A Review of the Dose Reconstruction Program of the Defense Threat Reduction Agency (2003) / Chapter Skim
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V. Committee's Findings Related to NTPR Dose Reconstruction Program
V. Committee's Findings Related to NTPR Dose Reconstruction Program
Pages 124-230
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From page 124... ...
In parallel with the discussions in Chapter IV, Section V.A discusses scenario determination, Section V.B the estimation of external dose, Section V.C the methods of estimating internal dose, Section V.D the dose reconstructions for occupation forces in Japan, and Section V.E the estimates of uncertainty and upper-bound doses from all radiations and exposure pathways combined. Section V.F summarizes the committee's findings regarding dose and uncertainty estimates obtained by the NTPR program.
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From page 125... ...
were typically difficult to document with certainty. Procedures to be followed by the NTPR program for dose reconstructions, as laid out in 32 CFR 218.3, specify that "possible variations in the activities, as well as possible individual deviations from group activities, with respect to both time and location, are considered in the uncertainty analysis of the radiation dose calculations." There is also an expectation that a veteran will be given the benefit of the doubt in determinations used to adjudicate a claim for a nonpresumptive disease under 38 CFR 3.311.
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From page 126... ...
Communication of radiation intensity from red-safe monitoring personnel to commanding officers in the field was sometimes unreliable. Generic estimates of shielding and time spent indoors versus outdoors used to estimate external dose are questionable for some participants.
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From page 127... ...
The committee's impression is that the contractor assumes that the veteran himself should not be regarded as a reliable source of information. When, on occasion, a veteran came forward with an account of what happened on the sometimes-chaotic day of a weapon test, his story may have been discounted by the analyst and may not even have influenced the calculation of uncertainty, that is, the assigned upper bound of the dose.
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From page 128... ...
Case #53: This case provides a good example of inconsistent application of assumptions used in estimating the external dose and upper bound from boarding target ships at Operation CROSSROADS. The dose memorandum states that the veteran was given the benefit of the doubt by assuming that he participated in two-thirds of the target-ship boardings by his unit.
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From page 129... ...
The fact that no upper bound was provided implies that the dose of 6 rem would be considered as a 95th percentile of this veteran's dose in any adjudication process (the veteran did not file a claim for compensation)
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From page 130... ...
I do not remember if we had film badges. He then describes an operation (apparently at Shot APPLE-II)
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From page 131... ...
Regarding the first account, about accompanying the two colonels after Shot MET, the analyst writes that the veteran "did not provide sufficient information to identify the specific project that he supported on shot day." Because the veteran commented on seeing burning mannequins, the analyst decided to assign him to Project 40.20, the Clothing Test Project, and accordingly assigned him a dose of 0.20 rem appropriate to that group, apparently discounting the veteran's statement that "I learned later this was a test of fire-proof clothing." Evidently, no inhalation dose was considered. Regarding the project to assess the correlation between readings on the ground and air-based readings, the analyst comments that although the veteran described this as a "major study," "such a project is not listed, per se, among the Desert Rock projects at operation TEAPOT." The closest documented match that the analyst could find was Project 40.19, CBR Defense Team Training, and the veteran' s dose from that activity was accordingly based on a reconstruction that had been done for that group, with the comment that his "dose resulting from this activity was certainly less than 1.7 rem." Again, no inhalation exposure was considered, nor was any allowance made for the possibility that the veteran's account may reflect an activity that was not represented in other surviving records from the time.
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From page 132... ...
Although the committee did not try to recompute the veteran's dose, there was consensus that his true external dose could have greatly exceeded the assigned 6 rem, and that there was also the potential for substantial inhalation dose and beta dose to the skin, exposure routes that were not considered. Contributed case: Another example, not among the 99 sampled cases but a record that was randomly pulled from the Science Applications International Corporation (SAIC)
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From page 133... ...
The analysts revisited the calculations at that time, and a revised dose assessment was reported. The second dose reconstruction began with the fact that 4 days after Shot MIKE, the external exposure rate at 4 in.
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From page 134... ...
The committee did not attempt to do a dose reconstruction for the veteran, but the committee took issue with every assumption that was applied and considers the assigned upper bound of 0.8 rem to be much too low to adequately reflect the uncertainties in scenario definition and estimation of dose. The extrapolation of the measured exposure rate backward in time is complicated by the fact that the plane would have had its highly radioactive air samplers removed immediately on its return and the possibility that it cooled off during the 2-h flight back to Kwajalein and was hosed down before day 4 to begin its decontamination.
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From page 135... ...
Very little uncertainty was assigned to the estimated dose for the veteran. The estimated dose and upper bound in this case do not adequately reflect plausible conditions of exposure and uncertainties in estimating the veteran's dose.
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From page 136... ...
, so the adjudication of his claim presumably did not take dose uncertainties into account but used only the reported central estimate of dose. The general who was contacted stated that the usual practice had been to leave the "permanent" badge behind on missions for which a mission badge was issued.
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From page 137... ...
and inhalation of radioactive dust produced by resuspension of radionuclides in previously deposited fallout. The veteran also was an observer in the trenches during shots.
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From page 138... ...
(The analyst clearly was frustrated by this case and offered in a memorandum that the veteran also may have been present at another series of tests, perhaps TUMBLER-SNAPPER.) Because the veteran's case was analyzed in 1983, he was assigned a dose but not an upper bound.
