Authors: - Lou Qualls, Oak Ridge National Labs, Oak Ridge, TN USA - Richard Hale, Oak Ridge National Labs, Oak Ridge, TN USA - David Fugate, Oak Ridge National Labs, Oak Ridge, TN USA - Sacit Cetiner, Oak Ridge National Labs, Oak Ridge, TN USA - John Batteh, Modelon, Inc., Ann Arbor, MI USA - Michael Tiller, Xogeny, Inc., Canton, MI USA As part of the advanced small modular nuclear reactor (AdvSMR) R&D program, Oak Ridge National Laboratory (ORNL) is developing a Dynamic System Modeling Tool (MoDSim) to facilitate research and development related primarily to instrumentation and controls (I&C) studies of small modular reactors (SMRs). The primary objective is to produce a demonstration product of a dynamic system modeling tool for SMRs. Functional Mockup Interface (FMI) has been used to allow the development of scoping models for non-Modelica users. This tool includes a web-based interface using Xogeny’s FMQ platform for model configuration with local application deployment for simulation using FMI Add-in for Excel from Modelon; this toolchain is designed to allow plug and play access for users of various skill levels. The web-based interface allows true web-based access and solutions without requiring local applications. The initial installation of this tool has been tested on a liquid-metal small modular reactor (ALMR) concept modeled using Dymola and exported via FMI. This tool allows simulation to be performed within Excel without expertise in the native simulation language (Modelica) or model development and simulation environment (Dymola). This toolchain fulfills the Department of energy (DOE) project scope goal of developing a tool “in a common and familiar environment to support a range of research activities requiring dynamic behavior simulation, modeling tools with easily re-configurable modules that reduce data input to typically available system level plant data”. Full text at: http://www.ep.liu.se/ecp/096/103/ecp14096103.pdf http://www.modelon.com/news/news-display/artikel/modelica-conference/

1. 1
Dynamic Modeling of Small
Modular Nuclear Reactors using
MoDSIM
March 12, 2014
Lou Qualls
Richard Hale
David Fugate
Sacit Cetiner
John Batteh
Michael Tiller

2. 2
Outline
• Project Background
• Modeling Overview
– Architecture
– Components
– Instrumentation & Controls
– Sample Results
• Web Application and Workflow
• Demo
• Summary and Next Steps

3. 3
Project Background
Project Introduction/Need
• The Small Modular Reactor (SMR) Dynamic System Modeling Tool project is designed to allow collaborative
modeling and study of various SMR configurations, including the use of multiple connected reactors at a
single site.
• In particular, the safety and control evaluations of the possible concepts depend on an understanding of the
system dynamics necessitating a number of mathematical models of the plants. A great many different
organizations and researchers may be involved in evaluating the concepts. To facilitate this collaboration the
project was instituted with the following goals and objectives.
Project Goal
The goal of the project is to provide a common simulation environment and baseline modeling resources to
facilitate rapid development of SMR models, ensure consistency among research products while minimizing
duplication of effort.
Project Objectives
The high level objectives include the following:
(1) define a standardized, common simulation environment that can be applied throughout the program,
(2) develop a library of baseline component modules that can be assembled into full plant models,
(3) define modeling conventions for interconnecting component models, and
(4) establish interfaces and support tools for users of various capabilities to facilitate simulation development
(i.e., configuration and parameterization), execution, and results display and capture.

4. 4
Model Architecture and Overview
• Modular model architecture for SMR
• Architecture based on early ALMR PRISM model (GE)
• First implementation is a Liquid Metal Reactor
• Common architecture and bus infrastructure supports
modeling of many variants via reconfiguration
DRACS – Passive Safety
System for Cooling
PHTS (Primary Heat Transport
System) – Reactor and primary
(liquid metal) coolant loop
IHX (Intermediate Heat
Exchanger) – Metal to water
Heat Exchanger
SG (Steam Generator) –two
phase steam generator
PCS (Power Conversion
System) – Turbine and auxiliary
systems
Grid – Imposed Grid Interface
ED (Event Driver) – Introduces
Faults and Transients to
simulation
CS (Control System) – Applies
Control System Strategies to
Reactor

