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WHC-SA-3023-FP

Hanford Waste Tank Cone Penetrometer CElV

Prepared for the U.S. Department of Energy Assistant Secretary for Environmental Management

Westinghouse Hanford Company Richland, Washington

Management and Operations Contractor for the U.S. Department of Energy under Contract DE-AC06-87RL10930

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Copyright License By acceptance of this article, the publisher and/or recipient acknowledges the U.S. Government's rioht to retain a nonexclusive, royalty-free license in and to any copyright covering this paper

Hanford Waste Tank Cone Penetrometer

R. Y. Seda

Date Published December 1995

To Be Presented a t Society of Hispanic Professional Engineers (SHPE) Eighteenth Annual National Technical

Seattle, Washington February 15-1 7, 1996

& Career Conference (NTCC96)

Prepared for the U.S. Department of Energy Assistant Secretary for Environmental Management

Westinghouse P.0 Box 1970 Hanford Company Richland, Washington

Management and Operations Contractor for the U.S. Department of Energy under Contract DE-AC06-87RL10930

W H C -SA-302 3 - F P

Copyright License By acceptance of this article, the publisher and/or recipient acknowledges the US. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.

Approved for public release

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This report has been reproduced from the best available copy.

Printed in the United States of America

DISCLM-2.CHP (1-91)

. HANFORD WASTE TAHK COWE P€%ZTROH,ET~

R,Y- Seda, Westinghouse Hanford P-0- Bux 1,970, HSIW €is-09, Richland, WA 99352

ABSTlUHX

A new toof is being developed to characterize tank waste at the kanford Reservation. This t o o l , known as the cone penetrometer, is capbble of obtaining chemical and physical properties in situ. For the past 50 y e a r s , this t oo l has been used extensively in so i l applications hand now has been modified for usage in Hanford Underground Storage tanks: These modifications include development of new "wasterf data models as ,Well as hardware design changes t o accommodate the hazardous and radioactive environment of the tanks. The modified cone penetrometer is schddule to be deployed at Hanford by Fall 1996.

At Hanford, the cone penetrometer will Se used as an instrumended pipe which measures chemical and physical properties as it pushes through tank waste. Physical data, such as tank waste stratification and mechanical properties, is obtained through three sensors measuring tip pressure, sleeve friction and pore pressure. C h e m i c a l data, such as chemical speciation, is measured u s i n g u Raman spectroscopy sensor. The sensor package contains other instrumentation as well, including a t i p and side temperature sensor, tank bottom detection and an inclidometer. Once t h e - c o n e penetrometer has reached the bottom of the tank, a moisture probe sill be inserted into the pipe. This probe is used to measure waste moisture content, water level, waste surface moisture and tank temperature.

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This paper d i s c u s s e s t h e development of this new measurement bys tem. Data from the cone penetrometer will aid in the selection of dampling tools, w a s t e tank retrieval process, and addressing various tank safety issues. This paper will explore var ious waste models as well' as the challenges associated w i t h tank environment.

INTRODUCTION

EACXGROUND

Hanford was the site of a weapons grade plutonium production pladt built during World War I1 as part of the Manhattan project. Since the p l a n t stopped production in 1989, the mission at Hanford has shift'ed from weapons production to cleaning up the waste generated from such activities. The by products from the generation of weapons were stored in 149 single shell tanks and 28 dauble shell tanks. These, tanks, located underground, were built to hold over I million gallons of hazardous and radioactive waste. Some of these tanks are as large 8s 70 feet in diameter and SO feet in depth. Over time, some waste by- products have been reprocessed to reduce their volume, thus increasing the a v a i l a b i l i t y of tank storage r o o m . Even though records were

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maintained on the materials o r i g i n a l l y stored in these tanks, the/ actual

Several methods are being implemented to characterize these unknown waste compositions, including core sampling and the use of bn-tank instrumentation. Drilling core samples from the contents of the tank and sending these samples to laboratories for a n a l y s i s is the sitandard method for obtaining certain chemical and physical data. kn-tank instrumentation includes systems which gather temperature I l i q u i d level and other measurements. Unfortunately no single method can ob+in all the information required for safely remediating the tank waste.! Since no one method is available, several methods are being considbred to obtain all the needed data. One of the most promising methods Wes the cone penetrometer to obtain chemical and physical properties d&a-

