Embed Size (px)
Citation preview
Paper Reference n° P2-31-64 poster board
OPERATIVE MODES OF THE PRIMARY CIRCUIT DEGASSEROF ATUCHA II N.P.P.
Ivanna Rodríguez (C.N.E.A.), Argentina ([email protected])Maximiliano Contino (C.N.E.A.), Argentina ([email protected])
Mauricio Chocrón (C.N.E.A.), Argentina ([email protected])Jorge Duca (N.A.S.A.), Argentina ([email protected])
ABSTRACT
Atucha II (N.A.S.A., Buenos Aires Province, Argentina) is a Pressurized Vessel Heavy Water Reactor designed bySIEMENS with a capacity of 740 MWe. After a long delay in construction the plant is close to the commissioningand among the many task that are carried out, chemistry and operation of devices related to it are underconsideration [1].
As it is known, Hydrogen or Deuterium dosing has the purpose of both: limitation of the water radiolysis and toprovide an appropriate reductive media for the structural materials, mainly stainless steel, A800 and Zr-4. Dealingwith a heavy water plant, it is critical to determine whether it is necessary to add D2 or if it is feasible to dose H2, byconsidering heavy water degradation and heavy water upgrading system capability. Those aspects have beenpreviously analyzed and presented [2]. It is also necessary to consider blankets and venting locations that addressto losses of the expensive D2.
In the present work several alternatives of hydrogenation are presented and evaluated, considering the Degasser(D), the Volume Control Tank (TCV) and the special features of the purification and volume control system of apressurized vessel heavy water plant where the primary circuit and moderator are partially mixed. Also theinfluence of venting through the pressurizer is analyzed.
Conclusions are obtained in connection to (i) the maintenance of a permanent blanket of H2/He, 4%, in the TCVdome at a given initial pressure, (ii) The same but constant pressure to reach 0.6 ppm of H2 in the Primary andModerator water circuit, (iii) transients while reducing pressure in the Degasser and considering contribution ofpressurizer venting, (iv) estimated contribution of the general corrosion of the system and (iv) differences if D2 isused.
ANALYSIS OF THE HYDROGEN INJECTION IN ATUCHA II NPP
Hydrogen concentration in the Primary System of water cooled nuclear reactors is a matter of great importance dueto the control of several water chemistry aspects. Also, hydrogen injection, control in operation, removal in differentconditions for water chemistry and/or considering its relative danger is still matter of study and publications [1-5].
Figure 1 shows a simplified scheme of Atucha II Primary-Moderator System (SPTC), Pressurizer (P) and VolumeControl Tank (TCV). After this Figure mass balances will be set up considering different initial conditions [6,7,8].
The design pressure of the TCV is 6 bar and it is normally operated at 2.8 bar. The design pressure of theDegasser is 13 bar and is operated among 1-10 bar. If a devoted SPTC hydrogenation system would be included,allowable pressure could be as higher as requested by the following examples.
In that sense, different strategies of hydrogenation of the moderator-coolant are considered and evaluated forAtucha II.
Paper Reference n° P2-31-64 poster board
Figure 1: Simplified diagram of the plant
CASE (ia): Hydrogenation of the SPTC through the TCV with a permanent blanket of 4% He/H2mixture.
This case analyzes the evolution of the system if hydrogenation is performed by adding a mixture of He/H2 at 4 %ratio at the gas phase of the TCV. This ratio has been considered after the Shappiro -Moffete diagram taking inconsideration that a wide safety margin exists for mixtures of air-hydrogen-steam. Ignition range for H2-air starts at4% H2 and ends at 78 % while detonation range lies between 18-55% H2. If there is steam present, those rangesbecome narrower and for samples containing 60% steam no risks of ignition or detonation are presented [11].The hypotheses for the problem are the following:
The system is in steady state for the global flow rates and temperatures (Figure 1) While the H2 is injected the corresponding mass balance is in transient situation. The ideal gases law is valid The Henry's law is valid for H2 gas-liquid equilibrium. It is supposed that the SPTC, P and TCV behave as perfectly stirred vessels. Pressure on the vapour phase of the TCV ensures 0.6 ppm of H2 in the system once the steady state is
reached (goal). Partial pressure of H2 in the TCV decreases along the evolution.
