LAPUR 6.0 Benchmark 

Against Data from the 

GENESIS Facility

Office of Nuclear Reactor Regulation

NUREG/CR-7047
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LAPUR 6.0 Benchmark 

Against Data from the 

GENESIS Facility

Manuscript Completed: March 2012

Date Published: March 2012

Prepared by:

Oak Ridge National Laboratory

P. O Box 2008

Oak Ridge, TN 37831-6010

Authors

Martin Rohde

Jose March-Leuba

Dr. Tai L. Huang, NRC Project Manager

NRC Job Code J4430

Office of Nuclear Reactor Regulation

NUREG/CR-7047

iii

ABSTRACT

This report contains an evaluation of the LAPUR6 code against stability data measured in 

the GENESIS facility in Delft University of Technology, Netherlands. LAPUR6, a computer 

program in FORTRAN, is a mathematical description of the core of a boiling water reactor 

(BWR). Its two linked modules, LAPURX and LAPURW, respectively solve the steady-state 

governing equations for the coolant and fuel and the dynamic equations for the coolant, fuel, and 

neutron field in the frequency domain. The result of these calculations is a closed-loop transfer 

function that relates power oscillations to external perturbations in core reactivity. The stability 

parameters of merit, decay ratio (DR) and frequency of oscillation are estimated from the 

calculated transfer function. The LAPUR code has been validated in the past against a 

reasonable array of BWR test data.

The GENESIS facility is located in the Reactor Institute of Delft University of Technology, 

Netherlands. It is a boiling, natural circulation facility where flows, void fraction, and density 

wave instabilities can be studied over a wide range of conditions. The facility was initially 

constructed to simulate the conditions of the ESBWR design and was scaled so that, using 

Freon 134a at low power, the results could be extrapolated to water at full ESBWR power and 

pressure. Previous publications describe the GENESIS scaling laws in detail. The GENESIS 

facility may be run on purely thermal-hydraulic mode, by keeping the thermal power constant, or 

with a simulated reactor neutronic feedback. For the later purpose, the core pressure drop is 

measured and the core-average void fraction is estimated based on a one-channel model. The 

reactivity feedback and the fuel response are modeled on a control computer, and the thermal 

power is modulated according to the predicted reactor response. All data used for this 

benchmark includes the simulated reactivity feedback. 

Twenty-seven GENESIS measurements at different operating conditions were simulated 

by LAPUR6. All geometry and measurements were scaled to water properties for use in 

LAPUR6. Ninety-two axial nodes were used to model GENEIS (17 for the core and 75 for the 

chimney). The results of these benchmark calculations show that LAPUR6 predicts an 

oscillation frequency of ~0.7 Hz, which agrees with the measured frequency, and indicates that 

the chimney has little or no effect on the dynamic oscillations. The DRs calculated by LAPUR6 

are in agreement with those measured in GENESIS.

v

CONTENTS

Page

ABSTRACT.................................................................................................................................iii

CONTENTS................................................................................................................................. v

LIST OF FIGURES.....................................................................................................................vii

LIST OF TABLES ...................................................................................................................... ix

1.0 INTRODUCTION ..............................................................................................................1

2.0 LAPUR6 DESCRIPTION ..................................................................................................3

3.0 GENESIS FACILITY DESCRIPTION................................................................................5

4.0 LAPUR6 MODEL..............................................................................................................9

5.0 LAPUR RESULTS..........................................................................................................13

5.1 STEADY STATE VOID FRACTION BENCHMARK ............................................13

5.2 STEADY STATE PRESSURE DROP BENCHMARK .........................................13

5.3 DECAY RATIO BENCHMARK ...........................................................................13

6.0 CONCLUSIONS .............................................................................................................29

REFERENCES..........................................................................................................................31

vii

LIST OF FIGURES

Page

Figure 1 Schematic of the GENESIS facility (M. Rohde et al. / Nuclear Engineering and 

Design 240 (2010) 375–384).....................................................................................8

Figure 2 LAPUR6 axial nodalization ....................................................................................10

Figure 3 Magnitude of Fuel Transfer Function (CBQ) for point 0602081340 ....................11

Figure 4 Phase of Fuel Transfer Function (CBQ) for point 0602081340............................11

Figure 5 Calculated void fractions at different power levels .............................................15

Figure 6 Comparison between predicted and measured core exit quality .......................16

Figure 7 Comparison between predicted and measured core exit void ...........................17

Figure 8 Calculated pressure drop as function of chimney void fraction.........................18

Figure 9 Thermal-Hydraulic (no feedback) transfer function for case 0602141115..........19

Figure 10 Closed loop (with feedback) transfer function for case 0602141115..................20