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From page 139... ...
V.A.3 Conclusions on Adequacy of Scenario Determinations The preceding discussion clearly illustrates that dose reconstructions performed in the NTPR program often fail to adequately establish the exposure
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From page 140... ...
If that approach is not followed, it is unlikely that credible upper bounds of doses will be obtained in many dose reconstructions, as intended by the NTPR program. V.B EXTERNAL DOSE ESTIMATION V.B.1 Introduction Reconstruction of external doses by the NTPR program includes gamma doses estimated from film-badge data and scientific dose reconstructions in cases in which film-badge data are not available.
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From page 141... ...
Upper bounds were reported for all but four of the 29. In 51 of the 99 cases, the veteran's external gamma dose was based primarily on his unit's generic dose reconstruction (22 associated with NTS testing and 29 with Pacific testing)
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From page 142... ...
In three cases (cases #54 in 1995, #82 in 1956, and #55 in 1994) , a possibly damaged film-badge reading was accepted but treated as an upper bound.
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From page 143... ...
For example, in case #11, mission badges were issued to a participant who serviced cloud-sampling aircraft; he was not issued a permanent badge. It was assumed that his mission badges accounted for his dose from fallout on the island during the period when the badges were assigned and his reconstructed dose from fallout was modified (on the basis of his unit dose reconstruction)
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From page 144... ...
In case #10, it is clear that the participant did not return all film badges. Reconstructed doses were usually estimated only for periods for which no film-badge data were found.
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From page 145... ...
The committee found that in many cases, the policy does not give the veteran the benefit of the doubt regarding his potential total and upper-bound external dose, particularly if readings from slightly damaged film badges were replaced with reconstructed doses, if possible mission-badge data were not located, if incorrect dates were used for periods when the badges were worn, if badges were not always worn continuously as required, or if incorrect badge data were used. The additional uncertainty in doses based on film-badge data should be reflected in estimated upper bounds, and this is discussed in more detail below.
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From page 146... ...
V.B.3 Reconstructed External Gamma Doses V.B.3.1 Central Estimates The committee examined the methods and models used to estimate average external gamma doses assigned to units on the basis of cohort film-badge data or radiation-survey data combined with assumptions about a unit's activities. In many of the unit dose reconstructions, the analysis was thorough and comprehen
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From page 147... ...
In many cases, the unit dose estimates are based on sparse survey data and questionable assumptions regarding exposure scenarios, particularly for exposure on some ships, so the dose to some individuals in the unit could substantially exceed the mean. For some smaller units, in which the specific daily activities of individual members could not be precisely determined, daily average doses to members of a subunit were estimated by using a daily weighted average of doses for various radiation-risk activities that was based on previous dose reconstructions, manpower requirements for each activity, and morning-report unit strengths (Ortlieb, 19951.
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From page 148... ...
However, as discussed below, the committee has concluded that the reported upper bounds are not always credible estimates of the 95th percentile dose to all members of the unit. V.B.3.2.1 NTS unit dose reconstructions For NTS test observers and maneuver troops, the estimated upper bound of an external gamma dose is based on assumptions that the radiation field was well documented, that the times spent by the troops in various locations were fairly
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From page 149... ...
. V.B.3.2.2 Pacific test site unit dose reconstructions exposure to fallout Upper-bound estimates of external gamma dose from fallout for participants in many of the earlier Pacific test series assume that participants were exposed at random locations when on deck or outdoors on a contaminated island or ship, rather than at or near a fixed duty station where the external exposure rate may have been higher or lower than the mean.
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From page 150... ...
in the mean exposure rate on an island or ship. However, the 50% CV estimate is itself highly uncertain for most events, and that uncertainty is not considered in estimating upper bounds.
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From page 151... ...
analysis for an exposure from to = to = 9 h to T= 120 h with the approximate upper bounds that would be reported by the NTPR program for similar scenarios: Dose UB-MC NTPR-UB Ship 6 13 ~7 Island 10 19 ~12 Similar comparisons could be expected for other intervals.
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From page 152... ...
For example, for Operation GREENHOUSE, as discussed earlier, the calculated upper bound is about 20% above the mean for a person exposed over 6Exposure to multiple events based on additional survey data would reduce the upper bound somewhat depending on the relative fallout levels. However, it is also not clear that the NTPR program properly accounts for the additional variance due to subtracting residual exposure rates from previous events to obtain the appropriate En.
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From page 153... ...
However, it is assumed that this 20% factor applies to a person exposed over a shorter period when the dose is calculated by integration with the t-i 2 rule, rather than by summing the daily doses and variances for the shorter period (see case #4~.8 V.B.3.2.3 Pacific test site unit dose reconstructions exposure on contaminated target ships The committee believes that upper-bound estimates of external doses received when boarding target ships in Operation CROSSROADS are unreasonably low. The available data used to calculate the mean exposure-rate curves for each ship are not given, but it is asserted that the upper bound of a total dose is less than a factor of 1.2 above the mean.
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From page 154... ...
In case #53, the veteran was assigned a reconstructed dose from boarding the USS Skate after Shot BAKER of 0.51 rem, with an upper bound of 0.6 rem, but film-badge data for 82 members of the Skate crew for August indicated a maxi~°A memorandum from DNA to the veteran in case #48 states highest topside dose rate was as much as 30 times the average. that for some target ships, the
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From page 155... ...
