Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM)

5 NORM MATERIAL MANAGEMENT

5.1 Non-radioactive Hazards of NORM Materials

The Guidelines provide recommendations based on the radiological properties of NORM. In determining an acceptable material management option, other hazardous properties such as chemical toxicity must be considered. In many cases, the non-radiological hazardous properties of NORM materials are the critical selection criteria for the preferred NORM material management option.

5.2 NORM Derived Release Limits

To assist in NORM material management, Derived Release Limits (DRLs) have been determined from the annual radiation dose limits. The DRL's provide an estimate of public dose from measured releases of NORM. A Radiation Assessment or Material Management program may compare measurement results to Derived Release Limits (DRLs).

5.2.1 Unrestricted Classification

The control of public exposure to radiation from NORM disposal is constrained to less than the public dose limit to allow for exposures from multiple sources. The Guidelines recommend that NORM may be released with no radiological restrictions when the associated dose is no more than 0.3 mSv in a year. The radioactive hazard associated with this dose is considered insignificant, and no further control on the material is necessary on radiological protection grounds. It may be necessary to consult and obtain approval from Provincial waste disposal regulatory agencies regarding non-radiological properties.

Derived Release Limits for the amount and concentration of NORM materials that meet this criteria have been calculated, and are presented in Tables 5.1, 5.2 and 5.3 as Unconditional Derived Release Limits.

5.2.2 Release with Conditions

NORM quantities in excess of the Unconditional Derived Release Limits may, after a specific site review, be released without further consideration. In such instances, the basic premise is that the material, in its final disposition, will not contribute a dose to an individual that is greater than 0.3 mSv/a. Outside those situations or conditions, the material falls within a more restrictive NORM classification.

5.3 Derived Release Limits for NORM Materials

5.3.1 Diffuse NORM

Diffuse NORM is generally large in volume, with a relatively low radioactive concentration that is uniformly dispersed throughout the material. Diffuse NORM by-products from industrial activity are usually stored close to the point of generation as the cost of long distance transportation is prohibitive. Phosphogypsum, a by-product of fertilizer production, is an example of diffuse NORM.

Disposal of diffuse NORM sources requires consideration of the effects of dilution, possible re-concentration of the material in the environment, and the manner in which the material may deliver radiation doses to the public.

Table 5.1 shows the Unconditional Derived Release Limits for Diffuse NORM. Unrestricted release of NORM at the listed concentrations will deliver a maximum effective dose of 0.3 mSv/a under conservative scenarios. The calculations are given in Appendix E. Actual effective doses arising from releases of NORM at Unconditional Derived Release Limits are expected to be substantially less than the 0.3 mSv/a.

Table 5.1 Unconditional Derived Release Limits - Diffuse NORM Sources

NORM RADIONUCLIDE		Derived Release Limit(a)
		AQUEOUS(b) (Bq/L)	SOLID (Bq/kg)	AIR (Bq/m3)
Uranium-238 Series (all progeny)		1	300	0.003
Uranium-238 (U-238, Th-234,Pa-234m, U-234)		10	10,000	0.05
Thorium-230		5	10,000	0.01
Radium-226 (in equilibrium with its progeny)		5	300	0.05
Lead-210 (in equilibrium with bismuth-210 and polonium-210)		1	300	0.05
Thorium-232 Series (all progeny)		1	300	0.002
Thorium-232		1	10,000	0.006
Radium-228 (in equilibrium with Ac-228)		5	300	0.005
Thorium-228 (in equilibrium with all its progeny)		1	300	0.003
Potassium-40		n/a(d)	17,000(c)	n/a

Notes:

(a) Pathways Considered:

Aquatic	Terrestrial	Air
1. Value 10X Guideline for Canadian Drinking Water Quality.	1. External groundshine from soil contaminated to infinite depth. 2. Soil-veg-ingestion//soil ingestion. 3. Inhalation of resuspended material.	1. Inhalation at concentration resulting in 0.3 mSv. 2. Exposure factor of 25% assumed.

