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SOLUBLE P I G FOR RADIOACTIVE WASTE TRANSFER L I N E S

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A-6001-401R 107~941

SOLUBLE PIG FOR RADIOACTIVE WASTE TRANSFER LINES

Phillip C. Oh1 Westinghouse Hanford Company

P: 0. Box 1970 Richland, WA 99352

Dr. Charles Pezeshki Washington State University

Pullman, WA 99164-2920 Department of Materials and Mechanical Engineering

ABSTRACT

F1 ushing transfer pipe after radioactive waste transfers generates thousands The use of gallons of additional radioactive waste each year at the Hanford site.

o f pneumatic pigging with waste soluble pigs as a means to clear transfer piping may be an effective alternative to raw water flushes. A feasibility study was performed by a group of senior mechanical engineering students for their senior design project as part of their curriculum at Washington State University. The students divided the feasibility study into three sub-projects involving: (1) materials research, (2 ) delivery system design, and (3) mockup fabrication and testing.

thermoplastic polymer combined 50:50 wt% with sucrose to meet the established material performance criteria. remote pneumatic delivery system and constructed a mockup section of transfer pipe for testing the prototype pigs.

Key Words: Hanford, corrosion, pigging, pipe, nuclear

The students screened through twenty-three candidate materials and selected a

The students also prepared a conceptual design of a

INTRODUCTION

The Hanford Site manages 253 million liters of radioactive liquid wastes in 177 1 arge underground storage tanks"'. Management of these wastes requires frequent transfer between tanks through a complex network of transfer piping. are numerous configurations of transfer pipe currently in use including pipe-in- pipe, direct buried pipe, and pipe in concrete trendways. materials involved in the transfer piping network including mild carbon steels, stainless steels, concrete, fiber-reinforced plastic, and vitrified clay pipe. The Hanford waste management facilities (Tank Farms) use on the order of 200,000 gal of raw water annually to flush waste from transfer lines into waste tanks following a waste transfer. while working around transfer lines following a transfer. corrosive raw water standing in the transfer piping thereby reducing the life of the carrier pipe. In addition to reducing the life of the carrier pipe, these flushes create new radioactive waste that must be 'evaporated or further processed for disposal .

There

There are also numerous

These flushes are required to minimize worker radiation exposure These flushes leave

The primary objective of a feasibility study performed by students at Washington State University was to remove residual liquids from transfer piping to extend the remaining useful life wh.ile reducing radiation doses to workers to As- Low-As-Reasonably-Achievable. volume of flush water required annually in the Tank Farms by providing an alternate means of removing residual radioactive waste from the transfer lines.

The concept for a pneumatic pipe flush system operates similar to "Smart Pig" internal pipe Non-Destructive Examination equipment. A solid slug (the pig) is driven through the pipe pneumatically thereby removing residual radioactive waste and stagnate solutions that could accelerate corrosion of the carrier pipe. In order to prevent line plugging and further maintain low operator exposures, the pig is completely soluble in the wastes.

A secondary objective of this task was to reduce the

SPECIFICATIONS

There are two primary designs involved with pneumatic pipe flushing. A delivery system must be designed to allow the pig to enter the carrier pipe and be driven by an external supply of compressed air. with specific material properties such that it will satisfactorily remove residual liquids as it moves through irregular sections of pipe and still dissolve in waste within a specific time period. following parameters were used:

The pig itself must be designed

For the purposes o f the prototype design, the

Carrier Pipe: 3", ASTM Type 304L, Sch. 40 SS Containment Pipe: 6", ASTM Type A537, Sch. 40 CS (Galvanized) Thermal Insulation: Polyurethane Foam, 1.5 in. Thermal Encasement: 10" Fiberglass Reinforced Plastic

For the purposes of the prototype design, the following waste chemistry parameters were used:

PH 7-12 Temp 25°C to 75°C OH- 0.01M to 10.OM N02- 0.01M to 5.5M N03- 0.1M to 3.OM

Prototype Pig

the pneumatic driving force. The pig was to be made of material(s) that will maintain configuration and compressive strength in a waste environment for a minimum of 4 hours but be completely dissolved within 36 hours. The pig material was specified to be non-hazardous as defined by WAC Dangerous Waste Listings. material was required to be flexible enough to accommodate standard dimensional tolerances for I.D. and ovality in the carrier pipe. The pig surface finish was specified not to be so abrasive as to cause an erosion corrosion concern for the pipe. for nominal carrier pipe sizes from 2" to 6" I.D.

Remote Delivery System

The delivery system was specified to'provide access to the carrier pipe through the thermal insulation and the containment pipe. The delivery system was required to meet any necessary requirements for secondary containment penetrations as outlined in Washington State Dangerous Waste Regulations ( 2 ) . Isolation from the carrier pipe needed to be provided to minimize operator exposure when loading the pig into the delivery system and to,minimize contamination spread. The delivery system was designed to minimize fluid flow characteristics resulting from the penetration. The delivery system was specified to provide an adequate supply of pneumatic pressure to drive the pig through 100 meters of carrier pipe, including three, 1 meter radius, 90 degree bends with a 1 meter total elevation drop. The carrier pipe was assumed to be open at the downstream end with 10% total pipe volume residual 1 iquids.

The pig needed to be designed with adequate compressive strength to withstand

The pipe

The pig fabrication process was required to be able to accommodate pigs sized

MATERIALS RESEARCH

In order to meet both the chemical and mechanical material properties identified in the specification, styrene-maleic-anhydride (SMA)'3' was chosen for strength compounded 50:50 wt% with disaccharide sucrose as a readily soluble binder. Test specimens were manufactured for testing using a standard laboratory heat press to apply a constant pressure of 21 MPa at 150°C. specimens was 3 . 8 cm diameter x 2.0 cm high.

