Chemical decontamination of a reactor cooling system

With the successful decontamination of the reactor cooling system and its subsystems in a German nuclear power plant, Siempelkamp NIS Ingenieurgesellschaft mbH has demonstrated a new trendsetting procedure which took four years to develop.

The objective of the so-called ASDOC_D-MOD procedure is to detach radioactive con-tamination adhering to the inner system surfaces by adding specifically formulated chemical additives to the reactor cooling system and to subsequently remove them from the system with the help of ion exchangers.

This decreases the contamination significantly. With the new procedure the dose rate can be reduced on average by a factor of 85. Thus, the scheduled dismantling of the power plant systems   is significantly simplified.  With regard to the personnel carrying out the dismantling work, the new procedure focuses in particular on minimizing the exposure to radiation.

The ASDOC_D-MOD procedure was used for the current project. This procedure specifically considers materials that, when using conventional decontamination solutions, can be susceptible to corrosion and therefore, it prevents impairment of the functional safety and integrity of the power plant systems included in the decontamination process.

The modified ASCDOC_D-MOD procedure was developed and successfully tested at the technical center of Siempelkamp NIS. One of the goals for the procedure was to minimize chemical reactions between the decontamination solution and metallic materials so that a safety-relevant formation of hydrogen wouldn’t occur. For the current project the hydrogen levels stayed below or right at the detection limit.

“The development of the procedure was very complex and a highly technical and scientific challenge. 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,” says Dr. Aldo Weber, Spokesperson of the Management of Siempelkamp NIS Ingenieurgesellschaft mbH.