[ RadSafe ] Thorium Surface Contamination Limit

[roseb at gdls.com]

Randy:

In response to your post of 07/07/2010, 06:44 AM:

>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)?

Per 10CFR835 (App. D, note 1), DOE 5400.5 (Fig. IV-1, note 2), and Reg 
Guide 1.86 (Table 1, note a), the surface contamination values apply 
independently to the alpha and beta-gamma emitting nuclides in the decay 
chain.

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

Thorium is not one of my company's primary isotopes of concern, however, 
U-238 is.  We previously used the following limits:

Management control limits:

alpha - 200 dpm/100 cm^2; removable or fixed + removable
beta - 600 dpm/100 cm^2; removable or fixed + removable

Permissible release limits (unrestricted):

alpha - 1,000 dpm/100cm^2 removable; 5,000 dpm/100 cm^2 fixed + removable
beta - 1,000 dpm/100 cm^2 removable, 5000 dpm/100 cm^2 fixed + removable

The management control limits were established based on: 1) the detection 
limits of our portable field survey instruments; and 2) the availability 
of resources to reasonably and feasibly manage surface contamination to 
these levels.  The permissible release limits were based on Reg Guide 1.86 
and Army Regulation 385-11: we could release products, equipment, 
facilities, or tools up to these limits for unrestricted use: 1) if 
measures taken to decon to the management control limits were not 
reasonable and feasible; and, 2) with authorization from my company's 
management and our customer, the U.S Army.  Under the previous limits and 
operations, we rarely encountered contamination above the management 
control limits and never released any item or facilities for unrestricted 
use above the management control limits.

We currently use the following limits:

Management control limits:

alpha + beta - 1,000 dpm/100 cm^2; removable or fixed + removable

Permissible release limits (unrestricted):

alpha + beta - 6,000 dpm/100 cpm^2 removable or fixed + removable

The current management control limit was established based on: 1) the 
detection limits of our portable field survey instruments; and 2) the 
availability of resources to reasonably and feasibly manage surface 
contamination to these levels.  The current permissible release limits are 
based on DA PAM 385-24 (Table 5-2) and ANSI/HPS N13.12-1999 (Table 1) 
(available at http://hps.org/hpssc/ , free to HPS members).  One limit 
(the screening level) is stated for both alpha and beta combined because 
progeny radionuclides were included with the parent radionuclide (U-238) 
in the determination of the screening level for U-238 (ANSI/HPS 
N13.12-1999, sec. 4.5, p. 6 ).  We can release products, equipment, 
facilities, or tools up to the permissible release limit for unrestricted 
use: 1) if measures taken to decon to the management control limits are 
not reasonable and feasible; and, 2) with authorization from my company's 
management and our customer, the U.S Army.  Under the current limits and 
operations, we frequently encounter contamination well above the 
management control limit but are usually able to decon to the management 
control limit.  We still do not release items or facilities for 
unrestricted use above the management control limits as our 
decontamination resources and efforts are normally reasonable, feasible, 
and effective.

Henry

Boyd H. Rose, CM, CIH, CHMM
Sr. Safety and Environmental Engineering Specialist
Corporate Radiation Safety Officer
General Dynamics Land Systems
38500 Mound Road
Mail Zone 436-10-75
Sterling Heights , MI 48310-3269
Tel: 586 825 4503
Fax: 586 825 4015
E-mail: roseb at gdls.com




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