ML12334A807

Official Exhibit - NYS000283-00-BD01 - the Hazard from Plutonium Dispersal by Nuclear-Warhead Accidents, Science and Global Security, Vol. 2, Pp. 22-41, S. Fetter and F. Von Hippel (1990) (Fetter Paper)

ML12334A807
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Site:	Indian Point
Issue date:	12/21/2011
From:	Fetter S, Vonhippel F Center for Energy & Environmental Research, Princeton Univ, Univ of Maryland - College Park
To:	Atomic Safety and Licensing Board Panel
SECY RAS
References
RAS 21598, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01
Download: ML12334A807 (21)

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United States Nuclear Regulatory Commission Official Hearing Exhibit Entergy Nuclear Operations, Inc.

In the Matter of:

(Indian Point Nuclear Generating Units 2 and 3)

ASLBP #: 07-858-03-LR-BD01 Docket #: 05000247 l 05000286 NYS000283 Exhibit #: NYS000283-00-BD01 Admitted: 10/15/2012 Identified: 10/15/2012 Withdrawn:

Submitted: December 21, 2011 Rejected: Stricken:

Other:

Science & Global Security,l990, Volume 2, pp.21--41 Photocopying permitted by license only Reprints available directly from the publisher

© 1990 Gordon and Breach Science Publishers SA Printed in the United States of America The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents Steve Fettef and Frank von Hippelb NUCLEAR WEAPONS are carefully designed. to have an extremely low probability of exploding accidently with an appreciable nuclear yield--even if they are involved. in a high-speed crash, struck by a bullet or consumed in a fire. 1 The principal concern when nuclear warheads are involved in such accidents is the possible dispersal of plutonium into the environment. In particular, an explosion could disperse a significant fraction of the plutonium in a warhead as particles of respirable size. 2 There are two incidents of which we are aware in which the chemical high explosive (HE) in US nuclear warheads exploded and contaminated an area with plutonium:3

• In January 1966, over Palomares, Spain, a mid-air collision between a B-52 and its refueling aircraft resulted in the four bombs from the B-52 being released. The braking parachutes of two bombs failed completely, and they struck the ground at high speed. The HE exploded, and plutoni-um was widely dispersed. Cleanup and reparation cost $100 million.

• In January 1968, near Thule, Greenland, a fire broke out on a B-52. The bomber was abandoned and crashed. into the ice at high speed. and burned; the HE in the four bombs it carried. exploded., spreading plutonium widely over the ice.*

a. School of Public Affairs. University of Maryland, College Park MD 20742 b . Center for Energy and Environmental Studies. Princeton University, Princeton NJ 08544

22 Fetter and Von Hippe/

Almost immediately after the Thule accident, the US Air Force stopped routinely flying its bombers with nuclear weapons. In addition, most US nuclear warheads designed during the past decade use "insensitive high explosive" (IHE), which is unlikely to be detonated by even high-speed impacts.

However, many of the older warheads still in the US nuclear arsenal and, for various reasons, a few of the newer ones-most notably the W88 warhead for the Trident II-still contain ordinary HE. Recently, the US weapon laboratories have chosen to raise the safety problems of these warheads as an issue. 5 The purpose of this article is to offer some perspective on this concern.

Consider a hypothetical worst-case accident in which the HE in several nuclear warheads explodes. Based on experiments and calculations, it has been estimated that 10-100 percent of the plutonium contained in the warheads, with a best estimate of 20 percent, would be converted by such explosions into a PU02 aerosol of respirable size (median aerodynamic diame-ter in the range of 5 microns or less).6Ifwe assume an accident involving all of the warheads on a missile carrying 10 warheads, and that each of the warheads contains approximately 3 kilograms of plutonium, then the resulting aerosol would contain on the order of 10 kilograms of PU02 *7 HEALTH RISKS FROM PLUTONIUM AEROSOLS The principal risk from exposure to a plutonium aerosol is via inhalation:

most of the radiation emitted by plutonium is in the form of alpha particles, which have such short range (about 50 microns in tissue) that they cannot even penetrate the skin. External radiation from the passing cloud and from plutonium deposited on the ground can therefore be neglected. s For an aerosol of I-micron median aerodynamic diameter, about 15 percent of the inhaled PU0 2 would be retained in the deep lung with a retention halfiife of about 1.4 years.9 Health effects from radiation exposure can be divided into two categories:

illnesses and deaths due to high doses, occurring within a year or so after exposure, and cancers due to low doses, occurring during the remainder of the lives of the exposed population, starting a few years after exposure. As shown

The Hazard from Plutonium Dispersal by Nuclear-warhead Acc/dents 23 in the appendix, high-dose effects are unlikely even in a worst-case plutonium-dispersal accident-especially beyond the boundary of a military base. We therefore focus here on the cancer risk.

