Serco Technical and Assurance Services has many years of experience relating to shielding design and assessment within the nuclear power industry. Our assessment work on reactor shield design has included the determination of radiological dose-rates, nuclear heating, radiation damage to materials and instrument response. Other assessment experience includes the design of transport flasks, fuel storage facilities (including dry-stores), re-processing plant and the shielding of nuclear waste.

In recent years, this expertise has also been applied to the design and operational analysis of Food Irradiation Facilities.

Picture Courtesy of MDS Nordion

Food Irradiation Process

Food irradiation is a growing international business. A typical process involves the use of high-energy gamma radiation, given off by a radioactive source, to kill bacteria in the food and hence preserve it. These high-energy gamma rays can penetrate products such as food to a depth of several feet. Hence the irradiation takes place in a chamber shielded by massive concrete walls, in order to protect workers from the gamma rays. The route into the chamber for the product is through a labyrinth, which provides further protection from radiation escaping from the chamber.

The main issues for Food Irradiation Facilities are:

• How much shielding is required to protect workers from the radiation
• How to ensure the product receives the correct radiation dose

Serco Technical and Assurance Services can carry out assessments on the Shielding Design and Operational Analysis of the plant

Shielding Design Assessment

Serco Technical and Assurance Services's experience includes the full shielding design assessment of Food Irradiation Facilities.

• Analyses include complete dose-rate assessments outside the shielded chamber under operational conditions. Direct radiation penetrating the bulk shielding of the walls and roof, and radiation streaming through labyrinths are all included
• Analyses also include dose-rate assessments inside the chamber under shutdown conditions, when the radioactive source is moved for safe storag

Operational Analysis Assessment

The radiation Dose Uptake by the Product can also be determined. The product to be irradiated is brought into the chamber and exposed to gamma rays for a defined period of time, as it travels past the radioactive source.

• Analyses can be carried out to determine the total dose absorbed by the product during irradiation
• Analyses can also determine the uniformity of the dose uptake by the product at various positions and for various designs of source

The Software

Serco Technical and Assurance Services' ANSWERS software codes MCBEND and RANKERN are used for these assessments.

MCBEND is a powerful Monte Carlo code used for full 3D radiation transport analysis.

RANKERN provides a rapid Point-Kernel method for the design and assessment of gamma-ray shielding and is particularly useful for labyrinths and streaming requirements.

Benefits

• Optimisation of Shielding Thickness to reduce manufacturing costs
• Optimisation of Source Design and Product Trolley speed to enhance Operational Productivity by:
  • ensuring the product receives the correct amount of dose;
  • the dose is uniformly distributed

What our customers say…

'Many thanks for your prompt response to our requests'

'As always, my experience with ANSWERS was wonderful: you really know how to treat your clients!'

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