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In-Situ Tuff Water Migration/HeaterExperiment: Instrumentation Designand Fielding

David R. WaymireExperiments Planning Division 1112

Carl 0. DuimstraField Instrumentation Division 1. 1124Sandia National LaboratoriesAlbuquerque. NM

AbstractIn conjunction with the Nevada Nuclear Waste Storage Investigation Project. .SandiaNational Laboratories conducted a Water Migration/Heater Experiment in weldedtuff at the Nevada Test Site. The heater and associated instrumentation were operatedunderground or about months during . The instrumentation measured waterdepth and alkalinity. temperatures. cavity pressures. relative humidity in-situ stresschanges. and displacement in the drill holes and surrounding rock mass. An on-line.calculator-based data acquisition system controlled the experiment and accumulated120 channels of data. Most instrumentation operate satisfactorily and almost all wasrecovered tr postmortem examination.

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ContentsIntroductionInstrumentation

Heater Design

Pressure TransducersAikalinity SensorLaser StrainmeterStressmetersData Acquisition SystemRelative Humidity IndicatorWater-Level IndicatorThermocouple InstrumentationGas and Water Collection SystemPower Distrihution and Alarm System

ConclusionsReferences ....

APPENDIX - Photographs of Experiment and Associated Instrumentation{COULD NOT BE CONVERTED TO SEARCHABLE TEXT}Figures

In Situ Tuff Water Migration/Heater Experiment:Instrumentation Design and Fielding

IntroductionThe in-situ Tuff Water Migration and Heater

Experiment was conducted in the welded tuff of theGrouse Canyon Member in the G-tunnel complex atthe Nevada Test Site in southern Nevadaduring FY80.1 Before this test. two other field experi-ments had beer conducted by the NNWSI Geotechnical Projects Division at Sandia National LaboratoriesISNL at Albuquerque. New Mexico. Both were fullscale near-surface heater experiments to thethermal thermomechanical and chemical responsesof shales when exposed to heat. The tests would partlydetermine the suitability of shales as candidate hostrocks for nuclear waste.

The first experiment included two heater siteslocated approximately 30..5 m i ) ft I apart at different depths and in different rock strata. The heaters.those heated sections were each about 0.30w m 112 inin diameter and :1 m 10 ft long were positioned in the

Conasauga formation on the Oak Ridge National Lab-oratory reservation in Tennessee.

The second field experiment was with a singleheater placed in the Eleana shale formation within theNTS. Data obtained from this test have been analyzedand reported.

The latest experiment the subject of this reportwas designed to provide data an the generation ofwater and its movement in the icinity of a heat sourceimplanted in welded volcanic tuff. The experimentfocused in an alcove mined 427 m beneaththe top ridge of Rainier Mesa in Area 12. The array ofdrill holes (Figures 1. A11 was inclined upward at 20from the horizontal. Such an incline permitted theholes to penetrate the overhead welded tuff and waterto collect in the holes against the packers.

We developed the general criteria for the experi-ment at the end of We defined and bought a newdata acquisition system DAS which was based on theHewlett-Packard 9845 calculator/controller specifiedpower requirements; and picked transducers to moni-tor temperatures pressures. stresses pH. relativehumidity (RH). and heater power.

We also designed a program to develop a stabi-lized laser strainmeter and an electronic water-levelsensor. The Instrumentation Development Division atSNL supplied the thermocouples, pressure trans-ducers, and stress meters we purchased other specialinstrumentation, such as pH and RH sensors andmeters.

The heater was centered at a depth of 18.5 m(61.5 ft. Most of the remaining instrumentation waslocated within 3.0 m of the heater's center. Table I is alist of instrumentation and channel identifications.Results and analyses of measurements have been re-ported separately

In the field we installed signal conditioning pow-er distribution, and the DAS in an air-conditioned.environmentally controlled alcove. Figure A is aphotograph of the alcove, including the DAS. a tele-phone alarm system and hardware for the signalconditioning system and its display. The collars forthe drill hole array IFigure I were located at the rearof this alcove.

Figure 1. Experiment Hole Array Layout at hole collardimensions in feet)

Table 1. Tuff Channel Identification Listing{COULD NOT BE CONVERTED TO SEARCHABLE TEXT}

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Instrumentation

Heater DesignThe heater that we designed and fabricated for

this experiment was an adaptation of previous designsused in shale experiments. The significant differenceswere reduced size and the elimination of air cooling forthe terminal section. The heater elements themselveswere long this can he compared aheated section n the full-scale experiments.

The heater was essentially a right cylinder thatused two hairpin. electrical-resistive heating elementssupplied by and which had een usedsuccessfully in previous tests. Also we used mechanti-

c ally operated RTV silicone packers rather than air-inflated of the holes and provide king-term water collection. The packers were expanded andsqueezed t the wail by electric motors driving a metalgone through the center of an RTV ring.

figure 2 is a sketch of the heater. instrumentation,and packer The mechanical design of theheater and other associated hardware have re-ported separately.

