Shizuka Takai and Kouichi Hagino

Abstract A photo-neutron (y, n) reaction with laser Compton scattering y-rays has been suggested to be effective for the nuclear transmutations of fission products. The photo-neutron reaction occurs via a giant dipole resonance, which has a large cross section and whose properties are smooth functions of mass number. The laser Compton scattering can generate effectively and selectively high-energy photons with a desired energy range. In this chapter, we investigate quantitatively the effectiveness of the transmutation with laser Compton scattering based on the Hauser-Feshbach theory using the TALYS code. We carry out simulations for high-decay heating nuclide ‘Cs, in which the cross sections for ‘Cs (y, y), (y, n), and (y,2n) reactions, and the total photonuclear reaction cross sections versus incident photon energy, are calculated. The incident photon energy obtained by laser Compton scattering is also optimized. It is shown that the transmutation with medium-energy photon with a flux of more than 1018/s effectively reduces the radioactivity of the target 137Cs.

Keywords 137Cs • Giant dipole resonance • Laser Compton scattering • Photo­neutron reaction • Radioactive wastes • Transmutation

1.1 Introduction

One of the major problems of the nuclear fuel cycle is the disposal of high-level radioactive waste that contains long-lived nuclides such as 129I and high-decay heating nuclides such as 137Cs. After the severe accident at the Fukushima Daiichi

S. Takai (*)

Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1115, Japan e-mail: takai. shizuka@jaea. go. jp

K. Hagino

Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan

© The Author(s) 2015

K. Nakajima (ed.), Nuclear Back-end and Transmutation Technology for Waste Disposal, DOI 10.1007/978-4-431-55111-9_1

Nuclear Power Plant, there is also a problem of 137Cs having been concentrated by treatment of contaminated water. Transmuting such nuclides into short-lived or stable nuclides is one possible way to resolve this problem. Neutron capture reactions have been proposed for transmutations of such fission products. However, the neutron capture cross sections differ significantly from nuclide to nuclide, and this transmutation method is not effective for nuclides with small neutron capture cross sections such as 137Cs.

Recently, photo-neutron (y, n) reactions with laser Compton scattering y-rays have been suggested as an alternative method for nuclear transmutations [1, 2]. Figure 1.1 shows a schematic illustration of this transmutation. This transmutation uses y-rays generated by laser photons backscattered off GeV electrons and photo­nuclear reactions via electric giant dipole resonance (GDR) [3], which has a large cross section for most nuclides. The GDR is a collective excitation of a nucleus that decays mainly by the emission of neutrons, and its total cross section is a smooth function of mass number. Therefore, this method is expected to be effective for transmuting fission products regardless of isotopes.

So far, transmutation with laser Compton scattering for some nuclides has been evaluated only in a simple manner. In this chapter, we investigate more quantita­tively the effectiveness of the transmutation with laser Compton scattering, espe­cially for 137Cs.