Executive Summary s2

Executive Summary During normal operation in the spent fuel treatment process, every so often molten salt must be removed the electrorefiners and replaced with fresh salt. Currently, Idaho National Lab has one method for removing electrolyte (molten salt) from their Mark-IV and Mark-V Electrorefiners. This process consists of dipping three ice cube trays in the molten salt using an overhead crane and pulling them out to freeze. After they solidify, they are emptied and go back in for another run while the frozen cubes are individually collected using master slave manipulators and placed into a bucket for transportation. The present process is slow and handling intensive. The complexity of the handling is a major factor in the low salt extraction yield rate because the electrorefiner is in an enclosed, argon filled, hot cell only accessible through the use of remote operated master slave manipulators and overhead cranes. An alternate method that utilizes a pump and pipe network was devised and a prototype built, but the testing of it went so poorly that they do not consider it a viable option. This document presents another method which will decrease the time it takes to remove the molten salt and increase the salt removed per evolution while maintaining the integrity of the system through the use of a rugged design.

1 Background When nuclear fuel gets used in a reactor, it becomes very “hot” (radioactive). At this point it has used approximately 5% of the useful uranium and the waste now has an enormous half life. By treating this fuel, the useful uranium can be removed and the half life of the waste can be drastically reduced. One process for doing this is called electrorefining.

Electrorefining is an electro-chemical process which separates the uranium from the rest of the fuel rod. This method is accomplished by chopping up fuel rods into short segments, then putting them in an anode basket. By running high current through the basket, you get an oxidation reaction with the uranium which then allows it to react with the electrolyte. When the uranium makes it over to the cathode where the circuit is completed, it is reduced through reaction and deposited on the cathode.

Idaho National Lab currently uses this process for treating fuel used in Experimental Breeder Reactor II with their Mark-IV and Mark-V Electrorefiners (see figure 1). One of the problems they face is that when the plutonium concentration in the molten salt gets too high, it must be diluted. The two ways of doing this are removing the electrolyte (molten salt) and recovering the plutonium from the molten salt. As of now, both are slow but it is still much quicker to remove salt.

Figure 1: Mark V Electrorefiner

2 As of now, there are two devices that were designed for salt removal. One is basically dipping three ice cube trays in the electrolyte and pulling them up to freeze once they are full. It currently takes a long time to remove a little salt this way due to all the handling involved in the assembly and disassembly of the trays, but is still faster than using a plutonium recovery method. The other system is a pump and pipe system that has yet to be assembled by hand without leaking. Inside a hot cell where all the work has to be done remotely, it would be even more difficult to keep it from leaking. Therefore, it was never put in the hot cell.

Problem Definition INL is looking for an improvement upon their current system of salt removal. The difficulty comes from the electrorefiners being in a hot cell, which is a room with a lot of radiation in an argon atmosphere, so it is impossible for a human to go inside. Operators use windows, master-slave manipulators, and overhead cranes to accomplish tasks inside the hot cell. This makes even simple operations complex and time consuming. Complicating matters even more, the salt has to freeze in small enough chunks that the grinder can take them. Using this information, the following problem statement was decided upon.

Problem Statement: Design, build, and test a method for pulling molten electrolyte out of an electrorefiner, which is inside a hot cell, and freeze it into small enough cubes for the grinder.

The goals of this project are to at least triple the current electrolyte removal rate, develop a working prototype and use it to prove the concept. This device will not have to go in the hot cell. The idea is to come up with something that works so INL can continue with the research in order to fully develop a method for salt removal.

Using the needs, wants, and goals of the client, target specifications (see specs on next page) were decided upon. Primarily, this device needs to remove 16,500 cm3 of salt per evolution and get it frozen into cubes that are no bigger than 2 in by 2 in by 2 in. All of the specs are either stating we need to accomplish this or are things that need to happen for our primary objective to be accomplished. Some include making the device so it can be easily used with cranes and manipulators, making sure all materials used can withstand the hot cell environment, and having every part set up so that either it is robust enough to not need any maintenance throughout its life or easily replaced.