Hydrogen mass balances are as follows:
H2 mass balance, SPTC control volume H2 mass balance, TCV control volume
)()(
)()(
RTCVR
TCVRP
R
PR
RRR
RTCVTCVRPPR
CCMQCC
MQ
dtdC
CMN
CCQCCQdtdN
)(
11
1
)1(
)(
TCVRTCVTCVTCV
TCVTCV
TCV
TCV
TCVTCV
TCV
TCV
TCV
TCVTCVTCV
TCV
TCVTCVTCVTCV
TCVRTCVTCV
CCkQdtdC
BM
k
CTRVH
B
kC
BMC
BCCMN
CCQdtdN
Paper Reference n° P2-31-64 poster boardH2 mass balance, Pressurizer control volume Initial conditions
CTRCHQCCQk
dtdC
BM
k
CTRVH
B
BMC
BCCMN
TCCVHn
nVQCCQ
dtdN
P
PPVPRPP
P
PP
P
P
PP
P
PPP
P
PPPP
P
PPPp
PP
VPRP
P
)(
11
1
)1(
)()(00
0
R
TCV
p
tCC see belowC
Where, for the current case:
Variable Value UnitHP 1.3191E+04 atm/(mol of H2/mol of H20)HTCV 7.5254E+04 atm/(mol of H2/mol of H20)BP 3.224E-06 1/KgBTCV 1.6294E-06 1/KgKP 3.0722E-06 1/KgKTCV 1.5960E-06 1/Kg
Definition of variables ( i = SPTC, TCV, P )
Ni: Total amount of Hydrogen [moles]Ci: Hydrogen concentration in the liquid phase [mg of H2 /Kg of H20]Vi: Volume [liters]Ti: Temperature [K]Hi: Henry's constant at Temperature [atm/(mol of H2/mol of H20)]C: Concentración of water [moles of H20 / Kg of H20]R: Gas constant [(l atm) /(( K mol)]Mi: Mass of the primary coolant (Kg)Qi: Flow rate (Kg/s)
As stated above initial condition of the TCV vapour phase is the one that ensures a concentration of 0.6 ppm of H2once the steady state is reached. This concentration is the one requested by the chemistry specifications of theSPTC [1]. Initial TCV pressure is 23.5 bar and initial H2 concentration is CTCV = 1.5 mg/Kg.
If dosing H2 through the TCV would be considered, then a total pressure of 23.5 bar, mixture 4% He/H2, in thevapour phase would be needed. This is an important value if a separate hydrogenation system is going to bedesigned. It has also to be considered that a proper good homogenization is requested in order to reach a gooddistribution and solubilization of H2 in the water.
If venting looses are considered and if 0.6 ppm of H2 are expected after a month of operation (during the monthapproximately 67.1 gr of H2 are vented) then as initial pressure 25.3 bar in the TCV is set up.
Paper Reference n° P2-31-64 poster boardResults: Case (ia)
It can be observed (Figures 2 and 3) that after 50 hours; the steady state concentration is practically reached.
Figure 2: Hydrogenation through TCV. H2 in the TCV vapourphase
Figure 3: H2 in Pressurizer vapour phase (always below 4%)
0 20 40 60 80 100 120 140 1600
0.01
0.02
0.03
0.04
0.05
0.06
0.07
tiempo [h]
porc
enta
je d
e H
2 en
el d
omo
[%]
Atmósfera Explosiva en el Presurizador
0 100 200 300 400 500 600 700 8001.5
2
2.5
3
3.5
4
tiempo [h]
porc
enta
je d
e H
2 en
el d
omo
[%]
Atmósfera Explosiva en el TCV
Figure 4: H2 lost through the pressurizer (venting) Figure 5: Total amount of H2 vented at time t
0 100 200 300 400 500 600 700 8000
10
20
30
40
50
60
70
80
90
100
tiempo [h]
vent
eo d
e hi
dróg
eno
[mg/
h]
Evolución de la masa de H2 que se va por el presurizador
0 100 200 300 400 500 600 700 8000
1
2
3
4
5
6
7x 104
tiempo [h]
mas
a de
hid
róge
no [m
g]
Masa total de H2 que se va por el presurizador en el tiempo t
Now if He is considered, it has to be taken into account that Henry's constant at 323K (TCV temperature) is 150000atm / (mol He/ mol H20) unlike that of H2 which is 7500 atm / (mol H2/ mol H20). Then He is also lost through thepressurizer venting.
Figure 6 shows the evolution of H2 and He the partial pressures. He concentration is reduced from 4% to 3 % insteady state. See also Figures 7 to 8.
Results: Case (iB)
In case in that the TCV pressure is going to be reduced then the target concentration of 0.6 ppm of H2 at the SPTCis not reached. As it can be seen if 10.16 bar is established at the TCV dome, then 0.6 ppm are achieved in theTCV liquid phase but not in the SPTC (Figure 10).
The reason after what the target concentration is not reached is because of the low H2 solubility in water and thepartial pressure of H2 in the TCV dome, 4%, which has been conservatively allowed.