Assumptions:

• All radionuclides and compartments in equilibrium.
• Typical values for uptake and transfer factors.
• No allowance for hold-up time.
• 25% "occupancy" factor for solid source (groundshine, soil ingestion, resuspension), 25% 'occupancy' factor for air, and 50% of vegetable intake grown on soil.
• No correction for shielding, surface roughness.

Where more than one long-lived radionuclide is present in a sample, the appropriate sum of the ratios of the activity of each long-lived radionuclide and its corresponding Release limit, must not exceed 1, eg

Concentration NORM Isotope A	+	Concentration NORM Isotope B	+... +	Concentration NORM Isotope N	≤ 1
Derived Release limit A		Derived Release limit B		Derived Release limit N

(b) Aqueous Release limits ~10x Guidelines for Canadian Drinking Water Quality. Subsequent dilution of the release is assumed. Refer to the Provincial Drinking Water Standard where planned diffuse NORM releases must meet provincial drinking water standards. (See reference 16

(c) Natural abundance of Potassium 40 in potassium chloride.

(d) No aqueous release limit is needed as potassium content of the body is under homeostatic control, and is not influenced by environmental levels.

5.3.2 Discrete NORM

Discrete NORM sources are small in size and exceed the concentration criteria for a diffuse source. Because of the possibility of high radiation dose-rates close to the source, the Unconditional Derived Release Limits are lower than for diffuse NORM.

Table 5.2 lists the Unconditional Derived Release Limits for discrete NORM sources. The material must also meet the applicable radioactive surface contamination values, shown in Table 5.3.

Table 5.2 Unconditional Derived Release Limits

NORM RADIONUCLIDE	Unconditional Derived Release Limit(a) (Bq)
Uranium Ore (in equilibrium with all progeny)	1,000
Uranium-238 (partitioned) (in equilibrium with thorium-234 and protactinium-234)	10,000
Thorium-230 (no progeny)	10,000
Radium-226 (in equilibrium with its progeny)	10,000
Lead-210 (in equilibrium with bismuth-210 and polonium-210)	10,000
Thorium-232 (in equilibrium with all progeny)	1,000
Radium-228 (in equilibrium with actinium-228)	100,000
Thorium-228 (in equilibrium with its short-lived progeny)	10,000
Potassium-40	1,000,000

Notes:

Unconditional Derived Release Limits, DRLs, (Activity and Concentration) relate to the long-lived parent radionuclide in equilibrium with its progeny. The use of Uranium Ore is considered appropriate for NORM-contaminated substances where equilibrium has not been disturbed by partitioning of the Uranium decay series. Where partitioning has occurred, the activity of each long-lived radionuclide must be found and compared to its appropriate Unconditional Derived Release Limit. Where more than one long-lived radionuclide is present in a sample, the appropriate sum of the ratios of the activity of each long-lived radionuclide and its corresponding Unconditional Derived Release Limit, must not exceed 1, e.g.,

Activity NORM Isotope A	+	Activity NORM Isotope B	+... +	Activity NORM Isotope N	≤ 1
Unconditional DRL A		Unconditional DRL B		Unconditional DRL N

5.3.3 Surface Contamination

Limits for surface radioactive contamination on equipment, tools or scrap surfaces intended for unconditional release are based on the analysis of personal radiation exposure pathways to a maximum annual dose of 0.3 mSv. Discrete NORM sources with surface contamination less than the Table 5.3 Surface Contamination Unconditional Derived Release Limits can be released without further investigation.

 

Table 5.3 Surface Contamination Unconditional Derived Release Limits - Discrete NORM Sources

Property	Limit
Dose Rate	0.5 µSv/h at 50 cm
Surface Contamination	1 Bq/cm2 averaged over a 100 cm2 area

Notes:

1. A thin window radiation detector is recommended when monitoring beta/gamma sources of surface contamination.
   
   
2. Table 5.3 release limits are only applicable to fixed surface contamination. Loose surface contamination must be completely removed or all accessible surfaces stripped to ensure complete removal.
   
   
3. In most cases, decontamination efforts which meet beta surface contamination limits will concurrently provide for the control of mixed alpha/beta/gamma sources.