ML20125C290
| ML20125C290 | |
| Person / Time | |
|---|---|
| Issue date: | 07/13/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Ahearne J, Kennedy R NRC COMMISSION (OCM) |
| Shared Package | |
| ML20125C287 | List: |
| References | |
| NUDOCS 8001080315 | |
| Download: ML20125C290 (11) | |
Text
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f1EMORAriDUM FOR:
Commissioner Richard T. Kennedy Commissioner John Ahearne
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.~ Executive Director for Operatio'n's"~ ~ ~""
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arold R. Denton, Director FROM:
H Office of Nuclear Reactor Regulation
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SUBJECT:
USE CF THYROID BLCCKIf!G AGEf!TS If! A!! El'ERGENCY
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RESP 0llSE PROGRA'i e
In your memoranda (dated June 22, 1979 and June 4, 1979) you requested a review of a Dr. Von Hippel letter to Science as well as answers to specific questions regarding the use of thyroid
_y blocking agents.
We have reviewed the various material enclosed
~ ' - i-in your memoranda and are herein providing a few g< neral comments es well as more detailed responses to the specific questions.
Thyroid blocking agents are one possible means for reducing thyroid o
exposure during a nuclear accident.
Other means for reducing exposure include shelter, respiratory protection, and evacuation.
For the general public. we believe that thyroid blocking agents would generally be less effective in an emergency than the other protective actions mentioned above.
This statement is based on the folicwing considerations: (1) thyroid blocking agents protect only the thyroid; and (2) potassium iodide, the drug most frequently proposed as a blocking agent, must be taken shortly before or within two hours following intake (e.g., via respiration or ingestion). Under many accident scenarios, shelter, respira-tory protection, or evacuation would appear to be easier to implemer and potentially more effective than the use of potassium iodide.
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Cc..:nissioner John I.hearne.
'.h Cer:i::issicnar T!icherd T. Kennedy 2
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Ehere institutional controls could be coidiiidoilsly naintained for lor.g periods of time, prcvisions for immediate distribution of potassium iodide could be desirable.
Hospitals, jails, c'ontrol rocas, fire stations and police departr.ents are examples of such places. The staff is presently loei;ing into the possibility of requiring that reactor licensees stockpile quantities of potassiura iodide for situations in which ;cople vould be unavoidably exposed to doses to the thyroid in cxcess of 10 rem, and institutional control 'could be r:aintained for long periods of tire.
The I:P.C staf f has been predisposed to require stockpiling of KI.
On page 1.101-2 of Annex A to Pegulatory Guide 1.101 - Ecercency Planning for f uclear Pcuer Plants, a copy of wi!ich is attached, you will (ind
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-~staterants:
}'easures that should be considered for persons th within the exclusion area include:.. 3.
Use of radioprotective drugs, e.g. individual thyroid protection".
The footnote states:
"Th9 U.S.
Food and Drug f.dciinistration is presently developing guidance for the use of radicirctective drugs".
l:cu that FDA has spoken, the IRC staff will be i:ceting mth FDA in the rear future to expedite consideratien of the r:atter.
Detailed responses to the specific quastions are contained in the enclostare.
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Harold R. Denton, Director Office of t,'uclear Peactor P.egulation
Enclosure:
Respo.ase~ te Ccc :iuioner I.hearne's Questions Concerning T!y: oid Olocking Agents cc:
Chairman !'..'rie Ccrrissioner ^.ilinsky Cc::r.issinnar :cadford SECY 90009263
Encl-o1 T:ESPONSE Y0 CC5"ilSSIONER I.'iE/CE'S QUESTIC"S D
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O CONCERiuMG TiiyROID BLCCKING AGENTS J
g Question 1 Is there other information on the side effects of thyroid biccking with potassium iodide?
Response
The National Council on Radiation Protection and l'easurement's (NCRP) Report No. 55, " Protection of the Thyroid Gland in the E'.ent of Releases of Radiciodine", is the most authorita-tive report on this subject.
We are not aware of any more recent publications that would change the major reccamenda'. ions in NCRP "o.
55.
Sone side effects have been observed in the clinical use of potassium icdide (KI).
These side effects have ranged from blood abnormalities to severe reactions, including death.
MCRP has estinatej that the risk of an asiverse effect uculd be between 10-g' and 10- per clinical dose (300 mg).
Risks for individuals tathg other drugs at the sane time wculd be higher.
