subcriticality measurements of accelerator-driven …...c. h. pyeon, kurri, japan 3 accapp2009,...

C. H. Pyeon, KURRI, Japan 1

AccApp 2009, Vienna, 4-8 May, 2009

C. H. Pyeon, T. Misawa, J. Y. Lim, S. Shiroya(Kyoto University Research Reactor Institute, Japan)

Subcriticality Measurements of Accelerator-Driven System in

Kyoto University Critical Assembly



2009/3/4 FFAG-KUCA ADS Experiment

1

10

100

1000

10000

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Time (sec)

Counts/ch

run 1

run 2

run 3

Spallation neutrons from target

Delayed neutrons in core

Fig. Time series of neutrons

Neutron multiplication by spallation neutrons generated by protons

First Injection of Spallation Neutrons



Target7 cm 14 cm 21 cm

Peak value- 14 % - 8 % - 9 %

Fig. Results of Gafchromic films varying the distance from target

Fig. Results of scanning data of Gafchromic films varying the distance from target

Top

Bottom

Proton Beam Characteristics



Fuel regionReflectorFig. Side view of ADS core in KUCA A-core Reaction rate distribution

� Measure 115In (n, γ) 116mIn (Exp. error: Too large)� Confirm calculation precision by MCNPX

W target

70.0 cm

In wire position

W target

70.0 cm

In wire position

Fig. Reaction rate distribution by In wire

Reaction rate (In wire in Axial)

0 20 40 600

0.02

0.04

0.06

0.08

Distance from target [cm]Re

actio

n rate

[Arbi

trary

units

] Neutron guide region SV regionVoid region

Experiment MCNPX Calculation



Contents� ADS IAEA Benchmark problems (KART in KUCA)� A unique optical fiber detection system� Kinetic parameter measurement using optical fiber

� Neutron multiplication� Neutron decay constant and Subcriticality

� IAEA benchmark problems Phase 2:Subcriticality measurements

� Pulsed neutron (PN) method� Neutron noise (NN) method

(Feynman-α and Rossi-α methods)� Neutron source multiplication (NSM) method



IAEA Benchmarks at KART (Phase 1 & 2)� Phase 1: Static experiments (14 MeV D-T neutrons)

- Indium (In) wire (Reaction rates) distribution- Reactivity (Excess reactivity and Subcriticality) - Neutron spectrum (Reaction rates and Unfolding analyses)

� Phase 2: Kinetic experiments (14 MeV D-T neutrons)- Neutron multiplication analyses (M=(F+S)/S)- Subcriticality measurement methods(Rossi-α, Feynman-α, Pulsed neutrons andNeutron source multiplication (NSM) methods)- Neutron decay constant (Relationship between α and ρ)



KUCA A-core

Fig. KUCA A-core (Reference core)Fig. Image of KUCA A-core and fuel assembly loaded

53.8cm

39.5cm

59.1cm

0.63cm(1/4")Polyethylene

0.3086cm(1/8")Polyethylene

0.15874cm(1/16")Enriched Uranium

152.4cm

Fuel Cell×36

Polyethylene

Fuelassembly

Aluminumsheath

Collimatorregion

Polyethylene

- KUCA A-core -A solid-moderated and -reflected core

F F F F F

F F F F FF F F F FF F F F F

12

C3 S5

S4 C1

C2 S6



Neutron guide and Beam duct

Fig. Top view of neutron guide core

F F F F F

F F F F FF F SV F FF F SV F F

22 SV 22s'

s s s

s s sb bs bs bs bb bs bs bs bf fs fs fs f

C3 S5

S4 C1

C2 S6

Fig. Side view of neutron guide and beam duct

Fuel assembly base

Tritium target

66.0 cm

In wire position

f: Fe – Shielding Fast neutrons around target

b: Boron – Shielding thermal neutronsmoderate in reflector region

s: Void – Streaming 14MeV neutronsfor Fuel region

Fuel assembly base

Tritium target

66.0 cm

In wire position

f: Fe – Shielding Fast neutrons around target

b: Boron – Shielding thermal neutronsmoderate in reflector region

s: Void – Streaming 14MeV neutronsfor Fuel region

Fuel regionReflector region



Optical Fiber Detection System

2mm

1mm

AssemblyAssembly

Al pipe

Remotely controlleddriving motor

0.3mm

PMT

Amp.

SCA ADC

MCAMCS

Core

Control room

6Li+

ZnS(Ag)

Plastic optical fiber

Fig. Remote driving system

Fig. Optical fiber covered by Al tube

� Main characteristics� Li: Scintillation material (obtained by 6Li (n, α) reaction)� ZnS: Convertor material � Size: Compound of (LiF+ZnS -> 1:1) optimized mixture

in 0.5 mm thickness and 1 mm diameter



Neutron Multiplication (k-source)

0 5 10 15 20 250

0.2

0.4

0.6

0.8

1.0

1.2

Subcriticality ρ [%∆k/k]0.411.102.274.03

Distance from the center of core [cm]

6 Li re

actio

n rate

[Arbt

rary u

nits] Core

regionReflectorregion

0 1.00 2.00 3.00 4.00 5.000

100.00

200.00

300.00

Subcriticality | ρ| (%∆k/k)

