Chemical SOP’s – Uranium & Thorium

                        Tuesday, March 27, 2007

 

Location

Eyring Science Center (ESC) Underground Laboratory U234

 

Introduction

This SOP is tailored to the use of uranium and thorium in U234 where these metals are used in a sputtering process.  Sputtering is one of the most reliable and, in principle, “green” methods of producing thin films of a great variety of materials for research and production. Using adequate exposure controls and safe work practices, sputtering work can be performed in a safe manner.  The greatest concerns being minimizing exposures and limiting contamination.  Learning how to use sputtering to deposit thin films congruent with 21st century sensibilities can contribute to the purposes of a BYU education in physics as it is a portion of a capstone, thesis or other research project, which can prepare the student for service, further education and a career.

 

Chemical Forms

Uranium Metal (Black to brown appearance)

Thorium Metal (Grey-white, lustrous metal)
Uranium Flakes (Black to brown appearance)

Thorium Flakes (Grey-white, lustrous metal)

Uranium Oxide- brown black to brown-yellow, insoluble

Thorium Oxide- white, insoluble

 

Specified Hazards

 

a)      Both uranium and thorium emit alpha particles, which have a relatively large kinetic energy but due to the (relatively) high mass and charge they will not penetrate the epidermal layer of the skin.  Since keratinized epidermal cells do not have a nucleus and are relatively metabolically inert, they are basically immune to damage due to ionizing radiation.  Therefore the outer layer of skin is an effective shield for alpha particles (the one exception is the eye where viable metabolically active cells are at the surface).  Damage from alpha particles occurs when they are injected, ingested or inhaled such that the alpha emissions interact directly with viable tissue.  If that occurs, alpha particles will cause approximately 20 times as much biological damage, per unit of energy absorbed, as gamma rays or beta particles.  It is important to ensure that airborne concentrations of uranium be minimized as far below the ACGIH (2006) limit of 0.20 mg/m3 of air as possible and that designated areas are cleaned when contaminated – this prevents the spread of contamination.  Problems can best be avoided by careful control of any finely divided material and by good hygiene practices.

b)      Uranium is more toxic than lead[1], and is radioactive.  Uranium exposure can lead to:

i)        Kidney damage and disease;

ii)       Lung fibrosis and malignant neoplasm formation in the lungs; and

iii)     Hematopoietic system damage and leukemia.  Uranium is a known human carcinogen.  (There is not an established safe level of exposure to a known human carcinogen.)

iv)  However, there are NO known cases of U intoxication in humans.

c)      Thorium[2] should be treated in a manner similar to uranium.  A study of heavy metal toxicity in general will indicate that exposure to heavy metals can lead to kidney damage and that many heavy metals are sequestered in the bone, including uranium, thorium and their daughter products.

 

Purchasing

Quantities of uranium and thorium materials will be limited to the smallest amount necessary to carry out the proposed function.  Only Prof. Allred or another member of the faculty is authorized to order uranium, thorium or their compounds. He will first check with the Radiation Safety Officer for additional information since the last time materials were ordered.

 

Storage

These are the storage requirements to protect the materials. 

  1. Store stock uranium and thorium targets in designated box in designated cabinet.
  2.  The cabinet with uranium and thorium materials should be locked each evening to prevent unauthorized access. If you leave the lab please check that cabinet is locked.
  3.  

 

Authorized Personnel

 

  1. Staff - The word "staff" in this document refers to all persons recognized by Brigham Young University as being members of a research project involving uranium or thorium, which includes professors and resident students.  When properly trained, these staff members are authorized to use and clean-up uranium & thorium.

 

Training

General staff training:  All staff must receive the following training prior to using uranium, thorium, or entering a designated area where these metals are sputtered:

1.)    Go online and view

a.       http://safety.byu.edu/onlineTraining/generalLabSafety/

b.      http://safety.byu.edu/onlineTraining/compressedGas_files/v3_document.htm

c.       http://safety.byu.edu/onlineTraining/generalElectrical_files/v3_document.htm[BB1]  [3]

d.      Radioactive materials and radiation sheet prepared by Dr. Allred at

U&Th Materials Plan www.physics.byu.edu/faculty/allred/safety-SOP/joeySOP0702.htm

 

2.)    Watch the following video clips (about 10 min ea.) at the HBLL LRC (4th floor):

a.       LABSAFETY  “Laboratory Safety”

b.       VC70-R PT.1  Segments: “Chemical Hazards,” “Emergency Response” 

c.        VC70-R PT.2  Segment: “Chemical Storage Hazards”

d.       VC70-R PT.3  Segment “Assessing Risks of Toxic Chemicals”

3.)    Review University Chemical Hygiene Plan with Prof. Allred and/or member of Risk Management. 