The contribution to dose from being alongside a target ship was generally a significant fraction of the total dose to most seamen other than those boarding the targets or those who were members of engineering units and thus were exposed to contaminated piping (Weitz et al., 1982~. V.B.3.2.4 Pacific unit dose reconstructions summary Most of the uncertainty in the calculated external gamma dose to participants on ships and islands is due to variations in the measured exposure rate.
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From page 156... ...
The upper-bound calculations for fallout-contaminated ships and islands and the upper bounds for the CROSSROADS target-ship dose calculations are cases in which the NTPR program's uncertainty analysis clearly is flawed. Those exposure scenarios affect a large fraction of the dose assessments that are based primarily on the unit dose reconstructions carried out for the CROSSROADS, CASTLE, GREENHOUSE, and IVY test series in the Pacific.
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From page 157... ...
Generally, the doses from such activities were relatively low, but it is not clear that the estimates always reflected at least the 95th percentile of possible doses. V.B.4.2 Upper Bounds Upper-bound estimates of external gamma dose provided by the NTPR program are based primarily on film-badge data or unit dose reconstructions, as discussed above.
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From page 158... ...
Thus, the committee has concluded that the estimated upper bounds reported by the NTPR program for most of the 99 cases examined do not represent a credible estimate of the 95th percentile upper bound in the dose from external gamma radiation exposure. V.B.5 Neutron Dose Estimates V.B.5.1 Central Estimates Most test participants were not exposed to neutrons, except for observers in trenches at NTS tests and a few cloud-sampling personnel.
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From page 159... ...
V.B.5.2 Upper Bounds Reported upper bounds of external dose from exposure to neutrons are based on generally accepted radiation-transport calculations and reasonable corrections to account for shielding by trenches, vehicles, and so on. However, estimated upper bounds of neutron doses do not include any uncertainty in the neutron QF.
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From page 160... ...
sampled individual dose reconstructions that included VA claims. However, for most of the cases involving skin cancer, no beta dose was calculated; beta dose was not routinely calculated in such cases until 1998.
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From page 161... ...
Before the beta-to-gamma dose ratios were applied, the upper bound of each component of the gamma dose was determined by multiplying the estimated gamma dose by an upper-bound factor (ratio of upper bound to central estimate)
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From page 162... ...
162 DOSE RECONSTRUCTION PROGRAM OF THE DTRA TABLE V.B.2 Summary of Nine Cases in Committee's Random Sample in Which Skin or Eye Doses Were Reported External Dose (ren Claim or Upper Inquiry Assessment Bound Skin-dose Case # Condition Date Date Dose location Skin 9 Skin cancer 2/25/00 12/13/00 5.2 Head, face, neck 30.3 Upper arm 30.1 Forearm 55.5 Back 8.5 12 Skin cancer 8/18/99 10/8/99 3.7 Lower leg 25 Skin cancer 8/11/00 10/6/00 1.5 Face (forehead) 39 Cataract 6/15/00 9/5/00 7.3 N/A N/A 40 Skin cancer 10/19/98 7/15/99 0.2 Face 64 Unknown 12/23/98 1/1/99 1.6 Not stated 1.6 66 Skin cancer 12/23/98 1/3/99 1.8 Face, back, arms 1.8 96 Skin cancer 4/3/98 8112198C 4.3 Arm 35 97 Cataract 3/19/99 4/14/99 1.9 N/A 0.3 N/A aMethods: A, Barss (2000)
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From page 163... ...
ted lack, arms 30.3 30.1 55.5 8.5 77.5 8.7 A N/A B 7 1 N/A A N/A 25.5 A 0.3 N/A B 1.6 1.6 C 1.8 N/A C 35 N/A B N/A 2.4 B "Date pair/upper bound request" in response to VA inquiry; no narrative dose assessment in file; calculations performed with mathematical software and annotated "Upper bound request" in response to VA inquiry; no narrative dose assessment in file; calculations performed with mathematical software and annotated "Date pair/upper bound request" in response to VA inquiry; no narrative dose assessment in file; calculations performed with mathematical software and annotated "Date pair/upper bound request" in response to VA inquiry; no narrative dose assessment in file; calculations performed with mathematical software and annotated Update of previous dose assessment based on request from veteran's family member; beta skin dose specifically requested by JAYCOR; update included detailed narrative and spreadsheet calculations "Upper bound request" in response to personal inquiry; no narrative dose assessment in file; external dose determined by reference to previous reports; no indication of how skin and eye doses were assessed "Upper bound request" in response to personal inquiry; no narrative dose assessment in file; external dose determined by reference to previous reports; no indication of how skin and eye doses were assessed Radiation dose assessment in response to VA inquiry; this update to the veteran's dose included narrative; two assessments were performed with mathematical software and annotated "Upper bound request" in response to personal inquiry; no narrative dose assessment in file; external dose determined by reference to previous reports; eye beta dose calculations performed with mathematical software and annotated 1 cited. if Barss
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From page 164... ...
This assessment, which was performed on June 8-15, 1998, preceded publication of Barss (2000) , but the method of assessing beta doses, which was based on multiplying gamma doses by beta-to-gamma dose ratios, appears to be fundamentally the same.
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From page 165... ...
