Ford Nuclear Reactor Phoenix Memorial Laboratory ‘I,H_L UN.LVI JTY NIEA1 IE’rcEcJF,‘rcM?VMTcDHLCAN U1’EILAV I1’VI EW Third Year, No. 9 North Campus Winter, 1989 2301 Bonisteel Boulevard Ann Arbor, Michigan 48109-2100 The Nuclear Reactor Laboratory Quarterly Review is published and distributed to University of Michigan faculty and staff members to inform them of the unique research capabilities of the Nuclear Reactor Laboratory and of the types of research in progress. Research projects started within the preceding quarter ar& listed first. A feature article that provides in-depth information about one particular technique or program follows. Updated descriptions of the remaining Nuclear Reactor Laboratory programs complete the Quarterly Review. FORD NUCLEAR REACTOR Nuclear Engineering Professor David K. Wehe and a graduate student, Tim DeVol, irradiated a small cobalt source to be utilized with a gamma camera. The gamma camera produces images from gamma rays emitted by radioactive materials. The researchers wanted a relatively pure source of cobalt to test the sensitivity of the camera to the specific gamma rays emitted by cobalt-60, 1.17 MeV and 1.33 rleV. As part of an undergraduate thesis entitled, “Cross Section of Yttrium—89”, George Piccard irradiated a one—inch diameter yttrium foil enclosed in cadmium. The cadmium reduces thermal activation by absorbing thermal neutrons before they reach the foil. Epithermal and fast neutrons produce yttrium—90 from yttrium-89. Professor Glenn F. Knoll is the thesis advisor. Page 1 The University of Michigan Nuclear Reactor Laboratory Quarterly Review Winter 1990 NEU’I’RON ACTIVATION ANALYSIS Chemistry Professor Adon A. Gordus and a graduate student assistant, Steve Roeder, have been utilizing neutron activation analysis at the reactor for forensic studies related to criminal cases. The objective of the studies is to detect gunpowder residue on the hands of individuals who are believed to have fired guns. Cotton swabs moistened with a few drops of nitric acid are applied to a suspect’s hands. The swabs are irradiated in the reactor. Following a short irradiation, they are analyzed for barium and antimony, both of which are present in gunpowder and would not normally be found on human skin in significant amounts. Chemical separation is utilized to remove radioisotopes other than barium and antimony to inprove levels of detection. Geological Sciences Professor Ben A. Van Der Pluijm is utilizing neutron activation analysis for elemental analysis of Paleozoic rock from the northern Appalachian mountains. He is particularly interested in the elements: yttrium, vanadium, titanium, and zirconium. Professor Samuel B. Mukasa is analyzing lava flows from Taiwan and the Philippine Islands using neutron activation analysis. He is looking at trace elements, and particularly rare earth elements, to determine the origins of the lavas. c0BALT-60 IRRADIATION SOURCE Electrical Engineering and Computer Science Professor Doreen A. Weinberger and an undergraduate student, Jeff Chu, have irradiated optical fibers to various gamma doses in order to induce defects in the fibers. Light frequency shifts have been observed in optical fibers which are thought to be caused by physical defects. Inducing defects with radiation may assist in understanding the mechanisms of the light shifts. Initial irradiations were conducted in the reactor with combined neutron and gamma ray fluxes, but the researchers have settled on use of the cobalt—60 gamma source for their work. University Hospital - Radiation Oncology Dr. Frances A. Farley utilizes the cobalt-60 irradiator to sterilize fresh, frozen, distal femur allographs for use as surgical implants. Page 2 The University of Michigan Nuclear Reactor Laboratory Quarterly Review - Winter 1990 IEV1’1Ji?.E A&?T I(LJi 1?.AD IA.1 IC)N DAM.AGL S_rUDIE FXJL NLJCL4FAJ IcWEI E1’3I 4EA[ A’r ‘ri-ii N UCL I?EAC’TcE LKk?AUc*W Introduction ‘I’wo long—term, accelerated, radiation damage studies are in progress at the Ford Nuclear Reactor. The first involves neutron and gamma irradiation of neutron shielding material test specimens for Westinghouse. The second is a reactor vessel steel damage study being conducted for Hattelle Columbus Laboratories. Damage from fast neutrons is the primary interest in the Battelle program. Ford Nuclear Reactor Irradiation Facilities The Ford Nuclear Reactor is a 2 Mw, open—pool, research reactor. The core is configured from rectangular, plate-type fuel elements placed vertically in an aluminum grid as shown in Figure 1 submerged e3.1 meters (20 feet) below the pool surface. An experiment grid is positioned adjacent to the south face of the reactor core for precise placement of sampleB and specimens for irradiation. Experiment grid locations 20A and 20C are committed to neutron activation analysis. Locations 40A, 50A, 60A, and 70A were used for the long-term reactor vessel steel damage study for Battelle Columbus Laboratories. Westinghouse neutron shield material specimens are being irradiated in irradiation capsules located in position 80A and rows C and D in the left half of the experiment grid. Approximate neutron fluxes and gamma dose rates in the irradiation locations range between the following maximums and minimums. Flux and Dose Rate Maximum Minimum Thermal Neutron, 2/s 0 n/cm (E<0.55 2 OOxlO’ eV) 5.OOxlO’ 5. Fast Neutron, 2 2 0 n/cm (E>1.0 1 .OOxlO’ /s MeV) 1. 