Paper Reference n° P2-31-64 poster board
Figure 6: He and H2 partial pressure evolution in the TCVdome
0 50 100 150
100
101
tiempo [h]
Aumento de la presión parcial de He en el TCV
Presión parcial de He [bar]Presión parcial de H2% en volumen de H2 [%]
Figure 7: Total amount of He vented at the TCV at time t
0 100 200 300 400 500 600 700 8000
5
10
15
20
25
30
35
40
tiempo [h]
conc
entra
ción
de
He
[mg/
Kg]
He a través del TCV
SPTCPresurizadorTCV
Figure 8: Mass of He vented at the pressurizer
0 100 200 300 400 500 600 700 8000
500
1000
1500
2000
2500
3000
3500
4000
tiempo [h]
vent
eo d
e he
lio [m
g/h]
Evolución de la masa de He que se va por el presurizador
Figure 9: Mass of He vented at the pressurizer at time t
0 100 200 300 400 500 600 700 8000
0.5
1
1.5
2
2.5
3x 106
tiempo [h]
mas
a de
hel
io [m
g]
Masa total de He que se va por el presurizador en el tiempo t
Figure 10: Concentration of H2 reached in the SPTC system with a constant pressure of 10.16 bar in the TCV dome
0 50 100 150 200 250 300 350 4000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
Paper Reference n° P2-31-64 poster boardCASE (ii): Continuous dosing of 4% He/H2 mixture to the TCV dome (constant TCV dome totalpressure)
In the case of that it is decided to keep a constant partial pressure of H2 in the TCV dome, which would implies acontinuous dosing of 4% He/H2 mixture in order to keep total pressure constant as well, the H2 mass balanceresults:
H2 mass balance, SPTC control volume
)()( RTCVR
TCVRP
R
PR CCMQCC
MQ
dtdC
Initial conditions
00
RCt
H2 mass balance, TCV control volume
0dtdCTCV
Initial condition
0
TCV
tC see below
H2 mass balance, Pressurizer control volume
CTRCHQCCQk
dtdC
P
PPVPRPP
P )(
Initial condition
00
PCt
Results: Case (ii)
The maximum concentration that can be achieved is that of the equilibrium at TCV pressure (which is constant).Figure 11 shows that if a total pressure of 2.8 bar is maintained then maximum concentration is below 0.6 ppm.After the slope it can be inferred that at longer times a balance is achieved between H2 added at the TCV and H2vented at the pressurizer. The pressure needed to reach a final concentration of 0.6 ppm is 10.16 bar (Figure 12).
Figure 11: System hydrogenation keeping a total pressure of2.8 bar at the TCV
Figure 12: system Hydrogenation keeping a total pressure of10.16 bar at the TCV (limit 0.6 ppm)
0 20 40 60 80 100 120 140 1600
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
After the calculations it can be seen that H2 concentration at the pressurizer dome is always below 4% (Figures 13and 14).
Paper Reference n° P2-31-64 poster board
Figure 13: H2 mass added to keep constant pressure at theTCV dome
Figure 14: Total mass of H2 added at time t in order to keepconstant the pressure at the TCV dome
0 20 40 60 80 100 120 140 1600
1
2
3
4
5
6x 104
tiempo [h]
Agr
egad
o de
hid
róge
no [m
g/h]
par
a m
ante
ner l
a pr
esió
n ct
e
Masa de H2 que ingresa para mantener la presión del TCV
0 20 40 60 80 100 120 140 1600
0.5
1
1.5
2
2.5
3
3.5
4
4.5x 105
tiempo [h]
mas
a de
hid
róge
no [m
g]
Masa total de H2 que ingresa al TCV en el tiempo t
Given that H2 is dosed together with He (at 4% ratio) in order to keep constant partial pressure and considering thatHe is much more insoluble, the latter will accumulate at the TCV dome and an increment in the total pressure willbe observed. Then, mass balance for He is solved as well and the results are presented in Figures 15 and 16. Inany case H2 partial pressure is below 4%.
Figure 15: He evolution at TCV dome Figure 16: He partial pressure increment at TCV dome
0 20 40 60 80 100 120 140 1600
2
4
6
8
10
12
14
16
18
20
tiempo [h]
conc
entra
ción
de
He
[mg/
Kg]
He a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600
2
4
6
8
10
12
14
tiempo [h]
Aumento de la presión parcial de He en el TCV
Presión parcial de He [bar]Presión parcial de H2% en volumen de H2 [%]
From Cases (i) and (ii) it can be concluded:
It has been observed that to fulfil H2 concentration request in the SPTC through the TCV but withoutkeeping constant the H2 partial pressure at the dome a total pressure of 25.3 bar, 4% He/H2 mixture, wouldbe needed.
