When precipitation occurs under the conditions described above, a crystallinegreen precipitate (A) is obtained (6,7). This precipitate can be dehydrated to a cream-colored compound in a vacuum desiccator over PsOs and KOH. In air, the dehydrated compound rapidly regains its green color. Thermogravimetric analysis of (A) in air indicated that it lost weight continually to circa 100 “C and showed no further weight change to 500 “C. Elementary analysis indicated 53.5 uranium, 1 4 . 8 z phosphorus, and a weight loss upon drying of 8 . 2 z . The X-ray powder pattern of compound (A) is similar to powder pattern of the material formed by the reaction of aqueous uc14 and H3POa. Compound A thus appears to be uranium(1V) phosphite, U(HPO& 2Hz0, which contains 54.8 % uranium, 14.3 phosphorus, and 8.3 water. The use of phosphorus compounds to precipitate uranium
z
z
-
z
(6) V. I. Spitsyn,V. G. Gulia, 0. G. Nemkova, and M. S . Golubkova in “Investigations in the Field of Uranium Chemistry,” V. I. Spitsyn, Ed., ANL-Trans-33, Argonne National Laboratory (November, 1964) pp 293-8. [Translated from the Russian (1963)l. (7) V. G. Gulia, 0. G. Nemkova, and E. V. Vedencheva, ibid., pp 299-304.
is not new (8, 9). To determine the zWJ/234U ratio, it is not necessary to precipitate the uranium in the plutonium sample quantitatively. Most homogeneous precipitation techniques involve the homogeneous generation of only the precipitant or the ion precipitated. In the case of uranium(1V) phosphite, this technique allows homogeneous generation of both the precipitant (phosphorus acid) and the ion precipitated, U(1V). For the precipitation step alone, the separation factor-Le., the ratio of uranium to plutonium in the precipitate when both were initially present in the same amount-is approximately 104. This factor may be difficult to realize in plutonium-238 systems where the background radiation may be as high as 109 counts/min. For the complete process-i.e., precipitation followed by solvent extraction-the separation factor is approximately 107. RECEIVED for review June 24, 1968. Accepted December 23, 1968. Mound Laboratory is operated by Monsanto Research Corporation for the U.S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53. (8) G. T. Seaborg and R. A. James, US. Patent 2,917,361 (1959). (9) H. N. Ray and N. P. Bhattacharayya, Analyst, 82, 164-6 (1957).
Apparatus for Measuring Gas Release of Ceramic Nuclear Fuel Materials at High Temperatures Merrill C. Burt Battelle-Northwest, Battelle Memorial Institute, Richland, Wash. 99352 OPERATION of nuclear reactors utilizing ceramic fuels, such as UOz or UOZ-PuO2, can be abruptly terminated by fuel cladding failure caused by internal gas pressure ( I ) . The fission gases which are produced upon irradiation are not directly under the control of the fuel fabricator, but adequate expansion volume must be provided in fabrication to accommodate them (2). Other gases may also be released by desorption and by chemical reaction of impurities in the fuel at high temperatures (I). It is important for the fabricator to be able to measure the gas release of the fuel material at various stages in the fabrication process to avoid exceeding the capacity of the fuel cladding. Measurements at temperatures up to 1650 “C are presently required in this laboratory on both powdered and solid material. This paper describes a vacuum extraction apparatus designed for that purpose. Because the equipment must handle extremely toxic material such as plutonium, it was necessary to build part of the apparatus in a glove box to provide contamination control. EXPERIMENTAL
Apparatus. The main components of the apparatus constructed in this laboratory and assembled as shown in Figure 1, are as follows: FURNACE SECTION.This section, which is contained in the glove box, consists of a fused silica furnace tube, a powder loading and unloading section, a pellet loading arm, an arm with a slide magnet for use in raising and lowering the crucible, and a high speed glass mercury diffusion pump. The tungsten crucible is heated by a 21/2-kw, 450-kHz induction generator designed for use with long leads required (1) H. J. Anderson and R. J. Anicetti, AEC Report, HW-74204, Richland, Wash., July 1962. (2) M. B. Reynolds, General Electric Company, GEAP-4325, San Jose, Calif., Sept. 1963.