3 Target Specifications

General Specific Requirements Acceptable Performance Tolerance/Targeted Requirements Performance Evolution (1 cycle Amount of salt 16,500 cm3 -500 cm3 from start to removed +infinity finish) Time 1 week 3 days (goal) Disassembly/Asse Time for disassembly 1 day  2 hours mbly (for or assembly maintenance # Parts 10  2 parts reasons) Consistent Fasteners Dowel pins for alignment N/A and socket head cap screws for fastening (all same size) Size Height 7 ft maximum Fit in 84 in by 60 in 2 pieces 1 piece (goal) airlock Footprint when resting 3 ft by 3 ft maximum Fit electrorefiner ports 10.75 in, 4in, or 8.875 in N/A Materials Survive dry and steel, aluminum, high N/A radioactive altitude brushes environment Withstand high 650 oC melting point for minimum temperatures all materials in ER Withstand beating ¼ in thick minimum Handling (for set Fit with cranes and Hooks and Handles N/A up and take down) manipulators Set up and take down Only N/A assembly/disassembly is trays Vertical Motion for 40 in  2 in entry/exit with ER Life Expectancy Time 10 years minimum Number of cycles 100 minimum Parts replaced during 1 (only if designed for maximum lifetime easy replacement) Time spent tweaking 1 hour per cycle average maximum mechanism over lifetime Electrical Power Available Power 110 Volts 10 Volts Source Salt Cubes Size 2 in by 2in by 2 in maximum Interaction with Gap between bottom of 4 in minimum ER vessel vessel and bottom of our device Salt level range device 16 in to 20 in from 0 in (but may work is designed for bottom outside that range)

4 Project Plan At the beginning of this project, a rough timeline was developed to help keep progress along the design process focused and on schedule so that it could be finished on time. The timeline started as a collection of all of the known deliverables and their respective due dates. This was supplemented by estimates of known future deliverable dates based on future project needs. The current timeline can be seen below.

Timeline (up to present day) Date Start End Task Sep. 11 Sep. 11 Team Formation Sep. 13 Sep. 28 Preparation for INL visit Sep. 13 Oct. 1 Mock-Up Idea Generation Sep. 29 Sep. 29 INL Visit Sep. 29 Oct. 16 Idea Generation Oct. 1 Oct. 13 Mock-Up Building Oct. 16 Nov. 11 Conceptual Design for 3 best Ideas Nov. 11 Nov. 11 Preliminary Design Review Proof on Concept for Conceptual Nov. 11 Dec. 4 Designs Dec. 4 Dec. 4 Decision on Conceptual Designs (Phone Conference with INL) Dec. 5 Dec. 5 Snapshot Dec. 15 Dec. 15 Design Report Figure 2: Timeline

In order to accomplish the established project goals, roles were assumed by each member of the group based on personal experience and skills. The following role assignments were proposed and accepted by consensus among the team.

 Gannon Johnson: Team Leader and Scribe  Brendan Crosbie: Budget Manager  Garrett Guinn: Client Contact and Webmaster

As of this date, no team organizational problems have yet occurred and communication and cooperation within the team is high.

Concepts Considered The first stage of conceptual design began with the development of a mock-up fixture designed to incorporate all the size ranges of access ports from the top of the electrorefiner. This mock-up was built on a wooden frame within a large plastic tank due to a lack of need for direct tensile strength. The top of the mock-up was designed with aluminum plates at the primary access port to ensure a high level of tolerance. With the mock-up built, any test designed around the interaction between the lid of the electrorefiner and a designed device can be performed.

5 Figure 3: Mock-Up: Without aluminum plates that have not been put on yet

The conceptual design of the salt removal device began with the division of the problem into four basic operations: removal method, transport, freezing, and transport to container. Ideas were then brainstormed for each of these operations, and a generalized morphological chart was generated so that a solution path could be determined from among the generated ideas. The general morphological chart can be seen in the figure below without any solution paths present.

Function Options Removal Pressure Dipping Tray Buckets Archimedes Screw Method Differential Transport Tool Elevator Crane Motorized Pipe Suction Venturi Freezing Trays Breaking Ice Maker Atomizing Transport to Flexible Metal Master-Slave Funnel Weir/Trough Container Tubing Manipulators Figure 4: Morphological Chart

Using the morphological chart, multiple design ideas were generated for each function. Some were determined that they did not have the ability to successfully accomplish the design specifications. The first of these ideas was a pump system that would draw molten salt up through a series of pipes. This design was not pursued due the fact that complex assembly would have to happen every time you set it up, and the previous experience INL had with a system like this demonstrated major trouble with leaking. The second

6 removal idea was a modification of the technique currently used in the hot cell, a dipping tray system that would extract salt and freeze it into its required size at the same time, this technique was not pursued due to an inability meet the required amount of salt removed per evolution spec. The final removal design that was not pursued was an Archimedes screw that would be directly driven by a motor and would extract salt along the length of its threads; unfortunately screws are typically used to transport solids so the tolerances required to move liquid salt would be too high for feasibility.