4.)    Review MSDS’s for uranium & thorium  

5.)    Review this SOP and online SOP for process at http://xuv.byu.edu/docs/sops/sopsMain.htm

6.)    Receive training on how to use Geiger counter and check yourself for contamination prior to leaving a designated area.

7.)    Receive Laboratory Orientation

8.)    Receive training on the use, maintenance and disposal of personal protective equipment (ppe) that has been selected for the work you will perform.  See next two sections for details.

9.)    Receive Level 1 clean-up training if you have been authorized to do such work by the Principle Investigator.  Level 1 clean-up activities include, and must be performed in accordance with the following:

 

Use of a HEPA vacuum to clean the sputtering machine, including the chamber, can lead to exposure if the HEPA vacuum is not functioning or maintained properly.  Use of the HEPA vacuum is considered a Level 1 cleaning activity.  Individuals are allowed to vacuum sputtering machine, including the chamber, with the HEPA vacuum after receiving the proper training – they must follow safe work practices and use the appropriate PPE.  Note: Flakes deposited within the chamber are typically fairly large, surface area> several mm2.  As such they can be fairly easy to capture and immobilize.

 

10.)Only the Principle Investigator (and those specifically trained to do so) are authorized to perform Level 2 clean-up work.  Level 2 clean-up activities include, and must be performed as follows:

 

Use of abrasive materials to remove metals deposited within the system rather than the substrate.  Individuals are not permitted to clean the inside of the sputter system with abrasive methods which could produce airborne particles of uranium/thorium.  Level 2 cleaning activities must be performed using the proper equipment (as designated in the applicable section below).  It is anticipated that this kind of cleaning only be done every 1-3 years in the course of normal operation.

 

11.)Receive training on how to clean and change the filter of the HEPA vacuum is you will be performing such work.

 

Designated Areas, for Use of Uranium and Thorium

 

Floor areas within ESC U234 have been marked with red tape, and signs hung at the periphery to these areas indicating that they are designated for use of uranium and thorium.  The footprint of such areas is based upon the level of contamination found upon surveying the laboratory prior to designating areas of use and anticipating where contamination may occur.  Note: Equipment, used for sputtering, which may become contaminated with uranium and thorium are marked with red tape or standard radiation stickers.  Effort should be made to NOT remove contaminated items from designated areas except as transported in the proper designated container. This is to eliminate contamination to other areas.

 

Designated areas must be cleaned-up following Level 1 clean-up procedures after removing, or placing a sample into the sputtering machine.

 

Activities during which Exposure May Occur to Uranium & Thorium

1)      Individuals may be exposed to airborne contamination is using a sputtering machine, and equipment associated therewith, that is not operating properly.

2)      Use of a HEPA vacuum to clean the sputtering machine, including the chamber, can lead to exposure if the HEPA vacuum is not functioning or maintained properly, or wet methods are not used in conjunction with the HEPA vacuum.

3)      During Level 2 clean-up activities, where abrasive materials are used to remove metals deposited within the system rather than the substrate.  Individuals performing Level 2 cleaning activities must use the proper equipment and have prior permission.

4)      HEPA vacuum filter change out and cleaning.

5)      Individuals may expose their hands to contamination if touching objects used in designated areas.

 

Controls used to Minimize Exposure

1.      Engineering controls used to minimize exposure to sputtered metals:

a.       Intact seals, vacuum pressure, and filtered vacuum air of the sputtering machine.

b.      HEPA vacuum

c.       Wet methods while cleaning HEPA vacuum, and changing filter

 

2.      Administrative controls used to minimize exposure to sputtering materials:

a.       Establishment of designated areas, signage, and identification of potentially contaminated equipment.

b.      Limit the spread of contamination by cleaning up contamination when it occurs, and checking yourself for contamination prior to leaving a designated area.

c.       Components of the sputtering machine are to be stored in designated containers and stored in the designated location in the laboratory.

d.      Training, specified by this SOP

e.       The sputtering machine and HEPA vacuum must be inspected prior to use to ensure proper function.  This is done by:

                                                               i.      Check sputtering equipment using SOP

                                                             ii.      Check the HEPA vacuum by following the manufacturer recommendations.

