" 99 . JUL 2 ' 1968 OAK RIDGE NATIONAL LABORATORY operated by ’ UNION CARBIDE CORPORATION m NUCLEAR DIVISION for the U.S. ATOMIC ENERGY COMMISSION ORNL- TM- 2238 A PROTON REACTION ANALYSIS FOR LITHIUM AND FLUCRINE IN GRAPHITE, USING A SLIT SCANNING TECHNIQUE R. L. Macklin, J. H. Gibbons, and T. H. Handley NOTICE This document contains information of a preliminary nature and was prepared primarily for internal use at the Ock Ridge National Laboratory. It is subject to revision or correction and therefore does not represent o final report. O TRIBUTION OF THIS OOCUMENS {3 UNLIMITED I LEGAL NOTICE —- — 1 i This report was prepared as on account of Government sponsored work. Neither the United States, I nor tha Commission, nor any person acting on behalf of the Commission: i A. Makes any warranty or representation, expressed or implied, with respect to the accuracy, | completeness, or usefulness of the information contained in this report, or that the use of ! any information, apparatus, methed, or process disclosed in this report may not infringe " privately owned rights; or B, Assumes any [jabilities with respect to the use of, or for domages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, '‘person acting on behelf of the Commission’’ includes any employee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or praovides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. ORNL- TM-2238 Contract No. W-T405-eng-26 Physics Division PROTON REACTION ANALYSIS FOR LITHIUM AND FIOURINE IN GRAPHITE, USING A SLIT SCANNING TECHNIQUE R. L. Macklin, J. H. Gibbons, and T. H. Handley JULY 1968 OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee Operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION This report was prepared as an account of Government sponsored work, Neither the United States, nor the Comminsion, nor any peracn aclting on behalf of the Commiseion: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, completeneas, or usefulnesa of the Information contajned in this report, or that the use of any information, apperatus, method, or process disclosed i this report may not infringe privaieiy owned rights; ar B, Assumes any liabilities with reapect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, ‘‘person acting on behalf of the Commissaion’’ includes any em- ployee or contractor of the Commdission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any Information pursuant to his employment or contract with the Commission, ¢r his employment with such contractor. R i ko ¢ PRI OPCRELE I S uflu e s a® e iii CONTENTS Abstract . . . . .+ . o . . . Introduction . Method and Apparatus Standards .+ ¢+ v e e 0 e e e e Sample . Results and Discussion . Microscopic Examination of Sample References . . . « + « + & o = w w w PROTON REACTION ANALYSIS FOR LITHIUM AND FLUORINE IN GRAPHITE, USING A SLIT SCANNING TECHENIQUE R. L. Macklin, J. H. Gibbons, and T. H. Handley ABSTRACT Protons from the ORNL 3 MV Van de Graaff accelerator were brought to a line focus and collimated thru slits of either 0.025 or 0.0075 cm. Cross sectional cuts of graphite samples were moved across the beam to study the distribution of ILi and F with depth by measuring the yields of neutrons and of gamma rays from the reactions TLi(p,n) and *9F(p,ay). A graphite sample exposed to molten fluorides in a loop experiment at the Oak Ridge Research Reactor showed about 20 and 100 ppm (by weight) Ii and F respectively, 2 mm below the exposed surface. The observed ratio of ILi to F was close to that characteristic of the molten salt down to 3 mm below the exposed surface. INTRODUCTION The proton induced reactions TLi(p,n) and l9F(p,ay) have been used to measure the concentration of the target nuclides in graphite.l This can be done in the presence of considerable radiocactivity from fission products, making the method attractive for studies of penetra- tion in graphite moderated molten salt reactors.2 In the previous workl, the exposed surface of a sample was ground away a layer at a time and the concentrations near each freshly exposed surface measured with a 0.32 cm diameter, 0.1-1 microampere proton beam. This process required special handliing for the radioactive material ground off and introduced considerable delay in the measurements. METHOD AND APPARATUS The ORNL 3 MV Van de Graaff accelerator proton beam is normally focussed to a ~ 1 mm diameter spot at the target with a magnetic quadrupole strong focus lens. By deliberately detuning this lens the beam can be brought to a horizontal (or vertical) line focus about 1.0 x 0.08 cm. By using several