I IWSTRUnarr GENERAL QESCRIPTIOX i

The cone penetrometer consists of an instrumented metal rod which is pushed through a material. provides structural support to t h e rod. The rod is screvinq hollowed rod sections i n t o t h e instrumented tip a6 it is pushed, and penetrates the material. The basic instrument /package consists of sensors to measure tip pressure, pore pressure and! sleeve friction. Load cells at the tip (tip pressure) measure resishnce of the materials ahead of the tip while side load cells (friction Isleave) measures t he friction as the cone pushes into the material. Elfltered hydrostatic pressure (pore pressure) is obtained using a sensinq device also located wi th in the t i p . Classification charts are then gelnerated by measurements taken from these three sensors. These c h a r t s are typically used to determine the type of soil or material! being penetrated- Figure 1 d a p i c t s a t y p i c a l data plot generated frod a push through different soil types ,

repackaging the tip, lowering another sensor down into the rod, of by a special rod tip. Many in-situ sensors are already available ifor the cune penetrometer, sensors to measure temperature, shear modul48, soil density, vislcosi ty , pH, chenical species, moisture, radiation, hydrocarbon dnd resistivity. Resistivity measurements are baed to determine t h e location and depth of groundwater. The resistiviqy probe has tvo electrodes mounted on an insulated sleeve above the cone. These two electrodes measure soil conductivity (resistivity) by pasking an electrical current between them. Since mineralized water ks very conductive, t h e sensor is ideal for locating water. S o i l , gas aqd water samplers can also be attached to the rod by unscrewing the traditional

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Originally, cone penetrometers vere developed for soil applicatigns such as locating firmer soils in sea locked countries like the Netherlands. Since then, cone penetrometers have been used in soil identiidcation, soil physical parameter determination, accessing so i l bearing caqacities

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chemical/physical composition is mostly unknown. ~

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The rod is supported by a guide

Other devices may be attached to t h e basic cone

tip and replacing it w i t h a sampler t i p . I

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and site characterization. Modern versions have the additional capacity of measuring physical and chemical characteristics without removing samples from the ground. Other capabilities include groutifng of boreholes produced a f t e r samples have been taken. Crout$ng t h e boreholes is necessary to avoid introducing contaminants from the surface to possible aquifers .

BODY

Hanford tank w a s t e is a mixture of sludge and saltcake materialk. The ~ Hanford s k i d mounted cone penetrometer system will be capable of penetrating these tank waste materials to obtain physical and chemical data. Sludge waste is a very weak material while saltcake vaste can be very hard. The data which will be obtained by the cone peneqometer includes: shear strength, compressive s trength, yield stress', waste stratification, chemical speciations, and moisture. These Perived measurements are in adhition to the d i r e c t measurements of t i p i s tress , sleeve friction, pore pressure, t i p and s i d e temperature, inclihation, bottom detection, and waste tank temperature. Figure 2 shows a schematic of the probe.

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Shear strength, compressive s t r e n g t h and yield stress are Ghysical properties needed f o r the safe retrieval of tank waste. Knowdedge of waste stratification profiles will a i d other existing sampling dools in the tanks since it identify the material penetrated. Fr6m this information, t h e appropriate sampling mode can be selectedt The sampling modes include t he usage of auger, push mode or rotary core samples. The "hardness" of the sampled material can affect the recovery rate of these systems. Chemical speciation data w i l l be b e d to determine the waste compatibility issues during the retrieval/prUcessing of the waste. Moisture and tank temperature are required to ansver many tank safety questions.

