ML20077M323
| ML20077M323 | |
| Person / Time | |
|---|---|
| Site: | U.S. Geological Survey |
| Issue date: | 08/07/1991 |
| From: | Danni Smith INTERIOR, DEPT. OF, GEOLOGICAL SURVEY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20077M326 | List: |
| References | |
| NUDOCS 9108130299 | |
| Download: ML20077M323 (9) | |
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August 7,
1991 Dochet LO 274 U.S.
Nuclear Rcqulatory Commincion Document Control Doch Wachington, D.C.
20555 l
Sirca A recent examination of the llatardo Summary lleport for the U.S.
j j
Geological Curvey'a 1000 hU !!arh 1 ThICA reactor facility l
(docket 50~274) hac revealed several inadequacice rcoarding the production and relcacc of Argon 41.
An analycin 10 given in thin letter to correct. those inadequacion and provide a more realistic cvaluation of the ha;*ardo p ro cen te d by the radioactive argon.
One prob 1cm with the original lla:a r d a Summary I;epvrt evaluation in that routino Argon-41 relcacco are not e v a l u a t.c d for the actual reactor room at the USGS reactor facility.
The evaluation given la for a TRICA facility with a alunificantly larger reactor room volume and a cubacquently higher dilution factor.
The other prob 1cm concernn accidental releases of argon.
The limiting hazard concerning relcane of Argon-41 from the facility is the potent.ial relcace of the Argon-4: qcncrated in the rotary apecimen rack (ItCR or lazy nucan).
This in becaunc the lazy cucan potentially contains the largest pource of Argon-41 at the reactor facility.
Thic accident van made moro credible in 1985 from the incta11ation of a neu lazy suaan with a pneumati: unload feature, where a blower is used to move the camples out of the irradiat. ion positions.
The neu lazy cucan was ovaluated by the reactor committoc and installed as a change authorized by 10c1'n50.59.
The recent closer examination of the Hazardo Summary Report revealed that, in fact, thic installation did conatitute an unrevicued cafety question.
There are tuo safety questiono, concerning the hazarda created by the routine Icahaqc of Argon-41 (from all cources) into the actual USGS reactor room l
and the hazardo created by the potential accident. of dincharging L
the maximum Argon-41 activity from the lazy suaan into the l
reactor room and then to the aurrounding environment.
Thin
[
Ictter addrecces thenc tuo items, requesto your revicu of the cafety analycca, and approval of (1) thcac changen to the original Hazarda Summary Report evaluation of argon ha:ards and (2) continued use of the pneumatic unload lazy susan, t
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ilhile waiting for your response, we have ceased use of the lazy ousan irradiation facility (citective July 19, 1991).
tie will not recume operation of the lazy ausan again until your revicu has boon complet.od and your approval roccived.
If you-would
-11);c to discuan any of these mattern by phone, ploooo call the Reactor Supervisor, Tim DcDey, at l'TS 7 7 6 4 7 2 6.
Cincorcly, y.
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w David Smith-lloactor Administrator 7
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Copy to:
Tim DeBey
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i UXISTIHG DAPUTY ANALYCIGi Scetion 8.2.1 of the Hazardo Summary Hoport discuocou the production of Argon-41 in pneumatic tranotcr tubco and the la:V ousan (HCR).
Uttoa the Hull 10 also frequently referred to ap 1
.the lazy oucan.
It otatco that prolonged operation at 1000 ku L
producco saturated activity icvolo of 4 mci and abo mC1 for a pneumatic tube and the RElt, respectivcly.
The report in then l
deficient by not ovaluating routino relcacco of Argon-41 into the USGS reactor facility and by not evaluating potential
- accident relcacco into the USGS reactor facility.
Although the total activity rolcased doco not depend on reactor room volume, the concentration of argon activity to direct,1y dopondent.
Cinco tho_USGC f acility has one of-the smallor-rcactor room i
volumeo of TRIGA facilitico in the U 8.,
our Argon-41 concentrations will be among the highcot.
The ronult in that Argon-41 concentrationo in the USGS reactor room have exccoded tho-1 cyclo evaluated in the Hazardo Summary heport cince the facility _baaan oporation in 1969.
