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Assessing the SCRRI and RIP runback performances of TRACE/PARCS for

Lungmen ABWR

Chia-Ying Chang a,, Tsung-Sheng Feng b, Jong-Rong Wang c, Hao-Tzu Lin c, Chunkuan Shih a

a Institute of Nuclear Engineering and Science, National Tsing Hua University, No. 101, Sec. 2, Kuang Fu Road, Hsinchu 30013, Taiwanb Department of Engineering and System Science, National Tsing Hua University, No. 101, Sec. 2, Kuang Fu Road, Hsinchu 30013, Taiwanc Institute of Nuclear Energy Research, No. 1000, Wenhua Rd., Longtan Township, Taoyuan County 32546, Taiwan

a r t i c l e i n f o

Article history:

Received 24 April 2013

Received in revised form 28 June 2013

Accepted 8 July 2013

Keywords:

Lungmen ABWR

SCRRI

RIP runback

FWPT

LOFH

a b s t r a c t

The TRACE/PARCS model is conventionally adopted as a best-estimate calculation approach for the Lung-

men advanced boiling water reactor (ABWR). This study assesses the performance of SCRRI and RIP run-

back simulated by TRACE/PARCS featuring three-dimensional evaluation. The effectiveness of TRACE/

PARCSis demonstrated by selectingthe two transients in the startup test prediction, feedwater pump trip

and loss of feedwater heater, which are involved with the initiation of both SCRRI and RIP runback. Cal-

culation results indicate that SCRRI is a slower measure than the runback mechanism in mitigating the

steam flow dumped into the main condenser, subsequently reducing the power to another state. Addi-

tionally, RIP runback is alternative approach to diminishing the power by reducing the core flow. More-

over, sensitivity studies involving different settings for RIP runback and SCRRI are also performed to

determine the SCRRI and RIP runback delay times, as well as RIP runback rate. Sensitivity studies reveal

that the operational settings of SCRRI and RIP runback influence the process during transients. Neverthe-

less, the setting does not significantly impact the final state of the transient.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

This study demonstrates the effectiveness of TRACE/PARCS in

terms of selected control rod run-in (SCRRI) function and Reactor

Internal Pump (RIP) runback for Lungmen advanced boiling water

reactor (ABWR).

As the fourth nuclear power plant (NPP) owned by Taiwan

Power Company (TPC) in Taiwan, Lungmen ABWR has two identi-

cal units with 3926 MWt rated power and 52.2 106 kg/h rated

core flow each. Also, the reactor core consists of 872 GE-14 fuel

assemblies with 205 control rods. The annular region in the lower

downcomer of the reactor pressure vessel accommodates 10 RIPs,

capable of providing core flow up to 111% of the rated capacity. Sixof the 10 RIPs are connected to a motorgenerator set (MG Set)

while the remaining four RIPs are not connected as such and are

powered directly by the 13.8 kV Bus (Taiwan Power Company,

2006).

TRACE is a thermalhydraulic systemcode developed by USNRC

for NPP safety analysis. As a feature of TRACE, 3-D reactor vessel

simulation allows for complex flow modeling (US Nuclear Regula-

tory Commission, 2012), and is incorporated in the Lungmen

TRACE model. PARCS code, a multi-dimensional core simulator,

can be coupled with TRACE. Developed recently, the coupling be-

tween TRACE and PARCS with 3-D neutronics models of the reactor

core into system transient is used hereinafter.

When transients such as feedwater pump trip (FWPT) and loss

of feedwater heater (LOFH) occur, the recirculation flow control

system (RFCS) reduces recirculation flow rapidly by running the

RIPs back to a minimum speed condition and initiating the SCRRI

function (Ma et al., 2011). SCRRI and RIP runback are designed to

reduce reactor power and mitigate the steam bypassed to the con-

denser as protection mechanisms without shutting down the

reactor.

The feedwater pump trip and loss of feedwater heater identifiedin the startup test prediction use both SCRRI and RIP runback as

protection mechanisms without shutting down the reactor (Yang

et al., 2012). These events involve control rod movements and core

flow reduction, which interact with each other between neutronics

and thermalhydraulic calculations. To perform best-estimate

analysis/calculation for FWPT and LOFH, this study performs the

transients with 3D core simulation by using the coupled code

TRACE/PARCS. Moreover, analysis results of the responses of the

major system parameters are compared with those shown in the

startup test prediction.

