The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
HYDROGEN SAFETY – ECART AND MELCOR MODELING
G. Manzini, S. Morandi and F. Parozzi RSE, Power Generation System Dept. - Nuclear and Industrial Plants Safety team, via Rubattino,
54, 20134, Milano, Italy
[email protected], [email protected], [email protected]
ABSTRACT
Safety of hydrogen is inherent to both conventional and nuclear sectors and its
challenges are very different such as production, easy leaking, low-energy
ignition, wide range of fuel-air mixtures flammability limits, metals
embrittlement, explosion. About nuclear power plants, the Fukushima Dai-ichi
NPP accident of 2011 further highlighted the importance of these phenomena.
This work is focused on modeling of hydrogen – air fast deflagrations, as they are
some of the most significant phenomena in case of hydrogen leakages in both
conventional and nuclear power plants accident scenarios.
In particular, the paper describes the modeling of this phenomenon finalized to
improve ECART numerical tool (lumped parameters code dedicated to the
simulation of accidental scenarios), enabling it to analyze accident scenarios with
hydrogen explosions.
A first validation of improved ECART code is currently in progress by means of
comparison with results of other computational tools simulations like MELCOR
and experimental data coming from the FP5 SAFEKINEX research project.
1. INTRODUCTION
The accidents that involved the nuclear units of Fukushima Dai-ichi in 2011 put in evidence the
consequences of hydrogen explosions on the plant buildings (Fig. 1), as well as the significant
capability of spreading radioactive pollutants to the external environment [1].
Indeed, the phenomenon of hydrogen explosion is modeled in severe accident codes through
simplifying assumptions that can be managed with the lumped-parameter approach typically
used for the thermal-hydraulics of severe accident computer codes.
The model described in this work simulates explosions in conventional and nuclear accident
scenarios, considering only fast deflagrations and not detonations phenomena. It calculates the
main effects of air - hydrogen mixtures explosions in terms of pressures and temperatures.
The hydrogen – air explosion modeling is finalized to improve ECART numerical tool (lumped
parameters code dedicated to the simulation of accidental scenarios, [2]) in order to enable it to
the analysis of accident scenarios with hydrogen leakages in conventional or nuclear power
plants.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
Figure 1 – Consequences of hydrogen explosion
in one unit of Fukushima Dai-ichi (Photo from
Air Photo Service/AP Photo/La Presse) [1].
The ECART model is dedicated to air – hydrogen mixture fast deflagrations and it is internally
divided into two sub-models relating, respectively, to the outdoor (open spaces) and indoor
(confined spaces) explosions. In particular, the former uses the so-called TNT (TriNitroToluene)
model with appropriate coefficients dedicated to take into account the efficiency of the explosion
and the geometry of areas surrounding the explosion (obstacles acting as shields). With regard to
explosion in confined environment, a sub-model based on results of FP5 SAFEKINEX [3]
research project was created. In particular, after a substantial thermodynamic analysis, some
interpolating functions of the above results have been developed.
Therefore, both sub-models consist of a set of correlations that provide the values of temperature
and pressure required for a calculation in the first approximation of the effects of explosion.
Both approaches were implemented, first of all, inside stand-alone sub-models.
The outdoor explosion sub-model calculates pressure as a function of time and distance from
explosion and the indoor explosion sub-model calculates pressure and temperature as a function
of time.
By means of such sub-models, some numerical simulations of sample cases were performed and
the main results are summarized (explosions of clouds of air – hydrogen mixture with different
sizes and concentrations). Later, a validation of a WiP version of ECART, in which these models
were implemented, was carried out by comparisons with results of experimental sample cases
(see Chap. 2, 3).
About that, also simulations by means of MELCOR [4] numerical tool (Lumped parameters code
selected for US-DOE Safety Analysis Application) have been performed about the same cases
with the aim to compare the results with those of ECART simulations.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
It must be remarked that ECART tool contained already numerical modules dedicated to thermo-
fluid-dynamics and combustion, then the work consisted of an integration of those modules in
order to obtain better results, and not of a simple implementation of the correlations previously
mentioned. A validation of the complete / improved version of ECART code is currently in
progress by means of comparison with results of other computational tools simulations,
references and experimental data.
(This work has been financed by the Research Fund for the Italian Electrical System under the
Contract Agreement between RSE S.p.A. and the Ministry of Economic Development - General
Directorate for Nuclear Energy, Renewable Energy and Energy Efficiency in compliance with
the Decree of March 8, 2006).
