VGB POWERTECH 7 (2021) - International Journal for Generation and Storage of Electricity and Heat

VGB PowerTech 7 l 2021
Study on the integrity of containment against hydrogen threats
Tab. 4. Summary of the containment model for the 3D analysis using the GASFLOW-MPI code.
Elements
Specifications
Mesh Number of cells : 71(X)×71(Y) × 81(Z) = 408,321
Cell size: 59.2cm×59.2cm ×90.7 cm
Passive heat sink
Components
PAR
A
Slab model: CAD structure
Wall model: Steel shell containment, concrete shield building
Sink model: Internal structures
Containment spray
Fan cooler
NUKEM model
Fig. 4. Containment model of the reference plant: (a) Containment mesh model,
(b) PAR arrangement in the containment.
B
in each cell under the condition that the
combustion model is activated. In addition,
it is possible to calculate the forced
combustion using an ignitor. Spontaneous
ignition spreads very quickly, while the
combustion using an ignitor takes longer
than spontaneous ignition until the flame
starts at one location and burns all the hydrogen
in the containment. Therefore, in
this study, both conditions can be applied
to produce conservative combustion loads
from the viewpoint of the structural analysis
of the integrity of the containment; this
ensures that the combustion is more active
and occurs in a short time. The A1, A2, and
A5 cases result in thermodynamic and gas
composition conditions in which combustion
cannot occur. In addition, the A7 case
showed no hydrogen release at the highest
containment pressure. Therefore, the
combustion load analysis was performed
in eight cases, except for A1, A2, A5, and
A7.
F i g u r e 5 and F i g u r e 6 show the typical
hydrogen concentration and containment
pressure distribution during combustion
for the B3 case, respectively, for the
analysis cases described in Ta b l e 6 . The
B3 case is a case in which a very conservative
condition with a very high hydrogen
concentration is applied as a result of the
combustion analysis assuming that there is
––
Compartment average maximum pressure
timing (AP)
––
Compartment average maximum temperature
timing (AT)
––
Compartment average maximum hydrogen
concentration timing (AH)
Ta b l e 5 shows the conditions of all the
cases for the combustion load analysis. A
total of 12 cases were selected by applying
three combustion condition points to four
severe accident scenarios. For the MLOCA
case, the maximum pressure condition
(A7) was not considered in the analysis because
there was no hydrogen discharge until
the point of reaching the maximum
pressure. The conservative analysis conditions
were also derived. The B1 case applies
the regulatory requirement for the
average hydrogen concentration in the
containment: 10 vol. % of the average hydrogen
concentration. The B2 case is reflected
in the maximum hydrogen concentration
value identified in the LOOP case
analysis using MAAP5 as the initial condition
of the entire containment. The B3 case
is the condition at the point where the
maximum average hydrogen concentration
in the containment is shown just before the
reactor vessel failure, assuming that PARs
do not work in the event of a SLOCA, which
is associated with the highest amount of
hydrogen discharge.
The GASFLOW-MPI code whether or not
spontaneous ignition is possible based on
the Shapiro diagram considering of the hydrogen,
oxygen, and steam concentrations
Tab. 5. Test matrix for pressure analysis due to hydrogen combustion under severe accident
conditions.
Case
Accident
Scenario
Time
[s]
Pressure
[kPa]
Temperature
[K]
H 2 O 2 H 2 O N 2
A1(LW-WP-AP)
44,046 210.8 398 0.024 0.070 0.491 0.416
A2(LW-WP-AT)
LOCCW
(LW)
45,950 210.5 398 0.022 0.068 0.494 0.416
A3(LW-WP-AH) 32,124 183.3 461 0.059 0.106 0.417 0.583
A4(LP-WP-AP)
20,820 259.3 413 0.042 0.071 0.559 0.328
A5(LP-WP-AT)
LOOP
(LP)
20,720 234.0 438 0.035 0.039 0.728 0.198
A6(LP-WP-AH) 24,222 193.6 478 0.059 0.081 0.444 0.417
A7(MC-WP-AP)
4,805 261.9 391 0.000 0.084 0.578 0.338
A8(MC-WP-AT)
MLOCA
(ML)
33,524 175.6 392 0.065 0.108 0.347 0.481
A9(MC-WP-AH) 33,424 154.2 375 0.065 0.106 0.354 0.476
A10(SC-WP-AP)
26,918 173.9 380 0.061 0.109 0.332 0.498
A11(SC-WP-AT)
SLOCA
(SL)
26,418 171.8 382 0.060 0.112 0.325 0.503
A12(SC-WP-AH) 28,718 156.0 415 0.072 0.109 0.277 0.541
B1(LMT) Limited - 150.0 400 0.100 0.168 0.100 0.632
B2(LP-WP-MH) LOOP 20,720 234.0 438 0.125 0.039 0.728 0.108
B3(SC-WOP-AH)
SLOCA
W/O
PAR*
30,020 159.9 360 0.123 0.130 0.230 0.518
* W/O PAR: Severe accident analysis performed without PAR consideration.
Tab. 6. Analysis results of the structural integrity of the containment against hydrogen threats.
Case
Membrane strain
[%]
Plastic strain
[%]
Equivalent stress
[MPa]
Displacement
[mm]
B1(LMT) 0.278 0.216 262.99 39.65
B2(LP-WP-MH) 0.447 0.366 265.17 43.94
B3
(SC-WOP-AH)
1.319 1.334 278.82 81.54
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