NPCI Scenario Identification, Analysis and L Mitigation measures related to Spent Fuel Pool Events for VVER-1000 P. Krishna Kumar , Y.K.Pandey, Gautam Biswas Fuel, Safety & Analysis Group, Directorate of Engineering-LWR, Nuclear Power Corporation of India Limited Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
NPCI ❖ 22 Reactors Operating - L at an Installed Capacity of 6780 MWe (BWRs, PHWRs & VVERs) ❖ 8 Reactors are Under Construction (PHWRs & VVERs) Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
VVER at KKNPP NPCI The VVER reactors belong to the L family of the Pressurized Water Reactors (PWRs), which is the predominant type in operation, world ➢ Rated Nuclear power: 3000 MW over. The advanced 1000MWe design of VVER (VVER-1000) has many ➢ Rated Electrical power: 1000 MW variants in different countries, which ➢ Water cooled water moderated are derived from the basic VVERmodelV-392. (VVER) reactor ➢ Fuel – Enriched uranium as fuel The VVER reactor at KudanKulam site is an advanced PWR, i.e., VVER ➢ Four loop heat transport system NSSS model Version V-412, ➢ Double Containment Steel lined VVERs Operation : 2x 1000 MWe at Kudankulam (KKNPP-1&2) Under Construction : 2x 1000 MWe at Kudankulam (KKNPP-3&4) 3 Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Steam Generator (4) Turbine (1 HP+3LP) Generator (1 ) REACTOR NPCI L Steam Condenser cooling water Primary Circuit Circuit Secondary circuit Reactor coolant Condenser (3) pumps (4) Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
NPCI L 5 Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
SPENT FUEL POOL IN VVER (1/2) The fuel pool in VVER is an in-containment spent fuel storage system is designed to cool the spent fuel taken out of the reactor in order to NPCI L reduce the former ’ s activity and residual heat to the values that are permissible at transportation. The in-containment spent fuel storage system is designed to keep and cool the spent fuel inside the reactor building considering the scheduled fuel reloading and the whole core unloading at any moment of NPP operation. The fuel pool is lined with stainless steel to provide a leak tight barrier. Spent fuel assemblies are kept in the racks. The storage bay has capacity to store spent fuel discharged for about 7 reactor years of operation in addition to provision for unloading of one full core load in case of emergency. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
SPENT FUEL POOL IN VVER (1/2) The Spent Fuel Storage racks are for NPCI 1. Maintain the capability to remove and insert fuel assemblies L and prevent physical damages to stored fuel. 2. Maintain the stored fuel in a proper geometry to ensure adequate cooling 3. Maintain the stored fuel in a sub critical configuration for all Plant Conditions. In the Fuel pool, Spent Fuel Assemblies (SFA) are stored in closely packed racks maintaining pitch in a triangular lattice, which provides Keff below 0.95 in case of racks completely loaded with fuel having maximum enrichment and being submerged into boron-free water. Moreover, the fuel pond is filled with Boric acid solution also Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Simple schematic of KKNPP Spent Fuel Pool and RPV NPCI L Fuel Pool Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
SFP Features ❑ The spent fuel pond cooling system is designed for residual heat removal from the spent fuel that are located in the spent fuel pond under all the operating conditions as well as under the design basis accidents and design NPCI extension conditions. L ❑ The Structures, Systems and Components (SSCs) of Spent fuel pools have been designed for Design basis Earthquake and Design basis flood levels. ❑ All pipelines at inlet and outlet of fuel compartments penetrate Fuel Pool from its top such that their ruptures would not result in level decreasing below 3 m above the active lengths of FAs. ❑ Besides, pressure pipelines going inside the fuel pool down to compartment ’ s bottom, are provided with siphon break device. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Spent Fuel Pool cooling Arrangement Emergency and Planned Cooling Down NPCI of Primary Circuit L & Fuel Pool Cooling System Normal Operation Function Reactor plant cool down after reactor shutdown, when heat removal from secondary side is less-effective . Residual heat removal from the fuel in the reactor ; Residual heat removal from spent fuel in the fuel pool in all unit operation modes. Protective Function Core flooding and residual heat removal from the reactor core during emergency conditions. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Spent Fuel Pool Cooling NPCI L Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Safety Features NPCI 4 train active Safety systems : L (To cater single-failure criteria, maintenance, knocked off by PIE) Active safety systems backed by emergency power supply (4x100% Emergency DGs) Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Po Post Fukushi st Fukushima ma S Safety Enha afety Enhanc ncem ement ent for SFP fo r SFP Hookup arrangement for water makeup Spent Fuel Pool to manage NPCI Extended Station Black out Scenario. L Adequate water Storage at site with Seismically qualified structure. Air cooled mobile DG for power supply to pumps, valves and for monitoring of parameters Additional diversified long-term closed loop systems is provided in KKNPP unit 3&4 which can remove the decay heat from Spent Fuel pool using diverse principle and powered by Air cooled DG. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
NPCI L SCENARIO IDENTIFICATION UNDER DIFFERENT PLANT STATES FOR SFP Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
Plant States Operational States Accident Conditions Practically Eliminated NPCI L Normal Anticipated Design Design Extension Large release of Operations Conditions Operational Basis radioactivity from Occurrences Accidents containment Acciden Accidents ts with Core without melt Core melt DESIGN EXTENSION CONDITION : Definition Accident conditions that are not considered for design basis accidents, but that are considered in the design process of the facility in accordance with best estimate methodology, and for which releases of radioactive material are kept within acceptable limits. Design extension conditions could include severe accident conditions. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, 15 Vienna, 02 – 05 September 2019
DEC without core melt :To limit the progression of accident and there by avoid core melting. NPCI DEC with core melt : Severe accidents where aim is to confine and L control the core melt so as to mitigate the consequences. The above philosophy is applicable to the events related to Spent Fuel Pool (SFP) also. Over and above, there are some of the events will be considered under practically eliminated events for spent fuel pools. The possibility of certain events occurring is considered to have been practically eliminated if it is physically impossible for the conditions /phenomena to occur or if the events can be considered with a high level of confidence to be extremely unlikely to arise. Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
SCENARIO IDENTIFICATION UNDER DIFFERENT PLANT STATES FOR SFP Considering the methodology, the events related to spent fuel NPCI pool have been identified under different plant states and L provided below. Internal events • Compensable leak in Spent Fuel Pool • Failures of Spent Fuel Pool cooling system • Boric Acid dilution in Spent Fuel Pool • Supporting system failures (Loss of Service Water to Heat Exchangers) • Loss of On-site electrical supply failure • Extended Station Black Out Technical Meeting on the Phenomenology, Simulation and Modelling of Accidents in Spent Fuel Pools, Vienna, 02 – 05 September 2019
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