IEA collaboration in fusion neutronics Contributions of TU Dresden

IEA collaboration in fusion neutronics

Contributions of TU Dresden

Workshop, Baden-Baden, 18 October, 2001 K. Seidel, TUD

1. Experimental validation of shut-down dose rates

H. Freiesleben, D. Richter, K. Seidel, S. UnholzerTechnische Universität Dresden, Institut für Kern- und Teilchenphysik, Mommsenstr. 13, D-01062 Dresden, Germany

Y. Chen1, U. FischerAssociation FZK-Euratom, Forschungszentrum Karlsruhe, Institut für Reaktorsicherheit, P.O. Box 3640, D-76021 Karlruhe, Germany1 Institute of Plasma Physics of Chinese Academy of Sciences, Hefei, Anhui, 230031 P. R. China

M. Angelone, P. Batistoni, M. PillonAssociazione Euratom-ENEA, Centro Ricerche Energie Frascati, Settore Fusione, Via E. Fermi 27, I-00044 Frascati (Roma), Italy

ITER Task T-426




The dose rates in and near fusion devices like the International Thermonuclear Experimental Reactor(ITER) have significant influence on the operation scheme of the machine. One of the questions concernsthe -dose rates inside the cryostat after shut-down, especially for guaranteeing occupational safety duringhands-on maintenance.

The -radiation originates from radionuclides produced by neutrons in the structural and coolant materialsof the reactor during the operation. The calculation of the -dose rate for given positions comprises, inprinciple, a three-step procedure:a) determination of the spectral neutron flux in the materials with transport code and data as MCNP and

FENDL,b) calculation of the radioactivity induced by the neutrons as a function of irradiation and decay time with

inventory code as FISPACT and corresponding activation and decay data libraries,c) -transport calculation from the activated materials to the position of interest and conversion of the flux

to dose rate.

For validating these complicated procedures, a neutronics experiment was performed in the framework ofITER Task T-426 in a collaboration of ENEA Frascati, FZ Karlsruhe and TU Dresden.

Motivation




neutron source

Pb

gam m a spectrom eter

dose ra te m eter

Pb

sta in less stee l

perspex

plug

SS316-new

SS316

Vertical and horizontal cut of the assembly




0.0E+0 4.0E+4 8.0E+4 1.2E+5t / s

0E+0

1E+6

2E+6

3E+6

Neu

tron

flux

/ ar

b. u

nits

9.60E+4 1.00E+5 1.04E+5 1.08E+5t / s

0E +0

5E +5

1E +6

2E +6

2E +6

3E +6

Neu

tron

flux

/ ar

b. u

nits

Irradiation: 1.95·1015 14-MeV neutrons during 2 days at FNG

Time profile of the neutron source strength as recorded during the irradiation (thin line) and as described in the calculations (thick line) for the complete campaign (left hand) and for the last three hours (right hand).


Contribution of TU Dresden

Fig. 4:Experimental and calculateddose rate as function of thedecay time. The backgrounddose rate, subtracted fromthe measured values, isshown as a dashed line.

1E+3 1E+4 1E+5 1E+6 1E+7t / s

0.1

1.0

10.0

100.0

1000.0

DR

/ (

Sv/

h)

h d w m

background subtracted

Experim ent: solid lineC alculation: points

Detector: tissue-equivalent scintillator(NE 105), 4.6 cm * 4.6 cm ø.Calibration: air-kerma reference value (W/e = 33.97 V) in standard photon fields (19.9 keV ... 6.7 MeV) at PTB.Measurement: quasi-continuously with integration intervals from 5 min to 3 h.

Dose rate measurement





Decay time / s DRexp / (Sv/h) DRcal / (Sv/h) C / E

4380618074881158017280244803408045780572407255090720

132000212400345600479300708500105000016700001710000

488. ± 19.415. ± 16.375. ± 15.268. ± 10173. ± 7.101. ± 4.50.6 ± 2.023.0 ± 0.911.7 ± 0.5

5.80 ± 0.233.56 ± 0.142.43 ± 0.091.78 ± 0.071.22 ± 0.05

0.952 ± 0.0370.759 ± 0.0300.667 ± 0.0260.613 ± 0.0240.614 ± 0.024

409.6 ± 2.9357.8 ± 2.6325.0 ± 2.3240.7 ± 1.7158.8 ± 1.394.25 ± 0.7547.42 ± 0.4621.39 ± 0.2110.71 ± 0.10

5.151 ± 0.0573.134 ± 0.0382.214 ± 0.0261.724 ± 0.0201.264 ± 0.0131.016 ± 0.012

0.8208 ± 0.00860.7115 ± 0.00750.6375 ± 0.00680.6318 ± 0.0067

0.84 ± 0.030.86 ± 0.030.87 ± 0.030.90 ± 0.040.92 ± 0.040.93 ± 0.040.94 ± 0.040.93 ± 0.040.92 ± 0.040.89 ± 0.040.88 ± 0.040.91 ± 0.040.97 ± 0.041.04 ± 0.041.07 ± 0.041.08 ± 0.041.07 ± 0.041.04 ± 0.041.03 ± 0.04

Experimental and calculated dose rate at several decay times

Calculation: Rigorous two-step formalism (U. Fischer), MCNP+FENDL/MC-2.0, FISPACT+FENDL/A-2.0Uncertainties: total experimental 3.9%; statistical uncertainty of about 1% for the calculated values




0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

1.0E+4

2.0E+4

3.0E+4

4.0E+4

5.0E+4

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 2.08 ha).847

Mn-

56

1.81

Mn-

56

2.11

Mn-

56

Flux spectra of the -rays at time t after the end of the irradiation as measured (thick line) and as calculated ( , thin line).