0306-4549/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.anucene.2013.07.008

Corresponding author. Tel.: +886 3 5715131x34267; fax: +886 3 5720724.

E-mail address: [email protected] (C.-Y. Chang).

Annals of Nuclear Energy 63 (2014) 18

Contents lists available at ScienceDirect

Annals of Nuclear Energy

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a n u c e n e
http://dx.doi.org/10.1016/j.anucene.2013.07.008mailto:[email protected]://dx.doi.org/10.1016/j.anucene.2013.07.008http://www.sciencedirect.com/science/journal/03064549http://www.elsevier.com/locate/anucenehttp://www.elsevier.com/locate/anucenehttp://www.sciencedirect.com/science/journal/03064549http://dx.doi.org/10.1016/j.anucene.2013.07.008mailto:[email protected]://dx.doi.org/10.1016/j.anucene.2013.07.008http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://crossmark.dyndns.org/dialog/?doi=10.1016/j.anucene.2013.07.008&domain=pdfhttp://-/?-

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2. TRACE/PARCS modeling of Lungmen ABWR

Transients on a thermalhydraulic system are performed using

the TRACE code, while the 3-D reactor core is simulated using the

PARCS code.

2.1. Lungmen TRACE model

Fig. 1 shows the TRACE model of Lungmen ABWR. The reactor

vessel is modeled by the TRACE 3-D VESSEL component with 11

axial levels, four radial rings, and six azimuthal sectors (separately

in 36, 36, 108, 36, 36, 108 apart) for 264 computational cells.

The 3-D VESSEL component rather than 1-D is used as the best

model available in the code. The four separate main steam lines

are connected to the four 36 sectors, and the six feedwater lines

are connected to the six azimuthal sectors individually. According

to the plant design, six feedwater spargers are equally spaced

around the reactor vessel in the Lungmen ABWR. Therefore, a lar-

ger sector implies a greater feedwater flow, in order to simulate the

even spray of feedwater.

Fig. 2 presents the distribution of the 10 PUMP components as

RIPs and the 18 CHAN components as fuel assemblies in the vessel.In the Lungmen TRACE model, the 18 CHAN components (repre-

senting 872 GE-14 fuel assemblies) are assigned to each division

of the three inner radial rings of 6 azimuthal sectors of the VESSEL

component. The 10 RIPs accommodated in the lower downcomer

are modeledwith PUMP components at the outer ring of the vessel.

These 10 RIPs are divided into three groups; the first two groups,

with three RIPs each, are connected to MG sets; meanwhile, the

third group (which has four RIPs) is not.

2.2. Lungmen PARCS model

PARCS is a multi-dimensional reactor core simulator which in-

cludes a 3-D calculation model to accurately represent a physical

reactor; 1-D modeling features are also available. The current

Lungmen PARCS model is based on the BOC state. The neutronics

model comprises 872 nodes, which represent the 872 fuel assem-

blies one-to-one. The active core height is 381 cm with 25 levels in

the Lungmen PARCS model. Two additional 15.24-cm-thick axial

reflector regions are found at the top and bottomof the active core.

The 205 control rods are also simulated, and are divided into 19

groups (Fig. 3).

The PARCS model uses a unique macroscopic cross-section file,

PMAX. This data file is created by GenPMAXS code in a format com-

patible with PARCS based on the results of the lattice calculation. In

this study, CASMO-4 (i.e. a lattice physics code) provides cross-sec-

tion information, and is reformatted by GenPMAXS to allow the file

to comply with the cross-section format required in PARCS.

2.3. Lungmen TRACE/PARCS model

When coupling TRACE and PARCS, the overall controls (e.g.,

convergence checks and trip initiations) are handled by TRACE dur-

ing a transient. TRACE provides the thermalhydraulic conditions

for PARCS as well. Notably, the maptab file is necessary for cou-

pling in order to correlate the 18 CHAN components in the TRACE

model with the 872 neutronics nodes in PARCS model. The 872 fuel

assemblies are mapped into 18 CHAN components corresponding

to the distribution of CHANs in the Lungmen TRACE model.

