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TRACE code application to
low operating pressure
research reactor safety analysis
Adolfo Rais (Switzerland)
D. Novog (Canada) and T. Hamidouche (Belgium)
Motivation
McMaster University Nuclear Reactor
safety analysis
TRACE
code assessment against:
1. Subcooled boiling experiments
2. IAEA 10MW reactor theoretical benchmark
Adolfo Rais, 2014
Subcooled boiling experiments
at low pressures
- Axial void fraction measurement
- Annular test section
- Controlled: P, G, θ, q’’
-
TRACE
&
Adolfo Rais, 2014
RELAP5
model
Heated Section
Results subcooled boiling
0.6
0.6
Run no. BC7
Run no. BC8
!"#$%& '()*++#,"-& .& /012& 34
0.4 5,"& .& 61007& 859
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0.3
0.2
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0.4 9$3) @) CDEAF) G9+
H) @) AIF) J?K(A.L
"MM) @) NOI) JPK(A
0.3
0.2
0.1
0.1
0.0
0.0
-0.04
Adolfo Rais, 2014
-0.03
) !120'$(03,+%
) 4567!
) 5!869:
0.5
Void Fraction
Void Fraction
0.5
& DIJ$E,>$"%9#
& KLM4D
& LDNM5O
-0.02
-0.01
DA(,#,)E,(>& F(9#,%G& ?& H$
0.00
-0.04
-0.03
-0.02
-0.01
!"#$%$&'$#() *#+%$,-) .) /0
0.00
Results subcooled boiling (cont’d)
Overall
TRACE
0.6
performance:
- Poor agreement with
experimental data
- Is this only happening at low
pressures?
TRACE Void Fraction
- Studies on TRACE’s models to
spot potential causes
0.5
0.4
0.3
0.2
0.1
0.0
0.0
Adolfo Rais, 2014
0.1
0.2
0.3
Measured Void Fraction
0.4
Subcooled boiling at various P
0.7
code-to-code comparison: TRACE vs. RELAP5
0.6
Void Fraction
0.5
0.4
15 MPa TRACE
15 MPa RELAP5
2 MPa TRACE
2 MPa RELAP5
Simulations for
fixed: G, θ, q’’
0.2 MPa TRACE
0.2 MPa RELAP5
Incr
0.3
e as i
ng p
re s s
ure
0.2
0.1
0.0
0.0
Adolfo Rais, 2014
0.1
0.2
Axial position (m)
0.3
Subcooled boiling at various P
0.7
code-to-code comparison: TRACE vs. RELAP5
0.6
Void Fraction
0.5
0.4
15 MPa TRACE
15 MPa RELAP5
2 MPa TRACE
2 MPa RELAP5
Simulations for
fixed: G, θ, q’’
0.2 MPa TRACE
0.2 MPa RELAP5
Incr
0.3
e as i
ng p
re s s
ure
0.2
Large divergence
at low pressure
0.1
0.0
0.0
Adolfo Rais, 2014
0.1
0.2
Axial position (m)
0.3
TRACE
TRACE
overprediction: potential causes
void fraction:
Interaction of three models
1. Void source
2. Void sink
3. Interfacial friction
Adolfo Rais, 2014
TRACE
TRACE
overprediction: potential causes
void fraction:
Interaction of three models
1. Void source
2. Void sink
3. Interfacial friction
Adolfo Rais, 2014
■ q’’ partitioning sub-model
■ Flow regime transitions
Overview
- TRACE code assessment against:
1. Subcooled boiling experiments
systematic overprediction
2. IAEA 10MW reactor theoretical benchmark
Adolfo Rais, 2014
Quick specs:
- Generic (idealized) MTR
- 10 MW nominal
- H2O cooled & moderated
- Graphite moderated
W - Water
G - Grafite
Transients considered: SFE - Standard
Fuel Element
- Fast loss-of-flow
CFE - Control
- Slow loss-of-flow
Fuel Element
- Slow reactivity insertion
- Fast reactivity insertion
Adolfo Rais, 2014
Water Reflector
IAEA 10 MW reactor benchmark
W
G
G
G
G
W
W
SFE
5%
SFE
25%
SFE
25%
SFE
5%
W
SFE
5%
CFE
25%
SFE
45%
SFE
45%
CFE
25%
SFE
5%
SFE
25%
SFE
45%
SFE
45%
SFE
25%
SFE
5%
CFE
25%
SFE
45%
SFE
45%
CFE
25%
SFE
5%
W
SFE
5%
SFE
25%
SFE
25%
SFE
5%
W
W
G
G
G
G
W
W - Water
G - Grafite
SFE
45%
Alum.
W
SFE
45%
SFE - Standard Fuel Element
CFE - Control Fuel Element
Water reflector
Results IAEA benchmark
TRACE’s results compared against:
|
RELAP5
|
PARET
|
RETRAC-PC
Transients considered:
- Fast loss-of-flow
- Slow loss-of-flow
- Slow reactivity insertion
- Fast reactivity insertion
Adolfo Rais, 2014
|
COBRA III-C
|
EUREKA-PT
| ...
