.. _section-3.15:
Input and Output
----------------
.. _section-3.15.1:
Input Description
~~~~~~~~~~~~~~~~~
The input variables used in the pre-voiding subassembly thermal
hydraulics calculations are listed in :numref:`table-3.14-1`. Some additional
comments on some of these input variables are listed below.
.. _section-3.15.1.1:
Per Pin Basis
^^^^^^^^^^^^^
All of the core channel thermal hydraulic input to SAS4A/SASSYS‑1 is on
a per pin basis rather than a per subassembly basis. Thus, the initial
flow rate, W0, is kg/s per pin; and the perimeters SRFSTZ and SER are
perimeters per pin. Also, ACCZ is a coolant flow area per pin, and the
variables DZIAB and DZIAT are ratios of inertial lengths to flow areas
per pin.
.. _section-3.15.1.2:
Structure/Duct Wall and Wrapper Wires
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Typically a SAS4A/SASSYS‑1 channel represents an average pin in a
subassembly. In this case, the structure normally represents one pin's
share of the duct wall, and it may also include the wrapper wire. If
there are N pins in the subassembly, then the thickness used for the
structure is the actual duct wall thickness, and the perimeter used for
the structure is the duct wall perimeter divided by N. The wrapper wire
can be either lumped with the cladding or included in the structure.
Since wrapper wires are in much better contact with the cladding than
with the duct wall, the most accurate treatment of the wrapper wire is
probably to lump it with the cladding by increasing the specific heat of
the cladding by enough to account for the total heat capacity of the
cladding plus the wrapper wire. The cladding dimensions would not be
changed.
The problem with lumping the wrapper wires with the duct wall to produce
a single "structure" is that typically the duct wall has a much larger
ratio of volume to wetted surface area than a wrapper wire, so the
wrapper wire temperature will respond much more rapidly than the duct
wall temperature to a change in coolant temperature. The heat capacity
of the duct wall is considerably greater than the heat capacity of all
of the wrapper wires in a subassembly, but the total perimeter of the
wrapper wires is greater than the perimeter of the duct wall. If the
duct wall and wrapper wires are lumped together, then the thickness of
the structure should be determined by the thickness of the duct wall,
since the duct wall contains most of the heat capacity. Then the
perimeter of the structure should be chosen to conserve the total volume
or total heat capacity of the duct wall plus wrapper wires.
A SAS4A/SASSYS‑1 channel can be used to represent a central pin rather
than an average pin in a subassembly. In this case, the duct wall would
