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Re:TMI releases
This is from a table that was put together for potential use in nuclear
power plant field team training during an emergency/release. It has long
been recognized that nuclear power plant drill scenarios often have to be
driven to what is commonly called the "blowing chunks" level to drive
emergency PAGs. It was thought that a review of what response and dose
assessment teams at TMI saw would be of some use (and yes it is recognized
that some of the dose assessment data would not have been immediately
known, but came from after the fact assessments, and that there have been
subsequent dose assessments done after the cited reports were published).
This of course is part of the movement to bring back a little realism to
drill scenarios.
Table VII. Keeping a Perspective: Summary of significant survey and dose
assessment data on and off site during the accident at Three Mile Island
for the period 28-Mar-79 to 4-16-79.
Description (a) and parameters
Highest ground reading onsite 3-28 2300
NW fence: 365 mR/h beta+gamma, 50 mR/h gamma
On 3-29 at 0500
WNW fence: 150 mR/h beta+gamma, 100 mR/h gamma
Highest reading during accident, helicopter 3-29 1410
15 ft over Unit 2 stack: 3000 mR/h beta+gamma, 400 mR/h gamma
Highest ground reading offsite, 3-29 0600
1 to 2 mile W: 30 mR/h beta+gamma, 20 mR/h gamma
3-28 DOE helicopter could detect plume out to 16 mi
0.1 to 0.2 mR/h
Highest offsite I-131 airborne concentration observed for period 3-28 to
4-12
32 picoCi/m^3 (3.2 × 10^-11 microCi/cm^3)
On 4-16, the highest immediate downwind I-131 concentrations were observed
during charcoal filter bank change-out operations
110 to 120 pCi/m^3 (max 1.2 × 10^-10 microCi/cm^3)
Occupational Doses
3 workers in excess of then 3 rem per quarter NRC limit (3.9 to 4.2 rem),
max 50 rem to skin and 150 rem to extremity
Max population dose estimate
3500 person-rem
Maximum estimated individual offsite whole body external dose
83 mrem
Maximum estimated internal doses to thyroid
Onsite: 53 mrem, adult
Offsite: 6.9 rem, newborn
Notes (b)
General emergency declared 3-28-79 at 0724. Initial dose projections 10
rem/h (Noble gas)to nearest community 1.4 miles away (5 rem evacuation
PAG), but field team measurements reported < 1 mR/h onsite at 0745 and at
nearest community at 0832. Offsite field team in nearest community did
report < 1 mR/h and I-131 near detection limits at 0900 and 3 mR/h at 1030.
Note that few dose rate measurements distinguished between open window
(beta+gamma) and closed window (gamma) instrument readings, or identified
the instruments used by the teams.
Initial air sample results using the Eberline SAM-2/RO-19 system (Dual
channel analyzer with NaI(Tl) scintillation detector, MDA ~5 x 10^-9
microCi/cm^3) indicated maximum onsite and offsite I-131 airborne
concentrations of 6.8 × 10^-7 microCi/cm^3 and 9.5 × 10^-7 microCi/cm^3,
respectively. Note that the present day 10CFR20 DAC for I-131 is 2.0 ×
10^-8 microCi/cm^3 (Table 2 value 2.0 × 10^-10 microCi/cm^3). Analysis by
GeLi reported I-131 less than MDA, but noble gases were identified.
Counting system could not detect I-131 in the presence of noble gases.
Initial dose projections grossly overestimated the actual dose rates
observed. The release was primarily noble gas with no significant levels of
radioiodine found offsite. No particulates were released.
Radionuclides released to the environment (From Table II-1):
Kr-88 (T_1/2 = 2.8 h) 3.75 × 10^5 Ci (15 % total), Xe-133 (T_1/2 = 5.2 d)
1.58 × 10^6 Ci (63 % total), Xe-133m (T_1/2 = 2.2 d) 2.25 × 10^5 Ci (9 %
total), Xe-135 (T_1/2 = 9.1 h) 3.0 × 105 Ci (12 % total), Xe-135m (T_1/2 =
15.3 min) 2.5 × 10^4 Ci (1 % total), I-131 (T_1/2 = 8.0 d) 1.5 × 10^1 Ci
(0.0006 % total)
(a) NUREG/CR-1250 1-80, Three Mile Island-A Report to the Commissioners and
to the Public, Vol. II, Part 2, Rogovin and Frampton U.S. NRC. Summary
descriptions found from page 384 to 400.
(b) NUREG /CR-1250 Vol. II, Part 3, p.344, 867 to 874 and 1037.
DJWhitfill
Opinions expressed are mine and do not reflect official policies or
positions of the Kansas Department of Health and Environment.
Jacques.Read@eh.do
e.gov To: Multiple recipients of list
Sent by: <radsafe@romulus.ehs.uiuc.edu>
radsafe@romulus.eh cc:
s.uiuc.edu Subject: Re:TMI releases
02/12/01 07:58 AM
Please respond to
radsafe
There is actually no direct evidence that any radioiodine escaped from the
TMI
containment. (One grass sample from a rural roadside had a few counts, but
may
have been spurious, or the result of a medical testee's al fresco urination
while driving home from the hospital, since there was nothing else anywhere
near.) Any that did escape would have evolved from solutions in the
auxilliary
building as methyl iodide. To attempt to estimate the iodine off-site from
a
xenon measurement is less than hopeless ...... if you get the raw data and
back-calculate it becomes apparent that the xenon off-site did not leak
from the
containment, but rather is the daughter activity of iodate dissolved in
the
sump solutions in the aux. building. Much later, when the containment was
vented, krypton-85 was deliberately released, but by then all the xenon
isotopes
were history.
There are several other very interesting radiochemical scenarios at TMI --
you
can, for example easily convince yourself by back-calculations that the lye
injections led to hydroxide precipation in the sump with the hydroxide
being
tritiated to the isotope ratio of the coolant during the melt-down. In the
weeks following the accident, the sump samples slowly increase in tritium
as the
the hydroxide re-equilibrates with the additional collant injections and
let-downs. There's also evidence in the time-histories of the iodine
isotope
ratios that at early times a lot of the iodine was AgI precipitated by the
silver dissolved from the control rods.
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