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Report No ..UNCLASSIFIED *■’ Rm c Wm - Sp*<uU F««tvrf« of Nivil KticUirt (M- 1679, Jlrd Ed ) ( MHHltii WOMt «k| m RADIATION EFFECTS ON BORON-CONTAINING COMPOUNDS by Donald J. Hamman Paul Schell \-JC 1$ ±Ji. i lkfc^ L.nso». **• u January 6, I960 RESTRICTED DATA - Thu document 4au m in the Atomic fneegy Act of U6*. UUl ot 4l»rfc*urc of lu content! in any iQtuittt uthovlMd porton u pcahibltrU. 4 BATTELLE MEMORIAL INSTITUTE 505 King Avenue Ceilumbu« 1, Ohio confidential • • • • • UNCIASSIFIFD •• •• • 0• I • •m • • • e • CONFIDENTIAL Jane! 4 TABLE O f CONTENTS Page ABSTRACT................................................................................................................................... 5 INTRODUCTION......................................................................................................... 5 EXPERIMENTAL PR O C E D U R E S...................................................................................... 5 Selection of Materials ................................................................................................. 5 Irradiation C onditions................................................................................................. S Prcirradiatlon and Poatlrradiation Examinations .............................................. IS R E SU L T S.................................................................................................................................. 16 Helium R e l e a s e ................................................................................................ 16 Motallographic E xam ination..................................................................................... 21 CONCLUSIONS...................................................................................................................... 25 R E F E R E N C E S ........................................................................................................... 25 CONFIDENTIAL • • •• t e es CONFIDENTIAL 5 RADIATION EFFECTS ON BORON CONTAINING COMPOUNDS Don*Id J. H inunin and Paul Schall f /ruMlW rarkide. aud iifrMUM dihartde were irradiated at reaetor amtuent lemprraiurt (ISO F t mud elevated Irmprrulurt a (MO to ?S0 F) to kmmafi r « |M | /»©» 20 to 95 per rial • / lAr boreulO iaatmpa /irrM im dtkmtide toaiainiug hath MtorW m W enriched ametMt af baron JO «hm evaluated The amount of helium releeued during irradiate* mo* mtaruttd, and X-eay diffractio*. mtialloftapkic, mod tkamtrmi eiamtaaitoai va n for form od hath kaforr amd after irradiation. 7ir tout urn dtbonde root atuiug natural hotou appeared to be tke mo*t p ro w 1*4 material from a keliumreteuho* il—dpomt. hone of tke material* eakikited a*ee atioe par heir fragmentation or dimeuaionml tkaugea dunug ike taur*e of ike etpenment* even though there mas evidente of temperature* math higher than dettgu cord it tout \ . INTRODUCTION Since helium ie produced during the irradiation of boron, the ability of the mate rial to retain this helium it of prime importance. Also important are the dlmon- •ional stability and all other properties consistent with reactor operating conditions. The program reported here on boron-containing compound* was fr>ng oT several to aesistjfhrknolls Atomic ^ower Laboratory )in the selection of alternate control ma- teriaUJand was supported by the Naval Reactor Branch of the United States Atomic) i Energy Commission* In the program, elemental boron, boron carbide, and airconium cfrWride were irradiated in the MTR at reactor ambient temperature (150 F) and elevated temperatures (500 to 750 F) to burnupe ranging from 20 to 95 per cent of the boron-10 isotope. Two capsules containing hafnium diboride are etill under irradiatiot at the ETR. EXPERIMENTAL PROCEDURES Selection of Materials The material# used for this program were powdere of known meeh site. This form was chosen to eliminate limitations imposed by dispersions,• compacts, etc., or specific geometries of control-rod construction. Selection of the materials to be studied during the program wss based on several factors. First, they were chosen to be representative of the most likely forms of CONFIDENTIAL L CONFIDENTIAL $ t>oron-containing material* which would bo confide rod (or control malarial* on tha bant of chemical and physical pro partial, The malarial* **iactad w*r* alamantal boron, boron carblda, and matal boride* of both th* diboride and hexaborid* typ**, Other m aul boride* such *• tha monoboridei, tstraborldes, and dodecaboridea are known but ar* usually harder to prapara and ara relatively unstable compared with the diboride* and hexaboridas. Tha matal borides selected were alrconlum and hafnium diboride* and dysprosium and europium Hexaborides. Of these materials, data have bean obtained only on the