2. NUMERICAL MODELING
2.1 Generalities
The approach was focused on the developing of some correlations able to calculate the pressure
and temperature of the fluids in the scenarios of interest as a function of time. This, in particular,
with the purpose of improving the potentialities of calculation of ECART simulation tool, which
development is carried out by the authors of this work [2].
ECART is focused on the consequences simulation of accidents in risk installations. It was
originally created to calculate the concentration of airborne radiotoxic substances inside nuclear
power plants in the case of a severe accident. As it is not related to a specific design, nuclear or
not, it can simulate the airborne transport of dangerous substances throughout a generic system
of rooms, pipes or plant components, together with the removal and the air-entrainment
mechanisms which may occur in the presence of structures, liquid sumps or water sprays.
The problem of complete analysis of complex systems or industrial installations is still quite
difficult using CFD codes, then, the possibility offered by the lumped-parameter fast-running
approach of ECART appears interesting.
A free version of the code and the related documentation can be downloaded from http://fus-
se.frascati.enea.it/ECART.htm.
With the aim to have reference data to compare the results of ECART and evaluate its
calculation potential about hydrogen explosion scenarios, also the code MELCOR [4] was used.
MELCOR is a fully integrated computer code that models the progression of severe accidents in
light water reactor nuclear power plants (it is developed at Sandia National Laboratories for the
U.S. Nuclear Regulatory Commission). A broad spectrum of severe accident phenomena in both
boiling and pressurized water reactors is treated in MELCOR in a unified framework. The main
use of MELCOR is the assessment of NPP severe accident source terms.
The code is composed of an executive driver and a number of modules, or packages, that
together model the major systems of a reactor plant and their coupled interactions.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
So far, hydrogen explosions in confined and open spaces were simulated by ECART (WiP
version) and only hydrogen explosions in confined space scenarios were simulated by MELCOR
(it requires some other hypotheses and modeling in order to be used for open space simulations,
as the work about that is in progress).
2.2 ECART Modeling
2.2.1 Confined spaces
The pressure model is simply based on experimental results fittings (FP5 SAFEKINEX project
[3]) and, with regard to gas temperature, on perfect gases thermodynamics.
The starting point of the model is the cubic law, defining a basic coefficient KG:
31V
dtdp
KMax
G ⋅
= (1)
where:
KG: explosion index [MPa⋅m⋅s-1
],
Maxdt
dp
:maximum rate of pressure rise [MPa⋅s
-1],
V : volume of the container/ box [m3].
Essentially by the Thermodynamics of an (almost) perfect gas mixture we have that:
i
f
i
f
p
p
T
T= (2)
( ) ( )( )v
HHif cn
qnTT
⋅∆⋅
=− 22
(3)
iv
HH
i
f
i
f
Tc
qx
p
p
T
T
⋅
∆⋅+== 221 (4)
where:
pi, pf: initial and final values of pressure in the container [Pa];
Ti, Tf: initial and final values of temperature in the container [K];
xH2: hydrogen initial mole fraction [molH2/mol];
∆qH2: hydrogen / oxygen reaction heat released [J/mol];
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
cv: molar heat capacity of gaseous mixture (mean value) [J/(mol⋅K)].
So, with the same composition (xH2, cv) and initial temperature (Ti), the mixture will have the
same final temperature (Tf) and therefore the same ratio between the temperatures (Tf / Ti) and the pressures (pf / pi) corresponding to initial and final states.
The values of that ratio can be calculated in closed-form with the following expression (based on fittings of exp. results [3], numerical scientific notation):
pf/pi = -7.7505437E-08(xH2%)5 + 1,1675447E-05(xH2%)
4 - 4.9263486E-04(xH2%)
3 - 3.8631742E-
03(xH2%)2 + 6.3120965E-01(xH2%) - 1.9295087E+00 (5)
(Ti= 293.15 K)
While the values of KG can be expressed in closed-form as follows (based on fittings of exp.