Figure 11 TH transfer function as function of outlet friction ...............................................21

Figure 12 Closed loop transfer function as function of outlet friction................................22

Figure 13 Closed loop transfer function as function of reactivity feedback coefficient....23

Figure 14 Comparison between measured and calculated decay ratios ............................26

Figure 15 Comparison between measured and calculated frequencies of oscillation ......27

ix

LIST OF TABLES

Page

Table 1 Available signals measured at the GENESIS facility .................................................7

Table 2 Scaling Rules..............................................................................................................10

Table 3 Analyzed GENESIS steady state operating conditions ...........................................24

Table 4 Analyzed GENESIS dynamic operating conditions. All data scaled to water .......25

1

1.0

This report contains an evaluation of the LAPUR 6.0 code [Refs.

INTRODUCTION

1 and 2] against stability data 

measured in the GENESIS facility [Refs. 3, 4, and 5] in Delft University of Technology, 

Netherlands.

LAPUR, a computer program in FORTRAN, is a mathematical description of the core of a boiling 

water reactor (BWR). Its two linked modules, LAPURX and LAPURW, respectively solve the 

steady-state governing equations for the coolant and fuel and the dynamic equations for the 

coolant, fuel, and neutron field in the frequency domain. The result of these calculations is a 

closed-loop transfer function that relates power oscillations to external perturbations in core 

reactivity. The stability parameters of merit, decay ratio (DR) and frequency of oscillation are 

estimated from the calculated transfer function.

The LAPUR code has been validated in the past against a reasonable array of BWR test data as 

documented in Refs. 6 through 12. These old validation data include:

1. Peach Bottom tests (see Ref. 6)

2. Vermont Yankee stability tests (see Ref. 6)

3. Dresden local stability test (see Ref. 7)

4. Browns Ferry single-loop stability test (see Refs. 8 and 9)

5. Susquehanna-2 stability tests (see Refs.10 and 11)

6. Grand Gulf-1 stability tests (see Refs. 10 and 11)

7. Cofrentes stability tests (see Ref. 12)

3

2.0

This section presents the computer program LAPUR, a version coded in the FORTRAN 

language of the mathematical description of a BWR. This program consists of two autonomous 

modules, LAPURX and LAPURW, which are linked by means of an intermediate storing device.

LAPUR6 DESCRIPTION

The first module, LAPURX, solves the coolant and the fuel steady-state governing equations as 

described in Sect. 3.2.1 of Ref. 1. Maps of core steady-state parameters are generated by 

LAPURX and stored into two data files for subsequent use by the dynamics module LAPURW.

The second module, LAPURW, solves the dynamic equations for the coolant, fuel, and neutron 

field in the frequency domain according to the formulations developed in Sect. 3 of Ref. 1.

General input requirements to run a problem are as outlined: 

For steady-state calculation (LAPURX), system operating status:

1. State parameters: reactor pressure, thermal power generated, core flow rate, and coolant 

temperature at the inlet plenum.

2. Power map: Vertical power shape of representative channels and either steam exit 

quality or amount of power generated in each channel.

3. Fraction of power deposited into the coolant by neutron moderation and γ ray absorption.

For steady-state calculation (LAPURX), system design parameters:

1. Mechanical: channel box and fuel pin dimensions.

2. Physical: hydraulic diameters, friction multipliers, orifice flow coefficients, fuel and clad 

densities, and gap thermal conductance.

For steady-state calculation (LAPURX), user options:

1. Error criteria for the iterative calculations.

2. Adjustable parameters for two-phase correlations.

3. Number of nodes desired in the boiling part of a channel.

4. Output options.

For dynamic calculation (LAPURW), systems parameters:

1. Recirculation loop pressure to flow rate gain and time constant.

For dynamic calculation (LAPURW), neutronic parameters:

1. Effective neutron lifetime table.

2. Steady-state core reactivity table.

3. Delayed neutron fractions and their time constants.

4. Doppler reactivity coefficient.

5. Table of density reactivity coefficients.
4

For dynamic calculation (LAPURW), output options:

1. Frequencies of interest for the dynamic analysis.

2. Edit and plotting options.

3. Stability calculation options.

Note that each sub core must be assigned a set of neutronic parameters.

Steady-state calculation LAPURX generates a map of the thermo hydraulic parameters in the 

core, that is, of the following:

1. Channel flow rate, pressure drops, and exit quality (or power) for each channel.

2. Nodal coolant density, void fraction, enthalpy, quality, velocities, and friction components 

at each node along each channel.

