Development of control technology for HTTR hydrogen production system with mock-up test facility: System controllability test for loss of chemical reaction

Nuclear Engineering and Design 236 (2006) 1396–1410

Development of control technology for HTTR hydrogen productionsystem with mock-up test facility

System controllability test for loss of chemical reaction

Hirofumi Ohashi ∗, Yoshitomo Inaba, Tetsuo Nishihara, Tetsuaki Takeda,Koji Hayashi, Shoji Takada, Yoshiyuki Inagaki

Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Oarai-machi,Higashi-Ibaraki-gun, Ibaraki-ken 311-1393, Japan

Received 27 June 2005; received in revised form 27 December 2005; accepted 5 January 2006

Abstract

The Japan Atomic Energy Agency has been planning the demonstration test of hydrogen production with the High Temperature Engineering TestRvastcA©

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eactor (HTTR). In a HTTR hydrogen production system (HTTR-H2), it is required to control a primary helium temperature within an allowablealue at a reactor inlet to prevent a reactor scram. A cooling system for a secondary helium with a steam generator (SG) and a radiator is installedt the downstream of a chemical rector in a secondary helium loop in order to mitigate the thermal disturbance caused by the hydrogen productionystem. Prior to HTTR-H2, the simulation test with a mock-up test facility has been carried out to establish the controllability on the heliumemperature using the cooling system against the loss of chemical reaction. It was confirmed that the fluctuations of the helium temperature athemical reactor outlet, more than 200 K, at the loss of chemical reaction could be successfully mitigated within the target of ±10 K at SG outlet.

dynamic simulation code of the cooling system for HTTR-H2 was verified with the obtained test data.2006 Elsevier B.V. All rights reserved.

. Introduction

The Japan Atomic Energy Agency (JAEA) has carried out theesearch and development on hydrogen production by applyingigh-Temperature Gas-Cooled Reactor (HTGR) as a heat source

Shiozawa et al., 2000). JAEA has constructed the High Temper-ture Engineering Test Reactor (HTTR) with a thermal outputf 30 MW and outlet coolant temperature of 950 ◦C (Saito et al.,994). The first criticality of HTTR was achieved in November998 (Fujimoto et al., 2000), and full power of 30 MW-thermalnd the reactor outlet coolant temperature of 950 ◦C were accom-lished in April 2004 (Fujikawa et al., 2004). An intermediateeat exchanger (IHX) installed in a reactor containment vesselan supply thermal heat of 10 MW to a nuclear heat utilizationystem. For the hydrogen production technology, JAEA has beeneveloping a thermochemical water splitting Iodine-Sulfur (IS)

∗ Corresponding author. Tel.: +81 29 266 7724; fax: +81 29 266 7608.E-mail address: [email protected] (H. Ohashi).

process (Kubo et al., 2004a,b). It enables to produce hydrogenfrom water at the temperature of lower than 1000 ◦C, while con-ventional thermal decomposition of water needs thermal energyof temperature above 4000 ◦C. Since IS process connected toHTGR can produce a large amount of hydrogen without CO2emissions, it is a one of promising candidate to solve globalwarming issue and satisfy a large demands of hydrogen in thenear future.

The system integration technology to connect the hydrogenproduction system to HTGR is one of the key technologies toput hydrogen production with nuclear energy to commercialuse. Research and development on the system integration tech-nology has been carried out about four items, i.e. (a) controltechnology to keep reactor operation against thermal disturbancecaused by the hydrogen production system (Inagaki et al., 1999);(b) estimation of tritium permeation from reactor to hydrogen(Takeda et al., 2004); (c) countermeasure against explosion; and(d) development of high temperature valve to isolate reactorand hydrogen production systems in accidents (Nishihara et al.,2004).

029-5493/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.nucengdes.2006.01.005

H. Ohashi et al. / Nuclear Engineering and Design 236 (2006) 1396–1410 1397

Nomenclature

A cross-sectional area (m2)Cp heat capacity (kJ kg−1 K−1)F heat transfer area per unit length (m2 m−1)K correlation coefficientNu Nusselt numberPr Prandtl numberQ heat exchange duty (kW)Re Reynolds numbert time (s)T temperature (K)W mass flow rate (kg s−1)X co-ordinate along with fluid flow (m)

Greek lettersα heat transfer coefficient (W m−2 K−1)η thermal efficiencyρ density (kg m−3)

SubscriptsAir cooling airHe heliumin at inletL heat lossout at outletR radiatorSG steam generatortx at surface of heat exchanger tube

JAEA has been planning a hydrogen production demon-stration test with HTTR to establish the hydrogen productiontechnology with HTGR. Prior to a HTTR hydrogen produc-tion system (Nishihara et al., 2003), a mock-up test facility bysteam reforming of methane was built to establish and demon-strate the controllability and to verify a dynamic simulation code(Ohashi et al., 2004a). Since the hydrogen production by steamreforming of methane is widely used in fossil-fired plants asthe most inexpensive hydrogen production process, the basictechnology on system layout, operational procedure, indispens-able components, etc. has been established. This process cansimplify the developmental issues, i.e. the control technologycan be developed without the development of the hydrogenproduction technology. The control technology established byusing steam reforming of methane can contribute to other hydro-gen production systems, e.g. IS process. The experiment onthe control technology with the mock-up test facility is clas-sified into three items: (a) normal start-up and shutdown test(Ohashi et al., 2004b); (b) system controllability test for fluctu-ation of chemical reaction (Inaba et al., 2005) and c) systemcontrollability test for loss of chemical reaction. This paperdescribes the experimental results of the system controllabilitytest for loss of chemical reaction and the results of the veri-fication of a dynamic simulation code with the obtained testdata.

