The 12th International Conference on Environmental ... - Events

Session 35-36 Abstracts
SESSION 35 - PANEL: THE UK OBJECTIVES AND STRATEGY FOR
THE MANAGEMENT OF ITS NUCLEAR LEGACY
ABSTRACTS NOT REQUIRED
SESSION 36 - D&D TECHNOLOGIES - PART 1 OF 2
1) OPTIONS FOR THE REMOVAL OF CONTAMINATED CONCRETE FROM THE BORE
OF THE WINDSCALE PILE CHIMNEY - 16083
Colin Campbell, Dr Jeremy Hunt, Sellafield Limited (UK);Stephen Hepworth, Sellafield Ltd (UK)
A legacy of the 1957 Windscale Pile reactor fire is the penetration of radioactive contamination into the internal surface concrete
of the chimney bore. Gamma imaging of Cs-137 has shown that the contamination is widespread throughout the chimney, and
core samples have shown that the contamination has penetrated to depths of around 5-25mm. <strong>The</strong> Pile chimney is 100m tall and
has an internal bore diameter of 15m. It is constructed of a hard concrete comprised of Whinstone aggregate. <strong>The</strong> baseline decommissioning
scheme is to remove approximately 5-25mm of the surface concrete from the entire bore of the chimney.
<strong>The</strong> technology baseline in 2006 was to remove layers of contaminated concrete by mechanical means using shavers or scabblers.
However, risks associated with mechanical technologies that may preclude their use include: the ability of mechanical devices
to remove the hard concrete; clogging of the devices due to wet concrete; and deployment of the delivery systems. This paper discusses
the options under consideration to reduce the risks associated with the removal of the contaminated concrete through application
of alternative techniques.
<strong>The</strong> present baseline technology is high pressure water jetting technique. Demonstrations have shown that this technology can
successfully remove concrete without significant reaction forces. However, an inherent problem with this technology is the production
of secondary liquid effluent waste, which would need to be treated by an appropriate conditioning process. To address the secondary
effluent waste issue, technologies that produce little or no secondary waste have been considered. <strong>The</strong> technologies that
have been considered are laser scabbling, microwave scabbling and nitrogen jet blasting. <strong>The</strong> paper discusses each technique in
turn, highlighting their advantages and disadvantages. <strong>The</strong> results of an in-active laser scabbling and high pressure liquid nitrogen
jetting trial are presented. <strong>The</strong> paper concludes with a discussion of the merits of each technology in support of the future strategy
for concrete removal.
2) DECOMMISSIONG OF ACTIVE EFFLUENT GANTRIES - AWE ALDERMASTON - 16099
Graham Rogers, NSG Environmental Ltd (UK)
Decommissioning of Active Effluent Gantries AWE Aldermaston
BNS Nuclear Services (formerly Alstec) together with NSG Environmental Ltd have successfully undertaken the decommissioning
and removal of a redundant active effluent gantry system operated since the 1950s, however in a deteriorating condition,
at AWE Aldermaston. <strong>The</strong> 18 month, (30,000 man hour) project due for completion in March 2009, has been undertaken to programme
and without any lost time incidents / accidents.
<strong>The</strong> scope of work included:
• the design and erection of a purpose built size reduction and HHISO loading facility including HEPA filtered ventilation
system
• BPM and Environmental Impact Assessments
• Generation of novel methodology and Safe Systems of Work for the containedremoval of 1300metres of potentially ILW
stainless steel pipework at height
• Size reduction, assay and segregation of over 70 te steel, with approx 30% being consigned as free release for recycling
• Sampling and DQA assessments for the leveling and removal of 1800 m3 of earth
3) VERIFICATION TEST OF CLEARANCE AUTOMATIC LASER INSPECTION SYSTEM FOR SURFACE
CONTAMINATION MEASUREMENT - 16109
Michiya Sasaki, Haruyuki Ogino, Takeshi Ichiji, Takatoshi Hattori,
Central Research Institute of Electric Power Industry (Japan)
Recently, the clearance automatic laser inspection system (CLALIS) has been developed for clearance measurement of metal
scraps and concrete debris. It utilizes three-dimensional laser scanning, gamma-ray measurement and Monte Carlo calculation, and
its outstanding detection ability has been verified. In Japan, when an object is removed from a radiation-controlled area, the activity
level must be lower than the surface contamination density standard of 4 Bq/cm2 for beta and gamma emitters, which is onetenth
of the surface contamination density limit. According to the clearance inspection report published by the Nuclear Safety Commission
of Japan, the activity level of waste must be compared with not only the clearance level but also the surface contamination
density standard for clearance inspection. To demonstrate that CLALIS can also be used for the measurement of surface contamination,
a verification test was carried out using actual metal waste samples of various shapes, sizes and activity levels at the Kashiwazaki-Kariwa
Nuclear Power Station of Tokyo Electric Power Company. As a result, it was clarified that CLALIS gives a conservative
value for surface contamination compared with the conventional GM survey meter measurement since the activities of metal
waste samples were estimated using the total count rate, a fixed average surface area of 100 cm2 and the conservative source position
assumed in the Monte Carlo calculation for the calibration factor. In a nuclear power plant, the actual judgment of whether an
object can removed from a radiation-controlled area is based on whether the result of surface contamination measurement is lower
than the detection limit, which is significantly lower than 4 Bq/cm2. According to this criterion, CLALIS provides an almost identical
judgment to the GM survey meter, which means that CLALIS can be used as a rational clearance monitor to carry out clearance
level and surface contamination inspections in a single radiation measurement. <strong>The</strong> prospective detection limit for CLALIS at
nuclear power plants is also discussed and compared with that for the conventional surface contamination monitors
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