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Title: PHISICS/RELAP5-3D Adaptive Time-Step Method Demonstrated for the HTTR LOFC#1 Simulation

Abstract

A collaborative effort between Japan Atomic Energy Agency (JAEA) and Idaho National Laboratory (INL) as part of the Civil Nuclear Energy Working Group is underway to model the high temperature engineering test reactor (HTTR) loss of forced cooling (LOFC) transient that was performed in December 2010. The coupled version of RELAP5-3D, a thermal fluids code, and PHISICS, a neutronics code, were used to model the transient. The focus of this report is to summarize the changes made to the PHISICS-RELAP5-3D code for implementing an adaptive time step methodology into the code for the first time, and to test it using the full HTTR PHISICS/RELAP5-3D model developed by JAEA and INL and the LOFC simulation. Various adaptive schemes are available based on flux or power convergence criteria that allow significantly larger time steps to be taken by the neutronics module. The report includes a description of the HTTR and the associated PHISICS/RELAP5-3D model test results as well as the University of Rome sub-contractor report documenting the adaptive time step theory and methodology implemented in PHISICS/RELAP5-3D. Two versions of the HTTR model were tested using 8 and 26 energy groups. It was found that most of the new adaptive methods lead tomore » significant improvements in the LOFC simulation time required without significant accuracy penalties in the prediction of the fission power and the fuel temperature. In the best performing 8 group model scenarios, a LOFC simulation of 20 hours could be completed in real-time, or even less than real-time, compared with the previous version of the code that completed the same transient 3-8 times slower than real-time. A few of the user choice combinations between the methodologies available and the tolerance settings did however result in unacceptably high errors or insignificant gains in simulation time. The study is concluded with recommendations on which methods to use for this HTTR model. An important caveat is that these findings are very model-specific and cannot be generalized to other PHISICS/RELAP5-3D models.« less

Authors:
 [1];  [2];  [1]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Univ. of Rome (Italy)
Publication Date:
Research Org.:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1374506
Report Number(s):
INL/EXT-17-41569
DOE Contract Number:
AC07-05ID14517
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
97 MATHEMATICS AND COMPUTING; CNWG milestone; HTTR; LOFC; time step enhancement

Citation Formats

Baker, Robin Ivey, Balestra, Paolo, and Strydom, Gerhard. PHISICS/RELAP5-3D Adaptive Time-Step Method Demonstrated for the HTTR LOFC#1 Simulation. United States: N. p., 2017. Web. doi:10.2172/1374506.
Baker, Robin Ivey, Balestra, Paolo, & Strydom, Gerhard. PHISICS/RELAP5-3D Adaptive Time-Step Method Demonstrated for the HTTR LOFC#1 Simulation. United States. doi:10.2172/1374506.
Baker, Robin Ivey, Balestra, Paolo, and Strydom, Gerhard. 2017. "PHISICS/RELAP5-3D Adaptive Time-Step Method Demonstrated for the HTTR LOFC#1 Simulation". United States. doi:10.2172/1374506. https://www.osti.gov/servlets/purl/1374506.
@article{osti_1374506,
title = {PHISICS/RELAP5-3D Adaptive Time-Step Method Demonstrated for the HTTR LOFC#1 Simulation},
author = {Baker, Robin Ivey and Balestra, Paolo and Strydom, Gerhard},
abstractNote = {A collaborative effort between Japan Atomic Energy Agency (JAEA) and Idaho National Laboratory (INL) as part of the Civil Nuclear Energy Working Group is underway to model the high temperature engineering test reactor (HTTR) loss of forced cooling (LOFC) transient that was performed in December 2010. The coupled version of RELAP5-3D, a thermal fluids code, and PHISICS, a neutronics code, were used to model the transient. The focus of this report is to summarize the changes made to the PHISICS-RELAP5-3D code for implementing an adaptive time step methodology into the code for the first time, and to test it using the full HTTR PHISICS/RELAP5-3D model developed by JAEA and INL and the LOFC simulation. Various adaptive schemes are available based on flux or power convergence criteria that allow significantly larger time steps to be taken by the neutronics module. The report includes a description of the HTTR and the associated PHISICS/RELAP5-3D model test results as well as the University of Rome sub-contractor report documenting the adaptive time step theory and methodology implemented in PHISICS/RELAP5-3D. Two versions of the HTTR model were tested using 8 and 26 energy groups. It was found that most of the new adaptive methods lead to significant improvements in the LOFC simulation time required without significant accuracy penalties in the prediction of the fission power and the fuel temperature. In the best performing 8 group model scenarios, a LOFC simulation of 20 hours could be completed in real-time, or even less than real-time, compared with the previous version of the code that completed the same transient 3-8 times slower than real-time. A few of the user choice combinations between the methodologies available and the tolerance settings did however result in unacceptably high errors or insignificant gains in simulation time. The study is concluded with recommendations on which methods to use for this HTTR model. An important caveat is that these findings are very model-specific and cannot be generalized to other PHISICS/RELAP5-3D models.},
doi = {10.2172/1374506},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 5
}