probably be ignored, and the "structure: would represent only the
wrapper wire. The perimeter of the structure would equal the perimeter
of a wrapper wire, and the thickness of the structure would equal one
half of the wrapper wire radius in order to conserve volume.
.. _table-3.15-1:
.. list-table:: Subassembly Thermal Hydraulics Input Variables
:header-rows: 1
:align: center
:widths: auto
* - **Variable**
- **Reference Eq. No.**
- **Input Variable**
- **Input Block**
- **Location Number**
- **Suggested Value**
- **External Reference**
* -
-
- NCHAN
- 1
- 1
- 1-34
-
* -
-
- IFUEL1
- 1
- 3
- 1-8
-
* -
-
- ICLAD1
- 1
- 4
- 1-3
-
* -
-
- ITKEL
- 1
- 7
- 0 or 1
-
* -
-
- IPOWOP
- 1
- 9
- 1
-
* -
-
- MAXSTP
- 1
- 11
- --
-
* -
-
- IPO
- 1
- 12
- 20-50
-
* -
-
- IPOBOI
- 1
- 13
- 20-50
-
* -
-
- IBLPRT
- 1
- 14
- 0
-
* -
-
- INAS3D
- 1
- 29
- 0
-
* -
-
- ISSNUL
- 1
- 87
- --
-
* -
-
- IPRSNL
- 1
- 88
-
-
* -
-
- EPSTEM
- 11
- 1
- .1 or less
-
* -
-
- DTMXB
- 11
- 6
- .01
-
* -
-
- DTFUEL
- 11
- 10
- 50
-
* -
-
- DTCLAD
- 11
- 11
- 30
-
* -
-
- POW
- 12
- 1
-
-
* - Ï
- 3.3.1
- COEFDS(1)
- 13
- 1
- 11080
-
* -
-
- COEFDS(2)
- 13
- 2
- 2.04x10\ :sup:`-5`
-
* -
-
- COEFDS(3)
- 13
- 3
- 8.70x10\ :sup:`-9`
-
* - k
- 3.3.1
- COEFK
- 13
- 4
-
-
* - k
- 3.3.1
- EXKTB
- 13
- 11
-
-
* -
-
- EXKTM
- 13
- 71
-
-
* - Ï
- 3.3.1
- RHOTAB
- 13
- 91
-
-
* -
-
- RHOTEM
- 13
- 251
-
-
* - k
- 3.3.1
- XKTAB
- 13
- 420
-
-
* -
-
- XKTEM
- 13
- 580
-
-
* - :math:`{\overline{c}}_{\text{f}}`
- 3.3-16
- CPFTAB
- 13
- 606
-
-
* -
-
- CPFTEM
- 13
- 766
-
-
* - T\ :sub:`sol`
- 3.3-92
- TFSOL
- 13
- 786
-
-
* - T\ :sub:`liq`
- 3.3-93
- TFLIQ
- 13
- 794
-
-
* - U\ :sub:`melt`
- 3.3-3
- UFMELT
- 13
- 802
-
-
* - U\ :sub:`melt`
- 3.3-3
- UEMELT
- 13
- 816
-
-
* - c\ :sub:`e`
- 3.3-32
- CPCTAB
- 13
- 819
-
-
* - Ï\ :sub:`e`\ c\ :sub:`e`
-
- COCTEM
- 13
- 879
-
-
* -
-
- CROETB
- 13
- 990
-
-
* -
-
- CROETM
- 13
- 1050
-
-
* - p\ :sub:`x`
- 3.12-1
- PX
- 14
- 1
-
-
* - T\ :sub:`in`
- 3.3-101
- TOTAB
- 14
- 45
-
-
* -
-
- TOTME
- 14
- 65
-
-
* - :math:`z_{\text{pll}}`
- 3.9-30
- ZPLENL
- 14
- 87
-
-
* - :math:`z_{\text{plu}}`
- 3.9-27
- ZPLENU
- 14
- 88
-
-
* - M\ :sub:`mix`
- 3.3-99
- XMXMSI
- 14
- 93
-
-
* - M\ :sub:`mix`
- 3.3-99
- XMXMS0
- 14
- 94
-
-
* - Ï„\ :sub:`mix`
- 3.3-101
- TIMMIX
- 14
- 95
-
-
* -
-
- IRHOK
- 51
- 3
-
-
* -
-
- NPLN
- 51
- 4
- 2-6
-
* -
-
- NREFB
- 51
- 5
- 1-5
-
* -
-
- NREFT
- 51
- 6
- 1-5
-
* -
-
- NZNODE
- 51
- 7
-
-
* - NT
-
- NT
- 51
- 14
- 4-11
-
* -
-
- IFUELV
- 51
- 15
- 1-IFUEL1
-
* -
-
- IFUELB
- 51
- 16
- 1-IFUEL1
-
* -
-
- ICLADV
- 51
- 17
- 1-ICLAD1
-
* -
-
- NGRDSP
- 51
- 18
- 0-10
-
* -
-
- IHGAP
- 51
- 24
- 0 or 1
-
* -
-
- NPIN
- 51
- 25
- 1 or more
-
* -
-
- NSUBAS
- 51
- 26
- 1 or more
-
* -
-
- MZUB
- 51