microamperes of current and a metal slit, sufficient beam could be passed through to a sample to perform the analysis over an area 0.0075 cm x 0.60 cm, or with better sensitivity (compared with background from F impurities in the slit collimator material) 0.025 cm x 0.60 cm. With this arrangement, a sample exposed in a reactor can be sectioned, cutting perpendicular to an exposed face TLi and 19F with depth studied by simply moving and the distribution of the sample across the proton beam. The apparatus we used for this is indicated schematically in Fig. 1. The graphite sample was mounted on a micrometer head and moved in to intercept the beam. The proton beam passing the sample induced a blue fluorescence in the quartz viewing plate at the left sc the point at which the edge of the sample just intercepted all of the protons could be easily noted. The profile of the beam passing through the slit was measured with a 0.005 cm Al foil glued to the end of the graphite blank. Figures 2 and 3 show the 27A1(p,y) yield from this foil using 0.025 cm and 0.0075 cm gold slits respectively. ©Slits of tantalum showed too much contamination with fluorine. The slight asymmetry of the scans is probably due to a few protons striking the exposed face of the Al foil rather than the edge as the blank sample was pulled up out of the beam. -3 - Gemma rays were detected by a 12.5 cm dia. x 17.5 cm long NaI(T1l) crystal through a 1.25 cm lead filter at the side of the sample housing. Neutrons were detected in the straight ahead position as in reference (1). As the graphite blank sample could readily be brought into the beam to check the background withcout dismounting the sample, we used 2.06 MeV protons (just below the 9Be(p,n) threshold) throfighcut, rather than dropping the energy below the TLi(p,n) threshold (1.88 MeV) to check background. STANDARDS Pressed samples of graphite powder containing weighed quantities T of 'ILiF were used as standards. SAMPLE The sample studied was taken from a molten salt convection loop exposed in the Oak Ridge Research Reactor (ORR) last year.3 The piece available for study is shown in Fig. 4 (ORNL Slide No. T42L45). The straightest side shown is the wall of a molten salt exit channel sectioned axially after exposure. The proton beam was centered along this surface, as nearly parallel to it as its irregularities would 19 permit. The reactor exposure history of the sample included over 10 235 fast neutrons per square centimeter (79% of it with U bearing molten salt) and a cracked outlet pipe with consequent air contamination. RESULTS AND DISCUSSION The homogeneity of the standards was disappointing. ©Scans of original and freshly cut surfaces showed considerable variability. The standard deviation at a single proton beam position appeared to be about L. 35%. An uncertainty of that size is indicated for the absolute scales of concentration. The standardization was, however, based on the grand average of all our measurements on the 200 ppm (TLiF by weight) stan- dard. Until more uniform standards are available or the cause of the observed nonuniformity is better understood, we hesitate to claim greater accuracy for the concentration scale. The fluorine and lithium concentrations in the sample as a function of distance from the flow channel surface are shown in Figs. 5 and 6. The rapid decrease in concentration in the first ten mils or so (0.025 cm) is expected. The persistence of moderate concentrations to much greater depths is puzzling. Figure 7 shows the ratio of F to Li concentration. The ratio is persistently near the ratio characteristic of the molten salt mixture rather than that for the LiF molecule or the progressively lower values expected for free ionic diffusion. It has been suggestedlF that the bulk of the material seen at depth may repre- sent liquid phase intrusion via a slant crack. It should be noted that the promotion of graphite wetting by the air contamination experienced in the ORR Loop should make smaller cracks than usual effective in this regard. MICROSCOPIC EXAMINATION OF SAMPLE The graphite sample was viewed (x 10 and x 20 magnification) with a binocular microscope. The surface is relatively quite rough, with saw markings a few thousandths of an inch deep and pock-marked with many voids several thousandths of an inch in diameter. There is evidence of at least one long groove or crack in the sample at about 20° inclination to the exposed surface. The surface is also irregularly -5 - discolored, reminiscent of differential heating effects. When wetted with acetone numerous bubbles rose to