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IAEA Technical Meeting, J4-TM-46463 – Aug 26-29, 2013, Vienna Atomic Energy Regulatory Board, INDIA

Regulatory Review Aspects of Post-Fukushima Safety

Enhancements in Indian NPPs

RAHUL PORWAL

Atomic Energy Regulatory Board

Mumbai, INDIA


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

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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

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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

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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

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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 stage-wise 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

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Atomic Energy Regulatory Board, INDIA IAEA Technical Meeting, J4-TM-46463 – Aug 26-29, 2013, Vienna

SAFETY OBSERVATIONS POST-FUKUSHIMA EVENT

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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

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• 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

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• 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

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POST FUKUSHIMA REVIEW RECOMMENDATIONS

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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

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• 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

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• 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

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IMPLEMENTATION OF RECOMMENDATIONS

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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%

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• 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

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• 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

Quick Boron Injection System


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RPV

QBIS

Tank

SG

PRZ

RCP

MOIV

MOIVAir

Air


• 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


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Additional System for Core Passive Flooding


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

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• 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

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• 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

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• 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

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THANK YOU

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