Economics of nuclear power plants to the extent of 3.4 billion pounds. In general, coal and nuclear plants have the same types of operating costs (operations and maintenance plus fuel costs). However, nuclear has lower fuel costs but higher operating and maintenance costs. Nuclear plants require fissile fuel. Generally, the fuel used is uranium, although other materials may be used (See MOX fuel). In 2005, prices on the world market for uranium averaged US$20/lb (US$44.09/kg). On 2007-04-19, prices reached US$113/lb (US$249.12/kg). On 2008-07-02, the price had dropped to $59/lb. Fuel costs account for about 28% of a nuclear plant's operating expenses. As of 2013, half
Interlanguage fossilization language learners can only eliminate with considerable effort. Moreover, it has also been noticed that this occurs particularly in adult second language learners' interlanguage systems. Selinker suggests that the most important distinguishing factor related to second language acquisition is the phenomenon of fossilization. However, both his explanation that "fossilizable linguistic phenomena are linguistic items, rules, and subsystems which speakers of a particular native language will tend to keep in their interlanguage relative to a particular target language, no matter what the age of the learner or amount of explanation or instruction he receives in the target language" and his hypotheses