Conceptual Study for the Dynamic Control of Fusion Power Plant J. S. Kang, K. J. Chung, S. Choi, and Y. S. Hwang NUPLEX, Dept. of Nuclear Engineering, Seoul National University, 599, Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea fatema@snu.ac.kr

General comparison of fission and fusion power plant system Contents Introduction General comparison of fission and fusion power plant system Tokamak system code Dynamic control concept model

Introduction In order to realize nuclear fusion as a future energy source, fusion power plant study is essential. Dynamic control of fusion power plant has not been studied so far Study on fusion reactor dynamic control is a critical element to complete fusion energy development. [2] F. Najmabadi , Fusion Engineering and Design 65 (2003) 143-164 [1] D. Maisonnier et al, Power plant conceptual studies in Europe, Nucl, Fusion 47(2007) 1524-1532

General Comparison of fission and fusion power plant - Nuclear fission power plant system Basic Strategy Nuclear reactor operation control system analysis         - Nuclear reactor core control system. Analysis of core neutron dynamics - Relationship between nuclear reactor thermal output and neutron behavior. Fission reactor core produce an atomic energy. Primary loop system transfer fission thermal energy to secondary loop through heat conduction Heated secondary loop water vaporizes to make steam turbine work. Condenser has a role of cooling secondary loop water with sea water <Overall schematic diagram of Fission reactor system – Black rods in reactor core are control rod.>

General Comparison of fission and fusion power plant - Nuclear fission power plant system Nuclear power plant operation control system can be classified according to measurements such as neutron flux, temperature, pressure, and water level. Thermal energy from fission reactor per unit volume and unit time can be expressed energy per fission reaction(κ), neutron flux distribution(Φ), and fission cross section(Σ). Neutron equilibrium relation in steady state operation Neutron production rate = leakage neutron + absorbed neutron Concentrate on only thermal neutron, neutron diffusion equation can be Then thermal power density distribution and thermal power inside fission reactor core is from fission reaction equation. Carbon rod control neutron flux but also fission reaction rate -> control knob

General Comparison of fission and fusion power plant - Nuclear fusion power plant system Plasma Turbine Heating Current Drive Magnets Cryogenics BOP Blanket, Shield M To Grid Recirculating Power [1] Pearson Coil Fusion power equation which uses deuterium and tritium fuel can be expressed fusion power is mainly concerned with fuel density and temperature. Cross-section for DT fusion reaction in a certain density and temperature condition is the same. Neutron does not directly participate in fusion reaction. fusion power is mainly concerned with fuel density and temperature. [1] B.G. Hong et al, Fusion Engineering and Design, Vol 83(2008)1615-1618

General Comparison of fission and fusion power plant - Comparison unstable stable A deterioration of confinement with increasing temperature is a stabilizing effect for alpha particle heating. [3] Reactivity and power profile. [2] Steady state operation Subcritical Multiplication Neutron flux control Criticality Start up Inertial current drive heating Ignition Fueling and auxiliary heating [2] MIT Open Courseware Nuclear Power Plant Dynamics and Control [3] J. Wesson, Tokamaks second edition, Clarendon press(1997), page 15

Tokamak system code System Code – Calculate physics and engineering parameters of Tokamak with theoretical and empirical formulas. <Role of System Code> Design of new experimental device Tokamak Reactor System Analysis Design and performance study of fusion power plant Dynamic Simulator ?

Tokamak system code Solve simultaneous equations for n variables (Physical parameters or device parameters) Usually, the number of variables exceeds the number of equations. Provide operating spaces as constraints to obtain a particular plasma state via control    Constraints      Variables   Power balance and confinement time Alpha and aux. heating power and energy losses Density limit Electron density Beta limit Pressure = density * temperature Safety factor Bootstrap current fraction, current drive power

Physics Modeling Plasma Elongation Using Menard formula the maximum κ Safety factor - number of toroidal rotations per poloidal rotation of a field line Scaling for ST plasma(Wong formulation) Plasma Current

Physics Modeling Beta Limits According to Menard an appropriate limit on Plasma Beta Lin-liu formula Toroidal Beta Poloidal Beta

Physics Modeling Density Density limit is given by greenwald limit at core region Borass limit at edge region Temperature - ion and electron temperature and densities are related to pressure - After numerical integration , density and pressure. then

Physics Modeling Neutral Beam Injection Energy assume that parobolic-like deposition profile with tangential injection at R0 beam distance Current Drive Efficiency from Start and Cordey fitting result Current Drive Power current to be driven is [plasma current*(1-bootstrap fraction)] therefore

Physics Modeling Plasma Power Balance Equation Electric power conversion coefficient is set to constant value. [1] [2] [2]L.M. Hively, “Convenient Computational Forms for Maxwellian Reactivities”, Nuclear Fusion, 17, p 873-876 (1977) [1]S. Glasstone and R.H. Loveberg, Controlled Thermonuclear Reactions (Van Nostrand, New York, 1960), Chapt. 2.

System code result Fusion power Q Low Q value Beta Limit Region Fusion power and Q value vs Elongation R=4m, A=1.5 Elongation can represent a magnitude of plasma shaping. Elongation range is determined by bootstrap current and Menard limit. Elongation value increase, fusion power and Q value tendency is opposite. Fusion power change is not so severe than Q value. In this calculation result, elongation value around 2.8 is favorable.

System code result Fusion power Q Fusion power and Q value vs Plasma current, Maximum elongation conditon R=4m, A=1.5 Plasma current provides basic Tokamak operation condition. Then,. Figure 4 shows tha reactor Q value would decrease high plasma current is not a recommendable operation condition.

Dynamic Control Concept Strategy to make analysis model of fusion reactor Static Analysis with System Code Cross check viability and performance spaces of fusion reactor Dynamic Analysis starting from magnetic and kinetic controls for basic plasma parameters (equivalent to neutron kinetics in fission) Find major parameters which can affect fusion reactor performance

Dynamic Control Concept Major fusion reactor core control parameters Plasma current Provide basic tokamak operation condition. Plasma position and shape Largest cross section area, D-shape cross section has better performance. Auxiliary heating To heat the plasma to millions of degrees until ignition for self-heated fusion processes. Fueling Control fusion power within plasma density and pressure limits. Build a simple fusion power simulator.

Dynamic Control Concept current drive power is not needed in reactor operation regime as in figure -> main control knob which is equivalent to a carbon rod should be gas puffing system (fueling). operator controls magnitude of fuel -> constrained variables would be changed -> density, temperature, and fusion power also vary. Operator will set these variables with limited regime to obtain a proper fusion power. This procedure will make dynamic control of fusion reactor possible.