ANALYSIS AND SENSITIVITY STUDIES OF EXERCISE 1 OF THE OECD/NRC BWR TT BENCHMARK

OECD/NRC Boiling Water Reactor Peach Bottom 2 Turbine Trip Benchmark ANALYSIS AND SENSITIVITY STUDIES OF EXERCISE 1 OF THE OECD/NRC BWR TT BENCHMARK 2002 ANS Winter Meeting Bedirhan Akdeniz and Kostadin Ivanov Pennsylvania State University

Peach Bottom 2 Turbine Trip Benchmark OUTLINE 2002 ANS Winter Meeting . Introduction . Objectives and Definitions . Performed Studies - Steady State Results - Transient Results - Sensitivity Studies Results . Conclusions

Peach Bottom 2 Turbine Trip Benchmark INTRODUCTION 2002 ANS Winter Meeting • Recent progress in computer technology has made development of coupled system thermal-hydraulic and neutron kinetics code systems feasible. • The OECD/NRC BWR Turbine Trip Benchmark has attracted the participation of a significant number of companies and organizations from different countries • Benchmark team of PSU is responsible for authoring the specifications, coordinating the benchmark activities, answering participant questions, analyzing the solutions submitted by participants, providing reports and summarizing the results for each phase of the benchmark

Peach Bottom 2 Turbine Trip BenchmarkOBJECTIVES and DEFINITIONS 2002 ANS Winter Meeting BWR Turbine Trip: • Begins with a sudden turbine stop valve closure and simulates the turbine trip transient • Coupling between core phenomena and system dynamics plays an important role • Available real plant experimental data makes this benchmark problem very valuable

Peach Bottom 2 Turbine Trip Benchmark OBJECTIVES and DEFINITIONS 2002 ANS Winter Meeting Purpose of Exercise 1: • to test the system thermal-hydraulics with fixed axial power profile • to initialise the participants’ system models TRAC-BF1: - Transient Reactor Analysis Code - An advanced best-estimate computer program for BWR accident analysis

Peach Bottom 2 Turbine Trip BenchmarkPERFORMED STUDIES 2002 ANS Winter Meeting • TRAC-BF1 model was developed for PBTT • After being sure that the model is reflecting the PBTT characteristics, steady state and transient studies were performed • The results were compared with RETRAN results and available measured dome pressure data • Sensitivity studies were performed for steam bypass flow and core by pass flow.

Peach Bottom 2 Turbine Trip Benchmark REQUESTED OUTPUTS 2002 ANS Winter Meeting 1- SEQUENCE OF EVENTS 3- TIME HISTORIES • Dome Pressure • Core Exit Pressure • Total Jet Pump flow • Turbine Bypass Flow 2- STEADY STATE • Core Inlet Enthalpy • Core Axial Pressure Drop • Core Average Axial Void Fraction Distribution

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting TRAC-BF1 Steady State Results • Steady state pressure drop, core inlet enthalpy and core average void fraction distribution are callculated as follows: Inlet Enthalpy: 1209.1 kJ/kg Pressure Drop: 137.6 kPa Plant Reference Parameters:

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting TRAC-BF1 Steady State Results

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting TRAC-BF1 Transient Results

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting SEQUENCE of EVENTS • TSVC : Turbine Stop Valve Closed • BVBO : Bypass Valve Begins Opening • BFO : Bypass Full Open • DPIR : Dome Pressure Initial Response • CEPIR : Core Exit Pressure Initial Response

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting SENSITIVITY STUDIES • In order to determine the jet pump behavior correctly sensitivity study was performed for pressure drop characterisics • Different number of channels were used to test the system thermal-hydraulics. Although few of them is sufficient to simulate the Exercise 1, 33 core channels were used because of the Exercise 2 and 3. • Main steam bypass flow modeling was performed • Core bypass flow modeling was performed. • In this presentation main steam bypass flow and core bypass flow sensitivity results will ve presented.

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting SENSITIVITY STUDIES Main Steam Bypass Flow Modeling: Accurate modeling of the steam bypass system is going to assure that the dynamic response of system pressure is well predicted. important issues are: - obtaining the steam bypass characteristics - an accurate geometric representation

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting MAIN STEAM BYPASS FLOW SENSITIVITY STUDY

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting CORE BYPASS FLOW SENSITIVITY STUDIES Bypass Channel Modellng: Additional 2 bypass channels added to 33 core channels in order to represent core bypass flow. Leak Path Flow Modeling: Instead of additional bypass channels TRAC-BF1 allows user to define leakage flow from channel to vessel component. TRAC-BF1 1-Dimensional Vessel Model

Steady State Core Bypass Flow Sensitivity Results Flow Rates Bypass Channel Model (kg/s) Leak Path Model (kg/s) RETRAN (kg/s) Total Core 10445 11031 10445 Channels 9603 9530 9603 Bypass 842 1501 842 Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting CORE BYPASS FLOW SENSITIVITY STUDIES

Peach Bottom 2 Turbine Trip Benchmark PERFORMED STUDIES 2002 ANS Winter Meeting CORE BYPASS FLOW SENSITIVITY STUDIES

Peach Bottom 2 Turbine Trip BenchmarkCONCLUSIONS 2002 ANS Winter Meeting For both steady state and transient simulations, TRAC-BF1 results are in very good agreement with measured data and RETRAN predictions. The Results from sensitivity studies are helpful to analyze participants’ results for the 1st Benchmark Exercise. It is also verified that TRAC-BF1 can represent the system thermalhydraulics at both steady state and transient conditions.

OECD/NRC Boiling Water Reactor Turbine Trip Benchmark 2002 ANS Winter Meeting T H A N K Y O U Bedirhan Akdeniz and Kostadin N. Ivanov The Pennsylvania State University

ANALYSIS AND SENSITIVITY STUDIES OF EXERCISE 1 OF THE OECD/NRC BWR TT BENCHMARK