The dose recuired to block the thyroid (130 mg for en edult) is the sane order of ma;nitude as the clinical dose.*
One of the linitations of KI is that it is only effective if administered within about two hours after intake (see Enclosure 1).
Consecuently, it would be necessary to either distribute the drug vary c.uickly or to administer the drug prior to the release of radio 2ctivity.
Since the effectiveness of KI decreases with time, it would be necessary to administer daily doses throuchout the ccurse of the accident.
Although the frquency of adverse effects per unit dose is not very large, scc e effects would be predicted in a large population over the cc;rse of an accident.
Assunic.g the midpoint of the risk estinate given by NCRP No. 55 (i.e., 5 X 10-7 effects / administered dose), if the drug were administered to one nillion persons cver a ten day period, then five advarse ef fects would be expected.
Based cn very iThe cne rercrted death was associated with a dose of 15 ng of KI.
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death fecm 10{cne death out of 16S reactions), " tid visk of one limited data doses would be about 1 cut of 30.
Risks from the drug should be balanced by a reduction in radia-tion dose to the thyroid.
The tiCRP has given some guidance in this area:
"If the estimate of thyroid total absorbed dose is less than 10 rad, it may be preferable to consider instructing people to remain indcors and to await further instructions, before deciding to administer biccking agents.
If the esti-nates of the total thyroid absorbed dose exceed 10 rad, blocking agents should be considered."
The " Final Generic Environmental Statement on the Use of Recycle Plutonium in Mixed Oxide Fuel in Light Water Cooled Reactors" (i:UREG-0CO2) contains estimates of nortality and cancer induction frcm thyrcid irradiation.
The risk of prenature death 'due to thyroid cac.cer is estinated to be Ocut 1.3 prcmature deaths per million thyroid-rca frcm internally deposited radioactive iodine.
The risk of thyroid cancer and benign nodules formation is about 25 tines greater than the risk of de'ath.
For.a dose of 10 rem to the thyroid ( :CRP's guideline dose), the risk of adverse reactions frca M:e drug (5 X 10-6 for 10 doses) would be about tuo order. of magni..de beicu the risk of thyroid cancers and benign nodules formation fecm irradiation of the thyroid (3.3 X 10-4).
For a dose of 10 rem to the thyroid, the risk of death from the drug (3 X 10-8 for 10 doses) would be about three orders of magnitude belcw the risk of death from the thyroid cancers (1.3 X 10 s).
Eased on these considerations alone, the drug could be given at an even icuer dose than reccmmended in f;CP.P llo. 55.
In cddition to the side effects from the drug, there is also the possibility of injuries resulting from a mass panic to 92t the drug.
The f?CRP cautions that:
"The short-and long-term consequences of inhalation of redicact.ive icdine are far less than the possible injury that might resul.
from individual or mass pnic arising frca efforts to obtain the blocking agent, ar.d this nodicum of ccmran sense should be remembered by each person."
It appears that the I;CRP guideline of 10 rem to the thyrcid has some built in conservatism to take into account the possibility of a mass panic.
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k jj Question 2 Should such blocking be advised as a part of',eme'rgency response?
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Response
Thyroid blocking agents, such as potassium iodide (KI), are of some use in an emergency response program.
However, other elements of response program would probably be more effective an emergency'g the general public in nost accidents.
in protectin These elements include shelter, respiratory protection and evacuation.
For low doses of radiation (less than 1 rce to the thyroid), the preferred response would be shelter and respiratory protection.
Whereas KI uculd protect only the thyroid, shelter and respiratory protection would protect the total body as well as the thyroid.
Shelter would reduce the whole body gamma cloud dose by a factor ranging from 10% to 305, depending on the building (see Enclosure 2).
Fcr puff releases (less than two hours of exposure), shelter would reduce the inhalation dose by a factor ranging frcm 15% to 655, depanding on the building ventilation rate (see Enclosure 3).
Respiratory protection can be provided by ccm on household itens (see Enclosure 4).
Several of these items could reduce the inhalation dose by about 90%.
In most cases, a ccmbination of shelter and respirctory protection would offer nore protection than KI, without any of the potential side effects of KI.
i For higher doses of radiation (greater than 1 rem to the thyroid),
it may be better to evacuate the population than to distribute the KI.
There has been nuch experience with nass evacuations.
The Environmental Protection Agency (EPA) has surnarized evacuation ex;erience over the time period 1959 to 1973.* This study has shown that masses of up to 150,000 persons have been evecuated safely in disasters.
Distribution of KI during an evacuatien cculd hampar the evacuatica.
