ENSURING SAFETY REGULATION FOR SUSTAINABLE DEVELOPMENT OF NUCLEAR POWER

Transcription

1 ENSURING SAFETY REGULATION FOR SUSTAINABLE DEVELOPMENT OF NUCLEAR POWER D Bhattacharya Atomic Energy Regulatory Board India 1 Topical Issues in Nuclear Installation Safety: Safety Demonstration of Advanced Water Cooled Nuclear Power Plants, IAEA, June 2017

2 Outline Development of new safety code for LWR Design Requirements from Design New Challenges Rearrangement in DID Practical Elimination Radiation Protection and Safety Goal Reinforcing and Enhancing Further Safety Conclusion 2

3 Development of new safety code for LWR Design AERB started developing a new safety code for Design of Light Water Reactor Based Nuclear Power Plants (AERB/NPP-LWR/SC-D) in Essentially in line with IAEA SSR-2/1. Design Extension Condition concept introduced. AERB published the code in January

4 Requirements from Design Design basis accidents (DBA) are considered in Defence-in Depth level III. Design of safety systems for DBAs require adherence to specific design rules like compliance to Single failure criteria, Redundancy, Diversity, Common cause failure, Fail safe design etc. 4

5 New Challenges If same set of rules are applied for systems required to function in Design Extension Conditions (DEC), the design becomes very complex. Further this can make nuclear power generation unsustainable. Design agencies require specific guidelines for designing systems to meet the safety requirements during DEC conditions. 5

6 Rearrangement in DID Design extension condition is subdivided into two part: Design Extension Condition A (DEC-A) which includes accident without core melt Design Extension Condition B (DEC-B) which includes accident with core melt. DEC-A is covered in DiD level IV-A DEC-B is covered in DiD Level IV-B Indian requirement is met remaining in line with IAEA philosophy. 6

7 Defense in Depth Earlier Approach Operational states Accident conditions NO AOO (a) DBAs Beyond design basis accidents (b) Severe Accidents Included in the design basis Beyond design basis Current Approach Operational states Accident conditions Cond. practically eliminated NO AOO DBAs Design Extension Conditions Design Extension Conditions No core melt Severe Accidents (core melt) Included in the design basis Beyond design basis 7

8 Additional Safety Systems Concept of Additional Safety Systems (ASS) is introduced to cater DEC-A condition. ASS are those systems which are required to cool the nuclear fuel but different than safety systems provided for cooling nuclear fuel during design basis accident e.g. Emergency Core Cooling System. Additional safety system may not meet the single failure criterion and redundancy but must meet diverse principle of action. Designers need to establish that in case of multiple failures, the additional safety system can prevent large scale fuel failure. 8

9 Complementary Safety Features Concept of Complementary Safety Features (CSF) is introduced for catering DEC-B condition. Complementary safety features may not meet the single failure criterion and redundancy criterion but should be able to meet the requirement of controlling the fission chain reaction, cool the molten corium and ensure containment function to prevent large and early radioactivity release. 9

10 Levels of defence in depth & System Design Normal Operation AOO Anticpated Operational Occurency DBA Design Basis Accident Normal operation systems Safety systems (Reliability, Physical seperation, Single failure...) Design Extension Condition (DEC) without core melt Design Extension Condition (DEC) with core melt or Severe Accidents Additional Safety System (Diverse than Safety Systems) Complementary Feature/System for Containment integrity / plant recovery 10

11 SAFETY DEMONSTRATION Events considered to occur and consequences considered in the design Events which have to be practically eliminated, as would lead to large or early radioactive release Single postulated initiating events DiD level 3 Multiple failure events DiD level 4A Confined fuel melt DiD level 4B Initiators (reactor vessel rupture ) Open Vessel Criticality with containment bypass Fuel melt sequences challenging the confinement Design basis* Design extension* Practical elimination 11

12 Practical Elimination All accident sequences which may lead to early or large radioactive releases must be practically eliminated. Means of practical elimination It is physically impossible for the accident sequence to occur, or The accident sequence can be considered with a high degree of confidence to be extremely unlikely to arise. Practical elimination of a condition cannot be claimed solely based on compliance with a general cut-off probabilistic value Any additional reasonable practicable design features to lower the risk should be implemented Practical elimination provisions shall remain in place and valid throughout the plant lifetime. 12

13 Radiation Protection and Safety Goal (1/2) Design basis accident (initiating event with consequential failure and taking credit of safety systems considering single failure criterion) For design basis accident (DBA) there shall be no need for offsite countermeasures (e.g. administration of prophylaxis, food control, shelter or evacuation) involving public. Dose limit = 20 msv DEC-A (multiple failure situations and rare external events) There shall be no necessity of countermeasures like sheltering or evacuation of public beyond exclusion zone Required control on agriculture or food banning should be limited effective dose, with such interventions considered, should remain same as for DBA. 13

14 Radiation Protection and Safety Goal (2/2) DEC-B (severe accident) The release of radioactive materials should cause no permanent relocation of population. The need for offsite interventions should be limited in area and time. Requirement of Vienna Declaration met for new reactor design 14

15 Reinforcing and Enhancing Further Safety Address the unexpected Foresee additional provisions to support accident management infrastructure that may be needed to handle extreme events along with failure of existing safety systems / features Diverse and flexible accident response capability development Portable and mobile backup to permanently installed plant safety systems Smart operators with given flexibility to respond as needed 15

16 Conclusion To meet the challenge of climate change and sustainable development, power generation from nuclear fuel is inevitable. Risk of nuclear accident can be reduced by suitable design provisions and emergency response provisions. Large scale acceptance of Nuclear power by public is possible if suitable regulation is implemented Nuclear power generation can be rendered very low risk other than risk due to extreme external events which are not considered in design. 16

17 Thank You For Your Kind Attention 17