That value of total pressure could be used in case a dedicated Hydrogenation system would be attached tothe TCV. It has also to be considered that a proper H2 dissolution and homogenization system should bedesigned as well.
A negative slope in the total pressure vs. time is also observed and this is due to the fact that gas is ventedat the pressurizer.
In the case, total pressure of 10.16 bar is maintained at the TCV dome, the expected H2 concentration, 0.6ppm, is reached. Here a practically horizontal slope is observed and this is due to that, close to the steadystate the H2 vented at the pressurizer is supplied at the TCV dome to maintain constant pressure there.
In the second case, He partial pressure rises with time due to its lower solubility and higher concentration inthe make up mixture (96 %).
Paper Reference n° P2-31-64 poster board
CASE (iii): Influence of venting the Pressurizer on the specified value of H2 in the SPTC
The current case shows how the system evolves if the partial pressure at the TCV dome is maintained after thespecified concentration, 0.6 ppm, is reached at the SPTC coolant while the pressurizer is continuously vented.
Hypothesis
The system is in steady state for the global flow rates and temperatures On the contrary, for H2, its concentration at all the control volumes is time dependent. The ideal gases law is valid The Henry's law for H2 liquid-gas equilibria is also valid. It is supposed that all the control volumes: SPTC, P and TCV behave as perfectly stirred tanks.
Figure 17 shows that if a constant pressure of 2.8 bar is maintained at the TCV dome, then the H2 concentration inthe system tends to the equilibrium value corresponding to that partial pressure. That is H2 is lost through thepressurizer venting and this is compensated through the supply at the TCV dome. If a total pressure of 10.16 bar ismaintained then at equilibrium conditions, H2 concentration in the coolant will be lower than 0.6 ppm, again this isdue to venting at the pressurizer.
Figure 17: H2 evolution for constant, 2.8 bar, at the TCVdome
Figure 18: H2 evolution for constant, 10.16 bar, at the TCVdome
0 20 40 60 80 100 120 140 160
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600.597
0.5975
0.598
0.5985
0.599
0.5995
0.6
0.6005
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
After those simulations what is important is to find the TCV dome pressure which ensures that H2 concentration inthe coolant-moderator and pressurizer is in the specifications range (0.6 - 2 ppm).
Figures 19 to 24 show steady state concentrations of H2 reached for different pressures at the TCV dome.
After Figures 20 to 22 it is concluded that if a constant pressure is not sustained, concentration diminishes belowthe specification in the coolant making necessary to add H2. Then if a constant pressure of 11 bar is maintained, fortwo weeks is ensured that H2 is inside the specifications range (Figures 23 and 24).
Paper Reference n° P2-31-64 poster boardFigure 19: H2 concentration reached in the coolant if totalpressure at the TCV dome is constant (10.2 bar)
Figure 20: H2 evolution in the coolant after initial totalpressure ,10.2 bar, in the TCV dome (not constant)
0 20 40 60 80 100 120 140 1600.599
0.5995
0.6
0.6005
0.601
0.6015
0.602
0.6025
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600.588
0.59
0.592
0.594
0.596
0.598
0.6
0.602
0.604
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
Figure 21: H2 concentration reached in the coolant if totalpressure at the TCV dome is constant (10.5 bar)
Figure 22: H2 evolution in the coolant after initial totalpressure,10.5 bar, in the TCV dome (not constant)
0 20 40 60 80 100 120 140 1600.599
0.6
0.601
0.602
0.603
0.604
0.605
0.606
0.607
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600.59
0.592
0.594
0.596
0.598
0.6
0.602
0.604
0.606
0.608
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
Figure 23: H2 concentration reached in the coolant if totalpressure at the TCV dome is constant (11 bar)
Figure 24: H2 evolution in the coolant after initial totalpressure,11 bar, in the TCV dome (not constant)
0 20 40 60 80 100 120 140 1600.599
0.6
0.601
0.602
0.603
0.604
0.605
0.606
0.607
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
0 20 40 60 80 100 120 140 1600.59
0.595
0.6
0.605
0.61
0.615
0.62
0.625
0.63
tiempo [h]
conc
entra
ción
de
hidr
ógen
o [m
g/K
g]
Hidrogenado a través del TCV
SPTCPresurizadorTCV
Paper Reference n° P2-31-64 poster boardHydrogenation of the System using an Absorber-Degasser (Tray Tower)
Figure 25 depicts a scheme of the proposed system. Considerations for this case are as follows [9,10,12]:
The system is in steady state for the global flow rates and temperatures
On the contrary, H2 concentration is time dependent.
