Surface Contaminated Objects and release limits

["Redmond, Randy (RXQ) " <redmondrr@Y12.doe.gov>]

This subject has been briefly touched on before.  Trying to get some dialog

going in an effort to resolve (to myself) once-and-for-all.  This is a

little lengthy, but anyone that ships radioactive material or releases

material from radiological areas should read.



A couple of links that will be helpful:

http://frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?TITLE=49&PART=173&SECTIO

N=443&YEAR=2001&TYPE=TEXT



http://www.rampac.com/NRCinfo/NUREG%201608.pdf





A few reference sections and definitions from 49 CFR 173:



Surface Contaminated Object (SCO) means a solid object that is not itself

classed as radioactive material, but which has radioactive material

distributed on any of its surfaces. SCO must be in one of two groups with

surface activity not exceeding the following limits: 

(1) SCO - I: A solid object on which: 

(i) The non-fixed contamination on the accessible surface averaged over 300

cm2 (or the area of the surface if less than 300 cm2) does not exceed 4

Bq/cm2 (10-4 microcurie/cm2 - 22,200 dpm/100 cm2) for beta and gamma and low

toxicity alpha emitters, or 0.4 Bq/cm2 (10-5 microcurie/cm2 - 2,220 dpm/100

cm2) for all other alpha emitters; 

(ii) The fixed contamination on the accessible surface averaged over 300 cm2

(or the area of the surface if less than 300 cm2) does not exceed 4x104

Bq/cm2 (1.0 microcurie/cm2 - 2,220,000 dpm 100 cm2) for beta and gamma and

low toxicity alpha emitters, or 4x103 Bq/cm2 (0.1 microcurie/cm2 - 222,000

dpm/100 cm2)  for all other alpha emitters; and 

(iii) The non-fixed contamination plus the fixed contamination on the

inaccessible surface averaged over 300 cm2 (or the area of the surface if

less than 300 cm2) does not exceed 40x104 Bq/cm2 (1 microcurie/cm2) for beta

and gamma and low toxicity alpha emitters, or 40x103 Bq/cm2 (0.1

microcurie/cm2) for all other alpha emitters. 



Low toxicity alpha emitters are defined as: (1) Natural uranium, depleted

uranium, and natural thorium; (2) Ores, concentrates or tailings containing

uranium-235, uranium- 238, thorium-232, thorium-228 and thorium-230; or (3)

Alpha emitters with a half-life of less than 10 days. 



Non-fixed radioactive contamination means radioactive contamination that can

be readily removed from a surface by wiping with an absorbent material.

Non-fixed (removable) radioactive contamination is not significant if it

does not exceed the limits specified in Sec. 173.443. 

Sec. 173.443 Contamination control. 

(a) The level of non-fixed (removable) radioactive contamination on the

external surfaces of each package offered for transport must be kept as low

as reasonably achievable. The level of  non-fixed radioactive contamination

may not exceed the limits set forth in table 11 and must be determined by

either: 

(1) Wiping an area of 300 square cm of the surface concerned with an

absorbent material, using moderate pressure, and measuring the activity on

the wiping material. Sufficient measurements must be taken in the most

appropriate locations to yield a representative assessment of the non-fixed

contamination levels. The amount of radioactivity measured on any single

wiping material, when averaged over the surface wiped, may not exceed the

limits set forth in table 11 at any time during transport; or 

(2) Using other methods of assessment of equal or greater efficiency, in

which case the efficiency of the method used must be taken into account and

the non-fixed contamination on the external surfaces of the package may not

exceed ten times the limits set forth in table 11, as follows: 

Table 11--Non-Fixed External Radioactive Contamination-Wipe Limits 

Beta and gamma emitters and low toxicity  alpha emitters - 2200 dpm/100 cm2

All other alpha emitting radionuclides - 220 dpm/100 cm2

(b) Except as provided in paragraph (d) of this section, in the case of

packages transported as exclusive use shipments by rail or public highway

only, the removable (non-fixed) radioactive contamination on any package at

any time during transport may not exceed ten times the levels prescribed in

paragraph (a) of this section. The levels at the beginning of transport may

not exceed the levels prescribed in paragraph (a) of this section. 

