atw 2018-1

atw Vol. 63 (2018) | Issue 1 ı January
OPERATION AND NEW BUILD 32
| | Fig. 2.
Comparison of the total annual effective dose obtained for several radionuclides with the model in RP101 [2] and with SUDOQU. Values labelled as SUDOQU*
are obtained by applying the same removable fraction and wipe-off efficiency as those used in RP101.
between these opposite effects. For
Co-60 and Na-22, the smaller value
of the external-radiation dose in
SUDOQU (with respect to that in
RP101) is not fully compensated by
the larger values of the other dose
contributions, leading to a slightly
smaller total dose in SUDOQU. For
the other considered nuclides ( Cs-137,
Sr-90 and Pu-241), the opposite
occurs, leading to more conservative
results in SUDOQU.
An additional comparison was
made by implementing in SUDOQU
the same assumptions as in RP101
concerning the removable fraction
and the transfer efficiency. These
results are shown in Figure 2 as well,
indicated by the label SUDOQU*.
Due to these assumptions, the
external-gamma-radiation exposure
in SUDOQU* now increases to values
larger than those in RP101, while the
other dose contributions decrease,
although still being larger than the
values obtained in RP101. As a result,
the annual dose values obtained with
SUDOQU* are more conservative for
all considered nuclides, but in good
agreement with the RP101-results.
4 Conclusions
The SUDOQU model [1] enables dose
evaluations for exposure to a surfacecontaminated
object. It is characterised
by the innovative and distinctive
assumption of time-dependent
surface- and indoor air-contamination
levels governed by mass-balance
equations based on the following
mechanisms: radioactive decay,
resuspension, wipe-off, deposition
and ventilation. These features make
the SUDOQU methodology a suitable
candidate for performing clearance
calculations based on reuse scenarios,
where the individual is likely to be
exposed to the same object throughout
the year, and for which the
assumption of constant contamination
levels would be unrealistically
conservative. In this work, a surfacecontaminated
bookcase released from
the controlled area of a nuclear facility
is studied, with the aim of assessing
the applicability of SUDOQU for
the development of surface-clearance
criteria for nuclear facilities. Deterministic
calculations of the annual
effective dose were thus conducted for
several nuclides in different scenarios
of use. First, the results in this paper
reveal a strong nuclide dependency:
even within the same category of
emitters there can be pronounced
differences in absolute dose values,
depending on the radiological characteristics
of the nuclides and their metabolic
behaviour and radiobiological
impact on the human body. Moreover,
the consideration of a mass balance
describing the time evolution of the
contamination levels causes the total
annual dose to be the result of
a delicate interplay of the involved
elements. In this way, a variation of a
certain input parameter may lead to
opposite effects on the various dose
contributions, and thus to a total dose
that either decreases, increases or
remains constant. The net outcome
again depends on the characteristics
of the nuclide and on the specifics of
the exposure scenario. The results
obtained with SUDOQU were benchmarked
against the results reported in
RP101 [2] for the reuse scenario of a
tool cabinet, and the two models
proved to be in good agreement.
The results presented in this paper
not only demonstrate the suitability of
SUDOQU for dose assessments related
to clearance of objects from nuclear
facilities, but they are also a good
starting point to better understand
the intricate interplay among the
involved mechanisms. Their interaction
also disclosed the importance and
difficulty of a detailed sensitivity
analysis. Future work will focus on the
development of surface clearance
levels based on probabilistic and
realistically conservative dose assessments.
References
[1] T. van Dillen, SUDOQU: a new dose
model to derive criteria for surface
contamination of non-food (consumer)
goods, containers and conveyances,
Radiation Protection Dosimetry,
164(1-2) (2015), pp. 160-164.
[2] Radiation Protection 101: Basis for the
definition of surface contamination
clearance levels for the recycling or
reuse of metals arising from
dismantling of nuclear installations,
European Commission, 1998.
[3] ICRP, Age-dependent Doses to the
Members of the Public from Intake of
Radionuclides - Part 5 Compilation of
Ingestion and Inhalation Coefficients,
ICRP Publication 72. Ann. ICRP 26 (1),
1995.
Authors
F. Russo
C. Mommaert
Bel V
Rue Walcourt, 148
1070 Brussels,
Belgium
T. van Dillen
National Institute for Public Health
and the Environment (RIVM)
P.O. Box 1
3720 BA Bilthoven,
The Netherlands
Operation and New Build
Clearance of Surface-contaminated Objects from the Controlled Area of a Nuclear Facility: Application of the SUDOQU Methodology ı F. Russo, C. Mommaert and T. van Dillen