During the first 40 years that nuclear waste was being created in the United States, no legislation was enacted to manage its disposal. Nuclear waste, some of which remains radioactive with a half-life of more than one million years, was kept in various types of temporary storage. Of particular concern during nuclear waste disposal are two long-lived fission products, Tc-99 (half-life 220,000 years) and I-129 (half-life 17 million years), which dominate spent fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Np-237 (half-life two million years) and Pu-239 (half-life 24,000 years).