ICEM11 Final Program 9.7.11pm_ICEM07 Final Program ... - Events

Abstracts Session 58
5) WASTE ASSESSMENT: A PRACTICAL APPROACH TO PROVING WASTE METALS SUITABLE
FOR CONSIGNMENT AS RADIOLOGICALLY EXEMPT MATERIALS (wP-59266)
Iain Carvel, RSRL; Richard D Gunn, Robin Strange, Christopher Orr, Babcock International Group (UK)
B220 at Harwell was built as a Radiochemical Research and Development facility in the latter part of the 1940s. The facility
has been operational since 1949 and has been extended several times, most notably the Plutonium Glove Box Wing in the 1950s
and the Remote Handling Wing in the 1980s. Only the Remote Handling wing remains operational, processing Historic Waste
which is being recovered from storage holes elsewhere on site. The remainder of the facility is undergoing progressive strip out and
decommissioning. In the Plutonium Wing and associated areas the waste fingerprint (nuclide vector) consists predominately of
alpha emitting radionuclides.
Decommissioning and Decontamination (D&D) operations often result in the production of large volumes of scrap metal waste
with little or no radioactive contamination. Proving that the waste is clean can be costly and time consuming, as the shape and size
of the metallic waste items often means that it is difficult or impossible to monitor all surfaces using conventional hand-held survey
meters. This is a particular problem for alpha contamination measurement.
Traditional radiological surveying techniques are very labour intensive and involve surveyors checking every surface using
hand held instruments and smear sampling the hard to access areas. Even then 100% monitoring cannot be guaranteed.
6) DEVELOPMENT OF A COMPUTER SYSTEM FOR SUPPORT AND DOCUMENTATION
OF CLEARANCE OF BUILDINGS OF NUCLEAR INSTALLATIONS (wP-59278)
Christoph Winkler, Stefan Woerlen, Stefan Thierfeldt, Frank Schartmann, Brenk Systemplanung (Germany)
Clearance of buildings of nuclear installations in Germany has to comply with general requirements laid down in Section 29
of the German Radiation Protection Ordinance (RPO; Strahlenschutzverordnung), clearance levels as stipulated in Table 1 of Annex
III RPO and technical guidance given in the technical standard DIN 25457. Clearance procedures are usually proposed by the
licensee and are made part of a decommissioning licence after appropriate review by the authorities. The clearance procedures consist
of a radiological characterisation of the various parts of the buildings, a decontamination step if necessary, followed by measurements
for checking the success of decontamination, and the actual decision measurements for demonstrating compliance with
clearance levels.
These three steps rely on various measurement methods, selected depending on the relevant radionuclides to be measured, like
sampling with subsequent gamma spectrometry (and if necessary separate evaluation of beta and alpha emitting nuclides), measurements
with surface contamination monitory and in situ gamma spectrometry. For a nuclear power plant, the number of samples
taken during this procedure can easily reach a few 10,000, while the number of single measurements can reach several 100,000 single
surface measurements and several 10,000 measurements with in situ gamma spectrometry. This large number of data together
with the correct interpretation according to the valid nuclide vector, the penetration depth of the contamination, the correction for
radioactive decay etc have to be managed, which is a error-prone process if carried out manually or with insufficient support by
customised software.
7) GEOSTATISTICAL METHODOLOGY FOR WASTE OPTIMIZATION
OF CONTAMINATED PREMISES (wP-59344)
Yvon Desnoyers, GEOVARIANCES; Didier Dubot, CEA/FAR/USLT/SPRE/SAS (France)
At the end of process equipment dismantling, the complete decontamination of nuclear facilities requires the radiological
assessment of residual activity levels of building structures. As stated by the IAEA: Segregation and characterization of contaminated
materials are the key elements of waste minimization.
From this point of view, the set up of an appropriate evaluation methodology is of prime importance. The radiological characterization
of contaminated premises can be divided into three steps. First, the most exhaustive facility analysis provides historical
and qualitative information. Then, a systematic (exhaustive or not) control of the radiation signal is performed by means of in situ
measurement methods such as surface control device combined with in situ gamma spectrometry. Besides, in order to assess the
contamination depth, samples can be collected at several locations within the premises and analysed. Combined with historical
information and radiation maps, such data improve and reinforce the preliminary waste zoning.
The relevance of the geostatistical methodology relies on the presence of a spatial continuity for radiological contamination.
In this case, geostatistics provides reliable methods for activity estimation, uncertainty quantification and risk analysis, which are
essential decision-making tools for decommissioning and dismantling projects of nuclear installations.
Besides, the geostatistical framework provides answers to several key issues that generally occur during the clean-up preparation
phase: How to optimise the investigation costs? How to deal with data quality issues? How to consistently take into account
auxiliary information such as historical inventory? How to integrate the remediation support into the modelling? How to quantify
uncertainties in the remediation costs while computing contaminated volumes?
8) DISCRIMINATION MONITORS FOR VARIOUS KINDS OF WASTE TO BE DOWN GRADED (wP-59117)
Susumu Naito, Syuji Yamamoto, Mikio Izumi, Masamichi Obata, Yukio Yoshimura,
Jiro Sakurai, Hitoshi Sakai, Toshiba Corporation (Japan)
During operation and maintenance, or decommissioning of nuclear power plant, various kind of waste should be treated, and
exposure control is also required. These wastes have a wide range of contamination, different composition of nuclides, and a different
shape, so each measurement instrument would be optimized for its use especially for very low level radioactivity measurement.
TOSHIBA provides appropriate equipment for any needs to discriminate the very low and non radioactive waste to save cost
of waste disposal, based on our original and innovative technology. For alpha emitting nuclides, we are ready to supply instruments
based on ionized particle measurement technology. For beta, gamma-emitting nuclides, we are ready to customize a shape of detector
based on our original plastic scintillation material. Some examples will be introduced.
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