard has to be taken for the design. Paks Nuclear Power Plant developed certain an applicable in the practice concept for the qualification of already implemented and design the new post-Fukushima measures that is outlined in the paper. The concept and practice is presented on several examples.

Accident Analysis of Fukushima Daiichi Nuclear Power Plant Unit 2 by the SAMPSON Severe Accident Code

2014 ◽  
Author(s):  
Atsuo Takahashi ◽  
Marco Pellegrini ◽  
Hideo Mizouchi ◽  
Hiroaki Suzuki ◽  
Masanori Naitoh
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Cooling System ◽  
Severe Accident ◽  
Accident Analysis ◽  
Unknown Boundary ◽  
Long Time ◽  
Fukushima Daiichi ◽  
Nuclear Power Plant Unit

The transient process of the accident at the Fukushima Daiichi Nuclear Power Plant Unit 2 was analyzed by the severe accident analysis code, SAMPSON. One of the characteristic phenomena in Unit 2 is that the reactor core isolation cooling system (RCIC) worked for an unexpectedly long time (about 70 h) without batteries and consequently core damage was delayed when compared to Units 1 and 3. The mechanism of how the RCIC worked such a long time is thought to be due to balance between injected water from the RCIC pump and the supplied mixture of steam and water sent to the RCIC turbine. To confirm the RCIC working conditions and reproduce the measured plant properties, such as pressure and water level in the pressure vessel, we introduced a two-phase turbine driven pump model into SAMPSON. In the model, mass flow rate of water injected by the RCIC was calculated through turbine efficiency degradation the originated from the mixture of steam and water flowing to the RCIC turbine. To reproduce the drywell pressure, we assumed that the torus room was flooded by the tsunami and heat was removed from the suppression chamber to the sea water. Although uncertainties, mainly regarding behavior of debris, still remain because of unknown boundary conditions, such as alternative water injection by fire trucks, simulation results by SAMPSON agreed well with the measured values for several days after the scram.

Design of Severe Accident Management Systems for Beyond Design Basis External Hazards at Paks Nuclear Power Plant

2018 ◽  
Vol 4 (2) ◽  
Author(s):  
Tamás János Katona ◽  
András Vilimi
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Severe Accident ◽  
Exceedance Probability ◽  
Basic Question ◽  
Existing Structures ◽  
Design Basis ◽  
Accident Management ◽  
Definition Of

Paks Nuclear Power Plant (NPP) identified the post-Fukushima actions for mitigation and management of severe accidents caused by external events that include updating of some hazard assessments, evaluation of margins of existing severe accident management (SAM) facilities, and construction of some new systems and facilities. While developing the SAM strategy, the basic question was what is the sufficient margin above the design basis level of existing structures, systems, and components for avoiding the cliff-edge effects, and what level of or hazard should be taken for the design of new structures and systems dedicated for SAM. Paks NPP developed an applicable in the practice concept for the qualification of already implemented SAM measures and design the new post-Fukushima measures that are outlined in the paper. The concept is based on the generalization of the procedure and assumptions used in the definition of acceptable margins for seismic loads, analysis of the steepness of the hazard curves and features of the hazards. Justification of the definition of exceedance probability of the design basis effects for the design of SAM systems is given based on the first order reliability theory. The application of the concept is presented on several practical examples.

Development and Verification of Severe Accident Simulation Capability for a NPP Simulator

2013 ◽  
Author(s):  
Zhifei Yang ◽  
Xiaofei Xie ◽  
Xing Chen ◽  
Shishun Zhang ◽  
Yehong Liao ◽  
...  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Simulation System ◽  
Severe Accident ◽  
Normal Operation ◽  
Feed Water ◽  
Accident Simulation ◽  
Accident Conditions ◽  
Relap5 Code

It is reflected in the severe accident in Fukushima Daiichi that the emergency capacity of nuclear power plant needs to be enhanced. A nuclear plant simulator that can model the severe accident is the most effective means to promote this capacity. Until now, there is not a simulator which can model the severe accident in China. In order to enhance the emergency capacity in China, we focus on developing a full scope simulator that can model the severe accident and verify it in this study. The development of severe accident simulation system mainly includes three steps. Firstly, the integral severe accident code MELCOR is transplanted to the simulation platform. Secondly, the interface program must be developed to switch calculating code from RELAP5 code to MELCOR code automatically when meeting the severe accident conditions because the RELAP5 code can only simulate the nuclear power plant normal operation state and design basis accident but the severe accident. So RELAP5 code will be stopped when severe accident conditions happen and the current nuclear power plant state parameters of it should be transported to MELCOR code, and MELCOR code will run. Finally, the CPR1000 nuclear power plant MELCOR model is developed to analyze the nuclear power plant behavior in severe accident. After the three steps, the severe accident simulation system is tested by a scenario that is initiated by the station black out with reactor cooling pump seal leakage, HHSI, LHSI and auxiliary feed water system do not work. The simulation result is verified by qualitative analysis and comparison with the results in severe accident analysis report of the same NPP. More severe accident scenarios initiated by LBLOCA, MBLOCA, SBLOCA, SBO, ATWS, SGTR, MSLB will be tested in the future. The results show that the severe accident simulation system can model the severe accident correctly; it meets the demand of emergency capacity promotion.

CANDU 6 Severe Accident Prevention and Mitigation Features

2012 ◽  
Author(s):  
Steven Ford ◽  
Boris Lekakh ◽  
Ed Choy ◽  
Kamal Verma ◽  
Sorin Ghelbereu
Keyword(s):  
Accident Prevention ◽  
Severe Accident ◽  
Multiple Failures ◽  
Core Damage ◽  
Severe Accidents ◽  
Design Basis ◽  
Accident Conditions

The CANDU 6 design includes features, both engineered and inherent, that act as barriers to prevent and mitigate severe accidents at progressive stages of a beyond design basis event such as that which occurred at Fukushima in March 2011. CANDU 6 has ample design margins including multiple layers of defense. Large inventories of water slow down any accident progression to severe accident conditions, even when multiple failures are assumed; giving operations staff more time to manage the event. Ongoing improvements to operating plants, and enhancements made to future evolutions of the CANDU design (including the Enhanced CANDU 6) improve upon these inherent features, further strengthening the CANDU 6 design to withstand severe core damage accidents.

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