results [3], numerical scientific notation):
pi= 0.1 MPa ⇒ KG= -9.2915799E-07⋅(xH2%)5 + 2.6212963E-04⋅(xH2%)
4 - 2.5070655E-
02⋅(xH2%)3 + 9.4432432E-01⋅(xH2%)
2 - 1.1349571E+01⋅(xH2%) + 3.7939734E+01 (6)
pi= 0.5 MPa ⇒ KG = -5.6597687E-07⋅(xH2%)6 + 1.1719357E-04⋅(xH2%)
5 - 8.7227693E-
03⋅(xH2%)4 + 2.7172619E-01⋅(xH2%)
3 - 3.0197646E+00⋅(xH2%)
2 + 9.2994156E+00⋅ (xH2%) +
3.6854281E+00 (7)
pi= 1 MPa ⇒ KG = -1.5529513E-06⋅(xH2%)6 + 3.3006398E-04⋅(xH2%)
5 - 2.5879701E-
02⋅ (xH2%)4 + 9.0512526E-01⋅(xH2%)
3 - 1.3661800E+01⋅(xH2%)
2 + 8.5859490E+01⋅(xH2%) -
1.8144386E+02 (8)
pi= 3 MPa ⇒ KG = -3.0172288E-06⋅(xH2%)6 + 6.2894474E-04⋅(xH2%)
5 - 4.8045699E-
02⋅(xH2%)4 + 1.6224736E+00⋅(xH2%)
3 - 2.3479106E+01⋅(xH2%)
2 + 1.4803566E+02⋅(xH2%) -
3.2804872E+02 (9)
(Ti= 293.15 K)
where xH2% is the hydrogen percent initial mole fraction.
By this way, we can obtain the maximum values of pressure (Eq. 5, pf) and of its derivative (Eq. 6 - 9, 1, dp/dtMax) and, by the perfect gas model (Eq. 4), the corresponding values of temperature
(Tf) and of its derivative (dT/dtMax), in order to obtain first approximation trends of p and T over time.
2.2.2 Open spaces
In the case of explosion in open spaces (unconfined vapor cloud explosion), the equivalent TNT
(TriNitroToluene) model is applied [5], [6], although the model, at least tendentially, overstates the pressure values close to the explosion and underestimates them at high distances.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
Essentially, such a method computes the pressure wave by applying known graphics and
correlations to the TNT equivalent mass that would produce the same effects as the actual amount of hydrogen involved in the explosion.
The TNT mass, mTNT [kg], which releases the same amount of heat as the hydrogen mass, is computed as:
186.4.1232.0 2
22H
TNT
HHTNT m
q
qmm ⋅≅
∆
∆⋅⋅=
η (10)
where:
mTNT: TNT equivalent mass [kg];
η: explosion efficiency (0 ≤ η ≤ 1).this factor is due to presence of obstacles acting as shields in the area surrounding the exploding mixture (actual values ranging from 0.1 to 0.2);
mH2: hydrogen mass [kg];
∆qH2 : hydrogen / oxygen reaction heat released [MJ/kg];
∆qTNT : TNT reaction heat released [MJ/kg];
The scaled distance z’ [m/(kg/bar)1/3
] is defined as:
31
0 )/('
pm
zz
TNT
= (11)
where z[m] is the distance from the explosion origin and p0 [bar] is the initial pressure.
The variables ps [Pa] and iTNT [Pa·s/(kg/bar)1/3
] are fitted by the following equations:
1 ≤z’≤ 10
)01,2(6 '1013.1 −⋅⋅=∆= zpp
MaxS (12)
)91,0('203 −⋅= ziTNT
(13)
10 < z’≤ 200
)16,1(5 '1083.1 −⋅⋅=∆= zppMaxS
(14)
)06,1('335 −⋅= ziTNT
(15)
Whence the impulse i of the hydrogen mass can be calculated as:
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
31
0
⋅=
pm
ii TNTTNT (16)
So, the values of ps and i (and so the rate of pressure increase) can be computed as functions of
the distance from the explosion point.
2.3 MELCOR Modeling
The code models the combustion of gases in control volumes without modeling the reaction kinetics and the flame front propagation. The deflagration (only deflagrations are modeled. no
detonations) and diffusion flame models are derived from HECTR 1.5 code [4]. A simple diffusion flame model allows for the burning of hydrogen-rich mixtures upon entry to volume
containing oxygen.
The combustion ignition and the combustion rate are simulated as functions of different variables
(mole fractions etc.). The rate is modeled varying with time.
3. MAIN RESULTS
3.1 Confined spaces
In this section, comparisons between ECART, MELCOR and some experimental results of
SAFEKINEX project [3] are summarized for the following scenarios:
1. Vessel with V= 0.0028 m3 (stationary volume) containing a mixture of H2 and air
(normal), Figs. 2 ÷5:
a. Initial pressure p0= 0.1, 0.5, 1, 3 MPa;
b. Initial hydrogen mole fraction of mixture xH2 %= 5 ÷ 70 %.