For most of the unit dose reconstructions, beta doses were not calculated, because the method had not been developed. Furthermore, letters to VA by the NTPR program as late as 1997 implied that doses of around 1,000 rem were needed to cause statistical increases in skin cancer (Schaeffer, 1997~.
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From page 166... ...
The unimportance of the inhalation hazard posed by fallout shortly after a detonation, compared with the hazard posed by external exposure, is attributed to such factors as: the presence of much greater activities of shortlived photon-emitting radionuclides that tend to result in high external doses per unit activity but much lower inhalation doses, compared with the activities of longer-lived radionuclides for which inhalation doses per unit activity often are considerably higher; the dominance of large, essentially nonrespirable particles in fallout relatively close to ground zero; and the insolubility of fallout particles, which can substantially reduce the extent of absorption of inhaled radionuclides into the body. However, there are exposure scenarios for participants at the NTS and in the Pacific in which activities of longer-lived radionuclides compared with
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From page 167... ...
, is obtained in all dose reconstructions for atomic veterans. Thus, the committee's evaluation of methods used in the NTPR program to estimate inhalation doses essentially involves an assessment of whether the methods are likely to yield credible upper bounds (at least a 95th percentile)
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From page 168... ...
At the time of the first National Research Council review, methods of estimating inhalation doses to atomic veterans were largely the same as the methods that have been used since then (Egbert et al., 1985; Barrett et al., 1986~. As described in Section IV.C.2, inhalation doses were estimated on the basis of estimates of concentrations of radionuclides in air at locations and times of exposure that were inferred from measurements of external photon exposure with film badges worn by veterans or field instruments, assumed resuspension factors, assumed breathing rates, and other assumptions about the physical and chemical composition of fallout particles or neutron-activated materials in soil.
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From page 169... ...
The view that inhalation doses generally were overestimated in the NTPR program and were unimportant was echoed in a later study (TOM/NRC, 1995~. V.C.3 Evaluation of Methods of Estimating Inhalation Dose The present committee' s evaluation of methods used in the NTPR program to estimate inhalation doses focuses on the question of whether the methods are likely to provide credible upper bounds of possible doses (see Section IV.E.4~.
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From page 170... ...
A comparison of dose coefficients for inhalation of radionuclides in respirable form (AMAD,1,um) often used in dose reconstructions for atomic veterans with values for workers for the same particle size currently recommended by ICRP (2002)
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From page 171... ...
is about a factor of 2 less than the value used in dose reconstructions, and i37Cs, for which the current dose coefficients for all organs and tissues are slightly lower than the values used in dose reconstructions. The data in these tables illustrate that doses per unit activity inhaled tend to be substantially higher for longer-lived radionuclides than for shorterlived radionuclides (see Section V.C.
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From page 172... ...
and often used in dose reconstructions for atomic veterans; values are based on dosimetric and biokinetic models in ICRP Publication 30 (ICRP, 1979a)
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From page 173... ...
That is the case especially when an organ of concern in a dose reconstruction is the thyroid, an organ in the GI tract, or the prostate,~9 and the assumption results in higher estimates of dose than would an assumed particle size of 1 ,um. An assumption of large particles is also used in some cases in estimating inhalation doses due to resuspension of deposited fallout.
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From page 174... ...
and often used in dose reconstructions for atomic veterans, except as noted; values are based on dosimetric and biokinetic models in ICRP Publication 30 (ICRP, 1979a)
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From page 175... ...
Doses to other organs and tissues, except those in the GI tract in many cases, also should be overestimated. Some dose reconstructions for atomic veterans assume that inhaled particles were respirable even when a substantial fraction of inhaled material probably consisted of large particles.
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From page 176... ...
A comparison of inhalation dose coefficients in Tables V.C.1 and V.C.2, which apply to respirable particles, with the corresponding ingestion dose coefficients in Tables V.C.3 and V.C.4, which describe much of the dose from inhalation of large particles, indicates that an assumption of respirable particles when large particles are inhaled also could result in substantial overestimates of dose to organs and tissues other than those in the respiratory and GI tracts. The extent of overestimation depends on the radionuclides inhaled and their relative activities.
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From page 177... ...
Use of 50-year committed doses from intakes of radionuclides is standard practice in radiation protection of workers. That approach takes into account that an acute intake of a radionuclide can result in a dose that is received over many years (see Section IV.C.2.2~.2° In dose reconstructions for atomic veterans who file a claim for compensation, the quantity of interest is the dose received in an organ or tissue of concern 20This practice is intended to ensure that if a worker is exposed continuously over a working life of 50 years at the annual limit on intake, the dose received in any year would not exceed the annual dose limit for occupational exposure.
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From page 178... ...
Thus, even if inhaled plutonium were rapidly transferred to bone or liver, the 50-year committed dose would overestimate the dose received in the first 25 years by about a factor of 2, and the degree of overestimation would increase somewhat if the inhaled plutonium was respirable and the low rate of absorption of insoluble forms of inhaled plutonium from the respiratory tract into blood is taken into account.2i Again, the difference between the 50-year committed dose and the dose received in an organ or tissue is potentially important only if the dose was due mainly to intakes of long-lived radionuclides that are tenaciously retained in the body. Thus, the importance of this difference in dose reconstructions for atomic veterans depends on the activities of particular radionuclides inhaled.
