Project CESR:

The Design of a World-Class

Cold-Neutron Source at NIST

Dylan Prévost

Nuclear Engineer

August 5th, 2015
Reactor Physics 101

NIST’s Cold Neutron (CN) Source

CESR: Cold-Energy-n Source Reactor

CESR design features and comparison

Summary of Successes

Topics of Discussion

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First, a crash course in reactor physics...

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4

In Terms of Neutronics

Δρ =

Keff1 − Keff2

Keff1∙ Keff2
CNs → 2/3 of all NCNR Research

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Project Inception

 2000+ users annually, from industry to academia

 Finite reactor life - built in the 1960’s!

 Politics - phasing out of highly-enriched fuels

 One of the greatest collections of instruments for CN 

experiments in the world

Task:

❑ Design a base conceptual model

❑ Optimize for CN production

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NBSR: Cut-away View

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 Vertical flux trap

 Highly enriched uranium fuel

 ~1.2m in diameter

 Thermal flux peaks in center

 Fast flux is high near CNS
Split-core Design (NBSR-2)

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 Horizontal flux trap

 Low enriched uranium fuel

 <0.5m across both cores

 More efficient thermal flux 

trapping

 Reduction of fast flux at CNS 

tubes

 Approximately doubles capacity 

for CN facilities
Proposition: Hexagonal Fuel Elements

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XY-plane, Z= 0.0cm XY-plane, Z= 20cm

CESR Design – Inside the Reflector Barrel

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neutron “reflector” 

pool

neutron 

“moderator”

channels

core box

control 

blades

D2O (heavy water)

H2O (light water)

Zircaloy-4

Natural Hafnium

Aluminum-6061

U3Si2“meat” batches

Rhombic 

Core-Half
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coolant 

channels

D2O (heavy water)

H2O (light water)

Zircaloy-4

Natural Hafnium

Aluminum-6061

U3Si2“meat” batches

fuel 

cladding

fuel 

meat

Hexagonal 

Fuel Element
Z = 33.64cm

Z =-33.64cm

SU ρex = 8.27% Δk/k

EOC ρex = 1.58% Δk/k

Control Rod Thickness Selection

1mm-thick rods:

32.1% Δk/k total worth at SU

35.0% Δk/k total worth at EOC

Above NRC standards

for NBSR

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Control rods 

are in “fully 

withdrawn” 

position

SU SDM = 19.63% Δk/k

EOC SDM = 25.04% Δk/k
0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

-33 -27 -21 -15 -9 -3 3 9 15 21 27 33

Keff of Reactor Core

Rod Withdrawal Height, all rods (cm)

Critical Rod Height

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Shut-down 

margin

Excess

reactivity
2

3

4 8 5

6

Z=0.0cm

Y=4.5cm

Y=4.5cm

Z=0.0cm

1

2 4 8

7

5

Eight Independent

Control Rods

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0.80

0.81

0.82

0.83

0.84

0.85

0.86

-33 -27 -21 -15 -9 -3 3 9 15 21 27 33

Keff of Reactor Core

Rod Withdrawal Height (cm)

Rod 1

Rod 2

Rod 3

Rod 4

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Independent Rod Worth
2 0 4 0 6 0 8 0 100 120

0

1

2

3

4

5

x 101 4

Flux [n/cm

2-s]

Radial distance from the core center [cm]

Thermal flux (Old core)

Fast flux (Old core)

Thermal flux (New core)

Fast flux (New core)

Flux Trap Comparison

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Thermal Flux (sq.-lattice)

Fast Flux (sq.-lattice)

Thermal Flux (hex-lattice)

Fast Flux (hex-lattice)
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Thermal Neutron Flux Distribution
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NBSR ATR

HFIR

CESR

ILL

0.00E+00

5.00E+12

1.00E+13

1.50E+13

2.00E+13

2.50E+13

3.00E+13

(N/CM2-S)/MWTH

Max thermal flux to operating power ratio

NBSR 2.00E+13

ATR 4.00E+12

HFIR 2.35E+13

CESR 2.50E+13

ILL 2.57E+13

Flux Heavyweight Champs
All Hail CESR

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 -5.5% fuel, and low-enriched $

 -13.1% FE size; compact but complex $

 -13.5% aluminum cladding mass $

 +0.23% neutron multiplication (Keff) $

 Room for control rods!
Future Work

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 CNS thermal/fast current ratio optimization

 Multi-physics modeling analysis

◦ Thermal hydraulic feedback

◦ Material degradation and life-extension studies

 Safety Analysis and Accident Scenarios
Acknowledgements

NSF – Program Funding

Dr. Zeyun Wu – Project Advising

Dr. Bob Williams – Project Advising

Michael Middleton – NIST contact

Dr. Carlos Castaño – NIST contact

Dr. Julie Borchers – NCNR Program Coordination

Dr. Brandi Toliver– SURF Program Coordination

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