United States
Environmental Protection
Agency
Research and Development
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
EPA/600/SR-94/195 January 1995
v/EPA Project Summary
RAETRAD Version 3.1 User
Manual
Kirk K. Nielson, Vern Rogers, and Vern C. Rogers
This report is a user's manual for the
RAETRAD (RAdon Emanation and
TRAnsport into Dwellings) computer
code. RAETRAD is a two-dimensional
numerical model to simulate radon
(222Rn) entry and accumulation in
houses from its calculated generation
in soils, floor slabs, and footings and
its movement by diffusion and advec-
tion through soil and concrete pores
and openings. User input defines nomi-
nal house size and foundation param-
eters, concrete properties, and soil
properties, including their distributions
of radium (226Ra), moisture, and related
properties.
RAETRAD is installed automatically
and operated on common personal
computers. It includes a graphical user
interface with interactive queries to as-
sist the user in defining model prob-
lems. Default values typical of the
properties of common soil textural
classes and concretes are provided to
assist in generic definitions otf unknown
parameters. Separate input files are cre-
ated for each problem and can be ana-
lyzed in batch mode or individually.
Six sample problems are provided with
the program diskette to verify proper
installation and operation of the soft-
ware.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Radiation doses from indoor radon de-
cay products are a significant cause of
lung cancer and are the dominant source
of natural radiation exposure in the U.S.
population. Indoor radon comes mainly
from decay of naturally occurring radium
in underlying soils, although contributions
from water, building materials, outdoor air,
and other sources are sometimes impor-
tant. Indoor radon levels are difficult to
predict; however, long-term average lev-
els can be estimated by mathematical
models, which simulate the complex pro-
cesses of radon generation, transport, and
indoor entry using soil and house param-
eters.
The RAETRAD model was developed
to provide simple but detailed simulations
of radon generation in soils and founda-
tion structures and entry into indoor envi-
ronments. It represents slab-on-grade
houses of different sizes and shapes on
soils with any distribution of radon sources,
physical properties, water contents, and
gas transport properties. It was developed
in part under the Florida Radon Research
Program (FRRP), co-sponsored by the
Florida Department of Community Affairs
and the U.S. Environmental Protection
Agency (EPA). It has been used in the
FRRP to characterize the effects of foun-
dation soil and fill properties on indoor
radon entry, to characterize the modes of
radon entry, to characterize soil radon po-
Printedon Recycled Paper
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tentlals for mapping of their geographic
distributions, to develop simplified lumped-
parameter models, and to support devel-
opment of radon-protective building
construction standards.
RAETRAD is particularly useful for ad-
dressing questions such as how strong
and how close to a house can a radon
source be for particular soil and ground
water conditions without excessively el-
evaling indoor radon levels. This informa-
tion is important for planning and regulating
soil excavation and replacement at ra-
dium-contaminated sites and also in regu-
lating building construction in areas with
high-radium strata or with fill soils of higher
or lower radium concentration. Version 3.1
of the RAETRAD computer code extends
many of its previous capabilities and op-
erates on personal computer systems.
Model House Configuration
RAETRAD represents the house floor,
foundation, and vicinity soils by two-di-
mensional arrays of properties for use in
finite-difference calculations. The arrays
are oriented vertically and horizontally as
shown in Figure 1. The house is rectan-
gular, with user-specified dimensions, and
Is represented with its floor slab, cracks,
footings, and foundation soils in elliptical-
cylindrical geometry to utilize efficient two-
dimensional finite-difference calculations.
The elliptical-cylindrical symmetry consid-
ers the aspect ratio (length/width) of the
rectangular house to represent it more
accurately than conventional, circular-cy-
lindrical or two-dimensional Cartesian ge-
ometries.
RAETRAD can analyze either simple or
relatively complex problems, depending on
the amount of information available to char-
acterize the house and its foundation soils.
It Is designed to represent as many dis-
crete regions as desired (e.g., concrete
slab, footings, fill soil, and foundation soil
layers). Each region is assumed to be
homogeneous and may consist of one or
more contiguous numerical mesh units.