The principal hazard from exposure to lower concentrations of Pu0 2 aerosols is an increased probability of cancer of the lung and of other organs to which the plutonium is transported, particularly the bone. A recent review of the risks associated with low radiation doses from inhaled alpha emitters obtained a (very rough) risk estimate of one cancer death per 1,400 lung-rad or 900 to 12,000 bone-rad for inhaled Pu02.10 The 30-year dose conversion factors in the literature for lung and bone-surface doses range respectively from 1,600-3,700 and 3,200-11,000 rads per inhaled milligram of 239J>u02 aerosol with a median aerodynamic diameter of 1 micron. ll We use the values 3,200 and 6,500 rads per milligram here. 12 After correcting for the 6-percent plutonium-240 in weapon-grade plutonium (WgPu),t3 the lung and bone dose conversion factors are 3,800 and 7,600 rads per inhaled milligram respectively. The total (lung plus bone) cancer risk is therefore 3 to 11 cancer deaths per milligram of WgPu aerosol inhaled.

For comparison, the method for estimating cancer risk advocated by the International Commission on Radiological Protection (lCRP) is to use an "effective dose equivalent" (EDE), which is the weighted average of the dose to certain organs, with the weight assigned to each organ determined by the relative probability that a fatal cancer will occur in that organ after a uniform whole-body dose. The EDE for 239pu02 aerosol is 15,000 rems per milligram inhaled, or 18,000 rems per milligram for WgPu. Dividing by the ICRP risk factor of 2,000 rems per cancer death14 would give 9 cancers per milligram of WgPu inhaled.

In the appendix on high-dose effects, it is estimated from experimental data on beagle dogs that the risk of death from pulmonary neoplasia (a cancer) would be approximately 100 percent for the inhalation by a human adult of more than 0.08 milligrams ofWgPu, if early death did not occur first as a result of some other cause. If this risk were extrapolated linearly to lower exposures, it would correspond to 12 cancer deaths per milligram of WgPu inhaled.

Thus, these three different approaches to the problem of estimating cancer risk from the inhalation of PU02 give risk factors in the range of 3 to 12

24 Fetter and Von Hippe/

cancer deaths per milligram of WgPu inhaled We make the usual approximation that the risk is linear with dose. 15 As a result, independently of whether a total of 1 milligram of PU02 were inhaled by 100 people (an average of 0.01 milligrams per person) or by 1,000 people (0.001 milligrams per person) there would be an expected 3-12 cancer deaths as a result.

Dispersal of the Aerosol For estimating the amount of plutonium aerosol inhaled by the population downwind of a release, one can use a Gaussian plume model (see the appen-dix) and explore the dependence of its predictions for different assumed meteorological conditions and population distributions. However, in situations like the present one in which the cancer risk is linearly proportional to exposure with no threshold, a much better "feel" for the estimates can be obtained by using an extremely simple atmospheric dispersion model, the "wedge model. ,,16 The simplicity of the results obtained with this model stem from the fact that, as noted above, for a cancer risk that is linearly proportion-al to the exposure, the total number of cancers in the population downwind will depend only on the total amount of the carcinogen inhaled by the popula-tion, not on the distribution of the doses within the population. The accuracy of the predictions of the wedge model in such applications is generally comparable to that of the Gaussian plume model because most of the cancers will ordinarily be due to very small doses at great distances from the release point where a Gaussian plume assumes a shape approximated by the wedge model.

In the wedge model, the concentration of a contaminant is assumed to be constant in the crosswind direction over the wedge opening angle e (typically ranging from 0.05-0.3 radians downwindl7 ) and in the vertical direction throughout the height H of the mixing layer (typically 300-2,500 metersI8 ).

Under these conditions, the amount of plutonium inhaled I (in milligrams) by a person a distance r (in meters) downwind is

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 25 I(r) = Q(r)b (1)

BrHu where Q(r) is the total amount of plutonium (milligrams) that remains in the air at distance r downwind, b is the assumed breathing rate (3.3.10 4 m 3 S-1 for an adult male performing light activity),19 and u is the wind speed (typi-cally between 0.25 and 7 meters per second20 ) :

In the absence of rain, the total quantity of airborne material declines with r because of deposition as (2)

The average distance an aerosol particle is carried before deposition is L = uH (3) u where u is the deposition velocity. For most aerosols, the observed deposition velocities range from 0.001 to 0.1 meters per second. 21 The recommended values for plutonium aerosols from non-nuclear explosions of nuclear war-heads is 0.01 meters per second.22 We will assume a range of 0.003 to 0.03 meters per second. L in the absence of rain can therefore range from tens to thousands of kilometers.

In the presence of rain, there would be an additional exponential term associated with a characteristic washout time constant 't' ranging from 103 seconds (unstable atmospheric conditions) to 104 seconds (stable conditions).23 The corresponding wet-deposition velocity

• It should be noted that, in principle, it would be possible to reduce considerably the amount of plutonium inhaled if the population stayed inside with windows and air intakes closed during the passage of the aerosol cloud and opened up and aired out the buildings immediately after it had passed. See, for example, Bernard Cohen, Health Physics, 32, 1977, pp.359-379.

26 Fetter and Von Hippe/

(4) is generally much larger than Vd with a range of 0.05-1 meters per second.

Under rainy conditions, the deposition velocities would be added (v = Vd + v w )'

According to the wedge model, the amount of PU02 inhaled by the total population downwind would be (5) where p(r) is the population density at a distance r downwind averaged over the width of the wedge.