25x10 3 Gamma Rays, (Eav:1.0 MeV) 1 00x10 6 rad/hr 5. 5. 00x10 ‘.J. Page 3 ‘Ihe University of Michigan Nuclear Reactor Laboratory Quarterly Review Winter 1990 Westinghouse Test Program Specimens of seven neutron shielding materials, six solid and one powder, are being irradiated for Westinghouse at controlled temperatures of 66, 149, 204, and 260 O (150, 300, ° 400, and 500 F) . Each ?r Por solid specimen is tOgH Ran1 L...1 Ring. * nominally 0.64 centimeters ton OaaO.ri (0.25 inches) x 2.54 centimeters (1.0 inch) 0 x 15.24 centimeters (6.0 inches) long. The Nggron powder material was HEAVY WAXER loaded into thin aluminum tAN! containers of the same Rid0tograp6v overall dimensions. The Fsct1iy attached specimens are — — - — to a 30.5-centimeter Sb-Be Neutron (12-inch) long heating 75 65 55 1.5 Sourci element within an Red - ET1EELI irradiation capsule. REACTOR Two axial layers of 77 67 57 7 37 27 17 7 specimens are attached ——— --—;w0— — CORE to each heating element. 8 68 58 38 1.8 8 are imbedded Rod Rod Thermocouples Fission Fission between specimens. The ChiaDir 2 I arrangement permits three Batteile DEE EEEED samples each of all seven 80 70 60 50 .0 30 20 1.0 materials to be irradiated — at the desired temperatures 80* 30* 20* 10* in six irradiation Ieutrcn WestInghouse 701 503 ‘03 303 203 105 >. P.ctivatxn capsules. —— Analysis %\ 700 600 SOC 0C 300 200 bC ‘rwo complete sets — of specimens are being 800 O00 irradiated to cumulative 100 ERflNt 8 rad and 80! 70! 60! 50! ‘0! 30! 20! 10! doses of 1x10 4x10’° cad with specified GRID dose fractions of fast 807 707 607 507 .0F 307 207 107 neutrons, thermal neutrons, and gamma rays. Gamma dose ICC 7CC 600 SOC ‘CC 300 2CC 100 rates are measured in rads/hr but neutron dose rates are 80$ 0H 60$ 50$ 60$ 30$ 2011 1011 n/cm2 /sec. measured in 801 701 60! 30! 601 301 20! 10! Many conversions between 2 /sec and rads are n/cm 80.3 70J 60.3 50.3 ‘.43 30.3 20.3 1.0.3 possible, but 1OCFR2O conversions were chosen because they are the only published values recognized by the Nuclear Regulatory Figure 1 Commission. Ford Nuclear Reactor Core Page 4 The University of Michigan Nuclear Reactor Laboratory Quarterly Review Winter 1990 l’he specimens being irradiated at 66 O( (150 OF) reached almost 149 0C (300 °F) without turning on the heaters because of radiation heating. They had to be placed far away from the core in experiment grid row D, in order to sustain temperatures as low as 66 0C (150 oF), which upset the desired dose fractions. In row 0, the irradiation time to achieve 1° 4x10 rads is approximately 7,360 hours at 2 Mw, which is about 1.25 calendar years based on 120 operating hours per week. Physical parameters measured include mass, dimensions, specific gravity, residual radioactivity, and specific radioactive isotope identification. As a control, unirradiated specimens were baked in autoclaves at the specified temperatures, and masses, dimensions, and specific gravities were measured to determine the effects of temperature alone. Measurement of the type and quantity of each gas emitted during irradiation was desired. Smaller pieces of .material were encapsulated in aluminum cylinders; tubes were run to the pool surface from the irradiation capsules; gasses were collected through hypodermic septum taps; and the gasses emitted are being analyzed utilizing a gas chromatograph. Some problems have arisen in the irradiation. Non-uniform dose and temperature profiles existed across the test specimens. Additional considerations with respect to dose are: (1) neutrons are thermalized in the test specimens so the neutron spectrum that enters the specimens changes across them; and (2) thermal neutrons are absorbed by boron in the specimens which alters the thermal spectrum, but more important, changes the damage effect because of the lithium atom, alpha particle, and 480 keV gamma ray produced by the boron—neutron. reaction. Significant axial variation in neutron and gamma intensity exists across the 61-centimeter (24—inch) height of the reactor core. Specimens positioned symmetrically about the axial centerline of the core have approximately a 10% variation in dose rate along the six-inch length of the specimens. Battelle Columbus Laboratories Test Program Pressure vessel steel specimens were irradiated in an instrumented encapsulation system.