ÎIn this stage the following activities were executed:

• Study regarding the methodology of establishing the requirements and constraints for decontamination, in view of nuclear installations decommissioning, as well as the radwastes management generated by decontamination and nuclear installations decommissioning.
• Study regarding evolution of decontaminating and radwastes management since nuclear installations decommissioning.
• Comparative study regarding the decontaminating methods, applicable to nuclear installations decommissioning

IAEA defines in IAEA – TECDOC – 1478, “Selection of decommissioning strategies: Issues and factors”, Vienna, 2005 three basic decommissioning strategies:

• immediate decommissioning;
• delayed decommissioning;
• entombment decommissioning.

 Following the assessment of requirements and dominant factors, the use of one of the above mentioned strategies can be indicated. Also, depending on constraints and important factors happening in practice, the feasible strategy can be determined by combining the decommissioning strategies or excluding one or another.

 Decommissioning the nuclear facilities in appropriate conditions depends on process careful and organized scheduling, by adequate identification of objectives. The final status derives from the objectives of the organization responsible for the decommissioning activity performance according to the requirements of the regulatory body and other qualified authorities.

 Once the organization responsible for performing the decommissioning activity sets the decommissioning strategy, the decommissioning conceptual plan is issued. The decommissioning conceptual plan has to include: a general description of the nuclear facility, a preliminary assessment regarding the nuclear safety, a general description of the decommissioning strategy, the arguments for the selected strategy, the financial arrangements set for performing the decommissioning.

 Figure 3  show the wastes flow considered for issuing the Plan for Radioactive Wastes Management.

The dimensions of such a plan, its content and the detail level depend on the complexity and hazards of the nuclear facility and on national regulations. In case of decommissioning a nuclear power plant, for optimizing the decommissioning integrated concept, the Decontamination and Management Plans for Radioactive wastes will be a part of the Decommissioning Plan.

 Once the date of the final shutdown is known, the organization responsible for decommissioning must initiate detailed studies and finalize the decommissioning proposals. On this line a management system will be developed and implemented including all the general means of planning, leading, achievement and assessment of decommissioning activities, elaborating the Management Plan which will be part of the Decommissioning Plan.

 Nuclear facility decontamination which is possible to be foreseen from the facility operational period will continue after the operation end with major implication on in depth contaminate materials, equipments and structures. The Decontamination Plan, considered in the Decommissioning Plan, leads function of contamination degree and function of resulting type of waste to radioactive waste volumes determination and classification, necessary to be processed and disposed.

 Then, the detailed decommissioning plan must be analyzed and approved by the regulatory body. The detailed decommissioning plan may need amendments or further processing as the decommissioning advances and even the regulatory body involvement.

Radioactive Waste Management, Decontamination and Decommissioning Integrated Plan assure that are met decommissioning conditions as unconditional release of the site from authorization and all radioactive waste disposal under safety conditions.

For optimum strategies and techniques selection we consider like an integrated assembly the processes of decontamination, decommissioning and the radioactive waste management, in accordance with AIEA most recently interpretation. In this scope, the nuclear field specialists must consider all the aspects involved in this process to determine the most adequate strategy. It is, also, very important to apply the principles of radioactive waste management in the release from nuclear control process of materials resulting from nuclear facilities decontamination and decommissioning activities.

The minimum information that the detailed decommissioning plan must contain are listed in table 1.

Nuclear facility decontamination

The decontamination process during the decommissioning aims first the reduction of radioactivity and second, the clearance of materials. The aggressive decontamination methods can be applied for the un-operational facilities.

The decontamination process should be conducted on an analysis upon the type of facility to be treated, the type of contamination and others constraints:

• The decommissioning strategy selected
• The available time for decontamination
• The available funds
• The exposure level of the workers
• Airborne and liquid emissions, and its radiological impact upon environment and public
• Industrial safety requirements
• The availability of waste management options, as well as the disposal options
• The available work labor
• The reuse intentions for other purposes
• Forta de munca disponibila
• Intentia de reutilizare a cladirilor pentru alte scopuri

Based on these constraints, the optimal decontamination method should be based on a multi-criteria analysis, including the economical benefits.

The decontamination method depends entirely on the decommissioning strategy: in case of a delayed decommissioning, the level of radiations will be reduced due the natural depreciation of the facility; on the other hand, for a long-term safe closing of the plant, the corrosion of metal layers or of the concrete surface will reduce the effectiveness of the decontamination process.

Function of structure which must be decontaminated, it can be used varied methods as shown in the  table2.

In the next stages of the project, will be analyzed different methods for decontamination of decommissioned nuclear facilities, especially those that are suitable for the CANDU plants.

For the documentation of decontamination methods it will be used a softwar modeling tool, ProVision Enterprise 6.0.1,  a last generation solution from Metastorm, leader in the industry of process modeling software applications.

Using the methodology and software tool presented in the Study, it will be realized the modeling of the contamination process for materials, structures and equipments, specific to a nuclear plant.

ProVision allows to identify and define constrainta regarding the activitaties’duration, process costs, and other parameters that can be optimzed. 

The process optimization allows the analysis of diferent decontamination methods, based on the structures’ type, the type and amount of contamination, available funds, available treatement period and the final purpose (recycle/reuse, disposal, etc.).

For achieving those goals it will be used a simulation software tool, ProVision 6.0.1 that use the Monte Carlo method.

The processes’ optimization requires the next steps:

• Defining the processes
• Defining the processes’ parameters regarding time
• Defining the processes’parameters regarding the costs of the activities
• Simulationof the processes using ProVision
• Generating reports based on simulation results, in order to sustain the optimal variant of process. 

Using this methodology, it will be determined the effectiveness of different decontamination methods, in case of superficial or deep contamination, by modeling the processes and allocating the necessary resources, by establishing of the constraints and the expected results from a treatement process.

During the project it will be defined specific methods for treatement and it will be detemined the optimal variant that allows the recovery of valuable materials.