Pressure TransducersWe used pressure transducers from Gulton Indus-

tries monitor gas pressures in Holes HH WM-l.WM-2. and WM-3. Another gage was mounted in theinstrumentation alcove to monitor changes in atmo-spheric pressure. The transducers Scrics --feature high-level (up to V dc linear variable dis-placement transformer LVDT) output with infiniteresolution and complete electrical isolation.

The electronics are self-contained in the same castaluminum housing as the all-welded pressure-sensorbellows. These particular transducers are very ruggedand can withstand a 50-g shock. rheir resposnse to astepped pressure change is less than the proofpressure i 1.25 times the range fr each type and theburst pressure is 3.10 Pa 1450 psig. ach onerequires 9 t 12 V dc regulated input voltage and amaximum input current of mA.

We mounted two pressure transducers in eachthe heater-array holes. was a Model

with a pressure range of fromand a temperature operating range of from

The other transducers in each hleand the in the alcove were Modelrated for topresents the calibration data for thetransducers and Table : for the five a gages.

Welded Tuff

Figure 2. Heater Aembly Including Heated. Insulated. Junction. Instrumentation Packer and Pressure Transducer

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Table 2. Calibration Data for GS-613-15-3-S

Before we installed the transducers in the field.they were calibrated at the SNL Standards Labora-tory. The sensitivity and offset of each individualtransducer were used in the automatic DAS to converttransducer output into pressures in lb/in. In the field.we mounted them inside an open steel canister on thealcove side of the packer section of the drill holes. Astainless steel tube connected the pressure port to thesealed cavity beyond the packers.

After several months in this environment, trans-ducers SN 1005 in Hole WM-1. S/N 1004 in HoleWM-2, and S/N 1018 in Hole W.M-2. started behavingerratically. During the cooldown phase of the experi-ment, SN 1004 stabilized at about -0.05 MPa

During the postmortem, the pressure cavity andbellows of all transducers appeared to be functionaland in good condition. However, the output sensitivity(of the three erratic gages had decreased and they drewabout twice the input current as the other units. Theelectronics on all units showed effects of humidity andcorrosion. especilly those that had behaved erratical-ly whose effects were severe enough to short outresistors, damage transistors nd cause other dam-ages. In the future, it would be advisable to encapsu-late the electronic section with some type of humidity-and temperature resistant material.

Alkalinity SensorThe pH of the water collected in the holes was to

using smell gal-filled sensors.were mounted on brackets in the instrumenta-

tion compartment just beyond the deep packet. Herethe electrode tip would be immersed in water as itpooled behind the packer.

We used the Sensorex Model sealed refer-ence combination pH electrodes with 23-m 75.ftcable lead and standard Beckman connectors. Theirsmal1 size allowed them t be mounted in the spaceavailable for instrumenation. Their rugged polymerbody protected the fragile tip from damage duringmounting and insertion.

The pH metrs were Model NX digital readoutinstruments supplied by Sargent-Welch Scientific Co.This particular meter has a relative accuracy of

0.01 pH ver the pH range of from 0 to 14. Therepeatability is also 0.01 pH. The recorder output isI mV/pH with accuracy. Separate slope andintercept controls are also provided and temperaturecompensation is either manual or automatic. As de-sired. ith calibration and standby modes are alsoavailable. The calibration mode is used in conjunctionwith slope intercept and temperature controls tocalibrate the meter. using buffered solutions. Standbyis used t disconnect the reference jack from thecircuit and to connect the intercept voltage only acrossthe digital voltmeter (DVM) terminals. This mode isused when electrodes are not immersed.

When we were assembling the sensors at NTS. anelectrical short occurred in the potted section of the

pH cable in the WM-1 package and the pH level wasnot measured in this hole. Instead the meter designat-ed for WM-I was connected to another Sensorexelectrode in the alcove. Whenever we took water forma drill hole, we measured the pH in the alcovecheck the in-sits measurements We considered hiscross-checking advisable because in-situ probes couldnot be cleaned stirred or recalibrated once the hdbeen inserted; they remained in place for 7, months

At the beginning each meter was adjusted andcalibrated with the electrodes that were to be actuallyinserted into the holes. Standard buffered solution of4. 7. and 10 pH were ued for calibration The electrodes were then disconnected and a standard cellconnected t the meters. This cell had been calitoratedat SNI. Standards Laboratory fr output accuracy.The meter output or standard cell settings and

were recorded for future meter adjustment.The leads from the in-situ electrodes periodi

ally removed from the meters input terminals duringthe in-situ test and the meter connected t the standard cell. We could then adjust the slope end interceptcontrols to restore the pH meter t the calibratedvalues in case it had drifted. However. we nted nosignificant drift throughout the experiment.

Calibration data fr the sensors and meterslisted in Table 4 PH-1 refers t the measurementsfrom HH-I. PH-2 to the electrode and meter used ormeasuring in the alcove, and PH-3 and PH theWM-2 and WM-3 respectively. The numbers ineach clumn refer to the SNL. property numbers ofeach meter.

