It is also important to secure nuclear materials in countries that enrich uranium for fuel.

VOA: standard.2010.08.06

So you start with your basic model, then you add in, you enrich the model, and you see if the results change, and that'll help you explain why you're getting different results in different settings.

你们从最原始的模型开始,加入约束条件来丰富这个模型,然后检验结果是否有变,这能帮助我们解释,为什么在不同条件下结果是不同的

耶鲁公开课 - 博弈论课程节选

"Last November,Iran announced that it would build In February, Iran said that it would begin to enrich uranium to nearly 20 percent-moving,closer to weapons-grade material."

VOA: standard.2010.06.09

Under the scheme, Russia would further enrich the uranium to the 20 per cent purity needed for use in a research reactor in Tehran which produces medical isotopes but is running out of fuel.

VOA: standard.2009.10.24