PHISICS/RELAP53D Adaptive TimeStep 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 RELAP53D, 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 PHISICSRELAP53D code for implementing an adaptive time step methodology into the code for the first time, and to test it using the full HTTR PHISICS/RELAP53D 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/RELAP53D model test results as well as the University of Rome subcontractor report documenting the adaptive time step theory and methodology implemented in PHISICS/RELAP53D. 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 »
 Authors:
 Idaho National Lab. (INL), Idaho Falls, ID (United States)
 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/EXT1741569
 DOE Contract Number:
 AC0705ID14517
 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/RELAP53D Adaptive TimeStep 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/RELAP53D Adaptive TimeStep Method Demonstrated for the HTTR LOFC#1 Simulation. United States. doi:10.2172/1374506.
Baker, Robin Ivey, Balestra, Paolo, and Strydom, Gerhard. 2017.
"PHISICS/RELAP53D Adaptive TimeStep 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/RELAP53D Adaptive TimeStep 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 RELAP53D, 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 PHISICSRELAP53D code for implementing an adaptive time step methodology into the code for the first time, and to test it using the full HTTR PHISICS/RELAP53D 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/RELAP53D model test results as well as the University of Rome subcontractor report documenting the adaptive time step theory and methodology implemented in PHISICS/RELAP53D. 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 realtime, or even less than realtime, compared with the previous version of the code that completed the same transient 38 times slower than realtime. 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 modelspecific and cannot be generalized to other PHISICS/RELAP53D models.},
doi = {10.2172/1374506},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 5
}

RELAP5 is a computer code, used to simulate transients in light water reactors and was designed primarily for large and small break lossofcoolant 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.

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