PASSIVE SAFETY COMPONENTS FOR LEAD-COOLED REACTOR FACILITIES

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1 Joint-Stock Company N.A. Dollezhal Research and Development Institute of Power Engineering PASSIVE SAFETY COMPONENTS FOR LEAD-COOLED REACTOR FACILITIES V.V. Lemekhov, M.K. Sarkulov IAEA Technical Meeting October 2015 Vienna, Austria

2 CONTENT Introduction Advantages of passive components (PC) of safety systems Complexities involved in designing and using passive components Specific features of lead-cooled reactor facilities Design options for lead-cooled reactors Reasonability of PC application in a lead-cooled reactor facility Key problems Conclusion 2

3 Introduction In traditional reactor facilities, safety is improved by increasing the number of safety system devices. REACTIVITY CONTROL MEMBERS (RCM) Principal: Rod-type, driven Liquid Additional: Dynamic, rod-type Floating Storage-type Liquid Bulk Gaseous Shape-memory 3

4 Introduction The same technical approaches are not fit for lead-cooled reactor facilities. Specific features of lead-cooled reactors Compliance with regulatory requirements Nontraditional (new) approaches: Active-passive components of safety systems Passive components of safety systems 4

5 Advantages of passive components of safety systems Passive component is a component the operation of which is linked to only the event It has been initiated by and does not depend on the operation of another active system (component), e.g., a control system, a power source and so on (NP General Provisions for Ensuring the Safety of Nuclear Plants). Passive components of safety systems eliminate: the need for the active actuation signal to be generated; the need for forming branched monitoring and alarm systems; the need for using external power sources. Passive components of safety systems make it possible to: simplify and make cheaper the design of reactivity control members; reduce the number of active devices and systems; use constant natural forces as the driving force; use physical properties of materials. 5

6 Complexities involved in designing and using passive components Actuation directly in response to the event is hard to implement both technically and from the point of view of further operation. The current drawbacks of passive safety components consist in that they: are disposable; are hard to monitor during operation; fail to satisfy to required parameters; require further experimental studies. Therefore, active and passive components are combined in safety systems nowadays: passive driving force making it possible not to use external power sources (cheaper equipment); an active retaining trigger generating the command (signal) for actuation (de-energization, switchover of a valve and so on). 6

7 Specific features of lead-cooled reactor facilities Safety-related properties of the BREST-OD-300 reactor: Small reactivity margin High heat capacity of the circuit Low fuel temperature Long reactor power excursion period Reduced requirements to speed of response of safety systems Coolant: High density (10500 kg/m 3 ) Reflection properties Passive driving Archimedes force Use of neutron leakage Use of passive safety components In lead-cooled reactor facilities, the events for the response of the reactor shutdown members are Coolant flow rate reduction (level variation); Increase in the neutron flux (reactivity ramp); Increase in the coolant temperature; Pressure increase in the gas cavity. 7

8 Design options for lead-cooled reactor faciliries Albedo properties of lead Passive feedback system (PFS) creating leakage of neutrons Event to respond to a lead flow rate (head level) variation 8

9 Design options for lead-cooled reactor plants High density of lead Archimedes force as RCA driving force Event to respond to the lead temperature threshold reached 9

10 Reasonability of PC application in lead-cooled reactor facilities Use of passive safety components will make it possible to: to switch from the current approach to improvement of safety through an increase in the number of safety system devices to ensuring safety of a lead-cooled reactor thanks to the complete revelation and use of its physical properties; use natural safety inherent in fast lead-cooled reactors; reduce the number of active systems and devices (control, support, monitoring); simplify operation; cut the cost of both the reactor development and operation. 10

11 Key problems Building passive safety components for lead-cooled reactors requires: further search for and development of new, parameter-sensitive materials to remain serviceable through the service life. Devices shall be, where possible, reusable and allow periodic serviceability inspections; that desired characteristics are ensured. Fast speed of response the time from the achievement of the parameter threshold value (occurrence of the event) to the immediate actuation of the device (RCA introduction into the reactor core, reactor shutdown); 11

12 Conclusion Traditional approach an increase in the number of safety system devices. Traditional approaches are not always suitable for lead-cooled reactor facilities. Thanks to its properties (small reactivity margin, high heat capacity of the circuit, low fuel temperature), the dynamic processes in the BREST-OD-300 reactor are more inertial which allows reducing the requirements to the speed of response of safety systems. It is practicable to use the reflection properties of lead and its high density for using Archimedes force as the driving force for the RCA introduction into the reactor core. The inertia of the processes allows using passive components of safety systems as principal components. This requires a thorough study, including search for materials and solution of the reuse issue. Properties of lead-cooled reactor facilities and peculiarities of passive components make it possible to switch to a new, passive approach to ensuring safety. There is no need for using branched (external, active) systems for parameter monitoring and signal generation. Passive components offer a solution not only to the safety problem but also to the cost reduction issue. 12

13 JSC NIKIET, Rosatom State Atomic Energy Corporation THANK YOU FOR YOUR ATTENTION! P.O.B 788, , Moscow, Russia 13