If we assume that the population density is constant, equal to Po, then we find that the total amount of plutonium inhaled is (6)

The average population density of the 48 contiguous US states is about 30 Table 1: The number of cancer fatalities caused by inhalation during the passage of a plume initially containing 10 kilograms of Pu02 aerosol for various deposition velocities and average population densities, for a risk factor of 3-12 cancers deaths per milligram of WgPu inhaled Deposition Population density Po velocity km-2 meters per second 30 300 3,000 0.003 100-400 1,000-4,(0) 0.01 30-120 300-1,200 0.03 10-40 100-400 1,000-4,000 0.1 rain 3--12 30-120 300-1,200

1. rain 0-1 3--12 30-120 1

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 27 per square kilometer; in the most densely populated states of the northeast it ranges around 300 per square kilometer, and 3,000 per square kilometer is a mid-range density for urban areas. For a risk factor of 3-12 cancer deaths per milligram of WgPu inhaled, table 1 shows our resulting estimates of the number of deaths for various combinations of population density and deposi-tion velocity.

It will be noted that in table 1 the entries associated with very low deposition velocity are not filled in for the highest population density. The reasons are that, for v = 0.003 or 0.01 meters per second, L would most likely be hundreds of kilometers-much larger than any urban area.

We have checked the predictions of the wedge model against the corre-sponding predictions of the Gaussian plume model and obtained quite close agreement, independent of weather conditions.

Although the largest entry in table I-four thousand cancer deaths-is high, the increase in the cancer risk for an individual in the exposed popula-tion would be small-typically on the order of one tenth of a percent. For example, for average conditions (H = 1,000 meters, e = 0.2 radians, u = 2 meters per second and v = 0.01 meters per second) the additional individual risk of cancer death would be 0.2-0.9 percent at a distance of 10 kilometers and 0.02-0.06 percent at a distance of 100 kilometers from the release. The small individual risk reflects the fact that the population risk would typically be spread among a very large population. For comparison, the individual cancer death risk in the US is at present about 20 percent. There may well already be many such large-scale cancer "events" occurring in the US due to the widespread release to the environment of carcinogenic chemicals that remain undetected against this large background. *,24

• We note in this connection that approximately 3,000 kilograms ofPu02 was dispersed into the global atmosphere by atmospheric testing during the late 1950s and early 19608, about 80 percent of it in the northern hemisphere. The resulting average inhalation by humans in the northern hemisphere was 0.13 nanograms. Using the above total cancer risk coefficients, this translates into an incremental cancer risk of 0.4-1.6 cancers per million persons in the northern hemisphere. Assuming that an average population of 3 billion in the northern hemisphere was exposed to the plutonium fallout (corresponding to an average population density of about 10 per square kilometer) about 1,000-5,000 people have died or will die from cancer due to plutonium inhalation, or roughly one person per kilogram of plutonium released.

28 Fetter and Von Hippel Table 2: The radial population density in the direction of Seattle from Bangor Naval Base Distance from Bangor 1'<"

Zone kilometers km-2 Kitsap County 0-18 130 Puget Sound 18-28 o Seattle 28-38 2.300 Lake Washington 38-41 o Bellevue 41-50 1.200 East suburbs 50-70 1.2OOexp(-0.24(r - 50>>)

Mountains 7(}-OO 10 As an illustrative example, we have estimated the consequences if a hypothetical10-kilogram release of WgPu aerosol should occur at Bangor Naval Base in Washington state, one of the two bases for US Trident subma-rines, with the wind blowing towards Seattle. AS Bangor is located just 30 kilometers from downtown Seattle, this may represent a near worst case for such an accident. Table 2 gives the radial population density in the direction of Seattle and beyond as a function of distance from Bangor and table 3 gives the wedge-model estimates for the cancer deaths that would result from the release if the wind were blowing in this direction for different combinations of deposition velocity, wind speed and mixing layer height. The average wind speed in Seattle is 4 meters per second, so that the average value of Hu is about 4,000 m 2 s-1, with a range from about 1,000 to 10,000 m 2 S-1. The estimated number of cancer deaths under dry conditions ranges from 20 to 2,000: These estimates agree well with the prediction obtained using a

• The wedge-model approximation will certainly break down when the plume reaches the mountains, but the contribution to the estimated number of deaths from the low-population-density region beyond 70 kilometers is relatively small.

The Hazard from Plutonium Dispersal by Nuclear-warhead Acc/dents 29 formula recommended by the Defense Nuclear Agency.*

LAND CONTAMINATION After the plume passed, it would leave a swath of land contaminated with Pu02

• The main hazard associated with this contamination would be that the plutonium might be resuspended and inhaled. The concentration of the plutonium contamination (J (mg m -2) at a particular point is simply related to the amount I that a person located at that point would have inhaled during the passage of the plume (J = vI (7) b where, once again, v is the deposition velocity (meters per second) and b is the breathing rate (m3 8-1 ).

