NBSR Thermodynamic Performance Analysis

CENTER FOR NEUTRON RESEARCH, NATIONAL INSTITUTE OF STANDARDS AND

T E C H N O LO GY, 1 0 0 B U R E A U D R . 

GAITHERSBURG, MD, USA 20899

Omar Cavazos

1
Background

•B.S. in Mechanical Engineering at Texas A&M University-Kingsville

• Graduated in May 2018

•Masters student in Engineering Technology (Mechanical Systems) 

at the University of North Texas starting Fall 2018

2
Motivation

• Optimized thermodynamic parameters increase the 

operational range of the NBSR secondary cooling system.

• Impact of environmental conditions.

• Monthly energy savings.

3
Project Overview

Reference Review

Analyze NBSR Cooling System 

Thermodynamic Model Development

Optimization

4
NBSR System Overview

Primary 

Loop

Secondary 

Loop

Heavy Water Water

Reactor

Main Heat Exchangers

Cooling Towers

Air Exit

Air Inlet

5
Thermodynamics of Cooling Towers

•Evaporative Cooling

•Dry & Wet-bulb Temperature

https://www.suezwatertechnologies.com/handbook/cooling_water_systems/fig31-3.jsp

Hensley J., “Cooling Tower Fundamentals.”, SPX Cooling Technologies, (2009).

United States Department of Energy, “ Cooling Towers: Understanding Key Components of 

Cooling Towers and How to Improve Water Efficiency.” (2011).

nn =

(ttii − ttoo)

(ttii − ttwwww) x 100

6
Assumptions and Limitations

Limitations:

•The reactor outlet temperature must be below 130 °F.

•The reactor inlet temperature is less than 110 °F.

•The secondary cooling flow rate can not be less than 6,000 GPM.

Assumptions:

•Cooling tower cells are combined.

•Heat transfer through the pipes and friction is neglected.

•Secondary and primary pumps are modeled as 1 pump each.

7

NIST, “Safety Analysis Report for the National Institute of Standards and Technology Reactor – NBSR.” National Institute of Standards and Technology
Secondary Loop Diagram

8
Input Process Parameters

•Reactor Power 20 MW

•Primary Flow 8,760 GPM

•Secondary Flow= 10,400 GPM

•Secondary Aux Flow= 711.4 GPM

•SCV-20 Position = 0%

9
Heat Exchanger Data

Hot Side Cold Side

Inlet Temp 

(°F)

Outlet 

Temp (°F)

Flow (GPM) Inlet Temp 

(°F)

Outlet 

Temp (°F)

Flow (GPM) Heat Duty 

(kW)

HE-1A 113.6 100.4 4250 77 90 4500 8,555.92

HE-1B 113.6 102.4 4250 77 92 4800 10,529.39

HE-2 103.16 80.52 170 77 83.44 102 89.45

HE-6 101.96 95.15 222.8 77 91.5 567.5 829.52

HE-9 108.43 102 7.96 77 82 41.9 30.67

HE-10 95 90 490 77 80 388.6 170.89

Table 1. Heat Exchanger Parameters

10
• Wet-bulb Temp = 67 °F

• Dry Bulb Temp= 87 °F

• Relative Humidity of Ambient Air = 34.94 %

• Cooling Tower Airflow= 405.99 mm3

ss

Cooling Tower Parameters

2

1

3

4

77°F

91°F

67°F

φφ = 34.94%

87°F

φφ = 100%

∑iiii mṁ h=∑oooo mṁ h=mṁ aa1

+mṁ 3h3 = mṁ aa2h2 + mṁ 4h4

mṁ aa =

mṁ 3(h3−h4)

h2−h1 −(ωω2−ωω1)h4

Çengel Y. A. Boles, M. A. “Thermodynamics: An engineering approach.” Boston: McGraw-Hill (2015).

11
12

Model Overview
13
Cooling Towers

14
Cooling Tower Efficiency Calculator

nn =

(ttii − ttoo)

(ttii − ttwwww) x 100

15
Model Verification

Historical Data Temperature (°F) Simulink Model Temperature (°F) Relative Error ( %)

Reactor Inlet 100.4 99.5 0.90

Reactor Outlet 114.5 114.7 0.17

Cooling Tower (Outlet) 75 76.6 2.13

Table 2. Case 1 at 7/15/18 11:30 a.m. 

Historical Data Temperature (°F) Simulink Model Temperature (°F) Relative Error ( %)

Reactor Inlet 104.5 102.4 2.01

Reactor Outlet 118.5 117.1 1.18

Cooling Tower (Outlet) 80 79.5 0.63

Table 4. Case 3 at 7/15/18 7:30 p.m. 

Table 3. Case 2 at 7/15/18 5:30 p.m. 