3. Set of coefficients for the dynamics calculation.

The dynamic calculation determines:

1. For the fuel, the response of the heat flux to the coolant and of the average temperature 

to driving perturbations of power generation, coolant temperature, and coolant flow rate 

at each node in every channel.

2. For the coolant flow in a channel box:

• The response of the coolant parameters at every node to driving perturbations of 

power generation at each sub core level, coolant flow rate, and coolant inlet 

temperature.

• The open-loop transfer function (TF) for the channel hydrodynamics, its natural 

frequency, and decay ratio.

• The reactivity feedback induced in each node by the driving perturbations. (This is 

accomplished by properly weighting the coolant density and fuel temperature 

perturbations with reactivity coefficients.)

3. For each nuclear sub core:

• Feedback reactivity TFs for driving perturbations in power at each sub core, inlet 

temperature, and core flow rate.

• Open-loop TF matrix; total core natural frequency and decay ratio.

• Closed-loop TF matrix of reactivity to power.

4. Nyquist and magnitude phase plots for all open-loop TFs; Bode plots for closed-loop TFs.
5

3.0

The GENESIS facility [Refs.

GENESIS FACILITY DESCRIPTION

3, 4, and 5] is located in the Reactor Institute of Delft University of 

Technology, Netherlands. It is a boiling, natural circulation facility where flows, void fraction, and 

density wave instabilities can be studied over a wide range of conditions. The facility was initially 

constructed to simulate the conditions of the ESBWR design and was scaled so that using Freon 

134a at low power the results could be extrapolated to water at full ESBWR power and pressure. 

The operating pressure of GENESIS is 11.4 bar [Ref. 3], compared to ~70 bar for a typical BWR. 

The power required is approximately 50 times smaller due to the boiling characteristics of Freon 

134a [Ref. 3]. Refs. 3, 4, and 5 describe the GENESIS scaling laws in detail. 

Figure 1 shows a schematic of the facility. A heated area with 25 heated rods is followed by a 

long adiabatic chimney. A heat exchanger at the top of the facility condenses the steam and 

returns feedwater flow through the downcomer. Two valves can be adjusted manually to 

simulate the inlet and steam separator pressure drops. To evaluate the K value of the valves, 

single phase flow is established with the pump and the pressure drop and flow are measured. 

For all other measurements, the flow is established by natural circulation as voids are formed in 

the heated section. Relevant instrumentation includes: (1) inlet temperature, (2) exit void 

fraction, (3) thermal power, and (4) pressure drops across the valves. Other instruments are 

included, as shown in Table 1.

The GENESIS facility may be run on purely thermal-hydraulic mode, by keeping the thermal 

power constant, or with a simulated reactor neutronic feedback. For the later purpose, the core 

pressure drop is measured and the core-average void fraction is estimated based on a onechannel model (see Refs. 3, 4, and 5 for details). The reactivity feedback and the fuel response 

are modeled on a control computer. The thermal power is modulated according to the reactor 

response predicted by the simulated point kinetics reactivity feedback. The GENESIS heated 

rods have a very fast time constant (< 0.5 sec), and the time constant of the reactor fuel must be

simulated in the control computer. Typically, the fuel time constant is simulated in the GENESIS 

control computer as ~5 seconds (see Refs. 3, 4, and 5 for details). 

A series of experiments have been conducted in the GENESIS facility to determine: (1) the 

natural circulation flow, and (2) the stability of the facility for a combination of operating 

conditions. Both the stability of the purely thermal-hydraulic system and the reactivity-feedback 

system were studied. The primary finding is that when the reactivity feedback is enabled, the 

frequency of the resulting oscillation changes significantly as the mode of oscillation changes 

from a loop- (manometer-) type to a density wave in the core. The complete results of these 

experiments are shown in Refs. 3, 4, and 5. 

7

Table 1 Available signals measured at the GENESIS facility

1 pressure inlet element 21 temperature vessel 1 (bottom) 41 void fraction outlet element (BGO)

2 pressure vapour outlet 22 temperature core 16 42 capacitance (void inlet riser)

3 pressure feedwater inlet 23 temperature vapour (tc) 43 capacitance (void outlet riser)

4 temperature core 13 24 temperature feedwater inlet (tc) 44 capacitance (void downcomer)

5 temperature core 1 25 temperature core 17 45 capacitance (level vessel)

6 temperature core 2 26 dT riser 46 voltage power supply 1

7 temperature core 3 27 temperature inlet (pt100) 47 voltage power supply 2

8 temperature core 4 28 temperature vapour (pt100) 48 voltage power supply 3

9 temperature core 5 29 temperature feedwater inlet (pt100) 49 voltage power supply 4