2. Vessel with V= 0.006 m3 (stationary volume) containing a mixture of H2 and air
(normal), Fig. 6÷9:
a. Initial pressure p0= 0.1, 0.5, 1, 3 MPa;
b. Initial hydrogen mole fraction of mixture xH2 %= 5 ÷ 70 %.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
pMax (p0= 0.1 MPa, V= 0.0028 m3)
0
0,2
0,4
0,6
0,8
1
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 0.1 MPa, V= 0.0028 m3)
0
100
200
300
400
500
600
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 2 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as
function of xH2% (initial hydrogen mole fraction of mixture). Vessel with V= 0.0028 m3.p0= 0.1
MPa.
pMax (p0= 0.5 MPa, V= 0.0028 m3)
0
1
2
3
4
5
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]
pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 0.5 MPa, V= 0.0028 m3)
0
500
1000
1500
2000
2500
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 3 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as
function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.0028 m3, p0= 0.5
MPa.
pMax (p0= 1 MPa, V= 0.0028 m3)
0
2
4
6
8
10
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]
pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 1 MPa, V= 0.0028 m3)
0
1000
2000
3000
4000
5000
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 4 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.0028 m
3, p0= 1
MPa.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
pMax (p0= 3 MPa, V= 0.0028 m3)
0
5
10
15
20
25
30
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 3 MPa, V= 0.0028 m3)
0
2000
4000
6000
8000
10000
12000
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/s
]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 5 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.0028 m
3, p0= 3
MPa.
pMax (p0= 0.1 MPa, V= 0.006 m3)
0
0,2
0,4
0,6
0,8
1
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]
pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 0.1 MPa, V= 0.006 m3)
0
50
100
150
200
250
300
350
400
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 6 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.006 m
3, p0= 0.1
MPa.
pMax (p0= 0.5 MPa, V= 0.006 m3)
0
1
2
3
4
5
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]
pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 0.5 MPa, V= 0.006 m3)
0
500
1000
1500
2000
0 20 40 60 80XH2 [mol/mol]
(dp
/dt)
Max
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 7 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as
function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.006 m3, p0= 0.5
MPa.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
pMax (p0= 1 MPa, V= 0.006 m3)
0
2
4
6
8
10
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 1 MPa, V= 0.006 m3)
0
500
1000
1500
2000
2500
3000
3500
0 20 40 60 80XH2 [mol/mol]
(dp/d
t)M
ax
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 8 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as
function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.006 m3, p0= 1
MPa.
pMax (p0= 3 MPa, V= 0.006 m3)
0
5
10
15
20
25
30
0 20 40 60 80
XH2 [mol/mol]
pM
ax [
MP
a]
pMax EXP
pMax ECART
pMax MELCOR
(dp/dt)Max (p0= 3 MPa, V= 0.006 m3)
0
2000
4000
6000
8000
10000
0 20 40 60 80XH2 [mol/mol]
(dp/d
t)M
ax
[M
Pa/
s]
(dp/dt)Max EXP
(dp/dt)Max ECART
(dp/dt)Max MELCOR
Figure 9 – Maximum values of pressure - pMax and of pressure increase rate - (dp/dt)Max as function of xH2 % (initial hydrogen mole fraction of mixture). Vessel with V= 0.006 m
3, p0= 3
MPa.
3.2 Open spaces
As regards the simulation of hydrogen deflagration in open spaces with ECART, two scenarios were analysed:
A. H2 – Air (normal) cloud with initial volume of V= 0.0028 m3 located outdoors (Fig. 10):
− Initial pressure p0= 0.1 MPa;
− Initial hydrogen mole fractions of mixture / cloud xH2 %= 5, 10, 20, 30, 40, 50, 60, 70 %.