Historical Data Temperature (°F) Simulink Model Temperature (°F) Relative Error ( %)

Reactor Inlet 104 101.3 2.60

Reactor Outlet 118.2 116.4 1.52

Cooling Tower (Outlet) 78 78.6 0.77

16
Analysis and Results

• Conducted by varying environmental wet-bulb 

temperatures, secondary flow rates, and SCVposition.

• MATLAB script was written to perform 

simulations.

• Model converged at 0.00001 deviation. 

17
Effect of Secondary Flow Rate at Benchmark

18

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

98

100

102

104

106

108

110

112

114

116

118

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

70

75

80

85

90

95

100

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

60

62

64

66

68

70

72

74

76

78

80

Optimal Efficiency(%)

• 67°F Wet-bulb, 34.94% Relative Humidity
Effect of Secondary Flow Rate during Summer

19

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

120

122

124

126

128

130

132

134

136

138

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

95

100

105

110

115

120

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

60

62

64

66

68

70

72

74

76

78

80

Optimal Efficiency(%)

• 90°F Wet-bulb, 60 % Relative Humidity
Effect of Secondary Flow Rate during Winter

20

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

70

72

74

76

78

80

82

84

86

88

90

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

40

45

50

55

60

65

70

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

6000 7000 8000 9000 10000

Secondary Flow Rate (GPM)

58

60

62

64

66

68

70

72

74

76

78

Optimal Efficiency(%)

• 35°F Wet-bulb, 60 % Relative Humidity
Effect of Wet-bulb Temperature at Benchmark

21

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

70

80

90

100

110

120

130

140

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

40

50

60

70

80

90

100

110

120

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

58

58.2

58.4

58.6

58.8

59

59.2

59.4

59.6

59.8

60

Optimal Efficiency(%)

• 10,400 GPM
Effect of Wet-bulb Temperature at 6,500 GPM

22

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

70

80

90

100

110

120

130

140

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

40

50

60

70

80

90

100

110

120

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

30 40 50 60 70 80 90

Wet-bulb Temperature (°F)

74.5

75

75.5

76

76.5

77

77.5

Optimal Efficiency(%)
Performance of SCV-20 at Benchmark

23

0 20 40 60 80 100

SCV-20 Position (%)

95

100

105

110

115

120

125

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

0 20 40 60 80 100

SCV-20 Position (%)

75

80

85

90

95

100

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

0 20 40 60 80 100

SCV-20 Position (%)

58

60

62

64

66

68

70

72

74

76

78

Optimal Efficiency(%)

• 67°F Wet-bulb, 34.94% Relative Humidity, 10,400 GPM
Performance of SCV-20 during Winter

0 20 40 60 80 100

SCV-20 Position (%)

70

75

80

85

90

95

100

Temperature(°F)

Reactor Inlet Temperature

Reactor Outlet Temperature

0 20 40 60 80 100

SCV-20 Position (%)

40

45

50

55

60

65

70

75

80

Temperature(°F)

Cooling Tower Inlet Temperature

Cooling Tower Outlet Temperature

0 20 40 60 80 100

SCV-20 Position (%)

74

76

78

80

82

84

86

88

90

Optimal Efficiency(%)

24

• 35°F Wet-bulb, 60 % Relative Humidity, 6,500 GPM
Key Findings

1. Secondary flowrate

•For every decrease of 500 GPM cooling tower efficiency increased by ~ 3.4% and increased 

reactor inlet temperature by ~ 0.5%. 

2. Wet-bulb temperatures

•For every 6.875 °F increase in wet-bulb temperature, reactor inlet temperatures increase by 

~7%.

3. SCV-20 position

•For every 10% SCV-20 position change, cooling tower efficiency will increase by ~2.5% and reactor 

inlet temperature will increase by ~0.6%.

25
Energy Savings

•If 6,500 GPM secondary flow rate was 

implemented during summer months cooling 

tower efficiency would increase by about 27 % 

and save approximately $5,800 per month.

26
Future Work

•Thermodynamic engine for NBSR Augmented 

Reality Simulator.

•Model will be available when further analysis is 

needed.

•Engineering changes affecting the reactor 

thermodynamics can be analyzed using the model.

27
Conclusion

•Thermodynamic model was created.

•Decreasing secondary flow rate improves cooling tower efficiency.

•Energy savings will be present.

28
Acknowledgements

•Dr. Daǧistan Şahin

•Dr. Xue Yang

•Daniel Mattes 

•Joseph Dura 

•Julie Borchers

•Reactor Operations and Engineering 

•Special thanks to Samuel MacDavid, Scott 

Arneson, Paul Liposky, Marcus Schwaderer, Dan 

Khan, Randolph Strader and NCNR reactor 

operators

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30
Disclaimer

Certain commercial equipment, instruments, or materials are identified in this 

study in order to specify the experimental procedure adequately. Such 

identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that 

the materials or equipment identified are necessarily the best available for the 

purpose.

31
Thank You

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