- 27
- 0-24
-
* -
-
- MZLB
- 51
- 28
- 0-24
-
* -
-
- ILAG
- 51
- 34
- 0
-
* -
-
- IEQMAS
- 51
- 118
- 0
-
* -
-
- IFRFAC
- 51
- 186
-
-
* -
-
- NCHCH
- 51
- 205
-
-
* -
-
- ICHCH
- 51
- 206
-
-
* -
-
- JJMLTP
- 51
- 214
-
-
* -
-
- IAXCON
- 51
- 284
-
-
* - A\ :sub:`c`
- 3.3-5
- ACCZ
- 61
- 1
- >0
-
* - Δ\ :sub:`z`
- 3.3-6
- AXHI
- 61
- 8
- >0
-
* - D\ :sub:`h`
- 3.3-9
- DHZ
- 61
- 32
- >0
-
* - d\ :sub:`sti`
- 3.3-45
- DSTIZ
- 61
- 39
- >0
-
* - d\ :sub:`sto`
- 3.3-47
- DSTOZ
- 61
- 46
- >0
-
* -
-
- PLENL
- 61
- 53
- >0
-
* -
-
- RBR
- 61
- 54
- >ROUTFP
-
* -
-
- RER
- 61
- 78
- >RBR
-
* - r\ :sub:`brp`
- 3.3-68
- RBRPL
- 61
- 102
- >0
-
* - r\ :sub:`crp`
- 3.3-73
- RERPL
- 61
- 103
- >RBRPL
-
* -
-
- RINFP
- 61
- 104
-
-
* -
-
- ROUTFP
- 61
- 128
- >RINFP
-
* -
-
- ZONEL
- 61
- 152
- >0
-
* - S\ :sub:`pt`
- 3.3-40
- SRFSTZ
- 61
- 159
-
-
* -
-
- AREAPC
- 61
- 166
- >0
-
* - d\ :sub:`ro`
- 3.3-59
- DRFO
- 61
- 169
- >0
-
* -
-
- RBRO
- 61
- 180
- >0
-
* -
-
- RERO
- 61
- 181
- >0
-
* - S\ :sub:`cr`
- 3.3-62
- SER
- 61
- 182
- >0
-
* - d\ :sub:`ri`
- 3.3-56
- DRFI
- 61
- 189
- >0
-
* - N\ :sub:`PI`
- 3.11-1
- XXNPIN
- 61
- 274
- >0
-
* - γ\ :sub:`s`
- 3.3-22
- GAMSS
- 62
- 2
-
-
* - γ\ :sub:`c`
- 3.3-6
- GAMTNC
- 62
- 4
-
-
* - γ\ :sub:`e`
- 3.3-23
- GAMTNE
- 62
- 5
-
-
* -
-
- PSHAPE
- 62
- 6
-
-
* - P\ :sub:`r`
- 3.3-22
- PSHAPR
- 62
- 30
-
-
* -
-
- AHBPAR
- 63
- 2
-
-
* -
-
- BHBPAR
- 63
- 3
-
-
* -
-
- CHIBPAR
- 63
- 4
-
-
* -
-
- HBMAX
- 63
- 5
-
-
* -
-
- HBMIN
- 63
- 6
-
-
* -
-
- HBPAR
- 63
- 7
-
-
* - k\ :sub:`si`
- 3.3-43
- XKSTIZ
- 63
- 11
-
-
* - k\ :sub:`so`
- 3.3-46
- XKSTOZ
- 63
- 18
-
-
* - εσ
- 3.3-4
- DEL
- 63
- 25
-
-
* - k\ :sub:`r`
- 3.3-57
- XKRF
- 63
- 28
-
-
* - (*Ï*\ c)\ :sub:`sti`
- 3.3-45
- RHOCSI
- 63
- 37
- >0
-
* - (*Ï*\ c)\ :sub:`sto`
- 3.3-47
- RHOCSO
- 63
- 44
- >0
-
* - (*Ï*\ c)\ :sub:`r`
- 3.3-56
- RHOCR
- 63
- 51
- >0
-
* - (*Ï*\ c)\ :sub:`g`
- 3.3-68
- RHOCG
- 63
- 58
- >0
-
* - R\ :sub:`g`
- 3.3-71
- RG
- 63
- 59
- >0
-
* - α\ :sub:`f`
- 3.10-4
- FUELEX
- 63
- 73
-
-
* - α\ :sub:`e`
- 3.10-5
- CLADEX
- 63
- 74
-
-
* - Y\ :sub:`f`
- 3.10-8
- YFUEL
- 63
- 75
-
-
* - Y\ :sub:`e`
- 3.10-9
- YCLAD
- 63
- 76
-
-
* -
-
- FULREX
- 63
- 77
-
-
* -
-
- CLDREX
- 63
- 78
-
-
* - :math:`(\text{HA}_{\text{I,M}}`
- 3.11-1
- HACHCH
- 63
- 82
-
-
* - 1/γ\ :sub:`ht`
- 3.3-116
- TAVINV
- 63
- 104
- .5-5
-
* - A\ :sub:`fr`
- 3.8-3
- AFR
- 64
- 1
- .1875
-
* - b\ :sub:`fr`
- 3.8-3
- BFR
- 64
- 2
- -.2
-
* - c\ :sub:`1`
- 3.3-9
- C1
- 64
- 3
- .025
- 2-5
* - c\ :sub:`2`
- 3.3-9
- C2
- 64
- 4
- .8
- 2-5
* - c\ :sub:`3`
- 3.3-9
- C3
- 64
- 5
- 4.8
- 2-5
* -
-
- DWMAX
- 64
- 6
- .2
-
* - Re\ :sub:`L`
- 3.9-3
- RELAM
- 64
- 7
- 2100
-
* - A\ :sub:`fL`
- 3.9-3
- AFLAM
- 64
- 8
- 64
-