One of the methods developed to parse frozen salt into an appropriate size for the grinder was to freeze it into sheets and break it using a shaped press, but due to a lack of information of the mechanical properties of frozen salt this idea was discarded. Also it had the problem of most likely being messy. Another design for a method to freeze salt into cubes was to create an ice maker and have it produce salt cubes at a constant rate, this was not deemed feasible due to a requirement for monitoring during the operation of the ice maker and the size of ice maker required to meet the desired salt evolution. One of the last ideas discarded for the transport of frozen salt to the storage container was the direct use of master slave manipulators to pickup individual cubes because it was decided that this process could be improved upon using a funnel or ramp.

The three ideas that most completely fulfilled the stated project requirements while maintaining a higher level of feasibility were further developed and refined. They were: a venturi pump extractor, a pulley extraction system, and a dipping bucket extractor.

The venturi pump extractor (see below figure) passes high velocity argon from the environment of the hot cell through a blower and into a venturi tube at a velocity of 450 [cfm], calculated from a venturi tube analysis math model (see Appendix 1), to create high enough negative pressure to draw molten salt up a long draw tube and into the throat of the venturi tube’s converging diverging nozzle section. Argon flow through the throat then forces the salt out of the venturi through a sharp expansion nozzle such that the salt will theoretically atomize and flash freeze resulting in a fine salt powder that is forced out of the end of the nozzle by the high speed argon flow. The powder will continue through flexible metal tubing at high speed into a cyclone separator that gradually reduces the velocity of the salt powder and allows it to fall into a container for transport to the grinder.

7 Figure 5: Venturi

The pulley extractor (see below figure) is designed with individual cube holders attached to a motor driven chain linkage that can be operated continually with little manual interaction. The cube holders are made of machined and polished stainless steel so that frozen salt cubes will not stick into them. During operation, the cube holders systematically go down into the electrorefiner and scoop out molten salt. The motor is designed to operate under low speeds to ensure that the salt freezes during the travel time from the inside of the ER to the top of the pulley linkage. The process of traveling past the apex of the linkage naturally turns the cube holder upside down so that the cube falls out and onto a trough or ramp where it slides down to a container for transport to the grinder. Based on testing (see Appendix 2) for freezing time of an individual cube, it will take about 12 minutes to freeze once outside of the electrorefiner. Due to the height of travel, to allow for 20 minutes of freezing time, it moves at a rate of 2 in/min. With up to 25 cubes going per revolution, the time per evolution would be as low as 7.5 hours, but with a worst case scenario that includes having to increase the spacing of the cubes, allowing for a gap so the pulley can be stopped without any cubes in the electrolyte, and a safety factor for 15% of cubes not falling out, the time per evolution could be increased to 15 hours. This ensures that under minimal supervision, successful operation of the extraction system should still be possible.

8 Figure 6: Pulley

The dipping bucket extractor (see figure below) starts by grabbing a bucket with the overhead crane inside of the hot cell. The bucket is then lowered through an access port on the top of the ER into the molted salt until it is completely submerged. Once full, the bucket is then lifted out of the ER while full of salt and transported over to a table where a tray assembly is positioned and the salt is emptied into the trays for freezing. There are two design options for emptying salt from the bucket. The first is to design the framing arms that the crane attaches to with hinges that would sit above the salt level when the bucket is in the ER to avoid salt freezing onto them and making a mess. With this design, a tool for the master-slave manipulators to tip the bucket would have to be made. The second option is to design the bucket with a valve in it such that the bucket could be positioned over the trays and the valve could simply be opened so that the salt can flow out. After the salt is emptied into the trays and frozen, the trays would then be flipped over onto a funnel such that the frozen salt cubes fall and are collected into a storage container for shipping to the grinder. To meet the evolution requirement, the bucket needs an inside diameter of 9.5 inches with a height of at least 14.5 inches. According to a math model (see Appendix 3), the design will have about 1 hour before the salt starts freezing.

9 Figure 7: Bucket Design

Concept Selection To select the final design solution path to move forward each of the three main ideas had to be analyzed for their inherent advantages and disadvantages and then analyzed compared. The advantages and drawbacks for each idea were all very different.

The venturi idea was compact, allowed for continuous usage with little handling requirements, and innately kept the most amount of heat from escaping the electro-refiner while in use. However these huge benefits came at the price of being the hardest to create proof that the idea would be possible. The atomization of the salt and the freezing of that atomized salt were not ensured and could not be proved.

The pulley system had similar benefits but had shortcomings in different areas. It has the power to run continuously and was favored if the time came to empty the entire electrorefiner. However, while the individual pieces were simple in nature, assembled it quickly becomes complicated and therefore an increased risk for increased maintenance. The pulley system idea also might cause the electrorefiner to loose too much heat while operating and would become messy as salt froze on the chain and broke off.

