Ryuta Takashima

Possibility of transmutation of Cs135 by ultraintense laser

The possibility of photo-transmutation of long-lived nuclide Cs135 by ultrashort ultraintense laser was analytically evaluated. The yield of Cs135(γ,n) Cs134 was strongly dependent on the laser intensity at around 1020W∕cm2. If Cs135 were irradiated by such a laser with the intensity of 1021W∕cm2 and 10 Hz for 30 min, characteristic γ-ray counting rate was estimated to be 3 Bq.

Capacity switching options under rivalry and uncertainty

Deregulated infrastructure industries exhibit stiff competition for market share. Firms may be able to limit the effects of competition by launching new projects in stages. Using a two-stage real options model, we explore the value of such flexibility. We first demonstrate that the value of investing in a sequential manner for a monopolist is positive but decreases with uncertainty. Next, we find that a typical duopoly firm’s value relative to a monopolist’s decreases with uncertainty as long as the loss in market share is high. Intriguingly, this result is reversed for a low loss in market share. We finally show that this loss in value is reduced if a firm invests in a sequential manner and specify the conditions under which sequential capacity expansion is more valuable for a duopolist firm than for a monopolist.

Decommissioning and Equipment Replacement of Nuclear Power Plants under Uncertainty

This study examines the optimal timing for the decommissioning and equipment replacement of nuclear power plants. We consider that the firm has two options of decommissioning and equipment replacement, and determines to exercise these options under electricity price uncertainty. This problem is formulated as two optimal stopping problems. The solution of this model provides the value of the nuclear power plant and the threshold values for decommissioning and replacement. The dependence of decommissioning and replacement strategies on uncertainty and each cost is shown. In order to investigate the probability of events for decommissioning and replacement, Monte Carlo calculations are performed. We also show the probability distribution and the conditional expected time for each event.

Numerical evaluation of nuclide analysis of I129, Sr90, and Cs137 using bremsstrahlung high energy x ray generated by ultrashort pulse laser

We analyzed numerically the feasibility of nuclide analysis of spent fuels using an ultraintense, ultrashort laser. The (γ,n) reaction yields for each nuclide such as I129, Sr90, and Cs137 were calculated using the bremsstrahlung spectrum and the nuclear reaction cross sections. The dependence of the (γ,n) reaction yield on the irradiation time was derived. We also calculated the dependence of the nuclide ratio on the bremsstrahlung photon temperature. In order to investigate the influence of electron temperature and target thickness on the bremsstrahlung photon spectrum, the calculations were performed using the Monte Carlo code GEANT4. When gold was used as bremsstrahlung converter target at a temperature of the incident electrons of 30MeV, the target thickness providing maximum nuclear reaction yield was found to be 5mm.We analyzed numerically the feasibility of nuclide analysis of spent fuels using an ultraintense, ultrashort laser. The (γ,n) reaction yields for each nuclide such as I129, Sr90, and Cs137 were calculated using the bremsstrahlung spectrum and the nuclear reaction cross sections. The dependence of the (γ,n) reaction yield on the irradiation time was derived. We also calculated the dependence of the nuclide ratio on the bremsstrahlung photon temperature. In order to investigate the influence of electron temperature and target thickness on the bremsstrahlung photon spectrum, the calculations were performed using the Monte Carlo code GEANT4. When gold was used as bremsstrahlung converter target at a temperature of the incident electrons of 30MeV, the target thickness providing maximum nuclear reaction yield was found to be 5mm.

Investment Timing, Capacity Sizing, and Technology Choice of Power Plants

Deregulation of electricity industries has created wholesale markets with uncertain prices and offered greater flexibility to investors to make decisions. In this chapter, we consider the problem of a typical investor who has discretion over not only the timing, but also the sizing of a new power plant. The interaction between these two types of managerial flexibility may be addressed analytically using the real options approach. Since an investor may also have discretion over technology choice, we allow for an investment opportunity in two mutually exclusive projects with embedded timing and sizing options. Via numerical examples, we illustrate how an investor may make decisions about timing, sizing, and technology choice. Sensitivity analyses to key parameters also highlight the intuition for how decisions are made.

The impact of convertible debt financing on investment timing

We develop a model to examine the timing of investment decisions in relation to the issuance of convertible debt by firms. Our model shows that when the demand shock has higher volatility, the firm finances the investment cost with high-coupon convertible debt. We find that default occurs earlier for firms that finance with convertible debt rather than with straight debt. We also find that firms with high-growth prospection, high volatility, and low capital costs that issue convertible debt tend to defer investments. Furthermore, we examine the investment decisions in which the convertible debt includes a call provision. We show that firms that use callable convertible debt invest earlier than those that use non-callable convertible debt by using suboptimal coupon payments. The opportunity from the forced conversion increases as the volatility increases. These results are consistent with recent empirical evidence.

Leaders, Followers and Equity Risk Premiums in Booms and Busts

In this paper, we study an investment problem in which two asymmetric firms face competition and the regime characterizing economic conditions follows Markov switching. We derive the value functions and investment thresholds of a leader and a follower. One of the interesting results is that in contrast to the case of no regime switching, even if the current market size is small, both advantaged and disadvantaged firms have an incentive to become a leader in some parameter settings.

Determination of the temperature of bremsstrahlung photon generated by ultraintense laser using various thickness attenuators

We evaluate the simplified method using the Lambert-Beer law to measure the temperature of bremsstrahlung photon generated by an ultraintense laser. Analytical values are compared to the results of the Monte Carlo calculation of GEANT4 and they agreed very well on the condition of the appropriate distance between the attenuator and the detector. We performed the experiment to measure the temperature of bremsstrahlung x-ray emitted from a metal target irradiated by a Ti:sapphire laser with 76 mJ, 72 fs, 2.2 × 10(18)  W∕cm(2). For a Cu target of 30  μm thick, the photon temperature was reasonably determined to be 0.18 MeV, which is in good agreement with previous studies.

Irreversible Investment, Operating Flexibility, And Time Lags

We consider an optimal investment problem when a firm such as an electric power company has the operational flexibility to expand and contract capacity with fixed cost. This problem is formulated as an impulse control problem combined with optimal stopping. Consequently, we obtain optimal investment timing, optimal capacity expansion and contraction timing, and the investment value. We also show investment, capacity expansion and contraction rule are influenced by the price volatility and the initial capacity is also influenced by the ratio between base-load plant and peak-load plant. In addition, we investigate how time lag between investment and operation influences the investment rule.

Effect of Power Generation Mix and Carbon Emissions Tax on Investment Timing

Electricity production accounts for around 40% of global energy-related CO2 emissions and it is expected that the electricity demand increases to twice the current level in 2050. Therefore it is necessary to invest in low-carbon thermal power plants, nuclear and renewable energy for realizing low-carbon economy. These policies may require a large amount of investment costs, and additionally, the uncertainty increases in a situation surrounding power generation projects and their investments. On the other hand, environmental policy for encouraging use of low carbon emission generation power includes an internalization of the externality for CO2 emissions such as carbon-emissions tax. In this study, we develop a real option model of power generation investments allowing for two uncertainties of the market risk and the introduction of the policy. We analyze the effect of the uncertainties on the power generation mix and the investment timing.