* - Re\ :sub:`TR`
-
- RETRAN
- 64
- 8
-
-
* - C\ :sub:`1`
-
- C1TRAN
- 64
- 9
-
-
* - C\ :sub:`2`
-
- C2TRAN
- 64
- 9
-
-
* - C\ :sub:`3`
-
- C3TRAN
- 64
- 9
-
-
* -
-
- W0
- 64
- 47
-
-
* - K\ :sub:`or`
- 3.9-12
- XKORV
- 64
- 48
-
-
* -
-
- XKORGD
- 64
- 64
-
-
* - :math:`\left(\frac{\Delta z_i}{A}\right)_{b}`
- 3.9-6
- DZIAB
- 64
- 65
- >0
-
* - :math:`\left(\frac{\Delta z_i}{A}\right)_{f}`
- 3.9-6
- DZIAT
- 64
- 66
-
-
* - T\ :sub:`out`
- 3.3.-100
- DTLMAX
- 64
- 69
- 15
-
* - U\ :sub:`1`
- 3.10-1
- TUPL
- 64
- 74
-
-
* - U\ :sub:`2`
- 3.10-2
- UACH1
- 64
- 189
-
-
* -
-
- UACH2
- 64
- 190
-
-
.. _section-3.15.1.3:
Empty Reflector Region
^^^^^^^^^^^^^^^^^^^^^^
Sometimes a reflector zone is used to represent an empty section of a
subassembly. The duct wall is usually represented by the structure; and
since there is nothing but sodium inside the duct wall, there is nothing
for the reflector to represent. The code requires a "reflector" in every
axial zone except the pin section, so some input for the reflector must
be included. The reflector perimeter, SER, cannot be zero; but it can be
set to a very small value, such as :math:`10^{-9}`, so that it would have
no impact on coolant temperatures. Also, the total reflector thickness,
DRFI plus DRFO, must be a reasonable value, 0.003 m or more, to prevent
numerical instabilities in the reflector temperature calculations in the
boiling module. The pre-voiding reflector temperature calculations are
numerically stable for any reflector greater than zero.
.. _section-3.15.1.4:
Structure and Reflector Node Thickness
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Two radial nodes are used in the reflectors and in the structure. The
only restrictions on node thicknesses are that the total reflector
thickness and the total structure thickness must be reasonable; 0.003 m
or more, to prevent numerical instabilities in the temperature
calculations in the boiling module. Usually, the node in contact with
the coolant, the inner structure node or the outer reflector node,
represents approximately :math:`10\%` of the total thickness; and the other node
represents the rest. Then the small node in contact the coolant will
react rapidly to rapid changes in the coolant temperatures, whereas the
larger node will dominate the longer-term response to the slow changes.
.. _section-3.15.1.5:
Coolant Re-entry Temperature
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If PRIMAR-1 is being used, then the re-entry temperature calculation
described in :numref:`section-3.3.6` uses the input variable TUPL for the bulk
temperature of the coolant in the outlet plenum. If PRIMAR-4 is being
used, then the outlet plenum temperature is computed by PRIMAR-4; and
TUPL is not used.
