2005 Radiation Safety Refresher Training

Sue Dupre, Radiation Safety Officer

Stephen Elwood, Health & Safety Specialist

Refresher Training Topics

• The results of the intensive audits of six labs conducted in 2004 by the Radiation Safety Committee

• A couple of minor contamination incidents

• Some general reminders about good practice and policies

• Policy and administrative changes

• The NRC inspection expected this spring

Audit: Survey Records

– Some of the labs audited were inconsistent or seriously deficient in maintaining survey logs.

– Remember to record every postoperational survey!

– Wipe surveys for H-3 use must also be noted on the Survey Log.

Audit: Protective Clothing

The audit team observed a person performing radioisotopework without a lab coat, while wearing sandals

– Protective clothing requirement for work with any open source:

• Lab coat

• Gloves

• Closed-toe shoes. No sandals permitted!

Audit: Liquid Waste Issues

– Inadequately labeled bottles of wastes. Label liquid wastes with isotope, activity, dates and chemical content

– Disposal of acidic wastes. The allowable pH range for sink disposal is 5-9.

– Some labs were storing bottles of liquid wastes due to concerns that the wastes contained too much activity or due to other uncertainties.

– The monthly disposal limit for P-32 is 300 µCi and for S-35 is 3 mCi but EHS can give special permission to dispose of larger amounts.

– Take advantage of the sink disposal option!

The audit team found several problems relating to liquid waste disposal:

Contamination Incidents

Two interesting contamination incidents

occurred in 2004. Although contamination

did occur, in both cases there were no

serious consequences, and the incidents

illustrate that many aspects of good

practice were being followed.

Incident 1

• Following H-3 use, a researcher conducted a postoperational wipe survey, put the wipes into the liquid scintillation counter to count and then left for the day without waiting to see the results. The researcher checked the wipe results the next morning and found that the wipe taken on her face contained low-level H-3 contamination.

• EHS responded and found no contamination on skin, the lab coat or the work area (the researcher had taken a shower the previous evening). EHS also conducted a urine bioassay and verified that there was no internal uptake of H-3.

Lessons from Incident 1

– Always count wipes as soon as possible after the survey and check the results before leaving the lab.

– If you’re in a hurry, do 1 minute counts to screen the critical wipes and then set the wipes up to count again for longer counts.

– Remember to record the results in the Survey Log.

Note: H-3 poses a hazard only if taken up internally in large amounts (it takes 80 mCi of H-3 taken up internally to reach the annual dose limit of 5000 millirems.)

Incident 2

• A researcher used P-32 on a Saturday, conducted a post-operational survey immediately afterwards, and found substantial P-32 contamination on his shoes and on the floor between the hood and the sink. No contamination had been tracked to the hallway outside the room.

• A post- operational survey had been conducted (and recorded) on the previous day and had found no contamination, so the contamination found on Saturday was attributed to the work done on Saturday.

• Public Safety was notified and responded appropriately by contacting EHS.

• EHS agreed that it was OK to lock the room and to put warning signs on the door so that the clean-up could be done on Monday.

Lessons from Incident 2

• Doing the postoperational survey immediately afterwards can prevent the spread of contamination to other areas

• Be sure to survey the path between the work area and the waste disposal area.

• Survey shoes, clothing, hands and face.

• Post-operational surveys are required but we also highly recommend that you perform a preoperational survey before you begin working to be sure that your work area is clean at the start of work.

Review of Incident Procedures

Incidents include:

• Spill of radioactive materials

• Widespread or unusual contamination

• Any case of contamination on skin or clothing

• Missing radioactive materials

• Exposure to an x-ray machine

Be sure you know where to find the Emergency Response book for your lab!

Radiation Incident Notification

• Call EHS during work hours

• Call Public Safety at 8-3134 after work hours

Radiation Safety Reminders

Count Rate and Activity

• A survey meter typically detects only a small % of what is actually being emitted by a spot of radioactive material, so counts per minutes are not equal to disintegrations per minutes (cpm ≠ dpm)

• Instrument Efficiency () = cpm/dpm

• What affects efficiency? – Shielding (even air acts as a shield for lower energy beta emitters such

as C-14 or S-35 or P-33)– Geometry (the radiations are emitted in a 4π geometry but a detector

placed directly over the radioactivity is only seeing half of the sphere of emissions, or a 2 π geometry)

– Distance of the detector from the contamination

• For a G-M meter, under the best circumstances, ~ 25% for P-32 and is <5% for S-35.

