Demonstrative testing of honeycomb passive autocatalytic recombiner for nuclear power plant

Nuclear Engineering and Design 241 (2011) 4280–4288

Contents lists available at ScienceDirect

Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes

Demonstrative testing of honeycomb passive autocatalytic recombiner for nuclear power plant Jae-Won Park a,∗ , Byung-Ryung Koh b , Kune Y. Suh c a b c

KEPCO E&C, 257 Yonggudaero, Giheung-gu, Yongin-si, Gyeonggi-do, Republic of Korea Korea Nuclear Technology, 1687-2, Shinil-dong, Daeduk-gu, Daejeon, Republic of Korea Department of Nuclear Engineering, Seoul National University, San 56-1, Sillim-dong, Kwanak-gu, Seoul, Republic of Korea

a r t i c l e

i n f o

Article history: Received 9 April 2011 Received in revised form 21 July 2011 Accepted 25 July 2011 Keywords: Passive autocatalytic recombiner PAR Catalyst Hydrogen safety

a b s t r a c t Passive autocatalytic recombiners (PAR) are widely being used as hydrogen control device in the current and advanced light water reactors (ALWRs). The PARs lend themselves to very effective means of circumventing buildup of combustible or detonable hydrogen gas mixtures in the reactor containment. Korea Nuclear Technology Inc. has recently developed a new PAR system with high porous catalyst material in the shape of honeycomb. The honeycomb PAR catalyst has a design characteristic of improved hydrogen removal performance by increasing the surface area and enhancing the flow rate through the catalyst at the same time, without increasing PAR size compared to the conventional PARs. The experimental study was focused on the development of the hydrogen depletion rate correlation of the honeycomb PAR. Two different sizes of PARs, KPAR-40 and KPAR-T2, have been employed in the tailor-made Integral Test Facility and Performance Test Facility. Multiple tests were conducted in various conditions of pressure, temperature, and hydrogen concentration. The hydrogen depletion rate correlation and the PAR performance constant were determined from the experimental results, which can be applied to the honeycomb PAR system. Also determined was the scale effect due to the PAR size, i.e., the number of catalysts in a PAR. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Numerous studies have been performed over the past several decades for the hydrogen generation (Cronenberg and Jan, 1992) and hydrogen control (Yang et al., 1991) in the nuclear power plants. A significant amount of hydrogen is rapidly produced in the oxidation process of fuel clad zircaloy in a severe accident involving core melt. This hydrogen would then be released to the reactor containment through a pipe break or a reactor vessel rupture. Without counter measures, the hydrogen may as well prompt deflagration and detonation (Sherman and Berman, 1988; Dorofeev et al., 1996; Behrens et al., 1991) possibly leading to early containment failure in light water reactors. A passive autocatalytic recombiner (PAR) has emerged as hydrogen control device (Royl et al., 2000; Bachellerie et al., 2003; Fischer et al., 2003; Reinecke et al., 2004; Deng and Cao, 2008). PARs do not require power. They instead use a platinum and/or palladium catalyst to recombine hydrogen and oxygen gases into water vapor upon contact with the catalyst. The heat produced during recombination process creates strong buoyancy effects which increase the

∗ Corresponding author. Tel.: +82 31 289 3827; fax: +82 31 289 4757. E-mail address: [email protected] (J.-W. Park). 0029-5493/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2011.07.040

influx of surrounding gases to the PAR inlet. These natural convective flow currents tend to promote mixing of combustible gases in the reactor containment. Different types of catalytic recombiners have been supplied by PAR manufacturers such as AREVA, NUKEM (formerly NIS), and AECL, just to name a few. AREVA and AECL utilized plate type catalysts while NUKEM invented a specialized cartridge containing pellet type catalysts. Korea Nuclear Technology, Inc. exerted extensive efforts to develop a distinctive PAR model with enhanced hydrogen removal capabilities. To meet this goal, the new catalyst is supposed to have a greater surface area and the characteristic to enhance the buoyancy-induced convective flow. The state-of-theart review had ended up selecting a honeycomb catalyst, which was then developed to enhance performance, i.e., high hydrogen removal rate. 2. Development of honeycomb PAR 2.1. Honeycomb catalyst Catalytic reaction is widely used due to its lower threshold temperature for the spontaneous catalytic reaction compared to the non-catalyzed reaction. Generally, catalysts have been developed in the shape of plate or pellet. The purpose of development of

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

4281

Nomenclature A a b C f M m N n P R RPAR T t V Greek   

performance constant of a PAR empirical constant to be used in parametric function empirical constant to be used in parametric function hydrogen volume concentration (%) function mass (g) molecular weight (g/mole) number of catalysts in a PAR number of moles pressure (Bar) universal gas constant (=8.206 × 10−5 m3 atm/mole K) hydrogen depletion rate by a PAR (g/s) temperature (K) time (s) volume (m3 )