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From page 179... ...
. In the respiratory-tract model used in dose reconstructions (ICRP, 1979a)
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From page 180... ...
Resuspension factors normally used in dose reconstructions for these scenarios are discussed in Sections IV.C.2.1.3 and IV.C.2.1.4 and are summarized in Table IV.C.2. In some exposure scenarios at the NTS or on residence islands in the Pacific, resuspension or suspension of radionuclides on the ground occurred mainly as a result of normal wind stresses or walking and other activities that did not involve vigorous disturbance of surface soil.
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From page 181... ...
In summary, the committee has identified several assumptions used in the NTPR program to estimate inhalation dose coefficients and concentrations of radionuclides in air that, in the committee's opinion, should tend to result in overestimates of inhalation doses to atomic veterans; these assumptions are briefly restated in Table V.C.5. The committee also emphasizes, however, that the discussions of these assumptions should not be used to draw conclusions about whether estimates of inhalation doses to atomic veterans provide credible upper bounds without also considering the importance of uncertainties in these assumptions and the importance of other countervailing assumptions used in the NTPR program that may tend to result in underestimates of inhalation doses.
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From page 182... ...
eConclusion applies mainly to scenarios in which resuspension of fallout deposited on the ground or suspension of neutron-induced activity in soil is caused by normal wind stresses or walking and other activities that do not involve vigorous disturbance of surface soil. V.C.3.2 Assumptions With Substantial Uncertainty or Tending to Underestimate Inhalation Dose The committee also is concerned that some assumptions used to estimate inhalation doses in the NTPR program may not tend to overestimate actual doses and thus may not lead to credible estimates of upper bounds for use in evaluating claims for compensation.
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From page 183... ...
The uncertainty results, first, from uncertainty in dosimetric and biokinetic models used to calculate dose coefficients and in data incorporated in the models and, second, from the variability in anatomic, physiologic, and metabolic characteristics among people. Those sources of uncertainty in dose coefficients should be acknowledged and addressed in dose reconstructions for atomic veterans if credible upper bounds of inhalation dose are to be obtained.
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From page 184... ...
. Uncertainty in inhalation dose coefficients of the magnitude indicated in Table V.C.6 clearly is important when methods of estimating inhalation dose used in the NTPR program are intended to provide credible upper bounds.
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From page 185... ...
However, a credible upper-bound estimate of the biological effectiveness of alpha particles is substantially higher than the assumed value. Dose coefficients for inhalation of alpha-emitting radionuclides used in dose reconstructions incorporate a standard assumption recommended by ICRP (1977;
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From page 186... ...
of alpha particles indicates that there is considerable uncertainty in the particular value that should be used to estimate equivalent doses in humans. That uncertainty should be addressed if credible upper bounds of doses from inhalation of alpha-emitting radionuclides, such as plutonium, are to be obtained in dose reconstructions.
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From page 187... ...
In this case, current ingestion dose coefficients for organs of the GI tract are little changed from the values used in dose reconstructions, but inhalation dose coefficients for these organs, assuming an AMAD of 1 ,um, are a factor of about 10 higher in the current recommendations. As a result of that increase, the usual assumption of large particles would result in an underestimate of dose to organs of the GI tract from inhalation of insoluble plutonium by a factor of about 5 in scenarios in which inhalation of respirable particles is likely.
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From page 188... ...
In addition, an assumption that the source region is infinite in extent, which is used to relate measured external exposures to concentrations of radionuclides on the ground or other surfaces, is probably not valid in cases of fallout on ships in the Pacific, and concentrations of radionuclides in deposited fallout may be substantially underestimated in these cases. Scenarios involving inhalation of radionuclides in descending fallout or in fallout that was deposited on the ground or other surfaces and then resuspended in the air are important in dose reconstructions for many participants at the NTS or in the Pacific.
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From page 189... ...
and calculations of external exposure rates per unit concentration of radionuclides on the surface, the desired concentrations on the surface, SA, are estimated as (SAID x I, where I is a measured exposure rate due to all radionuclides and (SAID is the reciprocal of the calculated exposure rate per unit concentration for the assumed mixture of radionuclides on the surface. As discussed in Section V.C.2, a previous committee of the National Research Council concluded that methods of estimating radionuclide concentrations in fallout deposited on the ground or other surfaces based on measurements of external photon exposure are not scientifically valid and that their reliability is unknown (NRC, 1985b)
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From page 190... ...
Therefore, the reliability of the methods has not been demonstrated, and uncertainty in the calculations has not been quantified. The committee's principal concerns involve two issues: fractionation of radionuclides in an atmospheric cloud, which determines relative activities of radionuclides in deposited fallout at specific locations compared with estimated relative activities in the cloud; and calculation of external photon exposure rates per unit concentration of radionuclides on a surface in cases of fallout on ships in the Pacific.
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From page 191... ...
The committee also notes that the extent of fractionation cannot be estimated reliably from measured external exposures, because relative activities of photon-emitting radionuclides in deposited fallout can vary widely and still give approximately the same reading on a film badge or field instrument and approximately the same dependence of exposure rate on time after a detonation. In the method used in the NTPR program to calculate external photon exposure rates per unit concentration of radionuclides deposited on the ground or other surfaces, the surface is assumed to be uniformly contaminated and infinite in spatial extent, and the source region is modeled to take into account a small shielding effect of about 0.7 due to ground roughness (Egbert et al., 1985; Barrett et al., 1986~.