Technical Report:

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  • RELAP5 is a computer code, used to simulate transients in light water reactors and was designed primarily for large and small break loss-of-coolant and operational transients. Development emphasized fast running, ease of use, and sufficient accuracy for most calculations. Models used in RELAP5 are briefly described and applications of the code to Semiscale and LOFT experiments are illustrated. Planned research at INEL to use RELAP5 in interactive, real time, and ultimately predictive modes are discussed.
  • The report details the logic, program layout, and operating procedures for the time-step MOTA (Materials Open Test Assembly) thermostat simulation program known as GYRD. It will enable prospective users to understand the operation of the program, run it, and interpret the results. The time-step simulation analysis was the approach chosen to determine the maximum value gain that could be used to minimize steady temperature offset without risking undamped thermal oscillations. The advantage of the GYRD program is that it directly shows hunting, ringing phenomenon, and similar events. Programs BITT and CYLB are faster, but do not directly show ringing time.
  • In order to reduce computation time, a long time step could be assumed in the numerical integrations involved in investigations of xenon instabilities in large high-flux reactors. The question of error introduced by this assumption is examined in tbe case of the linear approximation of the nonlinear problem. It is shown that, if corrections in the perturbation procedure of order higher than the first are negligible, there exists a simple relationship between the true time constant of any instability mode and the time constant calculated with the aid of a non-zero time step. (D.L.C.)
  • Research on the development of numerical techniques to simulate the space-time evolution of large tokamak plasmas is reported. A non-uniform spatial mesh technique is employed to allow more accurate calculations in the boundary of reactor size plasmas. A box integration method is used to maintain the accuracy of central differencing on the non-uniform spatial mesh and to preserve both the particle and energy flux. A variable implicit technique is used for the time expansion. The time-centered (Crank-Nicholson) technique used in most other models generally offers greater accuracy but can lead to severe limitations on the time step. Somewhat more implicitmore » treatments can remove the numerical limitations on the timestep without seriously affecting accuracy. The physical time scales, which can change by several orders of magnitude from startup to equilibrium, can then be used to continually adjust the timestep throughout a calculation. Sample calculations are presented for a near-term tokamak engineering test reactor (TETR) and a conceptual tokamak power reactor, UWMAK-III.« less
  • An important numerical constraint on self consistent Monte Carlo device simulation is the stability limit on the time step imposed by plasma oscillations. The widely quoted stability limit for the time step between Poisson field solutions, {Delta}t<2/{omega}{sub p} where {omega}{sub p} is the plasma frequency, is specific to the leapfrog particle advance used in collisionless plasma simulation and does not apply to typical particle advance schemes used for device simulation. The authors present a stability criterion applicable to several algorithms in use for solid state modeling; this criterion is verified with numerical simulation. This work clarifies the time step limitationmore » due to plasma oscillations and provides a useful guide for the efficient choice of time step size in Monte Carlo simulation. Because frequent solution of the Poisson equation can be a sizable computational burden, methods for allowing larger time step are desirable. The use of advanced time levels to allow stability with {omega}{sub p}{Delta}t{much_gt}1 is well known in the simulation of collisionless plasmas; they have adapted these implicit methods to semiconductor modeling and demonstrated stable simulation or time steps larger than the explicit limit.« less