Fig. 1. Honeycomb catalyst. Table 2 Specification of honeycomb PAR.

hydrogen removal coefficient in exponential function (s−1 ) efficiency of a PAR density (g/cm3 )

Weight Width Depth Height No. of catalyst

Subscript 0 initial value h hydrogen t total

KPAR-40

KPAR-80

KPAR-160

35.0 kg 33.4 cm 33.8 cm 140.0 cm 4

68.0 kg 63.8 cm 33.8 cm 140.0 cm 8

112.0 kg 126.7 cm 33.8 cm 140.0 cm 16

catalyst because the ceramic catalyst is fragile and vulnerable to impact. 2.2. KNT PAR

a honeycomb catalyst for PAR was to enhance hydrogen depletion performance. This meant that the new catalyst must have an enlarged surface area as well as a characteristic to enhance the flow rate through the catalyst at the same time. An optimization study was performed to increase the surface area of the catalyst and the spontaneous PAR induced flow rate. A total of five different catalyst models – two models in nickel form type and three in honeycomb type – have been developed for the optimization study. A honeycomb catalyst with mesh size of 20 ppi has been selected as the standard catalyst form according to the results of the previous hydrogen removal rate tests, as shown in Table 1. The porous nickel form catalysts and honeycomb catalysts with more dense meshes showed a tendency of slower reaction and lower hydrogen removal rate compared to the standard catalyst due to the high resistance to the air flow despite their large surface area. In addition, the porous nickel form catalyst was ignited on the sharp end point of the nickel material at 5.5% of the hydrogen concentration. On the other hand, the honeycomb catalyst was not ignited up to 9% hydrogen concentration. The support material of the standard honeycomb catalyst is a Cordierite (2MgO·2Al2 O3 ·5SiO2 ) ceramic material. It is coated with alumina (Al2 O3 ) sol and chloroplatinic acid (H2 PtCl6 ·nH2 O). Fig. 1 shows the standard honeycomb catalyst. The dimensions of the standard honeycomb catalyst support are 15 cm by 15 cm with the height of 5 cm. A protective metal frame is used to protect the

The KNT PAR is a stainless steel housing equipped with catalysts inside the lower part of the box. The bottom of the PAR is used as an air flow entrance. The upper part has exit openings in three directions and is designed to have chimney effects so that the heat generated in the catalytic reaction can promote a strong driving force for natural convective flow. The PAR exit has a free crosssectional area larger than the cross-sectional area of catalysts. The ceiling of the PAR is tailored in a reversed pyramid to lessen resistance of the natural convection. There are three different sizes of the commercial honeycomb PARs, i.e., KPAR-40, KPAR-80 and KPAR160. The specification of the honeycomb PARs is summarized in Table 2. Fig. 2 depicts the KPAR-40 model. Besides the commercial PARs, a smaller unit PAR containing only one honeycomb catalyst, named KPAR-T2, was created for the test purpose. 2.3. Test facility Two different test facilities have been built for the performance test of the honeycomb PARs-the Integral Test Facility (ITF) and the Performance Test Facility (PTF). The ITF comprises a carbon steel pressure vessel with an internal volume of 10.8 m3 . It was constructed to perform performance tests in varying conditions of pressure, temperature, humidity, hydrogen concentration and borated water spray. It has a cylindrical shape

Table 1 Comparison of performance among catalyst types. Catalyst type

H2 depletion rate (g/s m2 )

Inlet H2 conc. (%)

Outlet H2 conc. (%)

Conversion ratio (%)

10 ppi nickel form 40 ppi nickel form 20 ppi honeycomb 100 ppi honeycomb 200 ppi honeycomb

1.87 1.47 2.27 1.33 0.80

4.0 4.0 4.0 4.0 4.0

0.4 0.1 0.1 0.1 0.1

90.0 97.5 97.5 97.5 97.5

4282

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

Fig. 4. Photograph of ITF vessel. Fig. 2. Photograph of KPAR-40 Model.

with ∼2.0 m in diameter by ∼4.0 m in height. On top of the pressure vessel, a safety valve and a relief valve are installed for the purpose of pressurization protection and vent. Figs. 3 and 4 show the conceptual diagram and the view of the ITF, respectively. On the side are installed a manhole and penetration ports for the instrumentation and the injection of air and hydrogen. They are all composed of stainless steel piping and are sealed with leak tightness in high pressure. The vessel walls and heads are 1.6 cm thick and covered with 10.0 cm of glass wool insulation except the manhole area.