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From page 192... ...
[51 In estimating inhalation doses in scenarios involving exposure to descending fallout, the resuspension factor used to estimate concentrations of radionuclides in descending fallout based on estimated concentrations on the ground or other surfaces may underestimate airborne concentrations relative to concentrations on the surface when exposure did not occur during the entire period of fallout. The method used in the NTPR program to estimate concentrations of radionuclides in descending fallout is based on estimates of concentrations in fallout deposited on the ground or other surfaces and an assumed "effective" resuspension factor of 10-4 m-i (see Section IV.C.2.1.5~.
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From page 193... ...
Thus, even in scenarios in which an assumed resuspension factor is a credible upper bound, inhalation doses could be underestimated substantially, especially in cases of exposure at the NTS at times relatively late in the period of aboveground testing. The possibility of substantial inhalation exposure due to resuspension of aged fallout is an important concern at the NTS and on islands in the Pacific.
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From page 194... ...
As discussed in Section V.C.5, however, the committee does not believe that neglect of resuspension of aged fallout on islands in the Pacific has important consequences for dose reconstructions; that is, potential inhalation doses do not appear to be high. In dose reconstructions for participants at the NTS, the presence of fallout from previous shots was taken into account in some cases (Barrett et al., 1986~; see Section IV.C.2.1.1 and Table IV.C.1 (see also cases #21, 23, 27,80, and 87~.
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From page 195... ...
i ~ ~; 1 ~ -- ~ ;~ ~-,, -- ~l'`- :N 1_ ~.~ L \ ~ ' t ~ i ~< j . _ ~ O' ~000 ~ '_ I tFIGURE V.C.1 Fallout pattern at NTS from Operation PLUMBBOB, Shot SHASTA assumed in dose reconstructions for participants at PLUMBBOB Shot SMOKY (Goetz et al., 1979~.
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From page 196... ...
196 To 10 l ~ I I ~ ~ I I ~ I I Kilometers DOSE RECONSTRUCTION PROGRAM OF THE DTRA it- ~ _ ~ lol WW ~ _ Yucca Flat Control X (; make Point 3 \ Frenchman :~ I eke — ii==—Camp Mercury Camp Desert _ Rock / - UNCLE ~ SUGAR N - EASY BAKER, CHARLIE, DOG ~ ABLE FIGURE V.C.2 Locations of shots in Operation BUSTER-JANGLE in Areas 7, 9, and 10 at NTS (Oct.
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From page 197... ...
V COMMirTTEE'S FirNDirNGS RELATED TO NTPR DOSE RECONSTRUCTirON 197 HOW FOX j 1 ' 10 1 1 s 9 4 ~ r~ EASY ~ ~ 1 Yucca _ ~ BAKER (3) | CHARLIE DOG / -- -- ~ rBJY l ~ I GEORGE 1 Flat ~1 | News Noh Control X Point 16 o L I I I I I Kilometers 10 Ca I ucca \\ Lake Airstrip | \ ~J 1 \ 1 ._ _ _~__ _ 1 ~ ~ I ~.
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From page 198... ...
98 BADGER RAY NANCY— SIMON o Kilometers A) Ground Zero DOSE RECONSTRUCTION PROGRAM OF THE DTRA 1~ 1 1 1 ———~ 10 ~ 1 -- my \ 1 12 ~ 91 1 ~ ~ I .
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From page 199... ...
V COMMITTEE'S FINDINGS RELATED TO NTPR DOSE RECONSTRUCTION 199 APPLE 2 I / I ESS N ~__- ~ ~ 10U TURK I ~ ~ \` \ l ~2~ t ~~—~ ~ ZU CCH I N I APPLE 1 1 ~ \/ ~, ~ WASP ~ 7~ WASP PRIM 1 4 1 ~ HA I HADR 1 1 1 3 ___ 1 1 News Nob take——— I Control Airstrip | I Point x JO | 1 \ 1 is \ 1 . ~ __ ~—~—- - - - 1 1 ' , 1 3 I ~1 \ o I I I 1 1 1 10 Kilometers TESL A POST MOTH HORNET ~ MET Frenchman | ( 1__ ~ __1 ~ Camp Mercury Camp Desert _ Rock / FIGURE V.C.5 Locations of shots in Operation TEAPOT in Areas 1, 2, 3, 4, 5, 7, 9, and 10 at NTS (Feb.
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From page 200... ...
R ock __ ) ___J ~ .' Camp Mercury ~ ,_, FIGURE V.C.6 Locations of shots in Operation PLUMBBOB in Areas 1, 2, 3, 4, 5, 7 8, 9, 10, and 12 at NTS (May 20, 1957-Oct.
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From page 201... ...
The lack of consideration of the impact of fallout from prior shots in the area of PLUMB BOB Shot HOOD noted above seems particularly inexplicable, given that the existence of some prior fallout was considered at all other PLUMBBOB shots at the same location during the same period. That the omission of Shot HOOD from Table IV.C.1 is not an oversight by the NTPR program is indicated by an assumption used in unit dose reconstructions for participant groups in forward areas after the shot that the groups were exposed to suspended neutroninduced radioactive material "in the absence of a fallout field" (see Section 3 and Tables 35 and 37 through 40 of Barrett et al., 1986~.