The lla ardo Summary hoport givoo tho ' f alco improcolon that the Argon-41-concontration in the reactor room will be 1000 than 31 of the HPC for rectricted arcao, and that no hazard resulto.
The argon _probicm was partially recogniecd in 1969, caucing a Actter to be written to the AEC requenting an exemption from the 10 CPR 20 limit for Argon-41 releasco from the facility.
A copy-of-this letter 10 attached.
Thio requent resulted in Change No.
1 being incued t9 the tacility licence, allowing facility
-cffluent air to' average up to 4.8 x 10-6 uC1/ml Argon 41 averaged over a year.
The requent tailed to directly addroco the analynio delicjencico in the lla ardo Summary Hoport.
ADDITIONAL ANALYSCS:
Roactor room volume.
The USGS reactor room han dimencionc of 21 foot x 36.5 feat x 16.5 feet, giving a volume of 12,647 cubic feet.
This equala a volume of 3.58 x 108 ml.
In contract, the reactor room at the University of 1111 nolo (the bacio for the lla:ardo Summary
- Report analyclo) has n' volume of 4.26 x 109 ml.
This mahec the lla ardo Summary analyoto nonconservative by a factor of 11.9.
Routine argon releacci The evaluation provided in 1970 for licenso Change-No. 1 detalla more real10 tic relcanco from experimental facilitico during routino reactor operation'.
Theoc are nummari cd belovi-(a) Pneumatic systemas 4 Ci per year (b) Lazy Susan (HSH) 2.6 Ci per year i
(c) Central Thimblei 0.09 Ci per year l_
(d)' Reactor Water:
0,002 Ci per year l'
1 D
The total predicted annual reicano in approximately 6.7 CA.
Operational data sin:c 1970 has shown that actual argon releasco are higher than the 1970 predictiono, with a peak annual teleace of 11.4 C1.
The relcaced amounto corrclate with integrated pouct production, with higher power pr duction producing more argon.
Operational experience also absuo that moot of the argon rolcace comes from the reactor water and iary susan (RSR).
During the year when 11.4 C1 was rolcased, the reactor uno operated on 193 days (about 4 dayo por ucok).
This givco an averano relcano of 59.1 mci por operating day.
The nominal flow rate of the reactor room exhauot cyctem 1011000 cfm, or 4.08 x 108a al/ day.
The resulting relcace concentration for an average operating day to 59.1 mci / 4.08 x 101"m1, or 1.4b x
_10
- uC1/ml.
The Argon-4'.
activity typically bJildo up quickly durinQ the-first 20'minutco of full power operation to approximntely 40% of-i ts peak value.
A clouer increase occuro over the next 2 houro to about Bor of the peah value, then a very clow riac typicall" occura for the-remaining operating timo.
The peak argon activity typically oxista junt prior to chutdown.
Follouine c h u t.d o wn, t.hc airborne argon act.ivity normally dropa to about 10 't of its peak value within one hour, houtino Argonl 41 in reactor roomi The U800 reactor room 10 maintained at a negativo preocurc with respect to the control room and the out.cido envirinment.
Since the typical operating day conoisto of 8 houro of full power operation, the averaqo concentration of. Argon-41 in the reactor room air during full power operation can be approximated ao 3 timon the average daily concentration (24 hro/0 hro = 3
).
This gives 1.45 x 10-6 uC1/ml X 3 4.35 x 10-6 uct/ml.
This icyc1 to approximately 2.2 timco the curr nt 10CTR20
-limit for rcotricted areas.
The revised 10CTR20 14mit in 50%
higScr than the current limit.
Occupancy of the reactor room during full power reactor operation must average Icon than about 18 houro per ucch to prevent execeding the limito of 10CTR20.103.
Since typical occupancy tu Icon than 2 houro por ucek during reactor operation, exposure to the airborno argon lo uc11 below the applicabic limit.
The whole body donc resulting from continual immersion in an Argon-41 cloud at restricted area MPC (2 x 10-6 uC1/ml) in 12.6 Rem por year.
Exposure at this level of argon for 40 hourc a ucch over one year utvec 3.0 Rom.
Donimetry recordo for the reactor staff shou a maximum annual penetrating doco of 170 mrem
.over the last 3-yearc, from all sourcen.