For each defined region, individual values
are defined for the radium concentration,
radon emanation coefficient, density, po-
rosity, water content, radon diffusion coef-
ficient, air permeability, radon adsorption
coefficient, and anisotropies of the diffu-
sion and permeability coefficients. User-
specified radon concentrations and air
pressures are applied as boundary condi-
tions at the top of the floor slab and on
the outdoor soil surface.
The differential equations describing
pressure-driven air flow and radon gen-
eration, decay, and transport (both diffu-
sive and advective) are solved separately
in RAETRAD. This provides the steady-
state air pressure and velocity fields from
the first solution as input for calculating
the advective component of transport in
obtaining the second solution for the ra-
don equations. Multiphase radon equa-
tions are used to include moisture effects
in the calculations. For both equations,
coefficients defined by the properties of
each mesh unit are arranged into matri-
ces that are solved directly without itera-
tion.
Operating Environment and
Installation
RAETRAD is designed for use in the
Microsoft Windows® 3.1 environment on
an IBM*-compatible personal computer
system. The system ideally should be
equipped with a math'co-p'rocessor and a
VGA color monitor and graphics system
and should have at least 3 Mbytes of
unused random access memory (RAM).
RAETRAD will prompt the user if any of
these conditions are not satisfied but can
proceed anyway at the user's option.
Printed output is formatted for a 132 char-
acter-per-line printer.
An installation program install is included
on the RAETRAD Version 3.1 diskette.
The installation program creates a
RAETRAD subdirectory when started from
the Windows® File Menu. It also loads the
RAETRAD files into the subdirectory and
creates a RAETRAD program group and
icon for use in the Windows® desktop dis-
play.
Getting Started
Upon startup, RAETRAD displays five
main menu options. The INPUT FILES
option is used to create, modify, and de-
lete RAETRAD input files. The RAETRAD
ANALYSIS option lists all input files listed
on the input subdirectory for selection of
those to be, analyzed. Up to 30 files can
be selected for batch analysis. The
RAETRAD RESULTS option lists all out-
put files on the output subdirectory for
detailed or summary viewing on the screen
or for printout. The I/O PATHS option al-
lows specification of subdirectory locations
for data (input and output) files separate
from the RAETRAD system files. The EXIT
option is used to end the RAETRAD ses-
sion.
The I/O PATHS option should be se-
lected upon initial startup to define data
and system subdirectories. They need not
be redefined in subsequent sessions ex-
cept to rename the subdirectories. Input
file names are appended to a .RAE exten-
sion, and corresponding output files have
a .OTn extension, where n is a version
number to distinguish multiple analyses of
a file with the same name.
Input and output files for six sample
problems are furnished with the RAETRAD
Version 3.1 diskette to verify program in-
stallation and operation. The sample files
can be analyzed from Option 2 (RAETRAD
ANALYSIS).
Creating Input Files
A detailed user dialogue is furnished for
creating new input files under the INPUT
FILES menu. The dialogue is guided by a
graphical display of a house and up to 17
soil and concrete classes for parameter
selection. Default values, displayed with
most data queries, are selected by press-
ing without additional input. The
key allows the user to back_upjo
feaddress tfie previous question." ""'
General parameters are defined first,
including the maximum soil depth to be
analyzed and its radial extent and mesh
unit size. House parameters are defined
next, including the height of the indoor
volume, the width and length of the rect-
angular house, and its ventilation rate,
indoor air pressure, and indoor radon con-
centration. The specified indoor radon con-
centration is only a numerical boundary
condition and has little effect on the re-
sulting calculated indoor radon concentra-
tion.
Floor slab parameters are specified
next, including concrete thickness, ra-
dium concentration, bulk density, radon
emanation coefficient, porosity, and ma-
terial type. The material type selects a
set of default parameters (accessible in
the RAETRAD.SYS file) for succeeding
queries about water content, radon
transport constants, and adsorption.
