Nuvia: experts in the radiological waste characterisation and remediation

The least favoured option is disposal as this can be a costly process and occupies a finite resource. In the past, disposal of wastes to the UK Low Level Waste Repository (LLWR) have required minimal characterisation and frequently materials were consigned by default, hence needlessly occupying space. A change in emphasis at LLWR has now driven the requirement to fully characterise materials to minimise waste going to the national repository, and make use of other disposal facilities that have opened to accept the lower end of the LLW activity range.

Gamma-based surface mapping

Groundhog’s range of radiation monitoring tools and services encompass all gamma-emitting contamination possible to be detected in the field.

Using portable or vehicle mounted detectors, Groundhog provides a high density of survey measurements, automatically records all data, uses GIS to aid analysis and is suitable for areas of all sizes.

With a range of options available, particles of radioactive material the size of a grain of sand or smaller can be detected, with survey results used to support remediation strategies based on in-situ selective sentencing of waste.

Bulk monitoring technologies

Technologies used to assay materials need to be capable of measuring to very low levels of radioactivity in accordance with UK legislation. In addition, techniques used to assess bulk materials must be capable of giving accurate results, which, if challenged by the regulator, or other stakeholders, are defensible, and fully traceable back to national standards. Furthermore, contractors are required to keep to tight deadlines as the costs associated with remediation are high; assay technologies therefore need to be rapid so that downtime is minimal.

NUVIA’s Gamma Excavation Monitor (GEM) system to enable rapid screening of excavated materials

Nuvia has developed a range of gamma based systems for monitoring wastes. The High Resolution Assay Monitor (HiRAM), Gamma Excavation Monitor (GEM) and the new Information Management System (IMS) to track waste and support transport off site are three tools to support and enhance bulk monitoring systems. The GEM System is fitted with a low resolution gamma spectrometer which is used to measure activity in mechanical excavator buckets and is capable of real-time assay of excavated materials during clearance works. The measured results can then be related to a radionuclide fingerprint, i.e. radionuclide ratios for a particular operational area, to determine the specific activity (Bq/g) of the material, which may be soil, concrete, brick etc. The presence of the bucket, placed over the GEM, triggers the proximity switch to initiate the counting routine. At the end of the count time (typically 10 seconds), a coloured light is illuminated to indicate the determined material category. At all times the display lights can be seen by the mechanical digger operator, and the data for each bucket load is automatically stored, and can be downloaded onto a laptop. The system, therefore, eliminates the need for operatives to be near the moving bucket thereby improving the safety aspects of the process and increasing throughput.

The HiRAM comprises a cabin and turntable mounted on a trailer. High Resolution Gamma Spectrometry (HRGS) equipment is installed in the cabin, which is powered at 110 volts by a petrol-fuelled generator, or can be run from a mains supply using a step-down transformer. The turntable is operated from inside the cabin, which is equipped with lighting, heating and storage space for safety documents, user manuals and maintenance records.

The Information Management System (IMS) helps to speed up the data handling process, improve quality controls and reduce transcription errors. To track waste bags and manage the data, Nuvia designed and developed the IMS, comprising a database and associated software. Bags generated in remediation zones have barcode labels applied, and upon receipt into the waste assay facility, tablet devices, with barcode reader technology, are used to scan and log the bags into the database. The tablets are also used to interrogate the IMS, enabling the operators to locate bags and confirm their status.

The NUVIA designed Information Management System (IMS) to track waste, speed up the data handling process, improve quality controls and reduce transcription errors.

HRGS offers the advantage of being able to measure and quantify several individual radionuclides at the same time. Easily measureable radionuclides (eg Cs-137, Co-60, Eu-152) are used to factor in other radionuclides from a predetermined fingerprint.

Packaged materials (eg 200-litre drums, 1m3 bags, Dolav boxes) are rotated on the turntable, which reduces the effects of heterogeneity by averaging over the complete lateral surface of the package. The HRGS system is fully automated so that the operator simply keys in, when prompted on the laptop, physical dimensions such as waste package weight, fill height and material composition, and this information is used to generate a unique calibration for the package under investigation. At the end of a short count time (5-15 minutes) a spreadsheet of results is automatically generated, with the fingerprint factored in and the material category determined.  Production of this real-time data enables timely decisions to be made and materials to be transported out of the working area for reuse and/or disposal.

1m3 bags Assayed and processed by NUVIA’s monitoring instruments.

Screening technologies

Conveyor-mounted gamma monitors have for many years been successfully used in the coal industry for on-line monitoring of the ash content of coal loads. The technique utilises combined natural gross gamma radiation and on-line mass measurements to provide an estimate of the ash content of raw mined coal. Nuvia have deployed a similar system, the Conveyor Active Particle System (CAPS) which utilises a caesium iodide (CsI) detector, mounted under a conveyor belt and connected to an electronic control box. The 150x75mm CsI crystal and photomultiplier are housed in a compact casing and installed on the underside of the conveyor, with the long axis of the crystal orientated to line up with the centre line of the conveyor belt.

The system is designed to alarm when the count per second (cps) rate, detected by the sensor, exceeds a set alarm level. The cps rate may be smoothed over a number of seconds thereby providing the average cps. On top of the electronic enclosure is mounted a combined red flashing beacon and audible alarm. When an alarm condition is detected, both are activated. The alarm may be muted at any time, but the alarm beacon will only reset when the alarm condition is no longer present.

In the event of an alarm caused by the average cps rising above the alarm trip level, the sounder and the flashing light are activated, and the highest counts value, date and time of the alarm are stored in a temporary buffer. When the alarm is reset, information in the temporary buffer is written to an alarm log file, held in the battery-backed RAM of the processor. The alarm log file holds the last 600 alarms, and data may be downloaded from the control box to a laptop.

Continued development

Nuvia has built and deployed a suite of monitoring equipment to support operational, decommissioning and remediation projects, both in the nuclear and NORM generating industries. The technologies are subject to continued development to keep pace with the requirements of customers and changes in UK legislation for the management of wastes. In addition, flexibility in the deployment of the equipment is required to accommodate a wide variety of scenarios.

Applications / Projects

• Winfrith rubble stockpiles and Olen, Belgium mound
• Gamma depth profiles – gross gamma and spectral
• Drain surveys using a sodium iodide detector
• Tank survey using a sodium iodide detector mounted on an ROV
• Combined Groundhog and HRGS surveys to support delicensing
• HRGS of rooms for clearance
• Conveyor belt detector installed at the Olympic Park
• BEPO dose-rate survey of fuel and cooling channels
• Waste storage vault, Aktau BN-350 reactor Kazakhstan
• Remediation of the Harwell Liquid Effluent Treatment Plant (LETP)

CASE STUDY —LETP (Liquid Effluent Treatment Plant) Remediation, Harwell

CLIENT — Magnox

• Complete land remediation and characterisation of radiologically contaminated land at the site of a former LETP and restoration of the land to green field condition
• Excavating, Assaying and Processing 555 x 1m3 Waste Bags per week
• Over 60,000 x 1m3 bags to be Assayed and processed in total
• Tracking system for every waste bag
• Extensive and stringent standards prescribed by the ONR and the EA (UK regulators)

Find out more about Nuvia's radiological waste characterisation and remediation processes at www.nuvia.co.uk

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