The ratio of the concentration of resuspended aerosol to (J can be charac-Table 3: Cancer deaths predicted by the wedge model for olD-kilogram release of WgPu at Bangor Naval Base with the wind blowing towards Seattle Deposition Mixing height x wind speed Hu velocity v rrf S-1 meters per second 1,000 3,000 10,000 0.003 400-1700 180-700 80-300 0.01 300-1200 150-600 50-200 0.03 150-600 100-400 40-170 0.1 rain 20-90 45-180 30-120

1. rain 1-5 1-5 2-9

• Using a cookbook-style manual written for military commanders to assess the effects of destroying nuclear weapon stockpiles during a war, we have calculated that, over the entire range of meteorological conditions, the number of expected cancer deaths in Seattle alone would be 30--1,000, which compares with the 10--900 cancer deaths given for Seattle by the wedge model [Field Command, Defense Nuclear Agency, Estimation of the Hazard from Plutonium Dispersal, (Kirtland AFB, 1977)].

30 Fetter and Von Hippe/

terized by a "resuspension coefficient" K. It is therefore easy to make a comparison between the amount of resuspended plutonium inhaled Ir and I if one knows the resuspension coefficient K (m-1) as a function of time:

Ir(t) = v (' K(t ')dt , (8)

I Jo The resuspension coefficient can be expected to decline with time as the plutonium aerosol sinks into the soil and becomes attached to larger particles.

Based on a review of the small amount of available data, a 1974 Atomic Energy Commission study suggested for populated areas an initial value Ko =

10-5 m-1 declining to a long-term value K_ = 10-9 , and interpolated according to the formula K(t) = Koexp( -5t) + K_ (9) where t is measured in years.25 Using this function, we find Ir(t) = v (O. 2Ko [1 - exp( -5t)] + K_t) (10)

I Table 4: The ratio of the integrated inhaled dose from resuspension to that from plume passage, for several values of the deposition velocity at 1 month and after 1 year Deposition Exposure time 1" velocity Vd 1 month 1 year or greater meters per second 0.003 0.064 0.19 0.01 0.21 0.63 0.03 0.64 1.9 0.1 rain 2.1 6.3 1.0 rain 21 63

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 31 Table 4 shows values of Ir(t)/I calculated for various deposition velocities at 1 month and 1 year (after 1 year the resuspension dose rate will be negligible).

Note that resuspension can only be neglected for low to moderate deposition velocities ( $ 0.01 meters per second) and short exposure times (less than a month).

Evacuation and/or decontamination, as was done at Palomares, could reduce the hazard to that part of the population in the most heavily contami-nated area. In most cases, however, virtually all of the population dose would come from a very large area (on the order of 1,000 square kilometers for v =

0.01) of lightly contaminated land that might well be prohibitively expensive to either evacuate or decontaminate. The factors [1 + Ir(00)11] should therefore probably be used to multiply the cancer death estimates in table 1 except for the largest values of v ( ~ 0.1 meters per second) and in urban areas where the contaminated areas would probably be decontaminated. Table 5 gives the number of cancer deaths from inhalation during and after the plume passage under these assumptions.

CONCLUSION An accident involving the dispersal of kilogram-quantities of plutonium in aerosol form might, in a worst case (for example, an accident at Bangor Naval Table 5: The number of cancer fatalities caused by inhalation during and after the plume passage, assuming that urban areas (p = 3,()(X) km- 2) and small, highly contaminated areas (v ~ 0.1 meter per second) Ofe substantially decontaminated within 1 month Deposition Population density Po velocity km- 2 meters per second 30 300 3,000 0.003 120-500 1,200-5,000 0.01 50-200 500-2,000 0.03 30-120 300-1,200 1,600--7,000 0.1 rain 10-40 100-400 1,000-4,000

1. rain 7-30 70-300 700-3,000

32 Fetter and Von Hippel Base with the wind blowing toward Seattle with low wind speed and deposi-tion velocity), cause a few thousand cancer deaths during the subsequent decades with a probably undetectable increase in the resulting regional cancer rate. Even under worst-case conditions, no early deaths due to high doses would be expected-certainly not off the base. However, judging from the Three Mile Island and Palomares experiences, the psychological trauma and the costs of reparations and decontaminating the most heavily contaminated areas might be enormous.

To get an additional perspective on this risk, let us assume that the probability of a near worst-case accident is 0.1 percent per year.26 The expected number of deaths would then be on the order of one per year since, under average conditions, on the order of 1,000 cancer deaths would result from a worst-case accident.

This risk could be reduced, but not completely eliminated, by redesigning and rebuilding warheads with IHE-at a cost. A new warhead costs on the order of $1 million and lasts 20-30 years. If old warheads containing sensitive high explosives were retired an average of 10 years early in order to replace them with warheads containing IHE, the extra cost would be at least $300,000 per warhead. If this were done for the approximately 3,000 warheads that are to be deployed on US submarines after the reductions mandated by START, the cost would be on the order of $1 billion, or $100 million per year of reduced risk. Given that the expected value of the number of lives saved by such an expenditure is on the order of one life or less per year, the resulting cost per life saved would be 250-3,000 times that for other investments in life-saving that the US is currently making. 'J:l We therefore conclude that reducing the hazard of plutonium dispersal by converting warheads to IHE need not be dealt with through a "crash" pro-gram. However, for warheads that a government expects to replace upon their retirement, it would be desirable to have available replacement designs containing IHE. If such designs are not available already, their development should be given priority in any further testing before the achievement of a comprehensive test ban.