10 temperature core 6 30 dP inlet valve (PMD235) 50 voltage power supply 5

11 temperature core 7 31 dP riser valve (FMD533) 51 voltage power supply 6

12 temperature core 8 32 dP separator vessel (level) (PMD633) 52 voltage power supply 7 (1 rod only)

13 temperature core 9 33 dP inlet (Keller) 53 current power supply 1

14 temperature core 10 34 dP core (Keller) 54 current power supply 2

15 temperature core 11 35 dP core (not used yet) 55 current power supply 3

16 temperature core 12 36 VRF alpha_av 56 current power supply 4

17 temperature riser 1 (bottom) 37 ControlPower 57 current power supply 5

18 temperature riser 2 38 flow inlet element 58 current power supply 6

19 temperature core 14 39 flow vapour outlet 59 current power supply 7

20 temperature riser 15 40 flow feedwater inlet 60 level buffer vessel (NR Koeling)
8

Figure 1 Schematic of the GENESIS facility (M. Rohde et al. / Nuclear Engineering and 

 Design 240 (2010) 375–384)
9

4.0

The LAPUR code only describes in detail the core region. The recirculation loop, including the 

downcomer and recirculation pumps are only modeled by an integral momentum approach, 

which provides dynamic core flow feedback given changes in core pressure drop. However, it 

does not model variations in temperature and density of the downcomer necessary to model the 

U-tube or loop oscillations that were observed in GENESIS when the neutronic feedback is 

turned off. When the neutronic feedback is turned on in the GENEIS facility, the dominating 

dynamics occur on the core, and LAPUR6 is design to model that dynamic behavior.

LAPUR6 MODEL

The LAPUR6 model for GENESIS includes a single radial channel with 92 axial nodes (17 for 

the core and 75 for the chimney). The variable flow area feature of LAPUR6 was used to specify 

the areas of the core and chimney respectively. The axial nodalization is shown graphically in 

Figure 2. 

Six spacers were explicitly modeled as local losses. The inlet and outlet valves in the GENESIS 

facility were modeled in LAPUR6 as the channel-inlet and channel-outlet local losses. Note that 

the LAPUR6 channel for these simulations covers both the core and chimney regions. The core 

region is 3 m and the chimney is 12.81 m. These dimensions are scaled values for water. The 

real dimensions of the GENESIS facility are 47% smaller.

All dimensions, pressures, powers and flows were scaled to the water equivalent. Table 2 shows 

the scaling rules that were developed in Refs. 3 through 5. 

Table 3 describes the operating conditions for all points analyzed. The inlet and outlet valves 

were set at a constant value and not changed for the duration of the tests.

The GENESIS facility is designed to operate in purely thermo-hydraulic mode (i.e., constant 

power) or with simulated reactivity feedback. The reactivity feedback is simulated by estimating 

the core-average void fraction from the measured core pressure drop using a TH model. The 

point kinetics approximation is used to simulate the power feedback in a reactor core.

The GENESIS heaters are thin rods with a very fast thermal time constant. In reactors, the fuel 

has a slow time response, of the order of 5 seconds. The GENESIS facility simulates the fuel 

thermal conductivity in the computer side by filtering the power feedback before it is applied to 

the rods. For this purpose, a 5 second first order filter is used. For these LAPUR6 benchmark 

cases, UO2 fuel rods were used. The radius of the fuel rod was adjusted by trial and error for 

each case until the calculated fuel time constant was 5 seconds. In particular, the fuel rod radius 

was adjusted by trial and errors until transfer function CBQ calculated by LAPUR (see Refs. 1 or 

2) has a phase of -45 degrees at 0.2 Hz, which is equivalent to a first order 5 second delay. 

Figure 3 and Figure 4 show the LAPUR fuel transfer function CBQ for one example where the 

phase is -45 degrees at 0.2 Hz after adjusting the fuel radius.
10

Table 2 Scaling Rules

Variable Scaling 

Factor

Length 0.4700

Power 0.0230

Mass flux 1.0070

Time 0.6800

Pressure 0.1600

Flow area 0.2209

Mass flow 0.2224

Figure 2 LAPUR6 axial nodalization
11

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0.01 0.1 1

CBW Transfer Function Magnitude (dB)

Frequency (Hz)

Figure 3 Magnitude of Fuel Transfer Function (CBQ) for point 0602081340

-135

-90

-45

0

0.01 0.1 1

CBQ Transfer Fuction Phase (deg)

Frequency (Hz)

Figure 4 Phase of Fuel Transfer Function (CBQ) for point 0602081340

13

5.0

A number of operating conditions in the GENESIS facility had been analyzed with LAPUR6. 

LAPUR RESULTS

Table 3 shows the relevant input parameters for each operating point. All variables have been 

scaled to water-equivalent conditions.

