THERMO-HYDRAULIC AND DYNAMIC CHARACTERISTICS OF A MOISTURE SEPARATOR HEATER FOR NUCLEAR POWER PLANTS

Because the scope of risk assessments at nuclear power plants (NPPs) is being extended both spatially and temporally, conventional, or static fault trees might not be able to express failure mechanisms, or they could be unnecessarily conservative in their expression. Therefore, realistic assessment techniques are needed to adequately capture accident scenarios. In multi-unit probabilistic safety assessment (PSA), fault trees naturally become more complex as the number of units increases. In particular, when considering a shared facility between units of the electric power system (EPS), static fault trees (SFTs) that prioritize a specific unit are limited in implementing interactions between units. However, dynamic fault trees (DFTs) can be available without this limitation by using dynamic gates. Therefore, this study implements SFTs and DFTs for an EPS of two virtual NPPs and compares their results. In addition, to demonstrate the dynamic characteristics of the shared facilities, a station blackout (SBO), which causes the power system to lose its function, is assumed—especially with an inter-unit shared facility, AAC DG (Alternate AC Diesel Generator). To properly model the dynamic characteristics of the shared EPS in DFTs, a modified dynamic gate and algorithm are introduced, and a Monte Carlo simulation is adopted to quantify the DFT models. Through the analysis of the DFT, it is possible to confirm the actual connection priority of AAC DG according to the situation of units in a site. In addition, it is confirmed that some conservative results presented by the SFT can be evaluated from a more realistic perspective by reflecting this.

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Design of an Innovative Moisture Separator Technology for Use in Nuclear Power Plants: Numerical Approach — Part 1

Volume 1: Beyond Design Basis; Codes and Standards; Computational Fluid Dynamics (CFD); Decontamination and Decommissioning; Nuclear Fuel and Engineering; Nuclear Plant Engineering ◽

10.1115/icone2020-16193 ◽

2020 ◽

Author(s):

Loris Padovan

Keyword(s):

Nuclear Power ◽

Power Plants ◽

Nuclear Power Plants ◽

Water Film ◽

Operating Conditions ◽

Innovative Technology ◽

Separation Performance ◽

Major Advance ◽

Subsequent Formation ◽

Moisture Separator

Abstract The Moisture Separator Re-heater (MSR) is a key component of Nuclear Power Plants (NPP) both in terms of performance and avoiding erosion and erosion/corrosion damage. Wet steam is usually dried in a MSR by inertial separation using separator elements. Depending on the design of a MSR, the technology of separator elements contributes significantly to its size and performance, hence is seen as a subject for in-depth investigation, improvement and innovation. Computational Fluid Dynamics (CFD) has been used to understand the working principles of moisture separating devices, in particular the OpenFOAM platform has been utilized for this scope. Eulerian/Lagrangian models, wall-droplet interaction and water film formation models have been adopted to determine the physical phenomena occurring during the moisture separation process. Additional sub-models have been implemented to make a more robust solver and to solve in a comprehensive way all the possible physical processes: in particular a two-layers turbulence model and a film breakup model have been implemented. An out-of-the-box thinking approach was adopted to devise a new proposed chevron vane. Aerodynamic principles were used to design an innovative concept of separator panel, which can entrap the moisture droplets and water rivulets through a subsequent formation of recirculating steam representing artificial slots (hidden pockets) within the separator channel. The control of the steam separation on precise regions of the separator panel wall, helps the drainage of the water film without the utilization of physical obstacles (pockets or drainage channels). To validate the results achieved from the numerical simulation and to characterize separation performance of a new kind of separator technology, a bespoke test rig has been designed, built and put into operation at typical MSR operating conditions [1]. Throttling calorimeter methodology has been adopted to measure, with very good accuracy, the residual moisture content after the separator. The design developed has shown excellent separation performance. Particularly, this solution will allow improved MSR performance and significantly reduced MSR size. This represents an innovative technology which is a major advance on current technology available within the industry. The novel design features have been patented by General Electric. The first operation of a MSR with this technology is eagerly awaited.

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Design of an Innovative Moisture Separator Technology for Use in Nuclear Power Plants: Numerical Approach \u2014 Part 1

10.1115/1.0000288v ◽

2021 ◽

Author(s):

Loris Padovan

Keyword(s):

Nuclear Power ◽

Power Plants ◽

Nuclear Power Plants ◽

Numerical Approach ◽

Moisture Separator

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Design of an Innovative Moisture Separator Technology for Use in Nuclear Power Plants: Experimental Validation — Part 2

Volume 3: Student Paper Competition; Thermal-Hydraulics; Verification and Validation ◽

10.1115/icone2020-16550 ◽

2020 ◽

Author(s):

Carsten Hersberger ◽

Elias Waldvogel ◽

Joshua Bopp ◽

Beat Ribi

Keyword(s):

Moisture Content ◽

Nuclear Power ◽

Power Plants ◽

Nuclear Power Plants ◽

Operating Conditions ◽

Separation Performance ◽

Residual Moisture Content ◽

Test Rig ◽

Residual Moisture ◽

Moisture Separator

Abstract The Moisture Separator Reheater (MSR) is a key component of Nuclear Power Plants (NPP), both in terms of performance and prevention of erosion/corrosion. Wet steam is usually dried in a MSR by inertial separation of the liquid water using separator elements. Depending on the design of the MSR, the technology of the separator elements contributes significantly to its size and performance. An innovative concept of separator panels was conceived by means of aerodynamic principles as outlined in part 1 of this paper [1]. Computational Fluid Dynamics (CFD) has been used to understand the working principles of various moisture separating devices. The investigated separator panels are designed to capture the water droplets in a region of flow separation (invisible pockets) within the separator channels. To characterize the separation performance of these separator panels, a test rig has been developed and built at the University of Applied Sciences Northwestern Switzerland (FHNW). This test rig was then operated at typical MSR operating conditions. To meet the required moisture content and flow conditions, preheated water was injected into the saturated steam flow. In order to measure the residual moisture content after the separation the throttling calorimeter methodology has been adopted. The newly designed panels have shown very good separation performance. According to the measurements carried out, a residual moisture content of less than 0.1 % can be guaranteed. The innovative technology, which clearly differentiates the OEM, for who this research was carried out, from its competitors, will allow considerable size and cost reduction as well as opportunities to retrofit existing MSRs.

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