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Thyroid blocking agents would be useful for c..ployses and support personnel working r. ear the facility.
Thyroid bl::':ing agents might be given to persons who could not be evacuated easily (e.g.,
hospital patients or convicts).
Estinates have been made of the thyroid dose to the naximum off-site individual associated with the Three liile Island (EI) accident.**
The thyroid ecses from the lliI accident (less th n 10 mrem) were cver three orders of magnitude belcw the NCP.P guidel:as of 10 rem.
T E W cui;n ifi sW-An Evaluation, EPA-520/6-74-02.
- " Population Case and I:calth lopect of the Accide:,t at the Three Mile Island "aclear Station", NUREG-0558, "ay 19/9.
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4 Question 3~
should stockpiles of KI be maintained?
I P sponse 3
As stated in our response to quastions one ar:d two, potassium iodide (KI) may have a limited application in a protective action program.
Small quantities of the drug dould be stockpiled for use by empicyees and support personnel near the accident, as well as institutionalized persons who could not be easily evacuated.
However, there would be little use of this drug by the general public.
Other protective actions may of fer greater reductions in risk frc.a rrdiation without t,he side effects of KI.
L'hile the cost for producing the KI would not be excessive (Dr. von Hippel quotes a figure of one million dollars), the cost for naintaining a large scale distribution system over a ten or twenty
' year period would be greater.
Dua to its shelf life, it uauld be necessary to check the potency of the KI periodically.
There is little incentive to produce, on a large scale, a drug that may not ba used by the general public in an er.ergency.
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5 Question 4 f.ny ccmments on Professor von Hippel's r:aterial?
Response
Dr. von liippel's paper, " Thyroid Protection for People Counwind",
overemphasizes, in our opinion, the effectiveness of thyroid blocking agents.
As stated in our response to questions one and two, it is important to recognize some of the limitations of thyroid blocking agents.
First, thyroid blocking agents protect only the thyroid.
Other protective actions such as shelter and evacuation protect nany organs in addition to the thyroid.
Secondly, there are logistic
.a problems with storing and distributing potassium iodide.
- I iodide has a finite shelf-life.
Consequently, it would be necessary to check the potency of the tablets periodically.
There are many problems with distributing anything during an cmergency.
Distributing potassium iodide during an energency might interfer with some of the care effective protective actions such as shelter or evacuation.
Although NCRP discusses the limitations of thyroid biccking agents, Dr. vcn liippel's article does not discuss these limitations.
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'T/3LE VI 11-7 F?NJ.SE:; TAT 1'.'; S:!I E LDI::G PAC f0P.S F F.OM CidO'A CLGUD SCUF.CE
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>od frwa house with brick or stene vencer is approxi..ately epi.alent to a raconry house for shielding pur;oses.
(c) nic rar.ge c rainly due to dif ferent all r.iterials an.2 different gee.ctries.
(d) Tna relaction fa: tor deren:In on where the personnel ' ate located within the buildi.g (e.g., the 1.a ser 2nt or an incide roon).
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FIGUR!! VI 11 4 F.atio of the inhaled dose laside a shelter to that outside the shelter as a function of ventilation rate n (a'ir turnovars per hour).*
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It e m nesses mm cf H O vallens Lower Upper 2
- D.r.dk e r c hie f, man's cctica 16 36 32 94.2 92.5 95.5 Toilc! paper 3
'13 32 91.4 39.8 92.9 Iian d'-: e r c hi ef, man's c ct'.ca 8
.18 32 S3.9 35.5 91.6 liandk er c hief,
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man's cotton Crumpted 32 E8.1 25.1 90.5 Bat:1 towel, turkish 2
11 32 G 5.1 E3.3 55.3 Dath towel, turkish 1
5 30 73.9 70.7 70.3 Ced sheet, r.:es!!n 1
22 32 72.0 63.5 74.9 D ath to w.'t, turkish 1 (wet) 3 31 10.2 E 3.0 72.3 Shirt, ccaton 1 (we t)
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E 3.3 69.6 Un r.dk e r c hi ef, woman's cction 4 (wet) 34 32 63.C
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man's cction 1 (wet) 95 30 62.6 57.0 67.5 3
Dress mat erial, cotten 1 (wet) 1303 31 56.3 49.5 62.0 t
l'ar s c r c hi e f, we han'.s cottca 4
2 32 55.5 52.2 53.7 S:!;, rayon 1-0 32 50.0 46.2 53.6 Dres material, cettca 1
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