Another hazard that has been hinted at in the recent press stories on warhead safety is that, under certain circumstances, detonation of the chemical explosive in a warhead might result in a nuclear yield greater than

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 33 4 pounds of TNT equivalent. Specifically, there is apparently concern that this might occur in case of near simultaneous explosions of the HE in the W88 warheads of a 'Iiident II missile, which are closely clustered around the third-stage rocket motor.28 It is difficult for us to provide any perspective on this concern in the absence of public estimates of the size of the nuclear yield that might result in such an event.

Appendix THE RISK OF HIGH-DOSE EFFECTS Health Effects at High Doses Because it is relatively insoluble, a substantial fraction of inhaled Pu02 will remain in the lungs for a long time. Early effects are therefore dominated by damage to lung tissue.

Experiments with beagle dogs indicate that, if a relatively large amount of aerosol were inhaled, the lung damage from the resulting alpha irradiation would cause death from acute respiratory failure within a week. This would occur for an initial alveolar deposition of about 60 micrograms of 239PU02 per gram of bloodless lung,29 which corresponds to a total inhalation of about 100 milligrams of weapon-grade plutonium (WgPu) by an adult human.30 The same set of experiments with dogs indicates that, at lower doses, death occurs later because of respiratory insufficiency resulting from extensive fibrosis. The deposition of2 micrograms of 23%02 per gram of bloodless lung (corresponding to the inhalation of about 3 milligrams of WgPu by an adult human) will result in death within several months.31 At still lower doses, fibrosis develops more slowly. A least-(

squares fit to the relationship between Y, the initial alveolar deposition in micrograms ofplutonium-239 per gram oflung and t, the average length of time in days before the death of dogs given that dose is32 Y = 560t-1*028 (11)

At the maximum lifetime of the beagle (15 years) this relationship gives an alveolar deposition of 0.09 micrograms of 23%02 per gram of bloodless lung. (This also happens to be the lowest dose at which a dog died of fibrosis in the experiment.)

Pulmonary neoplasia (a cancer) began to occur in dogs that survived 3 to 5 years after exposure in these experiments and was the leading cause of death in exposed dogs that survived more than 5 years. The least-squares fit to the dose-longevity curves of dogs dying of neoplasia is33

34 Fetter and Von Hippel Y = 11 ,000t -1.416 (12)

This curve intersects the maximum beagle lifetime at Y = 0.04 micrograms per gram, which corresponds to the inhalation of about 0.08 milligrams of WgPu by an adult human.

Dispersal of the Aerosol at Short Distances The inhalation high doses that are the. subject of this appendix would occur, if at all, close to the release where the approximations made to obtain the wedge model would not hold. For the purposes of estimating the high-dose health effects from an accident we have used a Gaussian plume model to estimate the dispersal of plutonium at short distances. In this model, the time-integrated ground-level concentration of plutonium (mg*s m-3) downwind from the release is given by (13) where x is the downwind distance andy is the crosswind distance (m), Q(x) is the mass (milligrams) of plutonium aerosol remaining in the cloud when it arrives at x, Gy and G. are the horizontal and vertical standard deviations of the cloud concentration at point x, u is the mean wind speed (meters per second), and h is the centerline height of the cloud. Formulas for Gy and G. for a point source are given in the Reactor Safety Study for atmospheric conditions ranging from very unstable (class "A") to very stable (class "F");34 we have modified these formulas so that they give the initial standard deviations of the explosion-formed cloud, ~ and <f., at x = 0, and so that they are appropriate for an instantaneous (rather than a continuous) release. Since the mixed layer of the atmosphere normally has a finite height H (typically 300 to 2,500 meters),

we have also modified equation 13 to prevent plutonium from diffusing above the mixed layer and to account for reflections from the top of the mixed layer and the ground.

The amount of plutonium remaining in the cloud at distance x is given by (14) where Qo is the initial amount of plutonium in the cloud (milligrams) and v is the deposition velocity of the aerosol (meters per second). As mentioned above, a worst-case accident might involve the detonation of the HE in several ballistic-missile warheads

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 35 (and perhaps the missile propellants as well), releasing as much as 10 kilograms (107 milligrams) ofWgPu as respirable particles. As noted above, depending on the size and composition of an aerosol, v can range from 0.001 to 0.1 meters per second; a typical value for plutonium aerosols is 0.01 meters per second.

The initial height (h) and size (~ and <f.) of the cloud depends on the amount of explosive energy released. (Cold, ground-level releases of significant amounts of PU02 aerosol from smoldering chunks of plutonium are not considered credible.35) Since re-entry vehicles typically weigh 100 to 200 kilograms, warheads probably contain 20 to 50 kilograms of HE. Since normal HE is nearly twice as energetic as TNT, an accident could result in an explosion equivalent to between 40 and more than 400 kilograms of TNT, depending to the number of warheads involved. The detonation of the propellants in the third stage of a missile would be equivalent to an additional 4 to 8 tons of TNT. s6 Estimates of the initial cloud heights and radii for low, medium, and high-energy releases are given in table 6. S7 All else being equal, smaller explosions are more dangerous because the plutonium-bearing cloud remains closer to the ground.

