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Re: RADSAFE digest 2714
Jim,
Post attachments with caution (or never, as would be my preference!) ;)
Have you heard of another KI meeting?
regards
Martin
>------------------------------
>
>Date: Sun, 17 Oct 1999 14:25:11 -0400
>From: Muckerheide <muckerheide@mediaone.net>
>To: rad-sci-l@ans.ep.wisc.edu, ans-pie@nuke-ans.org,
>Subject: Science -- Ewing 286 (5439): 415
>Message-ID: <380A1454.63BFA04F@mediaone.net>
>
>This is a multi-part message in MIME format.
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>Group.
>
>Should the attached comparison radiotoxicity be for inhalation?
>
>Regards, Jim Muckerheide
>muckerheide@mediaone.net
>========================
>
>http://www.sciencemag.org/cgi/content/full/286/5439/415
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><!-- FULL -->
><H2 NAME=3DHEADLINE><FONT SIZE=3D-1>RADIOACTIVE WASTE:</FONT><BR>Less Geo=
>logy in the Geological Disposal of Nuclear Waste</H2>
><STRONG>Rodney C. Ewing</STRONG><A HREF=3D"#affiliation"><SUP>*</SUP></A>=
><P>
><STRONG>A</STRONG>t the end of the 20th century, one of the most pressing=
> problems, political and scientific, is the disposal and isolation of rad=
>ioactive wastes (<A HREF=3D"#ref1">1</A>). There is now a worldwide conse=
>nsus (<A HREF=3D"#ref2">2</A>) that effective long-term isolation for spe=
>nt nuclear fuel and high-level radioactive or transuranic waste can be ac=
>hieved by geologic emplacement. The chief elements of the geologic dispos=
>al strategy are as follows: (i) it was to be deep, permanent, and long te=
>rm, using to advantage the decrease in radioactivity, thermal output, and=
> radiotoxicity over time; (ii) the geologic history of stable regions was=
> taken as indicative of future stability and continued suitability; (iii)=
> the passive hydrologic and geochemical properties of the geologic format=
>ions were to be key to the isolation strategy. The large uncertainties in=
> predicted future behavior were to be reduced by a system of independent,=
> multiple barriers, geologic and engineered. However, the present approac=
>h in the United States, as embodied in proposed rules and standards, move=
>s away from the fundamental precepts of geological disposal.<P>
>In the United States, two sites have been selected for geologic disposal.=
> The Waste Isolation Pilot Plant (WIPP) in New Mexico now receives transu=
>ranic wastes generated by defense programs. The Yucca Mountain site in Ne=
>vada has been under active investigation for a quarter of a century as a =
>site for the disposal of high-level wastes, more than 90% of which will b=
>e spent fuel from commercial power plants. The Nuclear Regulatory Commiss=
>ion (NRC) has recently proposed rules for implementing the standards for =
>the disposal of high-level waste at Yucca Mountain, and the Environmental=
> Protection Agency (EPA) has just released the radiation protection stand=
>ards for Yucca Mountain. The EPA is responsible for developing "gene=
>rally applicable standards" for the repository, and the NRC is respo=
>nsible for promulgating rules or regulations, which if complied with, wil=
>l ensure that EPA's standards are met. The new rules and standards rely o=
>n a probabilistic performance assessment (PPA) of the repository to provi=
>de a single quantitative measure of compliance. This approach, when combi=
>ned with a proscribed compliance period that is short compared with the t=
>ime for geologic or climate change (10,000 years), a point of compliance =
>that is far from the site (20 kilometers), and the elimination of perform=
>ance standards on separate barriers, represents a significant deviation f=
>rom the original concept of long-term geologic disposal.<P>
><A NAME=3D"image1"><!-- null --></A><P><HR WIDTH=3D60%>
><A HREF =3D"/cgi/content/full/286/5439/415/F1"><IMG ALT=3D"Figure 1" ALIG=
>N=3DLEFT HSPACE=3D20 VSPACE=3D10 SRC=3D"/content/vol286/issue5439/images/=
>small/415-1-thumb.gif"></A>
>Relative radiotoxicity on inhalation of spent nuclear fuel with a burnup =
>of 38 megawatt-days/kg uranium (<A HREF=3D"#ref12">12</A>). The radiotoxi=
>city values are relative to the radiotoxicity (horizontal line) of the qu=
>antity of uranium ore that was originally mined to produce the fuel (8 to=
>ns of natural uranium yields one ton of enriched uranium, 3.5% 235U).