Results IAEA benchmark
TRACE’s results compared against:
|
RELAP5
|
PARET
|
RETRAC-PC
|
COBRA III-C
|
EUREKA-PT
| ...
✔ acceptable agreement
Transients considered:
- Fast loss-of-flow
- Slow loss-of-flow
- Slow reactivity insertion
- Fast reactivity insertion
Adolfo Rais, 2014
✖ unexpected behavior
Results IAEA benchmark (cont’d)
Fast reactivity insertion transient: $1.5 in 0.5 sec.
10MW
TRACE
RELAP5
200
power
1MW
Power (W)
100kW
clad
10kW
175
150
125
1kW
100W
100
coolant
10W
75
1W
50
0.4
Adolfo Rais, 2014
0.5
0.6
0.7
Time (s)
0.8
0.9
Temperature (°C)
100MW
Results IAEA benchmark (cont’d)
Fast reactivity insertion transient: $1.5 in 0.5 sec.
10MW
TRACE
RELAP5
200
power
30 °C
1MW
Power (W)
100kW
clad
10kW
175
150
125
1kW
100W
100
coolant
10W
75
1W
50
0.4
Adolfo Rais, 2014
0.5
0.6
0.7
Time (s)
0.8
0.9
Temperature (°C)
100MW
Results IAEA benchmark (cont’d)
Fast reactivity insertion transient: $1.5 in 0.5 sec.
TRACE
RELAP5
clad
5
Temperature (°C)
160
140
4
120
100
3 -Trans. boiling
80
3
2 -Nucleate boiling
2
60
1- Liquid convection
40
0.6
Adolfo Rais, 2014
0.7
0.8
Time (s)
1
0.9
Heat Transfer Regime No.
180
TRACE triggering Transition Boiling
without reaching Critical Heat Flux
Critical Heat Flux
10000
6
CHF
Heat Flux
1000
4
3 -Transition boiling
100
2 -Nucleate boiling
1- Liquid conv.
10
0.60
Adolfo Rais, 2014
3
0.65
0.70
Time (s)
0.75
2
1
0.80
Heat Transfer Regime
Heat Flux (kW/m2)
5
Conclusions
Subcooled boiling experiments
■ systematic void overprediction
■ overprediction only at low pressures
■ RELAP5: superior performance
IAEA theoretical benchmark
■ acceptable agreement between codes for
FLOF, SLOF, SRIA
■ FRIA: singular behavior (trans. boiling)
Adolfo Rais, 2014
Need to
revise TRACE models
to yield better results
Thank you!
Adolfo Rais, 2014
Thus finally,
✓
Tl
Tl,OSV
Tl,OSV
◆
Heat flux partitioning sub-model
00
qev
=
00
(qw
qf00c,2
)·
Tl,sat
(3.10)
To complete the description, the final expressions for wall heat flux partitioning implemented by relap5 and trace are presented in Table 3.1.
relap5
00
qev
=
00
qw
·
✓
Tl
Tl,sat
Tl,OSV
Tl,OSV
trace
◆
1
·
1+✏
00
qev
=
00
(qw
qf00c,2
)·
✓
Tl
Tl,sat
Tl,OSV
Tl,OSV
◆
Table 3.1: relap5 vs. trace heat flux partitioning models
High
@ low
not
vary much
It is clear that
bothsuppression
expressions in Table
3.1press
are similar. Does
The only
noticeable
di↵erences
are, for relap5’s expression,
in Lthe
the pumping
ε= f (ρ
/ρvlast
) term containingfrom
low to factor
high (✏),
P and
for trace, the term qf00c,2 . Both terms act suppressing the wall evaporation rate.
However, recalling Eq. 3.4, the pumping factor (✏) is densities ratio (⇢l /⇢v ) dependent,
hence it becomes exceptionally important at low-pressure conditions. The results suggest
that, at high pressures, the suppression resulting from the pumping factor ✏ in relap5
00
approaches
that
one
given
by
q
f c,2 in trace. This could explain the fact that both
Adolfo Rais, 2014
IAEA 10 MW reactor benchmark
Reactor core
Al. Cladding
Support
Plate
Light Water Moderator
amplification
Fuel Meat
Fuel ele
ment amplification
Fuel Plate
Adolfo Rais, 2014
©2013 Adolfo Rais
Homogeneous Equilibrium Model
Void fraction
Experimental
TRACE
HEM
Void Fraction
1
1
Run no. BC7
15 MPa
2 MPa
0.2 MPa
HEM model
G = 200 kg/m2-s
q’’ = 500 kW/m2
0
-0.4
-0.2
Adolfo Rais, 2014
0.0
0.2
Eq. quality (Xe)
0.4
0.6
0.8
-0.04
-0.03
-0.02
Equilibrium Quality - Xe
-0.01
0.00