The operation of the skid mounted cone penetrometer is straight4orward. A s t h e tip of the cone penetrometer is lowered i n t o t h e tank, information about chemical and material properties will be sent 'back to an on-board computer and analyzed. The computer, as well as the signal conditioning and processing equipment, is located i n specially design skid on the tank. OnC8 the tip reaches the desired location in 'a tank, such as the tank bottom, cables leading to the sensors in t h e t!ip will be removed to allow room for other instruments. A moisture sengor, fo r example, can be lowered vith a winch to obtain the moisture content of the surrounding tank waste material. Once all data have been obtained, the cone penetrometer rod is removed from the tank.

Hanford tank waste presents an unusual challenge to instruments like the cone penetrometers. Tank interiors can only be accessed through risers protruding out of the top of the tank. Risers are pipes which are used to reach the tank interiors. Tank contents are not easy to samp4e s i n c e

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the waste contained w i t h i n the tank is both hazardous and radiohive. As the cone penet rometer lowers its rod and guide tube down thej riser, they will be unsupported until the waste is reached. The guibe tube will provide structural support to the push rod as the push rod penetrates the waste. Due to the possibility of buckling, o&ratinq loads will be limited after completion of stress analysis and s t r , u c t u r a l testing completion. In typical soil applications, the so i l bsually supports the cone and rod as it is lowered.

I Other challenges pertain to t h e tank structure itself. The tank tops have limits to their Load capacities. Cone penetrometers achieve the necessary reaction force to push the rod down into the soil by either anchoring the cone penetrometer support s t r u c t u r e in the surrounding soil or by ballasting the support structure w i t h the necessary ;weight.- Since anchoring the cone penetrometer support structure onto theitank is n o t feasible , ballasting weight on the skid must be used to achkeve the necessary reaction force to penetrate the waste within the tank. This reaction force is limited by the total weight which the top of ?he tank can withstand without failure. Dome loading limitations a t ,Hanford tanks var ie s depending on the equipment loading and soil loadiqg. The maximum reactive force which the cone penetrometer will be ca@ble of exerting on t he tanks Will be 30 tons. I

Another structural problem unique to the tanks is how to determine where the location of the bottom of the tank. Since chemical reactidns have occurred within the Hanford tanks f o r decades, the bottom of the tank may be bowed due to t h e high heat associated with the reactiond of the waste. Tank b o t t o m s have also corroded with time. To cornpendate for these problems, an operational envelop limiting t h e forces apdlied to the b o t t o m of the t ank as well a s a bottom detection systom are being developed. The cone penetrometer bottom detection systen is a magnetometer sensor which will stop the rod once the sensor has detected the bottom of the tank. The magnetometer detects t h e tanks [ferrous material. Test indicate that the bottom of the tank can be 4easured within a feet of a s t e e l plate. The closer the magnetometer is to the steel bottom, t h e stronger the signal. This new sensor $as the potential of being used in other applications such as l oca t ing pipes and other ferrous structures in the soil applications.

DATA XODELS ! j

Since the cone penetrometer has never been tested in Hanford type waste, waste simulants were developed to simulate the materials in t$e tank, such as s a l t cake and sludge. Tank waste mechanical propertiks were determined by empirical formulations based on soil theory. W r each simulant, a waste classification chart was developed as a cal3bration guideline f o r future usage to determine what kind of the material the cone penetrometer vas penetrating. O t h e r data obtained during simulant testing included pushing requirements of the system.

Salt cakes and sludges are the major components of the tank waste.

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Salt cake can be hard a s cement whi le sludge can have t h e c l a y s . The cone penetrometer must penetrate through components to gather data on physical properties. properties of interest were sludge y i e l d s trength, sludge

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consisqency i of both of these The physical

shear skrength and saltcake compressive strength. These measurements w e r e obtaiqed from tip pressure, sleeve friction, and pore pressure sensors. ' , Waste classification char t s were developed and are depicted in the Apj?endix.

