Development of a Safety Case for a Centralised Radioactive Waste Storage

Facility- Ghana Experience

Eric T. GloverNational Radioactive Waste Management Centre

National Nuclear Research InstituteGhana Atomic Energy Commission

Ghana

Content• Introduction• Regulatory Framework• Radioactive Waste Management• Safe Case

Demonstration of SafetySite CharacterizationWaste Acceptance CriteriaOperational Radiation SafetySafety AssessmentRadiological Impact Assessment

• Conclusion

Introduction The use of radioactive materials in Ghana began in the early 1950s

in the then University of College of Gold Coast (now the University of Ghana).

Radioactive materials have since been in use in various sectors of the Ghanaian economy (medicine, agriculture, industry, research and teaching)

• Ghana Atomic Energy Commission (GAEC) was established by an Act of Parliament (Act 204) in 1963 which has been superseded by Act 588 in 2000.

• The main functions of the Commission include the promotion, development and peaceful application of nuclear and biotechnology techniques for sustainable development.

Regulatory Framework• The Radiation Protection Board (RPB) was established in 1993 as the

National Regulatory Authority in Ghana (PNDC Law 308, 1993)

• The RPB was empowered by the Radiation Protection Legislative Instrument (LI) 1559 of 1993;

• Its responsible for: development of regulations and guidance documents Issuance of licenses and authorizations for all activities involving

radioactive materials Inspections, monitoring and enforcement making recommendations to Government

• The Parliament of Ghana in June 2015 passed a bill into Law for the establishment of an National Nuclear Regulatory Authority independent of GAEC to carry out the regulatory functions

Radioactive Waste Management (1/3)• There are two long term management options for radioactive waste

materials. The first, entails repatriation to the country of origin-applicable to

disused sealed radioactive sources (DSRS) and spent fuel from the research reactor.

The second option is interim storage followed by permanent disposal in a suitably authorized disposal facility.

• The National Radioactive Waste Management Centre (NRWMC), was established to Manage of all radioactive waste materials generated in Ghana Establish facilities for management of radioactive waste materials

Radioactive Waste Management- (2/3)• Most of the radioactive waste materials are in the form of disused

sealed radioactive sources

• They contain radionuclides such as Co-60, Cs-137, Sr-90, Am-241

• Most of them are legacy sources and require safe storage, pending the development a disposal facility

• The NRWMC developed and operated a small capacity temporary storage facility which provided for short-term safe interim storage of radioactive waste materials.

• The facility had significant capacity and design limitations and the need was clear for an improved facility

Radioactive Waste Management- (3/3)• GAEC with assistance from the United States Department of Energy’s Office

of Global Threat Reduction Initiative (GTRI) have constructed a Centralized Radioactive Waste Storage facility.

• The facility is to provide for the safe and secure storage of radioactive waste materials for a period of 50 years. To allow for the decay of short lived radionuclides, To collect and accumulate a sufficient amount of radioactive waste

materials for treatment and conditioning prior to their disposal.

• The existing site was chosen for the development of the new storage facility in view of the supporting infrastructure, the availability of land and the location of the site.

Radioactive Waste Storage Facility

Old Facility Current Facility

Description of Facility• The Storage facility has three units;

a holding area for receipt and characterization of the radioactive waste materials,

a unit for storage of low activity waste and a unit for storage of high activity waste

Physical Protection System

Licensing Requirement• The licensing application requires specification or provision of

(a) the quantity, type and characteristic of radioactive waste including disused sealed radiation sources to be managed; (b) the suggested operation of the proposed facility or activity and equipment to manage the radioactive waste;(c) a safety case;(d )a proposed destination for the disposal of the radioactive waste;(f) a proposed system for record keeping(g) contingency plans in the event of emergency;(h) proposal for discharge and environmental monitoring ; and (i) any other details the Regulatory Authority may consider

necessary for the purpose

Safe Case- Table of Content• 1INTRODUCTION• 2CONTEXT OF THE SAFETY CASE• 3.STRATEGY FOR SAFETY• 4GENERAL DESCRIPTION OF THE FACILITIY, ACTIVITY AND WASTE

– 4.1Site Conditions– 4.2Description of the Facility and Activities– 4.3Description of the Waste Inventory

• 5SAFETY ASSESSMENT– 5.1Assessment Context and Approach– 5.2Assessment Endpoints– 5.3Description of Safety Elements and Functions– 5.4Development, Justification and Assessment of Scenarios– 5.5Performance of Calculations and Analysis of the Results

• 6ITERATION AND DESIGN OPTIMIZATION• 7LIMITS CONTROLS AND CONDITIONS• 8INTERACTING PROCESSES• 9INTEGRATION OF SAFETY ARGUMENTS• 10CONCLUSION

Safety Case• The purpose of the safety case is to

demonstrate that of safety requirements for the Centralized Radioactive Waste Storage Facility will be met,

adequate levels of safety will be achieved in the operation of the facility and

the facility is suitable for storage of the inventory of radioactive waste material currently in Ghana and that which will arise within the foreseeable future.

Demonstration of Safety

• In demonstrating compliance with safety requirement , the storage facility was constructed taking into consideration:

The site characteristics and credible external events and their influence on the design of the facility to ensure structural stability.

Quality assurance in the design, construction, maintenance

and modification the facility.