5.1. STEADY STATE VOID FRACTION BENCHMARK

Figure 5 shows the calculated void fractions for three conditions at different power levels. We 

can observe that the void fraction calculated by LAPUR increases in the core, but it remains 

constant in the adiabatic chimney. 

Figure 6 and Figure 7 show a comparison between the core exit quality and void predicted by 

LAPUR6 and the one measured in the GENESIS facility for the steady state measurements of 

Table 3. Excellent agreement is observed. This is an excellent validation of the LAPUR6 void 

correlations against a large number of experimental conditions covering exit qualities from 3% to 

25%.

5.2. STEADY STATE PRESSURE DROP BENCHMARK

Figure 8 shows the pressure drop calculated by LAPUR6 for all tests. This pressure drop 

encompasses both the core and chimney regions. Since the GENESIS facility is operated at 

natural circulation, the calculated pressure drop should be the same for all conditions because 

this pressure drop must equal the weight of the downcomer. 

We observe that LAPUR6 computes essentially the same pressure drop for all tests within a 

precision of ±1.5%. The only exception is a test point (0602201437) where the exit void fraction 

is very low (~30%) and the dP error is of the order of 8%. All other conditions have void 

fractions more representative of reactor operating conditions.

We conclude that LAPUR6 benchmarks the GENSIS pressure drops accurately.

5.3. DECAY RATIO BENCHMARK

LAPUR6 calculates transfer functions (TF) in the frequency domain for all the components of the 

dynamic response of the reactor. In particular, LAPUR6 computes the open-loop TF, which 

contains all the reactor dynamics minus the reactivity feedback. This open-loop TF represents 

the TH conditions in GENESIS when the reactivity feedback is turned off. The LAPUR6 closedloop TF joins together the open-loop TH TF with the point kinetics reactivity feedback to estimate 

the reactivity-to-power TF, which represents the GENESIS dynamics when the reactivity 

feedback is turned on.

Figure 9 shows the open-loop TH TF calculated by LAPUR for case 0602141115. We can see a 

small resonance (representative of an oscillation frequency) at ~0.2 Hz, which represents the 

loop time constant including the chimney. A smaller resonance can be observed at ~0.6 Hz, 

which corresponds to the channel residence time. When the reactivity feedback is turned on, we 

obtain the closed loop TF of Figure 10. We see that when the reactivity feedback is active, the 

0.2 Hz resonance disappears and only one main frequency at ~0.8 Hz is visible.

The above results are consistent with the observed behavior in the GENSIS facility when the 

feedback is enabled [Ref. 3 through 5]. Experimentally, The GENESIS facility exhibits a low 

frequency oscillation (0.1 to 0.2 Hz, depending on conditions) when the power is kept constant 

(purely TH conditions). This frequency is associated experimentally with the loop time constant, 
14

including the chimney. When the reactivity feedback is enabled and the power is allowed to 

oscillate as function of the measured void fraction, the low frequency component disappears and 

only a high frequency component (0.6 to 1 Hz, depending on operating conditions) is observed. 

This high frequency is associated experimentally with the residence time in the channel.

To further investigate this phenomenon, LAPUR6 simulations were conducted where the TH 

stability of the loop was reduced artificially by increasing the outlet friction coefficient (Kout). 

Figure 11 shows the open-loop TH TF as function of Kout. We observe that as Kout is increased, 

the ~0.2 Hz peak increases significantly, with Kout values ~500% of nominal, the TF is essentially 

unstable for these conditions (test 0602141115). The channel peak at ~0.6 Hz also increases in 

amplitude when Kout is increased, but the ~0.2 Hz is always dominant when the reactivity 

feedback is not enabled.

When the reactivity feedback is enabled, LAPUR6 obtains the results shown in Figure 12. We 

observe that when the TH conditions are de-stabilized by increasing Kout, the ~0.8 Hz peak is 

more dominant. For conditions that are almost unstable without feedback, a second peak starts 

forming at ~1 Hz, but the ~0.8 Hz peak is dominant.

To further study the effect of the reactivity feedback, Figure 13 shows a series of LAPUR6 

simulations where the reactivity feedback coefficient was decreased from 0.085 $/%void to 0.017 

$/%void. We observe that as the reactivity feedback magnitude is reduced, the ~0.8 Hz peak 

becomes less and less dominant.

All the above LAPUR6 results are consistent with the published GENESIS experimental findings 

[Ref. 3 through 5], which show an oscillation frequency of 0.1 to 0.2 Hz without feedback and 

oscillations of 0.6 to 1 Hz with feedback. These findings support the conclusion that the chimney 

dynamics play a minor role in density wave instabilities in a nuclear reactor.