2. Cooling system for the secondary helium in HTTRhydrogen production system

2.1. Necessity of cooling system

Fig. 1 shows a conceptual flow diagram of the HTTR hydro-gen production system by steam reforming of methane. Thenuclear reactor, HTTR, causes some technological problemsrelated to the system controllability. Both primary and sec-ondary helium consist of closed loop, i.e. the primary heliumcirculates between HTTR and IHX and the secondary heliumcirculates between IHX and the hydrogen production system.The high temperature heat transported from the primary to thesecondary helium is used for hydrogen production as energyfor an endothermic chemical reaction in a chemical reactor. Thechemical reactor can be considered as a heat sink of HTTR. Thefluctuations of the chemical reaction at the normal operation,which is the fluctuations of the thermal load of the hydrogen pro-duction system, causes the fluctuations of the secondary heliumtemperature at IHX inlet. It affects the primary helium tempera-ture at the reactor inlet and a large thermal disturbance causes areactor scram. In order to prevent the reactor scram at the normaloperation, the thermal load of the hydrogen production systemshould be kept constant and the fluctuation of the primary heliumtemperature caused by the hydrogen production system shouldbe mitigated within an allowable value at the reactor inlet byueotdcrocip

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sing a cooling system for the helium. A nuclear reactor is gen-rally designed based on the relative slow temperature changeperation. However, the temperature change speed and quan-ity of reactants of hydrogen production in the chemical reactoruring a start-up and shutdown are absolutely high and largeompared with the permissible ranges of those of the nucleareactor coolant. Therefore, the change of the nuclear reactorutput cannot be accorded with that of the thermal load of thehemical reactor during the start-up and shutdown. Therefore,t is impossible to start-up and shutdown the HTTR hydrogenroduction system without any cooling systems for the helium.

.2. Feature of cooling system for the secondary heliumith steam generator and radiator

In order to prevent the scram of HTTR throughout the oper-tion, e.g. from star-up to shutdown, a steam generator (SG)s installed at the downstream of the chemical reactor in theecondary helium loop as the cooling system for the secondaryelium, which can suppress any thermal disturbances caused byhe chemical reactor. The secondary helium temperature at theutlet of SG will be able to be kept within the allowable range athe saturation temperature of steam corresponding to the waterressure in SG. It enables to keep the primary helium tempera-ure within the allowable range at the HTTR inlet. Even if thehemical reactor losses its thermal load completely (the lossf chemical reaction) by some malfunction or accident at theydrogen production system, it is proposed to shutdown HTTRot with the scram of HTTR but by the normal operation pro-edure using the cooling system for the secondary helium withG and a radiator. It is required to cool the secondary helium

1398 H. Ohashi et al. / Nuclear Engineering and Design 236 (2006) 1396–1410

Fig. 1. Conceptual flow diagram of HTTR hydrogen production system by steam reforming of methane.

at SG instead of the chemical reactor and to keep the secondaryhelium temperature within the allowable value at SG outlet toprevent reactor scram as well as the normal operation. In theHTTR hydrogen production system, it is tried to suppress thefluctuation of secondary helium temperature within the rangefrom −10 to +10 ◦C at SG outlet using the cooling system withSG and the radiator to mitigate thermal disturbance to HTTR.

In the cooling system, the helium temperature at SG outletdepends on the water temperature in SG, i.e. the saturation pres-sure in SG. Therefore, the controllability of the water pressurein SG is important to keep the secondary helium temperaturewithin the allowable value at SG outlet.

2.2.1. At start-up, shutdown and normal operationFig. 2a shows the conceptual flow diagram of the cooling

system for the secondary helium at the start-up, shutdown andnormal operation. The water pressure in SG is controlled byusing a pressure control valve installed in SG to control thehelium temperature within allowable range at SG outlet. Thesteam used for pressure regulation is condensed at the radiatorinstalled above SG and the condensed water flows to a watertank. The operating pressure in SG and the radiator is around5 MPa and ambient pressure, respectively. For the hydrogen pro-duction system, which needs steam as a reactant for the hydrogenproduction, viz. the steam reforming of methane, SG has not onlyts

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the heat exchanger tube in SG. In this system, steam is reusable,viz. the condensed steam in the radiator is supplied to SG directlyas the feed water. All produced steam is supplied to the radia-tor and it is condensed into water at the radiator by the coolingair. Steam and water circulate between SG and the radiator bynatural circulation. Accordingly, it is unnecessary to have largecapacity water feed equipment and to control the water supply

Fig. 2. Conceptual flow diagram of the cooling system for the secondary heliumwith the steam generator and the radiator: (a) at start-up, shutdown and normaloperation; (b) at loss of chemical reaction.

he function of the thermal absorber but also the function of theteam supply to the chemical reactor.

.2.2. At loss of chemical reactionFig. 2b shows the conceptual flow diagram of the cooling

ystem for the secondary helium at loss of chemical reaction.n the case of loss of chemical reaction, the thermal load of SGncreased more than twice compared to that at normal operation,.e. steam generation rate in SG increased more than twice com-ared to that at normal operation. Therefore, the water supplyhould be increased more than twice to prevent the exposure of


to SG. The mechanism of the natural circulation is the follow-ing: Steam produced in SG flows into heat exchanger tubes inthe radiator and is cooled by the cooling air. Then, a part ofsteam condenses to water, and it leads to the decrease of steamvolume in the heat exchanger tubes of the radiator. As a result,the steam pressure in the heat exchanger tubes of the radiatorbecomes slightly lower than the water pressure in SG. The differ-ential pressure of steam in SG and the radiator causes the flow ofsteam from SG to the radiator. The condensed water in the heatexchanger tubes flows into a return pipe of SG and accumulatesin it. Finally, the condensed water returns to SG by gravitationwithout any pumps.

The water pressure in SG can be controlled by the coolingperformance of the radiator. When the water pressure in SG isstable, the heat balance in the cooling system can be expressedby the following equation.

QSG = QR + QL (1)

where QSG is the heat exchange duty of SG from helium towater in SG, QR is the heat exchange duty of the radiator fromsteam to air and QL is the heat loss to the atmosphere. QSG isproportional to the difference of the temperature between waterand helium in SG. Also, QR is proportional to the differenceof the temperature between steam and cooling air in the radia-tor. If QR is smaller than QSG, the water pressure in SG wouldidiaitii

of the temperature difference between cooling air and steam inthe radiator. As a result, the water pressure in SG approachesto the stable pressure corresponding to the condition expressedby the Eq. (1). On the other hand, if QR is larger than QSG,the water pressure in SG would decrease and approach to thestable pressure corresponding to the condition expressed by theEq. (1). In order to maintain the helium temperature within theallowable range at the outlet of SG, QR should be controlled tobalance with QSG under proper conditions of the water pressurein SG.