Inside the pressure vessel are installed a support girder for test PAR, two mixing fans, a spray nozzle and four electric heaters. A PAR gate is equipped at the PAR entrance to prevent air and hydrogen from going into the PAR before it is opened to start tests. The pressurization of the pressure vessel can be accomplished by: (1) steam generation from water filled at the vessel bottom using three 16 kW electrical heaters submerged in water, (2) direct heating of atmosphere using 10 kW electrical heater, and/or (3) injecting air using an air compressor. The maximum design pressure and temperature are 1.5 MPa and 200 ◦ C, respectively.

Fig. 3. Conceptual diagram of integral test facility.

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

4283

Fig. 5. Photograph of PTF chamber.

Fig. 6. Instrumentation and data acquisition system.

The PTF is a wooden chamber to perform the PAR performance test at normal room temperature and pressure. It was built to accommodate for any size of honeycomb PAR. The PAR exit is located outside the test chamber, which allows continuous injection and flow control of hydrogen during testing. A flow restrictor is installed along the bottom part of PAR so as to create a well mixing condition before the hydrogen flows into the test PAR. Fig. 5 illustrates the PTF. A PC-based data acquisition system (DAS) was utilized to control and monitor the course of the test online. The DAS provides instantaneous readouts of temperature, pressure, and hydrogen concentration. The system can control the targeted hydrogen concentration and the injection flow rate as well. One pressure transducer was used to measure the pressure in the PTF. The temperature was measured with three thermocouples at the catalyst, the exit of the PAR and the atmosphere of the PTF. A real-time gas mass spectroscopy (GMS) system was used to determine the concentrations of hydrogen at three sample points: the PAR entrance and exit, and the center of PTF. To ensure representative samples and minimize the delay time due to purging sample lines, each line had been purged for about 30 min prior to sampling. Other instrumentation included a thermohygrometer to measure the relative humidity and a flow meter. The thermohygrometer is a thin film type, and the measurement range is 0–100% for relative humidity and −40–180 ◦ C for temperature. The flow meter with the maximum rate of 400 L/min at 4 bar was used to measure the hydrogen injection flow rate. Fig. 6 demonstrates the instrumentation and DAS.

In addition, four R-C tests have been performed in PTF to find the parametric equation which depends on the hydrogen concentration. The R-C tests were performed at an initial temperature of 18 ◦ C and atmospheric pressure by changing the hydrogen concentrations to 2, 4, 6 and 8%. In these tests the hydrogen concentrations were adjusted and maintained at the target value by continuous injection of hydrogen and control of the injection flow rate during the test. Tests have also been performed to determine the scale effect of the PAR size using a scaled KPAR-T2 model. Three R-P tests in ITF and four R-C tests in PTF have also been conducted in order to compare the test results against those using the KPAR-40 model. 3.2. Test results The prototype KPAR-40 model was used in ITF for the R-T tests. The test vessel was heated using the 10 kW pin heater until the gas temperature reached the target value. The pressure was adjusted to 1.5 bar by injecting air into the vessel using an air compressor. Then, hydrogen was injected from the hydrogen source bottle into ITF at the flow rate of 50 L/min until the hydrogen concentration reached equilibrium at about 4%. After about 5 min delay, the PAR gate was opened. In the IT-RT-1 test, the temperature at the catalyst rapidly increased to about 430 ◦ C in a few minutes and then decreased as the hydrogen was removed by PAR. However, the temperature and the pressure at the center of ITF changed slightly. Fig. 7 shows the pressure and temperature profile in the IT-RT-1

4.0 400

3.5 3.0

300

o

Temperature ( C)

3.1. Test matrix Various PAR performance tests have been conducted to develop an appropriate hydrogen depletion rate correlation by using a scaled KPAR-T2 model and a KPAR-40 model in ITF and PTF. Table 3 lists the test matrix for the PAR performance test conducted in ITF vessel and PTF chamber. By using a prototype KPAR-40 model, four R-T tests and five R-P tests have been performed in ITF to evaluate the parametric equations which depend on temperature and pressure, respectively. The IT-RT tests were conducted at a fixed pressure of 1.5 bar by varying the gas temperatures (40, 60, 80 and 100 ◦ C), while the IT-RP tests were conducted at a fixed temperature of 60 ◦ C by varying the pressures (1.0, 1.5, 2.0, 3.0, 4.0 bar) inside ITF pressure vessel.

Catalyst Temp.

2.5 200 2.0 100

1.5

Vessel Temp.

1.0 0

Pressure

0

5

10

0.5 15

20

25

Time (min) Fig. 7. Pressure and temperature profile in IT-RT-1 test.

