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19 March 2010

Answer to Question #4909 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

The following question was answered by an expert in the appropriate field:

My RSO (radiation safety officer) asked me to find out about the NRC (Nuclear Regulatory Commission) policy about calibrating ion chambers (Victoreen 450P's). Previously these instruments were calibrated by the Radiation Standards and Dosimetry Laboratory in Redstone Arsenal in Alabama up to 5 R/hr. Last year we couldn't ship 450P's by air to the mainland because of the pressurized ion chamber. So, a new calibration box was installed here and currently 450P's are being calibrated to the level of 250 mR/hr. Is it the NRC requirement that these instruments should be calibrated to the level of 1 R/hr or can we continue to calibrate them up to 250 mR/hr?

Generally, you want to calibrate any health physics survey instrument over the full range of its capability. However, the NRC (in 10 CFR 20 Subpart F) only requires that surveys be performed to ensure compliance with their regulations and that the licensee periodically calibrate to the radiation being measured. If the radiation source(s) you have under your control cannot produce a radiation field above (say) 200 mR/hr, then I'd say you're okay to calibrate to 250 mR/hr only, but you need to flag this limitation on the calibration label placed on the instrument. You should boldly note on the calibration label that the higher scales are not calibrated. If there is any way to physically prevent the range switch (if there is one) from being positioned above the calibrated range, then I'd do that too.

I'd recommend you look over the references cited in the Instrumentation and Measurements area of our Ask the Experts feature and review the various related NRC Regulatory Guides and NUREGS.

Lastly, once you're confident this is a valid approach, you might just call the NRC and check with the person who performs your facility inspections. I'm sure he/she will be able to give you informal advice.

David J. Allard, CHP

Answer posted on 17 November 2005. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.