Clearance of Buildings of NPP Wu¨rgassen (Germany) Using an Innovative Clearance Concept

Abstract

The nuclear power plant Wu¨rgassen in Germany entered into decommissioning in 1995. The project has currently advanced to the clearance of the buildings. Clearance of buildings has commenced in 2007 with establishing the clearance procedure in pilot rooms. It has entered the “productive” phase in 2010 and will last until about 2014. In 2007, Brenk Systemplanung has been commissioned by E.ON / NPP Wu¨rgassen to perform clearance of the pilot rooms in the turbine building. It has been one of the goals of this work to establish an innovative clearance procedure which would not rely on 100% surface measurements but which should be based on the use of in situ gamma spectrometry and the application of approaches to minimise the number of clearance measurements. In 2010 and 2011 Brenk Systemplanung has been commissioned by E.ON / NPP Wu¨rgassen to perform clearance of rooms with partly considerably higher contamination levels in other buildings. Central points of the concept for clearance of buildings which is presented in this paper were the establishment of averaging areas of up to 10 m2, which is an ideal size for the use of in situ gamma spectrometry, and the application of statistical methods, which allow an efficient performance of the clearance measurements. As a first step the measurement instrumentation necessary for the performance of clearance measurements had to be qualified. The innovative concept was first tested and implemented in the pilot rooms and has now been used also in various other parts of the NPP Wu¨rgassen. The procedure which has been established by Brenk Systemplanung for NPP Wu¨rgassen allows rapid measurements making best use of the averaging area and measurement area of collimated in situ gamma spectrometry and minimising the number of single measurements in comparison to other clearance procedures for nuclear installations of similar size. The paper highlights the relevant approaches and the conceptual differences and innovations.