PAKISTAN NUCLEAR REGULATORY AUTHORITY P.O 1912, G-8/1,

Transcription

1 CNS-WM February, 2012 A Case Study for Safety Assessment of Pre-Disposal Waste Management Using SAFRAN Tool PAKISTAN NUCLEAR REGULATORY AUTHORITY P.O Box 1912, G-8/ /1, Mauve Area, Islamabad

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3 Table of Content 1. Executive Summary Background Introduction Description Results and Discussion Normal Situation Accident Situation Conclusion Reference

4 1. Executive Summary The purpose of this report is to present the work done on case study of predisposal management using the SAFRAN tool to develop SAFRAN tool operational skills. The sample problem for case study of safety assessment of predisposal management is based on SAFRAN tutorials download from SAFRAN website [1]. All the inputs parameters are selected from these tutorials so that output can be verified. By using the SAFRAN, assessment of management can be addressed in structured way. The results obtained can be used in the safety assessment of future submissions from licensee such as safety analysis reports of pre-disposal radioactive management facility for licensing and/or regulatory decision purposes. 1

5 2. Background The SAFRAN (Safety Assessment Framework) is user-friendly software and addresses all pre-disposal management activities. The main functions of SAFRAN are as follow [2]: To define facilities for storing or processing radioactive including their relevant design features. To define streams including all relevant radiological and nonradiological properties and their changes through the management activities. To define relevant requirements from the regulatory framework (criteria, endpoints, other requirements). To perform safety assessments for all steps of pre-disposal management. To perform calculations for quantitative analysis. To report the decision path and documenting the safety assessment justification. To trace changes in the safety assessment and of review comments to facilitate the development and review of safety assessments. To support the use of safety assessment results in various areas (e.g. sitting of facilities, definition of requirements for safety functions, operational limits and conditions, operational procedures). 3. Introduction [2] The purpose of this report is to present the work done as part of capacity building and gain the knowledge on how to generate a SAFRAN model for a sample case and further use the the safety assessment of actual site. To perform such an assessment we need to first define the site s configuration into the SAFRAN tool; consisting of facilities, rooms within those facilities and then distinct areas within those rooms along with properties of each room, area and management activity. These parameters include external dose rate, activity concentration in air, nuclides, etc. The Waste Management Activity carried out within each area is then defined, along with the associated output. 2

6 The streams are then defined, in a way that shows the properties at each stage through the different steps of processing, storing and clearing of those s. For example there may be reduction factors for volume or activity concentration of the, e.g. by sorting or compaction. The regulatory framework is then defined into the model, using national and/or IAEA frameworks as relevant. Examples of the regulatory criteria may include dose limits to workers and the public for normal and accidental situations. Safety assessment is required for both normal operations and accident conditions. The model is developed by defining: The links to the regulatory framework, The purpose of the safety assessment, e.g. compliance with regulatory criteria, The scope of the assessment (defining which areas need to be considered) and what level of assessment is to be carried out, The assessment approach (this may include Potential Initiating Events, screening of hazards, compliance with safety requirements), The endpoints, e.g. dose to the worker and public, The scenarios where those end points could occur, their properties, probabilities etc, The impacts that may result. The safety assessment is then carried out using the SAFCALC tool, and the results imported back into the SAFRAN tool. Finally a block of management activities (i.e. a process) that can be reused for other streams where relevant is defined to reduce the requirement for re-entering information. It also covers clearance of by comparing activity concentrations in the components against IAEA s and user defined clearance criteria [2]. 4. Description For SAFRAN calculation the general structure for site should be defined. Here a new site is described which consist of two facilities, a processing facility and a storage facility. The processing facility has two rooms; one for sorting and other for 3

7 compaction and packaging of the. And the storage facility has one room; drum storage room. And these rooms have associated areas and management activities. An overview of these facilities, rooms, areas and management activities is shown in table 1. Table 1: Overview of the facilities, rooms, areas and management activities [2] Facility Room Area Waste Management activity Outputs of management activity Processing facility Storage facility Drum storage room Sorting room Sorting area Sorting Compactable Non-Compactable Compaction Compaction Compaction Compacted and packaging room area Packaging area Packaging Packaged Drum storage area Storing of packaged Stored As described in table 1, there are different facilities, rooms, areas and management activities. These facilities, rooms, areas and management activities have specific properties and these properties are defined in table 2. Physical and safety elements should be defined clearly. Here arbitrary numerical values were considered for the case study. 4

