Spent Fuel Drying System Test Results (Dry-Run in Preparation for Run 8)

TL;DR: In this article, the results of a test "dry-run" conducted prior to the eighth and last of those tests, which was conducted on an N-Reactor outer fuel element removed from K-West canister 6513U.

Abstract: The water-filled K-Basins in the Hanford 100 Area have been used to store N-Reactor spent nuclear fuel (SNF) since the 1970s. Because some leaks in the basin have been detected and some of the fuel is breached due to handling damage and corrosion, efforts are underway to remove the fuel elements from wet storage. An Integrated Process Strategy (IPS) has been developed to package, dry, transport, and store these metallic uranium fuel elements in an interim storage facility on the Hanford Site (WHC 1995). Information required to support the development of the drying processes, and the required safety analyses, is being obtained from characterization tests conducted on fuel elements removed from the K-Basins. A series of whole element drying tests (reported in separate documents, see Section 7.0) have been conducted by Pacific Northwest National Laboratory (PNNL) on several intact and damaged fuel elements recovered from both the K-East and K-West Basins. This report documents the results of a test ''dry-run'' conducted prior to the eighth and last of those tests, which was conducted on an N-Reactor outer fuel element removed from K-West canister 6513U. The system used for the dry-run test was the Whole Element Furnace Testing System, described inmore » Section 2.0, located in the Postirradiation Testing Laboratory (PTL, 327 Building). The test conditions and methodologies are given in Section 3.0. The experimental results are provided in Section 4.0 and discussed Section 5.0.« less

Summary

1;0 Introduction

• The water-filled K-Basins in the Hanford 100 Area have been used to store N-Reactor spent nuclear fuel (SNF) since the 1970s.
• Because some leaks in the basin have been detected and some of the fuel is breached due to handling damage and corrosion, efforts are underway to remove the fhel elements from wet storage.
• An Integrated Process Strategy (IPS) has been developed to package, dry, transport, and store these metallic uranium fhel elements in an interim storage facility on the Hanford Site (WHC 1995) .
• This report documents the results of a test "dry&.m" conducted prior to the eighth and last of those tests, which was conducted on an N-Reactor outer fuel element removed from K-West canister6513U.
• The test conditions and methodologies are given in Section 3.0.

2.0 Whole Element Furnace Testing System

• A complete description for the Whole Element Furnace Testing System, including detailed equipment specifications, is provided in Ritter et al. (1998) .
• Some changes were made to the system configuration prior to the present test run.
• These included new calibrations for the system gas chromatography(GC) and mass spectrometer (MS), and the addition of several new pressure and moisture sensors.
• These modifications are discussed in the following systems overview.

2.1 Major Systems Overview

• Figures 2.1 and 2.2 are photographs of the equipment located inside and outside of G-Cell.
• The furnace (including retort) and some of the process piping, instrumentation, and valves are located inside the hot cell.
• The fimace sits on the cell floor, and the process piping is routed to a rack that hangs on the west cell wall.
• Process piping, electrical power, and instrumentation wires pass through several split plugs on the west side of the cell.
• The process piping on the outside of the cell is contained within a glove bag, which provides a secondary containment as a precaution in case the process piping lines.

2.2 Vacuum Pumping System

• . scroll pump for evacuating the system to pressures below 1.
• Torr q water condenser with refrigerated chiller for gross removal of water .
• Valves and piping for connecting the various components and controlling the flow direction .
• Heating cords with temperature controllers for preventing condensation in lines.

2.2.2 Water Condenser

• For the present test, an MKS Baratron model 626 pressure transducer was added into the system to accurately measure and record the outlet pressure of the condenser.
• This transducer was coupled to an MKS model PDR-C-2C two-channel power supply/readout unit.

2.2.3 Piping, Valves, and Filters

• Particulate filters are installed in the system on both the inlet and outlet to the retort to help prevent the spread of contamination to the system piping on the outside of the hot cell.
• These filters are constructed of a microporous fiberglass media in a stainless steel housing.
• They are 99.9°/0efilcient for particulate that are 0.2 microns and larger in size.
• Two different size filters, manufactured by Matheson, are used in the system.

2.3 Process Heating System

• An Inconel sample/transfer boat is used to load the fuel element into the fhmace.
• Inconel 601 sheet, which is formed into a flattened u-shape.
• The boat has a weir and a swivel handle on each end.
• The weirs are used to keep free water or particulate contained in the boat as required.

2.4 Gas Supply/Distribution System

• The gas supply system and vacuum pumping system together are capable of controlling the fuel element environment to vacuum or moderate pressure conditions, and/or exposing the fiel element to a variety of gases or gas mixtures.
• The gas loop is typically operated as a single-pass system with no capability for recirculation.
• The gas supply system consists of gas bottles; mass flow controllers; piping and valves for metering argon, air, or oxygen through the system.
• All gases are typically specified "ultra high purity" and are additionally filtered for water using molecular sieve columns.
• The recalibration resulted in a flow rate range of O-304 standard cubic centimeters per minute (seem) argon.

