ML20003D693

IE Circular 81-07, Control of Radioactively Contaminated Matl

ML20003D693
Person / Time
Site:	05000000
Issue date:	05/14/1981
From:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
IEC-81-7, NUDOCS 8103300375
Download: ML20003D693 (3)

Text

3 SSINS: 6830 Accession No.:

8103300375 IEC 81-07 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.

20555 IE Circular No. 81-07 May 14, 1981 Page 1 of 3 CONTROL OF RADI0 ACTIVELY CONTAMINATED MATERIAL Description of Circumstances:

Information Notice No. 80-22 described events at nuclear power reactor faci-lities regarding the release of radioactive contamination to unrestricted areas by trash disposal and sale of scrap material.

These releases to un-restricted areas were caused in each case by a breakdown of the contamin-ation control program including inadequate survey techniques, untrained personnel performing ::urveys, and inappropriate material release limits.

The problems that were scribed in IE Information Notice No. 80-22 can be corrected by implementing an effective contamination control program through appropriate administrative controls and survey techniques.

However, the recurring problems associated with minute levels of contamination have indicated that specific guidance is needed by NRC nuclear power reactor licensees for evaluating potential radioactive contamination and determining appropriate methods of control.

This circular provides guidance on the control of radioactive contamination.

Because of the limitations of the technical analysis supporting this guidance, this circular is applicable oniy to nuclear power reactor facilities.

Discussion:

I During routine operations, items (e.g., tools and equipment) and material:,

(e.g., scrap material, paper products, and trash) have the potential of becoming slightly contaminated.

Analytical capabilities are available to distinguish very low levels of radioactive contamination from the natural background levels of radioactivity.

However, these capabilities are often very elaborate, costly, and time consuming making their use impractical (and unnecessary) for routine operations.

Therefore, guidance is needed to establish operational detection levels below which the probability of any remaining, undetected contamination is negligible and can be disregarded when considering the practicality of detecting and controlling such potential contamination and the associated negligible radiation doses to the public.

In other words, guidance is needed which will provide reasonable assurance that contaminated materials are properly controlled and disposed of while at the THIS DOCUMENT CONTAINS Ol@b@@b POOR QlJALITY PAGES

IE Circular No. 81-07 Page 2 of 3 time providing a practical method for the uncontrolled release of materials from the restricted area. These levels and detection capabilities must be set considering these factors:

1) _the practicality of conducting a contamination survey, 2) the potential of leaving minute levels of contamination undetected; and, 3) the potential radiation doses to individuals of the public resulting frcm potential release of any undetected, uncontrolled contamination.

Studies performed by Sommers E have concluded that for discrete particle low-level contamination, about 5000 dpm of beta activity is the minimum level of activity that can be routinely detected under a surface contamiration control program using direct survey methods.

The indirect method of contamination monitoring

_(smear survey) provides a method of evaluating renovable (loose, surface) contamination at levels below wgich can b detected by tne direct survey method.

For smears of a 100 cm area (de facto industry standard), the corresponding detection capability with a thin window detector and a fixed sample geometry is on the order of 1000 dpm (i.e.,1000 dpm/100 cm ).

2 Therefore, taking into consideration the practicality of conducting surface contaminatiog surveys; contamination coprol limits should not be set below 5000 dpm/100 cm total and 1000 dpm/100 cm removable. The ability to detect minute, discrete particle contamination depends on the activity level, background, instrument time constant and survey scan speed. A copy of Sommers studies is attached which provid J

idance on establishing a contamination survey program.

Based an the 7tuoie of residupl radioactivity limits for decommissioning (NUREG-0613 2 and NUREG-0707 i ), it can ge concluded that surfam uniformly contaminated at levels of 5000 dpm/100 cm Ibeta-gama activity from nuclear power reactors) would result in potential doses that total less than 5 mrem /yr.

Therefore, it can be concluded that for the potentially undetecged contamination of discrete items and materials at levels below 5000 dpm/100 cm, the potential dose to any individual will be significantly less than 5 mrem /yr even if the accumulation of numerous items contaminated at this level is considered.

Guidance:

Items and material should not be removed from the restricted area until they have been surveyed or evaluated for potential radioactive contamination by a l

M ommers, J. F., " Sensitivity of Portable Beta-Gama Survey Instruments,"

S Nuclear Safety, Volume 1,6, No. 4, July-August 1975.

