This project aims at demonstrating explosive dismantling techniques on the biological shield of the nuclear power plant Niederaichbach (KKN), which was operated from 1972 to 1974 and is foreseen to be completely removed. The radioactive inventory of the shield is estimated in the order of 3.7E9 Bq (0.1 Ci). The level of activation is estimated to be in the order of 10 Bq/g, and the associated dose rates in the order of 10 micro Sv/h. Within this contract, blast peeling of the activated concrete from a 30C sector of the biological shield will be performed.
This technique will be applied as one of 2 main techniques (hydraulic hammer besides blast peeling) for the dismantling of the whole biological shield of KKN; for this, the licensing authorities have already given their agreement. This demonstration project will be conducted according to the guidelines of the ongoing total dismantling of KKN.
In particular, the generation of specific data on costs, working hours and job doses as well as on the amount of created secondary waste is considered as an important objective of this project. This will facilitate the application of this technology and acceptance from the safety point of view in future large-scale decommissioning operations.
The project is a follow-up of small-scale work on inactive samples performed jointly under contracts FI1D0011 and FI1D0012.
The work programme will be implemented jointly by three main contractors: Battelle Europe eV/Frankfurt (BE), acting as coordinator, Noell/Wurzburg (Noell) and Siemens/KWU (Siemens), as well as Stangenberg, Schnellenbach & Partner (SSP) as sub-contractor.
Further cooperation is foreseen with TUV Bayern for the assessment of air filter systems.
This project aims at demonstrating explosive dismantling techniques on the biological shield of the nuclear power plant Niederaichbach (KKN). The bore hole patterns for 3 selected sections were determined together with the layout of the explosive charges. Core drilling and full volume drilling will be performed respectively, depending on the presence of reinforcement steel. Finite element models have been developed to calculate the structural response of the reactor building and auxiliary building using personal computer (PC) programmes. A multicompartment blast model was developed to calculate the blast wave loading in various regions of the containment. The quasistatic pressure rise in the containment is calculated to be 1,5 mbar for a 15 kg blast which is far below critical limits for transient air pressure wave. However, conservative structural response calculations show that a 15 kg blast may exhaust the safety values for vibrational excitation for industrial buildings in use. Further calculations show that the maximum amount of explosive charge per blast is restricted by the requirement of structural integrity of blast area installations, eg adjustable working platform. The effect of the blast wave pressure on the working platform limits the explosive charge to about 1,8 kg for long vertical holes and 2,1 kg for short horizontal holes. Protective devices may allow these values to be increased.
1. Preparatory planning and design work for on-site equipment and regulatory requirements (BE, Noell)
1.1. Layout of blasting patterns and of bore holes charging, according to the area of application (BE)
1.2. Design of blasting schemes according to the area of application (BE)
1.3. Definition of blasting area subcontainments for the retention of dust, including associated filter systems (Noell, BE)
2. Demonstration blasting on the KKN shield by manual handling (BE, Noell)
2.1. Site preparation for the installation of tools and measuring devices (BE, Noell)
2.2. Assessment and implementation of auxiliary techniques such as bore hole drilling, cutting of the reinforcement by hydraulic shears, use of a hydraulic ram (Noell)
2.3. Main operation and concrete removal, consisting of a sequence of about 10 individual blasts, including pre- and post-blast working (BE, Noell)
2.4. Assessment of blasting performance, with respect to predetermined criteria such as concrete removal rate, safety aspects, integrated doses and generation of secondary waste (BE, Noell)
3. Assessment of dust retention by industrial filter systems with respect to efficiency and safety of handling (Noell, BE)
4. Assessment of structural safety (BE, Noell)
4.1. Modelling of shield response to the blast transient loading (BE)
4.2. Modelling of building response by simple models and comparison to pre-evaluations at selected safety-relevant locations (BE)
4.3. Safety control for compliance with limiting values by test accompanying measurements (BE, Noell)
5. Final assessment of the blasting procedure (BE, Noell)
5.1. Technical feasibility and reliability (BE, Noell)
5.2. Compliance with safety regulations concerning radiation protection, radioactivity release, contamination/decontamination and structural safety (BE, Noell)
5.3. Comparison with other concrete dismantling techniques, such as sawing by diamond or wire saw, core drilling, possibly combined with sawing, high pressure water jet with abrasives (Noell, BE)
5.4. Setting up of guidelines and rules for general application of the bore hole blasting technique to other shield structure, and of cost estimates (BE, Noell)
6. Related investigations of general applicability to various types of nuclear power plants (BE, Siemens-KWU, SSP).
6.1. Building response by advanced modelling for the reactor building (BE, SSP)
6.2. Local damage, prediction of cracks and material failure (BE, Siemens)
6.3. Blast loading limits with regard to the integrity of light structures in close vicinity to the charge location (BE)
7. Generation of specific data on costs, radioactive job doses, working time and secondary waste arisings, derived from the execution of items 2 and 6.
Funding SchemeCSC - Cost-sharing contracts