.. _section-3.15.2:
Output Description
~~~~~~~~~~~~~~~~~~
:numref:`figure-3.14-1` shows a typical thermal hydraulic output for one step of
the transient. The output is largely self-explanatory. Note that on the
first page of this output the axial location, coolant temperature,
saturation temperature, and pressure are the values at node boundaries;
whereas the cladding, structure, plenum, and reflector temperatures are
the values at node mid-points. Also, on the second page the radial fuel
temperatures are the values at node mid-points except for the inner and
outer fuel temperature, as indicated in :numref:`figure-3.2-4`; whereas the radii
are the values of radial node boundaries.
.. _figure-3.15-1:
.. figure:: media/image26.png
:align: center
:figclass: align-center
:width: 7.52292in
:height: 6.09236in
Sample Subassembly Thermal Hydraulics Output
.. figure:: media/image27.png
:align: center
:figclass: align-center
:width: 7.39236in
:height: 5.95417in
Sample Subassembly Thermal Hydraulics Output (Cont'd.)
.. figure:: media/image28.png
:align: center
:figclass: align-center
:width: 7.60000in
:height: 5.50764in
Sample Subassembly Thermal Hydraulics Output (Cont'd.)
.. _section-3.15.3:
Subchannel Information
~~~~~~~~~~~~~~~~~~~~~~
This section provides additional information that is necessary to
implement the subchannel model described in :numref:`section-3.14`. This includes
a brief user guide, followed by a sample problem, then a detailed
overview of the required input. More information about the
SAS4A/SASSYS‑1 preprocessor, which is available to expedite the input
creation process for the subchannel model, can be found in :numref:`section-A3.2`.
.. _section-3.15.3.1:
User Guide
^^^^^^^^^^
This user guide provides a quick summary of the grouping of channels and
subassemblies and how to properly prepare the required input.
Information about standard output and a binary plotting option is also
given.
.. _section-3.15.3.1.1:
Channels, Subassemblies, and Groups
'''''''''''''''''''''''''''''''''''
A basic feature of the core treatment is the concept of a channel. In
simple terms a channel consists of a fuel pin and its associated coolant
and structure. As used in the SAS4A/SASSYS‑1 code, a channel is a bit
more involved. :numref:`figure-3.15-2` shows some details of a SAS4A/SASSYS‑1
channel if the three dimensional thermal hydraulics model is *not* being
used. In the axial direction the whole length of the subassembly is
modeled. A channel includes the whole fuel pin, including the fuel
region, axial reflectors in the fuel pin, a gas plenum region at the top
or bottom of the fuel pin. Also, a channel includes axial reflector
zones above and below the fuel pins.
When the three dimensional thermal hydraulics model is used, the concept
of a channel is even more involved. The three-dimensional treatment is
used only in the pin section. Multiple channels are used in the pin
section of a subassembly, but in the axial reflector zones a single
channel treatment is used, as shown in :numref:`figure-3.15-3`. The first channel
used to represent a subassembly includes the pin section and the axial
reflectors. All other channels used to represent the subassembly only
include the pin section, as seen in :numref:`figure-3.15-4`.
.. _figure-3.15-2:
.. figure:: media/image29.png
:align: center
:figclass: align-center
:width: 6.31528in
:height: 5.71528in
Details of SAS4A/SASSYS‑1 Axial and Radial Nodes (if 3-D Thermal Hydraulics Model is not Being Used)
.. _figure-3.15-3:
.. figure:: media/image30.png
:align: center
:figclass: align-center
:width: 4.23819in
:height: 4.45417in
Breakdown of Axial Regions and Treatments
.. _figure-3.15-4:
.. figure:: media/image31.png
:align: center
:figclass: align-center
:width: 6.53056in
:height: 3.31528in
3-D Thermal Hydraulics Input Channel Structure
Coolant flow enters a single channel at the bottom of the subassembly,
flows through a single channel in the lower reflectors, splits into
multiple flow paths in the pin section, and re-combines into a single
flow path for the upper reflectors, as shown in :numref:`figure-3.15-5`. In the
pin section, cross-flow between the channels representing a subassembly
is accounted for.