The absorber is in steady state. Ideal gases law is valid. Henry's law is valid for the H2 equilibrium in the control volumes and the absorber. It is considered that the SPTC,TCV and pressurizer are ideal stirred tanks.
Figure 25: Diagram of the SPTC, Pressurizer and Tray Tower
H2 mass balance, SPTC control volume
)()( RTR
TCVRP
R
PR CCMQCC
MQ
dtdC
Initial condition
00
RCt
H2 mass balance, Pressurizer control volume
CTRCHQCCQk
dtdC
P
PPVPRPP
P )(
Initial condition
00
PCt
Then for the calculation of CT, a solution similar to that presented at [2] is set up, where from the absorber thenumber of equilibrium stages (Np), the inlet flow of H2 (QT) in mol/h (or the inlet molar fraction “y” and the carriergas flow rate) and the temperature T = 323 K are known. Total pressure can varies among 1 – 10 bar as a designcondition of the absorber.
In the results, Absorber total pressure, H2 inlet and number of stages have been considered as parameters. Figure26 shows the influence of the carrier gas flow rate. As far as QT is increments, the final concentrationapproximates: ynp+1/C. It is concluded that results are very similar using QT=1000 mol/h, 10000 mol/h or 100000mol/h.
Paper Reference n° P2-31-64 poster board
Figure 27 shows the influence of the number of stages of the absorber in the evolution of the system. It barely hasan impact. Figure 28 presents the effect of the absorber total pressure. The higher the pressure is, the faster theexpected concentration of 0.6 ppm, is reached. Figure 29 shows how H2 molar fraction that enters the absorberaffects time evolution. As expected again the higher the molar fraction is, the faster the final concentration isreached.
Figure 26: Influence of the carrier gas flow rate to the absorberon the H2 concentration evolution
Figure 27: Influence of the number of absorber stages on theH2 concentration evolution
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Tiempo [h]
Con
cent
raci
ón d
e H
2 [m
g/K
g]
Influencia del caudal del carrier (QT) en la evolución del sistema. P= 10 bar. NP=2. YNP+1 =0.04
Cr para QT= 1000 mol/hCp para QT= 1000 mol/hCT para QT= 1000 mol/hCr para QT= 10 mol/hCp para QT= 10 mol/hCT para QT= 10 mol/hCr para QT= 100 mol/hCp para QT= 100 mol/hCT para QT= 100 mol/hCr para QT= 10000 mol/hCp para QT= 10000 mol/hCT para QT= 10000 mol/hCr para QT= 100000 mol/hCp para QT= 100000 mol/hCT para QT= 100000 mol/h
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Tiempo [h]
Con
cent
raci
ón d
e H
2 [m
g/K
g]
Influencia de los NP del absorbedor en el sistema. P=10 bar. Caudal=1000 mol/h. yNP+1=0.04
Cr NP=2Cp NP=2CT NP=2Cr NP=4Cp NP=4CT NP=4Cr NP=6Cp NP=6CT NP=6Cr NP=8Cp NP=8CT NP=8
Figure 28: Influence of the absorber total pressure on the H2concentration evolution.
Figure 29: Influence of the H2 molar fraction supplied to theabsorber on the H2 concentration evolution.
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Tiempo [h]
Con
cent
raci
ón d
e H
2 [m
g/K
g]
Influencia de la presión del absorbedor en el sistema. NP=2. Caudal=1000 mol/h. yNP+1=0.04
Cr P=10 barCp P=10 barCT=10 barCr P=7 barCp P=7 barCT=7 barCr P=3 barCp P=3 barCT=3 barCr P=13 barCp P=13 barCT=13 bar
0 20 40 60 80 100 120 140 1600
1
2
3
4
5
6
7
8
Tiempo [h]
Con
cent
raci
ón d
e H
2 [m
g/K
g]
Influencia de la fración molar yNP+1 en el sistema. P=10 bar. Caudal=1000 mol/h. NP=2
Cr yNP+1=0.04Cp yNP+1=0.04CT yNP+1=0.04Cr yNP+1=0.1Cp yNP+1=0.1CT yNP+1=0.1Cr yNP+1=0.3Cp yNP+1=0.3CT yNP+1=0.3Cr yNP+1=0.5Cp yNP+1=0.5CT yNP+1=0.5
CASE (iv): H2 produced by corrosion
For comparison with the above calculations, bulk H2 production by general corrosion is estimated as follows: SPTCinvolved surfaces are mainly composed of Zr alloys, Alloy 800 and high grade SS type steel. Considering thesurface and a corrosion rate of 0.001 gr/m2.day (0.05 μm/yr), H2 generation would contribute with 0.5 mol/day whileto reach a concentration of 0.6 ppm in the whole system (525 Tn) 158 mol are necessary. Looking at the H2 flowrate vented at the pressurizer, 97 mg/h, H2 produced by corrosion would compensates only 42 mg/h.