Outdoor air pressure and radon bound-
ary conditions are defined next, followed
by detailed definition of soil layers. For
each layer, the thickness and number of
vertical mesh units are defined, followed
by radium concentration, density, ema-
nation coefficient, porosity, and material
type. The default soil properties stored
in the RAETRAD.SYS file are based on
soil moistures at -30 kPa matric poten-
tial and empirical correlations of radon
diffusion coefficients and air permeabil-
ity with soil properties.
The dimensions of the foundation foot-
ing and stem wall are defined next, along
with their radium concentration, density,
emanation coefficient, porosity, and mate-
rial type parameters. The fill soil thickness
is then defined, followed by the location,
distribution, and properties of floor cracks
and penetration openings. The openings
may be defined to go into the house or to
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an external vent and may have alternative
pressure and radon boundary conditions
to those specified for the house. Many of
the chosen parameters are displayed
graphically on the screen, and all are fi-
nally saved in the input file under the
chosen file name. Input files can be al-
tered with the Modify/Review option and
can also be manipulated outside the Win-
dows® environment with the DOS editor.
Processing Files and Managing
Output
The RAETRAD ANALYSIS option dis-
plays all input (.RAE) files for user selec-
tion. It then queries for disk storage or
printed output and whether to include de-
tailed air pressure and radon concentra-
tion arrays in the output. The RAETRAD
calculations are then started, displaying
on the screen the name of the current file
being processed. Upon completion, the
program returns to the main menu for
further instructions.
The RAETRAD RESULTS option per-
mits viewing of either the Summary Out-
put or Detailed Output on the screen.
Different sections are located using posi-
tioning keys. The option is also given to
print output to a previously initialized printer
with 132-character line width.
Sample Problems
The six sample problems utilize a 28.4
x 54.3 ft (8.7 x 16.6 m) slab-on-grade
house with 1 ft (0.3 m) of fill soil and a
stem wall that penetrates 2 ft (0.6 m)
below grade. Indoor air pressure and ra-
don boundary conditions are -2.4 Pa and
2 pCi/L, respectively, and outdoor values
are zero. The floor slab has different open-
ings in the different problems. For Prob-
lem 1, the slab has a 1-cm wide perimeter
crack. For Problem 2, it has the same
perimeter crack plus two utility penetra-
tions (100 cm? each) near the center. For
Problem 3, it has the same perimeter crack
plus two passive, external subslab vents
(100 cm2 each) at -5 Pa pressure. For
Problem 4, it has only the passive subslab
vents without the perimeter crack. For
Problem 5, it has only the subslab vents,
but at -20 Pa pressure. For Problem 6, it
has the perimeter crack plus the two
subslab vents at -20 Pa pressure.
The indoor radon concentrations com-
puted for Problems 1, 2, and 3 are similar
(2.75, 2.79, and 2.75 pCi/L, respectively),
indicating dominance by the perimeter
crack. Subslab ventilation (Problem 6) only
slightly reduced the indoor concentration.
Eliminating the perimeter crack in Prob-
lem 4 reduced the indoor radon level to
0.7 pCi/L, and adding more suction pres-
sure (Problem 5) made little additional dif-
ference. These results apply only to the
sample problems and can be very differ-
ent with different house and soil proper-
ties and configurations.
I House:
Center of Cn, Pn
Symmetry
I Floor Slab
I \ Fill Soil
Radial Dimension \ V
Shrinkage
Crack
\i
Pressure-driven
Air Flow:
Advective Radon
Transport
Footing /
' ' Outdoor Boundary:
§'•—••' •
ll
Q
2
1
i
i
P
.1
i
:i
acton G
«•/
v-*-
asD
ffusioi
I
1
i
S
oi
R
egi
ons
Figure 1. Two-dimensional grid and boundaries used to define house and soil regions for air and radon entry calculatio
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Kirk K. Nielson, Vem Rogers, and Vem C. Rogers are with Rogers and Associates
Engineering Corp., Salt Lake City, UT 84110-0330.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "RAETRAD Version 3.1 User Manual," consists of a
paper copy and a diskette. The paper copy (Order No. PB95-139689) and the
diskette (Order No. PB95-501995) are priced as a package for $140.00 (cost
subject to change) and will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
•Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
S300
EPA/600/SR-94/195
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
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