In the HTTR hydrogen production system, the water pressurein SG is to be controlled around 5 MPa. The saturation temper-ature of water is insensitive against the saturation pressure ofaround 5 MPa. Therefore, it is easy to control the helium tem-perature at SG outlet within the allowable range by controllingthe water pressure in SG, which is a good feature of this coolingsystem for the helium temperature controllability.

3. System controllability test for loss of chemicalreaction

3.1. Objective

In order to establish the helium temperature controllabilityusing the cooling system with SG and the radiator in the case oftsotc+tc

ram o

ncrease. With the increase of the water pressure in SG, QSGecreases due to the increase of the water temperature in SG,.e. the decrease of the temperature difference between heliumnd water in SG. The water pressures in SG and steam pressuren the radiator are almost the same, i.e. the steam temperature inhe radiator depends on the water pressure in SG. Therefore, QRncreases with increase of the water pressure in SG due to thencrease of the steam temperature in the radiator, i.e. the increase

Fig. 3. Schematic flow diag

he loss of chemical reaction in the HTTR hydrogen productionystem, a simulation test for loss of chemical reaction was carriedut with the mock-up test facility. It is intended to confirm thathe fluctuation of the helium temperature caused by the loss ofhemical reaction can be mitigated within the range from −10 to10 ◦C at SG outlet, and to investigate the transient behavior of

he cooling system for the verification of the dynamic simulationode.

f the mock-up test facility.


Table 1Design specifications of the mock-up test facility and HTTR hydrogen production system by steam reforming of methane

Items HTTR hydrogen production system Mock-up test facility

Pressure process-gas/helium (MPa) 4.5/4.0Temperature at inlet of steam reformer process-gas/helium (◦C) 450/880Temperature at outlet of steam reformer process-gas/helium (◦C) 580/585 600/650Methane (natural gas) feed (kg/h) 1400 43.2Helium circulation (kg/h) 9070 327.6Mole ratio of steam to carbon (S/C) 3.5Hydrogen production ability (m3/h) 4240 110Heat source Reactor (10 MW) Electric heater (0.38 MW)

3.2. Test facility

Fig. 3 shows a schematic flow diagram of the mock-up testfacility and a design specification is shown in Table 1. It sim-ulates the main components of the HTTR hydrogen productionsystem except HTTR, the primary helium loop and IHX. Anelectric heater of about 0.38 MW at the normal condition isused as a heat source to heat the helium up to 880 ◦C, i.e. thesame temperature as the HTTR hydrogen production system,instead of IHX of 10 MW. It is mainly composed of a heliumcirculation loop, a steam supply system including SG and theradiator, a methane supply system, including the chemical reac-tor, steam reformer (SR), a nitrogen supply system and a productgas combustion system. The helium circulation loop simulatesthe secondary helium loop in the HTTR hydrogen productionsystem. SG is installed at the downstream of the chemical reac-tor in the helium circulation loop as the cooling system. Fig. 4shows a schematic view of SG of the test facility, kettle typesteam generator (Ohashi et al., 2004c). Helium flows insideof heat exchanger tubes and heat of helium is transferred towater. The heat exchange duty between helium and water inSG is designed as 135 kW at the rated condition of the nor-

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mal operation. Fig. 5 shows a schematic view of the radiatorof the test facility (Ohashi et al., 2004c). The steam flows hor-izontally inside of the heat exchanger tubes and the cooling airflows vertically outside of the heat exchanger tube. The coolingperformance of the radiator can be changed by a cooling fan(installed at the inlet of the cooling air) and a louver (installedat the outlet of the cooling air). Hydrogen is produced in SR bythe steam reforming of methane with the high temperature heattransported from the helium through a reaction tube in SR, whichis the pressure boundary between the helium and a process gas,mixture of methane, steam and product gas. The reactions of thesteam reforming of methane are:

CH4 + H2O = 3H2 + CO; �H◦298 = +206 kJ mol−1 (2)

CO + H2O = H2 + CO2; �H◦298 = −40 kJ mol−1. (3)

The test facility can produce hydrogen at the rated value ofapproximately 120 m3/h. The simulation test can be carried outat the same conditions (temperature and pressure) as the HTTRhydrogen production system.

3.3. Experimental procedure and condition

In order to simulate the loss of chemical reaction in the hydro-gen production system, a feed of methane to the chemical reactorwas suspended during the hydrogen production. Fig. 6 shows adtetsusCiafsc

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ig. 4. Schematic view of the steam generator of the mock-up test facilityOhashi et al., 2004c).

etailed flow diagram of the test facility. During the test, heliumemperature and pressure at the inlet of SR were controlled atach rated condition, 880 ◦C and 4.1 MPa, respectively. Beforehe methane feed was suspended, flow rates of methane andteam to SR were controlled at each rates of 12 and 47 g/s bysing control valves A and B, respectively, and the water pres-ure in SG was controlled at 4.6 MPa by using a control valve. After the suspension of methane feed, nitrogen of 30 g/s was

ntroduced to SR to keep a pressure difference between heliumnd the process gas in the reaction tube of SR constant. Steameed to SR was stopped, and then a large quantity of producedteam was introduced to the radiator. The detail of the test pro-edure is as follows:

a) Close a stop valve A to stop methane feed to SR.b) Immediately, open a stop valve B to start nitrogen feed to

SR and control the flow rate at 30 g/s by using a controlvalve D.


Fig. 5. Schematic view of the radiator of the mock-up test facility (Ohashi et al., 2004c).

(c) After 0.17 h of procedure (a), close a stop valve C to stopsteam feed to SR, close a stop valve D to stop waterfeed to SG and close a stop valve E to stop the waterdrain.

(d) After 0.32 h of procedure (a), open a stop valve F to introducesteam to the radiator.

(e) After 30 s of procedure (d), open a stop valve G to returncondensed water from the radiator to SG.

(f) Change the flow rate of the cooling air by changing therotation frequency of the cooling fan to keep the heliumtemperature constant at SG outlet.

3.4. Experimental results and discussion

The solid lines in Fig. 7 show the experimental results andthe dashed lines in the same figure show the numerical results. A

ith t
Fig. 6. Detailed flow diagram of the cooling system for helium w he steam generator and the radiator of the mock-up test facility.