Experiments have shown that approximately 5 percent of the radioactivity in the cloud is initially found between the ground and T14, where T is the cloud-top height; 30 percent between TI4 and T12; 40 percent between TI2 and 3T14; and 25 percent between 3TI4 and T . We have modeled this situation by using four cloud sources containing the above fractions of plutonium with centerline heights of T18, 3T18, 5T18, and 7T18; ~ of R14, R13, R12, and R12, where R is the initial cloud radius; and <f. equal to T18. 3S The amount of plutonium that would be inhaled by an individual (milligrams) standing on open ground is given by I(x,y) = X(x,y)b (15) where b is the breathing rate (ms S-I). As noted above, for an adult male performing light activity, b = 20 liters per minute = 3.3,104 m 3 S-I.

Table 7 gives the results of the Gaussian plume model for a 10-kilogram release of Table 6: Cloud-top height and mean radius in meters for low, medium, and high energy releases from an accident involving the detonation of the HE in one or more nuclear warheads and possibly the third stage of a ballistic missile as well Yield Cloud-top Mean Estimate TNT equivalent height radius kilograms meters meters Low 40 230 19 Medium 400 410 44 High 4,0J0 740 110

36 Fetter and Von Hippel Table 7: The amount of plutonium inhaled by an individual (milligrams) during the plume passage at several points downwind on the plume centerline for unstable, neutral, and stable conditions , under worst-case assumptions about windspeed (u

= 1 meter per second), plume height (40-kilogram equivalent TNT explosive energy release) and thickness of the mixed layer (H = 300 meters).

Distance downwind Dose kilometers milligrams unstable neutral stable 0.1 0.08 0.07 0.08 0.2 0.1 0.06 0.06 0.5 0.07 0.04 0.05

l. 0.03 0.03 0.03

2. 0.02 0.02 0.02

5. 0.003 0.014 O.Dll

10. 0.002 O.Dll 0.006 WgPu under conditions that result in the highest doses to individuals (u = 1 meter per second, H = 300 meters) for unstable, stable, and neutral conditions.39 A maximum dose approaching 0.08 milligrams-the lowest dose likely to cause threshold effects-occurs only at close ranges ( < 500 meters) and low wind speeds ( ~ 1 meter per second). Therefore doses exceeding 0.08 milligrams are highly unlikely to occur anywhere near civilian populations.

Summary If the area around the release is evacuated after the plume passes to avoid chronic exposure to deposited plutonium, there will almost certainly be no acute health effects from a worst-case accident, even close to the site and under worst-case weather conditions. This is especially true of civilian populations, which are usually no closer than a few kilometers from locations where missiles or nuclear weapons are loaded or stored. Even if the surrounding population was not evacuated and the land was not decontaminated for long periods of time (conditions that are highly unlikely), the maximum off-site dose would exceed 0.08 milligrams only under a very limited set of weather conditions combined with a very low cloud height. Therefore, for all practical purposes, threshold health effects from such accidents can be ignored.

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 37 NOTES AND REFERENCES

1. US nuclear warheads are designed so that "in the event of a detonation initiated at anyone point in the high explosive system [rather than multiple points, which would occqr providing the authorization codes were properly entered and the environmental sensors registered the design launch to target sequence], the probability of a nuclear yield greater than 4 pounds [1.8 kilograms] of TNT equivalent shall not exceed one in one million." US Arms Control and Disarmament Agency, Fiscal Year 1979 Arms Control Impact Statements, p.92.

2. A survey of experiments involving the burning of plutonium metal in hot fires found that the fraction of plutonium converted into a respirable PU02 oxide aerosol ranges from less than 0.001 percent to a few percent. Ralph H. Condit, Plutonium Dispersal in Fires: Summary of What is Known (Livermore, California: Lawrence Livermore National Laboratory, 1986), p.io.

3. Ibid, p.ll.

4. For a report on the measurements of plutonium contamination and of the cleanup, see USAF Nuclear Safety Study 65 (Kirtland AFB, New Mexico: Directorate of Nuclear Safety, 1970), part 2, "Project Crested Ice."

5. R. Jeffrey Smith, "Defective Nuclear Shells Raise Safety Concerns," Washington Post, 23 May 1990, p.A-1. In a letter to Senator Edward Kennedy, dated 9 July 1990, Brent Scrowcroft, President Bush's national security adviser, argued that "recent revelations regarding safety of certain warheads underscore the importance of testing."

6. Supplementary Documentation for an Environmental Impact Statement Regarding the Pantex Plant (Los Alamos National Laboratory, report # LA.-9445-PNT-D, 1982);

Report on the Safety Criteria for Plutonium Bearing Nuclear Weapons, (Washington DC: US Atomic Energy Agency, report # RS/56401l032, 23 January 1973; declassified with deletions, 9 January 1989), summary, p.10.