U.S. Nuclear Regulatory Commission, " Residual Radioactivity Limits for U

Decomissioning, Draft Report," Office of Standards Development, USNRC NUREG-0613, October 1979.

E.S. Nuclear Regula+.ory Comission, "A Methodology for Calculating U

j Residual Radioactivity Levels Following Decomissioning," USNRC NL' REG-0707, t

October 1980.

~ _ _ _.

"5 l

IE Circular No. 81-07 Page 3 of 3 qualified

• individual.

Personal effects (e.g., notebooks and flash lights) which are hand carried need not be subjected to the qualified individual survey or evaluation, but these items should be subjected to the same survey requirements as the individual possessing the items.

Contaminated or radio-active items and materials must be' controlled, contained, handled, used, and transferred in accordance with applicable regulations.

The contamination monitoring using portable survey instruments or laboratory measurements should be performed with instrumentation and techniques (survey scanningspeed,countiggtimes,backgroundradiat{onlevels)necessaryto detect 5000 dpm/100 cm total and 1000 dpm/100 cm removable beta / gamma con-tamination.

Instruments should be calibrated with radiation sources having consistent energy spectrum and instrument response with the radionuclides being measured.

Ifalphacontaminationissuspected,appropriategurveys and/orlaboragorymeasurementscapableofdetecting100dpm/100cm fixed and 20 dpm/100 cm removable alpha activity should be performed.

In evaluating the radioactivity on inaccessible surfaces (e.g., pipes, drain lines, and duct work), measurements at other appropriate access points may be used for evaluating contamination provided the contamination levels at the accessible locations can be demonstrated to be representative of the potential contamination at the inaccessible surfaces.

Otherwise, the material should not be released for unrestricted use.

M rovides useful guidance for evaluating radioactive Draft ANSI Standard 13.12 p

contamination and should be considered when establishing a contamination control and radiation survey program.

No written response to this circular is required.

If you have any questions regarding this matter, please contact this office.

l M raft ANSI Standard 13.12, " Control of Radioactive Surface Contamination D

l on Materials, Equipment, and Facilities to be Released for Uncontrolled Use," American National Standards Institute, Inc., New York, NY, August 1978.

• A qualified individual is defined as a person meeting the radiation protection l

technician qualifications of Regulatory Guide 1.8, Rev. 1, which endorses i

ANSI N18.1, 1971.

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IE Circular No. 81-07 May 14, 1981 RECENTLY ISSUED IE CIRCULARS Circular Subject Date Issued To No.

Issued 80-23 Potential Defects in 10/31/80 All power reactor facilities Beloit Power Systems with Operating License (0L)

Emergency Generators or Construction Permit (CP) 80-24 AECL Teletherapy Unit 12/2/80 All teletherapy licensees Malfunction 81-01 Design Problems Involving 1/23/81 All power reactor Indicating Pushbutton facilities with an Switches Manufactured by Operating Licenses (OL)

Honeywell Incorporated or Construction Permit (CP) 81-02 Performance of NRC-2/9/81 All power reactor facilities Licensed Individuals (research and test) with an While on Duty Operating License (OL) or Construction Permit (CP) 81-03 Inoperable Seismic 3/2/81 All power reactor racilities Monitoring Instru-(reasearch and test) with an mentation Operating License (0L) er Construction Permit (CP) 81-05 Self-Aligning Rod End 3/31/81 All power reactor facilities Bushings for Pipe with an Operating Licenses Supports (OL) or Construction Permit (CP) 81-06 Potential Deficiency 4/14/81 All power reactor facilities Affecting Certain with an Jperating License Foxboro 10 to 50 (OL) or Construction Permit Milliampere Transmitters (CP) 81-04 The Role of Shift Tech-4/30/81 All power reactor facilities nical Advisors and Impor-with an Operating Licenses (OL) tance if Licensee Event or near-term Operating Licenses (0L)

Reports Enclosure

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.n Control and Instrumentation

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Edited.by.E. W. Hagen

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Sensitivity of Portable Beta-Gamma Survey Instruments so. r. s..,.-

Abstract: Developmeart of a new grneratioer of portable With radioactive surface Contamination limil8 and radiation survey instruments and application of the as low as guides.

procricabk* (AL47) philosophy here presented a problem of compliance wrth guides for radiosetive cont.smirsation costuol.

In tecent year: the loweting of litnits and the isola ted, low level. discrettparticle beta-germma con.