30

Pressuregage (Bar)

3. Experiment

4284

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

Table 3 Test matrix for performance test of honeycomb PAR. Test no.

PAR model

Pressure

R-T test

IT-RT-1 IT-RT-2 IT-RT-3 IT-RT-4

KPAR-40 KPAR-40 KPAR-40 KPAR-40

1.5 bar 1.5 bar 1.5 bar 1.5 bar

40 ◦ C 60 ◦ C 80 ◦ C 100 ◦ C

4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5%

R-P test

IT-RP-1 IT-RP-2 IT-RP-3 IT-RP-4 IT-RP-5 IT-RP-6 IT-RP-7 IT-RP-8

KPAR-40 KPAR-40 KPAR-40 KPAR-40 KPAR-40 KPAR-T2 KPAR-T2 KPAR-T2

1.0 bar 1.5 bar 2.0 bar 3.0 bar 4.0 bar 1.0 bar 2.0 bar 3.0 bar

60 ◦ C 60 ◦ C 60 ◦ C 60 ◦ C 60 ◦ C 60 ◦ C 60 ◦ C 60 ◦ C

4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5% 4.0–0.5%

R-C test

PT-RC-1 PT-RC-2 PT-RC-3 PT-RC-4 PT-RC-5 PT-RC-6 PT-RC-7 PT-RC-8

KPAR-40 KPAR-40 KPAR-40 KPAR-40 KPAR-T2 KPAR-T2 KPAR-T2 KPAR-T2

1.0 bar 1.0 bar 1.0 bar 1.0 bar 1.0 bar 1.0 bar 1.0 bar 1.0 bar

18 ◦ C 18 ◦ C 18 ◦ C 18 ◦ C 18 ◦ C 18 ◦ C 18 ◦ C 18 ◦ C

2.0% 4.0% 6.0% 8.0% 2.0% 4.0% 6.0% 8.0%

test. The relative humidity of the test vessel increased due to the steam generated in the recombination process after the PAR started operation. Fig. 8 presents the time-dependent hydrogen concentrations at the PAR entrance and the atmosphere of ITF. The overall hydrogen concentration in the ITF vessel had continued to gradually increase until the end of hydrogen injection, then remained at about 4% during the mixing time, and finally decreased exponentially to below 0.5% in 6–7 min after the PAR gate had been opened. However, the hydrogen concentration at the PAR entrance remained nearly 0% and rapidly increased to above 4% as soon as the PAR gate had been opened, then decreased exponentially similarly to the overall concentration. In R-P tests, the prototype KPAR-40 and the scaled KPAR-T2 models were used in the ITF test vessel. The test vessel was heated using the 10 kW pin heater until the gas temperature reached 60 ◦ C. The pressure was adjusted to the target values of 1 bar through 4 bar by injecting air into the ITF vessel using the air compressor. Then, hydrogen was injected from the hydrogen source bottle into the ITF vessel until the hydrogen concentration reached about 4%. After about 5 min delay, the PAR gate was opened. The test results were similar to those of the R-T tests. In R-C tests the prototype KPAR-40 and the scaled KPAR-T2 models were used in the PTF test chamber. All the R-C tests were

Temp.

H2 conc.

conducted at room temperature and atmospheric pressure. Four mixing fans were turned on to create a well mixing condition inside the test chamber. Then, hydrogen was injected into the test chamber by gradually increasing the flow rate until the hydrogen concentration reached equilibrium at the target value between 2% and 8%. In the PT-RC-1 test, the hydrogen injection rate was about 77 L/min when it arrived at the equilibrium state in the hydrogen concentration of 1.93%. Other R-C tests have been conducted in the same process and condition except the hydrogen injection rate. The test results showed similar trends except for the rate of change in the hydrogen concentration. Figs. 9 and 10 show the hydrogen injection flow rate and the hydrogen concentration measured in the R-C tests. 4. Honeycomb PAR performance analysis The PAR performance is characterized by the hydrogen depletion rate. Several correlations on the hydrogen depletion rate have been developed by PAR manufacturers or laboratories (Blanchat and Malliakos, 1999). The related parameters and the expressions are diverse indeed and specific to the characteristic of the PARs. Generally, the correlation on the hydrogen depletion rate can be developed by the experiments on the performance of the PARs.

300

Hydrogen Concentration (%)

Hydrogen Injection Rate (L/min)

PAR Entrance Atmosphere

5

4

3

2

1

KPAR-40 @8% KPAR-40 @6% KPAR-40 @4% KPAR-40 @2% KPAR-T2 @8% KPAR-T2 @6% KPAR-T2 @4% KPAR-T2 @2%

250 200 150 100 50 0

0 0

5

10

15

20

25

Time (min) Fig. 8. Hydrogen concentration profile in IT-RT-1 test.

