J. Plasma Fusion Res. SERIES, Vol.5 (2002) 565-569 Blanket Experiments Using Enriched Li2Tior/Ferritic Steel/ Beryllium Assemblies and D-T Fusion Neutrons KLIX Axel, OCHIAI Kentaro, SATO Satoshi, TERADA Yasuaki, MORIMOTO Yuichi, HORI Jun-ichi, YAMAUCHI Michinori, WADA Masayuki and NISHITANI Takeo Fusion Neutron Laboratory, Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka 319-1195, Japan (Received: 12 December 2001 | Accepted: l0 July 2002) Abstract At Fusion Neutronics Source (FNS), we have done experiments with thermal-type breeding blanket mock-rrps using lithium titanate as breeder material, beryllium as neutron multiplier, and reduced activat on ferritic steel F82H simulating structural material. The objective of the experiments is the neutronics performance evaluation of candidate materials for fusion reactor designs as well as the validation of neutron transport code and available neutron data libraries for these materials. A method for the dirr:ct measurement of the produced tritium based on liquids cintillation counting was developed. The activation of chromium, tungsten, and iron in F82H steel and titanium in lithium titanate was measured. Keywords: advanced breeder material, lithium titanate, thermal blanket, tritium breeding ratio 1. Introduction experiments with thermal-type blanket models including A sufficient tritium production of the breeding lithium titanate and D-T fusion neutrons are currently blanket is of <:rucial importance for the operation of a performed at Fusion Neutronics Source (FNS) of fusion reacto:'. Materials for recent designs for the JAERI. Preliminary MCNP calculations suggested a 6Li fusion DEMO reactor blanket include beryllium, 6Li- enrichment above 40Vo in order to obtain sufficient high enriched Li2f iO3 ceramics and reduced activation tritium production rates (TPR). The use of F82H steel ferritic steels (F82H: Cr 8Vo,W 2Vo, Fe balance). The will decrease the TPR due to the presence of tungsten. cross section for the important tritium-producing The reaction t86W(n,/) r87W causes absorption of reaction in th,:se thermal-type blankets. 6Li(n.a)T, is thermal neutrons needed for tritium breeding. very high at thermal and subthermal neutron energies. We have been measuring material activation of Therefore the fraction of those neutrons as well as their chromium, tungsten, iron, and titanate as well as the flux should t'e as high as possible in the breeding tritium production in breeding assemblies containing material. one layer of Li2TiO3 with a 6Li enrichment of 95Vo and Berylliunr acts as neutron multiplier and moderator 40Vo. The tritium production measurement was done for fast neutrons. Irradiation experiments with using liquid scintillation counting techniques. The beryllium-connining assemblies have been carried out, experimentally obtained tritium production and see for example []. However, these assemblies never activation of chromium and tungsten agreed well with included lithium titanat€. Therefore irradiation @20O2 by The Japan Society of Plasma Science and Nuclear Fusion Research 565 Klix A. et al., Blanket Experiments Using Enriched LiTiOr/Ferritic SteeVBeryllium Assemblies and D-T Fusion Neutrons MCNP [2] calculations using ENDF/B-VI [3] and neutron source was 200 mm away from the first steel saFe JENDL3.2 [4] nuclear data files, whereas showed a layer. The layer arrangements used in the experiments C/E ratio of about 1.2. are shown in Table 1. For the results presented here the We obtained a tritium production profile as one total source neutron yield was about 1016 neutrons per would expect for a thermal blanket, i.e., the tritium experiment. It was monitored by two solid-state a - production decreases with increasing distance from the detectors for the D-T reaction. sudace of the breeding layer due to self-shielding. 2. Experimental Setup The blanket neutronics experiments have been carried out at FNS using its 80 degree target which can FNS 80 deg. line supply up to 4*l0rr D-T neutrons per second. Three TiT target different arrangements of layers of F82H steel, \ beryllium, and lithium titanate ceramics were used, Fig. I shows one arrangement as example. Neutron fluence verification was done by means of activation foils located on the beam axis between each layer. Lithium titanate blocks of 50 mm x 50 mm x 12 mm forming a layer of 12 mm thickness were used as breeding material. To obtain the tritium production in the layer, pellets of lithium titanate with the same 6Li concentration and a size of 12 mm diameter and 2 mm \ F82H sheet(t= 1.0) thickness were inserted into a bore in one of the lithium ', 16 ,, 72 ,1 F82H sheet titanate blocks, see also Fig. 1. Six pellets fit into the (t = 1.6) bore and allowed to obtain the longitudinal tritium production distribution with a resolution of 2 mm. The pellets were 35 mm off the beam axis. The titanate block canying the pellets was wrapped in aluminum foil to