of Spent Nuclear Fuel Storage Pool in the Exsiccation Accident M. - - PowerPoint PPT Presentation

FEDERAL ENVIRONMENTAL, INDUSTRIAL AND NUCLEAR SUPERVISION SERVICE

Scientific and Engineering Centre for Nuclear and Radiation Safety

www.secnrs.ru

Technical Meeting on the Phenomenology Simulation and Modelling of Accidents in Spent Fuel Pools 2-5 September 2019, IEAE, Vienna, Austria

Assessment of Thermal Behavior

• f Spent Nuclear Fuel Storage Pool

in the Exsiccation Accident

• M. Karyakin

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Outline I. Introduction

• II. Scenario 1: Compartment of SNF storage

facility

• III. Scenario 2: Uncompensated leakage
• IV. Conclusion

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Introduction

➢ The accident at the Japanese nuclear power plant (NPP) Fukushima-1 in March 2011 showed that possibility of accidents with potentially serious radiation consequences couldn’t be excluded with large-scale measures for improvement of safety level ➢ In the presentation is given the description of the assumptions and approximations used by SEC NRS to create computational models of wet SNF storage for representative scenarios of

• ccurrence of accidents involving loss of decay heat removal from

the SNF

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Scenario 1: Compartment of SNF storage facility

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Scenario 1: Storage racks scheme

Principal scheme Computational zones

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Scenario 1: APROS capabilities

➢ determine the thermal-hydraulic characteristics of systems by solving the equations of heat and mass transfer in steam-water mixture ➢ modelling static and transient operating conditions and emergency scenarios ➢ real time simulations ➢ modelling NPP with different design (VVER, RBMK, PWR, BWR, CANDU, HTGR, etc.) ➢ three-dimensional nodal methods

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Scenario 1: Computational model of storage compartment, implemented with Apros

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Scenario 1: Time dependence of the flow rate

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• 0.3
• 0.2
• 0.1

0.0 0.1 0.2 0.3 0.4 100 200 300 400 Flow rate, kg/s Time, h Time dependence of the air water vapor mixture flow rate in supply (blue) and exhaust (red) ventilation systems

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 200 400 Water level, m Time, h

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Scenario 1: Time dependences of the water level and temperature of the rack structures

Time dependence of the water level in the storage compartment

100 200 300 400 500 600 700 800 900 200 250 300 350 Temperature, °С Time, h

Time dependence of the temperature

• f the maximum stressed section
• f the fuel rod cladding (blue) and

the covering tube (red)

100 200 300 400 500 600 700 800 1 2 3 4 Temperature, °С Fuel rods height, m 180 hours 230 hours 280 hours 330 hours

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Scenario 1: Vertical distribution of the fuel rod temperature for different times

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The temperature distribution in the cladding height for different development times of the accident

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Scenario 2: Uncompensated leak

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Scenario 2: ANSYS Fluent capabilities

➢ determine the thermal-hydraulic characteristics of systems by solving the equations of heat and mass transfer in steam-water mixture ➢ modelling static and transient operating conditions ➢ simulate multiphase flows ➢ simulate natural convection flow ➢ three-dimensional finite volume methods

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Scenario 2: Modelling of the fuel rods cladding heat-up using ANSYS Fluent

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200 400 600 800 1000 1200 3 6 9 Temperature, °С Time, d

Temperature-time dependence of the fuel rods cladding heat-up Computational model a b a b

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Conclusion

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✓ The presented qualitative analysis of the possibility of radiation consequences of the accident with the complete loss of power supply in the SNF storage indicates the need for a more detailed consideration of possible severe accidents at nuclear fuel cycle enterprises ✓ It is shown that for the early adoption of preventive measures for the organization of additional recharge emergency storage compartment at the initial stage of the accident, it is important to determine as accurately as possible the available time for their implementation ✓ The computational models are using in the safety assessments which are implemented at SEC NRS