30

0

5

10

15

20

25

Time (min) Fig. 9. Hydrogen injection rate in R-C tests.

30

35

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

4.5

10

PT-RC-1 PT-RC-2 PT-RC-3 PT-RC-4

8

Experimental Data Fitted Function

4.0

Hydrogen Concentration (%)

Hydrogen Concentration (%)

4285

6

4

2

3.5

-0.38 t

C = 4.1*e

2.5

Model Equation Reduced Adj. R-Sq

2.0

Hydrogen a Hydrogen b

3.0

Exp2PMo y = a*exp 0.00616 0.99397 Value Standard 4.09233 0.0185 -0.38484 0.00275

1.5 1.0 0.5

0

0.0 0

5

10

15

20

25

0

1

Time (min)

In the pressure vessel such as ITF which is a system with constant volume, the hydrogen depletion rate by a PAR can be expressed as the mass of hydrogen removed by a PAR per unit time as follows. dMh d d = − (h · Vh ) = − (h · C · Vt ) dt dt dt



h

dC d +C h dt dt

(1)

In the equation above, the second part on the right side is negligible compared to the first part, since the rate of change of hydrogen density is much smaller than that of hydrogen concentration at the tests in the ITF test vessel. In contrast, the hydrogen concentration will be exponentially decreased with the removal coefficient  by a PAR and can be expressed as (2)

Therefore, the hydrogen depletion rate by a PAR can be stated as RPAR = h · Vt ·  · C

(3)

If the ideal gas law is applied to hydrogen, the hydrogen depletion rate can be written out as RPAR =

m P  h RT

· Vt ·  · C =

m V  C · P h t R

T

(4)

If we define the PAR performance constant per unit catalyst A as (mh Vt /R)/N, the hydrogen depletion rate equation can be simplified as RPAR = A · N ·

1 T

·P·C

5

6

depletion rate must be modified by using parametric equations of the temperature, the pressure, and the hydrogen concentration as RPAR = A · N · f (T ) · f (P) · f (C)

(6)

4.2. Parametric equation



C = C0 e−·t

4

Fig. 11. Hydrogen depletion curve in IT-RT-1 test.

4.1. Theoretical equation

= −Vt

3

Time (min)

Fig. 10. Hydrogen concentration profile in R-C tests.

RPAR = −

2

(5)

The above equation implies that the hydrogen depletion rate is proportional to the number of catalysts in a PAR N, the reciprocal of the temperature 1/T, the pressure P, and the hydrogen concentration C. However, the actual hydrogen removal by a PAR does not behave in accordance with the equation due to the dissimilarity of hydrogen from the ideal gas and the characteristic of a PAR. Furthermore, the hydrogen removal coefficient , which constitutes the PAR performance constant A, is slightly dependent on the temperature and the pressure. In this study, the hydrogen depletion rate RPAR will be expressed in the form of parametric equations of temperature, pressure, and hydrogen concentration assuming that the PAR performance constant A is constant. Accordingly, the hydrogen

The parametric equations of the temperature, the pressure, and the hydrogen concentration were established based on the relation between the hydrogen depletion rate and the parametric value. The detailed explanation on the development of each parametric equation follows. The parametric equation of the temperature was established from the results of the R-T tests which had been conducted at the test pressure of 1.5 bar by varying the test temperature from 40 ◦ C to 100 ◦ C in the ITF pressure vessel. During each R-T test, the hydrogen concentration decreased from the initial value of ∼4% until it reached ∼0.5% as a PAR removed hydrogen. Fig. 11 shows the test result of the time-dependent hydrogen concentration in the case of IT-RT-1 which was conducted at 40 ◦ C. As shown, the hydrogen concentration exponentially decreased with time, and the hydrogen removal coefficient  by PAR was fitted to 0.38 min−1 . The hydrogen depletion rate was calculated as a function of the hydrogen concentration C from 4% to 1% using the Eq. (5) with the PAR performance constant and the value of pressure and temperature. Test results of IT-RT-2 through IT-RT-4 showed similar trends but with different  values of 0.41, 0.38 and 0.39 at the test temperatures of 60 ◦ C, 80 ◦ C and 100 ◦ C, respectively. Fig. 12 shows the relation between the hydrogen depletion rate and the reciprocal of the temperature at several different hydrogen concentrations. Note that the hydrogen depletion rate linearly increases to the reciprocal of the temperature in Kelvin. Accordingly, the parametric equation on the temperature can be written in the form of f(T) = a1 (1/T). The parametric equation of the pressure was established from the results of the R-P tests which were conducted at the test temperature of 60 ◦ C by varying the test pressure from 1 to 4 bar in the ITF pressure vessel. The processes of test and analysis were almost identical to the R-T test. The  values are summarized in Table 4 including ratios of the values between the prototype KPAR-40 tests and the scaled KPAR-T2 tests. Fig. 13 illustrates the hydrogen depletion rate as a function of test pressure. Observe that the hydrogen depletion rate is nonlinear to the pressure, but in the form of logarithmic function of f(P) = a2 + b2 ln(P). The constants a2 and b2 are proportional to the hydrogen concentration, and the ratio of b2 to a2 is 1.845 regardless of the hydrogen concentration. As a result,

