Nuclear Decommissioning Services Ltd

NDSL has achieved a series of successes with innovative solutions.

Commercial incineration of alkali metals.

This has been used for the disposal of sodium coupons and bulk sodium from the Janetstown facility near Dounreay. Very substantial cost-savings were achieved over alternative techniques, such as destruction through reaction with water. Incineration at an HTI is likely to be used again for the disposal of sodium and sodium-potassium alloys from several other sources, such as redundant alkali metals from the Joint Research Centre of the EU Commission at Ispra. For further information please see Sodium Coupons.

Deployment of commercial ROVs (Brokks) on a range of decommissioning projects.

NDSL suggested the use for Brokks for decommissioning the D8550 Plutonium Criticality Facility and the D1217 PIE Cells; Brokks have not been used at Dounreay before and we are responsible for their introduction to site. Brokks are widely used elsewhere in the nuclear industry and are small, commercially available, remotely operated demolition machines that can be equipped with a variety of tooling. The one for D85550 is for wall demolition and also for the steel criticality cell size reduction. In D1217 a Brokk will be used to cut up the benches in cells with high contamination and radiation levels.

Design of simple and cost effective survey device for the Dounreay Materials Test Reactor

At DMTR, an internal survey was necessary because there was insufficient information regarding the internal state of the reactor vessel. NDSL suggested a probe and a simple camera with lights on the end of drain rods inserted via the heavy water pipework into the reactor. For less than £10K NDSL gathered both good pictures of the reactor tank and also obtained excellent radiological dose data.

Tallow - a fuel particle recovery system

A survey of the D9814 pond within Building D1251 revealed a number of radiation hot-spots on the pond floor that were thought to be composed of small particles of irradiated fuel. These needed to be removed before decommissioning could proceed, and NDSL was asked to carry out an option study, produce the associated Safety and Environment documentation, and propose a detailed methodology. No doubt a high-tech, expensive and complicated mechanical solution to the problem could have been found but by borrowing the technology from sailing ships with the lead line a cheap but effective solution was found: trials using a piece of tallow showed that this material will satisfactorily capture swarf, sand and stainless steel balls up to 25 millimetres in size from the bottom of a tank full of water. Preparations for full implementation are now underway.

Use of ROVs for survey in D1204 and DFR.

At Dounreay, pictures from thereactor vault were required; NDSL proposed to lower an ROV with camera and gamma probe down an aperture from the charge floor to the walkway under the NaK filled coolant circuits. Excellent photos and useful radiological data were obtained. The photograph below shows a more sophisticated ROV prepared for a D1204 survey and fitted with two cameras, a gamma probe, a laser distance measurer and a highly dextrous arm.

Particle discrimination trial.

NDSL was asked to find a way of discriminating between particles and naturally occurring radiation on the seabed. We decided that it was easier to move the source and keep the probe static. We used three cattle troughs with different depths of sand to simulate the depth of the particle in the seabed and had an electric train carrying natural and man made sources under the tanks. By placing different instruments above the sand, which could have a few inches of water over it, we could mock up the right scenario, and carry out an easily repeatable trial.