ML19350B752
| ML19350B752 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 01/20/1980 |
| From: | Beyea J, Von Hippel F PRINCETON UNIV., PRINCETON, NJ |
| To: | |
| Shared Package | |
| ML19350B747 | List: |
| References | |
| PU-CEES-REPT-94, NUDOCS 8103230628 | |
| Download: ML19350B752 (11) | |
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um1TED CORRESPOWN
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t Nuclear Reactor Accidents: 1- -
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- The Value of Improved Containment 97 MAR 171981 > d.2 Oike of the
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,- E.ag j Jan Beyes and Frank von Hippel 4 Ca
( PU/ CEES Report #94 -
I January 20, 1980 i Center for Energy and Environmental Studies l Princeton University
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g Princeton, NJ, 08544 I
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- Address af ter IL2y 1930: Environmental Policy Division l National Audubon Society 950 Third Avenue New York, N.Y. 10022 i
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Table of Contents t..
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Abstract i .
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i Foreword !
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The Need for Improved Reactor Containment Systems - Overv ew d Given II. Calculations of Land Area Over Which Radiation Doses ExceeRelease of R Thresholds Following an Airborne Derivation of Upper Bound Land Contamination Areas I Appendix A: Using the Wedge Model.
g Derivation of Upper Bound Areas for Inhalation Deses Appendix B: Using the Wedge Model.
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!n i Sensitivity of Gaussian Plume Model i Results ion Parameter.to Uncerta n-Appendix C: ties in the Transverse Atmospheric D spers d
s Appendix D: Numerical Land Contamination Values and for Thyroid Areas Dose in Which Radiation Do Thresholds.
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Uncertainties in Thyroid Dose Calculations.
Appendix E:
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E The radioactive gases released from an;uncontained reactor core melt-l down accident could cause thyroid damage and serious contamination of land Reactor contain-by radioactivity over an area on the order of 10,000 km .
orevent such releases. However, ment buildings are not now designed to reliab))
significant improvements in existing containment buildings are possible at reasonable cost.
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The major results of this '
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,. ,1 % cluding calculations of areas
,< jj thresholds. section - in-4
- j Section II presents .
a our det ilover which oses exceed given ,c
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$ modeling the dispersion of r d
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$) tions and a discussion of some Technical details of these
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calcula-made in the thyroid dose a c l uncertainties in the physiol
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I-l Historically, effort in the area of nuclear reactor safety was focussed
! s almost completely on preventing the reactor
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g fuel from overheating. Relatively
' little attention was devoted to studying the possibilities of nuclear core melt-down accident containnent and mitigation because it was assumed that the proba-
, bility of such accidents had been reduced to negligible levels. At Three Mile Island reactor fuel did overheat and perhaps ev'en partially melt. This confirmed.
judgements concerning the difficulty of establishing for current nuclear power I plants upper bounds on the probabilities of core melting accidents. As a result there has been renewed interest in contingency planning with the objective of re-ducing the consequences downwind in case' a major release of radioactivity to the atmosphere should occur. There is still relatively little oublic discussion, how-ever, of the potential for improving the ability of reactor containment buildings to prevent the release to the atmosphere of this radioactivity.
l Currently, reactor containment buildings could be relatively ineffectual in preventing the release to the atmospherc of the radioactive gases and aerosols which would be boiled off from a reactor core during a melt-dows accident. The 1 !,
, 1! containments surrounding almost all the boiling water reactors which are in operation t
l today have such small volumes, for example, that they would probably.
be ruptured by the buildup of the hydrogen and carbon dioxide generated during
.i the course of such an accident. Release to the atmosphere of a sig,nificant frac-M tien of the enorrous core inventories of volatile fission products,- probably
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including more than 10 percent of the radiciodines and radiocesiums.- would fol-low. Larger volume containment buildings, such as those at Three Rile Island, have a lower, but still significant, probability of failing directly to the at-mosphere. (See Table I-1. )4,5 Civen a massive release of radioa.ctivity into the atmosphere, the probability of very large numbers of early fatalities resulting may still not be large., Early fatalities would be caused only by quite high radiation doses (greater than about
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Table I-1: Pressurization Contributions for'-Typical Reactor Containments Small Volume Steam Pressure Suppression Tyoe"
. s (designed to contain.4atm. overpressure )
H2 pressure from oxidation of 100 percent of zirconium in core 5-11at=.