In addition,_tuo Iilm l _
badges are unod to monitor the south and e-
.t wallo of the reactor room.
The south vall monitor showed a total gamma done of 2.3 Rom in.1990 and the cast vall monitor showed a total gamma donc of 0.62 Rem in 1990.
The couth wall monitor lo also near the radioactive 9toraac arca and the reactor tank, ylciding cignificant exposure from ocureco other than the Argon-41.
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-Dxposure to minors:
The1cxposure.-of-minors to airborne Argon-41-in limited to an average. concentration of.4 x 10-e uCi/ml averaged over a one vech period.
This lovel of exposure would result in a dose of about 4.9 mrom. -Minors are occasionally given tours of the reactor facility, including visits to the reactor room.
The reactor _roomiotay time is typically 10 to 15 minutes, but never morc_than 30 minutos.
A 30 minuto stay timo could be alloucd with a= maximum. concentration ofi_(4 x 10-" uC1/ml)(168 hrs ) / ( 0.~ 5 - hrs )
16.1 x 16-5;uci/ml.
This maximum
=
concentration is almost a factor of 4'more than the typical concentration during full power operation.
This concentration in also well above_the alarm actting on the argon monitoring system at about 7.x 10-6 uC1/ml.
The reactor operator would be informed of an abnormally high Argon-41 activity by the cyntem_ alarm no that he could clear any perronnel-from the reactor room, restrict'rcactor room acccan and tahc corrective action.
Over the last tuo years, ten groups containing minoro have been given react tours.
A total of 59 pocket ionization chambera-were c:r monitoring those groups.
The pocket chambers for t1^
1rn resulted in 58 cero donc readings and one.donc read..
o#
mrem.
All of theco recorded dones are Ichs than the mr-that would be roccived from exposure to Argan-41 at the.ect
.0 limit.
b Accidental releas'
,f argon The Maximum credibic accident for releasing Argon-41 into the reactor _ room'uould be discharging the'lany ausan (RSR) atmosphere into the-roam through the pneumatic unload cystem.
This accidert could relcanc approximately 860 mci of argon in a short timo_ period.
Distributing the 860 mC1 in the reactor room volume of-3._5 x 108 -ml vould q)vc-an-Argon-41= concentration-of 2.46 x __1 0 - 3 _ u C i / m l.
The_ reactor room'airborno activity would then be about 1230 timca the rostricted arca IIPC.
At the nominalLexhaust cystem flou rate of 1000 cfm, the reactor room nir-is replacod approximately 5 times per hour. 'The argon activity would'be rapidly exhausted to the environment above the reactor building where -it would be diluted with uncontaminated air.
Assuming a uniform concentration of argon in the reactor room and 12-minutes to-replace the contaminated air with; fresh
- air, a_ slug of air with an argon concentration of 2.45 x 10-2 uC1/ml would bc discharged to the environment in 12 minutes.
Applying the diffusion factor of 141'(sco January 7, 1970 document) and averaging over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period gives a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> average Argon-41 concentration at the site boundary ofi 1.45 x 10'? uC1/ml J(2.45 x 10-' -uCi/ml)/(141)
(12/24*60)
=
This Icvel is approximately 3.6 times the hPC for unrcotricted areas, which makes it less than the 10 time s !!PC limit for
' declaring an Unusual Event an defined in the facility Emergency Plan.
Thus, this accident would be Icos than the emergency classes ac defined in the Emergency Plan.
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4 Yearly averaging-.of the Argon-41 accident relcace can be performed"to meet the limita of 10CTR20.106 (Radioactivity in effluenta to unrcotrictcd areas).
The accidental releaso of 860 mci of= argon-from'the lazy sunan_(RSR) would require averaqing over only 4 days to be.lcan than the !!PC for unrentricted areas.
The accidental _relcane would therefore not execed the
~
limits of.10CFR20.
PRDCAUTIONARY !!EASURES
. 1
- 1 Several measures-are used at-the USGS reactor facility to reducc the hazard created by the airborne Argon-41 and to q
minimisc tho' potential for accidental reloaces.
( 1-) - The reactor room is normally unoccupied and-lo not a. normal working environment for-the statt.