Laser StrainmeterA Tropel Model 00. single-frequency helium-

neon laser was used as a strainmeter to monitor smalldisplacements caused oy thermomethanical effects inthe rock mass surrounding the heater. (Other experi-menters have also used such interferometers as strain-meters The meter consisted of the laser sourcemirrors, vacuum pipe with quarts windows. cats eyelens, and photodiode detectors (Figure 31. We mount-ed the laser on a flange fastened to the borehole collarand viewed the cat's eye through the line-of-sightvacuum pipe. Fringes, that is displacements detectedby the photodiodes were counted by an electroniccounting circuit.

Figur 3. System Diagram for the Laser StrainmeterIThrmoupie locations are indicated by TC. andlocations by

The laser operated at a wavelength if 632.8 nmwith a put power of Montoringthe output frequency permitted de-coupled

of the laser cavity length and active stabiliza-tion of the frequency. The laser tube used wasCoherent Model 80. with a polarized outputbeam.

The fringe sensing device was a silicon photo fieldeffect transistor (photoFET) that combines a sensi-rive silicon photodiode and a low-noise FET. Whenlight strikes it. photo current flows in the gate circuit,causing a positive voltage rise at the gate. PhottFEToutput from two channels is then combined in an X-Yfashion. Whenever the combined signal crosses eitherthe X or axis a count is registered in anelectrical octal-coded counter. The sense of rotation isalso maintained such that counts are automatically

added or subtracted as appropriate. The output of thedigital counter could be recorded by the HP9845-based DAS through the RS-232C interface or througha converter. These interfaces could also be used to send calibration data to theDAS. Calibration function switches were also avail-able on the electronic fringe counter, which was de-signed ointly by SNL and EG&G-Kirtland. Digitalcounts, and therefore analog voltages through theD-to-A converter, could be stepped or todesired level. Figure A shows the laser head andcounting electronics fielded in the laser alcove.

We attempted to protect the electronics fromeffects of humidity by blowing tunnel air into analcove at the end of the laser drift, a Brattice clothsheet providing the only barrier to the alcove. Inaddition, two dehumidifiers were placed next to thefringe counter.

We strapped an energized resistor to the pipeflange that held the quartz window at the location ofthe cat's eye and its heat prevented the window fromfogging. For diagnosis thermocouples (TCs wereplaced at the window, next to the cat's eye, and at thelaser optical head.

Inspite of our enclosing the laser head for protec-tion. several problems occurred. Electronic compo-nents failed in the fringe counter, which was installedin the laser drift Shorts and counting errors alsooccurred which were presumed to have been caused byhumidity. The interferometer system also appeared tobe sensitive to changes in temperature, humidity. andair currents. We do not yet know if this is true only totie extent that these changes affected some criticallength the measurement system.

Because of difficulties, we placed a fringe counterof design in the air-conditioned instrumen-tation acove and connected it in parallel with theoriginal counter. When we compared data from bothcounters, we found few discrepancies. Both recordedthe same rapid, extreme, short-term excursions seenwhenever recordable environmental variations oc-curred in the laser alcove. Recording the same phe-nomena indicates that they were the output of thelaser itself and not caused by the counting electronics.The two counters tracked each other quite consistent-ly indicating that the counters were operating cor-rectly. Slight deviations from each ether, however,suggest that each was sensitive in its own way torandom noise.

EG&G-Kirtland conducted laboratory tests to de-termine if environmental effects could influence thestabilty of the laser and of fringe-counting detectors.They varied temperature and barometric pressure,

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but noted no significant effect They compared threelaser systems in a Fabry-Perot interferometer to checkfor sensitivity variations, but none was detected

The reason for these results is probably that thelaser and photodiode detectors operated as expectedalthough there were long term drift effects associatedwith the counters sensitivity to random noise pulses.These effects can be substantially reduced to accept-able limits with improved electronics design and pack.aging but probably can never be totally eliminated.

The cause of the rapid excursions in the outputcounts was probably the intermittant drying and resa-turating of the rock wall on which the laser head wasmounted. These phenomena could have been causedby any environmental changes which would havechanged the humidity in the laser alcove, such asventilation. Further laboratory tests are being con-ducted with a laser interferometer and welded tuffcore samples to determine if this conclusion is correct

The laser strainmeter shows great potential formeasuring small displacements such as we expected inthis experiment. Improvements should be made toseal the counting electronics to the environment andto eliminate operator adjustments in the fringe counting system. Improved electronics could also increasethe resolution beyond the A/8 limit. However, in spiteof any new advances that may be made, a majorquestion remains How ahould the bemounted to the rock? One possibility would be tomount the laser head reference several feet into thedrill hole and thus avoid surface effects due to stressrelief and rock saturation. This problem may remain amajor source of uncertainty in laser strainmeter mea-surements in the future.

StressmetersCommercially supplied borehole inclusion stress-

meters were modified substantially at SNL with anextended platen design, and they were modified forstraingages in order to make them compatible withconventional data logging equipment. These changesproved advantageous in the experiment Other de-signs that use vibrating wires require special digitalreadout electronics, which would cause increased us-age of special digital BCD) interfaces. Figure 4 is a

of the mechanical design.We placed three stresameters in Hole SH- at

different depths (Table 1). The two deepest meterswere mounted to read horizontal stresses tradially to

the heater hole), and the shallowest was orientedvertically tangential to the heater hole Originally, thecenter meter was to be oriented at 45 from thehorizontal, but an equipment malfunction caused usto believe that the deepest stressmeter had not seatedproperly, so we oriented the second meter horizontallyto yield that important data. Later, we corrected theequipment malfunction, but the stresmeter remainedin the horizontal direction.