A different set of experimental values was analyzed to evaluate the decay ratio and oscillation 

frequency. These experimental points are those documented in Ref. 4. The operating 

conditions and measure decay ratios are shown in Table 4 along with the decay ratios and 

oscillating frequencies calculated by LAPUR6.

Figure 14 shows a comparison between the measured and calculated decay ratios. Overall we 

observe good agreement, but a larger bias is observed at larger subcooling values (lower 

temperatures). Figure 15 shows a comparison between the LAPUR6 and measured 

frequencies. For these GENESIS runs, LAPUR6 predicts two frequencies of oscillations (see for 

example the green line in Figure 12) and the automated algorithm to find the peak oscillation 

frequency “jumps” from one to the other. For this reason, the frequency benchmark for the 

GENESIS runs shows a large scatter about the measured frequency for real reactors, only one 

frequency is present and the LAPUR6 frequency finding algorithm has shown singifcant 

consistency on frequency estimation.
15

0

300

600

900

1200

1500

1800

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

Elevation (cm)

Void Fraction

921 kW

1235 kW

1400 kW

Figure 5 Calculated void fractions at different power levels
16

0%

5%

10%

15%

20%

25%

30%

0% 5% 10% 15% 20% 25% 30%

Exit Quality (LAPUR)

Exit Quality (Measured)

Figure 6 Comparison between predicted and measured core exit quality
17

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 20% 40% 60% 80% 100%

Exit Void Fraction (LAPUR)

Exit Void Fraction (Measured)

Figure 7 Comparison between predicted and measured core exit void
18

95%

100%

105%

110%

0% 20% 40% 60% 80% 100%

Core+Chimney Pressure Drop 

(Normalized) - LAPUR6

Chimney Void (Measured)

1.5% Error

Figure 8 Calculated pressure drop as function of chimney void fraction
19

0

1

2

3

4

5

6

7

8

9

0.01 0.1 1 10

Open Loop (TH) Transfer Function Amplitude

Frequency (Hz)

Figure 9 Thermal-Hydraulic (no feedback) transfer function for case 0602141115
20

0

1

2

3

4

5

6

0.01 0.1 1 10

Closed Loop (TH) Transfer Function Amplitude

Frequency (Hz)

Figure 10 Closed loop (with feedback) transfer function for case 0602141115
21

0

2

4

6

8

10

12

0.01 0.1 1 10

Open Loop TF Amplitude

Frequency (Hz)

Kout ~ 500%

Kout ~200%

Kout = nominal

Figure 11 TH transfer function as function of outlet friction
22

Figure 12 Closed loop transfer function as function of outlet friction
23

Figure 13 Closed loop transfer function as function of reactivity feedback coefficient
24

Table 3 Analyzed GENESIS steady state operating conditions

Point P (kW) Tinlet (C)

Mass flow 

(kg/s)

Core Outlet 

Void

Core Outlet 

Quality

0602060959 1053 257.8 3.17 65% 12.1%

0602071330 1040 262.9 3.09 67% 14.0%

0602071434 1324 261.4 2.96 73% 21.0%

0602071501 1378 261.5 2.93 75% 22.6%

0602071535 1201 262.8 3.01 69% 18.3%

0602081159 894 262.6 3.17 60% 10.3%

0602081340 921 266.1 3.10 65% 12.5%

0602081421 988 253.7 3.25 54% 8.8%

0602081548 1321 252.0 3.15 69% 16.0%

0602081615 1388 251.6 3.10 70% 17.6%

0602091140 1192 254.3 3.18 65% 14.0%

0602101357 1251 266.4 2.93 72% 21.4%

0602101413 1177 267.0 2.94 71% 19.7%

0602131122 1235 264.6 2.96 72% 20.1%

0602141115 1400 265.3 2.83 80% 25.3%

0602141621 827 252.5 3.19 46% 5.4%

0602171331 770 262.6 3.17 53% 7.7%

0602171451 785 270.4 3.07 61% 11.2%

0602171526 708 270.5 3.10 57% 9.4%

0602201437 636 253.1 2.95 32% 2.7%

0602201513 580 275.6 3.07 55% 8.5%

0602211422 1072 265.9 3.02 66% 16.3%

0602221156 1010 265.6 3.07 66% 14.4%

0602221344 958 266.2 3.08 64% 13.6%

0602221502 879 267.2 3.09 60% 12.1%

0602221620 1138 267.4 2.96 68% 18.8%

0603011234 1048 268.0 2.81 73% 18.4%
25

Table 4 Analyzed GENESIS dynamic operating conditions. All data scaled to water

Point Nzu Nsub

Flow 

(kg/s)

