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System Analysis for Reactor Core Problem of Chernobyl

System Analysis for Reactor Core Problem of Chernobyl. Comparison of empirical analysis of data and calculations by a theory. Yoshio Matsuki, D.Sc. Kyoto University’s Doctor of Science (Energy) 2009 – 2015: Professor, Institute of Applied System Analysis, NTUU “KPI”

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System Analysis for Reactor Core Problem of Chernobyl

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  1. System Analysis for Reactor Core Problem of Chernobyl Comparison of empirical analysis of data and calculations by a theory Yoshio Matsuki, D.Sc. Kyoto University’s Doctor of Science (Energy) 2009 – 2015: Professor, Institute of Applied System Analysis, NTUU “KPI” 1994 – 2000 Risk Management Specialist, International Atomic Energy Agency

  2. Nuclear Fission and Chain Reaction • Neutron slow down: by moderator • Heat energy transfer/control: by coolant • Neutron absorption: by control rod • Fuel heat (Doppler effect) • Fission products

  3. RBMK LWR Overview of Nuclear Reactors • Nuclear fuels • Moderator to slow down neutrons • Control rods to absorb neutrons • Contain vessel • Water (coolant) RBMK: Positive Void Coefficient LWR: Negative Void Coefficient CANDU: Positive Void Coefficient, but small FBR: Positive Void Coefficient Gas cooled reactors: Don’t care 

  4. Chernobyl Fukushima

  5. The reactivity balance with the control rods, the fuel’s Doppler effect and the moderator’s temperature effect is The neutron flux and thereby the reactor power increased very fast. Due to the thermal inertia of the fuel and the small value of the fuel temperature coefficient the Doppler effect could not break the power excursion. Therefore, to characterize the process at the initial phase, to use only the reactor kinetics equations is sufficient. Source: Frigyes Reich, Neutron Kinetics of the Chernobyl Accident, ENS News, Issue: 13, summer 2005 (July 2006

  6. Chernobyl type rector (RBMK) • The Chernobyl type of reactor has a positive void coefficient, which means that when a part of the water is replaced by steam, the power will increase. x(1)=N x(2)=c1 ………… x(7)=c6 the code is%Save as xprim7A.mfunction xprim = xprim7A(t,x,i)DeltaK=i*0.030*0.50; %voidcoef=i*0.030pcm/percent void change, void increase 50percentxprim=[(DeltaK/0.001-6.502)*x(1)+0.0124*x(2)+0.0305*x(3)+0.111*x(4)+0.301*x(5)+1.14*x(6)+3.01*x(7);0.2150*x(1)-0.0124*x(2);1.4240*x(1)-0.0305*x(3);1.2740*x(1)-0.1110*x(4);2.5680*x(1)-0.3010*x(5);0.7480*x(1)-1.1400* x(6);0.2730*x(1)-3.0100* x(7)]; Source: Frigyes Reich, Neutron Kinetics of the Chernobyl Accident, ENS News, Issue: 13, summer 2005 (July 2006)

  7. Delayed neutron data for thermal fission in U235 is used Decay constant  The initial values of the delayed neutrons’ precursors are;

  8. Data of Chernobyl TransientSource: Jose M. Martinez. VAL, Jose M. Aragonez, Emilio Mingues, Jose M. Peri. ADO, and Guillermo Velarde, An Analysis of the Physical Causes of the Chernobyl Accident, Nuclear Technology, Vol. 90, June, 1990, pp. 371-399

  9. Analysis by Selected Mathematical Method

  10. Benefit of this methodology • calculates the degree of changes within each valuable, not the absolute value such as average; • calculates and determines the relation with other variables. • focuses on the changes (distribution) of the variables. • emphasizes positive relations between the relative changes in the variables, while statistics examines the appropriateness of the estimated absolute values. • can analyze the variables of different unit together.

  11. Calculated Linear Model

  12. Transient of Chernobyl Reactor

  13. Reactivity and Void

  14. Slope of Reactivity and Void

  15. Comparison with theory • calculated the value of reactivity at the time of the reactor transient of the Chernobyl accident, is 0.015, by the calculated the value of reactivity at the time of the reactor transient of the Chernobyl accident, is 0.015, by the following equation, given 30 pcm/% of the void coefficient and 50 % void insertion by Xenon poisoning: On the other hand, the relation between REACTIVITY and VOID in the model (18), and the coefficient of VOID for REACTIVITY is 0.02266. This observation also suggests 30 pcm/% of the void coefficient, which was discussed by the theory.

  16. Conclusions • 4 parameters were selected for analyzing the process of transient before the explosion. • The result indicated that the reduction of the flow rate of the Main Circulation Pump was dominant over the void and the reactivity during the last few seconds to the explosion. • And, then, the relation between the void and the reactivity was investigated also with this methodology, and the result was compared with the simplified neutron kinetics model; and, the result of this comparison suggested the value of the void coefficient as 30 pcm/%.

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