Calculation of Doppler Reactivity Worth in Transient with Space Dependence of Self-shielding in Fuel Pellet

• Published in: Journal of the Atomic Energy Society of Japan / Atomic Energy Society of Japan Vol. 41; no. 7; pp. 797 - 801
• Main Authors: SANO, Tadafumi, TAKEDA, Toshikazu, IKEDA, Hideaki
• Format: Journal Article
• Language: Japanese
• Published: Atomic Energy Society of Japan 1999
• Subjects: Integral equations; Mathematical models; Neutron scattering; Nuclear fuel pellets; Nuclear reactor accidents; Radiation shielding; Reactivity (nuclear); Reactor startup; Temperature distribution; Transients
• ISSN: 0004-7120; 2186-5256
• DOI: 10.3327/jaesj.41.797

Doppler reactivity worth of a thermal reactor cell during a transient was evaluated with space-dependent effective neutron cross sections calculated by the multiband method. Temperature distribution in the fuel pellet was also taken into account in calculating the neutron cross sections. The temperature distribution was calculated from the kinetic equation based on the improved quasistatic approximation. The shape functions were obtained from solutions of the integral transport equation. As a transient, a start-up accident was considered with a ramp reactivity of 30$/s(total 1.5$). Compared with the Doppler reactivity worth calculated by the conventional method using the fuel-averaged effective neutron cross sections and the fuel-averaged temperature, a significant difference as observed under a steady state condition was not observed; the maximum difference was only 2.0% for the present transient. This is because the temperature distribution in the fuel pellet was nearly flat.