Power 

(kW) Tin (C) 

DR 

(data)

Freq 

(data)

DR 

(LAPUR)

Freq 

(LAPUR)

C01 6.15 1.48 2.70 1342.57 264.97 0.47 0.66 0.51 0.71

C02 5.87 1.32 2.70 1282.49 267.22 0.39 0.84 0.45 0.71

C03 5.66 1.59 2.70 1235.63 263.29 0.47 0.84 0.57 0.84

C04 4.33 1.33 2.70 945.99 267.12 0.15 0.69 0.33 0.61

C05 4.74 1.39 2.70 1034.45 266.22 0.21 0.79 0.60 0.70

C06 5.41 1.85 2.70 1181.89 259.56 0.57 0.71 0.52 0.63

C07 4.89 0.76 2.70 1067.10 275.47 0.23 0.75 0.19 0.46

C08 2.95 1.40 2.70 643.75 266.05 0.05 0.85 0.19 0.46

C09 2.91 0.75 2.70 634.69 275.62 0.11 0.80 0.27 0.75

C10 3.43 0.79 2.70 748.30 274.99 0.17 0.73 0.25 0.48

C11 3.72 1.65 2.70 812.76 262.43 0.17 0.81 0.26 0.51

C12 4.39 0.72 2.70 959.51 276.05 0.16 0.75 0.36 0.90

C13 7.80 1.51 2.70 1702.96 264.55 0.69 0.65 0.60 0.78

C14 7.53 1.47 2.70 1644.26 265.10 0.55 0.86 0.59 0.77

C15 6.75 0.71 2.70 1473.70 276.19 0.32 0.67 0.45 1.06

C16 7.47 1.50 2.70 1631.60 264.67 0.62 0.63 0.59 0.77

C17 7.20 1.25 2.70 1572.09 268.29 0.48 0.78 0.51 0.77

C18 7.08 1.54 2.70 1546.48 264.02 0.49 0.75 0.59 0.75

C19 6.37 1.51 2.70 1390.80 264.46 0.42 0.71 0.55 0.72

C20 6.71 0.77 2.70 1464.79 275.37 0.21 0.64 0.47 1.05

C21 6.86 0.90 2.70 1497.81 273.46 0.37 0.65 0.50 1.04

C22 5.99 1.32 2.70 1307.24 267.22 0.45 0.64 0.50 1.04

C23 7.49 1.21 2.70 1634.61 268.85 0.49 0.81 0.50 0.78

C24 5.74 0.73 2.70 1253.54 275.86 0.20 0.70 0.42 1.00

C25 4.11 1.73 2.70 896.60 261.34 0.17 0.70 0.32 0.53

C26 5.64 2.16 2.70 1231.90 255.03 0.75 0.83 0.54 0.60

C27 7.01 2.43 2.70 1531.63 251.07 0.93 1.05 0.73 0.66

C28 6.44 2.37 2.70 1406.11 251.89 0.90 0.81 0.67 0.63

C29 4.82 2.32 2.70 1051.68 252.57 0.61 1.01 0.36 0.53
26

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

LAPUR6 Decay Ratio

Experimental Decay Ratio

Tin ~255 C

Tin ~260 C

Tin ~265 C

Tin ~275 C

Figure 14 Comparison between measured and calculated decay ratios
27

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400

LAPUR6 Frequency (Hz)

Experimental Frequency Scaled to Water (Hz)

Tin ~255 C

Tin ~260 C

Tin ~265 C

Tin ~275 C

Figure 15 Comparison between measured and calculated frequencies of oscillation

29

6.0

The LAPUR6 code [Ref.

CONCLUSIONS

1 and 2] has been benchmarked against experimental data from the 

GENESIS natural circulation facility [Ref. 3 through 5]. The GENESIS experimental data was 

collected using Freon R134a as a coolant, and scaled to water-equivalent conditions using the 

methodology described in Refs. 3 through 5. The following are the major conclusions from this 

benchmarking exercise:

1. The steady state void fractions and qualities calculated by LAPUR6 compare favorably 

with those measured at the GENESIS facility. This benchmark validates the LAPUR6 

void models.

2. The pressure drops calculated by LAPUR6 compare favorably with those measured at 

the GENESIS facility. This benchmark validates the capability of LAPUR6 to calculate 

natural circulation conditions.

3. LAPUR6 predicts that the oscillation frequencies in GENESIS should be of the order of 

0.1 to 0.2 Hz when the reactivity feedback is not enabled. The actual frequency depends 

on the operating conditions. This is the range of oscillation frequencies observed in the 

GENESIS facility.

