Klaus Noack

STUDIES OF A STRAIGHT FIELD LINE MIRROR WITH EMPHASIS ON FUSION-FISSION HYBRIDS

Abstract The straight field line mirror (SFLM) field with magnetic expanders beyond the confinement region is proposed as a compact device for transmutation of nuclear waste and power production. A design with reactor safety and a large fission-to-fusion energy multiplication is analyzed. Power production is predicted with a fusion Q = 0.15 and an electron temperature of ~500 eV. A fusion power of 10 MW may be amplified to 1.5 GW of fission power in a compact hybrid mirror machine. In the SFLM proposal, quadrupolar coils provide stabilization of the interchange mode, radio-frequency heating is aimed to produce a hot sloshing ion plasma, and magnetic coils are computed with an emphasis on minimizing holes in the fission blanket through which fusion neutrons could escape. Neutron calculations for the fission mantle show that nearly all fusion neutrons penetrate into the fission mantle. A scenario to increase the electron temperature with a strong ambipolar potential suggests that an electron temperature exceeding 1 keV could be reached with a modest density depletion by two orders in the expander. Such a density depletion is consistent with stabilization of the drift cyclotron loss cone mode.

Efficiency and reliability in deep-penetration Monte-Carlo calculations

Abstract In this paper the effect of the weight-window splitting/roulette-technique and of the biasing method on the efficiency and a newly-defined quality characteristic called “reliability” has been studied by Monte-Carlo simulations of a monoenergetic shielding model. Both methods have utilized the same type of importance functions. It is observed that efficiency and reliability show qualitatively similar dependences on the calculational schemes, though quantitative differences are evident. Concerning the optimum effect of the weight-window method, the hypothetical concept of using the adjoint flux in determining the weight-window has been supported with respect to efficiency as well as reliability. The direct comparison of the biasing and splitting method in utilizing information on certain adjoint functions shows the great superiority of the biasing method.

THE GDT AS NEUTRON SOURCE IN A SUB-CRITICAL SYSTEM FOR TRANSMUTATION

In the last decade, a great progress was made in developing projects of sub-critical fission systems dedicated to transmutation of nuclear waste. In contrast to a fission reactor, such a device is fed with neutrons from an outer source in order to sustain a steady-state power generation. The Budker Institute of Nuclear Physics has made the proposal of a powerful 14 MeV neutron source based on a gas dynamic trap (GDT). This neutron source is primarily thought as irradiation facility for fusion material research. So, the question raises, whether the GDT based neutron source could be a candidate to efficiently drive such a sub-critical system too. The contribution pursues this question using results of first neutron transport calculations. The calculations were made for a simplified model of an actinides burner, which has been developed for an international benchmark exercise performed under the auspices of the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development (OECD). Important parameters of the burner are compared for two cases - when driven by a spallation or by the GDT neutron source. From this comparison some advices for further improvements of the GDT neutron source are concluded.

Safety and power multiplication aspects of mirror fusion-fission hybrids

Recently, in a research project at Uppsala University a simplified neutronic model for a straight field line mirror hybrid has been devised and its most important operation parameters have been calculated under the constraints of a fission power production of 3 GW and that the effective multiplication factor keff does not exceed 0.95. The model can be considered as representative for hybrids driven by other types of mirrors too. In order to reduce the demand on the fusion power of the mirror, a modified option of the hybrid has been considered that generates a reduced fission power of 1.5 GW with an increased maximal value keff =0.97. The present paper deals with nuclear safety aspects of this type of hybrids. It presents and discusses calculation results of reactivity effects as well as of driver effects.

The hybrid reactor project based on the straight field line mirror concept

The straight field line mirror (SFLM) concept is aiming towards a steady-state compact fusion neutron source. Besides the possibility for steady state operation for a year or more, the geometry is ...

Neutronic Model of a Mirror Based Fusion-Fission Hybrid for the Incineration of Spent Nuclear Fuel and with Potential for Power Generation

Abstract In the last decade the Georgia Institute of Technology (Georgia Tech) published several design concepts of tokamak based fusion-fission hybrids which use solid fuel consisting of the transuranic elements of spent nuclear fuel from Light-Water-Reactors. The objectives of the hybrids are the incineration of the transuranic elements and additional net energy production. The paper presents a rough scientific design of the blanket of a mirror hybrid which was derived from the results of neutron transport calculations. The main operation parameters of two hybrid options were specified. One is the analog to Georgia Techs first version of a “fusion transmutation of waste reactor” (FTWR) and the other is a possible near-term option which requires minimal fusion power.