suppress contamination. For the metal activation measurement, sheets of F82H steel of 1.6 mm and 1.0 mm thickness and a size Beryllium of 50 mm x 50 mm were inserted into the F82H layers. Li2Tio3 The total size of the blanket assembly was 1000 surrounded by BoC mm x 1000 mm with a thickness of 500 mm including Fig. 1 Cross sectional view of one of the assemblies. an outer layer of lithium carbonate to shield the Three different layer arrangements were used, assembly from room-returned neutrons. The D-T see Table 1 for details. Table 1 The layer arrangements and thicknesses used in the experiments. Zeroes mean the layer was not present, see also Fig. 1. All thicknesses in mm. Breeding layer Exp. Layer thickness in mm 6Li enrichement # F82H Be F82H Li2TiO3 F82H Be 95% 1 0016123200 2 0016129200 3 16503129150 40o/o 4 0016123200 5 16503129150 566 Klix A. et al., Blanket Experiments Using Enriched LirTiO,/Fenitic Steel./Beryllium Assemblies and D-T Fusion Neutrons 3. Experimental Results q uLi 3.1 Tritium sample preparation f 2.orl03 95% enriched -9a The tritiurn production was measured by means of liquid scintillation counting (LSC) of the accumulated = 1.sxlO{ tritium activity pellets. o in the The electrons emitted d during the deci'y of the tritium nucleus have a maximum o 1.oxl03 o energy of 18 with a range a few pm o leV of in liquids E and solids. Thtrrefore it is necessary to bring the tritium o 5.orlo' into close contitct with a scintillator. The lithium titanate pellets were dissolved in concentrated hydrochloric acid. 12 3456 Sn = Source neutron Pellet number The low pH value of the solution caused incompatibility with the used scintillator so that the solution was neutralized with sodium hydroxide before incorporation into the liquid scintillation cocktail. The current accuracy of tht: method is estimated to be 107o. Further validation is in progress, especially during the current series of expeliments we will obtain TPR values also from lithium carbonate detectors for which a well established trertment already exists, see for example [5]. 123456 Pellel numbet 3.2 Tritium production Fig. 2 Experimentally obtained tritium production rate Experime ttally obtained TPR values in 95Ea 6Li compare to MCNP calculations from experiment '1. enriched lithiurn titanate sandwiched between F82H and 3, see Table beryllium (experiment 3, Table 1) are presented in Fig. 2. The sp.atial resolution was 2 mm. The tritium distribution in the layer is characteristic for a BLi thermal- 95% enriched with type blanket. l'he tritium concentration decreases with 10. increasing distirnce from the surface inside the breeding IIJ layer. That is caused by a strong shielding effect due to . 10{ the very high cross section for the reaction 6Li1n,a)T at low neutron energies. tr ir. The neutron spectrum is depleted 14 ro" in slow neutr)ns inside the layer. Figure 3 shows calculated TPI{ spectra inside the layer and near the Fo i:: \ F 10' surface to illustrate this effect. : Psll€ts n@r the b€ry'lium layer r@ire a highq traction of 3low neuhs ins@ing It was also noted that the TPRs in all six pellets in the tdtum pfddion from \i experiment 2 were slightly lower than the corresponding 10" 1o! 10' 1ot 10" 1oo TPRs experiment of I indicating depletion of thermal ilev (incident neutron) and subthermal neutrons in the spectrum by F82H. Fig. 3 Calculated TPR spectrum of two pellets in the as- 3.3 Activation of titanium sembly illustrating the shielding effect in the breeding layer. Pellet 6 is near the surface. pellet 3 The measured activation of titanium is mainly is inside the layer. caused by (n,p) and (n,np) reactions, the product is scandium. Thr:se reactions are threshold reactions. Verification c,f the cross section of the reactions Their half-life time is 83.8, 3.4, and 1.82 days, re- 46Ti1n,p146Sc aTTi(n,np)46Sc :Lnd at neutron energies spectively. The activation of titanium could impose a around 14 MeV can be found for example in ref. [6]. major source of background noise for the LSC tritium The mear;urement was done two days after measurement because its activity is higher than that of irradiation, the'efore isotopes with a short lifetime had the tritium. However, the obtained tritium spectra do not already decayed. Three isotopes of scandium, 46, 47, show a significant gamma background. That indicates and 48, were lound by 7-spectroscopy of the pellets. that the scandium isotopes are not in solution despite s67 KIix A. et al., Blanket Experiments Using Enriched LirTiO3/Ferritic SteeVBeryllium Assemblies and D-T Fusion Neutrons *sc of c) E5 Eto' to" (! $6 gtr otr oc +tFeexp o o -Fe c ro' calc .9 E(! -* E *t' o +'*Wexp gB g t *r'*w calc E to" '*$'t F o "'Cr exp -o- u'cr ct -c- calc 2m 4(n 6(x) gn l(m rzm 1rO0 1oo Sn=SUr@ neUIrOn kev 468 Sheet number 1.4 Eltr tr I !t I I 1.2 1.0 t tr ul o 0.8 o r.o I JENDL3.2 0.6 tr ENDF/B.VI 0 2(D '100 600 8m 1m0 1200 1400 024681012 keV Sheet number Fig.