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835 by that date ? NIOSH is continuing to evaluate the post\1995 period ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Proposed Approach to Internal Dose Reconstruction (rev. 0) ? Extensive monitoring data available for routinely handled radionuclides (i.e., U, Pu, Cs, and tritium) ? Coworker models established in OTIB\0062 ? Sparse monitoring data available for non\ routinely handled radionucldes (i.e., exotics, mixed fission, and activation products) ? Approach to reconstruction relied on use of Pu, U, and Cs coworker data as surrogates for expsosure to non\routinely handled radionuclides ? ? ? ? Issues with Proposed Approach ? Original assumption that exotic radionuclides were handled, controlled, and monitored in a similar manner to U, Pu, and Cs could not be substantiated ? Exposures to exotics might be on an intermittent experimental basis leading to episodic exposures that are not represented by a chronic exposure model ? Comparability of operations that used exotics has not been established ? Short duration exposures might not have similar engineering controls in place as well\established operations ? ? ? ? ? ? ? ?? ? ? ? ? Feasibility of Internal Dose Reconstruction ? The available monitoring records, process descriptions, and source\term data are inadequate to complete internal dose reconstructions with sufficient accuracy for the evaluated class of employees during the period January 1,

1976 through December 31,

1995 ? Based on a presumption of compliance with

10 CFR 835, NIOSH finds that dose reconstruction is likely feasible by January 1,

1996 ? NIOSH is continuing to evaluate feasibility for the post\1995 period ? ? ? ? ? ? ? ? Feasibility of External Dose Reconstruction ? Majority of all workers monitored for photons after

1975 ? Personnel dosimeters were capable of measuring beta exposures ? Field beta measurements were taken in conjunction with photon surveys ? Neutrons monitored prior to

1980 can be assessed using appropriate N/P ratios ? Neutron exposures after

1980 measured using a combination of albedo and NTA film ? Occupational medical dose reconstruction possible using ORAU\TBKS\0013 ? ? ? ? ? ? ? ? ? ? ? ? ? ? Summary of Feasibility Findings (1976\1995) Source of Exposure Reconstruction Feasible Reconstruction Not Feasible Internal X \ Pu, U X \ H\3, MFP, MAP, Th, Am\241, Np\237, Ac\ 227, Pa\231, Cm\244 X External X \ Gamma X \ Beta X \ Neutron X \ Occupational Medical X\ray X ? ? ? ? ? ? ? Health Endangerment ? The evidence reviewed in this evaluation indicates that some workers in the class may have accumulated chronic radiation exposures through intakes of radionuclides. ? Consequently, NIOSH is specifying that health may have been endangered for those workers covered by this evaluation who were employed for a number of work days aggregating at least

250 work days within the parameters established for this class or in combination with work days within the parameters established for one or more other classes of employees in the SEC. ? ? NIOSH Recommendation All employees of the Department of Energy, its predecessor agencies, and their contractors and subcontractors who worked at the Los Alamos National Laboratory in Los Alamos, New Mexico from January 1,

1976 through December 31, 1995, for a number of work days aggregating at least

250 work days, occurring either solely under this employment or in combination with work days within the parameters established for one or more other classes of employees in the Special Exposure Cohort. ? ? ? ? ? ? ? NIOSH Recommendation\cont. ? Rationale for including all workers: ? NIOSH has determined that, due to undocumented worker movements across the site and limited claimant\specific information pertaining to work locations, it is unable to eliminate any specific worker from potential exposure scenarios based on assigned work location. ? NIOSH Recommendation\cont. ? For those not included in the SEC: ? NIOSH intends to use any internal and external monitoring data, and medical doses that may become available for an individual claim (and that can be interpreted using existing dose reconstruction processes or procedures). Therefore, partial dose reconstructions for individuals employed at Los Alamos National Laboratory during the period from January,