10 The bucket-tray system does not work continuously but in discrete cycles to remove the desired amount of salt. The benefits to this idea are that it is the simplest design, has a low set up time, and it utilizes proven concepts in the hot cell. However it is the most handling intensive idea and it can only be used to draw salt down to a minimum depth of 16 in.

Since each of these ideas performed differently in fulfilling the general areas of the specifications stated earlier so a direct comparison was not used. Instead each area of the specifications was weighted for importance to accomplishing the end goal and for stringency in design requirements. The highest score being the most important and/or the hardest requirements to accomplish. This weighting, captured in the figure below (using bucket-tray system as an example) was first decided upon by the Nuclear Cookies as a team then sent and affirmed by INL.

Figure 8: Spec Evaluation of Bucket Tray System

With this rating each team member most involved with the development of the idea evaluated the idea and presented it before the team for discussion. After a consensus was reached on how each one performed the results were presented to INL over a phone interview with a description of each idea. When the results were shown to INL, further pursuit all three ideas was determined to be required. This led to further discovery and proof of concept for each idea and was presented again to INL. In the second meeting everyone came to agreement with us that this was the best option out of the three to move forward with.

System Architecture The bucket-tray system (updated pictures shown in figures below) is a removes the salt from the electrorefiner by a steel bucket being lowered into the salt by an overhead crane so that it fills up by overflowing the top of the bucket. Afterwards it is removed by this same cane, capped to stop spilling, and held so that salt on the outside of the bucket freezes, and taken over to a table where our tray system is. The bucket will either release the salt into a single tray via a valve or by slowly tipping the entire bucket. The single tray allows for minimum handling time and does not require the valve to be opened and

11 shut multiple times if used. The trays will use the same basic layout as a standard household ice-cube tray, the cubes will be the maximum size allowed for the grinder placed closely together with a slight notch between them to allow overflow to fill each cube slot. The side walls will be higher as to prevent overflow and splashing. Then, after freezing, a mechanism will flip the tray and allow gravity to pull the cubes out into a funnel into a container that will transport the cubed salt over to the grinder.

Figure 9: Bucket Concept: Valve

Figure 10: Bucket Concept: Pouring

12 Figure 11: Tray Concept

Novel features built into the system are all to better functionality. The bucket will feature variable inserts to allow different amounts of salt to be taken out so the operator can choose how much to remove. It will also include insulation to prevent the salt from freezing. The last feature is a device to stop spilling from occurring while in transport. One idea for this is to simply cap the bucket off loosely and have a small catching tray underneath. We may not be able to tighten down a lid because the salt being used dries as an adhesive. Also being looked at is a displacement body to lower the salt level or something to raise the height of the walls.

Future Work In this design there are major tasks and decisions that must be made to further the development of this solution. They are choosing how the salt will be removed and the design of that sub-system, testing of trays, a sub-system keeping spilling from happening and making sure the bucket will not freeze by selecting the proper insulation while maximizing the salt still being removed.

The first proof of concept will be to liquefy a small amount of salt and place it into a scaled down version of a tray cube. The concept of the salt releasing easily from a polished stainless steel tray has only been used when the salt and steel cooled down together from the temperature of the electro-refiner. This will also be a crucial point on whether this system will work at all as proposed. Also getting tested here is square cubes versus cylindrical cubes. Currently, INL uses cylindrical cubes and we need to see if square cubes will release the salt if they are to be used.

The next step for the ‘Bucket Tray’ system to move forward is to select which method will be used to remove the salt from the bucket. This will be done by experimenting with putting water into a prototype wax tray by a similar bucket pouring it and by a valve. The

13 splashing and flow control will determine which method will be used. After we have that decided we can move onto the real design work of that sub-system.

The final hurdle to cross will be the design of a bucket so it will not spill or freeze when being used. This will be the last stage in our conceptual design questions and will only be reached if the first two stages determine that the Bucket-Tray solution can still be used.

Timeline (projected for next semester) Date Start End Task Dec. 6 Jan. 30 Weighing Bucket Options (Pouring vs. Valve and spill containment ideas) Jan. 4 Jan. 30 Cube testing (hot salt in cold tray) Feb. 2 Feb. 27 Detailed Design and Manufacturing Plan Feb. 20 Mar. 31 Building Working Prototype Mar. 2 Apr. 30 Testing device and proof of concept Figure 12: Timeline

14 Appendix 1: Venturi Math Model

15 16 Appendix 2: Salt Freezing Testing

17 Appendix 3: Bucket Freezing Math Model

18 19 20 21