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From page 202... ...
Thus, without the need to consider locations of particular shots and associated directions of fallout patterns and the extent of fallout, as has been done in dose reconstructions (Barrett et al., 1986) and in the committee's evaluation as given above, it is virtually certain that participants, including maneuver troops and observers, who engaged in activities in any of several areas, especially in the northeast quadrant of the NTS where most shots were detonated, during later periods of atomic testing received inhalation doses due to resuspension of previously deposited fallout.
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From page 203... ...
j~-o ~ . FIGURE V.C.7 Distribution of concentrations of 137Cs in surface soil at NTS as of January 1, 1990 (McArthur, 1991~.
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From page 204... ...
The potential importance of a blast wave on resuspension of previously deposited fallout at the NTS is indicated by the following considerations. First, FIGURE V.C.8 Photograph taken shortly after detonation of Operation PLUMBBOB, Shot PRISCILLA showing formation of dust cloud along the ground by blast wave produced by the detonation.
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From page 205... ...
A credible upper bound in the range of 10-2-10-3 m-i seems reasonable when one considers that values as high as 1o-3-lO~ m-i caused by vehicular and pedestrian traffic have been reported (Sehmel, 1984~. The committee also notes that a resuspension factor of 10-3 m-i is assumed in some exposure scenarios that involved vigorous disturbances of surface soil (see Table IV.C.2)
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From page 206... ...
Reports of activities of participant groups and individual dose reconstructions reviewed by the committee sometimes referred to high dust levels (see cases #21, 27, and 77) , and levels sometimes were so high that a planned activity was delayed or canceled (see case #21 and Appendixes E and F)
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From page 207... ...
In its review of randomly selected dose reconstructions for individual veterans, the committee encountered many cases in which consideration of blast-wave effects could be important for obtaining credible upper bounds of dose to participants at the NTS from all exposure pathways combined.26 [81 In several individual dose reconstructions reviewed by the committee, an internal dose of zero was assigned even though a substantial external dose was estimated and inhalation exposure was plausible. Regardless of the magnitude of possible inhalation doses, assigning a zero dose does not conform to the stated policy that the veteran will be given the benefit of the doubt in estimating dose, and it does not provide a credible upper bound.
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From page 208... ...
[91 Resuspension factors used in the NTPR program to estimate inhalation doses from exposure to fallout deposited on ships may not represent credible upper bounds of actual resuspension factors in many cases. Resuspension factors normally used to estimate inhalation doses to participants from exposure to fallout deposited on ships in the Pacific are summarized in Table IV.C.3.
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From page 209... ...
[101 In dose reconstructions for participants on residence islands in the Pacific, exposures to descending or resuspended fallout during the fraction of the time spent indoors normally are ignored; that is, concentrations of radionuclides in indoor air are assumed to be zero. That assumption does not provide a credible upper bound of possible inhalation doses indoors.
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From page 210... ...
In summary, the committee has identified several assumptions used in the NTPR program to estimate inhalation dose coefficients and concentrations of radionuclides in air that have substantial uncertainty that has not been taken into account in dose reconstructions, and the committee has also identified several assumptions that should tend to result in underestimates of inhalation doses to atomic veterans; these assumptions are briefly restated in Table V.C.7. Additional concerns about situations in which use of 50-year committed doses and assignment of committed doses to the year of intake could result in underestimates of the dose that could have caused a veteran's cancer are discussed in Section V.C.3.
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From page 211... ...
The basic question in evaluating methods used in the NTPR program to estimate inhalation doses is whether the methods provide credible upper bounds of doses from this intake pathway (see Section IV.E.4~. The question is difficult to answer in general terms, especially in the more important cases of exposure to fallout.
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From page 212... ...
Therefore, although some assumptions embodied in the methods of estimating concentrations of radionuclides in fallout are likely to be overpredictive or underpredictive, it often is difficult to judge whether the net effect of all such assumptions is that estimated inhalation doses from exposure to descending or resuspended fallout tend to be overestimates or underestimates and by how much. An example of a scenario in which credible upper bounds of inhalation dose probably are obtained in dose reconstructions involves exposure to descending fallout throughout the period of descent.
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From page 213... ...
. A clear example of when estimates of inhalation dose obtained in dose reconstructions almost certainly do not provide credible upper bounds involves a scenario for exposure to resuspended fallout at the NTS.
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From page 214... ...
are considered. However, neglect of uncertainties in breathing rates is not an important concern, because they clearly are small compared with uncertainties in other parameters used in calculating inhalation doses to atomic veterans, including dose coefficients and resuspension factors.
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From page 215... ...
of a probability distribution of inhalation dose based on assumed uncertainties in input parameters. Thus, when possible errors in estimating concentrations of plutonium in fallout and the need to include uncertain contributions to dose from resuspension of other radionuclides in fallout are considered, it is difficult to draw a definitive conclusion about whether estimates of inhalation dose obtained by the NTPR program for this scenario provide credible upper bounds.
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From page 216... ...
Taking into account uncertainties in ingestion dose coefficients (see Table V.C.6) , a credible upper bound would not exceed about 1 mrem hat.
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From page 217... ...