P g

tamination is beint detected with the new instruments. To determine the linuts of practicabtGry reqs.fres, tre turrr. the control has encouraged commercial dettlopment of determinetton of the Ilmits of dercetfort of"these surface sensitive sut4cy lastruments, the big improve.

mort contaminents. The d.sta and caltzolatfortsincludedin ihis crticle ment being detectors with thin windows. Peripheral imlicate the source detection frequencies that can be expected

(,,ggg,,,,y,y,,,,ggy;,,y,,,, y;g y,g;,,,,yg,,,g using the new generation of twsey Assaumentr. The authe points, external speakers (instead of earphones), and concimles that. in low population g oups ofdiscrete particles.

L-lectable metet time constants, sst common. Hos about 5000 dis!mbs of beta actruity per pricle is the minimum level of actielty per particle which is dppliesble fw ever, the strong commercial competitlun to supply this type of instrumentation, the extrtme competition for confident compEance with surface evntamination control funds that could be used to improve radiatiort pro.

guider. Lower evnaol levels are possnble wurh oddition*I demopnsent of krsauments or through high< ort changes be rodfatfore survey and contaminattorr. control methods. 4dg.

' reluctance or,msbility to provide adequate specafics.

donal analyses at ' required fw assessmens of the hazard caused by widely disperseddiscreteperttela conarminants.

• John F. Sornmers received jegrees la mathemade:(s.A.,

The common, historical way to classify surface radio.

1948) and phr5'es (B.s., 1950) trora on Uniwmity or active contamination has developed into standard Wyonung and was sketed to the Nadonal Honorsry Brus definitions, lirruts, and contsol guides which, m.

Society. SMrna Pi Sisma. La 1949. Undes as AEC fellowship some instances, are difficuit, if not impossible, to apply.

grant, he earned a cesuncais in radioI@as pysics frono ow Oak Rid s Instituts'of Nucleas Studies for work at VandcstWt C

In general, the definition of " removable" radio.

Univeritty and Oak R*.dge Natioast t.aboratory during 1950 actin contamination must be inferred from guides s and 1951. Since 1951, he has b en associated with the Idaho 3

and regulaticas on the significance of the quantity of Nadonal nedas 1.aboratory m) Vor@ me b radioactive materials removed. " Fixed" contaminatiott, honal Reactor Tesans station) as technical aurstant and as although not as uniquely defined. is, by inference, the man,ser of Applied Health rhysics in the safety groups of the radioactive contaminants that remain on a surface aftet pri ne contracion for AEC. At present, he is saperviwr of the Radiotope.at Engw'icering Section in the Safety Divnium of the surface has been checked and found to haw less

^*F' N"*3'*' C8"P"aY 8* P'ime ooeratirig con 1. cree far than some defined removable contamination fewl.

the Eurgy Re earch sad De* F Ornest Adminiuram There are many minor variations of these definitions, (ERDA) at INE1., where he is d,irectfy aivotred in development but these will suffice to outline a majoe problem that

,na,ppge,,;o, g, p,;i3,,_acdoo.u (u w as pescd.

applied health physicists have to verify compliance cable) program for contros d radiauon hecares to 1.NEI.

nuclear faataies.

NUCt.E AR SAFt!TY, Vor.18. No. 4..*uty-Auyws: 1975

454 CONTROL AND INSTRUMENTATION Figure 7 shows a similar comparison using a detection frequencies appear to converge at about 80A detector elocity of 3.5 cm/sec. Here, the difference h.

The results shown are averages of over 100 observa-detection frequencies narrows. and the alarm set point tions per datum point from two or more experienced metnod becomes better than the audio dete: tion surveyon. ' Die largest variations in the data occurred method far the 1stger sources at this low survey between individuais; I.e., the largest variables were

velocity, caused by tne physical and psychological conditioning Figure 3 compares experimental audio. output dau for three different survey velocities at 120 counts / min c,

background. The difference in source detection fre-1 I

i i

quencies is surprisingly small when compared with the 3

^

alarm. actuation method. His is explained by the adaptability of the human audio response; i.e., the v ' 8*

=

effective time constant (human) adapts, within boun,ds,

}

E

~2 to the source size that can be detected with a given j

s survey velocity and background count rate. Note that

^ " " * ' "

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.s at 500 counts / min (5000 betas / min), the source

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2 B = 120 counti/wdn _

r = noise man

• 15 enn/ mms l a tsounu/ mini nol l

2 I

I I

I 10 2

0 20 40 so ao too 120 P, tile

=

a C

r Fig. 6 Comparboe of smrce detsetion finguendes using

)

U 2

alasne set-point and pudio detectices methods.