4286

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

Table 4 Hydrogen removal coefficients in R-P tests. Value

Tests

KPAR-40 (␭1) KPAR-T2 (␭2) Ratio (␭1/␭2)

IT-RP-1 (P = 1.0 bar)

IT-RP-2 (P = 1.5 bar)

IT-RP-3 (P = 2.0 bar)

IT-RP-4 (P = 3.0 bar)

IT-RP-5 (P = 4.0 bar)

0.34 0.078 4.4

0.41 – –

0.40 0.097 4.1

0.34 0.086 4.0

0.30 – –

the parametric equation of pressure can be expressed in the form of f(P) = a2 (1 + 1.845 ln(P)). The parametric equation of the hydrogen concentration was established from the results of the R-C tests which were conducted at room temperature and pressure by varying the hydrogen concentration from 2.0% to 8.0% in the PTF test chamber. In R-C test the hydrogen depletion rate by PAR is the multiplication of the hydrogen injection rate and the hydrogen density when the hydrogen concentration is in equilibrium. The temperature inside the test chamber slightly increased from the initial value during the test due to the effect of the catalyst temperature. Table 5 summarizes the values of the test and analysis. As shown in Fig. 14, the hydrogen depletion rate by PAR is proportional to the hydrogen concentration. Accordingly, the parametric equation on hydrogen concentration can be written as f(C) = a3 C.

0.50 0.45

Experimental Data C=1%, P=1.5bar C=2%, P=1.5bar C=3%, P=1.5bar C=4%, P=1.5bar

Depletion Rate (g/s)

0.40 0.35

Fitted Function R = C x {21.89(1/T)+0.0050}

0.30 0.25 0.20 0.15 0.10 0.05 0.00

0.0026

0.0027

0.0028

0.0029

0.0030

0.0031

0.0032

o

1/Temp. (1/ K)

4.3. Hydrogen depletion rate correlation As aforementioned, the parametric equations can have a linear form on the hydrogen concentration and the reciprocal of the temperature and a logarithmic form on the pressure. The PAR performance constant A, which consists of the proportional constants of three parametric equations, that is a1 × a2 × a3 , can be determined from the results of the R-C tests. Table 5 lists the PAR performance constants of the KPAR-40 and the related values measured in R-C tests. The PAR performance constant ranges from 4.19 to 4.32. The standard PAR performance constant for the honeycomb PAR was conservatively determined to be 4.0 as a unique value. Therefore, the standard form of the hydrogen depletion rate correlation for the honeycomb PAR was finally determined as RPAR = 4.0 · N ·

C · [1 + 1.845 ln(P)] T

(7)

Fig. 15 compares the hydrogen depletion rates between the R-C test results and those calculated by the correlation, which demonstrates the conservatism of the correlation. Fig. 16 shows all the test results of hydrogen depletion rate with the two bounding correlation curves. Then, the hydrogen depletion rate correlation of the honeycomb PAR was compared against the correlations of NUKEM (formerly NIS) PAR which had previously been adopted in the Advanced Power Reactor 1400 MWe (APR1400) hydrogen analysis (Lee et al., 2003; Park et al., 2003). The two different correlations of the Battelle model and the Fischer model were used for comparison. The largest PARs were taken into account for the comparison: the KPAR-160 model for the honeycomb PAR and the PAR-88 model for the NUKEM PAR. Fig. 17 compares the correlation curves at the condition of 1.5 bar and 60 ◦ C between the honeycomb PAR and the NUKEM PAR. Note that the hydrogen depletion rate of the honeycomb PAR is higher than both models of the NUKEM PAR. The developed correlation on the hydrogen depletion rate of the honeycomb PAR should be used within the range of the environmental condition where the performance tests were performed.

Fig. 12. Hydrogen depletion rate vs. temperature in R-T tests.