2.5.1 Balzers Omnistar Mass Spectrometer

• A Granville-Phillips variable leak valve, series 203, was added to the gas sampling inlet of the MS to permit operation over a wide range of system pressures.
• Flow through the leak valve can be continuously varied from 0.4 I/s to 10-111/s, which allows the MS inlet pressure to be controlled to any pressure desired, even if the system pressure varies dramatically.
• This combination replaced the Cole-Parmer sensor that had both lower sensitivity and accuracy in this pressure 2.8 range and, thus, allowed for higher accuracy in the MS calibration.
• The inlet head pressure is divided by the pressure used for the calibration, and this factor is applied to the test data for calculating actual gas concentrations.
• Before the present tes~the MS was calibrated at -15 Torr head pressure with four certified gas standards consisting of 102, 103, 104,and 105parts per million by volume (ppmv) hydrogen in argon.

2.5.2 MTI M200 Gas Chromatography

• The MTI M200 Gas Chromatograph is a high-speed GC that is used to monitor the quantities of hydrogen and other light gases in the firnace testing system gas loop.
• This instrument is interfaced with a laptop computer to record data.
• At system pressures near atmospheric, the GC is configured to sample directly from the gas loop ahead of the system vacuum pump.
• No correction for the difference in the sample pressure and calibration pressure is applied, since both are -760 Torr (1 atrn).
• The GC was calibrated using the same four gas standards that were used for the MS calibration.

2.6 Process Instrumentation

• The furnace testing system contains several process instruments for monitoring moisture content; pressure, and temperature.
• The key instruments are as follows: q q q q q Vaisala moisture monitor Panametrics moisture monitor MKS Baratron pressure transducers Cole-Parmer pressure transducer Type-K thermocouples.

2.6.3 MKS Baratron Pressure Transducers

• An auxiliary high vacuum turbo pump is used to evacuate the inlet to PE-06 to well below 104 Torr so that the transducer can be accurately re-zeroed.
• The 270 signal conditioner used with PE-O1 does not have a remote zeroing capability.
• Both signal conditioners have analog outputs that are interfaced to the DACS so that system pressure is continuously recorded.

2.6.4 Cole-Parmer Pressure Transducer

• This pressure measurement is used to normalize the GC data so that actual gas concentrations in the system can be calculated from the relative concentrations measured.
• The readout unit (model H-68801-03) has an analog output that is interfaced to the DACS.

2.6.5 Thermocouples

• Thermocouples provide a simple, reliable method for measuring system temperatures.
• As shown in Figure 2 .3, over 20 thermocouples are installed at various locations in the system totprovide key temperature measurements.
• The retort temperatures are of primary importance, and these temperatures are measured by thermocouples TE-04 through TE-10, which are positioned equidistant along the length of the retort.
• Thermocouples TE-11 through TE-17 are used for controlling the temperature of the heated lines.
• All thermocouple readings are continuously recorded using the DACS.

2.7 Data Acquisition and Control System

• Limited control of the furnace can be performed with the DACS.
• Each of the three furnace zone temperatures can be remotely set by the DACS.
• In addition, the DACS allows the operator to start and stop the furnace and select one of four temperature profiles that are pre-programmed in the furnace temperature controllers.
• Note that these profiles must be programmed manually in the furnace controllers before using the DACS to select them.

3.0 Vacuum Drying Testing of Furnace System

• The drying test was performed in accordance with Test Procedure, Wet/Dry Run Testing of G-Cell Furnace System in Preparation for Run #8, 3M-TWD-PTL-013, Revision O.
• This document is located in the PNNL permanent project records for this test.

3.1 Initial Conditions

• Ten milliliters of water were added to the sample boat before the start of the test.
• The test conditions used were otherwise the same as those used for the subsequent drying test on Element 65 13U (Run 8).

3.2 System Drying

• The empty fuel element boat and fimace system was subjected to cold and hot vacuum drying.
• The drying process was conducted in six phases 1.
• The nominal design conditions used for these test phases are summarized in Table 3 .1.

3.2.1 Cold Vacuum Drying

• The furnace was first purged with argon to remove as much air as possible.
• The fhmace was then isolated and the furnace temperature increased to approximately 50°C and allowed to stabilize.
• When the system pressure became lower than the condenser could extract, the condenser was valved out of the gas loop and the argon flow stopped.
• The remainder of the CVD was conducted with the throttled vacuum pump.
• CVD was conducted at an ultimate pressure of-0.3 Torr for-l 9 hr.

3.2.2 Pressure Rke Test

• The Pressure Rke Test involved isolating the system and measuring any pressure increase while at CVD pressure and temperature conditions.
• The purpose of the Pressure Rise Test was to determine the effectiveness of the preceding CVD process.
• This test was conducted by valving the vacuum pump out of the gas loop and closing the exhaust valves.
• The condition for acceptance of this portion of the test was a total system pressure rise of less than 0.5.
• If this condition was not met, the system was re-opened to the vacuum pump and the Pressure Rise Test repeated.