Activity & Count Rate (cont’d)

Example: A G-M meter with pancake probe reads 10,000 cpm ona flat surface. If the lab uses both P-32 and S-35, how can youtell which isotope it is?

• Hold a piece of paper over the contaminated area and make another reading with the detector.

• If it’s S-35, the paper will absorb all of the betas, and the count rate will decrease to approximately background.

• If it’s P-32, many of the higher energy betas will pass through the paper, and there will be little change from the initial count rate.

Activity & Count Rate (cont’d)

Example: A G-M meter with pancake probe reads 10,000 cpm ona flat surface, and you have determined that the contamination isP-32.

• The activity is approximately 40,000 dpm (assuming 25% efficiency)

• Since 1 µCi = 2.22 x 106 dpm, the activity present is ~0.02 µCi

• For P-32, the dose rate on contact with 1 µCi spread over 1 cm2 is 7030 mrem/hr. In our example in which 10,000 cpm of P-32 is discovered on a surface, the dose rate directly on contact is 140 mrem/hr (annual skin dose limit is 50,000 mrem).

• Although this is a substantial dose rate, the dose rate will quickly decrease by orders of magnitude as you move a few centimeters away from the contamination.

Activity & Count Rate (cont’d)

Example: A lab wants to estimate the activity in a 1 liter container of P-32 liquid waste and places a G-M detector on contact. The countrate is 1500 cpm. How much activity does the bottle contain?

• Impossible to estimate, due to uncertainties in detector efficiency (e.g., wall thickness, width of the bottle, how curved the container is, the height of the liquid in the bottle, etc.)

• In this case, you must determine the activity empirically: Take a sample and count in a liquid scintillation counter (if needed, ask EHS or Mike Fredericks for help)

• Suppose you determine that a count rate of 1500 cpm corresponds to an activity of 0.1 µCi/ml. In the future, you could use the relationship of 1500 cpm = 0.1 µCi/ml, as long as you have the same geometry (same bottle type, same volume of liquid, etc.)

Reminder: Security

• Keep stock vials locked away except when in use and when you’re present

• Don’t leave empty labs unlocked for more than a few minutes.

• Acknowledge people who enter your lab

Reminder: Declared Pregnant Worker Program

• A pregnant woman may choose to formally “declare” her pregnancy.

• Fetal dose limit is 500 mrem for a Declared Pregnant Worker (instead of the 5000 mrem limit applied to other radiation workers)

• If you become pregnant, consider consulting with Sue Dupre for additional information and to determine if it makes sense to declare your pregnancy.

• More details are available at the EHS website.

Policy and Procedural Reminders

Shipping Hazardous Materials

• All hazardous materials must be shipped in compliance with U.S. DOT regulations

• Check with EHS if you are not certain whether your material is classified as hazardous or biohazardous under DOT regs

• Even dry ice in amounts > 2 kg is regarded as hazardous)

• EHS will assist you with the shipment

Complete the online Shipping Hazardous Materials form

Transferring Radioactive Materialsbetween University Labs

• RSC approved a new policy this past year:

– If you loan radioactive materials to another lab, you must go to the EHS website to check whether the recipient lab is authorized to possess the radioisotope in question.

– If authorization exists, you will send a notification e-mail to EHS via the website and may proceed to make the transfer.

– EHS will follow up to adjust inventories and send out a new Vial Use Log if necessary.

Quarterly Inventory Review

• Once a quarter EHS asks each lab manager to use the RITA database to look at the RITA record of the lab’s radioisotope inventory

• The lab manager reviews the actual inventory against the RITA record and contacts EHS to confirm the inventory or to request adjustments.

• Be sure to return Vial Use Logs to EHS promptly after disposal of vials to keep inventory current.

NRC Inspection

• Due in March or April 2005 (according to the NRC website)

• Can you answer the sample NRC Interview questions which EHS sent to each lab manager? Check with your lab manager if you haven’t received a copy of the sample questions.

• Check lab conditions and records and follow good practices

• Make sure training for all lab personnel is up-to-date

• Pay attention to security matters

Radiation Safety Website

Accessible through www.princeton.edu/ehs

Radiation Safety Program Feedback

• Your questions, comments, suggestions and feedback are welcome.