(c) Except as provided in paragraph (d) of this section, each transport

vehicle used for transporting Class 7 (radioactive) materials as an

exclusive use shipment that utilizes the provisions of paragraph (b) of this

section must be surveyed with appropriate radiation detection instruments

after each use. A vehicle may not be returned to service until the radiation

dose rate at each accessible surface is 0.005 mSv per hour (0.5 mrem per

hour) or less, and there is no significant removable (non-fixed) radioactive

surface contamination as specified in paragraph (a) of this section. 

(d) Paragraphs (b) and (c) of this section do not apply to any closed

transport vehicle used solely for the transportation by highway or rail of

Class 7 (radioactive) material packages with contamination levels that do

not exceed 10 times the levels prescribed in paragraph (a) of this section

if-- (1) A survey of the interior surfaces of the empty vehicle shows that

the radiation dose rate at any point does not exceed 0.1 mSv per hour (10

mrem per hour) at the surface or 0.02 mSv per hour (2 mrem per hour) at 1 m

(3.3 feet) from the surface; (2) Each vehicle is stenciled with the words

``For Radioactive Materials Use Only'' in letters at least 76 millimeters (3

inches) high in a conspicuous place on both sides of the exterior of the

vehicle; and (3) Each vehicle is kept closed except for loading or

unloading. 

Discussion - one could surmise that the vehicle itself would be meet SCO-1

criteria if it exceeds the "no significant removable" and/or 0.5 mrem per

hour dose rate limits noted in (c).  Further, one could surmise that if the

vehicle does not exceed (c), then the vehicle does not meet SCO-1 criteria.

>From here, one could conclude that the following guidelines to free release

to the public have been established:

Beta and gamma emitters and low toxicity  alpha emitters (removable) - 2200

dpm/100 cm2

All other alpha emitting radionuclides  - 220 dpm/100 cm2

Fixed - 0.5 mrem per hour.

BUT, there is some "clarification" on Surface Contaminated Objects in NUREG

1608.

NUREG 1608, section 3.1.2 - "International regulations (IAEA, 1990a) contain

a threshold value for contamination, below which a nonradioactive object

[i.e., an object having an average specific activity level less than 70 Bq/g

(2 nCi/g] can be shipped without regard to the radioactivity [See

clarification of contamination in Section 3.2.1].  The contamination

threshold value was inadvertently omitted from the 1996 DOT domestic

regulatory revisions (DOT, 1989; DOT, 1996).  Consequently, all objects

which are themselves not radioactive, but are slightly contaminated, could

still be construed to qualify as SCO-I.  DOT is currently addressing this

issue.

In the interim: an object with external contamination may be considered to

be excepted from classification as Class 7 (radioactive) material if:  (1)

contamination when averaged over each 300 cm2 (46.5 in 2 ) of all surfaces

is less than 0.4 Bq/cm2 (2200 dpm/100 cm2) for beta-gamma emitters and low

toxicity alpha emitters, and is also less than 0.04 Bq/cm2 (220 dpm/100 cm2)

for all other alpha emitters; and (2) the object itself has an average

specific activity less than 70 Bq/g (2 nCi/g)."

NUREG 1608, section 3.2.1 - "For the purpose of complying with the SCO

definitions in the domestic transportation regulations only (DOT, 1996; NRC,

1996a): Contamination is the presence of a radioactive substance on a

surface in quantities in excess of 0.4 Bq/cm2 (2200 dpm/100 cm2) for

beta-gamma emitters and low toxicity alpha emitters or 0.04 Bq/cm2 (220

dpm/100 cm2) for all other alpha emitters."  Note that these values aren't

associated with removable or fixed, but appear to be removable plus fixed

(total).  How many alpha or beta-gamma emitters have you run into that will

give a doserate of 0.5 mrem per hour with a surface activity of 2200 dpm/100

cm2?