2.4. Lungmen TRACE/PARCS steady-state performance

The Lungmen PARCS model consists of 872 neutronics nodes

representing the 872 fuel bundles individuals, where the relative

power of each fuel bundle can be calculated individually. Charac-

terized by three-dimensional core simulation, TRACE/PARCS can

determine the axial relative power and radial relative power.

Fig. 4 illustrates the animation of the relative power under SNAP

interface. The relative power has a lumped core power distribution,

Fig. 1. Lungmen TRACE model.

Fig. 2. The distribution of CHANs and RIPs.

2 C.-Y. Chang et al./ Annals of Nuclear Energy 63 (2014) 18

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in which each square represents a fuel assembly. The distribution

is generally quarter symmetrical. However, the corresponding

areas only slightly differ, owing to the different thermalhydraulic

feedback caused by connecting neutronics nodes in the PARCSmodel to different cells in the TRACE model. The axial power pro-

file in Fig. 5 displays a bottom-peaked shape consistent with the

BOC state.

3. TRACE/PARCS modeling of SCRRI and RIP runback for

Lungmen ABWR

The function of RIP runback is simulated in the Lungmen TRACE

model, while the function of SCRRI is simulated in the Lungmen

PARCS model. Hence, when coupling TRACE and PARCS, SCRRI as

well as RIP runback can be performed simultaneously.

3.1. SCRRI modeling

The SCRRI function protects the plant system to avoid excessive

power in the core. As designed, the total rod worth from SCRRI is

sufficient to bring down the reactor power to below 60% rod line.

Additionally, SCRRI lasts 145 s. Namely, SCRRI can position the

control rods 200 steps for 145 s. The selected control rods to be in-

serted are groups 7, 12, 13, 16, 17, and 19. Table 1 shows the initial

and target rod pattern, while Fig. 6 shows the history of control rod

movement from SCRRI.

3.2. RIP runback modeling

In terms of the RIPs design, the change rate of speed varies from

5% to +5% per second under normal operations (Taiwan Power

Company, 2007). However, when the runback mechanism is trig-

gered, the RIP speed reduces 10% of initial speed per second, and

the speed runs back to 31% of the rated speed, i.e. around

47.1 rad/s. This work implements the results from different run-

back speeds.

4. Simulation results of SCRRI and RIP runback performances

4.1. SCRRI performance

The protective mechanism, SCRRI, has been implemented under

the condition of 100% rated core power and 100% rated core flow

by TRACE/PARCS. As for the sole impact of SCRRI, the selected

control rods are inserted into the core followed by the power

reduction, as clearly observed in Fig. 7. Moreover, the steam flow

rate decreases as well, as shown in Fig. 8. The deduction of power

originating from SCRRI is around 50%, confirming the criteria of

4060% in the GE startup test prediction (Ma et al., 2011). After

SCRRI is initiated, the core inlet flow rate increases, owing to the

Fig. 3. Lungmen control rod pattern.

Fig. 4. The relative power distribution in radial direction.

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decreasing of steam flow rate and the fixed RIP rotation speed as

well. Additionally, Fig. 9 shows the corresponding trends of differ-

ent reactivities. The control rod reactivity declines as the selected

control rods are inserted into the core, followed by a reduction of

power.

4.2. Performance of RIP runback

This study demonstrates the results at two RIP runback rates:

5% and 10% of rated rotational rate separately. Figs. 7, 8 and 10

show the curves of power, steam flow rate and core inlet flow rate

resulting from the RIP runback. Ten RIPs start to runback at 0 s

with the change rates of 5% and 10%, which are maintained at aconstant speed until RIP rotational speed reaches 31% of the rated

speed. The core inlet flow rate related directly to the RIP rotational

speed decreases markedly and even drops more significantly with

an increasing RIP runback rate. Moreover, the core power as well as

the steam flow rate diminishes quickly and reaches another stable

state as RIPs runback to a constant speed. Final states of the plant

systemare extremely close to each other among the cases at differ-

ent runback rates of 5% and 10%.

4.3. Performance of SCRRI with RIP runback

This section describes the performance of SCRRI accompanying

RIP runback at different runback rates. According to Fig. 8, SCRRIfeatures a slower measure than the runback mechanism to

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Relative power

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

Layer

Fig. 5. The relative power distribution in axial direction.

Table 1

Control rod movement for SCRRI.