by the glove box application. By using a load coil of l/gW copper tubing consisting of two layers of six turns each, a heating range of 900-1700 “C, as read on an optical pyrometer, is obtained. Teflon (DuPont) spacers keep the coil turns separated from each other and the furnace. The cooling water jacket of the silica furnace tube and the diffusion pump are cooled by a closed recirculating water system to eliminate the possibility of plutonium contamination entering the building water system. Should a break occur in the closed water system, a pressure actuated switch turns off the diffusion pump, the circulating pump, and the induction heater generator. ANALYTICAL SECTION.The apparatus on the outside of the glove box includes a second mercury diffusion pump for transferring gases from the furnace section to the analytical section, the calibrated analytical section, and the main vacuum pumps for evacuation of the entire system. The main pumps are a 285-L/sec oil diffusion pump and a 5-cfm mechanical pump. The calibrated analytical section consists of a three range McLeod gauge, a Toeppler pump for transferring gas to an evacuated bulb for subsequent mass spectrometric analysis, a thermocouple gauge, an ionization gauge, and a calibrated expansion volume. The use of large diameter (28 mm 0.d.) tubing to keep the pumping speed at a maximum (3) increased the system volume and raised the detection limit. Assuming a five-gram sample and a final pressure at least five times the blank, the detection limit is approximately 0.01 ml/gram (STP). Two quartz wool plugs in the vacuum line between the two main sections of the system filter out particulate plutonium. The resistance to gas flow imposed by the quartz wool plugs is overcome by using the two mercury diffusion pumps in series. (3) Andrew Guthrie, “Vacuum Technology,” John Wiley and Sons, Inc., New York and London, 1963, pp 56-60, 414-421. VOL. 41, NO. 3, MARCH 1969
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n.
Figure 1. Vacuum outgassing apparatus A. Oil dinusion pump B. Cold trap C. Toeppler pump D. Calibrated expansion bulb E. Ionization gauge F. Thermocouple gauge C. McLmd gauge H. Mercury diffusionpump I. Magnesium perchlorate trap
I; Mechanicalpump
K. Stopcocks M. Glove box wall N, Quartz wool plug 0.Mercury diffusion pump P. Magnetarm p. Pellet loading arm R, Furnace tube S. Powder loading device Figure 3. Powder container in dumping position in the powder loading section
Figure 2. Cutaway view of powder container showing construction details A magnesium perchlorate trap is incorporated between the mercury diffusion pumps to absorb water from the gas. SAMPLE LoAnmo ANn HANnLrNo. Solid samples are easily manipulated while in a vacuum system. The weighed samples are pushed along the sample arm by a magnetic pusher which is manipulated from the outside. The outgassed crucible is raised to a funnel mouth at the top of the furnace tube and the samples are pushed in (operating manual for Type 917B vacuum hydrogen determination, NRC Equipment Corp., Newton Highlands, Mass.). The outgassing of powders is more complicated in that they are not easily manipulated while in a closed vacuum system. In the present system, powders are manipulated by using a small magnetically movable sample container (Figure 2) which is moved into the funnel in the powder loading section. As the container enters the funnel, its bucket turns upside down and the sample falls into the crucible which is suspended beneath (Figure 3). At present seven powder samples can be analyzed in one loading. The number of samples accommodated can be increased simply by making the three loading arms longer. The crucible is inverted for emptying by holding the magnetic cylinder, which hangs below the crucible, stationary against the wall of the powder loading section and lowering the crucible past the cylinder. Procedure. Solid samples of convenient size are weighed and loaded into the loading arm. Powder samples are put in tared containers, weighed and loaded in the side arms. The system is evacuated to approximately 100 millitorr with the mechanical pump and then the diffusion pumps are turned on. The outgassing of the crucible is started after the pressure decreases to less than I millitorr. In order to obtain an acceptably low blank at 1650 O C , several hours of heating may be required. A blank is considered acceptable when the pressure 550
ANALYTICAL CHEMISTRY
in the analytical section increases less than 1 millitorr per minute. System blanks are periodically taken between sample runs to make certain it is remaining constant. After a satisfactory blank is obtained the crucible is allowed to cool and a sample is loaded. As the sample is heated, pressure readings are taken on the McLeod gauge every five minutes until the readings are constant or equal the blank rate. This usually takes less than thirty minutes. If gas composition analysis is required the gas is transferred to a glass bulb with the Toeppler pump and analyzed by a gas mass spectrometer. While the system is being evacuated, the crucible is cooled, the spent sample is dumped, and another sample loaded. RESULTS AND DISCUSSION
