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

Study on the integrity of containment against hydrogen threats VGB PowerTech 7 l 2021
no PAR condition in a SLOCA accident scenario,
which is associated with the greatest
amount of hydrogen generation. F i g -
u r e 5 shows the hydrogen concentration
in the containment with the combustion
analysis. Combustion begins at the center
of the containment, where ignition begins
with the ignitor. The ignitor is set to generate
sparks only for 0.01 seconds at the start
of the calculation. Once combustion starts,
it takes approximately 2.8 seconds for the
flame to spread to the entire containment
from where the first flame started and to
burn approximately 90 % of the hydrogen.
F i g u r e 6 shows the pressure increase at
the end of the combustion compared with
the initial amount of hydrogen before combustion.
Unlike the hydrogen concentration
shown in F i g u r e 5 , the pressure in
the containment varies with a uniform distribution
over time without any local difference.
F i g u r e 7 shows the behaviour of the
combustion pressure in the containment
during combustion. Although the tendencies
of the pressure are slightly different
with the combustion, it typically takes less
than 10 seconds to complete the combustion.
In F i g u r e 4 ( b ) the B-series is a
case where the initial amount of hydrogen
is greater than that in the (a) A-series case,
and flame propagation is faster than that in
the A-series. In B-series, the flame burns
within 0.5 seconds and lasts than 3 seconds.
Maximum pressure reached were
also relatively high. In terms of structural
integrity, the results of the B-series, which
have high rates of pressure change in the
containment during combustion, and high
post-combustion pressure values, can be
said to be more conservative. Therefore,
the results obtained from the B-series analysis
were applied as the pressure load conditions
for the integrity evaluation of the
containment structure.
Industry Code). Generally, the structural
integrity of a containment should be sufficiently
conservative to ensure the design
state with the linear static analysis in KEP-
IC. The purpose of this study was to conduct
a structural integrity analysis through
a dynamic analysis based on the hydrogen
behavior; therefore, the SRP, which is considered
to be more conservative than the
KEPIC code, is applied as the evaluation
criterion. To evaluate the safety in case of
accidents exceeding the design basis accident
pressure, the criteria of the SRP require
the evaluation of the pressure resistance
capability of the containment. When
the maximum global membrane strain
away from discontinuities (the hoop membrane
strain in a cylinder) reaches 1.5 %,
the internal pressure capacity was evaluated.
Therefore, the analysis and evaluation
were performed by applying this criterion.
In terms of the integrity of the containment
structure, the dynamic load due
to the hydrogen combustion is conservative
when the gradient of the pressure
change is sharp and the maximum pressure
is also high. In this respect, the results of
the combustion load analysis described in
Section 3 show that the B-series combustion
condition is more conservative than
(a) 0.0s (b) 0.2s (c) 0.4
(d) 0.6s (3) 0.8s (f) 1.0s
4. Evaluation of structural
response for the integrity of
containment
The structural response analysis of the
combustion load in the containment was
assessed using the commercial code,
ABAQUS. The calculated results of the
combustion pressure by the GASFLOW-
MPI code were considered in the ABAQUS
analysis. Using the finite element analysis
model based on the 3D CAD configuration
of the containment, a dynamic structural
response analysis was performed with the
hydrogen combustion load of the containment.
There are two criteria for evaluating
the structural integrity of a containment.
One is the criterion for evaluating the ultimate
capacity of steel containments in the
SRP (Safety Review Plan) for pressurized
water reactor-type NPPs in Korean regulations
[10], and the other is the design criterion
for the KEPIC (Korea Electric Power
(g) 1.2s (h) 2.0s (i) 2.8s
Fig. 5. Hydrogen concentration from the combustion analysis for B3 case (SLOCA without PAR).
(j) 3.6s (k) 4.0s (l) 4.6s
Fig. 6. Pressure behavior from the combustion analysis for B3 case (SLOCA without PAR).
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