slrconiuin diboride. The hafnium diboride is currently being irradiated, and effort on the hexaborides hae been limited to preparation of eetiefactory materials. Several different crystal structures are represented by the materials selected for thie program. The elemental boron is known to exist in an amorphous gftjjf™ end in two (hexagonal and tetragonal) crystalline states^). Therefore, boron might undergo changes in either crystal structure or degree of crysUllinlty during irradiation as the result of displacements of boron atoms and the production of lithium and helium. How ever, boron is quits stable over a wide range of lattice imperfections, and this property may denote reasonably good radiation stability. Preliminary experiments indicated that boron carbide was between elemental boron and the metal boridee with respect to expected structural radiation stability. The D4C crystal^) structure or B ^C ) consists of a linear chain of 3 carbon atoms with 12 boron at^ms at the points of a nearly regular icosahedron and tha whole arranged in * a rhombohedral structure. The matal diboridee and metal hexaborides normally have separate and distinct * crystalline structures of good stability. The two tyjpee of structure vary considerably. The diboride* have a primitive hexagonal structured similar to graphite in that they are layered with the boron and metal forming alternate layers. Th* hexaborid*• form a complex structured in which the six boron atoms are at the points of a regular octahedron, and each octahedron i* linked to six other octahadra, forming s continuous network of cubic symmetry with the metal atoms In the interstices. Radiation-stability differences are suggested by the large volume of the hexaborid# octahedra, which may effectively contain the lithium or helium atoms. If there are dimensional changes in the crystal structure, they would be expected to be anisotropic in the case of the dl- borides and isotropic in the hexaborides. Nuclear properties were also considered In the selection of the compounds to be studied. Elemental boron has an absorption cross section of 750 barns for the neu trons having a velocity of 2200 m per sec, and, being a 1/V absorber, ie effective over a fairly wide neutron-energy range. By using a compound of boron in which the second component la also a strong absorber, especially in th-, resonance-energy region, its effectivsness as a control material can be significantly improved. On this basis hafnium diboride was selected, and tho hexaborides chossn were those of dysprosium and europium. The results obtained for several boron-containing materials on helium release during irradiation and during postirradiation heat treatment and on structural stability (1) Reference! it end of text. CONFIDENTIAL • • ... • 1*. « .* • • • • • • . r • • • • • . • • • • • •. • •... • • • .«• >* ...... • • * ■ 1 « . • ...• • . • »| . • • • • . ■ .. CONFIDENTIAL T « • w a te r mined by meuUo graphic examination and X-ray diffraction arc presented in the following diacusaion. The experimental program consisted oI tha irradiation of two aariaa of c epaulet fiat TabU 1) and pra irradiation and pot tir radiation a nomination a. Thar a war a ala capsules in tha fir at aariaa with two aach containing alamantal boron, boron carbide, and airconium diborida. Tha aacond tarlaa conaiatad of two capaulaa of airconiiam diborida containing natural boron, ona capaula of airconium diborida conUlating boron anrichad SO par cant in tha boron-10 taotopa, and ona of boron carbida containing natural boron. TABLE l . LIST OF CAPSULES Number Target Design of Boron Temperature, Cycles Where Burnup, Capsule C o n te n ts^ F Irradiated ]Irradiated per cent Thermocouple BMI-7-1 B(N) ISO 1 MTR 70 No HMI-7-2 B(N ) ISO ) MTR 90 No BMI-7-J Z rB 2 (N) 150 1 MTR 70 No BMI-7-4 Z rB 2 (N) 150 1 MTR 90 No 11 MI-7-5 B4C (N) 150 1 MTR 70 No BMl-7-6 B4C (N) ISO 1 MTR 90 No BMI-7-14 Z rB 2 (N) 150 a MTR SO No BM1-7-15 Z rB 2 (E) 500-750 16 MTR 60 Yea BMI-7-16 Z rB 2 (N) 500-750 19 MTR 80 No BM1-7-17 b 4c (N) 500-750 20 MTR so No BMI-7-20 HfB2 (E) 500-750 19(h) ETR 90 Yea BMI-7-21 HfB2 (N) 500-750 19(b) ETR 90 No (a) (N) denote I natural baton, (t) denote! boron enriched in the baon-10 tiotope. (b) There ceptulci are m il being Inaduud. The aeriaa of six capaulaa was intended to provide data on tha comparative radia tion stability of tha three material*, and the aariaa of four waa intended to provide more complete data on tha stability during irradiation at elevated temperatures of boron carbide and airconium diborida. In addition to theae there are two capsules of hafnium diboride, one containing natural boron and the other containing boron enriched to SS. 6 per cant in the boron-10 isotope, being irradiated in the ETR. , CONFIDENTIAL co*ru>t>nt t trro4l*«un»