Fig. 7. Experimental and numerical results of the system controllability test for loss of chemical reaction using the mock-up test facility.

horizontal axis is the time axis indicating an elapsed time fromthe suspension of methane feed. Before the start of the suspen-sion of methane, the methane and steam flow to SR and could becontrolled at each rated condition, i.e. 12 and 47 g/s (see Fig. 7a).At the moment of 0 h, the methane flow rate was decreased dras-tically from 12 to 0 g/s. And at the moment of 0.17 h, the steamflow rate to SR was decreased drastically from 47 to 0 g/s bythe closing of the stop valve C installed at the inlet of a steamsuperheater (see Fig. 6). The hydrogen production rate decreased

from about 120 to 0 m3/h due to the suspension of methane feed(see Fig. 7b). Fig. 7c shows the helium temperature at the inletand outlet of SR and SG. At the moment of 0 h, the SR out-let helium temperature started increasing from 632 ◦C and itreached to 833 ◦C at 1.4 h due to the loss of chemical reaction.And it leads to the increasing of the SG inlet helium temper-ature, and it increased from 548 to 793 ◦C. The SR outlet andthe SG inlet helium temperature increased about 200 and 245 K,respectively. However, helium temperature at SG outlet showed


almost stable value, and profile was the same as those of thewater pressure and water temperature in SG as shown in Fig. 7dand e. After the suspension of methane feed, the water pressurein SG increased gradually from 4.61 MPa at 0 h to 4.75 MPa at0.32 h because of the increasing of the steam generation rate inSG with the increasing of the SG inlet helium temperature. Itresulted in the increasing of the water temperature in SG from258.7 to 260.2 ◦C and the increasing of the SG outlet heliumtemperature from 262.5 to 264.5 ◦C. At the moment of 0.32 h,when the stop valve F was opened, the water pressure in SG andthe steam pressure at the radiator inlet changed, i.e. decreasedand increased. These pressures became almost same, however,the water pressure in SG was slightly higher than the steam pres-sure at the radiator inlet. At the same time, the steam flow rate atthe radiator inlet increased drastically as shown in Fig. 7f. Andthe condensed water temperature at the outlet of the radiatorincreased drastically from about 75 to 253.4 ◦C by the openingof the stop valve F as shown in Fig. 7g. At the moment of 0.33 h,when the stop valve G was opened, the steam and condensedwater start to circulate between SG and the radiator. After thestart of the natural circulation, the water pressure in SG and thesteam pressure at the radiator inlet were kept decreasing. At themoment of 0.40 h, both pressures reached the minimum value ofabout 4.26 MPa. With the decreasing of the water pressure in SGfrom 4.75 MPa at 0.32 h to 4.26 MPa at 0.40 h, the water temper-ature in SG decreased from 260.2 to 256.2 ◦C. As a result, thehmiitewFwAtftbtrop

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helium can be used in N-HYPAC. N-HYPAC consists of twomodules—(a) SG module: code for the calculation of vaporiza-tion, condensation and heat transfer in SG, the radiator and thesteam superheater and (b) SR module: code for the calculationof heat and mass balance in SR involving chemical reaction, andheat exchange and fluid flow of the helium and the process gas inpipes and other components. Both modules can be either run asa “stand alone” code for the calculation of each main componentsuch as SR and SG, or can be executed together for the calcu-lation of the whole system of the HTTR hydrogen productionsystem.

In order to verify the SG module, the numerical analysis ofSG and the radiator was carried out using the SG module as thestand-alone code with the data of the mock-up test facility.

4.1. Architecture and basic equation of SG module inN-HYPAC

In order to simulate the thermal-hydraulic phenomena in SG,the radiator and the steam superheater, the thermal-hydrauliccomputer code, RELAP5/MOD2 (Ransom et al., 1985), isemployed in the SG module. A numerical model for the heliumflow in the heat exchanger tube in SG and the steam super-heater, a helium module, and a numerical model for the coolingair flow at the outside of the heat exchanger tube in the radi-ator, an air module, were integrated with RELAP5/MOD2. IntrbuhtmftRuca

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elium temperature at SG outlet decreased from 264.5 ◦C to theinimum value of 261.3 ◦C. After that, the water pressure in SG

ncreased with the increasing of the helium temperature at SGnlet. In order to maintain the water pressure in SG stable, i.e.o maintain the helium temperature stable at SG outlet, the heatxchange duty between steam and the cooling air in the radiatoras increased by the increasing the cooling air flow rate (seeig. 7h). The water pressure in SG was held at about 4.3 MPa,hich is corresponding to 255 ◦C of the water temperature in SG.s a result, the helium temperature at SG outlet could be con-

rolled at the same temperature before the suspension of methaneeed, 262.3 ◦C (see Fig. 7c). From these results, it was confirmedhat the thermal disturbance of the helium temperature causedy the loss of chemical reaction was successfully mitigated byhe cooling system with SG and the radiator. The fluctuationsange of the helium temperature was from −1.2 to +2.0 K at SGutlet, which is within the target range of the HTTR hydrogenroduction system.

. Verification of dynamic simulation code

A dynamic simulation code, N-HYPAC (Nuclear Hydro-en Production Analysis Code), was developed to simulate theynamic behavior of the hydrogen production system at theownstream of IHX in the HTTR hydrogen production system.he main features of N-HYPAC are as follows: (1) object com-onents for the numerical analysis are the steam reformer, thetem generator, the radiator, IHX, the steam superheater, a rawas pre-heater, a helium cooler, a secondary helium circulator,ipes, valves and control systems; (2) methane, hydrogen, car-on monoxide, carbon dioxide, nitrogen, air, steam, water and

he SG module, RELAP5/MOD2 calculates the heat exchangeate between water and the heat exchanger tube in SG and thatetween the steam and the heat exchanger tube in the radiator. Bysing these calculation results, the helium module calculates theelium temperatures and the heat transfer coefficients betweenhe helium and the heat exchanger tubes in SG. Also, the air

odule calculates the cooling air temperature and the heat trans-er coefficient between the cooling air and the heat exchangerube in the radiator. These calculation results are transferred toELAP5/MOD2 each calculation time step. The helium mod-le uses one-dimensional model and the helium temperature isalculated using the following energy conservation equation asbasic equation.

