MODULE “PROJECT MANAGEMENTAND CONTROL”

SAFETY ASSESSMENT DURING DECOMMISSIONING

SAFE DECOMMISSIONING OF NUCLEAR POWER PLANTS

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci”

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 2

CONTENTS

1. Critical tasks of decommissioning

2. Areas of management

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 3

TRAINING OBJECTIVES

Upon completion of training trainees should be able to: Explain the conditions of the nuclear facility that impact on

decommissioning safety assessment. Identify the risks typical for separate decommissioning activities. Describe the critical tasks of decommissioning. Describe the parameters for assessment of decommissioning impact

on the personnel. Describe the parameters for assessment of decommissioning impact

on the environment. Describe the non-radiological risks during decommissioning. List the areas of decommissioning management.

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 4

OPERATIONS RELATED TO CHANGE OF RISK AND SAFETY ASSESSMENT AFTER THEIR

COMPLETION

Removal of spent fuel Processing, conditioning and disposal (storage) of

radioactive waste Decontamination prior to dismantling, demolition and

processing, conditioning and disposal (storage) of radioactive waste at decommissioning

Cleaning of site (demolition) and its environmental release or utilization in other nuclear facility

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 5

TYPICAL RISKS ASSOCIATED WITH DIFFERENT DECOMMISSIONING OPERATIONS

Decontamination prior to dismantling Dismantling Decontamination after dismantling Decontamination of building materials

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 6

TYPICAL RISKS ASSOCIATED WITH DIFFERENT DECOMMISSIONING OPERATIONS – CONTN.

Dosimetric control Demolition and reconstruction of site Radioactive waste management Treatment of non-contaminated waste

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 7

CRITICAL TASKS AT THE PHASE OF FINAL SHUTDOWN

Fuel cooling and removal Standard decontamination of

equipment with the help of operational systems

Circuit drainage Treating and conditioning of

operational radioactive waste Tripping of equipment that is not

further needed

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 8

INITIAL CHARACTERIZATION OF THE INSTALLATION

Ensures input data for safety assessment. Allows for specification of inventory and layout of

radioactive and dangerous materials. Supports preparation of radiation maps and contamination

maps. Allows to determine penetration depth and contamination

extent. Used for choosing appropriate procedures for

decontamination or dismantling. Used to determine the inventory of hazardous chemicals,

materials and substances.

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FUEL REMOVAL

Time for implementation:• At the end of operation;• At the beginning of decommissioning activities.

Time for removal depends on:• Type and size of reactor;• Fuel condition;• Constraints related to its transportation;• Constraints related to its off-site management.

Utilization of on-site interim storage facilities for spent fuel. Shipment of new fuel in case of stocks.

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 10

TRANSPORT OF SPENT FUEL

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CONTAINMENT MAINTENANCE AND MODIFICATION

Important element of defence in depth. Containment systems need to be retained as long as

possible. Changes:

• Radioactive materials are removed;• Facility is modified.

Deferred dismantling:• Ensures proper maintenance;• Regular assessment of containment protection systems integrity

and reliability.

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DECONTAMINATION

Types:• Partial or complete;• Prior, during or after dismantling.

Decontamination objectives:• Decrease exposure during decontamination activities;• Minimization of volume of materials classified or disposed as solid

radioactive waste; and• Increase of possibilities for equipment, materials or buildings

recycling or reuse.

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DISMANTLING

Reactors shutdown at end of operations without accidents or incidents

Reactors shutdown after an accident Decommissioning of facilities

significantly contaminated withalpha-nuclides

Dismantling and demolitiontechniques and methods

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 14

MAINTENANCE

Important element ensuring safety in case of deferred dismantling.

Implementation of periodical monitoring of safety related components.

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FINAL RADIOLOGICAL SURVEY

Objective:• To demonstrate that residual activity complies with the criteria set

by the National Regulatory Body.• To demonstrate that all objectives of decommissioning are fulfilled.

Time for implementation:• Upon completion of all decommissioning activities;• In phases depending on implemented activities.

Survey results are included in final decommissioning report.

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NON-RADIOLOGICAL RISKS DURING DECOMMISSIONING

Toxic materials – asbestos Safety measures at its removal:

• Face masks;• Special outfit;• Ventilation;• Temporary barriers.

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PARAMETERS DEFINING IMPACT ON STAFF

Individual exposure dose• External irradiation• Internal irradiation

Collective dose

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ENVIRONMENTAL IMPACT

Parameters:• Gas releases;• Liquid releases.

CRITERIA FOR CLEARING MATERIALS FROM REGULATORY CONTROL

Disposal of RAW from decommissioning process• Disposal facilities of surface type – 400 Bq/g for medium total

concentration of alpha-emitting radionuclides

Release of materials in the environment• “De minimis” principle• Radiological standard limit for individual equivalent dose of 10

µSv/y

Project BG/04/B/F/PP-166005, Programme “Leonardo da Vinci” 19

NON-RADIOLOGICAL HAZARDS AT DECOMMISSIONING

Work with electrical equipment Work performed on heights Work with toxic substances

• Asbestos• Lead

Work with chemicals Others – lifting heavy loads, noise, vibrations, etc. ...

 

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ISSUES TO BE CONSIDERED DURING DECOMMISSIONING

Staffing and training; Organization and administrative control; Radiation protection; On-site and off-site radiological monitoring; Waste management; Emergency planning; Physical protection and safeguards; Quality assurance and documentation. 

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REFERENCES

Decommissioning of Nuclear Power Plants and Research Reactors, Safety Guide, SS № WS-G-2.1 (1999)

Organization and Management for the Decommissioning of Large Nuclear Facility, TRS № 399 (2000)

The Decommissioning of WWER-Type Nuclear Power Plants, IAEA-TECDOC-1133 (2000)

The principles of radioactive waste management, SS № 111-F (1995)