Figure 4. Mechanical Design of Stressmeter

We istalled the stressmeters as soon as the stresshole was drilled, in order to watch any long-termrelaxations and see if subsequent drilling in the holearray and mining of the laser drift affected the stresssignificantly. We also placed a TC in the stress hole tocollect temperature correction data if it should proveuseful.

We installed the stressmeters with an insertiontool that uses hydraulic pressure to drive a wedge,thus preloading the platen against the rock to providea solid anchor. Preloading is also necessary in casethermal expansion due to heat should cause the holeto open. We did not remove the stressmeters after theexperiment because the wedge is designed to break ata predetermined load.

The stressmeters were calibrated in a universaltesting machine to indicate their output when a load(force) is applied to then. (Figure 5). These calibratedsolid block data were then used to obtain stress vsforce data from welded tuff block tests (Figure 6.Bridge excitation on all channels was maintained at18.0 V de.

The stressmeters all operated as expected. Afterinitial voltage changes caused by stress relief fromgage preloading in the borehole, we saw no othereffects of stress relief before the power was turned onin the heater. Data from the stressmeters (Figure 7)shows that transducer output dropped below preloadvalues after the heater was turned off, indicating the

importance of preloading the meters to keep themanchored. We had gained such experience in previoustests in shale.

Figure 7. Actual Stressmeter Data SE28 and SE wereoriented radially to the heater. SE13 was orientedtangentially.

Data Acquisition SystemThe DAS that we used was based on the Hewlett

Packard 9845T calculator/controller. The systembasically the HP30-52A that utilizes theprogram nable digital multimeter, two,scarners with low thermal and TC reference asem-blies, and the clock for interrupts(Figure 8,. System software for the field experiment isdetailed in Reference 8.

Figur Force vs Output Clibration for Stressmeters S7.S13. and S28

Figure 6. Delta Stress v: Delta Force for Stressmeter in aBlock ,f Welded Tuff (tested in the laboratory

Figure 8. the In-Situ Tuff WaterHeater Fieid Experiment Data Acquisition System:

Analog voltage or resistance sources were wireddirectly to the scanner's plug-in assembles On anInterrupt signal from the real time clock, the 9845Tcontroller commanded the scanners to close selectedrelays sequentially and the digital multimeter moni-tored the voltage level or resistance from each chan-nel. The multimeter output was then stored in arraysin the controller's memory. These data were laterstored on cassette tapes and flexible magnetic disksand, even later retrieved for analysis.

Thermocouples were connected to relays num-bered 1 through 19 in each TC reference card: Channel

as hardwired to a thermistor attached to an iso-thermal connector block. Resistance readings of thethermistor permitted the calculator/controller to de-

the reference junction temperature. As theindividual TC voltages were scanned and monitoredpolynomial fits were performed t determine te TCjunction temperatures. We discuss TC specificationsin detail ater in this report

Each plug n asssembly thus included 20 channelsof three-pole. low-thermal dry-reed relays. The relaysfeatured break before make operation with contactsrated to 42-V peak voltage and a current of 40 mAnoninductive. Maximum input voltages were 42-V

peak between any two terminals and 42-V peak fromguard to chassis. Switching time is i-ms maximumwith greater than resistance between high and1ow. There is also less than differential EMFthermal offset between high and low fr ambienttemperature changes of Thermistor accuracy isspecified to be A steady-state temperaturegradient along the terminal from the reference tem-perature is less than maximum for ambi-ent temperature deviations.

Analog signals from stresmeters thermistors. pHmeters voltage starndards laser interferometer. RHsensors power meters. and water-level indicators ailcame into, 20-channel low-thermal relay assemblies.Operation voltage ratings thermal offset isolation.and switching time specifications for these low-thermal asemblies all the same as for the19-channel TC assemblies In fact. the two assembliesare identical except for the replacement of Channel 0by the thermistor reference in the TC assembly.

Each 3495 scanner could four plug-in assemblies for a total capacity of channels of relays.

The HP3455a digital multimeter features up to6 1,2 digit resolution; It is a fully guarded integratingmultimeter capable of measuring dc voltage. rmsac vltage and resistance. It isprogrammable and includes an autocalibration.

removable reference assembly for do resistancecalibration.

Up to 24 readings per second on dc measurementsis possible with sensitivity. Inrut resistance isgreater than 10 billion ohms from 0.1- toranges. Normal mode rejecion at 60Hz is greater than60 dB. Maximum input voltage rtings arepeak between high- and low-input terminals.peak from guard to chassis and 200-V peak fromguard to coded decimal BCD)data from the powermeters was also record-ed using th DAS. through the BCD inter-faces that puged directly into the 9845.