B. H2 – Air (normal) cloud with initial volume of V= 0.006 m3located outdoors (Fig. 11):
− Initial pressure p0= 0.1 MPa;
− Initial hydrogen mole fractions of mixture / cloud xH2 %= 5, 10, 20, 30, 40, 50, 60, 70 %.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
pMax (T0= 293,15 K, V0= 0,0028 m3 - p0= 0,1 MPa)
0,100
0,105
0,110
0,115
0,120
0 2 4 6 8 10 12 14 16 18 20
l [m]
pM
ax [
MP
a]pMax ([H2]%=5)
pMax ([H2]%=10)
pMax ([H2]%=20)
pMax ([H2]%=30)
pMax ([H2]%=40)
pMax ([H2]%=50)
pMax ([H2]%=60)
pMax ([H2]%=70)
Figure 10 – Maximum values of pressure - pMax as function of distance from initial cloud (mixture of H2 and air) for various xH2 % (initial hydrogen mole fraction of mixture / cloud).
Initial volume of cloud V= 0.0028 m3, p0= 0.1 MPa.
pMax (T0= 293,15 K, V0= 0,006 m3 - p0= 0,1 MPa)
0,100
0,105
0,110
0,115
0,120
0 2 4 6 8 10 12 14 16 18 20
l [m]
pM
ax [
MP
a]
pMax ([H2]%=5)
pMax ([H2]%=10)
pMax ([H2]%=20)
pMax ([H2]%=30)
pMax ([H2]%=40)
pMax ([H2]%=50)
pMax ([H2]%=60)
pMax ([H2]%=70)
Figure 11 – Maximum values of pressure - pMax as function of distance from initial cloud (mixture of H2 and air) for various xH2 % (initial hydrogen mole fraction of mixture / cloud).
Initial volume of cloud V= 0.006 m3, p0= 0.1 MPa.
4. CONCLUSIONS
The fast running approach adopted for the lumped-parameter calculation method allowed a fast
and conservative evaluation of pressure and temperature values both in the case of open and confined space for the experimental situations here considered. The “correlations” model focused
on ECART improvement is still at the implementation stage, as well as the code version, that is presently used for the testing and validation process, involving sub-models and thermo-
hydraulics and chemical numerical modules of ECART.
About MELCOR, only simulations of confined space transients were carried out with default
models. Others simulations, related to transients in open space cases, are object of computational tests. These simulations need different scenario modeling, as the code is based on defined control
volumes, and this requires development stages longer than previous ones.
The 15th
International Topical Meeting on Nuclear Reactor Thermal - Hydraulics, NURETH-15 NURETH15-248 Pisa, Italy, May 12-17, 2013
5. ANNEX - HYDROGEN COMBUSTION AND EXPLOSION
The hydrogen oxidation process can be modeled as a one step reaction as:
H2 + ½ O2 → H2O + ∆q (17)
Where ∆q is the heat generated by the reaction which can be assumed equal to LHV (Lower Heating Value, 119.96 MJ/kg) because, in case of explosions in accidental scenarios, reactants and products are in gaseous phase (LHV is defined as the amount of heat released by combusting
a specified quantity - initial T= 25°C - and returning the temperature of the combustion products to 150°C, which assumes the vaporization heat of water in the reaction products is not recovered
– US DoE).
About others fuels, for example methane (CH4 - LHV: 47.13 MJ/kg) and propane (C3H8 - LHV:
46.28 MJ/kg) have values which are significantly lower than the hydrogen one.
The flammability limits of air - hydrogen mixtures are 4 - 75 vol% (values function of pressure
and temperature of the mixture) [7]. Thus the flammability range is extremely large.
About the rapidity of hydrogen combustion, it is known as such value is often high, generating
fast deflagrations or, sometimes, even detonations.
6. REFERENCES
[1] F. Parozzi, Fukushima, “Anatomia di un incidente”, Le Scienze (Italian edition of
Scientific American), n. 514, June 2011,
[2] F. Parozzi, S. Paci, “Development and validation of the ECART code for the safety analysis of nuclear installations”, 14th International Conference on Nuclear Engineering
ICONE14, Paper ICONE14-89275, Miami, Florida USA, July 17-20, 2006,
[3] FP5 EU-Project, “SAFEKINEX - SAFe and Efficient hydrocarbon oxidation processes by KINetics and Explosion eXpertise”, Programme on Energy, Environment and
Sustainable Development, Contract Number EVG1-CT-2002-00072, 2003 – 2006,
[4] SANDIA Labs, “MELCOR Computer Code Manuals”, Vol 1: Primer and Users’ Guide. Version 2.1, Draft version, September 2011,
[5] F.D. Alonso, E.G. Ferradas, J.F. Sanchez Perez, A.M. Aznar, J.R. Gimeno and J.M. Alonso, “Characteristic overpressure–impulse–distance curves for the detonation of
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