Control rod group

number

Initial rod position

(step)

Target rod position

(step)

7 117 0

12 83 0

13 200 64

16 200 136

17 58 0

19 200 64

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

0

20

40

60

80

100

120

140

160

180

200

Controlrodposition(

steps)

Control rod movement from SCRRI

Bank 7

Bank 12

Bank 13 & 19

Bank 16

Bank 17

Fig. 6. History of control rod movements from SCRRI.

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

0

20

40

60

80

100

120

Normalized

power(%)

Power

SCRRI

RIP runback rate = 5%


SCRRI with RIP runback rate = 5%


Fig. 7. Power curve from SCRRI and RIP runback.


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decrease the power. At the outset, the RIP runback produces a sud-

den decline in the core inlet flow which, simultaneously, reduces

the power. Until the RIPs runback to the minimum speed condi-

tion, the SCRRI function plays a leading role in power.

5. Startup test prediction

This study analyzes two transients in the GE startup test predic-

tion concerning SCRRI and RIP runback (i.e. FWPT and LOFH) to

verify SCRRI and RIP runback abilities in the Lungmen TRACE/PARCS model.

5.1. Initial condition

Prior to transient simulation, steady-state analysis should be

performed as the initial condition to ensure that the data com-

puted in the Lungmen TRACE/PARCS model correlate with the de-

sign values. Table 2 lists the major thermalhydraulic parameters

at the steady state condition for Lungmen ABWR.

5.2. Feedwater pump trip (FWPT)

5.2.1. Event description

In Lungmen ABWR, three sets of turbine driven feedwater

pumps (TDRFP) and a set of motor driven feedwater pump

(MDRFP) constitute the feedwater pump system. FWPT begins with

the trip of one of the two normally operating TDRFPs, which makes

its flow reduce to zero in 5 s. Although a MDRFP with a full flow of

20% rated capacity actuates within 510 s, this situation leads to a

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

0

20

40

60

80

100

120

Normalizedmassflowrate(%)

Steam flow rate

SCRRI





Fig. 8. Steam flow rate curve from SCRRI and RIP runback.

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Reactivity

($)

Reactivity - SCRRI

Total reactivity

Doppler reactivity

Control rod reactivity

Void reactivity

Fig. 9. Reactivity from SCRRI.

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

0

20

40

60

80

100

120

Normalizedmassflow

rate(%) Core inlet flow rate

SCRRI





Fig. 10. Core inlet flow rate.

Table 2

Steady state condition.

Parameters Reference TRACE/PARCS model

Thermal power (MW) 3926 3926

Steam flow rate (kg/s) 2122 2121.2

Core flow rate (kg/s) 14,500 14,610

Dome pressure (MPa) 7.2 7.16

Narrow range water level (m) 13.42 13.43

Table 3

Summary of TRACE/PARCS analysis for RIP runback capability studies in FWPT.

Parameters/cases FWPT-

Base

FWPT-1 FWPT-2 FWPT-3

Minimum power (% of rated)/

time (s)

48.79/

13.96

49.72/

17.96

47.24/

11.96

43.12/

9.96

RIP runback speed (%/s) 5 4 6 10

Margin to L3 (cm)a 54.83 50.14 59.06 63.83

Margin to L8 (cm)b 33.07 31.63 33.82 34.95

a

Difference between minimum NRWL and L3.b Difference between maximum NRWL and L8.

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low water level. Consequently, RFCS runs RIPs back immediately to

decrease the core power to an acceptable level for the remaining

TDRFP and MDRFP. The water level must be maintained between

L3 (0.8275 m from bottom of the dryer skirt) and L8 (1.6581 m

from bottom of the dryer skirt) to prevent triggering either low

or high scram setpoints.

5.2.2. Analysis results

At the loss of one TDRFP to zero flow in 5 s, MDRFP is initiated

and RIP runback is actuated simultaneously. MDRFP reaches its full

flow in 10 s, for the base case, the RIP runback is at 5% rate in

12.78 s. The extent to which RIP runback can reduce the power

at different settings is explored as sensitivity studies.

Table 3 summarizes the analysis results of sensitivity studies for

the RIP runback setting in FWPT. Fig. 11 indicates that RIP runback

rates significantly affect the power decrease rate. Of the four cases

with different runback rates, the 10% runback rate contributes to

the lowest power in the first 10 s; after 10 s, the power increases

more than other cases with a slower runback rate. However, these

four cases eventually reach the same power level. Moreover, NRWL

of all cases remain within the area between L3 and L8 where the

scram setpoints are not triggered.