HeρHeCpHe∂THe

∂t+ WHeCpHe

∂THe

∂X= FHeαHe(Ttx − THe)

(4)

nd to calculate the heat transfer coefficient between the heliumnd the heat exchanger tube in SG, αHe, Dittus-Boelter’s corre-ation is applied as follows:

u = 0.23Re0.8Pr0.4. (5)

he air module uses one-dimensional model as well as theelium module. In the air module, the following equation issed as the basic equation of the energy conservation equationo calculate the cooling air temperature in the radiator.

airρairCpair∂Tair

∂t+WairCpair

∂Tair

∂X= Fairαair(Ttx − Tair) (6)

nd Jameson’s correlation (Jameson and Schenectady, 1945)s used to calculate the heat transfer coefficient between the


Fig. 8. Nodalization scheme of the cooling system of the mock-up test facility.

cooling air and the heat exchanger tube in the radiator, αair. It isexpressed as:

Nu = 0.092Re0.723Pr0.333. (7)

4.2. Analytical model of SG module for mock-up test facility

Fig. 8 shows a nodalization scheme of the SG module forthe cooling system with SG and the radiator of the test facilityincluding the steam superheater. It contains 14 single volumes(Sv), three time dependent volumes (Tv), 16 single junctions

(Sj), two time dependent junctions (Tj), four pipes (Pi), fourbranches (Br), five valve junctions (Vj) and 72 heat structures(Hs) of RELAP5/MOD2, two tubes (Tu) of the helium moduleand one tube (Tu) of the air module. The detail of the analyticalmodel is as follows:

4.2.1. Steam generatorThe model of SG is mainly classified into four parts: (a) an

upper plenum part; (b) a heat exchanger part; (c) a lower plenumpart using Br070; and (d) a down stream part using Pi060 withtwo sub-volumes. The upper plenum part is modeled into three


regions: a steam region using Br110, a steam/water boundaryregion using Sv100 and a water region using Br050. As for theheat exchanger part, the water region is divided horizontally intotwo parts: a high temperature part and a low temperature part.Both parts are divided vertically into three regions using singlevolumes, i.e. Sv010, Sv012 and Sv014 for the high temperaturepart and Sv020, Sv022 and Sv024 for the low temperature part.The helium fluid flow in the 27 heat exchanger tubes in SG ismodeled into single channel using Tu01. It is divided into 15sub-volumes in order to calculate the heat exchange from thehelium to water and the heat loss from the helium to atmosphereat plenums and pipes. The heat exchanger tube in SG is modeledusing Hs. It is divided into 30 Hs, i.e. horizontal 10 Hs as wellas the helium gas in the heat exchanger tube and vertical threeHs as well as the water region in the heat exchanger part. Onesub-volume of Tu01 is associated with three vertical Hs and fivehorizontal Hs are associated with one Sv of the heat exchangerpart. The heat loss from SG to the atmosphere is considered usingHs associated with Br110, Sv100, Br050, Pi060 and Br070.

4.2.2. RadiatorFor the radiator, the fluid flow of the steam in the heat

exchanger tube and that of the cooling air at the outside of theheat exchanger tube are modeled as the cross flow. The steamfluid flow in the 41 heat exchanger tubes is modeled into singlechannel using Pi360 with five sub-volumes along with the steamflcumiiat

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control variables are as follows: water pressure in SG; water levelheight in SG; flow rate of steam to the steam superheater. Thewater pressure in SG is controlled using the control componentof RELAP5/MOD2 for Tj341. The water level height in SG iscontrolled by controlling the flow rate of feed water using thecontrol component of RELAP5/MOD2 for Tj201. The flow rateof steam to the steam superheater is controlled using the controlcomponent of RELAP5/MOD2 for Vj249.

At the loss of chemical reaction, the boundary conditions forSG and the radiator are as follows: temperature, pressure andflow rate of helium at the inlet of SG and those of the coolingair at the inlet of the radiator. There are no control variables atthe loss of chemical reaction.

4.3. Verification of SG module at steady state

4.3.1. Verification of steam generator modelIn order to verify the numerical model of SG at steady state,

the numerical analysis of SG under the rated condition of the nor-mal operation, i.e. the hydrogen production, was carried out. Thenumerical results were compared with the experimental results.The boundary conditions were as follows: 546.1 ◦C, 4.06 MPaand 0.091 kg/s for the helium at the inlet of SG; 223.6 ◦C and4.61 MPa for the feed water to SG. The desired values for thecontrol variables were 4.61 MPa for the water pressure in SG,0.700 m for the water level height in SG and 0.047 kg/s for thefl

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ow. The cooling air fluid flow in the radiator is modeled by fivehannels of Tu03 and each channel is divided into five sub vol-mes along with the cooling air flow. The heat exchange tube isodeled using Hs as well as SG. It is divided into 25 Hs and it

s associated with each sub-volume of the cooling air fluid flow,.e. horizontal five Hs and vertical five Hs. The vertical five Hsre associated with one sub-volume of Pi360. The elevation ofhe radiator is also taken into account.

.2.3. Steam superheater, valves and pipesSingle pipe, Pi260 with two sub-volumes, two Hs, and sin-

le tube, Tu02 with 2 sub-volumes, are used to simulate theteam superheater. The stop valves C, E, F and G (see Fig. 6) areodeled by the valve junctions of RELAP5/MOD2 as Vj239,j381, Vj342 and Vj382, respectively. Vj381 is modeled using

ervo valve and other valves are modeled using the trip valve ofELAP5/MOD2. The control valve of steam flow to the steam

uperheater, i.e. control valve B (see Fig. 6), is modeled by theervo valve of RELAP5/MOD2 as Vj249. The pressure controlalve, i.e. control valve C (see Fig. 6), is modeled by the timeependent junction of RELAP5/MOD2 as Tj341. The pipes ofhe test facility for steam and water flow, installed between eachomponent, i.e. SG, the radiator and the steam superheater, areodeled using the Sv and Br. The heat loss from the pipes to the

tmosphere is considered using Hs associated with each hydro-ynamic volume.

