Validation of Dose Calculation Codes for Clearance Page: 2 of 12
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The fuel rack was melted for volume reduction in the Studsvik facility in the middle of January
2001, in the presence of project team including the dose modellers, who then made code
calculations to estimate the dose uptake of the workers.
All personnel involved in the project operations were equipped with electronic (display)
dosimeters. The measurements showed that segmenting was the work operation that gave the
highest dose, almost 65 % of the total dose incurred, while melting itself accounted for only about
13 %.
A comparison of the measured doses with corresponding calculation results indicated that, even
with a carefully controlled reflection of reality with respect to geometry and exposure time and
with a "best judgement" choice of densities for each operation, the calculation programmes have
tended to overestimate the measured values of the total dose by a factor 4 to 6, i.e. about an order
of magnitude. It seems reasonable to state that the use of 'enveloping' scenarios, which
necessarily cover a wide range of scenarios in connection with the calculation of clearance levels,
would tend to accentuate this tendency of overestimation of dose uptake in most individual cases
of recycling by melting by, say, one or even more orders of magnitude higher than those actually
taken.
INTRODUCTION
For the nuclear industry, the minimisation of the volumes of radioactive waste arising from the
refurbishment or decommissioning of nuclear facilities has been a high priority goal. The
recycling of very low level radioactive material (or its reuse or disposal) without radiological
restrictions, instead of disposal as radioactive waste, has long been identified as a significant
means of achieving this aim. For regulators, it is important to develop guidance for recycling that
adequately protects human health and the environment. Various international and national bodies
such as the International Atomic Energy Agency, the European Commission, the US Nuclear
Regulatory Commission have put forward proposals or guidance documents to regulate the
"clearance" of this surplus material from regulatory control, in order to allow its recycling as a
material management practice.
All these proposals are based on predicted scenarios for subsequent utilisation of the released
materials. The calculation models used in these scenarios tend to utilise conservative data
regarding exposure times and dose uptake as well as other assumptions as a safeguard against
uncertainties.
Another aspect is common to all these calculation models and codes: none of them has ever been
validated by comparison with the actual real life practice of recycling. The Swedish Radiation
Protection Institute initiated the Validation Project in order to validate some of the assumptions
made in these calculation models, and, thereby, better assess the radiological consequences of
recycling on a practical large scale.
The validation was proposed to be carried out by the following chain of operations:
- Two consignments of contaminated scrap, each of about 30 tons, were to be melted at
Studsvik RadWaste, Sweden.
- Ingots resulting from this melting, which have decayed to activity concentrations below
release levels established by Swedish authorities, were to be transported to Akers AB,CPD/PC/02/66-2002-11-21
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Menon, S.; Wirendal, B.; Bjerler, J.; Studsvik & Teunckens, L. Validation of Dose Calculation Codes for Clearance, article, February 27, 2003; (https://digital.library.unt.edu/ark:/67531/metadc787300/m1/2/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.