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E.5
The Reactor Safety Study(a) (RSS) of the Nuclear Regulatory Commission (1975; this
is commonly known as the Rasmussen Report) included an effort by an Advisory Group on Health
effects to update and extend the conclusions of the BEIR Report (NRC 1975). Among the 17
members of this Advisory Group were five who also had served on the BEIR Committee. The RSS
derived three classes of risk estimates: an "upper-bound estimate," a "central estimate,"
and a "lower-bound estimate." In contrast to the different BEIR Report risk estimates, the
RSS estimates purport to establish a range within which the true value should be found. The
RSS risk estimates for organs of interest to this Statement, and as applied to low-dose
exposure, are listed in Table E.1.1. The details of the temporal exposure patterns, age
distributions, and computational approaches employed in the BEIR and RSS Reports are not
identical, and the risk estimates are therefore not strictly comparable; but errors from
this source are negligible in comparison to the other uncertainties involved.
In arriving at upper-bound estimates, the RSS made two significant changes in BEIR
assumptions and modified several numerical values on the basis of newer data. The "relative
risk model" of the BEIR Report was eliminated and all estimates were based on the "absolute-
risk model" and the plateau period for expression of non-leukemic cancer following postnatal
exposure was taken as 30 years; the duration-of-life plateau option of the BEIR Report was
dropped. The rationale for these changes is presented in the RSS Report. The major change
resulting from new data was a 40% reduction in the leukemia risk of in-utero exposure; this
was based upon revised dosimetry provided by the authors of the publication from which the
BEIR risk estimate was primarily derived. The upper-bound estimates shown in Table E.1.1
are taken directly from Table VI 904, p. 9-33, of the RSS Report (NRC 1975), except for the
thyroid cancer risk; this is derived from a "case" estimate of 134 per million man-rem modi-
fied by a mortality estimate of 10% (NRC 1975, p. 3-26 and 9-27).
The RSS central estimate "modifies the upper-bound estimate by correcting for risk
reduction caused by both the ameliorating effects of dose protraction and the lesser effec-
tiveness of very small acute doses" (NRC 1975, p. G-7). This correction acknowledges the
preponderance of data from experimental studies, which indicate that the dose-effect relationship
is not linear and that low doses of low LET (linear energy transfer) radiation
delivered at low dose rates afford a significant opportunity for repair of radiation damage.
The RSS discusses and references the extensive radiobiological literature on this subject
and concludes that at doses below 10 rem, or at dose rates below 1 rem/day, a "dose-
effectiveness factor" of 0.2 is justified (i.e., for a given total dose the dose efectiveness
in producing a "health effect" is less at smaller dose rates). This was still
considered a conservative position, the RSS Advisory Group on Health Effects was "of the
unanimous opinion that the dose effectiveness factors they recommended probably overestimate
the central estimate" (NRC 1975, p. 9-22). It should be recognized that some may not agree
in applying such a factor in the human case, where the very limited data do not entirely
a) Since the Reactor Safety Study (RSS) represents the conclusions of a respected body of
scientists, many of whom were also members of the BEIR Committee, the values reported in
the RSS were not adopted but rather were considered when the values in Table E.1.2 were
derived.