7. We infer from note 6 that at least some nuclear weapons contain plutonium-23B to power a radioisotope thermoelectric generator (RTG). The amount of plutonium-23B depends on the power requirements for nuclear weapons; 1 gram of plutonium-23B generates about 0.57 watts of heat, which could be converted to no more than 0.06 watts of electric power. Although 14.5 grams of plutonium-23B presents about the same health hazard as 4 kilograms of plutonium-239 (assuming the hazard scales with radioactivity), it could only be used to generate about 1 watt of electrical power. If power requirements are greater than 1 watt, then plutonium-238 should be considered in a hazard analysis. We do not, however, know what the power requirements of nuclear weapons are, and in any case the plutonium-238 in the RTG should be much better protected from dispersal during an accident than the plutonium core. We therefore ignore the contribution of plutonium-238 to health effects in this paper, although we flag the issue here.

38 Fetter and Von Hippel

8. The amount of the aerosol inhaled is proportional to its concentration Co in the air (measured in mg m-3) and the length of exposure (To). A 30-year dose due to inhala-tion will then be DibToCo, where b is the breathing rate (about 3.3*10-4 m 3 S-1 for an adult male involved in light activity) and Di is the dose per milligram of plutonium aerosol inhaled. Below, we will see that Di = 3,800 and 7,600 rads per milligram respectively for the lung and bone-lining cells-the organs in which the cancer risk would be greatest following the inhalation of Pu02* The external whole-body dose from the cloud would be D.,coTo and the external dose from plutonium deposited on the ground would be DFoTovT. Dc = 1.2*10-8 rad rn3 mg-1 s-\ Dg = 6.6.10-10 rad m 2 mg-1 S-1 for plutonium-239, v is the deposition velocity (of order 10.2 meters per second in the absence of rain), and T is the duration of exposure to the contaminated ground in seconds. The ratio of cloud to inhalation dose is therefore D/(bDj ) = 10-8 and the ratio of the ground to lung inhalation dose is (DgTu)/(D;b) = 4*10-12T. Since the lung would account for a significant fraction of all cancers caused by external whole-body gamma radiation, the cloud dose brings with it negligible additional risk, and it would take about 10,000 years for the integrated ground dose to equal the inhalation dose. The ratios for plutonium-240 are similarly low. See Steve Fetter, Internal Dose Conversion Factors of 19 Target Organs and 9 Irradiation TImes and External Dose-rate Conversion Factors for 21 Target Organs for 259 Radionuclides Produced in Potential Fusion Reactor Materials, (Idaho Falls: Idaho National Engineer-ing Laboratory, report # EGG-FSP-8036, 1988).

9. Reactor Safety Study (Washington DC: US Nuclear Regulatory Commission, report

1. NUREG-75/014, 1975), appendix VI, pp.D-2-D-7.

10. Health Risks of Radon and Other Internally Deposited Alpha-Emitters (BIER N)

(Washington DC: National Academy Press, 1988), p.332.

11. According to table 23 of Ionizing Radiation: Sources and Biological Effects (New York: United Nations, 1982), the average dose commitment to the human lung and the bone-lining cells from the inhalation ofPu02 from atmospheric nuclear testing was 1.6 and 4.8 millirads per becquerel respectively. Since plutonium-239 has a specific activity of 0.06204 curies per gram, this translates to 3,700 and 11,000 rads per milligram.

Reactor Safety Study (Washington DC: US Nuclear Regulatory Commission, 1975),

table VI D-2, gives a 30-year dose to the lung and bone of 2.9.108 and 5.2.108 rems per curie. Since the study set Q = 10 rems per rad for alpha particles, this translates to 1,800 and 3,200 rads per milligram.

D.E. Dunning Jr, G.G. Killough, S.R. Bernard, J.C. Pleasant, and P.J. Walsh, "Estimates of Internal Dose Equivalent to 22 Target Organs for Radionuclides Occurring in Routine Releases from Nuclear Fuel-Cycle Facilities," vol. III, ORNU NUREGtrM-190N3 (Oak Ridge, Tennessee: Oak Ridge National Laboratory, 1981),

pp.43-44, give 50-year dose conversion factors for lung and bone surfaces of 580 and 4,160 rems per microcurie. After dividing by the assumed Q = 20 rems per rad for alpha particles and multiplying by the ratio of the 30-year and 50-year doses given by Fetter, this translates to 1,600 and 9,300 rads per milligram.

I Il l

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 39

12. Fetter, Internal Dose Conversion Factors, addendum, gives 30-year lung and bone-surface doses of 2.9.108 and 5.2.108 rems per curie respectively. Since Q = 20 rems per rad for alpha particles in this study, this translates to 3,200 and 6,500 rads per milligram of plutonium-239.

13. The specific alpha activity of fresh weapon-grade plutonium is 1.17 times that of pure plutonium-239. After one halfiife (14 years) of plutonium-241 , the activity would increase by an additional 1 0 percent because of the alpha decay of americium-241.

14. International Commission on Radiological Protection, Recommendations for the Commission-1990, ICRP/90/6-01, draft, February 1990, p.3-13.