4. LAPUR6 predicts that, when the reactivity feedback is enabled, the oscillation frequency 

increases to the 0.6 to 1.0 Hz range and that the 0.1 to 0.2 Hz thermal-hydraulic 

oscillation is not present. The change in frequency was observed experimentally in the 

GENESIS facility.

5. The decay ratios calculated by LAPUR6 compare favorably against the measured data in 

the GENESIS facility

31

REFERENCES

1. Escrivá, A., J.L. Muñoz-Cobo, J. Melara San Roman, M. Albendea Darriba, and J. 

March-Leuba, “LAPUR 6.0 R.0 User’s Manual,” NUREG/CR-6958, ORNL/TM-2007/233, 

Oak Ridge National Laboratory, December 2007

2. Otaduy-Bengoa, P. J. "Modeling of the Dynamic Behavior of Large Boiling Water 

Reactor Cores," Ph.D. dissertation, University of Florida, 1979.

3. Rohde, M., C.P. Marcel, A. Manera, T.H.J.J. Van der Hagen, and B. Shiralkar,

“Investigating the ESBWR stability with experimental and numerical tools: A comparative 

study,” Nuclear Engineering and Design 240 (2010) 375–384

4. Marcel, C.P., M. Rohde, T.H.J.J. Van der Hagen, “Experimental Investigations On The 

ESBWR Stability Performance,” Nuclear Technology 164 (2008) 232-244

5. Marcel, C.P., M. Rohde, T.H.J.J. Van der Hagen, “Fluid-to-fluid modeling of natural 

circulation BWRs for stability analysis,” International Journal of Heat and Mass Transfer 

51 (2008) 566–575

6. March-Leuba, J. A. and P. J. Otaduy, "A Comparison of BWR Stability Measurements 

with Calculations Using the Code LAPUR IV," NUREG/CR2998, ORNL/TM 8546, Oak 

Ridge National Laboratory, January 1983.

7. March-Leuba, J. A., D. N. Fry, M. E. Buchanan, and C. O. McNew, Local Stability Tests 

in Dresden 2, ORNL/TM-9054, Oak Ridge National Laboratory, March 1984.

8. March-Leuba, J. A., R. T. Wood, P. J. Otaduy, and C. 0. McNew, "Stability Tests at 

Browns Ferry Unit 1 under Single-Loop Operating Conditions," Nucl. Techno. 74 38–52 

(May 1986).

9. March-Leuba, J. A. and P. J. Otaduy, "The Importance of Momentum Dynamics is BWR 

Neutronic Stability: Experimental Evidence," Trans. Am. Nucl. Soc. 50 563–564, 

November 1985.

10. March-Leuba, J. A. and D. N. Fry, Grand Gulf-1 and Susquehanna-2 Stability Test,

ORNL/NRC/LTR-87/01, Oak Ridge National Laboratory, April 1987.

11. March-Leuba, J. A. Stability Calculations for the Grand Gulf-1 and Susquehanna-2 

Boiling Water Reactor, ORNL/NRC/LTR-87/08, Oak Ridge National Laboratory, 

September 1987.

12. Melara, J., A. Escriva, J.L Muñoz-Cobo,, M.E.Montesinos, J. March-Leuba, and M. 

Albendea “Validation of LAPUR 6 for Stability Prediction. Application to Cofrentes NPP” 

American Nuclear Society. San Diego CF, June 2008

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NUREG/CR-7047

LAPUR 6.0 Benchmark Against Data from the GENESIS Facility

03 2012

JCN J4430

Martin Rohde

Jose March-Leuba

Technical

Oak Ridge National Laboratory

PO Box 2008

Oak Ridge, TN 37831

Division of Safety Systems

Office of Nuclear Reactor Regulation

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001

Dr. T. L. Huang, Project Manager

This report contains an evaluation of the LAPUR6 code against stability data measured in the GENESIS facility in Delft

University of Technology, Netherlands. Twenty seven GENESIS measurements at different operating conditions were simulated

by LAPUR6. All geometry and measurements were scaled to water properties for use in LAPUR6. Ninety two axial nodes were

used to model GENEIS (17 for the core and 75 for the chimney). The results of these benchmark calculations show that

LAPUR6 predicts an oscillation frequency of ~0.7 Hz, which agrees with the measured frequency, and indicates that the

chimney has little or no effect on the dynamic oscillations. The DRs calculated by LAPUR6 are in agreement with those

measured in GENESIS.

LAPUR

BWR

BWR Stability


UNITED STATES 

NUCLEAR REGULATORY COMMISSION

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NUREG/CR-7047 LAPUR 6.0 Benchmark Against Data from the GENESIS Facility