.. _figure-3.15-5:
.. figure:: media/image32.png
:align: center
:figclass: align-center
:width: 4.76944in
:height: 4.27708in
Subchannel Model Flow Diagram
If one is modeling a reactor without solid duct walls, then accounting
for cross-flow between subassemblies is desirable. In order to handle
this situation, the concept of a group of channels was incorporated in
the model. If solid duct walls are used, then there will be a one-to-one
correspondence between subassemblies and groups. If solid duct walls are
not used then a group can include many subassemblies, maybe even the
whole core. Cross flow between adjacent channels in the whole group is
accounted for, but again cross flow is only accounted for in the pin
section. The reflector zones are included only in the first channel in a
group. Channels are still combined into subassemblies for some edits,
even if multiple subassemblies are included in a group. The maximum
number of channels that can be included in a group is limited only by
the amount of computer memory available for temporary storage of coolant
variables during the simultaneous solution of the coolant conditions in
all channels in the group. This temporary storage memory is allocated
dynamically at run time based on the maximum group size.
Subassembly numbers are assigned by the user by setting the input
variable ISUBAS (location 89 of block 51). Group numbers are assigned by
the code on the basis of input variable JJMLTP (location 214 of block
51). If JJMLTP for a channel is greater than or equal to zero, then a
new group is started. If :math:`\text{JJMLTP} < 0`, then the channel is part of the
current group.
.. _section-3.15.3.1.2:
Preparing Input for a Case
''''''''''''''''''''''''''
One issue to be addressed when preparing input for a case using the new
three dimensional thermal hydraulics core model is the amount of detail
to be used for various parts of the core. If enough computer memory and
computer speed are available, then one could analyze every coolant
subchannel and every fuel pin in the core. It is also possible to
analyze some subassemblies with the detailed subchannel treatment shown
in :numref:`figure-3.14-1`, to analyze other subassemblies with a somewhat less
detailed treatment such as that shown in :numref:`figure-3.15-6`, and to analyze
the rest of the core using one channel to represent a subassembly or a
group of similar subassemblies.
The amount of input required for even a moderately sized case can be
considerable. Some input is required for each channel, and the number of
channels can easily be very large. Fortunately, most of the input for
the new model is fairly repetitive, and much of it can be automated by a
preprocessor. :numref:`section-A3.2-3` describes a preprocessor that has been
written for the SAS4A/SASSYS‑1 code with the new model.
.. _figure-3.15-6:
.. figure:: media/image33.png
:align: center
:figclass: align-center
:width: 5.41528in
:height: 4.06944in
Subchannels Grouped in Rings
.. _section-3.15.3.1.3:
Controlling the Amount of Standard Output
'''''''''''''''''''''''''''''''''''''''''
The standard output from SAS4A/SASSYS‑1 includes tables of temperatures,
pressures and coolant flow rates for each axial node and each radial
node in each channel. These tables are printed out for the steady-state
results and for every IPO (location 12, input block 1) time steps during
the transient. Even before the new three-dimensional thermal hydraulic
model was added to the code, the problem of excessive amounts of output
from the code was recognized. An input variable, IPRSKP (location 274,
block 51) can be used to skip output from specified channels. Also,
before the new model was added to the code, reactivity feedback
components for each channel were printed out for each step of the
transient. Now the reactivity feedback components are printed out for
each subassembly rather than for each channel.
.. _section-3.15.3.1.4:
Binary Output for Plotting
''''''''''''''''''''''''''
The new model includes a provision for writing a binary output file on
unit 24. This output file can contain user specified values calculated
by the new model. It is anticipated that plotting programs will use this
file to plot results from the new model. The user can specify which data
is included on unit 24, how often that data is written, and for which
channels.
The SAS4A/SASSYS‑1 code writes a number of binary output files other
than the unit 24 file mentioned above. The CHANNEL.dat binary file
reports reactor power and reactivity feedback in addition to
temperatures of fuel, clad, and structure, and coolant flow rates for
all channels. The CHANNEL.dat file can be extremely large if using the
subchannel model, as a full thermal hydraulic dataset is provided for
each subchannel in the binary output. While the user cannot control what
channels are included in CHANNEL.dat, the user can control the frequency
of output using the MSTPLA, MSTPLB, MSTPL1, MSTPL2, and MSTPL3
(INPCOM:107-111) input fields.