><P>
><FONT SIZE=3D-2>CREDIT: SKB (SVENSK KÄRNBRÄNSLEHANTERING AB, SW=
>EDISH NUCLEAR FUEL AND WASTE MANAGEMENT CO.)</FONT><BR><HR WIDTH=3D60%><P=
>>
>The concept of geologic disposal began in the 1950s and over the next 30 =
>years evolved with the publication of criteria for a geologic repository =
>(<A HREF=3D"#ref3">3</A>) and an analysis of the types of information tha=
>t would be required and the complexity and uncertainties inherent in a sa=
>fety analysis of a geologic repository (<A HREF=3D"#ref4">4</A>).<P>
>The Nuclear Waste Policy Act of 1982 represented a clear commitment to pe=
>rmanent geologic disposal and provided for the investigation of three sit=
>es that represented a variety of rock types (bedded salt, basalt, and vol=
>canic tuff). However, the investigation of multiple sites proved to be ex=
>pensive and time-consuming, and in 1987, Congress (in the Nuclear Waste P=
>olicy Act Amendments) limited Department of Energy (DOE) focus to a singl=
>e site, Yucca Mountain in Nevada. In 1992 (Energy Policy Act), Congress d=
>irected that the EPA prepare standards specific to Yucca Mountain and tha=
>t EPA arrange for an analysis by the National Academy of Sciences (NAS) o=
>f the technical basis for proposed standards (<A HREF=3D"#ref5">5</A>). T=
>hus, geologic disposal of high-level nuclear waste in the United States i=
>s now discussed in the context of a single site and site-specific standar=
>ds. Approximately 3 billion dollars have been spent on studies of the pro=
>posed Yucca Mountain site, and considerable responsibility and pressure r=
>ests on the shoulders of all involved federal agencies. In 1998, DOE comp=
>leted a total system performance assessment-viability assessment (TSPA-VA=
>) and has reported to Congress that there are no "showstoppers."=
>; Work proceeds toward a license application as a repository in 2001.<P>
><FONT SIZE=3D+1><STRONG>Probabilistic performance assessment</STRONG></FO=
>NT><BR>
>During recent years, there has been a move toward "risk-informed, pe=
>rformance-based regulation" (<A HREF=3D"#ref6">6</A>), and this appr=
>oach combined with the analysis of total system performance is now the ke=
>y to licensing a nuclear waste repository. The PPA methodology, as applie=
>d to geologic disposal of nuclear waste, has developed from roots in prob=
>abilistic risk assessments of nuclear reactors (<A HREF=3D"#ref7">7</A>).=
> There is no doubt that PPA (for example, the recent TSPA-VA of Yucca Mou=
>ntain) is an essential and highly informative method for analyzing comple=
>x systems and focusing work and resources on their most important element=
>s.<P>
>Although PPA is useful, PPA modeling of the complex behavior of a geologi=
>c system over extended periods of time has not been shown to be effective=
>=2E The limitations of PPA are especially important when it is applied to=
> natural systems for which there is a sensitive dependence of the final r=
>esult on initial or bounding conditions (<A HREF=3D"#ref8">8</A>). In suc=
>h "chaotic" systems, errors and uncertainty may increase expone=
>ntially with time. A typical PPA of a repository contains hundreds of sub=
>system models (often highly simplified descriptions of the physical and c=
>hemical phenomena), requires thousands of input variables (fixed and samp=
>led over ranges, many based only on expert opinion), and often does not a=
>ccount for nonlinear coupling between important elements of the system. I=
>f the PPA is to be the single quantitative criterion, then it is essentia=
>l to distinguish between a result that is driven mainly by assumptions ab=
>out boundary conditions (for example, climate change and assumed rates of=
> human intrusion) versus the actual properties and behavior of the reposi=
>tory (such as sorptive capacity). If the results of the PPA depend mainly=
> on assumed boundary conditions that are often probabilistic, then the ge=
>ologic properties of the site have little bearing on the analysis.<P>
>Actual experience with specific subsystem models of hydrologic and geoche=
>mical processes has shown how disappointingly unpredictive they can be (<=
>A HREF=3D"#ref7">7</A>). The uncertainties in the fundamental database, k=
>nowledge of the site, conceptual models, expert opinions, probabilities a=
>ssigned to initiating or bounding events, and knowledge of the effects of=
> coupled phenomena on the total system performance pose serious obstacles=
> to a convincing demonstration of compliance (<A HREF=3D"#ref7">7</A>). E=
>ach of these uncertainties will propagate through the PPA, and although t=
>he different types of uncertainty can be described mathematically (<A HRE=
>F=3D"#ref9">9</A>), little has been done to test the methodology against =
>the behavior of actual geologic systems. The large uncertainties could ob=
>scure the analysis of the performance and mask the actual environmental a=
>nd health impacts of the repository.<P>
><FONT SIZE=3D+1><STRONG>Multiple barriers</STRONG></FONT><BR>
>One early tenet of geologic disposal was that uncertainties in the assess=
>ment would be large, but could be reduced by requirements placed on indiv=
>idual geologic or engineered barriers (such as release rates of radionucl=
>ides, groundwater travel times). The present NRC rulemakings substantiall=
>y reduce the importance of multiple barriers by eliminating specific perf=
>ormance standards. This is partly because it is difficult to identify tru=
>ly independent barriers in a repository system. Another argument against =
