Potassium Iodide -Reply -Reply

["Sorensen, Scott" <ssorensen@doeal.gov>]

RadSafers,

I don't have a good reference handy, so I'm winging this guestimate...

NCRP Report 93 states that the average dose within a 10 mile (16 km)
radius of the Three Mile Island (TMI) plant was 8 mrem (80 uSv).  Making
the assumption that this dose resulted only from radioiodine intake (Wt
= 0.03 from ICRP 26), the average thyroid dose would be about 270 mrem
(2.7 mSv).  This value is clearly below the proposed 10 rad (100 mGy)
threshold (assuming that 1 rem = 1 rad).

The question remains, would potassium iodide (KI) be administered to the
populace during the TMI accident?  The dose threshold clearly has not
been exceeded, but this is after-the-fact knowledge.  Given the extent
of confusion during the initial hours of the TMI accident, I would think
that the emergency managers would have probably given a "go" to KI
administration.  Besides, my guess is that local populace would probably
take the KI anyway if it had been pre-issued (I certainly would have at
the time).

Extrapolating from the NCRP Report, I estimate the 10 mile radius
population to be about 90,000 people (which seems about right per my
memory).  This equates to a collective dose of 24,300 person thyroid-rem
(243 person thyroid-Sv). Using the factors provided by Mr. Rozental, I
get the following:

Excess tá.r¨idú¯ancer prevented:  1.8 cancers/event
Excess fatalities prevented:  0.18 LCF/evenÓ
Potential deaths from KI administration:  2.7e-4 deaths/event
Potential severe adverse side effects:  3.6e-2 severe effects/event
Potential mild adverse side effects:	54 mild effects/event

Even when assuming that the prophylactic KI program would prevent all
excess thyroid cancers, this scenario appears to have both minimal
protective benefit and minimal adverse effects.  The 54 mild adverse
side effects from KI may be inconsequential compared to other maladies
caused by the psychological stress of the accident (?) (i.e., there may
be some value realized by minimizing the general apprehension of the
local populace through KI administration).  

But at what cost?  I don't have a good feel for the cost for initiating
and managing a prophylactic KI program for 90,000 people over the life
of a nuclear power plant.  Anyone care to provide a guess?  Regardless,
I would expect that the local real estate values would decline once
potential residents understand that they would be issued an emergency KI
kit for their homes!  On the other hand, legal liability may prove to be
a "wildcard" which could make a KI program more cost effective (?).  My
over-all gut feeling is that the benefits would not out-weight the costs
for the TMI accident scenario.

I agree that emergency managers shouldn't only plan for a TMI-type
accident, given that Chernobyl did occur.  However, I submit that the
most likely reactor accidents in the future will be more on the level of
TMI, given that most western reactors are within containment, well
regulated (maybe too well), and that (hopefully) we learn from past
mistakes.  

That's my very rough-cut estimate on the efficacy of the proposed NRC
guidelines.  I welcome all thoughts/corrections concerning this estimate
and/or the assumptions...  My thanks to J. Rozental for his input!

-Scott Sorensen
ssorensen@doeal.gov