Flux spectra of decay -rays

Detector: liquid scintillator (NE 213), 3.8 cm * 3.8 cm øResponse: matrix of pulse-height distributions on absolute scale; unfolding with DIFBAS code (PTB)

0.0 0.5 1.0 1.5 2.0 2.5E / M eV

1.0E-6

1.0E-5

1.0E-4

1.0E-3

1.0E-2

1.0E-1

(

E)

/ (

MeV

-1 c

m -2

)

Structure of the spectra: flux in the cavity at t= 4380 s per one -ray started in SS316, calculated with the FISPACT energy groups (blue) and with E = 0.01 MeV




0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

4.0E+2

8.0E+2

1.2E+3

1.6E+3

2.0E+3

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 15.9 hb).8

47 M

n-56

1.81

Mn-

56

2.11

Mn-

56

1.38

Ni-5

7

0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

2.0E+2

4.0E+2

6.0E+2

8.0E+2

1.0E+3

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 25.2 hc)

.740

Mo-

99.8

47 M

n-56

1.38

Ni-5

7

1.81

Mn-

56




0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

1.0E+2

2.0E+2

3.0E+2

4.0E+2

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 4.00 dd)

.811

Co-

58.7

40 M

o-99

.320

Cr-

51

1.38

Ni-5

7

0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

5.0E+1

1.0E+2

1.5E+2

2.0E+2

2.5E+2

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 8.20 de)

.811

Co-

58.8

35 M

n-54

.320

Cr-

51




0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

4.0E+1

8.0E+1

1.2E+2

1.6E+2

2.0E+2

t = 12.2 df).8

11 C

o-58

.320

Cr-

51

0.0 1.0 2.0 3.0 4.0E / M eV

0.0E+0

5.0E+1

1.0E+2

1.5E+2

2.0E+2

2.5E+2

(

E)

/ (

MeV

-1 c

m -2

s -1

)

t = 19.3 dg)

.811

Co-

58

.320

Cr-

51




Measured flux of the -rays with E > 0.4 MeV in comparison to the calculations

Decay time exp / (cm-2s-1)

calc / (cm-2s-1) C / E

2.08 h15.9 h25.2 h4.00 d8.20 d12.2 d19.3 d

(1.30 ± 0.06)104

523 ± 22178 ± 9

67.6 ± 3.938.2 ± 2.233.7 ± 2.327.3 ± 1.8

(1.40 ± 0.01)104

474 ± 5142 ± 2

55.7 ± 0.636.6 ± 0.432.4 ± 0.429.6 ± 0.4

1.08 ± 0.050.91 ± 0.040.80 ± 0.040.82 ± 0.050.96 ± 0.060.96 ± 0.071.08 ± 0.07

Calculation: rigorous two-step method (U. Fischer), MCNP+FENDL/MC-2.0, FISPACT+FENDL/A-2.0.Uncertainties: total experimental, statistical only of the calculation




Neutron flux spectrum

neutron sourceneutron detector

Vertical cut of the assembly with NE 213 detector0.0 4.0 8.0 12.0 16.0

N eutron energy (M eV)

1.0E-8

1.0E-7

1.0E-6

1.0E-5

1.0E-4

1.0E-3

Neu

tron

flue

nce

(M

eV -

1 cm

-2 ) ____ M easurem ent

Calcu lation

Fluence per one source neutron for E > 13.7 MeV, Experiment: (5.91 0.35)·10-5 Calculation: (5.96 0.32)·10-5 ———————————————— C/E = 1.01 0.07




Results

Gamma dose rates measured in a materials mock-up of the ITER shielding system with an uncertaintyof about 4% over a period of three weeks after irradiation of the assembly with 14-MeV neutrons areconsistent with the flux spectra of the decay -rays measured in that period.

Rigorous two-step calculations with the MCNP code, using FENDL/MC-2.0 data, and with the FISPACTcode, using FENDL/A-2.0 data, result in ratios of calculated-to-experimental values of C/E = 0.80 ... 1.08for both dose rates and -flux, if material composition and irradiation scenario are described in detail.

Underestimation of experimental values of 10 ... 20% is observed for the first week of decay, whereasoverestimation up to 8% is obtained at the end of the campaign.

ITER design calculations for similar assemblies and decay times with the codes and the data libraries,used in this task, have been validated within that uncertainties.

Experimental data and calculated results may be used for investigating other (faster, simpler, approximate)calculation schemes.




2. Experimental investigation of radioactivity induced in the fusion power plant structural material EUROFER and in other steels by D-T neutrons

K. Seidela, R. A. Forrestb, H. Freieslebena, V. D. Kovalchukc,

D. V. Markovskijd, D. V. Maximovichc, and S. Unholzera

a Technische Universität Dresden, Institut für Kern- und Teilchenphysik, 01062 Dresden, Germany b EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon OX143DB, United Kingdom

c Coordination Centre ”Atomsafety”, 141300 Sergiev Posad, Moscow Region, Russia d Russian Research Centre ”Kurchatov Institute”, 123182 Moscow, Russia

Contribution to 10th International Conference on Fusion Reactor Materials, Baden-Baden




3. SiC benchmark experiment

SiC assembly shipped fromJAERI/FNS to Frascati

TUD measurements in September 2001:

Neutron flux spectra with NE213 spectrometerand hydrogen-filled proportional counter at 4positions for E = 50 keV.... 15 MeV

Gamma flux spectra with NE213 spectrometerat 4 positions for E = 20 keV.... 12 MeV

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IEA collaboration in fusion neutronics Contributions of TU Dresden