System design description for the whole element furnace testing system

TL;DR: In this paper, a detailed description of the Hanford Spent Nuclear Fuel (SNF) Whole Element Furnace Testing System located in the Postirradiation Testing Laboratory G-Cell (327 Building) is provided.

Abstract: This document provides a detailed description of the Hanford Spent Nuclear Fuel (SNF) Whole Element Furnace Testing System located in the Postirradiation Testing Laboratory G-Cell (327 Building). Equipment specifications, system schematics, general operating modes, maintenance and calibration requirements, and other supporting information are provided in this document. This system was developed for performing cold vacuum drying and hot vacuum drying testing of whole N-Reactor fuel elements, which were sampled from the 105-K East and K West Basins. The proposed drying processes are intended to allow dry storage of the SNF for long periods of time. The furnace testing system is used to evaluate these processes by simulating drying sequences with a single fuel element and measuring key system parameters such as internal pressures, temperatures, moisture levels, and off-gas composition.

Summary

2.1 Major Systems Overview

• -The SAS consists of an argon gas bottle, solenoid actuated valves, and piping.
• The SAS functions witih the DACS to shut down the system ahd provide an argon purge if the furnace temperature rises above a pre-determined set point.
• Section 3.0 provides more detmled descriptions of the components for these systems.

2.2 System Arrangement

• Fuel elements are transferred to and from the cells using a transfer cask that is maneuvered through the hot cell canyon with an overhead crane.
• Typically, the transfer cask is positioned flush to the hot cell wall and a cell plug is removed to allow insertionhemoval of the element.
• Once it is inside the cell, the fuel element is handled remotely with mechanical manipulators.
• After a fuel element has been loaded into the retort and the retort resealed, the system is completely controlled from equipment located outside the hot cell.
• For a typical drying test, all of the valve manipulations itre performed inside the glove bag, and the components are controlled using the DACS along with equipment located in the instrument rack.

2.3 General Performance Characteristics

• The system is equipped with instrumentation to monitor key system parameters.
• A high accuracy pressure sensor is located at the retort inlet to provide system pressure measurement from 0.01 Torr to 1000 Torr.
• Moisture levels ranging from a dew point of -1 10°C to 20°C can be measured with the moisture sensor.
• The MS is typically configured to monitor hydrogen, nitrogen (for air in-leakage), krypton, xenon, and other elements during a drying test.
• The GC provides a second method for detecting hydrogen, and is more sensitive to small concentrations of hydrogen than the MS.

3.1 Vacuum Pumping System

• Each component is described in more detail below.
• Specifications for all of the valves, instruments, and system components are tabulated in Appendices B through D.

3.1.1 Varian Scroll Pump

• The system vacuum pump is a Varian model #300DS scroll pump.
• This purnp has an ultimate vacuum pressure less than lo-*.
• Therefore, a metering valve was installed on the pump inlet to throttle the flow to lower levels as required.
• The desired system pressure can be achieved by either using the throttling valve or metering UHP argon into the system through the entire gas loop or via a direct injection of ballast gas at the pump inlet.
• The use of argon gas helps to prevent the in-leakage of moisture-containing air through very small system leaks (which are difficult to eliminate) that would interfere with process monitoring equipment.

3.1.2 Water Condenser

• The condenser was custom fabricated specifically for this system.
• The bottom is bellshaped to funnel the collected water into an acrylic 1 00-mL graduated cylinder located directly below the condenser housing.
• A 3/8-in.-OD by 4-ft-long copper tube was formed to a 2 3/4-in.-OD coil to provide the cold surface for condensing the free water.
• Chiller lines are connected to the copper coil, and a thermocouple is installed in the line: to monitor the cooling water temperature.
• Another thermocouple is located inside the housing to provide the bulk gas temperature.

3.1.3 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% efficient for particulates that are 0.2 microns and larger in size.
• Two different size filters, manufactured by Matheson, are used in the system.

