Siempelkamp develops primary circuit clean-up process

A new process for the chemical decontamination of the reactor cooling system and subsystems in nuclear power plants has been developed by Germany's Siempelkamp NIS Ingenieurgesellschaft mbH. The procedure - which took four years to develop - has been successfully demonstrated in a German nuclear power plant.

A new process for the chemical decontamination of the reactor cooling system and subsystems in nuclear power plants has been developed by Germany's Siempelkamp NIS Ingenieurgesellschaft mbH. The procedure - which took four years to develop - has been successfully demonstrated in a German nuclear power plant.

ASDOC_M-MOD test equipment (Image: Siempelkamp)

During the normal operation of a nuclear power plant, protective oxide coatings are formed on the inner surfaces of the pipelines and components of the primary circuit. Radionuclides are incorporated into the oxide matrix.

Siempelkamp said the aim of its Advanced System Decontamination by Oxidising Chemistry (ASDOC) procedure is to detached radioactive contamination adhering to the inner system surfaces by adding specifically formulated chemical additives. These chemicals are injected into the reactor primary system via the plant's dosing installations. The process solutions are circulated through the primary system by normal reactor system operation. Dissolved ions and nuclides from the primary system's oxide layers are removed by means of the plant's ion exchange water clean-up system.

The modified ASDOC_D-MOD procedure, the company added, decreases contamination significantly, with the dose rate being reduced on average by a factor of 85. This greatly minimises the exposure to radiation of workers and simplifies the schedule for dismantling power plant systems. Contamination of metallic piping and components is also sufficiently reduced for it to be freely recycled or melted.

In a demonstration at an undisclosed German nuclear power plant, the procedure specifically took into consideration materials that, when using conventional decontamination solutions, can be susceptible to corrosion. This therefore prevented impairment of the functional safety and integrity of the power plant systems included in the decontamination process.

The ASDOC_D-MOD procedure was developed and tested at the technical centre of Siempelkamp NIS. It said one of the objectives of the procedure is to minimise chemical reactions between the decontamination solution and metallic materials so that a safety-relevant formation of hydrogen will not occur.

"The development of the procedure was very complex and a highly technical and scientific challenge," said Siempelkamp NIS spokesman Aldo Weber. "We suffered some setbacks until we arrived at the point where we could successfully demonstrate the practical use of it, which to date we have done twice."

Researched and written
by World Nuclear News