Neutr

on m

ultipl

icatio

n M

Meff = 1 / ( 1 - keff ) Mexp-abs (Absolute value) Mexp-rel (Relative value) Mcal-abs (Absolute value) Mcal-rel (Relative value)

Fig. Axial Li reaction rates by optical fiber detection system varying subcriticality

Fig. Neutron multiplication by Area ratio methodapplied to Li reaction rates

Principle of an attachment at top in optical fiber� LiF (ZnS): 6Li (n, α) reaction for thermal neutrons => 1/v distribution of X-sec in thermal energy region� ThO2 (ZnS): 232Th fission reaction for fast neutrons => Threshold reaction in 9 MeV for neutrons� F: Total number of neutrons by nuclear fission reactions� S: Total number of neutrons generated by outer source

F SMS+

=



Neutron Decay Constant

Pulsed neutron method (PNM)� Good evaluation of subcriticality at both core and reflector positions� Examination of validity of methodology and position dependency

Fig. Measured neutron decay behavior by opticalfiber detector system.

0 0.002 0.004 0.006 0.008 0.01010-3

10-2

10-1

100

Time [Sec.]Re

lative

Li re

actio

n rate

[Arb.

units

]

- Core - Experiment MCNP

- Reflector - Experiment MCNP

LiF fiberF F F F F


10 SV 10s'

s s s


S4 C1

C3 S5

C2 S6

ThO2 (or Al, ZnS, LiF) fiber: Monitoring outer source neutrons



Pulsed Neutron (PN) Method

F F F F F


10 SV 10s'

s s s


S4 C1

C3 S5

C2 S6

○: LiF Optical fiber●: ThO2 optical fiber

Table Comparison of measured subcriticality by pulsedneutron method varying detector positions

11.93±0.1212.28±0.1210.24±0.1010.38±0.03

8.64±0.098.18±0.087.55±0.087.41±0.03

6.87±0.076.54±0.075.89±0.066.24±0.03

3.63±0.043.25±0.033.40±0.033.45±0.03

2.42±0.023.12±0.032.55±0.032.55±0.03

1.78±0.022.15±0.021.88±0.021.83±0.03

0.99±0.010.96±0.010.99±0.010.97±0.03

Fiber #3(%∆k/k)

Fiber #2(%∆k/k)

Fiber #1(%∆k/k)MCNP



Neutron Noise (NN) Method

*: Reference a was obtained using pulsed neutron method**: Stochastic Feynman-α***: Deterministic Feynman-αNote that these data were provided by Dr. Y. Kitamura of JAEA

Fig. Top view of KUCA A-core

F F F

F F F F FF F F FF F F F FF F F F F

FC2 S6

C1S4

C3 S5

Table Comparison of measured neutron decay varying Feynman and Rossi-α methods(pulsed period 20 ms)

599±7631±2601±4598±42.07±0.02

500±5508±1495±3494±31.58±0.02

368±2383±1373±2369±30.99±0.01

263±1285±1253±1266±20.50±0.01

Rossi(1/sec)

Feynman***α (1/sec)

Feynman**α (1/sec)

Reference* α (1/sec)

Subcriticality (%∆k/k)



Neutron Source Multiplication (NSM) Method

5.19 (12.9%)6.44 (7.5%)5.96±0.45

7.09 (18.1%)10.46 (20.8%)8.66±0.69

2.52 (7.4%)2.88 (5.9%)2.72±0.22

0.67 (6.9%)0.69 (4.2%)0.72±0.06

Higher-mode SM method(%∆k/k)

MCNP(%∆k/k)

Ref. Exp. value

(%∆k/k)

Table Comparison of measured subcriticality with calculated ones (with JENDL-3.3).

( ): Relative difference, Cal. error: 0.03%∆k/k

F F F F F


22 SV 22s'

s s s


C3 S5

S4 C1

C2 S6

BF

BF

BF

BF252Cf

BF3 detectors

Subcriticality (Source Multiplication method)� Confirmation of measurement technique� Detector position dependence� Improvement of precision and methodology



� Phase 1: Static experiments (14 MeV D-T neutrons)Reaction rate distribution, Neutron spectrum, Reactivity

� Phase 2: Kinetic experiments (14 MeV D-T neutrons)Neutron multiplication, Subcriticality measurement methods(Rossi-α, Feynman-α, Pulsed neutrons andNeutron source multiplication (NSM) methods)

� Phase 3: Static and Kinetic experiments (150 MeV protons)Above topics, γ-ray distribution, Power monitoring, etc.

� Fuel: HEU, Thorium, NU� Reflector: Polyethylene, Graphite, Aluminum, Beryllium� Core: Any combinations of Fuel & Reflector

IAEA Benchmark Problems



Summary� Confirming the detection system using a unique optical fiber:

� Multiplication M using reaction rate distribution(vs. one point reactor approximation)

� Neutron decay constant α and Subcriticality ρ� Good evaluation of subcriticality

� IAEA benchmark problems (Phase 2):Subcriticality using PN, NN and NSM methods, confirming� Detector position dependence� Each measurement technique

subcriticality measurements of accelerator-driven …...c. h. pyeon, kurri, japan 3 accapp2009,...

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