5 T = 0.o159 met

'[

l 0

l I

[

2 v = 15 cm/ses

- 3 120 counts /A

~ F = 0 0159 erWue 2

l l

l l

. 5 o = 3.5 sm/ses Io 0

20 40 so ao too a

f P (%8 g

2 Fig. 4 Effect of background on wurce startreactuation fro-Ar.rm tcaec)

A'a8* (**st que ncy.

- gg2 l

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20 43 80 so too

1. N 5

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i Fig. 7 " Comparison of source dessetloa aequencies udag M

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alarm and audio desection methods.

/g 2

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_i 10

( '._

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i of e - 120 counts / min j

Calculams j

---o --- Emperw=atas

-f = 0.0153 anen we

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r-M i s - no.unu/m.,.

2

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'2 "-- f a 0 0159 men s/p v = 15 cm/sse i

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o ao ao ao too o

20 40 00 N

100 P t%I g

r, fila F"5.5 Cornparuon of espaimental and calculated dats ce F~e,3 Comparisosi of audio source desecdom frequencies and wurca detection frequench h

rebdtles, NUCLE AR SAFETY. Ves.16. No. 4. July-Autpsst 1975 m

J

CONTit01. AND INSTRIJMENTAT808d 456 RESULT 3 4

e i

s A!arra set points vs. background count rate were

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calculated from Eq.1. These are illustarted in Fig.1 icoa for time constants of 0.0159 and 0.159 min. De k I

value selected. 4.89, uniquely defines the probability fsoo p,

of an alarm being caused by a constant average j

oco background as 5 x IU. mini.

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Figore 2 shows that the short. time. constant set point is more sensitive for source detectiori, even 200 p,,$,,,_,

though the long time. constant set point is.the lowest.

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The relative difference between the two becomes less e

20e, 400 sac toe tono as the source residence time increases.

s tcoums/mial Figure 3 illustrates the improved sensi ivity to be expect;d as the source residence time increases (de-Rg.1 Effect of backpoond on Or imura shres set point.

tector w!ocity decreases). De set point is obtained from Eq. I or Fig.1.Este that with a source residence time of I sec (5 cni/sec), it takes 5000 betas /.nin ' 500 s

(

counts / min) at a back;;round of 60 counts / min to-i l

1

1. - _

cause an alarm 90% of the time. As a practical f

_m illustration, if.an individual surveys himself at 10

? - c.12 W emhee, it will take about 3 min for him to survey half

?

the surface area of his body, and the particles he i

{ 3,a 3 dhcovers with a 90% confidence level will haw a E

beta. emission rate of about 9000 per minute (900 g

Z Z

counts / min).

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5 s

Figure 4 illustrates the benefit of selecting low-background areas to perform ecntamination surveys.

n.

As indicated by Eq.1, the alarm set point has to be

,. $' g "d*

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changed each time the background changes,and,il the

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g time constant is not dependable (known), the set point 3,

e,,

may not be correct. Changing background count rates p, is3 are a common occurrence in our ope' rations, and our inability to make tims constant determinations in the Fig. 2 E# set of tnerummt time constant on soons detachon field has caused us to abandon the alarm set point

gueng, method for contamination surveys.

Figure S shows that the calculational method of determtmng source detection freqJencies using the z! arm set point is valid in comparison with experi-2-

mental data. Both the time constant and the alarm set

". foe"eI""" g 3

g 3

reint were verified on the instrument used. In practics, 10

'7

=

there vmuld be some ambiguity in the setting of the 3

2 2

afarm owing to the crude alarm set point dial furnished

, -1 3

ca, :: tis modelinstrument.

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Figure 6 compares calculated alarmectuation fre.

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is quencies widt experimental dsta on audio-output,

2 murce detection frequencies at *. _verage background 2.4 of l':0 counts / min and a rr ative surface-window 21 I

I 1

3a wloetty o( 15 cm/sec. Using the speaker output 0

20 do 100 08 methodismsfler sources are detected with the same

s (58 frequency that is obtained using the alarm set-point nethod.The improvement is about a factor of 3.

F:g. 3 ETTect of pube weJocity os source detection trequency.