>performance criteria for individual barriers has been that performance sp=
>ecifications for subsystems can lead to less than optimal design and perf=
>ormance of the total system. In the extreme, such an argument is inherent=
>ly illogical. An inert waste form that does not release radionuclides wou=
>ld improve total system performance. The absence of groundwater flow in t=
>he unsaturated zone (above the water table) would not allow release of wa=
>ter-borne nuclides. In real life, however, there is no "silver bulle=
>t," and each subsystem may fail to some degree over extended time. N=
>o subsystem can (or should) account for the total system performance; how=
>ever, a system of arguably independent barriers (for example, the corrosi=
>on rate of a canister in the unsaturated zone is not closely related to t=
>he flow-rate in the saturated zone) can reduce uncertainty and increase c=
>onfidence. More important, in a complicated system, components are more e=
>asily analyzed than the whole. If the components cannot be analyzed, then=
> the analysis of the total system is not made more tractable or useful by=
> combining the subsystem models in order to obtain a single quantitative =
>measure of successful performance.<P>
>Most important, understandable and clear subsystem requirements may contr=
>ibute to increased public acceptance. A geologic repository for which tra=
>vel times to the accessible environment are less than 1000 years or waste=
> package release rates are in excess of reasonable materials science perf=
>ormance standards is certainly not acceptable, regardless of the positive=
> results of a "quantitative" PPA.<P>
><FONT SIZE=3D+1><STRONG>Compliance period</STRONG></FONT><BR>
>The compliance period of 10,000 years is based on three considerations: t=
>he decay of short-lived fission products will substantially reduce the ac=
>tivity; the period is long enough to capture the essential performance fe=
>atures of the repository; extrapolation of models beyond 10,000 years is =
>unrealistic. Although there will be a substantial reduction in radioactiv=
>ity during the first 10,000 years, the repository will still contain subs=
>tantial quantities of long-lived fission products and actinides that cont=
>inue to contribute to elevated exposures (see graph on page 415). The rec=
>ent TSPA-VA of Yucca Mountain showed that the highest levels of exposure =
>due to <SUP>237</SUP>Np, <SUP>239</SUP>Pu, <SUP>99</SUP>Tc, and <SUP>129<=
>/SUP>I occurred well after 10,000 years. The NAS committee that examined =
>the technical basis for the Yucca Mountain standards recommended that the=
> compliance assessment be extended to the time when the highest risk occu=
>rs (<A HREF=3D"#ref5">5</A>). This is typically well beyond 10,000 years.=
> Selecting such a short period, with no analysis extending beyond 10,000 =
>years, has the effect of eliminating from consideration the effects of ev=
>ents, seismic and volcanic, that occur at low probabilities.<P>
><FONT SIZE=3D+1><STRONG>Point of compliance</STRONG></FONT><BR>
>The total system performance of a repository is taken as a measure of dos=
>e to an individual or critical population at some distance from the repos=
>itory; in the case of Yucca Mountain, this distance has been set at appro=
>ximately 20 km. Such a calculation is appropriate and reasonable in the e=
>valuation of risk, but it has little to do with the performance of the un=
>derground facility. The calculation of risk is qualitative, again because=
> of the large inherent uncertainties. In order to effectively compare dif=
>ferent repository designs or disposal strategies at a single site, the ca=
>lculation of radionuclide release should be made over a much shorter dist=
>ance in order to emphasize the properties and performance of the reposito=
>ry. The attractiveness of the Yucca Mountain site was, at least initially=
>, based on its location in an arid environment and the absence of flowing=
> groundwater in the unsaturated zone. On the basis of the present approac=
>h, the site may now be judged to be acceptable because of retardation, di=
>spersion, and dilution effects during transport over the 20-km path to th=
>e point of compliance.<P>
>The sole reliance on PPA to provide a quantitative criterion, in conjunct=
>ion with the elimination of performance standards for individual barriers=
>, the geologically short compliance period, and the extended distance of =
>the point of compliance all combine to reduce substantially the role of t=
>he geologic properties of the repository in the waste containment strateg=
>y. Such a shift in approach does little to build public confidence in the=
> repository site; however, as others have noted, the "U.S. geologic =
>disposal program is making a last stand at Yucca Mountain" (<A HREF=3D=
>"#ref10">10</A>). This last stand now relies heavily on engineered barrie=
>rs (for example, zircaloy cladding and extended waste package lifetime) a=
>nd the probabilistic analysis of their behavior during the first 10,000 y=
>ears (<A HREF=3D"#ref11">11</A>). The conclusion that there are no insurm=
>ountable obstacles in the present strategy and analysis begs the question=
> of whether Yucca Mountain provides effective geologic barriers to radion=
>uclide release and whether the present analysis provides the resolution r=
>equired to recognize a showstopper.<P>
><STRONG><STRONG>References</STRONG></STRONG><BR>
><OL>
><A NAME=3D"ref1"><!-- NULL --></A><LI>J. F. Ahearne, <EM>Phys. Today</EM>=
> <STRONG>50</STRONG>, 24 (1997); K. D. Crowley, <EM>ibid.</EM>, p. 32.
