Summary of Recent Neutronics Integral

Experiments on C/E

M. YoussefUCLA

ITER TBM Project Meeting, UCLA, February 23-25, 2004

Background• Various fusion neutronics integral experiments have been completed or in progress using 14 MeV neutron sources: FNS and Oktavian facilities (Japan), FNG facility (Frascati

Italy)SNEG-13 facility (RF), • The purpose is to validate nuclear data libraries and transport codes through comparing the calculated-to-experimental parameters (C/E) for important parameters such as:

• In system neutron and gamma spectra, leakage spectra, nuclear heating,• Tritium production rate (TPR)• Activation rates, decay spectra, dose rates, sky shine, etc

• Recent activities in this area were reported during the IEA collaboration on fusion neutronics, Kyoto, Japan, December 9, 2003 (started in 1993). This is an example of international collaboration supported by the fusion community. Previous example was the US/JAERI Collaboration 1983-1993)

• We review recent C/E values, particularly for of TPR in mockups of test blanket module for ITER (i.e. the Japanese WCPB concept and the EU preparation for testing the HCPB concept at FNG).

• Brief discussion on improving techniques for tritium production measurements is discussed.

First WallReduced Activation Ferritic

Steel (F82H)

Neutron Multiplier bed layer

Breeder bed layer (Li2TiO3 or Li2O) 　

Cooling Water

Concept of the Solid Breeding Blanket designed by JAERI

Fusion Neutronics Source (FNS) facilityThe TPR distribution was measured with pellets of Li2TiO3, embedded in the Li2TiO3 layer.

Control room

Work area

TOFduct

D+ beam- Vac :400 kV - Ib :20 mA

Accelerator

Ns :4x1012 n/sRotating T-Target

Ns :3x1011 n/sFixed T-Target

Target Room IN Target Room II

0 5 10m

Max.

Max.

In this experiment,Neutron yield;~2X1011 n/s

FNS D-T Target

F82H/95-%Li2TiO3/Be Assembly

Li2CO3-block Detector(NE213)

Assembly-50 x 50 x 30 cm-F82H/Li2TiO3(6Li:95%)/Be assembly surrounded by Li2CO3 and B4C blocks

D-T neutron conditions-Neutron flux: 1.5 x 1011 n/sec/mA-Irradiated time: 10 ~ 20 h

200 200

300

25

Li2CO3

FNS target 1000

F82H 16mm

F82H 3mm6Li-95% Li2TiO3

12mm

Be

31

500300

200

(Unit: mm)

Single Layer Experiment (2001-2002)

TPR for Li2TiO3 and the ratio of the calculated to the experimental result, C/E.

• For this particular single layer experiment the calculated TPR with Monte Carlo method is within the experimental error of 10%.

• This is not the case however with the most recent experiment with three layers

Three Layers Experiment and Analysis

A blanket assembly

Shielding (Li2CO3)

Be

F82H　1.6mm×10 F82H 　1.0mm×3

2 8 26Li2CO3 (13)1.23x1022 6Li/cm3

40-%6Li2TiO3(12)1.23x1022

6Li/cm3

The assembly was enclosed in a cylindrical SS-316 reflector to shield the neutrons reflected by the experimental room walls and to simulate the incident neutron spectrum at the DEMO blanket.

Three 12-mm thick 40% enriched 6Li2TiO3 layers with a thin F82H layer are set up between 50- and 100-mm thick layers of beryllium

Detectors (NE213)

T target

1372mm

SS316 source reflectorBe

120

0mm

350mm

630

mm

Part of the assembly and the target

C/E values for local TPR

Distance from the assembly surface (mm)

1st breeding layer

2nd 3rd

TPR

The calculation of local TPR is overestimation by 10% to 30%

Average1.21 Average1. 09Average1.12

DESIGN OF TBM NEUTRONICS EXPERIMENT (ENEA/TUD/FZK/JSI)

1. Design of mock-up, pre-analysis for measurements of the tritium production and nuclear heating

Helium Cooled Pebble Bed (HCPB) Concept

Beryllium

Breeder layers

TBM (HCPB) mock-up in front of FNG target

MCNP model of TBM mock-up

Pre-analysis

Calculation of neutron spectrum & comparison with Test Blanket Module in ITER• Calculation of background / optimisation of surrounding shielding • Calculation of total tritium production• Tritium production ratio and measurament feasibility• Nuclear heating

