Regulatory Review Aspects of Post-Fukushima Safety Enhancements in Indian NPPs

Transcription

1 Regulatory Review Aspects of Post-Fukushima Safety Enhancements in Indian NPPs RAHUL PORWAL Atomic Energy Regulatory Board Mumbai, INDIA

2 Outline Introduction AERB Safety Review Methodology Safety Observations Post-Fukushima Event Post-Fukushima Review Recommendations Implementation of Recommendations Kudankulam NPP: Salient Features Kudankulam NPP: Implementation Status 2

3 Introduction (1/2) Fukushima Accident: Outcome of tsunami generated due to high magnitude earthquake NPPs suffered extended station blackout, which could not be mitigated Systems for ECC did not function after power restoration due to flooding Four hydrogen explosions damaged reactor buildings of the NPPs Units 5&6 survived due to air cooled DG 3

4 Introduction (2/2) Large radioactivity release implementation of off-site emergency measures Accident rated at level-7 of INES Accident revealed shortfalls in certain safety aspects of the NPPs Actions were initiated by all concerned AERB constituted an Expert Committee to review the safety of Indian NPPs against External Events of Natural Origin 4

5 AERB Safety Review Methodology (1/2) AERB: constituted in 1983 Has developed robust procedure for safety review, regulatory inspections & issue of consents AERB Regulatory documents have been developed in the form of Safety Standards: Safety Codes & Safety guides These documents cover various safety aspects to be considered during Siting, construction, commissioning, operation, radiation safety, QA & desommissioning stage of NPPs 5

6 AERB Safety Review Methodology (2/2) Development and revision of these documents is a continuing process at AERB AERB has a unique three-tier review process for stagewise clearances of NPPs First-tier safety review is carried out by Site Evaluation Committee (SEC) / Project Design Safety Committee (PDSC) Second-tier review is done by Advisory Committee for Project Safety Review (ACPSR) Third-tier safety review is carried out by AERB Board 6

7 SAFETY OBSERVATIONS POST- FUKUSHIMA EVENT 7

8 Safety Review Observations (1/3) Post Fukushima review basis: basic nuclear safety viz. reactivity control, core cooling & radioactivity confinement during ESBO (BDBE) Tsunami capable submarine faults at more than 800km from Indian coast coincidence of earthquake & tsunami almost non-existent Sufficiently conservative design requirements for postulated initiating events Implementing Safety up-gradation over a period of time based on outcome of various safety reviews 8

9 Safety Review Observations (2/3) Periodic safety review for all operating NPPs are conducted Implementation of operating experience feedback and lessons learnt from operational incidents in India and abroad are considered as appropriate Most of the NPPs in India are PHWRs. Core cooling by natural convection flow through SGs is possible in these NPPs Water inventory make-up to SGs through diesel driven fire water pumps is envisaged in PHWR design 9

10 Safety Review Observations (3/3) For spent fuel of PHWRs, water inventory in fuel pools is much larger w.r.t. the heat load of the spent fuel Submergence of the spent fuel is assured for at least one week taking into account the following:- conservative assumptions maximum decay heat of the spent fuel No operator action 10

11 POST FUKUSHIMA REVIEW RECOMMENDATIONS 11

12 Review Recommendations (1/3) NPPs to be re-evaluated for addition of provisions such that basic safety functions are not hampered under BDBEs. Emphasis on functionality of most of the safety related SSCs even under extreme events without demand for operator action Voiding during natural circulation flow during heat removal be avoided. Back-up provisions for inventory make-up to important systems be available 12

13 Review Recommendations (2/3) Preparation of Emergency operating procedures for postulated accidents initiated by BDBE Establishment of a seismically qualified emergency facility with adequate radiation shielding which will remain functional under BDBE Safety analysis for SBO to be done for beyond 24 hrs upto 7 days demonstrating that all the safety parameters are within acceptance limits 13

14 Review Recommendations (3/3) Provisions for accident management to be made as part of Severe accident management guidelines (SAMG) Analysis for hydrogen generation for all NPPs and implementation of mitigatory measures to be taken up For SFPs, site specific safety assessment for structural integrity, leak-tightness, stability of fuel racks & handling equipment was suggested 14

15 IMPLEMENTATION OF RECOMMENDATIONS 15

16 KK NPP: Salient Features (1/5) Kudankulam NPP: 2x1000 MWe VVERs Unit #1 attained first criticality on July 13, 2013 Engineered safety features provided for catering to DBEs as well as BDBEs Each active safety system is backed up by passive safety system and each is capable to perform the intended safety function While each active safety system has redundancy of 4 100%, for passive systems it is 4x33% 16

17 KK NPP: Salient Features (2/5) Safety system trains are completely segregated in terms of location and layout Operator actions to disable actuated safety system are blocked in the first 30 min to exclude human error All safety systems are supplied with power from dedicated independent diesel generators and battery banks 17

18 KK NPP: Salient Features (3/5) Systems provided for BDBA scenario Quick boron injection system Passive heat removal system Annulus passive filtration system Additional system for core passive flooding System for retaining and cooling of molten core RPV MOIV Air PRZ QBIS Tank Quick Boron Injection System Air RCP MOIV SG 18

19 KK NPP: Salient Features (4/5) Core decay heat can be removed by natural circulation of primary coolant through SGs in case of SBO Water inventory in the SGs can be conserved with PHRS PHRS facilitates heat removal from SGs to atmospheric air as UHS 19

20 KK NPP: Salient Features (5/5) Additional System for Core Passive Flooding 20

21 KK NPP: Implementation Status (1/4) Post-Fukushima safety enhancements for Kudankulam NPP as submitted by the utility was reviewed in detail Implementation of Recommendations was identified as short-term (within 6 months) and long-term (within 2 yrs) plans from start of initial fuel loading With systems already in place for BDBA, as a matter of abundant precaution, back-up provisions for addition of water into the RCS, SFP & SGs were made 21

22 KK NPP: Implementation Status (2/4) The details are as follows :- a separate tank with borated water inventory with a plunger pump for injecting water into RCS seismically qualified emergency water storage tank located at a higher elevation for make-up to SGs & SFP transfer of water from this tank by on-site fire tenders to the hook-up points inventory make-up to the steam generators and spent fuel pool through external hook-up points adequacy of the availability of the fire-tenders at site in this regard was also reviewed 22

23 KK NPP: Implementation Status (3/4) A separate mobile air cooled DG is provided. Loads catered by this DG include:- newly introduced systems pre-identified existing systems instruments for monitoring of important parameters emergency lighting communication systems 23

24 KK NPP: Implementation Status (4/4) Battery operated portable hand-held instruments for local monitoring of important parameters are made available Appropriate LCO and surveillance requirements for new systems are being finalized Analysis of existing SSCs with regard to their available margins vis-à-vis BDBE in under progress and is being followed up as part of long-term plan 24

25 THANK YOU 25