The HP98035A real-time clock provides calendarand time-of-day information. The clock can interruptthe system at programmable intervals and at selecta-ble times-of-day for pacing data acquisition.

The HP984ST controller used enhanced BASIClanguage with 448 Kbvtes of read-write memory. A

cm .12-in.) cathode ray tube CRT screen dis-played data and commands. The CRT can display 24

of 80 characters each as well as perform fullgraphic and plotting. An character internal ther-mal line printer that prints lines per minute is also

feature of the The also features dual-tape cartridge drives with capacity for eachtape and a tape-data transfer rate of

The system used the input/outputA graphics and the

storage read only options. In additionto the dual tape cartridge we added a dualflexible disk drive system, the master and

to enhance data storage capabilities.The drives are random access removable mass-storage devices with a capacity up perdisk. Double-density read write enhances the rate ofaccess and increases storage capacity. The system alsofeatures a write-verity operation to ensure that datarecorded n the disk identical to the source infor-mation in the memory. A file-by-name systemmaintains user files in a directory. The disk tate at

rpm. average access time andtime is 11.1 ms per record t a rate

A fr-pen based plotter themade data graphs. The is com

pletely programmable through theplotting area is 2 mm n the and in the

direction. Addressable resolution is mm withan accuracy of of with arepeatability of mm. The pen speed is program-mable up a maximum and printingspeed is typically three characters per second.

Relative Humidity IndicatorWe did not know if water would, in collect

against the packers in the instrumentation holes If itdid not or if ambient conditions prevented the liquidphase. we decided it would be valuable to use RHsensors as a backup to measure the presence of andchanges in moisture content. Initial thermal-modelingcalculations indicated that the instrument section inthe heater hole and the water collection hole at aradius of 0.61 m from the heater, would remain below

during the experiment Therefore, that is wherewe decided to install the RH sensors

The only commercial RH sensor that could fit intothe holes and withstand 8OC was Thunder ScientificCorp's hybnd H2CHDT-2A modified for 100Cwith Option 21. We bought two complete sensor sys-tems including circuitry tead-out unitsand spare transducer with accompanying circuitry.Reference 9 gives pecifications and operating n-

During procurement additional modeling indi-tated that Holes WM-2 and WM-3 at about 0.2 mfrom the heater would not reach Three transducers had already been ordered and we orderedanother one so that RH sensors could be installed inthese t hole as well Ploblems in delivery and inhigh-temperature calibration caused us to real thetemperature criteria for two transducers from to

the standard design temperature for ThunderScientific's sensors.

The Physical Standard Laboratory at SNL cali-brated two the original transducers. The thirdfailed at the beginning of calibration and had t bereturned fr The pretest calibration data forthe t transducers shown in Tables 5 and 6. inwhich the measured RH is listed as a function oftemperature and reference RH The third transducerrepaired and the fourth, ordered later, arrived duringthe field assembly at NTS and were checked only tosee if they worked and compared with the calibratedtransducers at te ambient humidity and tempera-ture; the two were specified t operate to

During assembly, we checked both temperatureand humidity from the sensors In order toget the transducer into the experiment package wehad to cut and the cables, at which time all fourchannels be functioning so we did not

test in the tunnel beforeinto te drill holes; no readout

were available in the tunnel at that time.

After we had installed all the instrument packagesand connected and checked out the DAS. we foundthat only two of the four RH channels were function-ing properly; this was before any temperature changedue to heater power. The two working channels readabove RH because the transducer had beensaturated with moisture which we were aware of Onexamining them at thus time, we discovered that noneof the transducer circuits were wired ac-cording to the supplied by the manufactur-er. This may have caused electrical damage to onechannel when we were assembling them in the tunnel

When we discovered this problem we deemed itunwise to completely dismantle the pipe strings andretrieve each experiment package from the drill holes

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because of the risk of damage to other more iportantduring retraction. dissassembly re-assaembly.

We felt that prospects were not goodrepairing transducers in a reasonable time even if

the experiment were dismantled. Therefore we madeno attempt to remove them, although we did tryseveral times to correct the problem at the linearizingcircuit mounted in the alcove.

During the experiment it appeared as if one trans-ducer operated normally. Another recovered from sat-

for a few days and yielded usable data. It thenbecame erratic, and appeared to be resaturated for theremainder of the experiment.

When we recovered the instrumentation after theexperiment. we sent the transducer that apparentlyoperated properly to Physical Standards Laborator-

calibration Table 1. The other threewere returned t the manufacturer who upon analyz-ing tated that the transducer that operated sporati-

during the test was still operational and that thehad suffered high temperature damage.

TC data indicate that none of the trans-experienced temperatures over 77-C. which

temperaturespecified in the original purchase agreement. More-

the transducers had failed at room temperaturethe heater was turned on.

measure the presence of water and to provide watercollection-rate data from the holes. We undertook adevelopment program to design and build a sensormeeting these criteria. Several schemes were proposedand tested:

Fluid/air conductivity differencesFloat and tilt indicatorsAir flow through the liquidChange in index of refraction in air and water.