CASE (v): Deuterium or Hydrogen
As it was explained in detail at [2], it is feasible to add H2 instead of the expensive D2 keeping the economy of thefuel, given that there is enough capability of the heavy water upgrading system (i.d. distillation columns) tomaintain the specified D2O concentration in the SPTC system.
Paper Reference n° P2-31-64 poster boardCONCLUSION
If is decided to perform the Hydrogenation through the TCV, total initial pressure of the 4% He/H2 mixture shall be23.5 bar. This value is also important if a dedicated vessel for hydrogenation is included in the system. Goodhomogenization to ensure H2 dissolution has to be considered as well.
If venting is taken into account, H2 is lost (67.1 gr/month) and to achieve a concentration of 0.6 ppm in themoderator-coolant then pressure at the TCV dome must be, after a month, restablished at 23.5 bar.
If a pressure of 2.8 bar is maintained at the TCV dome, then H2 concentration in the system is gradually reduced upto the corresponding equilibrium value in the liquid phase and 0.6 ppm is not achieved.
If the pressure at the TCV dome would be set up at 10.16 bar, then a concentration slightly lower than 0.6 ppm willbe reached in the system. This is attributed to the venting at the pressurizer. Then if a pressure of 11 bar is set up,it will be assured that during two weeks the system is in the specified concentration range.
After the H2 and He evolution in the system, respective slopes show that the effect of venting is low and can becompensated by the supply at the TCV.
He effect has to be considered as well in the evolution of the TCV dome total pressure.
If the absorber-degasser is used for hydrogenation instead of the TCV dome, then carrier gas flow rate can beregulated and in turn H2 supplied to the system. This alternative will be evaluated once in operation.
The contribution of general corrosion to the supply of H2 is low and compensated by the continuous venting at thepressurizer. It is not necessary to dose D2 to compensate D2O degradation.
ACKNOWLEDGMENTS
Mr. F. Roumiguiere (AREVA NP) and Mr. M. Guala (N.A.S.A., CNAII) are gratefully acknowledged for the fruitfuldiscussions.
REFERENCES
[1] CNAII Water Chemistry Guidelines: Primary and Moderator System[2] Chocrón M., Duca J., Fandrich R., Fernandez R., Ramminger U., Roumiguiere F., Schonbrod B., Sell H.J.,.
"Feasibility of the injection of H2 in the primary coolant of ATUCHA II”, NPC'10, Quebec, Canada, 2010.[3] IAEA Technical Meeting on Water Chemistry of Nuclear Power Plants, 1-3 October 2007, Moscow,
Russian Federation.[4] Morey D. et al., "Modeling PWR reactor coolant H2 during plant shutdown", NPC Conference 2006, Jeju
Island, Korea[5] Kelén T. et al., "Computer modeling of H2 accumulation in BWT piping", NPC Conference 2004, Los
Angeles, USA.[6] CNA2 XG-JA-K-115515: Reactor System, Reactor Coolant System.[7] CNA2 XG-JF-K-115516: Moderator System.[8] CNAII-TS13-44-119-OS-1615: Sistema de Control de Volumen-KBA.[9] CNAII-TS12-44-023-OS-1615: Sistema de Desgasificación del Refrigerante y Moderador-KBG[10] Robert Treybal. “Mass Transfer Operations”. 2nd. Ed., Mc Graw Hill.[11] Cohen P., “The ASME Handbook on Water Technology for Thermal Power Systems”.1989.[12] Eyser, Auslegun des KBG-coolant and Moderator Degasing System und seiner Komponenten,
R352/34/1982.
OPERATIVE MODES OF THE PRIMARY CIRCUIT DEGASSEROF ATUCHA II N.P.P.Ivanna Rodríguez (C.N.E.A.), Argentina ([email protected]) - Maximiliano Contino (C.N.E.A.), Argentina ([email protected])Mauricio Chocrón (C.N.E.A.), Argentina ([email protected]) - Jorge Duca (N.A.S.A.), Argentina ([email protected])
INTRODUCTION
CONCLUSION
Atucha II (N.A.S.A., Buenos Aires Province, Argentina) is a PHWR designed by SIEMENS with a capacity of 740 MWe. After a long delay in construction the plant is close to the commissioning and among the many tasks that are carried out, chemistry and operation of devices related to it are under consideration.
