PROBABILISTIC SAFETY ANALYSIS of TRANSPORTATION of SPENT FUEL by Chitra Subramaniam Health Physics Division
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BARC/1999/E/036 IN0000257 V© re "o PROBABILISTIC SAFETY ANALYSIS OF TRANSPORTATION OF SPENT FUEL by Chitra Subramaniam Health Physics Division 1999 9 . •'Kj BARC/1999/E/G36 g GOVERNMENT OF INDIA 2 ATOMIC ENERGY COMMISSION PROBABILISTIC SAFETY ANALYSIS OF TRANSPORTATION OF SPENT FUEL by Chitra Subramaniam Health Physics Division BHABHA ATOMIC RESEARCH CENTRE MUMBAI, INDIA 1999 BARC/1999/E/036 BIBLIOGRAPHIC DESCRIPTION SHEET FOR TECHNICAL REPORT (as per IS : 9400 -1980) 01 Security classification: Unclassified 02 Distribution: External 03 Report status: New 04 Series: BARC External 05 Report type: Technical Report 06 Report No.: BARC/1999/E/036 07 Part No. or Volume No.: 08 Contract No.: 10 Title and subtitle: Probabilistic safety analysis of transportation of spent fuel 11 Collation: , 179 p., figs., tabs., 3 ills. 13 PrpjectNo. :• 20 $ef&pma!authoifs) : ' Chitra Subramaniam 21 Affiliation of authors): Health Physics Division, Bhabha Atomic Research Centre, Mumbai 22 Corporate authors): BMbha Atomic Research Centre, Mumbai - 400 085 23 Originating unit : Health Physics Division, BARC, Mumbai 24 Sponsors) Name: Department of Atomic Energy Type: Government Contd... (ii) •l- 30 Date of submission: October 1999 31 Publication/Issue date: November 1999 40 Publisher/Distributor: Head, Library and Information Services Division, Bhabha Atomic Research Centre, Mumbai 42 Form of distribution: Hard copy 50 Language of text: English 51 Language of summary: English 52 No. of references: . reft. 53 Gives data on: Abstract: The report presents the results of the study carried out to estimate the accident risk involved in the transport of spent fuel from Rajasthan Atomic Power Station near Kota to the fuel reprocessing plant at Tarapur. The technique of probabilistic safety analysis is used. The fuel considered is the Indian Pressurised Heavy Water Reactor fuel with a minimum cooling period of 485 days. The spent fuel is transported in a cuboidal, naturally-cooled shipping cask over a distance of 822 km by rail. The Indian rail accident statistics are used to estimate the basic rail accident frequency. The possible ways in which a release of radioactive material can occur from the spent fuel cask are identified by the fault tree analysis technique. The release sequences identified are classified into eight accident severity categories, and release fractions are assigned to each. The consequences resulting from the release are estimated by the computer code RADTRAN 4. Results of the risk analysis indicate that the accident risk values are very low and hence acceptable. Parametric studies show that the risk would continue to be small even if the controlling parameters were to simultaneously take extreme adverse values. 70 Keywords/Descriptors: SPENT FUELS; RAJASTHAN-1 REACTOR; RAJASTHAN-2 REACTOR; R CODES; TRANSPORT; PROBABILISTIC ESTIMATION; CASKS; RADIATION PROTECTION; DOSE RATES; FAULT TREE ANALYSIS; CONTAMINATION; VALIDATION; PUBLIC HEALTH; RISK ASSESSMENT 71 INIS Subject Category: E1510; E3400 99 Supplementary elements: -li- Probabilistic Safety Analysis of Transportation of Spent Fuel Chitra Subramaniam Health Physics Division BARC ABSTRACT The report presents the results of the study carried out to estimate the accident risk involved in the transport of spent fuel from Rajasthan Atomic Power Station near Kota to the fuel reprocessing plant at Tarapur. The technique of Probabilistic Safety Analysis is used. The fuel considered is the Indian Pressurised Heavy Water Reactor fuel with a minimum cooling period of 485 days. The spent fuel is transported in a cuboidal, naturally-cooled shipping cask over a distance of 822 km by rail. The Indian rail accident statistics are used to estimate the basic rail accident frequency. The possible ways in which a release of radioactive material can occur from the spent fuel cask are identified by the fault tree analysis technique. The release sequences identified are classified into eight accident severity categories, and release fractions are assigned to each. The consequences resulting from the release are estimated by the computer code RADTRAN 4. Results of the risk analysis indicate that the accident risk values are very low and hence acceptable. Parametric studies show that the risk would continue to be small even if the controlling parameters were to simultaneously take extreme adverse values. Contents Chapter 1: Introduction 1.0 Introduction 1 1.1 Risk 4 1.2 Probabilistic Safety Analysis 4 1.3 Probabilistic and Deterministic Analyses 5 1.4 Application of PS A for Transportation of Radioactive Materials 5 1.5 Transport PSA - General Methodology 6 1.6 Review of Earlier Work 8 1.7 Scope of Present Work 10 