The first model tested for conductivity differenceshad carbon pencil lead as electrodes. We used ordi-nary tap water as a reasonable approximation of tuffwater. We also ran tests with distilled water, saltbrine, and distilled water equilibrated with pulverizedtuff samples. For soldering we coated one end of thecarbon leads with a flash coat of copper and, at first,used a pin spacing of 2.54 mm 0.1 in.). However.preliminary tests indicated that surface tension andwetting caused problems when the pins were tha:close, so we doubled the spacing, solving this problem.In addition to the 13 pins required provide a63.5-mm 12.5-in. range we used two other pins tomeasure conductivity of the water, thus requiring twoseparate circuits Figure 9).{COULD NOT BE CONVERTED TO SEARCHABLE TEXT}

Twice we attempted to mold prototype gages inthis configuration, but the lead electrodes epeatedlybroke. Tests in a very humid environment indi-cated that for this proposed geometry and design,condensation and moisture led to conductivitychanges similar to those experienced with completesubmersion.

Because of these problems we decided to design afloat-type sensor with tilt gages that had a 12 angu-lar degree range and the capability of measuring

hole. Frictionand clogging of

bearings and minimum depth required forbouyancy caused us to this scheme.

Although hardware was purchased for irdex-ofrefraction measurement of water depth two consider-ations caused us to abandon this method. Each sensorcould measure only the presence of water at one depth,therefore several sensors with associated cables andelectronics would be needed for each hole. Waterconditions and purity in the field were not known andit was possible that a glass probe would be coated withmineral deposits possible leading to erroneous indica-tions of presence of water the holes.

An air bubbling scheme was also not pursued asfeasible. Several air tubes would have been requiredfor each hole and pressure or flow diagnostice andelectronics would have been extensive. cumbersome,and costly. We also felt that the method would nothave been very accurate for the low levels of waterexpected. We therefore redirected design efforts toschemes of electrical conductivity measurement withhope of improving the method. Pins were made of goldwire to prevent breaking and corroding and werespaced 12.70 mm 40.5 in.) apart to mitigate surfacetension and wetting problems. The way we arranged'he pins (Figure 101 allowed us to measure water level

intervals. Laboratory measurements. using the circuit shown in Figure 1 indicatedthat we could measure 10 discrete, repeatable stepswith voltage steps of 300 to 400 mV per step. Figure 12presents final calibration data for the four probes.

In spite of the encouraging calibration data forthese probes, we knew potential problems existed. Onemajor concern was the possible coating of the pins andtenon holder with material, either conducting or non-conducting. which could change the voltage output ofthe sensor as a function of water depth. We hopedthat, in this case at least, a voltage change, even ifdifferent from he calibration steps, would indicatesubmersion of individual pins. Temperature, humidity and other chemical effects on the hardware wereother concerns

Figure 10. Pin Placement of Water-Level Probe

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Figure 12. Calibration Data for the Water-Level Indicator

Major circuitry features of the water-level sensorare the following.

The gage is excited by a -k Hz sine wave 20.5 Vpeak to peak for the heater hole and V forthe water-migration probes.As the various gold pins are submerged, thesteering diodes are shunted in turn, allowingconduction from pin to pin through a seriesresistor. Each time an additional pin is sub-merged the ac signal level increases.The output signal from the probe is fed into ahigh-impedance operational amplifier (LH -7 40)operating as an emitter follower with, unity gain.The signal out of the amplifier is transformer-coupled through isolation transformers (UTCA-20) to a full-wave bridge rectifier.The de signal resulting from rectification is thenfed into 10 comparators (LM-393).Each comparator has a fixed reference voltagethat is applied to one side; as the voltage levelincreases from the bridge circuit, additionalcomparators are turned on.The output of the comparators are then routedto light-emitting diode (LED) displays, theHP9845, and individual DVMs through buff

As originally designed and calibrated, a separatelight came on as each pin was submerged. However,the light display in actuality was tied only to thecomparator voltages and was only an indication ofvoltage. If the water conductivity was different fromthat of the calibration water, input excitation voltagesvaried, or coating of the pins occurred, the light dis-play may not be a true reading of pin submersion. Insuch a case the DAS should at least indicate steps involtage corresponding to water leveL

The water-level sensors performed well during the7-month burial. Some of the effects mentioned abovewere present and affected the light display. When irstinstalled the signal output yielded discrete steps whenpins were submerged. As the experiment progressedthe steps became less distinct and sometimes we foundit difficult to determine which pins were actuallysubmerged.

In spite of these problems, the water-level indica-tors did gis us enough information for collecting anddraining the water collected during the field experi-ment.

At the time the instruments were recovered. acoating of yellow slime was found in the holes up tothe level where water had been standing (Figure A4).We do not know the source or the chemical composi-tion of this material. but possibly it was at leastpartially responsible for the observed behavior of thesensors.

Thermocouple InstrumentationIn addition to the rather extensive TC monitoring

of temperatures in and around the main heater holeand the three water migration holes. TC strings werealso installed in two temperature holes. TH-I andTH-2 (see Figure I . Originally both TC holes were tohave been drilled to size NQ 5.7 mmbecause of drilling problems. we used a 96-mm(3.78-in. HQ hole initially intended for water migra-tion: we designated this hole TH-1.