The objective is presented and evaluated several alternatives of hydrogenation. As it is known, H2/D2 dosing has the purpose of both: limitation of the water radiolysis and to provide an appropriate reductive media for the structural materials, mainly stainless steel, A800 and Zr-4. Therefore, it is important to know how is carried out the hydrogenation process.
Pressurizer (P)Tp = 573 K
Pp = 114 barVp = 61000 l
Mp = 17239 Kg
SPTCTR = 573 K
PR = 114 barMR = 544916 Kg
TCVTTCV = 323 K
PTCV = VariableVTCV = 12000 l
MTCV = 12845 Kg
Qp = 54000 Kg/h
QTCV = 84600 Kg/h
Qv = 30 Kg/h
High Pressure Pump
SIMPLIFIED DIAGRAM OF THE PLANT. THE DESIGN PRESSURE OF THE TCV IS 6 BAR AND IT IS NORMALLY OPERATED AT 2.8 BAR. THE DESIGN PRESSURE OF THE DEGASSER IS 13 BAR AND IS OPERATED AMONG 1-10 BAR.
� The evolution of the system if hydrogenation is performed by adding a mixture of He/H2 at 4 % ratio at the gas phase of the TCV (Control Volume Tank). � The initial condition of the TCV vapour phase is the one that ensures a concentration of 0.6 mg/kg of H2 once the steady state is reached (chemistry specifications of the SPTC - Heat Transport Primary System). The initial TCV pressure has to be 23.5 bar (mixture 4% He/H2) and initial H2 concentration has to be CTCV = 1.5 mg/Kg to fulfil this objective.
The pressure value is important if a separate hydrogenation system is going to be designed. If venting looses are considered and if 0.6 mg/kg of H2 are expected after a month of operation (during the month approximately 67.1 gr of H2 are vented) then as initial pressure 25.3 bar in the TCV is set up.
�If the TCV pressure is going to be reduced then, the target concentration of 0.6 mg/kg of H2 at the SPTC is not reached. As it can be seen if 10.16 bar is established at the TCV dome, then 0.6 mg/kg are achieved in the TCV liquid phase but not in the SPTC.
If partial pressure of H2 in the TCV dome is constant, it will imply a continuous dosing of 4% He/H2 mixture in order to keep the total pressure constant as well
� If a total pressure of 2.8 bar is maintained then maximum concentration is below 0.6 mg/kg. � After the slope it can be inferred that at longer times a balance is achieved between H2 added at the TCV and H2 vented at the pressurizer. � The pressure needed to reach a final concentration of 0.6 mg/kg is 10.16 bar.
� After the calculations it can be seen that H2 concentra-tion at the pressurizer dome is always below 4%.
� Given that H2 is dosed together with He (at 4% ratio) in order to keep constant partial pressure and considering that He is much more insoluble, the latter will accumulate at the TCV dome and an increment in the total pressure will be observed.
� The current case shows how the system evolves if the partial pressure at the TCV dome is maintained after the specified concentration (0.6 mg/kg of H2) is reached at the SPTC coolant while, the pressurizer is continuously vented. � If a constant pressure of 2.8 bar is maintained at the TCV dome, then the H2 concen-tration in the system tends to the equilibrium value corresponding to that partial pressure. That is H2 is lost through the pressurizer venting and this is compensated through the supply at the TCV dome.
Results are very similar using QT=1000,10000 or 100000 mol/h. It barely has an impact. The higher the Pressure is, the faster
the expected conc. of 0.6 mg/kg is reached.The higher the molar fraction is thefaster the final conc. is reached.
Acknowledments: Mr.F.Roumiguiere (AREVA NP) and Mr. M.Guala (N.A.S.A., CNAII) are gratefully acknowledged for the fruitful discussions.
The reason why the target concentrationis not reached is the low H2 solubility in water and the partial pressure of H2 in the TCV dome, 4%, which has been conservatively allowed.
If a constant pressure is not sustained, concentration diminishes below the specification in the coolant making necessary to add H2. A pressure of 11 bar is necessary to fulfil the chemical specification during 1 week without maintaining a constant pressure in the TCV.
HYDROGENATION OF THE SPTC THROUGH THE TCV WITH A PERMANENT BLANKET OF 4% He/H2 MIXTURE.
