Guidance on Long-Term Reevaluation of Intakes

DOE-STD-1121-98

9.4 GUIDANCE ON LONGTERM REEVALUATION OF INTAKES

The purpose of long-term reevaluations is to verify the accuracy of projected bioassay patterns and

thereby verify the accuracy of assigned intakes and doses. Since by their very nature long-term

reevaluations are performed at long times after intake, there is little merit in reopening the administrative

investigation of an intake based on a reassigned dose, regardless of whether or not the reassignment

changes the original standing with regard to administrative control levels or dose limits. By the time a

reevaluation is completed, workplace actions appropriate to the events that caused the intake are usually

long past. Thus, the reasons for updating a worker's dose assessment are to adjust the cumulative total

effective dose equivalent and to update projected values of future bioassay results. Identifying and

confirming subsequent intakes requires knowing the expected magnitude of future excretion rates and

retained quantities. There is no requirement, and indeed no actual mechanism in place, for reporting

revised intake and dose assessments to the DOE Radiation Records Repository after the annual calendar

year reporting.

It is a good practice for sites to use long-term reevaluations to update assessments of lifetime dose.

The adjustments to lifetime dose from significant intakes of radionuclides (especially plutonium and

americium) can affect the worker's status with regard to the RadCon Standard Lifetime Control Level.

It is suggested that long-term reevaluations be performed when the CEDE is likely to affect the

lifetime control level or when projected long-term bioassay measurements indicate that there may be

impairment of ability to detect new intakes due to an elevated baseline.

9.5 GUIDANCE FOR PRACTICAL REPORTING OF INTERNAL DOSES

The uncertainty associated with dose assessments suggests that some rounding of doses is

reasonable. The decision to round to two significant figures is consistent with the accuracy associated

with the biokinetic models and dose factors. However, this can lead to the issue of how to sum (for

example) a 1.2-mrem tritium dose with a 3.1-rem plutonium dose. Most database recording systems will

treat the results as integer values and end up reporting 3,101 mrem. From a technical standpoint, the

tritium dose would certainly be insignificant relative to the plutonium dose; however, from the regulatory

perspective, both must be considered absolute values suitable for direct addition. Thus, it is

recommended that once a dose is assigned for an intake, it be treated as an absolute value, with all the

significant figures implied. This is not meant to imply that individual intake assessments should be

recorded to the nth decimal place. The suggested practice is to round an internal dose to two significant

figures for assignment to a specific intake, unless the dose is less than 10 mrem, at which point it is

reasonable to round to the nearest integer value.

9.6 GUIDANCE ON CUMULATIVE TEDE

10 CFR 835.702(c)(5)(iii) requires maintaining records of cumulative total effective dose equivalent

for each radiological worker for intakes occurring after January 1, 1989. It is a good practice to keep

additional, separate records of calculated doses that are not limited to intakes occurring after January 1,

1989, but includes TEDE contributions from intakes prior to this time. This lifetime TEDE is consistent

with the guidance concept of lifetime effective dose equivalent contained in NCRP Report 91 (1987). It

provides a more complete estimate of lifetime cumulative dose for comparing with the RadCon Standard

lifetime control level. While determination of TEDE for intakes received prior to January 1, 1989, is

recommended to improve the consistency of available information, such determinations may not be

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