We made TC strings for each of the TC holesby using .17-mm 0.125-in.stainless-steelsheathed. chromel-constantan TCs. In addition to theTCs, two thermistors were installed in each string forcomparison and as a field test of their ruggedness.

We expected difficulties and uncertainties whensecuring the TCs in with grcut or sand in slightlyupward-inclined holes in the highly jointed and frac-tured welded tuff. Voids would cause thermal conduc-tivity asymmetries and errors. In addition, we did notconsider it desirable to fill the existing open fractureswith grout because of chemical, thermal mechanical,or permeability problems.

ered outputs.* A clock S/N 52-555) was added to provide the

option of blinking light display to alert theoperator to a water-level indication.

21

- Therefore we potted the TC into a 25.4-m-PVC pipe with the tips bent outward so they

would rub against the rock and make good thermalThe and thermistor locations in these

are listed Table 8. We elected these locationst avoid large fractures and cids, which we deter-mined through core logging and borehole televisionanalysis.

Table 8. and Thermistor

Although the TC3 were not individually calibrat-ed, given material specifications, we could trace theirmeasurements to NBS standards by using NBS poly-nomials which determine temperature from TC out-put voltages. All TCs seemed to operate normallythroughout the entire experiment. Data from all ove rthe array were consistent with their placement andwith the expected thermal profiles. We recovered andvisually inspected all the TCs and observed no corro-sion. ome of the TC sheaths had been worn byabrasion during insertion and extraction. Several steelcentralizer springs had broken, but we do nt knowthe exact time of failure although the cause seems tobe related to stress corrosion. The rubber baffleswhich had been used to minimize convection. mayhave helped keep the TC strings centralized; howeverconsistency of TC data indicates that the failure oc-curred during recovery and not before.

Gas and Water Collection SystemTo sample gas and water from packed sections of

any hole, we used stainless steel tubing and a valveand collection manifold in the instrumentation alcove.A vacuum pump and reservoir were used when avacuum was needed. Pressure and vacuum gages diag-nosed the gas and water collection system. Each holehad a 3.17-mra (0.125-in.) tube for gas sampling andboth a 3.17-mm and a 6.35-mm (0.25-in.) tube forwater sampling. The larger diameter tube was forstandby use in case the smaller one should becomeplugged. It could also be used if water collected toofast for the small tube to drain, thus preventingdamage to instrumentation in the hole.

We sampled gas by closing all valves to the arrayand then evacuating the sampling manifold and a150-cm. stainless-steel sampling cylinder. The vacu-um system was then disconnected and the valve to t hedesired sample tube opened. After the sample wastaken we closed the valve and removed and labeledthe sample cylinder. Gas samples were taken beforethe heater was powered, just before the heater wasturned off and before the instrumentation was re-moved.

Water sampling was somewhat similar to gas, thecollection manifold and cylinder being evacuatedwhen necessary. In some cases gravity flow wasenough; a valve leading to the hole with the samplewas opened and water ran into a buret. Thewater was transferred into plastic bottles, labeled andsaved for shipment to the laboratory.

We placed rubber baffles along each TC string atseveral locations to minimize the effects of thermalconvection along the holes Steel leaf-spring centraliz-ers maintained the string position in the hole andheld the TCs against the hole wall. Shrink tubing onall the TCs in the strings-except in the region of thetips-provided electrical isolation of the TC sheaths.Sheath-to-sheath electrical resistance checks ensuredthat all TCs were making contact with the rock.

Originally we did not design an insertion tool. Wewere to insert the TC strings by pushing on the TCsheaths. However, we had difficulties in inserting theTCs to the desired depths and had to use black waterpipe in addition to the PVC pipe to add stiffness andovercome the roughness of the holewall. During thisprocess we inserted, extracted. and reinserted one ofThe strings. Thermocouples that had been bent duringextraction had to be reconfigured to rub against thedrill hole and reinserted at the proper depth.

Later, we devised a semi-automatic water sam-pling scheme during nonworking hours, water wasdrawn from the heater hole upon command from theDAS and deposited in a large bottle (Figure A5). Wethen transferred it to platic bottles, labeled them,and prepared them for shipment.

Power Distribution and AlarmSystem

In order for the experiment to succeed, power tothe heater had to be uninterrupted and the DAS hadto operate continuously. Also, the temperature of therocks in the heater holes had to be prevented fromexceeding design limits, water had to be extractedsuccessfully, and the safety of personnel had to heemphasized.

Power requirements were met by the power distri-bution and alarm system. We expended considerableeffort to provide an autostart, backup heater powersystem and uninterruptable power for the DAS. Weinstalled alarms-automatic telephone messages, andcomputer-based-to warn of power outages, tempera-ture excursions, and potential pressure safety prob-lems.

A start-on-demand diesel generator (Figure 13)provided heater power in case commercial power waslost. (Heater power loss for more than a few secondscould have caused TC measurement fluctuations not

only in the heater hole, but also in adjacent holes.) Wepositioned the diesel and is sensing, starting, andswitch gear at the G-tunnel portal and ran specialinstrument power lines to a substation near the alcove,a run of about 19 km (1.25 mi).