HYDROGENATION THROUGH TCV. H2 IN THE TCV VAPOUR PHASE WITH INITIAL PRESSURE OF 23.5 BAR IN THE TCV
0 20 40 60 80 100 120 140 1600
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
0 20 40 60 80 100 120 140 1600
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
SYSTEM HYDROGENATION KEEPING A TOTAL PRESSURE OF 10.16 BAR AT THE TCV (LIMIT 0.6 mg/kg)
CONTINUOUS DOSING OF 4% He/H2 MIXTURE TO THE TCV DOME (CONSTANT TCV DOME TOTAL PRESSURE)
INFLUENCE OF VENTING THE PRESSURIZER ON THE SPECIFIED VALUE OF H2 CONCENTRATION IN THE SPTC
HIDROGENATION OF THE SYSTEM USING AN ABSORBER-DEGASSER (TRAY TOWER)
�Different alternatives to perform the hydrogenation in the Primary Circuit of the CNAII have been analyzed, in order to achieve the chemical specifications.�If a dedicated vessel for hydrogenation is included in the system, the analyzed pressures are important for the design.
HYDROGENATION THROUGH TCV. H2 IN THE TCV VAPOUR PHASE WITH INITIAL PRESSURE OF 23.5 BAR
IN THE TCV
0 20 40 60 80 100 120 140 1600
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Hours [h]
H2 p
ecen
tage
in T
CV
dom
e [%
]
0 100 200 300 400 500 600 700 8000
10
20
30
40
50
60
70
80
90
100
Hours [h]
H2 v
ent [
mg/
h]
H2 LOST THROUGH THE PRESSURIZER (VENTING)
HYDROGENATION WITH INITIAL PRESSURE OF 10.16 BAR IN TCV
0 50 100 150 200 250 300 350 4000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Hours [h]
H2 c
once
ntra
atio
n [m
g/K
g]SPTCPresurizadorTCV
SPTCPresurizadorTCV
H2 EVOLUTION IN THE COOLANT AFTER INITIAL TOTAL PRESSURE, 11 BAR, IN THE TCV DOME
(NOT CONSTANT)
0 20 40 60 80 100 120 140 1600.59
0.595
0.6
0.605
0.61
0.615
0.62
0.625
0.63
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
SPTCPresurizadorTCV
H2 CONCENTRATION REACHED IN THECOOLANT IF TOTAL PRESSURE AT THE
TCV DOME IS CONSTANT (11 BAR)
0 20 40 60 80 100 120 140 1600.599
0.6
0.601
0.602
0.603
0.604
0.605
0.606
0.607
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
SPTCPresurizadorTCV
SPTCPresurizadorTCV
INFLUENCE OF THE NUMBER OF ABSORBER STAGES ON THE H2 CONC. EVOLUTION.
P=10 bar. QT=1000 mol/h. YNP+1=0.04
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
Cr NP=2Cp NP=2CT NP=2Cr NP=4Cp NP=4CT NP=4Cr NP=6Cp NP=6CT NP=6Cr NP=8Cp NP=8CT NP=8
INFLUENCE OF THE ABSORBER TOTAL PRESSURE ON THE H2 CONC. EVOLUTION.
QT=1000 mol/h. NP=2. YNP+1=0.04
0 20 40 60 80 100 120 140 1600
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
Cr P=10 barCp P=10 barCT=10 barCr P=7 barCp P=7 barCT=7 barCr P=3 barCp P=3 barCT=3 barCr P=13 barCp P=13 barCT=13 bar
INFLUENCE OF THE H2 MOLAR FRACTION SUPPLIEDTO THE ABSORBER ON THE H2 CONC. EVOLUTION.
QT=1000 mol/h. P=10 bar. NP=2
0 20 40 60 80 100 120 140 1600
1
2
3
4
5
6
7
8
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
Cr yNP+1=0.04Cp yNP+1=0.04CT yNP+1=0.04Cr yNP+1=0.1Cp yNP+1=0.1CT yNP+1=0.1Cr yNP+1=0.3Cp yNP+1=0.3CT yNP+1=0.3Cr yNP+1=0.5Cp yNP+1=0.5CT yNP+1=0.5
INFLUENCE OF THE CARRIER GAS FLOW RATE TOTHE ABSORBER ON THE H2 CONC. EVOLUTION.
P=10 bar. NP=2. YNP+1=0.04
00 20 40 60 80 100 120 140 160
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Hours [h]
H2 C
once
ntra
tion
[mg/
Kg]
Cr para QT= 1000 mol/hCp para QT= 1000 mol/hCT para QT= 1000 mol/hCr para QT= 10 mol/hCp para QT= 10 mol/hCT para QT= 10 mol/hCr para QT= 100 mol/hCp para QT= 100 mol/hCT para QT= 100 mol/hCr para QT= 10000 mol/hCp para QT= 10000 mol/hCT para QT= 10000 mol/hCr para QT= 100000 mol/hCp para QT= 100000 mol/hCT para QT= 100000 mol/h
Comisión Nacionalde Energía Atómica
NUCLEOELECTRICAARGENTINA S.A