3.1.4 System Line Heaters

• All of the stainless steel tubing that carries gases into the furnace retort and resultant gases from the retort are heated to about 75 "C to ensure condensible water vapor remains in the gas phase.
• Simple heat "cords" capable of being wrapped upon each other (as required at tees, elbows, and other connections) were found to be a good heating method for this system.
• A type-K thermocouple is installed on t:ach heat-traced line, and the temperature is monitored and recorded by the DACS.

3.2 Process Heating System

• Typical temperature profiles for the retort are shown in Figure 9 .
• These temperatures were measured during a dry run of the furnace, without a fuel element inside the retort.
• For the nominal temperature setting of 50"C, the retort is under a vacuum of less than 1 Torr without an argon gas purge.
• For the 75 "C and 400°C settings, the retort pressure is approximately 18 Torr with an argon gas purge of about 300 sccm.
• This dropoff was much worse before the heat reflector was installed.

3.3 Gas Supply/Distribution System

• The GSS and the VPS together are capabIe of controlling the fuel element environment to vacuum or moderate pressure conditions, and/or exposing the fuel 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 GSS consists of gas bottles, mass flow controllers, piping, and valves for metering argon, air, or oxygen through the system.
• A bubbler is also available for adding water vapor to the process gas stream as required.

3.3.1 Mass Flow Controllers

• The GSS contains three Matheson mass flow controllers calibrated for argon, air, and oxygen.
• Argon is the principal inert gas used; it is more dense than air, provides reasonable thermal conductivity, and requires simpler handling procedures than lighter gases such as helium.
• Air and oxygen are not typically used because any oxidative steps have been deleted from the current IPS for the SNF.
• The argon flow controller (FE-0 1) is an oxygen controller with a range of 0 -200 sccm that was recalibrated for argon.

3.4.1 Bakers Omnistar Mass Spectrometer

• It of early system testing and calibration to improve the time response to small changes in hydrogen pressure.
• The residence time of each gas could be measured in the quadrupole chamber, and it was observed that the hydrogen decay time was approximately four times as long as helium.
• This was not unexpected as turbomolecular pumps have a lower pumping efficiency for very light gases.
• In standard practicc this is acceptable, but for these tests, where determining hydrogen could be very important, steps were taken to improve the hydrogen decay time.
• Under vacuum the gate valve can be opened, exposing the getter to the system to help scaveng hydrogen from the system following the analysis.

3.4.2 MTI M200 Gas Chromatograph

• The MTI M200 Gas Chromatograph is a high-speed GC that is used to monitor the quantities of hydrogen, nitrogen, and oxygen in the furnace testing system gas loop.
• This instrument is interfaced with a laptop computer to record dam.
• At system pressures near atmospheric, the GC is configured to sample directly from the gas loop ahead of the system vacuum pump.
• When the system is under vacuum, the GC is configured to sample from the exhaust side of the vacuum pump.
• The gas output from the pump is sufficiently compressed so that the GC can sample and analyze this gas.

3.5 Process Instrumentation

• Panametrics moisture monitor MKS Baratron pressure transducers .
• Cole Parmer pressure transduceis Varian multi-gauge pressure transducers Type-K thermocouples.

3.5.1 Panametrics Moisture Monitor

• The Panametrics moisture monitor model #MMS35 uses a solid electrochemical probe (model #M2L), which measures moisture by measuring the characteristic capacitance of the probe as a function of the moisture in the gas phase.
• Previous testing indicated that contamination by radioactive elements (e.g., cesium) causes the probe to go out of calibration and moisture readings to drift as a function of time.
• To prevent contamination of the probe tip, the probe is installed in the gas loop downstream of two particulate filters.
• Further, the probes will be changed following each test and surveyed for radioactive contamination.
• This procedure is time intensive; approximately 2 weeks are required to calibrate one probe over the range of moisture likely to be encountered in these tests.

3.5.2 MKS Baratron Pressure Transducers

• Two MKS Baratron Model 690 calibrated pressure transducers coupled with MKS Model 270 signal conditioners are used as the primary measurement for the overall system pressure.
• As shown in Figure 7 , PE-01 measures the system pressure downstream of the retort outlet, whereas PE-06 measures the system pressure at the retort inlet.
• In addition, the 270 signal conditioner procured with PE-06 has a special capability to remotely zero the transducer, which provides more accurate pressure measurements below 1 Torr.
• The 270 signal conditioner for PE-01 does not have this capability.

