It all looks good on paper. But then, nuclear power always does. The industry has been plagued by delays and cost overruns for decades.Existing sodium-cooled reactors, most of which are experimental, have a spotty record.A plant in Japan suffered a serious fire in 1995 and was shut down for over a decade.The Superphénix reactor in France, built in 1974, proved extremely unreliable, and was offline for years at a time. It closed for good in 1998.(Other reactors, such as the Fast Flux Test Facility in Washington state, have better records.)The Union of Concerned Scientists, an American not-for-profit organisation, argues in a report published in March that sodium's advantages as a coolant are counterbalanced by drawbacks.One is that a reactor which ran too hot might see its power output rise as a consequence.Unlike water, the loss of which shuts a reactor down for lack of moderation, sodium slightly damps the chain-reaction.If bubbles of sodium vapour formed in the coolant, that damping effect would diminish, risking a dangerous feedback loop of rising temperatures and growing power output.
从纸上看一切都很好。但话说回来，核能总是如此。数十年来，该行业一直受到工期延误和成本超支的困扰。现有的钠冷却反应堆大部分都是实验性的，其记录参差不齐。日本的一家工厂在1995年遭受了严重的火灾，并被关闭了十多年。法国的Superphénix反应堆建于1974年，事实证明它非常不可靠，一度中断了好几年。它于1998年永久关闭。(其他反应堆，比如华盛顿州的Fast Flux Test Facility，有更好的记录。)美国非营利组织“忧思科学家联盟”在3月份发表的一份报告中指出，钠作为冷却剂的优点被其缺点抵消了。一个是，反应堆运行过热可能会导致其功率输出上升。与水不同的是，钠会轻微地抑制链式反应，而水的流失会导致反应堆因缺乏节制而关闭。如果在冷却剂中形成钠蒸汽的气泡，这种阻尼效应将会减弱，冒着温度上升和功率输出增加的危险反馈回路的风险。