ON POSSIBILITIES FOR TRANSMUTATION OF NUCLEAR WASTE AND ENERGY PRODUCTION WITH A“STRAIGHT FIELD LINE MIRROR” NEUTRON SOURCE

Abstract A pure fusion mirror device suffers from the predicted low values of the Q factor (energy gain factor). A much higher energy production may be achieved in a fusion-fission reactor, where the fusion plasma neutron source is surrounded by a fission mantle. The fusion neutrons are capable of initiating energy producing fission reactions in the surrounding mantle. A mirror machine can probably be designed to provide sufficient space for a 1.1 m wide fission mantle inside the current coils, and the power production from the fission reactions can in such a case exceed the fusion power by more than two orders of magnitude (Pfis/Pfus ≈ 150), suggesting a realistic reactor regime for a mirror based fusion-fission device. An energy producing device may operate with an electron temperature around 1 keV. Transmutation of long-lived radio active isotopes (minor actinides) from spent nuclear fuel from fission reactors can reduce geological storage from 100 000 years to only 300 years. Since the energy of D-T fusion neutrons are above the threshold for the most important transmutation reactions desired for treatment of nuclear waste, there may be an interest for a mirror transmutation device even if no net energy is produced. Recent theoretical simulations have considered the possibility to use the Gas Dynamic Trap (GDT) at Novosibirsk as a subcritical burner for transmutation by fusion neutrons. In the present work, possibilities for mirror based fusion-fission machines are discussed. Means to achieve sufficient end confinement for a straight field line mirror fusion-fission system with a thermal barrier are briefly analyzed. End leakage can alternatively be avoided by connecting the ends of a magnetic mirror with a stellerator tube, while the fusion neutrons are produced in the mirror part where a high energy sloshing ion component is confined. A zero dimensional model for such a mirror-stellarator system has been developed. The computed results indicate some possible parameter regimes for industrial transmutation and power production.

Hybrid Reactor Studies Based On The Straight Field Line Mirror

The straight field line mirror (SFLM) hybrid reactor studies aim to identify a concept where the safety of fission power production could be enhanced. A fusion neutron source could become a mean to achieve this. The SFLM studies address critical issues such as reactor safety, natural circulation of coolants, steady state operation for a year or more and means to avoid too strong material loads by a proper geometrical arrangement of the reactor components. A key result is that power production may be possible with a fusion Q factor as low as 0.15. This possibility arises from the high power amplification by fission, which within reactor safety margins may exceed a factor of 100. The requirements on electron temperature are dramatically lower for a fusion hybrid compared to a stand-alone fusion reactor. This and several other factors are important for our choice to select a mirror machine for the fusion hybrid reactor studies.

Radial drift invariant in long-thin mirrors

In omnigenous systems, the guiding centers are constrained to move on magnetic surfaces. Since a magnetic surface is determined by a constant radial Clebsch coordinate, omnigenuity implies that the guiding center radial coordinate (the Clebsch coordinate) is constant. Near omnigenuity is probably a requirement for high quality confinement and in such systems only small oscillatory radial banana guiding center excursions from the average drift surface occur. The guiding center radial coordinate is then the leading order term for a more precise radial drift invariant Ir, where higher order corrections arise from the oscillatory “banana ripple” associated with the excursions from the mean drift magnetic surface. An analytical expression for the radial invariant is derived for long-thin quadrupolar mirror equilibria. The formula for the invariant is then used in a Vlasov distribution function. To model radial density profiles, it is necessary to use the radial invariant (the parallel invariant is insufficient...

Neutron diagnostics for mirror hybrids

Fusion-fission (FuFi) hybrids will need instrumentation to diagnose the deuteriumtritium plasma, whose 14-MeV neutron emission is the driver of the sub-critical fission core. While the fission neutron yield rate (Yfi and hence power Pfi) can be monitored with standard instrumentation, fusion plasmas in hybrids require special diagnostics where the determination of Yth (∝Pfu) is a challenge. Information on Yfu is essential for assessing the fusion plasma performance which together with Yfi allows for the validation of the neutron multiplication factor (k) of the subcritical fission core. Diagnostics for hybrid plasmas are heuristically discussed with special reference to straight field line mirror (SFLM). Relevant DT plasma experience from JET and plans for ITER in the main line of fusion research were used as input. It is shown that essential SFLM plasma information can potentially be obtained with proposed instrumentation, but the state of the hybrid plasma must be predictably robust as derived from full...