Safety and security functions in the design of the facility

Modification control process.

Site Characterization

Previous study in the area (site specific information)

Description of the waste inventoryDescription of Facilities and ActivitiesFoundationBuilding StructureFinishingShieldingAccessBuilding Layout

Data Sources

Building Design• The storage facility is a reinforced concrete building with dimensions of

11.30 m by 14.075 m by 3.250 m concrete wall thicknesses of 35cm (for high dose area) and 24 cm

(for the decay store and working areas) with concrete density of 2.3 g/cm3

The building has vehicle access point; A separate personnel door The absence of windows to improve shielding and security

performance.

Facility Operation• Operations undertaken in the facility include;

Receipt of waste packages; Radiation and contamination monitoring of the waste

packages on receipt; Off-loading of the waste packages from the transport vehicle; Acceptance and transfer of the waste packages into the storage

unit; Placing of the waste packages into their storage location within

the storage building; Periodic inspection and radiological monitoring of the storage

building and the waste packages;

Waste Acceptance Criteria• No limit is applied to the activity content of disused sources,

but the packaging must ensure that the ambient dose rate inside the storage facility is not increased by more than 1 μSv/hr.

• The mass of individual packages should not exceed 3 tn.• The outer surfaces of packages should free of removal

contamination• Waste packages should be free from defects and handling

fittings must be in good physical condition• Packages must be indelibly labeled indicating the content in

terms of radionuclide, activity, date of determination and external dose rate

Operational Radiation Safety • The storage facility has been designated as a radiological

controlled area

• The Staff are designated as occupationally exposed persons and undergo a dosimetry control programme.

• Other radiation protection programme being implemented

covers monthly radiological monitoring of the facility and weekly atmospheric airborne monitoring

• The programme makes provision to monitor external radiation levels and surface contamination of waste packages.

• The monitoring instruments are periodically tested and calibrated

Safety Assessment

• The radiological safety criteria used as a basis for evaluation of safety and protection.

The dose limit for workers from all planned exposure is an effective dose of 20 mSv in a year.

To comply with the public dose limit (1 mSv), the calculated dose to the representative person who might be exposed as a result of the operation of the facility dshould not exceed a dose constraint of 0.3 mSv in a year.

Safety Assessment• Used SAFRAN software • Operations in the storage facility involve

the reception of waste packages, characterization of the packages in terms of radiation and

contaminations levels, emplacement of packages within the storage facility and routine inspection, surveillance, cleaning and maintenance

activities

• The same personnel may be involved in all of the respective management activities at the facility.

• Doses received during the various activities are therefore accumulated for these worker

Safety Assessment-Reception• Unloading of waste packages and characterization of waste takes place in

the reception area

• Two people are involved in these operations which take up to 20 minutes to complete and such operations take place approximately once per month.

• Cs-137 nuclear gauge of 1.3E+09 Bq at an average distance of 50 cm from the persons results in a dose rate of 5.69 E-15 Sv/hr

• The calculated dose indicates an accumulated annual individual dose of 280 μSv.

Safety Assessment-Emplacement• Transfer of the waste package into the store and emplacement is

carried out by three people and takes approximately 30 minutes

• The operator are on average a distance of 50 cm from the package.

• During emplacement, the operators are exposed an ambient radiation levels within the store during this 30 minute period

• The calculated dose indicate an accumulated annual individual dose of 435 μSv.

Safety Assessment-Public• The storage facility is located in the secured area of the

GAEC site, some 100 m from the fence.

• Some farming activities take place on the site outside the secured area

• The representative person works and lives just beyond the secured area fence spending some 6 000 hours per year in this location.

• Based on this scenario, dose calculations indicate an accumulated annual individual dose of 26 μSv.

Safety Assessment-Accident• The assessment of radiological impact from accidents were

undertaken by identifying the events that could initiate an accident and screening out those that are not relevant or could not cause

significant damage to the facility

• The remaining scenarios were then evaluated to assess the associated radiological impact

• The list of significant events were considered in terms Internally Generated Hazards (Acceptance of incoming waste External Events – Natural Origin ( Lightning, flooding, seismic External Events – Human Origin ( Fire, aircraft crash, civil strife

Safety Assessment-Accident• Dropping of waste package – leading to degradation of shielding

and containment functions with workers present.

• This could occur during transfer operations or could arise from failure of the storage racks due to e.g. a seismic event.

• Calculation of dose to workers in the vicinity assume a point source configuration, a residence time of 45 minutes and an average distance from the source of 50 cm.

• The sources selected represent the higher activity sources and the

majority of activity in the store.

• The outcome of the calculation indicated a total dose of 27 mSv.

Radiological impact assessment -Normal operation

• The radiation doses are as low as reasonably achievable and that safety and protection are optimized.

• Calculated occupational exposure with the present inventory is 1.2 mSv per annum compared with occupation dose limit of 20 mSv.

• The results of personal monitoring of workers in the facility are in the range 1-2 mSv/year

• This could rise to 2 mSv within twenty years of operation.

Stakeholder Engagement-Commissioning

Conclusion

• The assessment shows a good level of safety

• Radiation doses to both workers and members of the public are assessed to be within radiation dose limitations with a good margin of safety, both now and over the projected lifetime of the facility.

• In view of the low level of radiation doses there is little need for further optimization of safety and protection.

.

Thank You