8 Table 2: Specification of properties for rooms, areas and management activities [2] Processing facility Parameter Value Sorting room Concentration in air Co E-02 Bq/m 3 Sorting (WM activity) Concentration in air Cs E-02 Bq/m 3 External dose rate 6E-07 Sv/h Volume, mass and total 80% of initial volume, activity of compactable mass and activity Volume, mass and total activity of non-compactable 20% of initial volume, mass and activity Capacity 0.5 m 3 Compaction and Concentration in air Co E+01 Bq/m 3 packaging room Concentration in air Cs E+01 Bq/m 3 Release rate of Co E+06 Bq/y Release rate of Cs E+06 Bq/y Ventilation, filtration 90% efficiency Compaction area External dose rate 3.2E-06 Sv/y Compaction (WM Capacity 0.5 m 3 activity) Volume of after compaction 35% of volume of before compaction Packaging area External dose rate 2E-06 Sv/h Packaging (WM activity) Capacity 0.5 m 3 Packaging (WM activity) Properties of the after packaging Solids. Compacted s within 500 litre annular grouted drum (0.8 m dia, 1.2 m high) Mass of one package: 600 kg Storage facility Parameter Value Drum storage room Concentration in air Co E-03 Bq/m 3 Storing of packaged (WM activity) Concentration in air Cs E-03 Bq/m 3 External dose rate 2.67E-06 Sv/h Properties of the Solids. Compacted components s within 500 litre annular grouted drum (0.8 m dia, 1.2 m high) Mass of one package: 600 kg 5

9 After specifying the properties of facilities, rooms, areas and management activities, the streams should be defined for the facilities i.e. which processes take place from production of to its storage and this stream structure is shown in figure 1. A stream consists of a primary component which can be modified through different steps. All changes of properties are captured within the stream, ensuring that for purpose of safety assessments the properties at each step are known to SAFRAN tool. Waste from producer Sorting Compactable Non Compactable Waste Compaction Compacted Packaging Packaged Storing packaged Stored Figure 1: Waste stream structure [2] 6

10 All the properties for components resulting of a management activity will be calculated by SAFRAN on the basis of data given for the component i.e. from producer. Input data on components are needed before an assessment can be carried out. This input data is related to general properties, classification and amount of etc. The properties of the are given in table 3. Table 3: Waste properties from producer [2] Parameter Value Total Volume 27 m 3 /y Total Mass kg Total activity of Co E+13 Bq/y Total activity of Cs E+11 Bq/y Waste classification ILW other Corrosive, Toxic, Records available After defining all parameters for facilities, properties of ; a regulatory framework should be defined, which is applicable to safety assessment. The list of criteria for safety assessment is described in table 4. This criterion should be based on national regulations and/or IAEA regulations or a user can define its own definitions of general regulatory requirements and specify the types of outcomes and criteria used in different safety assessment. The ALARA principle and the application of Graded Approach are provided as general criteria which always have to be satisfied. Table 4: List of dose criterion for safety assessment [2] Situation Application Criterion s name Value Unit Normal Worker Dose limit to worker 0.02 Sv/y Normal Public Dose limit to Public Sv/y Accidental Worker Dose limit to worker Sv Accidental Public Dose limit to Public Sv 7

11 5. Results and Discussion 5.1 Normal Situation Table 5 and figure 2 show the comparison of doses received by the worker in different scenarios when job is performed inside (i.e. when work with sorting, compaction, packaging and storage). The doses received during these jobs are within limits defined in criterion. Table 5: Doses to worker during different scenarios Figure 2: Doses of different scenarios during normal operation. 8

12 Figure 3 shows the dose outside (dose to the public), due to release of radioactivity to the air during compaction and packaging and is within limit. Figure 3: Dose received due to release to air during packaging and compaction. 5.2 Accident Situation Table 6 and figure 4 show the dose received by the worker during two accidental situations. (1) Fire in compaction and packaging room and, (2) drop of drum condition. Dose to the worker during drop of drum condition is 2.52X10-2 (Sv ) which is greater than the limit defined in criterion. Table 6: Comparison of doses to worker for accidental conditions 9

13 Figure 4: Doses received for accident situations. At the end of this case study of safety assessment, a clearance level is performed for the generated from the medical field (hospitals). In figure 5 the process for clearing from the medical field (hospitals) is shown. The is checked for defined clearance level if the level of dose is within clearance level limit then it s cleared and the remaining process is completed as shown in figure 5. 10

14 Figure 5: Process for clearing from the medical field 11

15 6. Conclusion SAFRAN tool is used for the safety assessment of pre-disposal management of radioactive. The sample problem provided in the SAFRAN TUTORIALS has been successively run and obtained results of different cases are discussed in section 5. These results are compared with the results provided in the SAFRAN TUTORIALS and found acceptable. The SAFRAN tool now can be used for assessment of actual facility provided the data and necessary input is available. 7. Reference SAFRAN TUTORIALS 12