 

3.      PPE- Personal Protection equipment needed when performing the activities during which exposure may occur:

 

a.       Use the following personal protective equipment when placing or removing samples from the sputtering machine, and while performing a deposition:

                                                               i.      Thin walled nitrile gloves. (Latex may be used with PI permission.) 

b.      When performing Class 1 clean-up activities use the following ppe:

                                                               i.      Thin walled nitrile gloves.

c.       When performing Class 2 clean-up activities the following ppe must be worn:

                                                               i.      Air purifying respirator.

                                                             ii.      Unvented goggles, if respirator is not full face.

                                                            iii.      Tyvek suit with booties

                                                           iv.      Thin walled nitrile gloves

d.      When changing the HEPA vacuum filter use the following ppe (this is in case of a bad filter/unexpected release of contamination:

                                                               i.      Air purifying respirator

                                                             ii.      Unvented goggles, if respirator is not full face

                                                            iii.      Tyvek suit with booties

                                                           iv.      Thin walled nitrile gloves

 

4.      Use thin walled nitrile gloves anytime you are entering a designated area, and when touching objects used in a designated area.

 

Use, Maintenance, & Disposal of PPE

 

Only use the following personal protective equipment once, check it for contamination and then dispose of it:

 

After using the ppe, check it for contamination by visual inspection and use of the Geiger counter.  If level of radiation detected is above background then the ppe must be disposed of as hazardous radioactive waste.  If the equipment is free from visual contamination and radiation is not detected using the Geiger counter then the equipment can be thrown away in the trash.

 

Respirators may only be used by individuals who have been fit tested, have current medical approval, and received training from Risk Management & Safety.  Note: medical approval is not needed if using a filtering facepiece when exposures are below those determined safe by Risk Management & Safety

 

Elastomeric respirators and unvented goggles must be decontaminated prior to storing them in a tote where they are protected from damage, such as but not limited to, sunlight, excess moisture, dust, chemical contamination, extreme temperatures and deformation.  Totes used to store ppe bear the name of the user and are kept in the area designated and signed for ppe storage within the laboratory (located outside the designated areas).

 

Decontamination procedures for elastomeric respirator and goggles:

 

Decontamination procedures are performed in a designated area unless designated otherwise.

  1. After removing respirator from face, discard respirator cartridges as contaminated radioactive waste.
  2. Use two respirator cleaning wipes (alcohol free), one to wipe the exterior of the respirator and the other to wipe the interior.  Use another wipe to clean the goggles.  Be sure to wipe all surfaces.  Used wipes must be disposed of as radioactive waste.
  3. Disassemble the respirator in accordance with manufacturer recommendations.
  4. Wash all parts of the respirator, and the goggles in the mild soap solution/warm water solution prepared before you began Level 2 clean-up.  Do not dump water in tub down the drain.
  5. Rinse washed goggles and respirator components in the sink and set them on paper towels to air dry prior to storage.  Note: this step is performed in a non-designated area.
  6. Set tub of water aside and let the water evaporate from the tub.  Once evaporated use the Geiger counter to determine if interior of tub is contaminated.  If tub is contaminated then clean it using a respirator wipe, then use the Geiger counter again to determine if contamination exists.  If the tub won’t wipe clean then note that it is contaminated on the label of the tub.  Store the tub in its designated area.

 

Clean-up Procedures Including Facility Decontamination

 

Level 1 Clean-up Procedures

  1. Visually check HEPA vacuum to determine if it is fit to use.  Stop here if vacuum is in need of repair.
  2. Use HEPA vacuum to vacuum surfaces.
  3. You may use damp chem wipes (alcohol) on surfaces to clean surfaces.
  4. Towels, rags, and other such items used to clean up need to be checked with a Geiger counter. If there are above background, disposed of as radioactive waste. Otherwise, as ordinary lab waste.
  5. Only small amounts of solvents (alcohols and acetone) in designated plastic squeeze bottles are to be kept in U234.  They will be refilled in C129 ESC.  Please keep solvents bottles in designed places when not in use. 