NUCt. EAR SAFETY Vol.18. Me. 4, Jidy--Augpase 1973

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• MC CONTR0t. AND INSTRUMENTA710N because the source velocity vector will hardly ever tion of calculated data these sources are counted with exactly bisect the circular window projection on the an elliciency of 0.1 count per beta at h in, from the surface being surveyed.

center of 1.7 mg/cm',"$-cm diameter windows of Using the ideal survey conditions and an. average

" pancake type semishielded Geiger-Mueller tubes..

background count rate B, a source with a net equilib.

Extrapolation of the data to other beta emitters is a rium count rate S will cause a count. rate as large as, or practical exer,cise;i.e., from Evans,' beta transmis ica larger than, A, with a probability Pg. that is uniquely factors through 3.0 mg/cm* (air plus window) were

{

defined by the constant Kg when the source residence calculated and shown to be greater than 72% for betas time under the window is i and the time. dependent with energy spectra having maximum <nesgy betas trTeter response term is 1 - s-'/' The count rate A can (Emax)' greater than 0.2 MeV. Thus **'Cs betas,with then be expressed as a mean Ema, a 0.58 McV, provide a beta-counting efficiency from the thin wmdow detectors which is

' A 6(1 -ad')(B + S + K ir'M(B +.S)h ) (2) typical of beta emitters with Ema, greater than f

l 0.2 McV. Also, backgrc,und and source size data are By substitu, tion of the alarm set. point count rate A presented in counts per minute, so that changes in beta from Eq.1 into I"q. 2 and rearractement, the source energies of sources and/or source--window distances strength is found to be can be noin alized, using observed counting effl.

ciencies, to the calculated data presented in this articia.

L-e gg (g + gj7-% g%l)

With some manipulation of Eq.3, a computer 1 - e-'er program was used to ol rain an iterative set of solutions

-(B +K IrH(B + S)M ) (3) f I

The alarm set points were determined using Eq.1.

Analysis of Eq.3 shows that P, is the probability, or Selections of background count rr tes, relative time dependent frequency, that S wilt cause an alarrn

• • "~ 8"# '*

• when Kg is positive,and (1 -P,)is the probability that c n tant were arbitrary but withm the ranges chosen th3 alarm will be actuated when K[is negatin.

I" **

8' d "*

N***

""E Solutions for S can be obtained using s.lected values of known probabilities of alarm actuation.

[

K, B, r, t, and T.

An extensive set of experimental data was obtained f

by moving calibrated sources past the detector windows at measured velocities and source-window METHODS distances t check the validity f the calculations.The same experimental setup to determine source detection in order to' determine expected alarm actuation frequencies was used with the audio (speaker) output i

frequencies during standard contamination surveys,

, of the survey meters. The use of audio output during experimenters estabhshed the following conditions.

Esse conditions would also allow an experimental contamination surveys is a wellknown practice and wdi not be described further, check of the calculated alarm. actuation probabilities When the experimental and calculated source that occur when the source strength, background, detection frequencies were cornpare i, it became instrument time constants, and source residence time apparent that the time constants of the commercial are changed.

survey instruments were not equal to specified values.

Commercially available (two manufacturers)

Variations were noted between instrumenta of one portable survey instruments were used as models for model and between the different alarm set points on tha calculadons and experiments. Selectable time the other model. By measuring the buildup of the comtants of 0.0159 and 0.159 min were calculated indicated count rates to 90% of equilibrium, we were from the manufacturers' quoted time-response c as, able to determine the actual time constant on the 8

acteristics "90% of the equilibrium count rates in 2.2 Instrurnents for arry particular alarm set point.

or 22 seconds." Surwy w!ocities between 2.4 and De experirnental data were obtained on'an irutru-15 cm/sec were selected for' analysis, velocities that ment that exhibited the advertised time constants cause the source residence times under the. 5-dm-Howewr, the poor (time-dependent response) per-diameter detector windows to range itom 0.33 to formance of these instruments as a poup ! as caused us 2.1 sec. Cesium.137 sources having small diameter and to abandon the alarm set point method for source low backscatter were used experimentauy for verifica.

detection under field conditions.

NUCt. EAR SAFETY. Vad.18. No. 4, My-August 1975

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CONTROL ANO INSTMtJMENTAT1088 454 ti:ns have left soniething to be desired in quality and owrallperformance of m.ny of the instruments.

under the detector is on the same order of magnitude of or less than the time con'stant of the meter; the Although present beta-gamma contamination.

count rate of the instrurnent increases as the source-control pi.ictices'ue more rigorous than in the past, window distance decreases; and the response of the there is still less th2n complete control of low-activity count rate meter increases as the scurce residence time low density parrlaulats sources within the operating under the detector window increases.

areas. In a typied situatiori the highest density of t.hese On the hasis of the approximate Caussian distribu.