5. 5
Primary Heat Transport System (PHTS)
• Includes reactor and primary
sodium loop.
• Connected to passive heat
transport system (DRACS) and to
Intermediate Heat Exchanger
(IHX)
• Current medium library includes
liquid sodium, liquid NaK, LiF-
BeF2, KF-ZrF4, LiF-NaF-KF, and
LiF-NaF-BeF2
• Coolant channel geometry in
core includes two assembly
configurations; square pitch and
triangular pitch
• Dynamic coolant flowrate based
on pump curve and coolant
density (temperature dependent)
• 5 Implementations
PHTS Boundary Condition Value
Core mass flow rate (kg/s) 2,256.8
Core coolant inlet temperature (ºC) 319
Core coolant outlet pressure (bar) 1.01325

6. 6
Intermediate Heat Exchanger (IHX)
• Interface between
primary heat transport
system and intermediate
heat transport system
• HX modeled as separate
elements to provide
flexibility for changes in
potential design
concepts
• Modeled as two flow
channels thermally
interacting through a
metal tube
• Hot sodium on the shell
side flows down, cooler
sodium flows upward
inside the tubes
• 4 Implementations
Parameter Primary Fluid Intermediate Fluid
Inlet Temperature (ºC) 468.33 282.22
Flow Rate (nominal conditions) (kg/s) 1,126.42 1,152.88
Pressure Drop (nozzle to nozzle) (kPa) 27.5 ± 20% 131 ± 20%
Inlet Pressure (kPa) 103.4 758.4
LMTD (ºC) 39.4

7. 7
Intermediate Heat Transport System (IHTS)
• Includes mechanical
sodium pump, sodium
expansion tank, and
piping
• Serves as interface
between IHX and SG
• Pressure drops
matched with total
piping length of 30m
• Pump follows PRISM
design pump head
curve
• 5 implementationsFlow Rate
(m3/s)
Head
(m)
0.63 140
1.26 130
1.89 120
2.52 100
3.15 65

8. 8
Steam Generator (SG)
• Serves as the
interface
between IHTS
and PCS
• Vertically
oriented, shell
and tube counter
flow heat
exchanger
• Water steam on
the tube side and
sodium on the
shell side.
• Employs two
cylindrical tubes
to account for
double walled
construction
• Single
implementation

9. 9
Power Conversion System (PCS)
• Serves as interface
between SG and
Grid
• Converts steam to
mechanical power
via series of
turbines
• No specialized
ALMR PRISM
modules
developed
• Simplified version
of standard power
conversion system
• 4 Implementations

10. 10
Grid/Event Driver/CS Models
• Remaining pieces
include;
– Simplified grid model
– I&C strategies
– Event Drivers for
fault and transient
introduction
Grid Model
Event Driver Architecture
PHTS Control System Model PHTS Event Transients

11. 11
Simulation Capability
• Current models simulate various
potential transients
• Focused on overcooling,
undercooling, and reactivity
transients currently
• Transients help define system
behavior under off-normal
conditions
• Supports engineering work to
correctly design and size
subsystems and components and
develop associated controls

12. 12
PRISM Simulation Results
• Simulation
shows two
different
control
strategies
associated
with a single
transient
• Transient is
step change in
reactivity
• Control
strategy #1 is
controlling
outlet
temperature
• Control
strategy #2 is
controlling
differential
temperature

13. 13
Instrumented Model
• Live objects to display key flowrates, temperatures,
distributions, and grid results

14. 14
Web Application and Workflow
• Web application for model configuration and
parameterization built using FMQ platform from Xogeny
• Platform allows for redeployment of web app via
standardized text files describing architectures, subsystems,
and FMUs
• User configured FMUs downloaded for local simulation and
automated plotting using FMI Add-in for Excel from Modelon
• Collaboration enabled via GitHub for source code
development

15. 15
Web Application Demo

16. 16
Summary and Next Steps
• ORNL Modelica-based Dynamic System Modeling Tool will allow
rapid development, increased flexibility and improved
collaboration in studying SMR behavior
• Initial component and system models complete, more under
development
• Initial demonstration of an end-to-end ALMR complete
• Initial prototype of web application to support model configuration,
parameterization and local simulation complete using FMQ platform
with FMI Add-in for Excel
• Additional SMR concepts can now be modeled and studied within
this environment
• Active collaboration with other DoE partners in hybrid energy
• Collaboration features still under development