NUREG 1608, section 3.4.5 offers some more "clarification" on how wiping

efficiency is used in determination of contamination on package external

surfaces versus SCOs.  "Non-fixed contamination on package external surfaces

is regulated by DOT in section 49 CFR 173.443 Contamination control.  The

contamination level may not exceed the non-fixed external radioactive

contamination-wipe limits specified in Table 11, and must be determined by

wiping or other methods of assessment of equal or greater efficiency.  The

amount of radioactive material on the wipe, when averaged over the surface

area wiped, is limited to the values specified in Table 11 (e.g., 0.4 Bq/cm2

, 2200 dpm/100 cm2). DOT further specifies that the actual package surface

contamination may not exceed ten times the Table 11 wipe material

contamination limits.  In other words, the wipe limits in Table 11 are 10

percent of the maximum permitted surface contamination.  The Table 11 values

are based on the assumption that, unless otherwise specified and documented

by the shipper, the efficiency of surface wiping, (i.e., the fraction of the

surface contamination captured by the wipe) is 10 percent.  For example, if

a wipe measurement reaches the Table 11 contamination-wipe limit of  0.4

Bq/cm2 (2200 dpm/100 cm2), the actual surface contamination is 4.0 Bq/cm2

(22,000 dpm/100 cm2), because the wipe is only capturing 10 percent of the

contamination.  . . .  .. . The SCO contamination limits do not incorporate

a wiping efficiency.  The wiping efficiency used by the shipper must be

accounted for in all SCO contamination determinations.  Failure to do so

could result in underestimating the actual SCO contamination levels.

Shippers are responsible for ascertaining the wiping efficiency used in

determining contamination levels on SCOs.  Shippers using the (assumed) 10

percent wiping efficiency for package external surface contamination

determinations could use that method for SCOs, provided the contamination

and surfaces are similar, and their SCO wipe measurements were compared to

10 percent of the SCO contamination limits. . ."

Now let me see if I "understand" (which I do not) the NUREG 1608

clarification using an example.  I just unloaded a radioactive shipment

(beta-gamma emitter) from an exclusive use vehicle.  I wipe the floor in the

vehicle to release it.  The wipe is 300 dpm/100 cm2 beta-gamma.  I perform a

dose rate survey on the floor and it is less than detectable.  I release the

truck because it does not exceed Table 11 values.  But unfortunately, my

smear collection efficiency is only 10 percent.  The floor of the truck is

actually 3000 dpm/100 cm2 beta-gamma - the truck should be shipped as SCO-I

because it exceeds 2200 dpm/100 cm2?  Further, if this had been an alpha

emitter shipment, I'd be looking for 22 dpm/100 cm2  removable - there goes

being able to use all my field instruments to release anything; hope there's

plenty of money in the Federal budget to buy low background lab counters and

man them.

More madness

DOE Order 5400.5 Figure IV-1 establishes surface radioactivity limits for

release.  With the exception of tritium, the values are the same as Reg.

Guide 1.86.  I'm primarily interested in the uranium category - 1000 dpm/100

cm2 removable and 5000 dpm/100 cm2 total alpha.  Unfortunately, some of the

uranium contamination I deal with isn't defined as a "low toxicity alpha

emitter" because it isn't natural or depleted (a discussion for another day

- maybe someone could enlightened me as to why a given activity, e.g., 1 mCi

of U-234/U-235 is more hazardous than 1 mCi of U-238).

DOE order 5400.5 permits free release to the public if an object does not

exceed 1000 dpm/100 cm2 removable and 5000 dpm/100 cm2 total uranium alpha.

DOT doesn't want a vehicle used for an exclusive use shipment released if it

exceeds 220 dpm/100 cm2 removable alpha which assumes a 10 percent smear

collection efficiency (2200 dpm/100 cm2 ) .  NUREG 1608 states that anything

above 220 dpm/100 cm2 taking the smear efficiency into account would have to

be classified as SCO.  What am I missing?  

Questions:

(1) Has DOT offered clarification beyond NUREG 1608?

(2) Is there time to make an attempt to stop this madness?

(3) What criteria/limits are your DOE site or NRC regulated facility using

to release material?

(4) Am I misinterpreting this?

Any comments, recommendations, or aspirin is appreciated.  



Disclaimer - My comments and understanding of this subject do not

necessarily reflect the comments and understanding of my employer.



Randy Redmond

Radiological Control Organization

BWXT Y-12 L.L.C.

Oak Ridge, TN

865-574-5640



	 



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