! CO pressure from thermal decompoAition during melt-through of c l cyfinder of concre'te 6 meters in diameter and 2.5 m. thick 4-9atm.
l Large Volume Type (designed to contain 3atm. overpressure )
Initial pressurization by steam from p,rimary coolant 2.5atm.' .
Additional pressurization in subsequent three hours in absence g of containment cooling 3 atm.
- Actual f ailure' pressure could be considerably higher. Ref. 4 estimates the failure overpressure for a small volume containment at 9-12 arm. (n.
VIII-37) and for a large volume containment at 5-7 atm. (p. VIII-22).
Notes a) TypicalofcontainmengsusedinmostoperatingUSBoilingWaterReactors.
Free volume = 7 9 x 10'm (40% over the vapor suppression pool - ref. 4,
- p. VIII-8). The higher pressure values apply if the noncondensible gases are swept by steam into, and are trapped in, the free volume dver the vapor suppression pool as assumed in ref. 4.
b) 56,000 kg Zr (ref. 5,.p. E-7). At Three Mile Island approximately 50 percent of the zirconium was oxidized (ref. 1, p. 30).
c) Ref. 4 (p. VIII-30) assumes this quantity of concrete decomposes.
Ref. 5 (p. D-6) assumes four times as much. The concrete has a density of 2.4 and is approximately 25 percent CO2 be weight (in CACO 3, Ref. 5, p. D-2).
d) Typical of those used in most'US Pressurized Water Reactors. Free volume = 5.1 x 10'm3 (Ref. 4, p. VIII-4).
e). 0Initial mass of water in the primary coolant system = 1.9 x 105 kg at 1 300 C (ref. 4, p. VIII-4).
. f) Ref. 4, Fig. VIII 2-6. .
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I-3 150 rem whole body dose).
Atmospheric dispersion, the distances of nuclear power plants from densely populated areas, \ and evacuation would all tend to
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8 reduce the numbers of people uposed to such high doses.
of people could be af fected, however, by the longer term consequences (cancers, genetic def ects, thyroid damage, etc.) from radiation doses too low to lead to L
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early fatalities.
In this report we provide'a quantitative measure for the need for improved b
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reactor containment buildings by estimating the areas which would be seriously I !
is affected by two of'the long-term consequences of a massive release of radioactiv-f {
- 1) land and property contamination by long-lived
ity f rom a melt-down accident:
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radioactive cesium, and 11) thyroid damage resulting from exposure to airborne In most cases larger numbers of people would be affected h radioactive iodine.
i In any ' case, to the
'I . by these than any other consequences of such accidents.
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)- extrat that these consequences could be reduced by a reduction in the re eases ld
'of radioactive gases and aerosols in an accident, most other consequences wou
, be reduced as well. "
We measure the severity of the radioactive contamination from a reactor accident in terms of the area over which, in the absence of ef fective land and l
I property decontamination, any resident population would receive a cumulative body dose from external gamma irradiation greater than, or equal to 10 rem over This ten rem boundary dose would be
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the first 30 years following the accident.
d 3 approximately three times higher than the average dose from natural backgroun W
radiation over the same 30 years and might cause, among the exposed 7 population, 2),
- an increase in the death rate on the order of one-tenth of one percent.
The long-term gamma dose from the aerosols boiled of f from an uncontained y 8 30 year half 4 reactor core melt-down would be dominated by radioactive cesiums:
g 137 and 2 year half life Cs 13'. The core in a 3000 Megawatt (thermal) life Cs .
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nuclear power plant typically contains on the order of 10 Curies of each of l
these isotopes.' Taking into account thk estimsted average shielding effects of N
building walls and of the leaching of the cesiums into the grounli, a 30 year whole body dose of 10 rem from a deposition of Cs (and the associated Cs )
would resul't from an initial ccncentration of Cs on the ground of about 30JiC1/m2 ,10 In addition to land contzaination, thyroid damage downwind from a reactor accident is a major concern. Becadse a large fraction of the iodine absorbed by the body is concentrated in the thyroid, the doses to the thyroids of people exposed to the " radioactive aerosols fros an uncontained melt-down accident could be 2-3 orders of magnitudes higher than the inhalation and other short-term doses given to other parts of their bodies.
tie define the area downwind f rom a reactor accident within which there would be a significant risk of thyroid damage as the area in which the dose to the adult thyroid would be greater than 30 rem. (The dose to the thyroids of exposed l
children in the same area might exceed 150 rem.ll,12) The Environmental Protec-l tion Agency's guideline threshold dose for mandatory evacuation is 25 rem.