V.C.4.2 Example Analysis of Potential Ingestion Doses in the Pacific As in the previous section, two scenarios for ingestion exposure on residence islands in the Pacific are considered here. The first scenario involves ingestion of locally produced terrestrial and aquatic foodstuffs that were contaminated by fallout.
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From page 218... ...
Furthermore, on the basis of the consideration that most of the fallout on Rongerik was in the form of large particles, the analysts concluded that internal doses were dominated by ingestion that resulted from deposition of fallout on foods while they were being consumed and that intakes by inhalation were relatively unimportant.32 Dose reconstructions reviewed by the committee indicate that estimated external doses to most participants who were stationed on residence islands are less than 1 rem. If the ratios of internal to external doses to personnel on Rongerik Atoll given above are assumed to apply to participants on residence islands and if skit should be noted that as a result of an assumption that ingestion intakes were dominant, estimated internal doses to some organs and tissues are similar to estimated external doses.
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From page 219... ...
Ingestion doses to most participants probably were around a few mrem or less. Doses of that magnitude are unimportant, so neglect of intakes of radionuclides by ingestion in dose reconstructions for atomic veterans does not appear in most cases to be an important concern with regard to evaluating claims for compensation for radiationrelated diseases.
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From page 220... ...
Furthermore, the committee has identified exposure scenarios in which neglect of resuspension of previously deposited fallout by the blast wave produced in most detonations at the NTS almost certainly has resulted in underestimation of upper bounds of inhalation doses by a factor of at least 100. Such scenarios are important because thousands of participants at the NTS could have been exposed to substantial airborne concentrations of fallout that was resuspended by a blast wave.
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From page 221... ...
However, because of experience with a bioassay program that was recently undertaken to assess internal exposures to plutonium and difficulties with the use of present-day measurements to estimate intakes that occurred many years ago, as discussed in Section VI.D, the committee believes that urinanalysis is not likely to provide useful information on the reliability of methods used to estimate inhalation doses to atomic veterans. A potentially more fruitful approach would be to compare estimated radionuclide concentrations in deposited fallout or in neutron-activated soil used in the NTPR program with measurements that were made at the NTS or in the Pacific after the period of atomic testing ended.
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From page 222... ...
That assumption is reasonable at the NTS and on residence islands in the Pacific, but it probably results in underestimates of concentrations of radionuclides in fallout deposited on ships. Estimates of concentrations of radionuclides on the ground or other surfaces used in dose reconstructions are of crucial importance because calculated inhalation doses in most scenarios depend on those estimates.
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From page 223... ...
[21 An important deficiency in dose reconstructions for many participants at the NTS is the lack of consideration of resuspension of previously deposited fallout by the blast wave produced in aboveground detonations. When combined with the frequent neglect of aged fallout that accumulated at the NTS during the period of atomic testing and the general neglect of fractionation in fallout, neglect of resuspension caused by a blast wave could result in underestimates of upper bounds of inhalation doses by a factor of at least 100 in some scenarios in which participants engaged in activities in forward areas within a few hours after a shot, and perhaps by a factor of as much as 1,000 in the worst cases.
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From page 224... ...
Thus, the key question in evaluating methods of estimating inhalation doses used in dose reconstructions is whether the methods provide credible upper bounds. If they do, estimates of inhalation dose to atomic veterans are appropriate for use in evaluating claims for compensation for radiation-related diseases.
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From page 225... ...
However, the types of exposure scenarios for which estimates of inhalation dose obtained in dose reconstructions probably are credible upper bounds are somewhat limited. In many frequently occurring scenarios, such as scenarios of exposure to previously deposited fallout in forward areas at the NTS, the committee believes that uncertainties in assumptions used to estimate inhalation dose are sufficiently important that doses estimated by the NTPR program may not be credible upper bounds even if some parameter values used in the calculations, especially resuspension factors, are credible upper bounds.
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From page 226... ...
Inhalation doses to most of those participants probably were too low for possible underestimation of upper bounds to have affected decisions about compensation. The committee also believes that neglect of possible ingestion doses in dose reconstructions is unlikely to be important for most participants at any site.
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From page 227... ...
The committee concurs with the assessment by the NTPR program that the dose to even the most exposed of the occupation troops in Japan from both internal and external exposure was probably well below 1 rem. V.E COMMITTEE EVALUATION OF METHOD OF ESTIMATING UNCERTAINTY IN DOSE AND UPPER BOUNDS As stated in Section II.A, dose reconstruction is an inexact science.
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From page 228... ...
. To the extent that the external gamma-plus-neutron dose upper bounds and inhalation dose estimates are reasonable estimates of at least 95th percentile or higher doses, the VA practice of summing the reported upper-bound external
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From page 229... ...
However, the committee has documented numerous examples in which the NTPR program has failed to establish the participant's exposure scenario adequately; that is, plausible scenarios could be developed, on the basis of available information, that would have resulted in higher estimates of dose. The committee finds that estimates of uncertainty in external dose obtained by the NTPR program in unit dose reconstructions often are not credible and do not adequately reflect the upper bound (95th percentile)
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From page 230... ...
Furthermore, beta doses from direct contamination of skin or clothing apparently have not been considered in dose reconstructions in any cases in which a veteran filed a claim for skin cancer. The committee believes that upper bounds of neutron doses reported by the NTPR program are not credible, because of neglect of the uncertainty in the biological effectiveness of neutrons.
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Key Terms
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