1. Section BR, all pages: A triangular approach is again chosen. A host of data show the breathing rate to be lognormally distributed. It is not clear, therefore, why the programs (codes) prefer the triangular distribution. In nature, most variables have distributions with “rounded” corners.

PNWD 2033: Iodine-131 Releases from the Hanford Site, 1944 through 1947 (Volumes 1 and 2)

This is an impressive two-volume document summarizing iodine releases for the critical early years of reactor operation. The release of 685 kCi of iodine-131 constitutes the most important airborne-source term. However, the committee notes the following:

  1. Appendix B: The estimate of the iodine-131 released is based on calculated releases that assume constant losses due to iodine volatility, presumably as I2 from all plants, according to fuel-burnup records. Those substantial releases do not appear to be correlated with stack-monitor measurements. Appendix B in Volume 1 lists some “evaluated release factors,” but this seems to refer only to losses from solution due to iodine volatility. As the Three Mile Island experience has shown, the assumption of I2 volatile release as the only chemical species can lead to appreciable overestimation of dose.

  2. Page 3.1: In Section E, the summary of data quality and quality assurance is disconcertingly superficial and minimal. The author seems to confuse precision with accuracy in paragraph 3, in which he speaks of precision under the heading of accuracy. In addition, he draws an incorrect inference: he specifies that having a small standard deviation of the Monte Carlo simulations “assures us that the computed value encompasses the actual value with a high degree of confidence.” On the contrary, one could have a very precise but inaccurate (i.e., biased) estimate that would not encompass the real value.



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OCR for page 51
THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS Section BR, all pages: A triangular approach is again chosen. A host of data show the breathing rate to be lognormally distributed. It is not clear, therefore, why the programs (codes) prefer the triangular distribution. In nature, most variables have distributions with “rounded” corners. PNWD 2033: Iodine-131 Releases from the Hanford Site, 1944 through 1947 (Volumes 1 and 2) This is an impressive two-volume document summarizing iodine releases for the critical early years of reactor operation. The release of 685 kCi of iodine-131 constitutes the most important airborne-source term. However, the committee notes the following: Appendix B: The estimate of the iodine-131 released is based on calculated releases that assume constant losses due to iodine volatility, presumably as I2 from all plants, according to fuel-burnup records. Those substantial releases do not appear to be correlated with stack-monitor measurements. Appendix B in Volume 1 lists some “evaluated release factors,” but this seems to refer only to losses from solution due to iodine volatility. As the Three Mile Island experience has shown, the assumption of I2 volatile release as the only chemical species can lead to appreciable overestimation of dose. Page 3.1: In Section E, the summary of data quality and quality assurance is disconcertingly superficial and minimal. The author seems to confuse precision with accuracy in paragraph 3, in which he speaks of precision under the heading of accuracy. In addition, he draws an incorrect inference: he specifies that having a small standard deviation of the Monte Carlo simulations “assures us that the computed value encompasses the actual value with a high degree of confidence.” On the contrary, one could have a very precise but inaccurate (i.e., biased) estimate that would not encompass the real value.

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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS Page 3.2: The last paragraph gives two examples of quality-assurance procedures used to verify the iodine-131 content of material. However, no data are presented on how well the two programs or sources agreed, nor what was done when the programs or sources did not agree. Page 3.3: The last sentence states that “data entry from records was verified,” but again no information is given on what percentage was verified or what the error rate was. Page 3.3: Although the author checked to see that the sampling results followed the distribution function he intended to follow in the model (paragraph 1), no attention seems to have been paid to how the result might have been different if other (probably just as plausible) distribution functions had been used. For example, on page 4.18, triangular distribution functions are used for two major variables “because these are peaked distributions.” It does not appear that other peaked distributions were considered, such as a Gaussian distribution, or that fits of various distributions were compared with reference data. A sensitivity analysis was not done, i.e., the HEDR project did not model how much different the results would be if plausible alternative distribution functions were used. The public expressed concern at the meeting in Richland that there might be more data that have not been found. There is no way for the committee to evaluate this speculation fully but the documents clearly point out where data gaps are missing. The documents deal extensively with the missing data and with uncertainty. The author asserts that even if those data are found, they will not significantly change the findings and estimations. The committee supports that assertion because of the compilation of operational data to support the source-term estimate of iodine-131 release, the most important parameter in the dose reconstruction. There might be little to gain scientifically in further extensive efforts to uncover documents that might or might not exist, especially if the uncertainties in the remainder of the dose reconstruction are even larger than those for the source term. Efforts need to be made to follow up on public reports of releases to

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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS find pertinent data. Public credence in the project and the scientific validity of reconstructed doses will suffer if responsible consideration is not given to these concerns. The committee agrees that iodine-131 activation can be ignored, but it questions the use of ORGIN for activation data. The Chart of Nuclides(Walker et al., 1989) reports the thermal-activation cross section as 0.7 barn, instead of 0.33 barn, and a resonance-interval cross section of 8 barns. The committee has some concern about the daily releases of iodine-131 from the reactors themselves. On the basis of fuel technology at the time, such releases were probably measurable, but the committee suspects that these releases were only small fractions of releases from fuel reprocessing. For completeness, in dose reconstruction there is the need to model direct reactor releases as continuous low-level releases, whereas the fuel-reprocessing releases need to be modeled as short-term episodic releases that occurred for a few hours or less. There is no information on the physicochemical form of the iodine released. This information might be provided in another document, but it should at least be summarized here because it is an important component of the source term. The organization of the document could be improved if Sections 4.3 and 4.4 and part of Section 4.5 were moved up before Section 4.2.2. Interesting information—like the mass of uranium in the reactor, the number of reactor production runs, the average cooling time, the number of dissolver cuts, and the average fraction of iodine-131 released—is hidden in the text; it should be given more prominence and mentioned in Section 1.1 (Background). Page 1.8: Available information on releases of iodine-131 from the reactors should be summarized.

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THE HANFORD ENVIRONMENTAL DOSE RECONSTRUCTION PROJECT: A REVIEW OF FOUR DOCUMENTS Page 2.6: In the second paragraph, one would expect to read that the selection of the values and the distributions of the release fractions appear “in the following section,” but this information is not provided until 30 pages later. Page 4.1: Some equations between equation 4.1 and equation 4.2 are not numbered. Page 4.2: It is not clear what the dimensions are in the equation P = κΣfΦ. There is a switch from “second” in equation 4.1 to “day” in equation 4.2. In addition, it is unusual to choose “Ci” as a symbol because it is also a unit of activity. Page 4.3: Equation 4.3 does not clearly follow from equation 4.2. Does “Ci” mean the same thing in both equations? Page 4.4: Is “ICON” the same as “Ci” and “DPP” the same as “Pi”? Page 4.13: The constant “24174” is given as “24200” in equation 4.3. Pages 4.14 and 4.15: The release factors RFAC and RF are used but discussed only later in the text. For that reason, Section 4.2.2. should be moved to a later section.