3.2.3 Hot Vacuum Drying, Step 1

• Following completion of the Pressure Rise Test, the vacuum pump was re-opened to the system reto~, argon gas flow was established at a rate of-304 cc/rein; and the retort temperature was increased to -75°C.
• This condition was held for a period of-25 hr.
• This portion of the test can be used to obtain isothermal hydrogen and water release data for assessing oxidation of the fuel at low temperatures.

3.2.4 Hot Vacuum Drying, Step 2

• The second step of the HVD process involved raising the temperature of the retort from -75°C to -400"C at a carefilly controlled rate (1O°C/hr) while maintaining the same argon flow and pressure conditions.
• Any release of gas species during this temperature rise could be assigned to a specific temperature.
• The second step of HVD was conducted for about 34 hr.

3.2.5 Hot Vacuum Drying, Step 3

• The final step of the HVD process involved holding the temperature of the retort at -400°C while again maintaining the same argon flow and pressure conditions as in steps 1 and 2.
• This step will yield isothermal release data for any remaining hydrated species on a fiel element and for oxidation of uranium by any remaining water.
• This final step of the HVD process was conducted for about 8 hr.

4.0 Experimental Results

• In the following sections, the experimental data collected during the dry-run test are expanded and plotted for each segment.
• Summary results from the test are shown in Figure 4 .1.
• This figure shows the system moisture level response to the pressure changes and the retort tube temperatures during the test.
• The temperatures shown in Figure 4 .1 were recorded from one of seven thermocouples (TE-07) on the system located near the center of the retort.
• The pressure data were taken from the Oto 1000 Torr Baratron sensor (PE-06) located upstream of the retort.

4.1 Cold Vacuum Drying

• The CVD phase started at an elapsed time (ET) of 253 min.
• Pumping was continued by the throttled vacuum pump alone.
• Small drops in the moisture pressureatET311 and 468 min coincide with small jumps in the retort pressure read by both PE-01 and PE-06.
• The second was likely due to outgassing of some system component.
• Approximately 3 ml of water were observed in the condenser during the CVD phase.

4.2 Pressure Rise Tests

• Comparing the data from the two Pressure Rise Tests indicates that the total pressure rise observed in the initial post-CVD test was only partially caused by residual moisture and/or air in-leakage.
• Specifically, the difference between the total pressure rise and the moisture pressure rise for the post-CVD test (-0.3 Torr/hr) is significantly higher than the air in-leakage rate into the retort as measured in the post-HVD test (-0.05 Torr/hr).
• This suggests that other sources of gas are responsible for some of the observed total pressure rise in the post-CVD test, even with no fuel element present.

4.3 . Hot Vacuum Drying

• Following the final HVD phase, the system was allowed to cool to -50°C in preparation for the posttest Pressure Rise Test discussed above.
• Water removed during the system cooldown was -6 mg.
• Total system pressure remained constant at -19 Torr during HVD-3 and cooldown.

4.4 Gas Chromatograph Measurements

• Measured hydrogen release during the HVD segments of the drying testis shown in Figure 4 .9.
• Hydrogen signals showed a slow increase over HVD fi-om about 0.3 mTorrl/min to about 8 mTorrl/min.
• Other than this slow increase, no trends were observed in the hydrogen signal.
• Approximately 1.5 Tom] (-0.2 mg) of hydrogen was released during the entire HVD process over a time period of -67 hours.

4.5 Mass Spectrometer Measurements

• The drying system was designed so that the Balzers Omnistar MS could be used in conjunction with the GC to collect hydrogen and other gas release data over the test run.
• Hydrogen release values from the MS are also shown in Figure 4 .9.
• Because of technical problems with the MS, MS data are missing for two segments of HVD.
• In contrast to the GC dat'~the MS hydrogen release values are higher and closely follow the moisture signal, with local maximum at -170"C, and another at the maximum temperature of -400"C. Earlier tests, at much higher hydrogen levels, have shown good correlation between the GC and MS hydrogen data, with the GC values being somewhat higher.

5.0 Discussion

• In contrast to the GC data, MS hydrogen data dur@g HVD showed higher levels that correlated closely with the moisture signal.
• Because of the close correlation with the moisture data, however, it is likely that the hydrogen signal is simply from cracking of water vapor by the MS source filament.
• Earlier tests at much higher hydrogen levels have shown good correlation between the GC and MS hydrogen data.

Full text

PacificNorthwest
National Laboratory
Operated by Battelle for the
U.S. Department of Energy
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PNNL-12136
UC-602
Spent Fuel Drying System Test Results
(Dry-Run in Preparation for Run 8)
B. M. Oliver S. C. Marschrnan
G. S. Klinger P. J. MacFarlan
J. Abrefah
G. A. Ritter
July 1999
Prepared for
the U.S. Department of Energy
under Contract DE-AC06-76RL0 1830
Pacific Northwest National Laboratory
Richland, Washington 99352

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