0.5 0.8

0.6

Experimental Data Modified Data

Fitted Function R = 0.0417 C * {1 + 1.845 ln(P)}

0.4 R = 0.05753 C + 0.003565

Depletion Rate (g/s)

Depletion Rate (g/s)

0.7

Experimental Data C=1%, T=333K C=2%, T=333K C=3%, T=333K C=4%, T=333K

0.5 0.4 0.3 0.2

0.3

0.2

R = 0.05145 C + 0.01530

0.1

0.1 0.0 0.0 1.0

1.5

2.0

2.5

3.0

3.5

Pressure (Bar) Fig. 13. Hydrogen depletion rate vs. pressure in R-P tests.

4.0

0

1

2

3

4

5

6

7

8

Hydrogen Concentration (%) Fig. 14. Hydrogen depletion rate vs. hydrogen concentration in R-C tests.

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

4287

Table 5 PAR performance-related values in R-C tests. Value

Test condition C = 2%

C = 4%

C = C = 6%

C = 8%

77.0 19.2

150.9 39.8

220.9 59.8

260.6 77.9

H2 inj. rate (L/min)

KPAR-40 KPAR-T2

H2 conc. (%)

KPAR-40 KPAR-T2

Temp. (◦ K)

KPAR-40 KPAR-T2

RPAR (g/s)

KPAR-40 KPAR-T2

0.115 0.029

0.225 0.059

0.329 0.089

0.388 0.116

PAR performance constant (A)

KPAR-40 KPAR-T2 Ratio

4.32 4.48 0.96

4.19 4.15 1.01

4.21 4.14 1.02

4.22 4.25 0.99

1.93 1.89 291.0 296.6

The correlation was developed with the limited range of 1–4 bar, 40–100 ◦ C, and 0.5–8% of hydrogen concentration in order to meet the design requirements of the hydrogen mitigation system of the APR1400. Since the lower range of hydrogen concentration may affect the threshold of the catalytic reaction and the initial selfstarting, the correlation should be applied within the range of hydrogen concentration not less than 0.5%. That is, the hydrogen

Depletion Rate (g/s)

0.6

KPAR-T2 x 4 KPAR-40 x 1 Correlation

0.5 0.4 0.3 0.2 0.1

C = 4.0*N*C*{1+1.845 ln(P)}*(1/T)

0.0 0

2

4

4.05 4.21

6

8

10

Hydrogen Concentration (%)

6.04 6.44

302.1 294.9

7.24 8.47

309.2 299.5

315.2 310.8

depletion rate becomes zero below 0.5% of the hydrogen concentration. Above 8% of the hydrogen concentration, the hydrogen depletion rate at 8% hydrogen concentration must be applied. The hydrogen concentration for the initial self-starting of a PAR is less than 1.5%. 4.4. Scale effect on PAR size The scale effect on the PAR size must be confirmed so that a standard hydrogen depletion rate correlation could be used for any size of honeycomb PARs. The scale effect has been studied in two different ways by comparing the performance between the scaled PAR (the KPAR-T2 model) and small commercial PAR (the KPAR40 model). The first method is to compare the hydrogen removal coefficient  between the KPAR-T2 model and the KPAR-40 model which were taken from the R-P test results performed in ITF. In closed loop tests such as those in the ITF, the hydrogen depletion rate is directly proportional to the hydrogen removal coefficients . Table 4 compares the hydrogen removal coefficient  between the KPAR-T2 model and the KPAR-40 model. The hydrogen removal coefficient  of the KPAR-40 model is about four (4) times greater than that of the KPAR-T2 model, which is due to the difference in the number of catalysts in the PAR between two models. The other method is a comparison of the PAR performance constants A between the KPAR-T2 model and the KPAR-40 model which were taken from the R-C test results conducted in PTF. In the open loop

Fig. 15. Comparison of correlation with R-C test results.

2.0

Depletion Rate (g/s)

1.6 1.4

3.0

o

Correlation at 4 Bar, 18 C o Correlation at 1 Bar, 100 C KPAR-T2 x4 KPAR-40 x1

KNT KPAR-160 (KNT Model) NUKEM PAR-88 (Battelle Model) NUKEM PAR-88 (Fischer Model)

2.5

Depletion Rate (g/s)

1.8

1.2 1.0 0.8 0.6 0.4

2.0 1.5 1.0 0.5

0.2 0.0

0.0 1

2

3

4

5

6

7

Hydrogen Concentration (%) Fig. 16. Test results with bounding correlations.

8

0

1

2

3

4

5

6

7

Hydrogen Concentration (%) Fig. 17. Comparison of hydrogen depletion rate correlation.