.2.4. Boundary conditions and controlsAt the normal operation, the boundary conditions for SG are

s follows: temperature, pressure and flow rate of helium at thenlet of SG; temperature and pressure of feed water to SG. The

ow rate of steam to the steam superheater.The numerical and the experimental results of the helium

emperature at SG outlet, the heat exchange duty of SG, the waterressure in SG, the water temperature in SG, steam productionate in SG and the steam flow rate to the steam superheater areisted in Table 2. The experimental result of the heat exchangeuty of SG, QSG, was calculated by equation:

SG = ηSGWHeCpHe(THe,SG,in − THe,SG,out). (8)

SG is the thermal efficiency of SG, WHe is flow rate of helium,pHe is heat capacity of helium and T is helium temperature at

he inlet and the outlet of SG. ηSG was set at 0.92, which wasbtained from the performance test. The numerical results havegood agreement with experimental results. The water pressure

n SG and the steam flow rate to the steam superheater coulde controlled at each control value. The numerical result of theelium temperature at SG outlet corresponded to the experimen-al result. The numerical result of the heat exchange duty of SGas slightly lower than the experimental result, however, the

able 2omparison between the experimental and the numerical results of the steamenerator at rated condition of hydrogen production

tems Experimentalresult

Numericalresult

elium temperature at SG outlet (◦C) 262.5 262.5eat exchange duty of SG (kW) 128.6 127.9ater pressure in SG (MPa) 4.61 4.61ater temperature in SG (◦C) 258.7 258.9

team production rate in SG (kg/s) 0.0613 0.0618team flow rate to steam superheater (kg/s) 0.0470 0.0470


Table 3Boundary conditions for the verification of the numerical model of the radiator at steady state of natural circulation of steam and condensed water between the steamgenerator and the radiator

Items Run 1 Run 2 Run 3 Run 4 Run 5 Run 6

Helium at the inlet of SGTemperature (◦C) 792.2 758.3 724.0Pressure (MPa) 4.06Flow rate (kg/s) 0.091

Cooling air at the inlet of radiatorTemperature (◦C) 11.8 11.0 10.8 10.8 11.8 11.8Pressure (MPa) 0.1013Flow rate (kg/s) 1.51 1.81 2.35 3.03 1.596 1.467

Fig. 9. Comparison between the experimental and the numerical results at steady state of natural circulation of steam and condensed water between the steamgenerator and the radiator: effect of flow rate of cooling air at the radiator.


relative error of the numerical result against the experimentalresult was only −0.6%. And the relative error of the numericalresult of the steam production rate in SG against the experimen-tal result was only 0.8%. From these results, it is confirmed thatthe numerical model of SG in the SG module can simulate thestatic behavior of SG, i.e. temperatures, pressures, heat exchangeduty, and steam production rate.

4.3.2. Verification of radiator modelIn order to verify the numerical model of the radiator at steady

state, the experimental data on the effect of the flow rate of the

cooling air and the SG inlet helium temperature was collected.Table 3 shows the experimental conditions and results of thetemperatures, pressures and flow rates of the SG inlet helium andthe radiator inlet cooling air. They are the boundary conditionsof the numerical analysis. For the experiment from Run No. 1to No. 4 in Table 3, the flow rate of the cooling air was variedfrom 1.51 kg/s to 3.03 kg/s by the cooling fan during the naturalcirculation under the rated condition of the helium at the inlet ofSR, i.e. temperature of 880 ◦C, pressure of 4.1 MPa and flow rateof 0.091 kg/s. For Run No. 5 and No. 6 in Table 3, the SR inlethelium temperature was varied at 840 and 800 ◦C, respectively,

Fg

ig. 10. Comparison between the experimental and the numerical results at steadyenerator and the radiator: effect of helium temperature at steam generator inlet.

state of natural circulation of steam and condensed water between the steam


in order to change the SG inlet helium temperature. The waterpressure in SG was controlled around 4.6 MPa by adjusting theflow rate of the cooling air. Each experimental conditions weremaintained over 12 h in order to obtain the stable temperatures,pressures and steam flow rate. For the numerical analysis, inorder to simulate the closed loop between SG and the radiatorduring the natural circulation, Vj239 and Vj381 were closed,Tj341, Vj342 and Vj382 were fully opened and the feed waterwas stopped using Tj201.

Fig. 9 shows the relationships between the flow rate of thecooling air and the experimental and the numerical results of theheat exchange duty of SG, the helium temperature at SG outlet,the water pressure in SG, the steam pressure at the radiator inlet,the water temperature in SG and the condensed water tempera-ture at the radiator outlet. The solid circles and the dashed linesshow the experimental and the numerical results. The numericalresult of the heat exchange duty of SG showed the same tendencyas the experimental results, viz. increase with the increasing ofthe flow rate of the cooling air. Also, the numerical results ofthe pressures and temperatures showed the same tendency of theexperimental results to decrease with the increasing of the flowrate of the cooling air. However, the numerical result of the heatexchange duty of SG was slightly higher than the experimentalresult. The numerical results of the pressures were lower thanthe experimental results by about 1 MPa. Also, the numericalresults of the water temperature in SG and the condensed watertmdwFttpotAntaoatirabmraecrKtbt

Fig. 11. Relationship between the sum of squares of relative error of the numer-ical result against the experimental one and the correlation coefficient for theheat transfer coefficient between the cooling air and the heat exchanger tube inthe radiator.

that the heat transfer coefficient of the test facility is smaller thanthat calculated by using the Jameson’s correlation. In order totake into account the effect of the number of tube rows and toincrease an accuracy of the numerical analysis, the numericalmodel of the radiator is correlated using a correlation coeffi-cient, K, for the heat transfer coefficient between the coolingair and the heat exchanger tube in the radiator, the Jameson’scorrelation, as shown by the following equation:

Nu = K0.092Re0.723Pr0.333. (9)

The optimum value of correlation coefficient was parametricallysurveyed in order to minimize the sum of squares of relative errorof the numerical result against the experimental one on the vari-ables shown in the Figs. 9 and 10. The sum of squares of therelative error showed minimum value at the correlation coeffi-cient of 0.75 as shown in Fig. 11. The numerical results using thecorrelation factor of 0.75 is shown in Figs. 9 and 10 by the solidlines and it relatively agreed well with the experimental results.The average of the relative error of the numerical results againstthe experimental results decreased from 12 to 4% by using thecorrelation factor of 0.75. The difference between the numericaland the experimental results of the helium temperature at the SGoutlet decreased from the range from 4 to 25 K to the range from1 to 7 K.