.. _section-3.15.3.2:
Sample Problem
^^^^^^^^^^^^^^
:numref:`figure-3.15-7` shows output from a sample problem run with the new model.
This test case uses two 19 pin subassemblies with
subassembly-to-subassembly heat transfer. Selected coolant temperatures
from one of the subassemblies are shown in :numref:`figure-3.15-7`. The transient
was a simulated scram with a delayed pump trip and little natural
circulation head in the primary loop. Temperatures drop rapidly due to
the scram and then rise after the pump trip until enough buoyancy is
established in the subassemblies to increase the flow rate and stop the
temperature rise. Flow reversal occurred in the center subchannels from
22.5 seconds to 83.5 seconds in the transient. Flow reversal occurred in
the edge subchannels from 22.0 seconds to 111.25 seconds.
The case described above used two subassemblies, each containing 19 pins
and 42 coolant subchannels in the pin section. Four axial nodes were
used in a lower reflector below the pin section, 24 axial nodes were
used in the core, 6 axial nodes were used in the gas plenum region above
the core, and 5 axial nodes were used in a reflector above the pins. A
null transient of 50 steps with a time step of 1.0 second was used for
each subassembly separately. Then a 50 step null transient using both
subassemblies and subassembly-to-subassembly heat transfer was run with
a time step of 0.5 seconds. Finally the regular transient was run for
1200 steps using a time step of 0.25 seconds. The null transients
started with 35 iterations per step and got down to 2 iterations per
step as they converged on a steady-state solution. The regular transient
required between 12 and 21 iterations per step. The total running time
was 867 seconds on a Sun Blade computer with a 500 MHz processor.
.. _figure-3.15-7:
.. figure:: media/image34.png
:align: center
:figclass: align-center
:width: 4.72292in
:height: 5.62292in
Results for a Scram with a Delayed Pump Trip
.. _section-3.15.3.3:
Input Description
^^^^^^^^^^^^^^^^^
Input for the SAS4A/SASSYS‑1 code is read into numbered locations in
input blocks. Each input block has a name and a number. Below is a
listing of the additional input variables that are used for the new
three-dimensional thermal-hydraulic core model. A description of each
input can be found in the User Guide in :numref:`Chapter %s<section-2>`.
.. _table-3.15-2:
.. list-table:: Detailed Subchannel Model Input Variables
:header-rows: 1
:align: center
:widths: auto
* - **Variable**
- **Reference**
**Eq. No.**
- **Input Variable**
- **Input Block**
- **Location Number**
- **Suggested Value**
- **External Reference**
* -
-
- ISSNUL
- 1
- 87
-
-
* -
-
- ISCH
- 1
- 115
-
-
* -
-
- ISUBAS
- 51
- 89
-
-
* -
-
- JJMLTP
- 51
- 214
-
-
* -
-
- JCHMPN(K)
- 51
- 215-218
-
-
* -
-
- NUMKLT
- 51
- 219
-
-
* -
-
- KSWIRL
- 51
- 220
-
-
* -
-
- NULSTI
- 51
- 221
-
-
* -
-
- IFT24
- 51
- 495
-
-
* -
-
- ILATF
- 51
- 496
-
-
* -
-
- NFT24
- 51
- 501
-
-
* -
-
- JCFT24(K)
- 51
- 502-521
-
-
* -
-
- ITYPE24(K)
- 51
- 522-541
-
-
* -
-
- NULPT1
- 51
- 542
-
-
* -
- 3.14-7
- UACHM1(K)
- 64
- 197-200
-
-
* -
- 3.14-8
- UACHM2(K)
- 64
- 201-204
-
-
* -
-
- ALATRL(K)
- 64
- 205-208
-
-
* -
-
- XKLAT(K)
- 64
- 209-212
-
-
* -
-
- DPLTLM
- 64
- 213
-
-
* -
-
- XKSWRL
- 64
- 214
-
-
* -
-
- DTNUL1
- 64
- 215
-
-
* -
-
- EPSFLW
- 64
- 216
-
-
* -
-
- EPSTMP
- 64
- 217
-
-
* -
-
- EPSPRS
- 64
- 218
- 1.0
-
* -
-
- XCMPRS
- 64
- 219
-
-
* -
-
- XLINRT
- 64
- 220
-
-