Experimental Study of Photonuclear Transmutation Driven by Laser-Wakefield Acceleration

摘要: The sustainable development of nuclear energy depends greatly on the proper disposal of spent nuclear fuel (SNF). Fast reactors (FRs) and accelerator-driven systems (ADS), based on neutron-induced reactions, show high efficiency in transmuting most actinides and long-lived fission products (LLFPs) in SNF. For a small set of nuclides with relatively low neutron-capture cross-sections, such as 93Zr and 126Sn, complementary strategies are needed. Also, under neutron-induced reactions, successive neutron captures could potentially change stable nuclides into long-lived radioactive ones(e.g., 133Cs to 135Cs). To broaden nuclide transmutation scope and boost overall efficiency, photonuclear transmutation was proposed as a supplement to neutron capture. It uses high-flux γ rays in the giant dipole resonance (GDR) energy region to start photonuclear reactions, converting long-lived nuclides into short-lived or stable ones. In this research, laser-wakefield acceleration (LWFA)-driven photonuclear transmutation was experimentally carried out at Peking University’s Compact Laser Plasma Accelerator (CLAPA). Laser pulses with an intensity of 1019 W/cm2 generated 200 MeV electron beams. These electrons impinge on a Ta converter to produce broadband bremsstrahlung γ rays, which irradiated a CsI target with 133Cs and 127I as LLFP surrogates. Offline activation spectra measured by a high-purity germanium (HPGe) detector showed clear characteristic lines of 132Cs, 126I, and 124I. Combining activationspectrum analysis with Geant4 simulations, the total transmutation yield normalized to incident laser pulse energy was estimated at 1.35 × 105 J−1. This performance is better than that of laser-induced bremsstrahlung and nuclear-resonance γ-ray sources, and is comparable to electron linac bremsstrahlung. With further setup optimization and laser technology progress, especially in pulse energy and repetition rate, the LWFA-driven γ source is expected to further improve its transmutation ability and serve as an effective complement to FRs and ADS.