 

Level 2 Clean-up Procedures

Prior to performing a Level 2 clean-up procedure, make sure you have prepared the polyethylene tub used to decontaminate the respirator and goggles.

 

  1. Don necessary ppe.
  2. Visually check HEPA vacuum to determine if it is fit to use.  Stop here if vacuum is in need of repair.
  3. Vacuum up any loose flakes
  4. Use steel wool to dislodge residual flakes
  5. Vacuum up loose flakes
  6. Repeat steps 4 and 5 until sputtering equipment is clean.
  7. Dispose of contaminated cleaning items as radioactive waste.

 

Facility Decontamination Procedures

 

Use these procedures to clean-up contamination when performing a laboratory survey, and if a spill/release of uranium/thorium oxide occurs:

 

  1. Use the HEPA vacuum to collect any loose contamination.
  2. Use a damp cloth and bucket of mild soap solution and water to wipe contamination that the HEPA vacuum did not collect from contaminated surfaces.  Then use the Geiger counter to determine if radioactive contamination is still present.  Repeat process until area is cleaned up, or it is determined that such work is futile.
  3. Set bucket of water aside in a designated are and let the water evaporate.  Once the water is evaporated use the Geiger counter to determine if interior of bucket is contaminated.  If bucket is contaminated then clean it using a damp towel and then use the Geiger counter again to determine if contamination is still present.  If the bucket won’t wipe clean then note that it is contaminated on the bucket label.  Store the bucket in its designated area.
  4. Towels, rags, and other such items used to clean up need to be disposed of as radioactive waste.

 

HEPA Vacuum Filter Change Out

 

This procedure is done in the laboratory in a designated area:

  1. Don appropriate ppe
  2. Change the filter of the vacuum in accordance with manufacturer recommendations
  3. If an unexpected release did not occur and the ppe (other than the gloves) was most likely not contaminated then use the Geiger counter to determine lack of contamination.  Throw the gloves away, clean and store the respirator appropriately, and store the goggles and Tyvek suit properly.
  4. Dispose of filter, gloves, and Tyvek suits (when contaminated) as contaminated radioactive waste.

 

Radiation Surveys

 

Risk Management & Safety (the RSO) will oversee periodic surveys of the facility to detect contamination.  Individuals working in the laboratory will use the Geiger counter to ensure contamination is not taken out of designated areas on persons leaving such areas.  Contamination needs to be cleaned up as soon as possible once contamination occurs.

 

Spill Response

Spills can be cleaned up using a local response, by the laboratory, following facility decontamination procedures.

 

Phone Numbers

Emergency University Response: 422-2222

Emergency (City) Response: 911

Poison Control: 1-800-222-1222

Professor Allred: 422-3489, home 225-4967

Risk Management & Safety (RM&S): 422-4468

Chemicals Management (a division of RM&S that handles waste response): 422-6156


 

[1] LD50 oral for Pb (in Pb- acid Batteries) is 500 mg/Kg). For rats the LD50/21 days was 6 mg of uranium ore per kilogram body weight (6 mg U/kg).  (http://www.mkbattery.com/images/MSDS_smallsealed_line.pdf http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3959530&dopt=Abstract 

This is comparable to the ORL-RAT LD50 for diarsenic pentoxide (As2O5) which is 8 mg/kg—meaning that it would only take 600 mg (0.6 g, about half the mass of a dollar bill) of ingested As2O5 to kill off a 75 kg human.  The only plus is that U oxides are mostly insoluble. The RfD for uranium (soluble salts) is 0.003 mg/kg/d based on body weight loss and moderate nephrotoxicity in rabbits.  http://www.sos-arsenic.net/english/uranium.html#chap3 

[2]  Animal studies:   LD50 value: thorium nitrate: 48mg/kg (IVN rat); thorium oxide: 400mg/kg (IMS mice); LC50 value: No information available. Annual limit of intake (human) : 200 Bq; http://www.bocedwards.com/pdf/P120-10-000_Ion_Gauge_Filaments.pdf 

[3] This training presentation does not review procedures for working on parts energized at or above 50 Volts.  If such work is performed then additional training is needed.  Equipment which reaches above 50 V is to be deenergized before working on it.


 [BB1]This training presentation does not review procedures for working on parts energized at or above 50 Volts.  If such work is performed then additional training is needed.