References 11 Chapter 2: Spent Fuel Transport System Description 2.0 Introduction 14 2.1 Route Description 14 2.2 Mode of Spent Fuel Transport 17 2.3 Description of Reference Spent Fuel Rail Shipping Cask 17 2.3.1 Stay Rods 20 2.3.2 Cask Lid 23 2.3.3 Cask Body 24 2.4 Cask Design Criteria 25 2.4.1 Structural Integrity 25 2.4.2 Permissible Limits of Contamination and Radiation Level on the 26 Cask Exterior 2.4.3 Criticality 26 2.4.4 Heat transfer and Temperature Limits 26 2.5 Test Procedures for Spent Fuel Cask 27 2.5.1 Mechanical Tests 27 2.5.2 Thermal Test 28 2.5.3 Water Immersion Test 28 2.5.4 Overall Test Pass Criteria 28 2.6 PHWR Fuel Bundle 29 2.7 Significant Radionuclides in spent fuel 29 References 34 Chapter 3: Transport Accident Environment 3.0 Introduction 35 3.1 Railway Accident Rates 35 3.2 Rail Accident Environments 37 3.2.1 Impact Jsnviipument 38 3.2.2 Puncture Environment 40 3.2.3 Fire, Environment 41 3.2.4 Crush and Immersion Environment 42 3.3 Cask Failure Thresholds 43 3.3.1 Mechanical Thresholds 43 3.3.2 Thermal Thresholds 45 References 46 Chapter 4: Accident Sequence Identification and Evaluation 4.0 Introduction 47 4.1 Fault tree construction 47 4.1.1 Fault Trees for Shipment of Spent Fuel 49 4.1.2 Basic Event Probabilities 50 4.2 Accident Release Sequences Evaluation 70 4.3 Accident Severity Categories 72 4.3.1 Accident Severity Categories for Each Population Zone 75 4.4 Release Fractions 76 4.4.1 Release Mechanisms 76 4.4.2 Release Fractions for Various Accident Severity Categories 78 References 83 Chapter 5: Consequence Evaluation 5.0 Introduction 84 5.1 Atmospheric Dispersion Model . 84 5.1.1 Gaussian Dispersion Model 85 5.1.2 Atmospheric Dispersal Inputs 88 5.2 Population Distribution Model 90 5.3 Dose Calculation Model 97 5.3.1 Exposure pathways 97 5.3.2 Calculation of Dose from Direct Inhalation of Dispersed 99 Materials 5.3.3 Calculation of Dose from Resuspension 100 5.3.4 Calculation of Dose from Immersion in Radioactive Cloud 103 5.3.5 Calculation of Dose from Groundshine 105 5.3.6 Calculation of Dose from Ingestion of Food Materials 107 5.3.7 Calculation of Dose Rate due to Direct Exposure 107 5.4 Health Effects Model 110 5.4.1 Expected Acute (Non-stochastic) Health Effects 111 5.4.2 Expected Latent Health Effects (Stochastic Effects) 114 References 116 Chapter 6: RADTRAN 4 Computer Code 6.0 Introduction 117 6.1 RADTRAN 4 - Component Models 118 6.1.1 Material Model 120 6.1.2 Transportation Model 120 6.1.3 Accident Severity and Package Release Model 121 6.1.4 Meteorological Dispersion Model 122 6.1.5 Population Distribution Model 122 6.1.6 Health Effects Model 122 6.1.7 Economic Model 122 6.1.8 Module for Incident-free Transportation 123 6.1.9 Module for Accident Risk Calculations 123 6.2 Code Inputs 124 6.3 Code Outputs 124 6.4 Limitations of the Code 125 6.5 Verification and Validation Studies 126 References . 127 Chapter 7: Results, Discussion and Conclusion 7.0 Introduction 129 7.1 The Risk of Transporting Spent Fuel for the Reference Shipping System 129 (Standard Case) 7.2 Sensitivity Analysis 139 7.2.1 Effect of Fraction of Travel on risk 139 7.2.2 Effect of Population Densities on Risk 140 7.2.3 Effect of Spent Fuel Cooling Period on Risk 140 7.2.4 Effect of Meteorological Data on Risk 142 7.2.5 Effect of Variation in Release Sequence Probabilities 144 7.2.6 Effect of Variation in Release Fractions 144 7.3 Comparison of Radioactive Material Transport Risk Assessments 146 7.4 Discussion and Conclusion 147 7.5 Future Work 148 References 149 Appendix-A 150 Appendix-B 152 Appendix-C 163 List of Tables 2.1 Characteristics of Reference Spent Fuel Shipping Cask 20 2.2 Characteristics of Design Basis PHWR Fuel 29 2.3 Inventories of Significant Radionuclides in PHWR Spent Fuel after 32 Varying Cooling Periods 3.1 Trend of Rail Accident on Indian Railways (1991-96) 37 3.2 Frequency for Train Accidents for a Given Velocity Change 39 3.3 Probability of Puncture 40 3.4 Summary Of Spent Fuel Cask Mechanical Failure Threshold Estimates 44 3.5 Summary of Spent Fuel Cladding Mechanical Failure 45 Threshold Estimates 4.1 Fault Tree Symbols 48 4.2 Basic Event Probabilities 62 4.3 Listing of Release Sequences Identified from Fault Trees 72 4.4 Accident Severity Category Frequencies per Shipment for Each 75 Population Zone 4.5 Fraction of Radionuclides Available for Release During Outgassing 77 from the Pellet-Cladding Gap 4.6 Fission Product Release from UO2 under Oxidising Condition 78 4.7 Accident Release Fractions for Various Accident Severity Categories 80 5.1 Parameters to Obtain cry and az (P-G Model) 88 5.2 Areas and Time Integrated Concentrations 89 5.3 Frequencies of Occurrences of Various Stability Classes 90 5.4 Data from Census of India 1991 (Final population totals) 91 5.5 Stations Along the Route from Kota to Boisar 92 5.6 Distribution of the Route into Different