U.S. Reactor Containment Technology: a Compilation of Current Practice in Analysis, Design, Construction, Test, and Operation, Volume 1 Page: 1-09
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techniques for approval. The fundamental assumptions on which the cal-
culations were based are quoted, along with some estimation of the degree
of conservatism represented.
The report4 states that:
"1. Experts agree and experience to date, though limited,
confirms that there is only an exceedingly small probability of
a serious accident in reactors approved or likely to be approved
for construction.12 The probability is still lower for an ac-
cident in which significant amounts of fission products are re-
leased into the confined primary coolant system and a great deal
lower for accidents which would release significant quantities
of radioactivity from the primary system into the reactor build-
"2. It is assumed that the reactor is a pressurized water
type for which the maximum credible accident will release into
the reactor building 100 percent of the noble gases, 50 percent
of the halogens and 1 percent of the solids in the fission prod-
uct inventory. Such a release represents approximately 15 per-
cent of the gross fission product activity.
"3. Fifty percent of the iodines in the containment ves-
sel is assumed to remain available for release to the atmo-
sphere. The remaining fifty percent of the iodines is assumed
to absorb onto internal surfaces of the reactor building or
adhere to internal components. Rather than the assumed reduc-
tion factor of two, it is estimated that removal of airborne
iodines by various physical phenomena such as adsorption, ad-
herence and settling could give an effect of 3-10 reduction
in the final result. Credit has not been taken for the effects
of washdown or filtering from protective safeguards such as
cooling sprays and internal air recirculating systems. Wash-
down features and filtering networks could provide additional
reduction factors of 10-1000.
"4. The release of available (airborne) radioactivity
from the reactor building to the environment is assumed to
occur at a constant leakage rate of 0.1 percent per day. The
leakage and pressure conditions are assumed to persist through-
out the effective course of the accident, which for practical
purposes, would be until the iodine activity becomes insignifi-
cant. The maximum pressure within the reactor building and the
leakage rate would actually decrease with time as the steam
condenses from contact with cooling surfaces. By assuming no
change in leak rate as a function of pressure drop, it is esti-
mated that the final off-site doses calculated may be too high
by factors of 5-10.
"5. Atmospheric dispersion of material from the reactor
building is assumed to occur according to the well-known rela-
tionship developed by O. G. Sutton13 involving meteorological
factors of wind velocity, atmospheric stability, and diffusion
parameters. Application of this treatment to reactor hazards
analysis was discussed in WASH-740 (ref. 12) and AECU-3066
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Cottrell, William B. & Savolainen, A. W. U.S. Reactor Containment Technology: a Compilation of Current Practice in Analysis, Design, Construction, Test, and Operation, Volume 1, report, August 1965; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc101033/m1/37/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.