. particles, outside of contamination-control zones, may tion of a count rate'around the true awrage count rate, be on the order of one detectable particle per 10 to.

2 an alarm set point A has a probability p of being 8

8

,10 ft. The particles are removable beta-gamma reached and causing an alarm due to an average actidty, but because of the large areas involwd, the background co mt rate B during a counting laterval T multiple. types of surfaces on which they are deposited,

• that can be expressed as and the low asea density of the particles, they are not subject to detection with any sensible frequency using A = (I - <#/') (B + klT4 M

B I)

(1) the smear or wipe techrdque. Dus survey instruments must be used to detect and measure the activity of the where r is the tirne constant of the count. rate meter removable parricles.

and k is a constant that uniquely /r(the fraction defines the prob.

The particlee tend to be trapped and concentrated ability of alarm.* De term 1 -e#

on certain types of surfaces, such as mopheads and.

equilibrium count rate obtained duringT)is timited by urylic fiber rugs. From these deposits it has been design considerations of count rats meters to the determined that the specific activities of most of the accuracy of the metu wiput. Most instruments have partie!es range from about 2 x 10 to 2 x 104 dis / min.

1% (or fu!I-scale reading) or larger accura limits. For.

8 In order to determine why the particles escape detec.

this ressr:,n the value of 0.99 = I -e4 has been

~

tion and control within the operating areas, experi.

assigned for this study. Knowing the value of 7 allows menten devised a rigorous test to determine the s luti n for T, and the solution is used la the second expected frequency of detection of the particles using term of Eq.1. His solution can be thought of as the standaid survey methods. The results of these experi.

practical, constant, integrating interval observed by the rnents have shown that the main hope for improvement count rste ineter.

lies in the deve!apment of more sensitiw sarvey he approximate response of an instrument to hstruments and portal monitors a.,3 the devel.ipment small-diameter sources can be calculated by defitting and application of contamination control methods standard survey conditions and relating them to the similar to those used in facilities where the much rrore response characteristics of the instrument. For these hazardeus alpha <mitting materials are handled.

calculations the velocity vector y of a fht circular

~

window of the detector is assumed to be parallel to the

' surface being surveyed, and the velocity is held THEORY

""5'*"' D' 5 "'ce5 Passing under the window of the detector bisect the circular projection of the window The ability of a count rate meter to provide reliable on the surface. The beta-coanting efficiency of the information for detection of small-diameter sources instrument is assumed to be positive and constant during surveys for radioactive contaminants depends when a source resides in the circular projection of the upon a number of factors.These factors,for any given window on the surfac ; otherwise, the efficiency for type ind energy of radiation sources, are the specific counting the source is zero. This !atter assumption may activity of the sources, the influence of background csuse significant perturbations of experimental data ndiation, the instrument time constant, the source-from csiculated data when source-wiridow distances detector *,eometry, and the relatiw source-detector are larger than 2.5 cm. Gamma counting efficiencies, velecities. When an starm ses point is used to indicate the same order of magnitude as the beta; counting the presence of radioactive sources, investigation shows efficiencies, may also cause sgruficant pejturbation of that the sensitivity of the instrument is increased by experimental results, depending on Oc d'etector shicid-wuing the 2iarm set point as low as possible without ing contiguration and effectiveness. The ideal source l

caaing alarms due to the fluctuations of background; residence time i is assumed to be equal to the window th2 response of the count rate rneter is modified from diameter d divided by the velocity vector r, Under field the equdibrium count rate when source residence time conditions,i will usually be less than the ideal value NOCLEAR SAFETY, Vaf. 16, No. 4. Jee -August 1975 v

l

,J e

CONTROt. ANO INSTRUMENTATION 467 of the surveyors. The lower detection frequencies have and thus control, a health hazard of consequencer been ignored because of the statistical deviations that Krebs

• and Healy' have presented upments on the occurred. The time consumed to cotain reliable data at relative hazar.ds of discrete particle and small-area the higher detection faquencies was considerable,and, sources in relatloa to more diffuse sources. !!owewr, as our interest is he setting high confidence. level.

