Over the years, several studies have been conducted as part of seismic and structural analysis of NPP components for supporting the regulatory review process. Some of the important studies include:

• Seismic re-evaluation of NPPs
• Seismic margin assessment of safety system by analysis and testing
• Structural integrity assessment of RPV during severe accident
• Rotor dynamics analysis of primary sodium pump of PFBR
• Failure probability evaluation of NPP components

(a) FE model of AHX; (b) Shell model of header and tube junctions; (c) Von Mises stress during SSE

Integrated FE Model of secondary sodium system for seismic capacity assessment

A comprehensive research program on various aspects of hydrogen generation, distribution and mitigation in NPPs is in progress at SRI. This consists of numerical as well as experimental activities as described below.

• Development of in-house CFD models (HDS suite of codes)
• Safety studies on coolant channel heat-up behaviour and hydrogen generation during LCDA in existing and upcoming PHWRs
• Hydrogen Distribution Studies
  • Helium distribution experiments in AIHMS facility, in collaboration with IITM.
  • Development of models for quantification of mixing and deflagration potential of a distribution.
  • Numerical study of hydrogen distribution in dry and steam environment within the nuclear reactor containment.

• Hydrogen Mitigation Studies
  • Development of innovative PAR concepts
  • Validation of in-house CFD model within the REKO-3 Geometry.
  • Setting up of in-house experimental facility called Hydrogen Mitigation Facility (HYMIF).

Contour plots for coolant channel heat-up during LOCA + failure of ECCS in 700 MW PHWR.

AIHMS experimental facility: (a) Layout; (b) Test enclosure with dimensions and locations of helium concentration sensors.

Hydrogen distribution in BWR Mark-1 containment for a DBA scenario: (a) Geometry of simplified primary containment; (b) contour plots obtained at different time instances.

Numerical studies on hydrogen mitigation within the REKO-3 geometry: (a) computational domain; (b) contour plots of velocity, temperature, hydrogen and steam mole fractions.

Fire safety issues in NPP and fuel cycle facilities that are of regulatory interest are addressed using numerical techniques. The emphasis is mainly on investigating enclosure fire development and mitigation aspects. CFD codes such as FDS (Fire Dynamics Simulator) as well as in-house models developed for specific scenarios are employed for such safety assessments. CFD tools are also applied for simulating the in-house experiments in CFTF. Some recent activities are listed below:

• Fire hazard analysis for postulated lube oil spill in a typical Steam Generator Building of a Fast Reactor
• Hot cell fire safety assessment under operating conditions
• CFD simulation of experiments in Compartment Fire Test Facility (CFTF).

a) 3D model of the SG building;

Snapshots of fire development for various ventilation conditions in CFTF

Safety analysis in the area of core and containment thermal hydraulics are carried out to support the regulatory review of existing and new reactor systems and components.  Commercial software such as RELAP is used to obtain reactor system transients. Containment analysis is mainly carried out by mathematical models developed in-house at SRI. Apart from this, commercial CFD tools are also used for safety review and assessment of specific systems and components. Some recent works are given below.

• Safety review and assessment of functionality of 700 MWe PDHR system
• CFD simulation of annulus gas flow in AGMS channel of KAPS 1&2
• LBLOCA studies in 220 and 700 MWe PHWRs using RELAP 5/ MOD 3.4
• Development and up-gradation of in-house numerical model for containment analysis
• Numerical studies for estimation of leak size in the coolant channel of KAPS-1
• PHWR and BWR containment system transients under postulated accident scenarios
• Safety review of proposed Containment Filtered Venting System for existing and upcoming reactors.
• Numerical simulation of thermal striping phenomena in FBRs
• Safety studies on SGDHR system of PFBR

Studies on radionuclide migration in geo-environment are being carried out at SRI as part of regulatory review. The focus is on providing input for a detailed radiological impact assessment for any site. Commercial software as well as in-house developed mathematical models are employed for the safety assessment. Recent activities are highlighted below:     

• Independent assessment of NSDF and other radioactive waste disposal facilities at Kalpakkam.
• Development of models for calcium leaching from engineered concrete barriers.
• Benchmarking exercise using PORFLOW software

Radio-nuclide migration in waste disposal facility: (a) Schematic model of the facility; (b) Concentration of Tc-99 at the end of 300 years of storage.