5.3. Loss of feedwater heater (LOFH)

5.3.1. Event description

LOFH is an anticipated operational occurrence (AOO) in Lung-

men startup test prediction. Upon sensing the reduction of 37 C

in feedwater temperature, the feedwater control system (FWCS)

sends out two signals, which actuate RIP runback and SCRRI to de-

crease the core power. Under normal operations, the RIP runback

rate is designed at 5% of rated speed per sec, and the function is de-

layed by 0.275 s; the delay time for SCRRI initiation is set to 0.09 s.

Moreover, the water level fluctuates between L3 and L8, having

sufficient safety margins to avoid either low or high water level

scram setpoints being reached.

5.3.2. Analysis results

Initially during the transient, the feedwater temperature

dwindles to approximately 37 C with a 30 s constant decay curve,and the RIP runback along with SCRRI is initiated instantly. The

0 10 20 30 40 50 60

Time (sec)

0

20

40

60

80

100

120

Normalizedpower

(%)

FWPT_Power





Fig. 11. Power responses of the prediction analysis in FWPT.

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

30

40

50

60

70

80

90

100

110

Normalizedpow

er(%)

LOFH_Power

TRACE/PARCS

Fig. 12. Power responses of the prediction analysis in LOFH.

0 20 40 60 80 100 120 140 160 180 200

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($)

LOFH_Reactivity

Total reactivity

Doppler reactivity

Void reactivity


Fig. 13. Reactivity responses of the prediction analysis in LOFH.

Table 4

Summary of TRACE/PARCS analysis for SCRRI delay time studies in LOFH.

Parameters/cases LOFH-

Base

LOFH-

1A

LOFH-

1B

LOFH-

1C

LOFH-

1D

SCRRI delay time (s) 0.09 1.09 10.09 20.09 30.09

RIP runback rate (%/s) 5 5 5 5 5

Max. power after RIP

runback (%)

67.8 67.9 69.5 70.9 72.0


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0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400

0 50 100 150 200 250 300 350 400

0 50 100 150 200 250 300 350 400

0 50 100 150 200 250 300 350 400

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($)

LOFH_Reactivity(SCRRI delay time=0.09s)


Total reactivity

Doppler reactivity

Void reactivity

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($

)

LOFH_Reactivity

(SCRRI delay time=1.09s)


Total reactivity

Doppler reactivity

Void reactivity

(b)(a)

(d)(c)

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($)

LOFH_Reactivity



Total reactivity

Doppler reactivity

Void reactivity

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($)

LOFH_Reactivity(SCRRI delay time=20.09s)


Total reactivity

Doppler reactivity

Void reactivity

Time (sec)

-1.5

-1

-0.5

0

0.5

1

Reactivity($)

LOFH_Reactivity



Total reactivity

Doppler reactivity

Void reactivity

(e)

Fig. 14. Reactivity responses of the sensitivity studies for SCRRI delay time in LOFH (a) 0.09 s, (b) 1.09 s, (c) 10.09 s, (d) 20.09 s, and (e) 30.09 s.

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sensitivity studies on RIP runback delay time and runback rate are

shown as follows.

Once LOFH occurs, the increasing subcooling attributed to the

cooler feedwater temperature collapses the voids, subsequently

increasing void reactivity, reducing the water level and, finally,

increasing the core power, as shown in Fig. 12. After sensing the

reduction of 37 C in feedwater temperature, RIP runback and

SCRRI are initiated by FWCS; the power diminishes as response;

in addition, the trends of core power are similar as shown in

Fig. 8. Fig. 13 shows the corresponding reactivity during the tran-

sient, indicating that SCRRI reduces the reactivity of the core and

the core temperature. Additionally, deduction of the core temper-ature increases the Doppler reactivity. Moreover, the increase of

void reactivity and Doppler reactivity is offset by the reduction

due to SCRRI.

Several sensitivity studies are performed to evaluate the perfor-

mance of runback mechanism and SCRRI under different settings in

LOFH. Table 4 lists the analysis results of the sensitivity studies for

SCRRI delay time in LOFH. With the sameRIP runback rate, a longer

delay in which SCRRI is initiated implies a higher core power.