Timo spent inside the i
reactor room during reactor operation in minimited, both for experimental purposes, caintenanca, and tourn.
(2). The air. exhausted from the reactor room is continuously
)
monitored for argon. activity and thic information'is available,
]
- along with an alarm signal, to the reactor operator.
The. tho-reactor operator has the authority and ability to evacuate reactor room, ubut down the reactor and control acccca-to the reactor-room.
(3)- 'The lazy cusan (RSR) is normally operated with a nitrogen-gas environment to reduce its naturated Argon-41 activity.
This significantlyfroducen-the consequences of accidental discharge of the lary sucan. gas-into the reactor room.
_ (4). The blouer for the'lany_nucan' pneumatic system in
- interlocked with a switch in the control room and cannot.bc turned on without the reactor operator activating this switch.
This switch muct be-on to make the blowe r - switch functional-in
- the reactor room.
Thic effectively eliminatos the potential for
-someono-in the roactor-room accidentally turning on the -lazy, sucan pntumatic-bloucr.
~
SUlul ARY :
The production andLrelease of Argon-41 at the USGS reactor-facility repreacnto a hazard that, with proper monitoring and access control, la well-within the limitations of 10CPR20.
Routine operation of the facility is such that' personnel are not exposed to airborne radioactivity in exccan of the limitations for restricted areas.
WithLthe time averaging allowed, the maximum credible accidental release is well within the limitations for rolcaccu to unrectricted arcan and is below the emergency action levels of the facility Umorgency Plan.
The revined 10CFR20 limit for Argon-41 concentrationo in rootricted arcan 10 50*i.
higher than the current limit, providing a-laract margin between actual and alloucd exposure.
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ilAZARDU U UlH! AliY ItDpORT POlt A 1000 MU Tn1CA ItARK 1__.I.RCl[Oli AT Tl!U U.C.
GUOI.0C I C A1 Ull VUy Subject. PDODUCTION AHI) I!E L M I,S U O F HADICACTIVE CACUU PdlM iMil.t 31 PaciItlCD Page S - 3, delete lact paragraph of section 0.2.1.
Add the following raragraphs:
The USGS reactor room han dimencions of 21 feet 36.5 feet x 16.5 fect, giving a volume of 12,647 cubic feet.
Thic equals a volume ot 3.58 x 10e ml.
In contract, the reactor room at the University of Illinois (the banic for the lla ards Summary Report analysic) has a volume of 4.2G x 10' ml.
Operational data from '969 through 1990 has choun that a c t t.a 1 argon releaten are highe. than initial predictions, with a peak annual release of 11.4 Ci.
The released amounts correlate with jntegrated pouer production, with higher pouer production producing more argon.
Operational cxperience also ahous that mont of the argon relcane comes from the reactor water and lazy nucan (RCR).
During the year when 11.4 Ci uno released, the reactor uac operated on 193 dayn (about 4 days per week).
This gives an average release of 59.1 mci per operating day.
The nominal flow rate of the reactor room exhaust avstem in 1000 cfm, or 4.08 x 102" ml/ day.
The resultino release concentration for an average operatino a y in 59.1 cCi/ 4.08 x 101"ml, or 1.45 x 10 6 uC1/ml Rince the typical operating day c o n s i o t :, of b hours of tull power operation, the average concentration of Argon 41 in the reactor room air during full power tperation car be aparoximated as 3 times the average daily concentration (24 hrs /0 hrs 3
1.
a 4.35 10-'
uCi/ml Thic givca 1.45 x 10 - '- uti/ml X 2 Thic level is approximately 2.2 times the current 10CPR20 limit for teatricted areas.
The revised 10CPR20 limit (effective 1993) is 501 higher than the current limit occupanc', of t h e.
reactot rcom during full power reactor operation must averayc leon than about 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> pcr week to prevent excccding the limitc of 10CPR20.103
.Cince typical occupancy 10 leac than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> por ucck during reactor operation, exposure to the a i. r b o r n e argon in ucll below the applicable limit.
The whole body doce resulting from continual immersion in an Argon-41 cloud at rectricted arca 11PC (2.
10-'
uti/ml) in 12.6 R?m per year.
Exposure at thic level of argon for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> a ucek over one year givec 3.0 Etm.