3.5.3 Cole Parmer Pressure Transducers

• These pressure measurements are used to normalize the MS and GC data so that actual gas concentrations in the system can be calculated from the relative concentrations measured.
• Both readout units have analog outputs that are fed to the DACS to continuously record these pressures.

3.5.4 Varian Multi-Gauge Pressure Transducers

• The Varian multi-gauge pressure transducers are uncalibrated Convectorr-type sensors that provide qualitative pressure measurements at several locations within the system.
• These locations include the scroll vacuum pump inlet (PE-03), the interior of the water condenser (PE-02), and the system pressure (PE-05) on the MS sample line upstream of the leak valve (LV-01).
• These pressures are also recorded using the DACS through an RS-232 communications link.

3.6 Data Acquisition and Control System

• In addition to controlling the furnace and the SAS, the DACS allows the operator to control the oxygen gas solenoid for oxidation tests.
• This solenoid can be toggled open or closed, as well as configured by the operator to automatically open and close on delay, based on user-defined start and stop times.

3.7 Safety Argon System

• As noted in Section 3.6, the user must manually reset the high-temperature alarm using a toggle button on the main display of the DACS.
• The DACS will not allow the alarm to reset until all of the retort temperatures are below the alarm temperature limit.

3.8 System Interfaces

• To protect the computers and instrumentation from potential power failures, three battery-backed UPSs are installed in the instrument rack.
• All of the power for the WEFTS equipment is supplied through a UPS, except power for the furnace, the vacuum pump, and the heat trace controllers.
• These components are powered &om a 240 VAC source, which does not have a UPS.

4.1 Overview

• For each of these modes, the valves can be configured to allow sampling with or without the GC andor MS.
• In addition, the system temperature can be varied for each of these configurations, and the type of gas or gas mixture can be varied for gas purging.
• The following sections describe each of these operating modes in more detail.

4.2.1 Vacuum Drying

• To evaluate the "dryness" of the system after CVD has been performed, a pressure risehebound test is typically performed.
• A limited pressure rise (less than about 0.6 Torr) during a 1-hour period indicates that the system has attained an acceptable level of dryness according to the IPS.
• To perform the dryness test, the system is isolated by closing the vacuum pump isolation valve (V 10) and then monitoring the subsequent pressure rise, if any, using the high accuracy pressure sensor (PE-06).

4.2.2 Vacuum Drying with Gas Purging

• Gas purging during vacuum drying is desirable for three reasons.
• First, gas purging helps to sweep away gases during the drying process, especially air caused by system in-leakage.
• Second, purging allows for gas sampling with the GC.
• The GC is not able to pull in a sample under vacuum conditions and therefore must sample the vacuum pump exhaust line.
• Without additional gas flow through the system, the GC will sample the hot cell air that back flows into the GC sample line because the pump exhaust flow is negligible.

4.2.3 Gas Purging

• The vacuum pump and condenser are bypassed, and the flow is redirected through V25 and V12 to exhaust to the hot cell.
• This configuration is typically used between drying tests to keep the system dry, but can also be used during a drying test if desired.
• If this configuration is used, V25 should not be opened until the system pressure has increased to slightly above atmospheric pressure.
• Otherwise, hot cell air will back flow into the system, which could be very detrimental to the data during a test.

4.2.4 Gas Sampling

• For each of the three configurations described in the previous sections, the system can also be configured to allow sampling using the MS and/or GC.
• As mentioned in Section 4.2.2, the GC cannot sample without some gas purge through the system.
• Figure 15 shows a vacuum drying with gas purge configuration where the flow path has been modified for MS and GC sampling.
• Valve VI3 is opened for MS sampling, and the pump exhaust is redirected to the GC sample line by closing V12 and opening.

Vll, V33, and V34.