1 The physical properties soil models used to develop the corrdlations between mechanical properties and the cone penetrometer sensor readings were based on the spherical cavity model- Estimates for the1 sludge shear strength employed t h e following equation:

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'peak = ( q, - Q"., 1 / N,, I

where 4% = cone bearing (bearing force/bearing area) = "0 - - overburden pressure (density of the materid1 times

t h e depth) . In materials with 3 p s i or less of shear strength, pore pressure over dif fdrential

Cone fac tor (generally obtained f r o m e , p i r i c a l d depth can be used. correlations). In c lays , it is normally between 10 and 20 I

The empirical correlations based on the test results were the fol'lowing:

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Nk, -

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Yield strength Shear strength Compressive strength

These models were o n l y va l id f o r the simulants tested- The sdmulants were t w o clays for sludges (Kaolin and Bentonite) and KSMag (a fertilizer or cattle supplement) €or saltcake, All these materials are non-hazardous. Further testing will be completed so that the different waste types a re classified and the accuracy of the instrument is accessed.

The test results indicate that the sirnulants occupied distfnctide areas in the uaste classification charts. The appendix shows the d i f 4erences in the tip stress profiles and sleeve stress profiles. A preliminary waste classification chart has been created in which the weak 'sludges and strong saltcakes are displayed.

rnISTuRB PROBE I

The moisture probe is lowered in the cone penetrometer push rod inner diameter and programmed to automatically take readings every inc for 10 to 50 seconds. inches of material can be effectively measured. The technique'used to measure moisture is through neutron thermalization. This techniques has

The testing results have shown that the s u m o 9 nding 6

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been used in other appl-ications to measure moisture on soil surfice and within oil-logging holes. Neutrons are emitted by a sourc8,: Cf-252 source, in t h i s case, onto the material of inspection. Thei source neutrons scatter and lose some energy. Neutrons lose nost of i t s ] energy when scattering from a hydrogen nuclei (proton) because it has *&e same mass. Neutrons scatter several times and eventually slow down to thermal energies. A thermal neutron sensitive detector, located near the neutron source, detects source neutrons which become thermalhzed by the hydrogen w i t h i n the waste and scatter back t o the detector. The more water present, the more hydrogen and the greater the count Zate in the thermal neu t ron detector. The count rate is correlated to mbisture con ten t i n waste material. This technique is sensitive to the adount of hydrogen in waste, it is also sensitive to the amount of organic whl.ch contain hydrogen.

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CONCLUSION

The cone penetrometer is scheduled to be deployed in the Hanfodd waste sampling process in 1936. This system will join several other mdasuring systems currently being used to CharaCteriZ8 tank waste. Cone penetrometer usage in the tanks represents a new applicatihn that deviates from its traditional uses in soil analysis. For tan* waste, the cone penetrometer will acquire physical and chemicaz waste properties required for remediation and processing as w e l l 'as t h e resolution of tank safety questions.

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A C X N ~ E 3 4 E W P I i

I would like to acknowledge my husband, John Blyler, for h i s sudport in I the development of this paper.

REFERENCES

W.L. Bratton, D.E. Chitty, S . P . Farrington, ARA Report No. 15968-2, "Development of correlations between cone penetrometer testing lresults and physical and mechanical properties f o r Hanford saltcake dimulant materials'q, August 1995 .

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W.L. Bratton, D.E. Chitty, M. Gildea, ARA Report 5968-1, ttDevelobment of correlations between cone penetrometer testing results and physical and mechanical proper t i e s :€or Hanford sludge simulant materialsn, June 1995-

using Cone Penetrometer T e s t s and CPT with pore pressure measurimentsn, November 1989. I

P . R . Robertson, R . G . Campenella, "Guidelines for Geotechnical. i Design

NOHENCIATURE

cone bearing averburden pressure

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Cone factor Yield strength Shear strength Compressive s t r e n g t h

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APPENDIX

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0 I!; 10 !i U 750 19000 2 4 fi 0 40 00 120 0.1 1 10 100

The (inin) Sloovo Frlctloci Tip Frlctlori POfQ

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Figure 1:

Pore Pressure Dissipation Tests

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Typical Soi l Cone Penetrometer Data

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Moisture Probe l-

Sleeve Load Cell

Tip Temperature Gage

Pore Pressure Gage

Side Temperature Sensor

F’riction Sleeve

Bottom Detector 7

Figure 2: Cone Penetrometer Sensor Tip Schematic

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