the data used involved higher specific activity than that control criteria, it was considered not practicahic to of the particles we have been observms. IIcaly has cbtain good, small source, detection-frequency published' a comprehensive resuspension hazards statistica.

analysis for diffuse contaminants which is difficult to apply to the low density particle population we ob- '

DISCUSSION AND CONCLUSIONS ww. God hamds analyms are needed on the resuspension of discrete particles ha the size rangs A method has been shown whereby detection frequencies of small-diameter radioactive sources can under discussion.Dewlopment of portable fnstruments for surveying large areas with a practical expenditure of be calculated for portable survey instruments that have time and effort appears possible, but it will take time known time constants and alarin set points. Sc=ce and money to design, develop, and make them com-detecticn frequencies are strongly dependent upon merdaDy available. In the meantime, the advisory, (1) source sitength, (2) surwv wlocities, (3)bacle.

standards, and regulation agencies need to look at the ground activity, (4),letector sensitivity, and (5) the control guides and limits to assure that the con.

time constant of the survey meter. With activity of a -

servatism applied using the ALAP philosophy is, in large, area uniform surface, the survey velocity and the fact, practicable for complians with the equipment time constant of the survey meter are immaterial and methods available to the industry. For this (within reasonable bounds). He calculations show particular problem (low-density discrete particles of that, even under the most rigorous conditions (survey removable beta-gamma activity), I suggest that 're.

velocities <2.5 cm/sec), small-diameter sources movable contamination be defined in two categories, emitting 3000 betas / min can only be detected in

" uniform" and " dispersed " and then resuspension low background areas with a confidence of about 90%

factors applied that have some reality in the calculation using the alarm set point method. At more sensible of exposure hazards. His is the only way at this time surwy velocities of 10 to 15 cm/see, it takes sou.ces that the industry has any hope for practicable com.

emitting 10,000 to 15,000 betas /rnin to prodde the pliance with contamination.controllimits.

same detection frequency using the alarm set-point detterion method.

REFERENCES At the higher probe velocities investigated, source detection frequencies are larger using the audio output

1. Administrative Guide for Packaging and Transportma Radio-Maieriais. ANSIW14.lal-1M3, 5 7 Amedc== No-rather than the alsrm set-point method. With small.

ac diameter sources emitting 5000 betas / min, source rional Standards Institute.New Yost.

detection frequency at 120 counts / min background is

2. Department of Transpostation, Hazardous Materials Regule.

tions or the Department of Transportation, code ofredmit about 80% using the speaker output, regardless of the Reruktfoas, Tith 49,173.397, e4Tective Sept. 13,1973.

survey velocities between 3.5 to 15 cm/sec. With 3000 3.Cencluding Statenut d tk AEC Regulatory Staffla the.

beta / min sources, the 5P'*ker detection fre9"ncy, "As Im As hac&abP Heaks, M Mny, IM t

l using the slowest stuvey w!ocity (3.5 cm/sec),is only 443 452 Unly-Augurs 1974).

4. A. A. Janert, Statistical Memods Used in the Menurement sbout 65%. At this velocity the alarm set point method of Radioactivity (Some Useful Graphs). USAEC Report is as good as or better than the audio method with AECU 262,194L

ources larger than 3500 betas / min. Although most of

5. R. D. Evans, Die.d rom /c Nucleier, pp. 627-628, McGim de exPcrimental data were obtained at only one omPaay, be, New Yort,1MS.

background '.evel (120 counts / min), it is apparent that

6. J. S. Kirbs, ne Response 3f Mammafian SMn to Inadiation with Particles et Reactae Detris, Report USNRDL.

It is not practical to set contamination <ontrol limits TR-67111, U. S. Naval Radiciosical Deafense Latmratory, on discrete particles of beta-f,2mma activity much September 1967.

below 5000 be'tas/ min if we are to have confidence in 7.J. W. Healy, A Proposed Interha Standard foe Phalerstura la our ability to detect discrete-particle sources before A

• Port f.A.348m, Appeasd, W they escape the contamination <ontrol areas.

Alamoe 5denafic Laboestory, January 1974

8. J. W. Ifcaly, Surface Contaminatsoo: Dectsion laveh, These results then pose several problems. Are the USAEC Report LA.4555 MS. Los Alamos 5ciennfic tabora-particles of beta-gamma activity that escape detection, tory, septemtiee iWI.

Nuct.EAH SAFETY. Ved. to. No. 4. Juev-Aiga 1ers

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