Dosimetry Iccords for the reactor staff chou a maximum annual penetrating doce of 170 mrem from 1988 through 1990, from all courcco.
In addition, film badges used to monitor the south and cant wallc of the reactor room showed a total gamma doce of 2.'
Rcm and 0.62 Rem in 1990, ECGpectiVely.
The South wall monitor waL algo near the radioactive storagc area and the reactor tank, yielding significant exposure iram coutcca other than the Argori 41.
j l
The exposure of minora to airborne Argon-41 in limited to an average concentration of 4 x 10 o uCi/ml averaged over a onc ucek' period.
This level of expocure would result in a dose of j
-about 4.9 mrom.
Ilinora arc occasionally given tours of.the reactor facility, including visito to the reactor _ room.
A typical 30 minute stay time could be allowed withEa maximum concentration ofi (4 x 10'8 uCi/ml)(168 hra)/(0.5 hvo) 16.1
' ci /ml.. This maximum concentration in almont'a factor x 10-8 u
of 4 more than the typical concentration during full power operation._ Thic. concentration in also voll above the alarm actting on the argon monitoring system at about 7 x 10-+
uCi/ml, The reactor. operator _uould be informed of an abnormally high Argon-41 activity by the-cystem alari no that he could.
clear any personnel from the reactor room, restrict reactor room
-accoon and take-corrective action. -Pocket ionization chambers are used'for monitoring-visitor groupa to assure that expocure limita are not cxeceded.
The maximum-eredibic accident for releasing Argon-41 into
-j
'the reactor room:uould be discharging the lazy nucan (RSR) atmosphere into'the room through the pneumatic unload system.
-Thia accident could-relcace approximately 860 mC1 of argon in a i
short-time' period.
Distributing the C60 mci in the reactor room volume-of 3.5 x 10e m1 would give-an Argon--41 concentration of-2.46 x 10-'
uC1/ml. -The reactor room airborno activity would then be about 1230 times the rentricted area !!PC.
At the
-nominal exhaust system flow rate of 1000 cfm, the reactor room air in replaced approximately 5 timco per hour.
The argon activity would be rapidly exhausted to the environment above the -
reactor building uhcre it would be-diluted with uncontaminated air.
cAssuming a uniform concentration.of. argon in the r actor room and_12 minutes to replace the contaminated air u fresh air,--a slug of air with an argon concentration of 2.A 10-)
uC1/ml_uould be discharged to the environment in 12 m.nuten.
Applying the diffusion factor of 141-(ace January 7, 1970
~ document) and' averaging over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period gives a 24-hour average Argon-41 concentration at the cite boundary ofi (2.45 x 10-) uCi/ml)?(141)
(12/24*60) 1.45 x-10-'
uC1/ml
=
-Thic--level lo approximately 3.6 times the !!PC for unrestricted ataan (1991 limits), uhich.makes it less than the 10_ ti.me n llPC limit-for declaring in unusual = Event as defined in the facility Emergency Plan.
Thou, thic accident uould be Icss than the emergency _ classes au defined in the Emergency Plea.
Yearly averaging of the Argon-41 accident icleanc_can be performed to meet the limita of 10CPR20'106 (Radioactivity in effluents to unten;ricted arcas).
The accidental relcace of 860 mci of argon from the lazy cusan (RSR) would require averaging over only 4 days to be 1cn0 than th* !!PC for unrentricted areas.
The accidental relcane uoald therefore not exceed the l'imita of 10CPR20.
In cummary, the production and release of Argon-41 at the USGS reactor facility represents a hazard that, with proper nonitoring and accesa control, is ucIl uithin the limitations of 6
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i 10CTR20.. Routine-operation of the facjlity in such that personnel are not exposed to airborne radioactivity in.excena.of.
the limitations for~rostricted areas.
With the-time averaging allowed, the maximum credibic accidental relenco-in-uoll within the limitations for relcacos to unrestricted areas and ic below the cmergency action levels of the facility. Emergency Plan.
The-revised 10CTR20 limit (cffective'in.1993) for Argon 41-concentrations ~in restricted areas is 50% higher than the current limit, providing a larger margin botueen actual and
. alloucd expor.uro.
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