8

4288

J.-W. Park et al. / Nuclear Engineering and Design 241 (2011) 4280–4288

tests such as those in PTF, the hydrogen depletion rate is directly proportional to the hydrogen injection rate or the PAR performance constant A. Table 5 compares the PAR performance constant A between the KPAR-T2 and KPAR-40 models. Since the PAR performance constant is a value per unit catalyst in a PAR, it is almost the same in both the KPAR-T2 and KPAR-40 models. In summary, the ratio of the hydrogen removal coefficient  between the KPAR-T2 and KPAR-40 models corresponds to the ratio of the number of catalysts in the PAR. Also, the PAR performance constant per unit catalyst is almost identical in both the PAR models. Therefore, no prominent scale effect exists and the hydrogen depletion rate correlation developed for the KPAR-40 model should be applicable to any size of honeycomb PARs. 5. Conclusions A new honeycomb PAR has been developed featuring enhanced hydrogen removal performance. Experiments were performed in ITF and PTF which had been custom-built for the environmental qualification and performance check on the honeycomb PAR. The hydrogen depletion rates were measured using a prototype PAR and a scaled test PAR in various conditions of pressure, temperature, and hydrogen concentration. The test condition spanned 1–4 bar, 40–100 ◦ C, and 0.5–8% of the hydrogen concentration. The testing shed light on the relation between the hydrogen depletion rate of the PAR and the environmental condition. A correlation was developed for the hydrogen depletion rate for the honeycomb PAR through performance analysis of the experimental results. The correlation of hydrogen depletion rate consists of three parametric equations on pressure, temperature and hydrogen concentration, and PAR performance constant. The hydrogen depletion rate was concluded to be proportional to the hydrogen concentration and the reciprocal of the absolute temperature and have a logarithmic function on the pressure. There was no prominent scale effect observed, which means that the hydrogen

depletion rate is proportional to the number of catalysts regardless of the PAR size. References Bachellerie, E., Arnould, F., et al., 2003. Generic approach for designing and implementing a passive autocatalytic recombiner PAR-system in nuclear power plant containments. Nuclear Engineering and Design 221, 151–165. Behrens, O., et al., 1991. Deflagration detonation transition in hydrogen in hydrogen-air-steam mixtures: relevance of experimental results for real accident situations. Nuclear Engineering and Design 130. Blanchat, T.K., Malliakos, A., 1999. Analysis of hydrogen depletion using a scaled passive autocatalytic recombiner. Nuclear Engineering and Design 187, 229–239. Cronenberg, H., Jan, 1992. Hydrogen generation behavior in the LOFT FP-2 and other experiments: comparative assessment for mitigated severe accidents. Nuclear Technology 97. Deng, J., Cao, X.W., 2008. A study on evaluating a passive autocatalytic recombiner PAR-system in the large-dry containment. Nuclear Engineering and Design 238, 2554–2560. Dorofeev, S.B., Sidorov, P.O., Dvoinishnikov, A.E., Breitung, W., 1996. Deflagration to detonation transition in large confined volume of lean hydrogen-air mixtures. Combustion and Flame 104, 95–110. Fischer, K., Broeckerhoff, P., Ahlers, G., Gustavsson, V., Herranz, L., Polo, J., Dominguez, T., Royl, P., 2003. Hydrogen removal from LWR containments by catalytic-coated thermal insulation elements (THINCAT). Nuclear Engineering and Design 221, 137–149. Lee, B.C., Park, J.W., Lee, S.M., 2003. Evaluation of the APR1400 hydrogen mitigation system using sophisticated LP code coupled with 3-dimensional model. In: Proceedings of International Congress on Advances in Nuclear Power Plants (ICAPP), Cordoba, Spain, 4–7 May 2003. Park, J.W., Lee, S.M., Park, H.G., 2003. Hydrogen control using PARs and igniters. In: Proceedings of the 11th International Conference on Nuclear Energy (ICONE), Tokyo, Japan, 20–23 April 2003. Reinecke, E.A., Tragsdorf, I.M., Gierling, K., 2004. Studies on innovative hydrogen recombiners as safety devices in the containments of light water reactors. Nuclear Engineering and Design 230, 49–59. Royl, P., Rochholz, H., Breitung, W., Travis, J.R., Necker, G., 2000. Analysis of steam and hydrogen distributions with PAR mitigation in NPP containments. Nuclear Engineering and Design 202, 231–248. Sherman, M.P., Berman, M., 1988. The possibility of local detonations during degraded core accidents in the Bellefonte nuclear power plants. Nuclear Technology 81, 63–67. Yang, J.W., et al., 1991. Hydrogen combustion control and value-impact analysis for PWR dry containments. NUREG/CR-5662 (May).