Lata Mishra Bhabha Atomic Research Centre, INDIA

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 one step ahead of functionality Safety 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

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