SMA/disaccharide in various waste chemistries at 25°C and at 75°C. tests required placement of the test specimens in 500 ml unagitated waste simulants and logging the time it took for the specimen to be severely dissolved. Dissolved was defined as that point when the specimen would suffer complete loss of dimensional stability when agitated.

Standard laboratory equipment was used to determine Young's modulus to be 247 MPa for pure SMA and 220 MPa for the 50:50 wt% SMA/Disaccharide compound. Compressive strength, tensile strength, shear modulus, and hardness were not tested due to time and equipment limitations available.

a bullet or spherical shaped Flexible Pig (figure 1 ) . geometry can be accomplished by using a die to create a cylindrical raw pig by applying appropriate heat and pressure to achieve a thermoplastic set. The cylindrical raw pig can then be machined to create the "I" shape.

The final size of the test

Table 1 shows the solubility data for the 50:50 wt% compound of The solubility

Severely

The high modulus of elasticity necessitated a Rigid I-Pig geometry rather than Manufacture of the I-Pig

DELIVERY SYSTEM CONCEPTUAL DESIGN

Industrial pigging systems typically utilize direct insertion into the pipe at

This necessitated conceptual design of a remote delivery system.

The procedure for performing

a flanged connection or by use of a rotating barrel coupling. options is feasible for the Hanford system because of high radiation exposure workers would see. After several design sessions, the system shown in figure 2 with a maximum air pressure of 80 psig was determined to be appropriate. the pneumatic flush is as follows:

Neither of these

1 ) Insert pig into launch tube above grade. 2 ) Open gate valve # 1 and turn on air #I to send pig into chamber. 3) Actuate hydraulic press to load pig from chamber into pipe. 4 ) Open gate valve #2 and turn on air #3 to send pig right-to-left.

Open gate valve #3 and turn on air #2 to send pig left-to-right.

No prototype was constructed due to time and material limitations on the students.

MOCKUP FABRICATION AND TESTING

A mockup of a typical Hanford pipe run was created in the attic of the Thermal and Fluids Building at Washington State University. The mockup consisted of 70 lineal feet of 3 inch schedule 40 PVC pipe with three 1 meter radius 90 bends. Low spots could be simulated in the mockup by hanging weights from unsupported spans of pipe and he elevation drop could be simulated by adjusting the mockup supports. A commercially available bullet shaped flexible pig constructed of Styrofoam was used to test the mockup. The air supply to the mockup was able to deliver constant pressures of 0 to 55 psig. A collection system consisting of a 33 gallon garbage can was used to collect the water placed in the mockup to simulate standing flush water in a pipe.

Using the commercial pig to test the system, it was determined that elevation drop did not have a significant effect on pig velocity. It was also determined the velocity leveled off at roughly 12 ft/sec after a supply pressure of 40 psig. this pressure, the commercial pig tended to hang up in the 90 bends. Volume recovery of the standing water placed into the mockup was unsuccessful as the collection system could not be relied upon to work satisfactorily. pressure without the pig resulted in none of the 10 liters of standing water being flushed through the pipe. Accurate estimates of the percent of remaining water after flushing with the pig were not found due to the unsatisfactory collection system, however, splash pattern estimates at the collection site indicated roughly 95% complete removal of the water.

Below

A trial at full

CONCLUSIONS

The feasibility study identified a waste soluble material that may be able to Although the be used for pneumatic flushing of Hanford waste transfer piping.

50:50 wt% SMA/Disaccharide appears to meet the solubility requirements, additional study is necessary to determine if a Rigid I-Pig could effectively remove residual liquids without damaging the protective oxide layer on the inside of the piping. Additional study is also necessary to determine if there are safety or regulatory compatibility concerns associated with the SMA/Disaccharide compound.

Cost estimates associated with retro-fits should be performed to determine the total

The conceptual design meets the stated criteria for remote operation.

b e n e f i t o f i n s t a l l a t i o n . A r e t r o - f i t would r e q u i r e s i g n i f i c a n t m o d i f i c a t i o n t o contaminated t r a n s f e r l i n e s and p e n e t r a t i o n o f contaminated p i t s .

ACKNOWLEDGEMENTS

The authors wish t o thank t h e s tudents i nvo l ved i n t h e s e n i o r des ign c l a s s f o r p r o v i d i n g a use fu l f e a s i b i l i t y s tudy a t a tremendous cos t sav ings t o t h e Un i ted S ta tes Department o f Energy.

M a t e r i a l s Research: Mark Schwarz, P h i l l i p Matz, and A m i r Shabanzadegan

D e l i v e r y System Conceptual Design: Mark Higgins and Mike Sundstrom

Mockup F a b r i c a t i o n and Test ing: Mark Telander, Randy Palmer, C ra ig Samson, and Khoi Thai

1

REFERENCES

1) Hanlon, B. M., "Waste Tank Summary Report f o r Month Ending June 30, 1996," WHC- EP-0182-99, Westinghouse Hanford Company, Richland, Washington, September 1996.

2) Washington A d m i n i s t r a t i v e Code, "Dangerous Waste Regulat ions" , Chapter 173-303, Washington S ta te Department o f Ecology, Olympia, Washington, March 1992.

3) M a t e r i a l s Sa fe ty Data Sheet, CAS No. 26762-29-8, Styrene Ma le i c Anhydride Resin, ELF ATOCHEM, Ph i l ade lph ia , Pennsylvania.

TABLE 1 SOLUBILITY DATA FOR 50:50 WT% SMA/DISACCHARIDE

** Defined as the time required f o r the specimen to be approximately 90% dissolved.

Figure 1 - Typical Pig Geometries

Air 1

Rigid I-Pig ' Bullit Pig

0 Spherical Pig

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