There are no ceramic nuclear fuel standards available for evaluating the apparatus. The precision of the method and the equipment was established by analyses of a uniform batch of UOz powder at 1400 "C. Analysis of eleven samples with a mean gas release of 0.70 ml/gram (STP) indicated a relative standard deviation of 7.1 %. To determine the accuracy of the system, samples of National Bureau of Standard unalloyed titanium were analyzed at 1400 "C using a thoria lined molybdenum crucible. Results of these analyses (Table I) indicate an average relative error of 5.2% which is not significantly different from the precision of the system. Table I. Analysis of Standard Samples H, in Titanium Standard NRS 352 NBS 353 NBS 354 215 + 6 ppm 32 f 2 pprn 98 f 5 ppm
Average Mean error
29 36 27 33 31 37 38 -
110 111 110 108 108 110 -
33 +1
109 fll
199 234 208 216 203 220 210 207 212 -3
To determine the effect of temperature on gas release, samples of UOZ were heated to 1000 "C and held until gas release was complete. This procedure was repeated at 200 "C intervals up to 1600 "C, at which temperature the material was at least partially sintered. On the material tested the gas release was 0.15 ml/gram (STP) at 1000 "C and increased linearly to 0.31 ml/gram at 1600 "C. One obvious problem is the possible loss of gas from the sample while it is in the vacuum system but before it is heated. If there is an appreciable loss, one would expect the apparent gas content to decrease as a function of the time the sample was under vacuum before analysis. Four of the samples included in the precision data were left under vacuum for extended periods of time (20,42,54,and 79 hours) before being analyzed. Results from these four samples were in the same
range as the remainder of the eleven samples which were under vacuum less than twenty hours before analysis. The apparatus as described provides a reasonably precise and accurate measure of gas content in ceramic fuel material. Because of problems related to the use of glove boxes, all crucible bake out is done during normal working hours. With crucible bake out and sample loading time, approximately 16 analyses can be performed in two days. The powder containers and associated glassware are a major improvement and greatly simplify the handling of powdered material.
RECEIVED for review November 12, 1968. Accepted December 27, 1968. Research supported by the U S . Atomic Energy Commission under Contract No. AT(45-1)-1830.
Versatile Temperature-Jump Cells with Long Light Path Rufus Lumry and Richard Legare1 Laboratory for Biophysical Chemistry, Department of Chemistry, Unicersity of Minnesota, Minneapolis, Minn. 55455 MOSTTEMPERATURE-JUMP CELLS use windows made of quartz or glass slugs, and the heated optical path is usually 1 cm long. Even the highest quality silica slugs display stars caused by crystallization and other imperfections when placed between crossed Nicol prisms. Thick glass windows contain strains built-in during manufacture and additional strains are introduced when the windows are rigidly glued into the cell. As a result of the strains and imperfections, it was not possible to obtain a dark field-i.e., a suitable null condition, when attempting to measure chemical relaxation by changes in optical rotation. When thin windows were used in cells even approximating conventional design, the shock wave produced by rapid heating of the cell contents destroyed the windows or produced vibrations in the windows causing spurious signals caused by the strain-induced birefringence. Furthermore, the conventional cell design can be modified for light paths of more than 5 cm only with difficulty, and then with a large total cell volume ( I ) . CELL DESIGN
The most generally satisfactory type of cell design we have developed is shown in Figure 1. For work with water solutions, any insulating plastic is satisfactory. For nonaqueous solvents Teflon by Du Pont or Kel F is recommended, and, compared with the other plastics, seems to reduce the tendency to arc through the solution and along the plastic walls at high potential gradients. The cell shown has a 10-cm heated path length and a 20-ml total volume. The heated volume is 5.3 ml. It is important to avoid reflection of the light beam from the walls in optical-rotation work, and shorter cells simplify the optical problem. However, cells of this design with at least 20 crn of heated path length appear to be practical. The inter-electrode distance is 0.6 cm and the beam width should be no greater than 3 mm. The heated area is outlined by longitudinal plastic ridges extending up from the bottom of the cell and down from the top. Contact to the electrodes Present address, Allegany Ballistics Laboratory, Cumberland, Md. (1) R. Legare, Dissertation, University of Minnesota, 1962.
Figure 1. Cell design may be made in any number of ways as required by the construction of the cell housing. The high-voltage electrode in our arrangement is connected through the long rod shown emerging from the cell. The plastic portion of the cell rests in a brass and plastic block which is thermostated, and the block itself rests on pins which center it and provide contact to the ultimate ground. The outside configuration of the cell can be modified to adapt it to other versions of T-jump apparatus. The novel feature of the cell as well as its most important feature is the provision of wells at either end of the cell connected to the main compartment by holes of 4- to 5-mm diameter. The windows are small quartz flats of 1-mm thickness or pieces of microscope slide glass, and are held in place against the outer face of the wells either by grease or by wedgVOL. 41,NO. 3, MARCH 1969
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