the surface, clearly implying penetration of the liquid into sub-surface voids. In short, this sample shows gross irregularities and imperfections compared to the sample taken from the MSRE that we studied earlier‘.:L -6 - REFERENCES R. L. Macklin, J. H. Gibbons, E. Ricci, T. Handley, and D. Cuneo, to be published in Nuclear Applications. H. G. MacPherson, Power Engineering, January, 1967, p. 2-8. Molten-Salt Reactor Program Semiannual Progress Report for Period Ending August 31, 1967. ORNL-4191, Part 15. E. G. Bohlmann, private communication. Fig. 1 - Fig. 2 - Fig. 3 - Fig. L4 - Fig. 5 - Fig. 6 - -7 - FIGURE CAPTIONS Schematic side view of the scanning system. The graphite sample (from a specimen exposed to molten salts containing TLi and lgF) is cut so that the exposed surface is uppermost in the TLi(p,n) and lgF(p,ay) yields indicate concentration figure. The as a function of depth as the sample 1s moved up across the collimated proton beam. Proton beam profile using the .025 cm slit-collimator as measured by the 27Al(p,y) reaction yield from a .005 cm Al foil seen edge-on. The small random deviation of the points from the curve is largely an indication of mechanical precision and reproducibility in the experiment (about 0.0003 cm). Proton beam profile for the .0075 cm slit-collimator measured using the .005 cm Al foil. At the left the beam is hitting clean graphite, whereas at the right it can graze tangentially the flat face of the Al foil (see Fig. 1) producing a slight tail in the composite resolution function shown. Location and orientation of the sample cut from the 1967 ORR Loop Specimen. The molten salt flow was largely upwards through the drilled hcles and channels shown in the photograph. Fluorine concentration as a function of depth in the ORR Loop graphite sample. The data taken at two slit widths are self- consistent. The results cannot be accounted for by simple ionic diffusion and may reflect non-homogeneous structure of the graphite. Lithium concentration as a function of depth in the ORR Loop graphite sample. The data obtained with the two slit-collimators -8 - are self-consistent. The lithium concentration beyond 10C mils depth decreases more rapidly than expected. Fig. 7 - Mass concentration ratio, F/Li, versus depth. The closeness of the ratio observed to that typical of the bulk salt suggests that most of the material found (at depths down to 30 milg) may represent a liquid intrusion. ORNL-DWG 6€8-6554 MICROMETER DRIVE MOUNT CLEAN GRAPHITE FOR BACKGROUND CHECK 0.005cm Al FOIL FOR SCANNING BEAM PROFILE W GAMMA RAYS 7 ¥ CONVERGING --— PROTON BEAM ‘/‘% NEUTRONS |, \ S 0.0075 x 0.60 ¢cm COLLIMATING SLIT t SAMPLE TO BE SCANNED MICROMETER DRIVE MOUNT QUARTZ PLATE FOR VISUAL ALIGNMENT Fig. 1 RELATIVE COUNT RATE - 10 - ORNL-DWG 68-6552 6000 | 9 mils L 5000 e - / 17 4000 7 e / \0 ' \ 2000 ,// 9 ® / FWHM 9.9 mils \ 2000 / /. \ 1000 //J N O .....__--_‘.L/_ ...._‘1_ —— —p— —— — EfiCfiRQPN_D o — . e _-_\_.3-. 40 42 44 46 48 50 52 54 56 58 60 DISTANCE (mits) Fig. 2 RELATIVE COUNT RATE - 11 - ORNL-DOWG 68-6553 10,000 8000 N, 6000 // \\ ¢ ® 4000 / \\ / " ® . 2000 N N, 0 e @ e o e e e — e e —— __\ S —— 14 16 18 20 22 24 26 28 DISTANCE (mils) Fig. 3 - 12 - ORNL-DWG 68-6736 SURFACES OF MOLTEN SALT FLOW CHANNELS CROSS SECTIONAL SURFACE CUT AFTER EXPOSURE PROTON BEAM POSITIONS AT VARIOUS DISTANCES FROM EXPOSED SURFACE 3 PROTON BEAM - 13 - ORNL-DWG 68-6556 {0,000 5000 ® {O-mil SLIT °© 3-mil SLIT 2000 1000 500 200 O+ 359% (ppm) 100 |- 50 20 {0 ' { 2 5 10 20 50 100 200 500 DEPTH BELOW SURFACE (mils) Fig. S {000 500 - 14 - ORNL-DWG 68-6554 o {0-mil SLIT o 3-mil SLIT 5 {0 20 50 {00 200 500 DEPTH BELOW SURFACE (mils) Fig. 6 - 15 - ORNL-OWG 68-6555 1000 500 o {0-mil SLIT e 3-mil SLIT 200 100 50 9 /7Li RATIO 10 FOR FUEL SALT RATIO FOR LiF i 2 - S 10 20 50 100 200 500 1000 DEPTH BELOW SURFACE (mils) Fig. T \O Co—1 O\ WD O RN REYR PN E NN Y I, SN NN N E I E YRR R E G R n t"‘t"l?:l"df.'lg _z:.z.o_r't.:fl?q:ngwzm?umwuwg:mmw@mmhjmmrxmw U)E?H?Ut*jc-ll—‘ . Weinberg MacPherson . Wigner . Boyd . Fowler . Compere Evans, III Wechsler Holmes Kirslis Cuneo Blankenship Cook Lyon Kelley iced Handley Bettis Bohlmann Briggs . Ditto . Eatherly . Ferguson Grimes . Grindell . Haubenreich . Kasten MacPherson McDuffie McCoy Moore Nicholson Oakes Perry Rosenthal ap Scott Skinner Thoma Weir . Whatley White . Billington - 17 - DISTRIBUTION k748, 49, ORNL-TM-2238 Central Research Library Document Reference Section Laboratory Records Department Laboratory Records, ORNL R.C. ORNL Patent Office DTIE Laboratory and Unlversity Division, ORO R. L. Macklin