lata mishra bhabha atomic research centre, india · regulatory body atomic energy regulatory board...
TRANSCRIPT
Lata Mishra
Bhabha Atomic Research Centre, INDIA
Outline of presentation
Legal & Regulatory provisions / requirements
Safety criteria & Safety objectives
PIE’s
Safety & Seismic categorization
Safety provisions in various SSC’s
Conclusions
Legal provisions
In India activities concerning establishment and utilization of Nuclear Fuel Cycle Facilities (NFCF) and use of radioactive sources are carried out in accordance with the provisions of the Atomic Energy Act, 1962
Provisions of the Act
Power to the Government to provide for control over radioactive substances or radiation generating plant in order to
Prevent radiation hazards
Secure public safety and safety of persons handling the plant
Ensure safe disposal of radioactive wastes
Regulatory Body
Atomic Energy Regulatory Board (AERB) has been entrusted with the responsibility of laying down safety standards for such activities to ensure the safety of members of the public, occupational workers as well as protection of environment.
Compliance of Regulatory limits imposed by AERB ensure that air borne contamination and exposures to occupational workers and general public are maintained at levels that are “as low as reasonably achievable” (ALARA).’
Safety Codes & Guides
AERB has developed safety standards, codes of practice and related guides & manuals, covering all stages of a project
Codes set the minimum requirements that are to be fulfilled mandatorily by the facilities
Codes formulated on the basis of internationally accepted safety criteria
Guides contain detailed guidelines to implement specific parts of a safety code
Guide on consenting processes
AERB has issued a safety code on ‘Regulation of Nuclear & Radiation facilities’ &
Safety guide on ‘Consenting processes for NFCF’s
From site selection to decommissioning, a well laid out process for acquiring consent from regulators is in place
Following the procedure ensures that the system is reviewed for safety by the regulatory body and necessary submissions are made to the regulatory body by the agency seeking consent, at every stage.
Guide on consenting processes contd..
This guide is valid for Recycle plants comprising of spent fuel Reprocessing & Waste management plants
The consenting processes include review of safety aspects as presented in the Safety Analysis Report (SAR)
Typical format & contents of the SAR is a part of the guide
Experience
Good amount of experience has been gained in construction, commissioning, operation, decommissioning and decontamination of NRF’s
Importance to
Safety Safety
one step ahead
of functionality Functionality
Safety criteria for design
In line with this philosophy of according highest level of importance to safety
A document on Safety Criteria for Design of Nuclear Recycle Facilities has been made
It specifies the safety criteria to be followed for all systems at component level
OBJECTIVE
The document has been prepared essentially to
identify safety issues in the various systems and specify design provisions that should be followed
to prevent unsafe situations
BASIS
Safety criteria is based upon experience gained in the operating plants
&
AERB safety guidelines for design of Nuclear Recycle facilities
RELEVANCE
Will be relevant during
the various stages of the project
&
will be a reference for
Designers, Operating personnel
&
Regulators for ensuring the safety of the facility
Safety Related Systems addressed
Civil and structural safety
Safety & Seismic categorization of SSC’s
Process Systems including auxiliary systems
Ventilation System
Radiological and Criticality safety
Utility and services
Fire safety
Civil and structural safety
Possible design events under both normal & abnormal conditions are first postulated and structures designed to withstand or mitigate the consequences of these postulated conditions.
Postulated initiating events (PIE’s) that would result in an accident scenario are also identified and consequences of resulting accident analyzed to specify design inputs for the structure
Postulated Initiating Events (PIE’s) Anticipated normal events
Wind loading
Water Level (Flood) design
Seismic design &
Anticipated abnormal events
Red Oil formation
Criticality
Leakage from HLW tank
Beyond Design basis earthquake
Structural Design Structures designed for anticipated normal events
eg. Safe Grade Level , Seismic Design
Abnormal events avoided & safety ensured by :
Multiple physical barriers for radioactive source
Control of steam temp, organic in aqueous
Control of geometry, mass & conc. of fissile material
Selection of good material of construction
Safe Grade Level Final Grade Level is arrived at, considering :
a storm surge, calculated for the most severe storm in the vicinity of the site (probability of 1 in 100 years)
such a severe storm coincides with the highest high water level (joint probability of such an event will be still lower)
the most severe storm directly hits the site
The frequency of such an occurrence would be of the order of 1 in 1000 years or so
Safety & Seismic categorization Structures / Electrical systems / Process
equipment & piping / I&C systems of NRF’s are classified based on their safety functions
Purpose : to establish a gradation approach in the design, construction and maintenance of the SSC’s
Seismic categorization is based on the hazard potential of facility and its requirements of integrity & functionality during or after seismic event
Level of earthquake for design
During an earthquake the NRF’s do not have operability requirement like NPP’s, hence various systems and components are designed for a single level of earthquake load in line with international practices. All the static civil and mechanical structures are designed for structural integrity against the design basis earthquake loads
Design & Safety objective All systems are designed to achieve the functional
objectives of the plant while ensuring adequate safety
Fundamental safety objective is to protect
Occupational worker
Environment and
General public
from harmful effects of ionizing radiations.
