Development of a Computer System for Support and Documentation of Clearance of Buildings of Nuclear Installations

Clearance of buildings of nuclear installations in Germany has to comply with general requirements laid down in Section 29 of the German Radiation Protection Ordinance (RPO; Strahlenschutzverordnung), clearance levels as stipulated in Table 1 of Annex III RPO and technical guidance given in the technical standard DIN 25457. Clearance procedures are usually proposed by the licensee and are made part of a decommissioning licence after appropriate review by the authorities. The clearance procedures consist of a radiological characterisation of the various parts of the buildings, a decontamination step if necessary, followed by measurements for checking the success of decontamination, and the actual decision measurements for demonstrating compliance with clearance levels. These three steps rely on various measurement methods, selected depending on the relevant radionuclides to be measured, like sampling with subsequent gamma spectrometry (and if necessary separate evaluation of beta and alpha emitting nuclides), measurements with surface contamination monitory and in situ gamma spectrometry. For a nuclear power plant, the number of samples taken during this procedure can easily reach a few 10,000, while the number of single measurements can reach several 100,000 single surface measurements and several 10,000 measurements with in situ gamma spectrometry. This large number of data together with the correct interpretation according to the valid nuclide vector, the penetration depth of the contamination, the correction for radioactive decay etc have to be managed, which is a error-prone process if carried out manually or with insufficient support by customised software. For this reason, a versatile software tool has been developed by Brenk Systemplanung GmbH that supports the operator in all aspects of clearance of buildings, based on the extensive experience with various clearance procedures in nuclear power plants that Brenk Systemplanung has carried out in the past. Many steps of the data evaluation and report generation during the clearance process outlined above can now be carried out automatically. This includes the time-consuming steps of: • support during the acquisition of the geometry data for a room, • generation of the lists for sampling and measurements, • automatic acquisition of the measurement and sampling results from the instruments, • evaluation of compliance with clearance levels, both for measurements on the entire surface and for statistically distributed measurements or samples, • generation of the documentation on clearance, • storage of all data, generation of nuclide vectors, correction for radioactive decay, connection with photo, CAD drawings etc.