Journal of Nuclear Fuel Cycle and Waste Technology

This study integrates MCNPX and MATLAB to analyze decay heat and radioactivity evolution in spent nuclear fuel (SNF) over 10¹⁰ seconds. MCNPX models burnup-dependent isotopic inventories, while MATLAB solves Bateman equations for decay analysis. Six phases, defined by dominant isotopes, dictate safety protocols. For decay heat, the short-term phase (¹⁴⁰La, ²³⁹Np, ¹⁴⁴Pr) requires active cooling; intermediate (¹⁴⁴Pr, ¹⁰⁶Rh, ⁹⁵Nb, ⁹⁵Zr) permits passive dry cask storage; and long-term (¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am, ²⁴¹Pu) necessitates geological repositories. Radioactivity evolves through three phases: immediate with high gamma emitters (⁹⁵Nb, ¹⁴⁴Ce, ¹⁴⁴Pr, ⁹⁵Zr) demanding shielding; intermediate dominated by ¹³⁷Cs, ²⁴¹Pu, ⁹⁰Sr, risking cask integrity; and long-term radiotoxicity from ¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am, ²⁴¹Pu, requiring geological confinement. These temporal transitions highlight phase-specific risks: short-term strategies prioritize active cooling and shielding, while long-term solutions focus on multi-barrier isolation. The study provides a roadmap for optimizing cooling systems, shielding designs, and repository architectures to mitigate risks across the SNF lifecycle. By mapping isotopic contributions over time, the framework supports balanced technical-regulatory decisions, enhancing safety from reactor discharge to permanent disposal.

Keywords

Spent nuclear fuel, Decay heat, Fuel composition, Spent fuel radioactivity