Process Systems : General
High standards of MOC, fabrication
Remote operations for handling high active equipment
Adequate shielding wherever necessary to prevent exposure of working personnel
SS lining in areas for easy decontamination
Provision of redundancy w.r.t critical equipment used for containing radioactivity
Process systems Negative pressure in equipment always better than
the specified value with requisite interlocks & cut offs
Suitable provisions for detection, collection & disposal of spills/ leakages from in-cell equipment
Provisions to prevent unintended & Inadvertent transfers & minimize entrainment of active liquids
Hold ups in pipelines minimized
Provisions to avoid blow back of active fluids into inactive areas
Avoiding Blowback
Process systems
Cooling provisions for vessels handling high active liquids, including emergency cooling
Provisions to prevent entry of organic into evaporators
Provision for accurate accounting of SNM
Sampling provisions
Suitable enclosures with mechanized handling for powder processing equipment
Shielded cubicles planned in inactive areas (as in pumps) to facilitate maintenance
Shielded Cubicles
Niches
Process & Waste Management
HLLW storage tanks provided with two sets of cooling coils for removal of the decay heat
Cooling & off gas system availability enhanced with dedicated Class III DG sets for vessels handling high active liquids
Storm water system to be totally isolated from PAD system
All kinds of wastes discharged from the plants to meet stipulated guidelines of regulatory bodies
Lines laid underground to have secondary containment with provisions for inspection
Instrumentation
Monitoring of plant parameters & radiation status under normal & anticipated operational occurrences
Seismically qualified UPS & dedicated air reservoir with sufficient back up for monitoring critical plant parameters for safe shut down of plant
Instrumentation
Control systems & Interlocks designed to maintain important process variables
Hardwired backup for important safety alarms & trips
Auto restart of devices on electrical power resumption prevented
Utility & Services
Class III power supply for critical systems
Elaborate off gas cleanup system with adequate capacity & static pressure & redundancy
Remote operation & auto changeover during failure of blowers
Steam temperature to be limited to set value
Communication system, emergency alarm & response system – first priority selection
Ventilation system Operation capability during normal power outage
to confine contaminants
Fire resistant system
Designed to support radiological zoning
Graded flow from less potential area for contamination to higher potential area
Once through ventilation in areas with potential for contamination
Redundancy of equipment with auto changeover
Class III supply to exhaust fans, with auto changeover on Class IV failure
Ventilation pattern
Radiological & Criticality safety
Adequate shielding for radioactive sources
Segregation of active & inactive areas with radiation zoning for contamination control
Emergency exit doors at suitable points
Radiation monitoring & survey equipment
Adequate breathing air stations
Safety interlocks for preventing mal operations
Geometry, mass & concentration control
Exposure limits Safety provisions in design shall ensure that under
Design Basis Accident conditions, accident analysis should demonstrate that the exposure to a member of the public at the site boundary does not exceed
30 mSv per year & 100 mSv in a 5 year block for occupational workers and
1 mSv/year for members of public
All radiation sources provided with adequate shielding so that the field on contact outside the shielding is less than 1 μSv/h (as per AERB guidelines) where full occupancy is envisaged
Criticality safety
Criticality safety is achieved by keeping one or more of the following parameters of the system within sub critical limits in normal operations, for anticipated occurrences and for design basis accident conditions
Mass of fissile material present in process
Geometry of processing equipment
Concentration of fissile material in solutions
The safety of the design for the facility is demonstrated by means of a specific criticality analysis wherein the K-eff of individual tank / equipment and as a layout does not exceed 0.9 under all circumstances.
Fire safety Principle of defence-in-depth adopted in design of
fire protection systems
System shall consist of fire prevention, detection and suppression systems & shall be achieved through
Structural safety –
Detailed fire hazard analysis in initial design
Appropriate fire detection & annunciation systems -
Fire & Smoke detection & alarm system
Adequate fire fighting systems
Conclusion
The document identifies various safety issues related to Nuclear Recycle Facilities in India
The provisions specified in the document are as per International practices
Design ensures safety even during anticipated abnormal events
Thank You