If, for any reason, instrument power was lost tothe heater alcove, the diesel would automatically fur-nish regulated instrument power to the alcove. nomi-nally within 10 a.

Uninterruptable power was also required for theHP9845T data acquisition controller because eventransient power outages would cause loss of the vola-tile memory and hence, data Autostart capabilitiescould reset the memory and start collecting dataagain, but loss of some data was possible if even short-term power outages occurred.

The uninterruptable power supply used was anElgar Model UP2500, rated at 2.5 kW. Tests conduct-ed with the system load showed that there was noappreciable ac voltage drop after 7 h of running onrechargeable batteries, with no input power. The pow-er supply uses a dc-to-ac converter that changes about90 V d to isolated 115-V ac, 60-Hz power. Duringnormal operation the batteries are continuouslycharged by the input ac power. When input power islost, the batteries immediately supply uninterruptedpower to the converter. A reverse transfer switchtransfers power back to normal line power only if theuninterruptable power supply itself fails.

Figure 13 Power Distribution System and Alarms

23

To cover long periods (such as weekends) whenthe experiment was to run unattended, we installed analarm system to alert us if power was lost. The ele-phone dialer alarm used was a Model L700D, suppliedby Acro-Larm. It was connected to heater rock-walltemperature output in order to insure that tempera-tures did not exceed limits that could cause degrada-tion of the heater hole rock wall, In addition, poweroutage messages and alarms were recorded.

The alarm system consisted of a preprogrammed,continuous-loop tape cartridge that had the telephonenumbers of personnel and messages prerecorded ontwo tracks, each of which could be triggered indepen-dently of the other and which could contain differentnumbers and wording. The continuous-loop tookabout 5 min to run and could easily accept up to aboutive different phone numbers and messages per track

The system operated satisfactorily.The HP3052A DAS could also determine if over-

temperatures existed. Also, CRT messages, audiblealarms, and relay closures for lighted alarms outsidethe alcove indicated potentially dangerous pressuresmeasured in any of the holes.

ConclusionsIn general the instrumentation designed and

fielded for the In-Situ Tuff Water Migration/HeaterExperiment operated as designed:

The pH sensors operated nominally with quali-fications based on the fielding conditions.Some of the pressure transducers failed, but latein the test.The laser strainmeter demonstrated its sensitiv-ity, but is counting electronics and mountingdesign must be modified before it can yieldquantitative results.The RH sensors did not operate satisfactorilyThough the output of the water-level was notrepeatable during the experiment because of pincoating, it was useful to indicate changes inwater levels.

The DAS performed well under less-than-idealconditions; only minor hardware problems wereencountered and problems with the softwareresulted from on-line development testing ofimprovements, and expanded capabilities.The water collection system, TCs, and stress-meters seemed to have operated without diffi-culties.

ReferencesJ. K. Johnstone, In-Situ Tuff Water Migration/Heat-

er Experiment: Experimental Plan SAND79-1276 (Albu-querque: Sandia National Laboratories, Augus: 1980

J. L Krumhansl, Final Report: Conasauga Near Sur-face Heater Experiment. SAND79-1855 (Albuquerque:Sandia Laboratories, November 1979).

A. R. Lappin. R. K. Thomas and D. F. McVey EleanaNear-Surface Heater Experiment Final Report. SAND2137 (Albuquerque Sandia National Laboratories. April1981.

J. K. Johnstone In-Situ Tuff Water Migration/Heat-er Experiment: Final Report. SAND81-1918 (Albuquerque:Sandia National Laboratories, Nd). To be published.

C. 0. Duimstra, In-Situ Tuff Water Migration/HeaterExperiment: Hardware Mechanical Design DefinitionSAND8I-1048 Albuquerque: Sandia National Laborato-ries November 1981

J. Berger and R. H. Lovberg, Earth Strain Measure-ments with a Laser Interferometer.ber 1970.

C. W. Cook and E S. Ames. Borehole-InclusionStressmeter Measurements in Bedded Salt. SANDAlbuquerque: Sandia National Laboratories, July 1980

D. R. Waymire and C. O. Duinistra In-Situ TuffWater Migration/Heater Experiment The Data

and Playback System. SAND81-1059 AlbuquerqueSandia National Laboratories October 1981

Operations Manual For Digital Humidity Tem-perature Measurement system Modelinclude Discrete Relative Humadity Transducers Model

Albuquerque Thunder ScientificCorp September 24, 1979

:4

Figure Al. Drill Hole Pattern for the Heater Array (Black hose contains cables for installed stressmeters

{COULD NOT BE CONVERTED TO SEARCHABLE TEXT}

Figure A3. The Laser Alcove Where the Laser Head is Mounted on the Rock Wall (Included in the photo are the electroniccounting system, power supplies and test equipment)

Figure A4. The Instrumentation Section of the Heater Assembly. Showing the the Water level Indicatorto taken immediately after recovery.

Figure A. The Gas and Water Sampling Manifold, Including the Automated System