• A "leak" valve (LVO1, also called a gas dosing valve) was installed on the MS sample line so that the MS can sample under a large range cf system pressures.
• Without the leak valve, system pressures above about 40 Torr produce too much flow through the MS capillary tube, which overwhelms the turbo pump used to pump down the MS sample chamber.
• The leak valve allows the flow to be continuously varied from 0.4 L/s to lo-" L/s.
• The M S inlet pressure can therefore be controlled to any pressure desired, even if the system pressure varies dramatically.
• The MS sample line pressure is monitored using PE-07.

5.1 Maintenance Philosophy

• No specific maintenance plans 01-procedures have been developed for the WEFTS.
• Equipment functional checks and other miscellaneous tasks are performed before and after testing, and these activities are typically covered in the test procedure.
• Because the equipment is operated within a radiation and contamination area, performing routine equipment maintenance and repairs can be a difficult task.
• At times it may be easier to simply replace items rather than repairing them.

5.2 Routine Maintenance 'I'asks

• This section describes typical system maintenance tasks, most of which are covered in the test procedure.
• The following tasks, as a minimum, must be performed for proper function of the WEFTS:.

5.3 Instrument Calibration

• The WEFTS has several instruments that require periodic calibration.
• The instruments that require calibration were calibrated prior to installation in the system.
• The calibration period is typically 1 to 2 years, so many of the instruments will maintain their calibration for the duration of the fuel element drying tests.
• For pressure sensors, the calibration can be checked by using a reference sensor connected to the system via a port installed through a glove bag sleeve.
• The mass flow controllers are located outside the hot cell, inside the glove bag, so that calibration can be performed more easily.

5.3.1 High Accuracy Pressure Sensor

• The high accuracy pressure transducer and corresponding signal conditioner used to measure the retort pressure (PE-06) was purchased with a "remote-zero" option.
• In order to maintain accurate pressure measurements below 1 Torr, checking and adjusting the zero of the sensor must be performed periodically.
• To re-zero the sensor, a pressure well below the sensitivity of the transducer is applied using the auxiliary turbo vacuum pumping system .
• Thi!; configuration allows the turbo pump to pump down the sensor head and be roughed through V38 using the scroll vacuum pump (Pl).
• After the entire system is roughed below about 5.

5.3.2 Gas Chromatograph and Mass Spectrometer

• Calibration of the GC and MS is performed periodically by connecting gas standards to the system via a line routed through the glove bag to the calibration gas port.
• A known mixture of gases is injected into the system, and samples are drawn into the GC or MS and analyzed for comparison with the standard.
• There are several differenit ways to configure the valves to calibrate the GC and MS.
• This calibration gas is either allowed to flow through the system using the vacuum pump (by opening V10) or bypassing the vacuum pump (opening V25), depending on the system pressure desired.
• After a sample reference standard has been iicquired, the GC and MS are then calibrated according to the manufacturer's instructions.

5 . 2 . 3 Remote Furnace Controls

• The conditioning furnace can be controlled remotely by the DAS to change temperature setpoints and operating modes.
• All LabVIEW DAS furnace controls are located in the SETUP screen.

E-8

• Position the on-screen pointer over the UPDATE button and click the left mouse button to update the temperature alarm limit value in the DAS.
• To reset the high temperature alarm, press the ALARM RESET button on the MAIN DISPLAY screen.
• The high temperature alarm will not reset until all of the retort temperatures are below the alarm limit.

NOTE:

• In the AUTO mode, the oxygen solenoid valve can be manually controlled without affecting automatic operation.
• Ending the DAS program also stops data logging and closes the active data logging file.

Full text

DISCLAIMER
Portions
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this document may be illegible
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System Design Description
for
the
Whole
Element
Furnace
Testing System
G.
A.
fitter(”)
S.
C. Marschman
P.
J.
MacFarlanfi)
D.
A.
King(’)
May 1998
Prepared for
the
U.S.
Department
of
Energy
under Contract DE-AC06-76RLO
1830
Pacific Northwest National Laboratory
Richland, Washington 99352
PNNL-
1
1807
UC-602
(a)
Fluor
Daniel Northwest
(b)
Duke Engineering
&
Services
Hanford
(c) SGN
Eurisys
Services
Corporation

.