Surrounding shield (Be, steel,PE, optimised in order to produce the proper spectrum inside module)

Air

metallic beryllium (1.85 g/cm3)

breeder double layers Li2CO3 powder (7.5% 6Li, 2.3 g/cm3) thickness 1.2 cm separated by steel 1-mm-thick walls.  

rear ceramic block box AISI-316, dim. 31.0x12.7x31.0 cm3,Li2CO3 powder (7.5% 6Li, 2.3 g/cm3

Box of stainless steel (AISI-316) external dimension 31.0 cm (x) x 29.0 cm (y) x 31.0 cm

1.E+10

1.E+11

1.E+12

1.E+13

1.E+14

1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Energy (MeV)

Neu

tron

Flue

nce

(n/c

m2 )

Mock-up at 8.3 cm (norm.)

TBM at 3.4 - 5.4 cm

TBM at 5.4 - 8.4 cm

TBM at 8.4 - 11.4 cm

in beryllium

The International Comparison of Measuring Techniques, ICMT-2

• Goal: To measure TPR with an uncertainty not exceeding ± 5% for 3H activity level ~ 10 Bq/g

• Participants: 9 groups out of 7 countries, however only 7 groups out of 5 countries received the final results

• Experiments– Irradiation of the Li-containing pellets inside the cavity of lithium

assemblies (Li2O/FNS, Li/LOTUS) irradiated by D-T neutrons at: FNS and LOTUS

– Blind samples of water containing tritium

The goal was not met Standard deviation exceeds the deviation of 5% Agreement depends from the activity level Errors assigned by participants are not consisted with the

observations

Potential Errors Associated with TPR Measuring Techniques

• Triton escapes from boundaries of the pellet surface (recoil triton) during neutron irradiation

• Tritium releases from the pellet during irradiation• Retention of tritium in the pellet after irradiation• Tritium labile fraction, namely, the fraction of tritium that

goes into solution during pellet dissolution• Dissolving and counting procedures

All techniques suffer from a small systematic loss of tritium. In each case, the magnitude of these errors is impossible to predict and can be only be assigned

Tritium Escape Factor as a Function of Pellet Material and its Size (Ratio Surface/Volume)

0

2

4

6

8

10

5 10 15 20 25 30 35

Ratio S/V, rel. units

Triti

um e

scap

e fa

ctor

, %Li metalLi2CO3Li2O

Irradiation of lithium-containing pellet by thermal neutrons

Measured Tritium Production Rates for ICMT-2 (FNS Irradiation)

Only two organizations (JAERI and MEPhI) have the consistent results for all samples

2.5

3

3.5

4

4.5

5

5.5

1 2 3 4 5Sample number

TPR

, x10

-29 1

/Li a

tom

/neu

tron

Calcul.

AECL

CEA

IGA

MEPhI

OsakaU

TokyoU

JAERI

Calcul. Levelaccuracy ?

Minimal Errors Associated with the TPR Measuring Technique for Fusion Neutronics

Source of uncertaintySource of uncertainty Magnitude, %Magnitude, %Neutron yield 2Counting efficiency 1.5Lithium atoms 0.5Incomplete recovery of 3H 3Counting statistics 1Half life 0.2Irradiation, cooling, measuring 0.1Weight 0.5Total ~ 4

Benchmarking of experimental techniques for tritium measurement & assessment of uncertainties

(ENEA/TUD/JAERI) Objective

Reduce uncertainties in TPR measurements

Collaboration between ENEA, JAERI and TUD established

HTO samples with different specific activities are prepared by each group: 1/3 samples are measured in the laboratory of origin, the other samples sent to the other laboratories check the calibration

(in progress, close tocompletion)

Li2CO3 pellets (starting with pellets enriched in Li-7, all prepared by JAERI) will be irradiated at each laboratory in a pure 14 MeV neutron field. 1/3 pellets are measured on site, the remaining two sets, 1/3 each, sent to the other laboratories (next step)