4

tofita

emperature at the radiator outlet were lower than the experi-ental results by about 20 ◦C. The almost same tendency of the

iscrepancy between the experimental and the numerical resultsas observed on the SG inlet helium temperature as shown inig. 10. The reason why the pressures and the temperatures of

he numerical results are lower than those of the experimen-al results is can be considered as follows: the heat exchangeerformance of SG of the numerical result is smaller than thatf the experimental one, i.e. the calculation result of the heatransfer coefficient in SG is smaller than the experimental one.nd/or, the heat exchange performance of the radiator of theumerical result is larger than that of the experimental one, i.e.he calculation result of the heat transfer coefficient in the radi-tor is larger than the experimental one. The numerical resultf the heat exchange performance of SG at the normal oper-tion was agreed well with the experimental one. It suggestshat the heat transfer coefficient in the radiator of the numer-cal result is larger than that of the experimental one. In theadiator, the heat transfer coefficient between the cooling airnd the heat exchanger tube is dominant compared with thatetween the steam and the heat exchanger tube. Therefore, theain reason of the discrepancy is supposed that the numerical

esult of the heat transfer coefficient between the cooling airnd the heat exchanger tube in the radiator is larger than thexperimental one. In the banks of finned tubes, the heat transferoefficient decreases with the decreasing of the number of tubeows due to decreasing of the turbulence of the stream (Kern andraus, 1972; Sparrow and Samie, 1985). The eight-row finned

ube banks were mainly employed in the experiment carriedy Jameson and Schenectady (1945), whereas three-row finnedube bank is installed in the radiator of the test facility. It seems

.4. Verification of SG module at transient

The numerical analysis of SG and the radiator on the sys-em controllability test for loss of chemical reaction was carriedut with the correlation coefficient for the heat transfer coef-cient between the cooling air and the heat exchanger tube in

he radiator of 0.75. The boundary conditions for the numericalnalysis were the helium temperature at SG inlet (see Fig. 7c),


the SG inlet helium pressure of 4.06 MPa, the SG inlet heliumflow rate of 0.091 kg/s, the radiator inlet cooling air flow rate(see Fig. 7h), the radiator inlet cooling air temperature of 10.8 ◦Cand the radiator inlet cooling air pressure of 0.1013 MPa. Beforethe suspension of the methane feed, the experimental results ofthe water pressure in SG (4.61 MPa) the water level height inSG (0.700 m) and the steam flow rate to the steam superheater(0.047 kg/s) were used as the control value for Tj341, Tj201and Vj249, respectively. And the experimental procedure of thevalve opening/closing was simulated as the trip condition in thenumerical analysis.

The numerical results are shown in the Fig. 7 by the dashedlines. All numerical results, the helium temperature at SG outlet,the water pressures in SG and the steam pressure at the radiatorinlet, the water temperature in SG, the condensed water temper-ature at the radiator outlet and the steam flow rate at the radiatorinlet, show similar transient behavior of the experimental result.After the loss of chemical reaction, the minimum value of thewater pressure in SG of the experimental and the numericalresults were 4.26 and 4.35 MPa, respectively. And the maximumvalue of the pressure in SG of the experimental and the numericalresults were 4.48 and 4.83 MPa, respectively. The fluctuation ofthe SG outlet helium temperature of the numerical result was therange from 0 K to +8.4 K, while that of the experimental resultwas the range from −1.2 K to +2.0 K. Both fluctuations werewithin the target of ±10 K at the outlet of SG. It is confirmedtuw

ibott

5

dpdtvssahtthT

1

radiator. This fluctuation range was within the target rangeof the HTTR hydrogen production system, from −10 K to+10 K at SG outlet. We can conclude that HTTR can be oper-ated without reactor scram caused by the loss of chemicalreaction in the hydrogen production system by applying thecooling system for the secondary helium with SG and theradiator.

2. A dynamic simulation code for the cooling system with SGand the radiator in the HTTR hydrogen production systemwas verified with the test data at the loss of chemical reaction.It can predict well the transient behavior of the SG outlethelium temperature as well as the pressures, temperaturesand flow rates of steam and water in the cooling system.

These results contribute to the system integration betweenHTTR and the hydrogen production system such as IS process.

Acknowledgements

The present study is the results of “Development of NuclearHeat Utilization Technology” in fiscal year 1997, 1999, 2000,2001 and 2004 entrusted by Ministry of Education, Culture,Sports, Science and Technology (MEXT) to Japan AtomicEnergy Research Institute (JAERI) succeeded by into JapanAtomic Energy Agency (JAEA). The authors are indebted toDr. S. Shiozawa and Dr. M. Ogawa in JAEA for their helpfulaFMLYiCCa

R

F

F

I

I

J

K

K

hat the numerical model of the SG module can practically sim-late the transient behavior of the cooling system for the heliumith SG and the radiator at the loss of chemical reaction.At the loss of chemical reaction, the water pressure in SG,

.e. the helium temperature at SG outlet is significantly affectedy the heat transfer performance of the radiator, e.g. the numberf tube rows of the heat exchanger tube. Therefore, it should beaken into consideration for the design of the cooling system ofhe HTTR hydrogen production system.