The thyroid dose for persons exposed to the radioactive cloud downwind from the accident would be dominated by inhalation of 8 day half-life I and 0.9 day half-life 1 1
. A nuclear pawer reactor core will typically contain on the order of 10 8 Curies of eacho'f these isotopes. An adult would receive a thyroid dose of 30 rem (and a four year old child might receive a thyroid dose of about 1
l 150 rem) from a time-integrated exposure to 1 of about 30 (p.C1/m )-hr.
l In Figure I-l we show " realistic" upper bound and " typical" areas over.which the long-term doses from ground contamination and the thyroid inhalation demee I
would exceed the limits specified above as a function of the percentage releases into the atmosphere of the corresponding reactor inventories. The upper bound curves e
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dl thyroid dose l
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The two sets .of curves indicate the areas:1) l i over which the a u twhole bod would exceed 30 rem and 2) over which the cumu The curves at veare functions of f,h .,
30 years from contaminated land could p eed 10 rem.d the radiocesium inventorie pf' the percentage releases of the radiciod;< > an ively of a 3000 Mw(th)~ reactor. The, solid lines represent the results of c tions of realistic upper bounds and the dashe ~
culations for " typical" atmospheric conditions.
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It will also be seen that, under " typical" atmospheric conditions and for rcen- large p l
J tage releases () I percent), the areas in which land contamination and thyroidoses d A
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9 times lower than the upper bound areas.15'1
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The lower limit 1:hl t
for the area which could be affected in these releases is essentially zero.
For example, a heavy rain could remove the radioactive aerosols from the air very quickly, restricting the radioactivity to a small area close to 7'
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It is apparent from the figure that
![ the areas at risk are potentially very l
large - on the order of 10,000 km
) when major fractions of these radioactive j, !@ inventories are released.
[' ! It is also apparent from the figure, however, that
! 5 the areas at risk would be decreased dramatically if the containment wereeffective 9
@k 3- enough to reduce any releases below, for example,1 percent of the core inventories.
} Design of a better containment requires knowledge of mechanis=s by which cur -
rent containments could fail. We therefore offer a brief listing here.16 s
} } Overpressurization:
i ! As has already been mentioned, a small volu=e containment t
i could fail in a core melt-down accident as a result of the buildup of large quan -
l tities of noncondensible gases.
Even a large volume containment could fail as a 4
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result of the buildup of steam pressure unless active containment atmosphere g;
$ cooling syste=s were effective in offsetting the continued heating effect of the g core's radioactivity and of possible hydrogen fires.
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g; Isolation Failure:
4 Containment buildings have many penetrations to allow for the J
passage of personnel, equipment, water, steam, and ventilation air [ In case of a 3 i loss of coolant accident, a
d all of these penetrations are supposed to be sealed,
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1 but " isolation failures" can and do occur.
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Steam Explosions:
Occasionally, when molten metal falls into water, the heat transfer becomes so rapid that a "staam explosion" occurs.
In a core melt-down accident enough energy would be available for a steam explosion to rupture g
the containment - through the conversion of a piece of the pressure vessel into o missile for example.
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' I- 8 External Impacts: A loss of coolant accident could be initiated simultaneously with a breach of the containment as a result of the impact of' a large enough l
energetic missile such as a piece of the' power plant's turbine rotor or a jet t
airplane.
f The most frequent proposal for improving the resistance of containments 1 This to most of these failure modes has been to place reactors underground.
vould make the containment less vulnerable to steam explosions and external im--
pacts and, in case of overpressuritation, the overburden, depending on its pro-(In Europe concern perties, =ight act as a filter for the released gases.
over protection in time of war has been an additional motivation to look at l
underground cont'ainment.)
I Although underground containments would not be an option for existing reactors, other potential significant improvements could be "back-fitted" into existing reactor containments. Thus, for example, the likelihood of centain=ent failure by overpressure could be drastically reduced by fitting containment
'10 If pressure inside the contain-buildings with filtered release systems.
ment reached dangerously high levels, or, if leakage were already occurring due
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to isolation failure, the pressurecould be reduced by venting some of the gases in the containment through a large filttation system which would cleanse them of most radioactivity other than that carried by radioactive noble gases.
l In conclusion, therefore, there would appear to be both compelling reasons and good opportunities to complement the enormous efforts which are currently being devoted to the prevention of core melt accidens with the installation of ,
improved containment. systems which would reduce the consequences to the public should such an event occur.
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