According to Fig. 14, the curves of control rod reactivity resulting

from SCRRI shift in parallel with the SCRRI delay time. However,

different SCRRI delay times do not affect the final state in LOFH

transient.

Table 5 summarizes the results of a sensitivity study on RIP run-

back rate in LOFH. Fig. 15 reveals that a different RIP runback rate

significantly affects power history where power declines faster

with an increasing RIP runback rate. Since the RIP runback mecha-

nism alleviates the core inlet flow, followed by an increase of the

core temperature, the void in core increases as the void reactivity

decreases in proportional to the RIP runback rate (Fig. 16).

6. Conclusions

TRACE coupled with PARCS can achieve the SCRRI and RIP run-

back for Lungmen ABWR. The deduction of power originating from

SCRRI is around 50%, which conforms to the criteria of 4060% inGE startup test prediction. Upon initiation of the RIP runback, the

core inlet flow rate related directly to the RIP rotational speed de-

creases markedly and even diminishes more significantly with an

increasing RIP runback rate. Simulation results indicate that SCRRI

is a slower measure than the RIP runback in reducing the core

power. Additionally, FWPT and LOFH are involved with the SCRRI

and RIP runback actuation during the transients and have been

implemented by the Lungmen TRACE/PARCS model. The responses

simulated by TRACE/PARCS correlate well with GE startup test pre-

diction. Moreover, consequences of the mitigation function under

different settings are investigated by undertaking sensitivity stud-

ies, which include SCRRI delay time and the RIP runback rate.

Based on the results of this study, we conclude the following: (a)

power declines faster with an increasing RIP runback, (b) sincethe final RIP speed is fixed by the designated minimum pump

speed of 31% rated, the only difference, affected by the different

RIP runback rates derives from the void feedback effect during

the runback stage, and (c) the SCRRI delay time does not signifi-

cantly impact the final power and reactivity.

References

Ma, S.S. et al., 2011. Integrated control system responses using load rejection

transient for Lungmen ABWR Plant. Ann. Nucl. Energy 38, 14581472.

Taiwan Power Company, 2006. Lungmen ABWR Training Manual.

Taiwan Power Company, 2007. Final Safety Analysis Report for Lungmen Nuclear

Power Station Units 1&2, Taipei, Taiwan.

US Nuclear Regulatory Commission, 2012. TRACE V5.0 Theory Manual.

Yang, C.Y. et al.,2012. ABWR power tests simulation by using a dual RELAP5nuclear

power plant simulation platform. Nucl. Eng. Des. 249, 4148.

Table 5

Summary of TRACE/PARCS analysis for RIP runback capability studies in LOFH.

Parameters/cases LOFH-

Base

LOFH-

2A

LOFH-

2B

LOFH-2C

RIP runback rate (%/s) 4 5 6 10

Min. power within 100 s (%)/

time (s)

61.1/

50.3

59.64/

47

58.3/

44.9

54.7/40.7

Max. void reactivity ($)/time

(s)

0.428/

57.9

0.435/

54.6

0.442/

53.1

0.452/

49.75

0 10 20 30 40 50 60 70 80 90 100

Time (sec)

50

60

70

80

90

100

110

Normalized

power(%)

LOFH_Power





Fig. 15. Power responses of the sensitivity studies for RIP runback delay time in

LOFH.

0 10 20 30 40 50 60 70 80 90 100

Time (sec)

-0.6

-0.4

-0.2

0

0.2

0.4

Reactivity($

)

LOFH_Void Reactivity





Fig. 16. Void reactivity responses of the sensitivity studies for RIP runback rate in

LOFH.

http://refhub.elsevier.com/S0306-4549(13)00363-0/h0005http://refhub.elsevier.com/S0306-4549(13)00363-0/h0005http://refhub.elsevier.com/S0306-4549(13)00363-0/h0010http://refhub.elsevier.com/S0306-4549(13)00363-0/h0010http://refhub.elsevier.com/S0306-4549(13)00363-0/h0010http://refhub.elsevier.com/S0306-4549(13)00363-0/h0010http://refhub.elsevier.com/S0306-4549(13)00363-0/h0005http://refhub.elsevier.com/S0306-4549(13)00363-0/h0005

1-s2.0-s0306454913003630-main

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