. Conclusions

The Japan Atomic Energy Agency has been planning theemonstration test of hydrogen production with the High Tem-erature Engineering Test Reactor. In the HTTR hydrogen pro-uction system, it is required to control the primary heliumemperature within an allowable value at the HTTR inlet to pre-ent the scram of HTTR. It is proposed to install the coolingystem with the steam generator and the radiator at the down-tream of the chemical rector in the secondary helium loop asthermal absorber. In order to confirm the controllability of

elium temperature at the loss of chemical reaction, the simula-ion test has been carried out with the mock-up test facility. Andhe verification of the dynamic simulation code of the HTTRydrogen production system, N-HYPAC, has been carried out.he results could be summarized as follows:

. The thermal disturbance of the helium at the chemical reac-tor outlet caused by the loss of chemical reaction, more than200 K, was successfully mitigated from −1.2 K to +2.0 Kat SG outlet by using the cooling system with SG and the

dvices. The authors also want to express gratitude to Mr. K.ujisaki; Mr. M. Kato in JAEA; Mr. H. Aita in JAEA; Mr. N.orisaki in JAEA; Mr. A. Shimizu in Choryo Designing Co.,

td.; Mr. A. Sakaki in Mitsubishi Heavy Ind. Co., Ltd.; Mr.. Maeda in Hitachi Ltd. for their valuable help in the exper-

ment and to Mr. H. Sato in Ishikawajima-Harima Heavy Ind.o., Ltd. and Ms. M. Kishida in Advanced Reactor Technologyo., Ltd. for their valuable help in performing the numericalnalysis.

eferences

ujikawa, S., Hayashi, H., Nakazawa, T., Kawasaki, K., Iyoku, T., Nakagawa,S., Sakaba, N., 2004. Achievment of reactor-outlet coolant temperatureof 950 ◦C in HTTR. J. Nucl. Sci. Technol. 41, 1245–1254.

ujimoto, N., Nakano, M., Takeuchi, M., Fujisaki, S., Yamashita, K., 2000.Start-up core physics tests of High Temperature Engineering Test Reactor(HTTR), (II) first criticality by an annular form fuel loading and itscriticality prediction method. J. Atom. Energy Soc. Jpn. 42 (5), 458–464(in Japanese).

naba, Y., Ohashi, H., Nishihara, T., Sato, H., Inagaki, Y., Takeda, T., Hayashi,K., Takada, S., 2005. Study on control characteristics for HTTR hydro-gen production system with mock-up test facility system controllabilitytest for fluctuation of chemical reaction. Nucl. Eng. Des. 235, 111–121.

nagaki, Y., Nishihara, T., Takeda, T., Hada, K., Hayashi, K., 1999. Out-of-pile test of hydrogen production system coupling with HTTR. In:Proceedings of the 7th International Conference on Nuclear Engineer-ing, Tokyo, Japan, ICONE-7101.

ameson, S.L., Schenectady, N.Y., 1945. Tube spacing in finned-tube banks.Trans. ASME 67, 633–642.

ern, Q.D., Kraus, D.A., 1972. Extended Surface Heat Transfer. McGraw-Hill Book Company, New York, p. 564.

ubo, S., Nakajima, H., Kasahara, S., Higashi, S., Masaki, T., Abe, H.,Onuki, K., 2004a. A demonstration study on a closed-cycle hydrogen


production by the thermochemical water-splitting iodine–sulfur process.Nucl. Eng. Des. 233, 347–354.

Kubo, S., Kasahara, S., Okuda, H., Terada, A., Tanaka, N., Inaba, Y., Ohashi,H., Inagaki, Y., Onuki, K., Hino, R., 2004b. A pilot test plan of the ther-mochemical water-splitting iodine–sulfur process. Nucl. Eng. Des. 233,355–362.

Nishihara, T., Sakaki, A., Inagaki, Y., Takami, K., 2004. Development of hightemperature isolation valve for the HTTR hydrogen production system.Trans. Atom. Energy Soc. Jpn. 3, 381–387 (in Japanese).

Nishihara, T., Shimizu, A., Inagaki, Y., Tanihira, M., 2003. Flow scheme andcontrollability of the HTTR hydrogen production system. Trans. Atom.Energy Soc. Jpn. 2, 517–524 (in Japanese).

Ohashi, H., Inaba, Y., Nishihara, T., Inagaki, Y., Takeda, T., Hayashi, K.,Katanishi, S., Takada, S., Ogawa, M., Shiozawa, S., 2004a. Performancetest results of mock-up test facility of HTTR hydrogen production system.J. Nucl. Sci. Technol. 41 (3), 385–392.

Ohashi, H., Nishihara, T., Inaba, Y., Takeda, T., Hayashi, K., Takada, S.,Sato, H., Maeda, Y., Inagaki, Y., 2004b. Simulation test on normal start-up and shutdown of HTTR hydrogen production system using mock-upmodel test facility. In: Proceedings of the 6th International Conferenceon Nuclear Thermal Hydraulics, Operations and Safety, Nara, Japan,N6P234.

Ohashi, H., Nishihara, T., Takeda, T., Maeda, Y., Sato, H., Inaba, Y.,Hayashi, K., Takada, S., Inagaki, Y., 2004c. Experimental and analyti-cal study on chemical reaction loss accident with mock-up model facilityof HTTR hydrogen production system. In: Proceedings of the 12th Inter-national Conference on Nuclear Engineering, Arlington, USA, ICONE12-49419.

Ransom, V.H., Wagner, R.J., Trapp, J.A., Feinauer, L.R., Johnsen, G.W.,Kiser, D.M., Riemke, R.A., 1985. RELAP5/MOD2 Code Manual, IdahoNational Engineering Laboratory, NUREG/CR-4312, EGG-2396, Decem-ber 1985.

Saito, S., Tanaka, T., Sudo, Y., Baba, O., Shindo, M., et al., 1994. Designof high temperature engineering test reactor (HTTR). JAERI 1332, JapanAtomic Energy Research Institute (JAERI) (in Japanese).

Shiozawa, S., Ogawa, M., Inagaki, Y., Katanishi, S., Takeda, T., Nishihara,T., Shimizu, S., Miyamoto, Y., 2000. Research and development of HTTRhydrogen production system in JAERI, vol. 2. In: Proceedings of the 12thPacific Basin Nuclear Conference, Seoul, Korea, pp. 1007–1018.

Sparrow, E.M., Samie, F., 1985. Heat transfer and pressure drop results forone- and two-row arrays of finned tubes. Int. J. Heat Mass. Transfer 28(12), 2247–2259.

Takeda, T., Iwatsuki, J., Inagaki, Y., 2004. Permeability of hydrogen anddeuterium of Hastelloy XR. J. Nucl. Mater. 326, 47–58.

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Development of control technology for HTTR hydrogen production system with mock-up test facility: System controllability test for loss of chemical reaction