[ RadSafe ] Thorium Surface Contamination Limit

Redmond, Randy (RXQ) redmondrr at y12.doe.gov
Wed Jul 7 05:44:26 CDT 2010

This is a continuation of a previous inquiry I made concerning thorium limits.

What is your interpretation of the 10 CFR 835 Appendix D, DOE 5400.5, and Regulatory Guide 1.86 Thorium Surface Contamination Values: applies only to alpha; applies independently to alpha and beta-gamma emitting nuclides in the decay chain; applies to both (alpha and beta-gamma must be summed)?

What contamination limit(s) do you use for thorium and what is the justification?

We have historically used:
200 dpm/100 cm2 alpha removable, 1,000 dpm/100 cm2 alpha total, and
1,000 dpm/100 cm2 beta-gamma removable, 5,000 dpm/100 cm2 beta-gamma total.

10 CFR 835, Appendix D,  footnote 1 supports this position - where surface contamination by both alpha and beta-gamma emitting nuclides exists, the limits established for alpha and beta-gamma emitting nuclides apply independently.  Upon further digging, I ran across an NRC position paper which promotes the position that the Reg. Guide 1.86 limit for thorium includes alpha and beta-gamma.

Randy Redmond
B&W Y-12
Radiological Engineering

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