15. For a discussion of this approximation, see Health Risks of Radon and Other Internally Deposited Alpha-Emitters, appendix II.

16. "Report to the American Physical Society by the Study Group on Light-Water Reactor Safety," Reviews of Modem Physics, 47 (1975), p.S45.

17. Reactor Safety Study, table VI A-I.

18. Ibid, figures VI A-4 and A-5.

19. Health Risks of Radon and Other Internally Deposited Alpha-Emitters, p.147. The ratio of breathing rate to lung mass does not vary by more than a factor of two with age (Reactor Safety Study, tables IV D-4 and D-5).

20. Reactor Safety Study, table VI 5-2.

21. Reactor Safety Study, table VI B-1.

22. GA Schmel, "Particle and Dry Gas Deposition: A Review," Atmospheric Environ-ment, 14 (1980).

23. Reactor Safety Study, appendix VI, p.E-13.

24. Four thousand cancer deaths in the lifetime of the US population of 250 million corresponds to an average individual risk of about 10-5

• This is in the range where the US Environmental Protection Agency (EPA) tends to set the limits of acceptable risks for the carcinogens that it regulates. [See for example Eliot Marshall, "EPA's High-Risk Carcinogen Policy," Science, 218 (1982), p.975.]

25. U.S. Atomic Energy Agency Proposed Final Environmental Statement Liquid Metal Fast Breeder Reactor Program, (WASH-1535, 1974), appendix II-G.

40 Fetter and Von Hippel

26. The two large plutonium releases from US nuclear weapons that occurred in the first 50 years of the nuclear age were in areas of low population density, and the practice that resulted in these releases-routine flights by nuclear-armed bombers-has been discontinued.

27. Bernard Cohen, "Reducing the Hazards of Nuclear Power: Insanity in Action,"

Physics and Society, 16 (1987), p.2, quotes cost estimates in the range of $20,000-140,000 per life saved for various types of cancer screening, $400,000 for kidney dialysis, and $30,000-$300,000 per life saved by various highway safety improvement programs undertaken by the US Department of Transportation in the early 1980s.

28. R. Jeffrey Smith, "Defective Nuclear Shells Raise Safety Concerns," Washington Post, 23 May 1990, pA-1.

29. W.J. Bair, J.E. Ballou, J.F. Park, and C.L. Sanders, "Plutonium in Soft Tissues with Emphasis on the Respiratory Tract," in H.C. Hodge, J.N. Stannard, and J.B.

Hursh, eds., The Handbook of Experimental Pharmacology, Vol. 36: Uranium-Plutoni-um-Transplutonic Elements (New York: Springer-Verlag, 1973), p.548.

30. The specific alpha activity of fresh weapon-grade plutonium (6 percent plutonium-240) is 72.5 microcuries per milligram-1.17 times that ofplutonium-239. The bloodless lung of man weighs about 500 grams. The fraction of inhaled material initially deposited in the alveoli ranges from 5 percent to 50 percent for aerosols with a mass median aerodynamic diameter (MMAD) oflO to 0.2 microns; for a MMAD ofl micron, the fraction is about 25 percent. Thus, 100 milligrams ofWgPu inhaled is equivalent to an alveolar deposition of 0.06 milligrams of plutonium-239 per gram of bloodless lung. In a human being, about 60 percent of this deposition would remain in the lung with a retention halflife of 1.4 years.

31. The dose-mortality curve in Bair et al., p.548, gives an initial alveolar deposition of 2 micrograms per gram for a survival time of 6 months, which corresponds to an adult human inhaling 3 milligrams ofWgPu.

32. Ibid, p.548.

33. Ibid.

34. Reactor Safety Study, table VI A-I.

35. Report on the Safety Criteria for Plutonium-Bearing Nuclear Weapons, appendix, p.28.

36. Assume a third stage carrying 10 warheads weighing 100 to 200 kilograms each gives them a velocity increment of 2.5 kilometers per second and has an exhaust velocity of 2.5 kilometers per second. Also assume that the postboost vehicle (including propellants) weighs as much as the warheads, and that the total stage mass is 1.1 times the propellant mass. Then, using the rocket formula, the propellant mass in the

The Hazard from Plutonium Dispersal by Nuclear-warhead Accidents 41 third stage would be equal to (e - 1)*2'10/(1.1 - 0.1e) = 40 times the mass of a single warhead, or 4 to 8 tonnes in all.

37. H.W. Church, Cloud Rise from High Explosive Detonations (Albuquerque, New Mexico: Sandia National Laboratory, report # TID 4000, UC/41 , 1969), gives the following formulas for the cloud-top height T and the cloud radius R: T = 76WO*25 ,

R = 3.5WO*375, where T and R are in meters and W is in pounds of TNT equivalent.

38. Supplementary Documentation for Environmental Impact Statement Regarding the Pantex Plant: Dispersion Analysis for Postulated Accidents, LA-9445-PNTX-D (Los Alamos, New Mexico: Los Alamos National Laboratory, 1982).

39. The dose at a given point is approximately inversely proportional to u and, at distances of less than 10 kilometers, is relatively insensitive to factor-of-ten increases in v andH.