><A NAME=3D"ref2"><!-- NULL --></A><LI>L. C. Hebel <EM>et al.</EM>, <EM>Re=
>v. Mod. Phys</EM>. <STRONG>50</STRONG>, S1 (1978); NRC, <EM>A Study of th=
>e Isolation System for Geologic Disposal of Radioactive Wastes</EM> (Nati=
>onal Academy Press, Washington, DC, 1983); NRC, <EM>Rethinking High-Level=
> Radioactive Waste Disposal</EM> (National Academy Press, Washington, DC,=
> 1990); Nuclear Energy Agency, <EM>The Environmental and Ethical Basis of=
> Geological Disposal</EM> (Organization for Economic Cooperation and Deve=
>lopment, Paris, 1995).
><A NAME=3D"ref3"><!-- NULL --></A><LI>NRC, <EM>Geological Criteria for Re=
>positories for High-Level Radioactive Wastes</EM> (National Academy Press=
>, Washington, DC, 1978).
><A NAME=3D"ref4"><!-- NULL --></A><LI>J. D. Bredehoeft <EM>et al.</EM>, &=
>quot;Geologic Disposal of High-Level Radioactive Wastes--Earth-Science Pe=
>rspectives." <EM>U.S. Geol. Surv. Circular</EM> 779 (1978).
><A NAME=3D"ref5"><!-- NULL --></A><LI>NRC, <EM>Technical Bases for Yucca =
>Mountain Standards </EM>(National Academy Press, Washington, DC, 1995).
><A NAME=3D"ref6"><!-- NULL --></A><LI>Interview with NRC chairman, Shirle=
>y Ann Jackson, in <EM>Nuclear News</EM> (August), 24 (1999).
><A NAME=3D"ref7"><!-- NULL --></A><LI>R. C. Ewing, M. S. Tierney, L. F. K=
>onikow, R. P. Rechard, <EM>Risk Analysis</EM> (in press).
><A NAME=3D"ref8"><!-- NULL --></A><LI>N. Goldenfeld and L. P. Kadanoff, <=
>EM>Science</EM> <STRONG>248</STRONG>, 87 (1999).
><A NAME=3D"ref9"><!-- NULL --></A><LI>J. C. Helton, <EM>J. Statist. Compu=
>t. Simul.</EM> <STRONG>57</STRONG>, 3 (1997).
><A NAME=3D"ref10"><!-- NULL --></A><LI>L. J. Carter and T. H. Pigford, <E=
>M>Arms Control Today </EM><STRONG>29</STRONG>(1), 8 (1999).
><A NAME=3D"ref11"><!-- NULL --></A><LI>Civilian Radioactive Waste Managem=
>ent System, Management and Operation Contractor, <EM>Total System Perform=
>ance Assessment, Viability Assessment of a Repository at Yucca Mountain</=
>EM> <STRONG>3</STRONG> (TRW Environmental Safety Systems, Las Vegas, NV, =
>1998).
><A NAME=3D"ref12"><!-- NULL --></A><LI>Allan Hedin, <EM>SKB Tech. Rep.</E=
>M> 97-13, 60 pp. (1997).
></OL><A NAME=3D"affiliation"> </A>
><HR WIDTH=3D60%>
>The author is in the Department of Nuclear Engineering and Radiological S=
>ciences, University of Michigan, Ann Arbor, Michigan 48109-2104. E-mail: =
><A HREF=3D"mailto:rodewing@umich.edu";>rodewing@umich.edu</A>
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><H5>
>Volume 286, Number 5439 Issue of 15 Oct 1999, =
>
>pp. 415 - 417
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><BR>©1999 by The American Association for the Advancement of Science=
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