What happened

Shares of uranium giant (and joint owner of Westinghouse Electric Company) Cameco  (CCJ 0.39%) have been on a tear these past three months, surging by 34% from early July through Friday's close.

On Monday, however, these shares took a breather from their long run upward, and were down by 5.2% as of the close of trading.

So what's worrying Cameco investors? The good news is that there's no bad news -- yet. The bad news is that bad news for nuclear energy stocks could be just around the corner.

So what

Cameco stock's surge has accompanied -- and indeed, ridden -- a rising wave of higher prices for the uranium it mines. From early July through Friday's close, TradingEconomics.com reports that the price of uranium has increased by 27%.

That makes a lot of sense, of course. Cameco mines uranium. Uranium is worth more. Therefore, Cameco stock is worth more. But here's the thing: Now that uranium costs $70 a pound, there's more incentive for Cameco and other uranium companies to mine more of it.

Now what

How do we know this?

Well, back in 2021, when uranium prices were still shy of the $50 mark -- but climbing -- the experts at MiningReview.com pointed out that after reviewing the economics of uranium mining, it appeared that prices of about $60 per pound would suffice to make uranium sufficiently profitable that it would incentivize miners to mine more.  

And here's the thing: Uranium prices have surged so fast this time that they only just passed the $60 mark about a month ago. That means that miners probably haven't had enough time to ramp up production in response -- yet. But with prices already in the $70 range, you can bet that's exactly what they're doing -- mining more uranium, and putting more supply on the market.

And what does Economics 101 tell us happens when supply rises in a world of constant or slower-growing demand? That's right: Prices fall.

This, in a nutshell, is what I believe we're seeing happen with Cameco stock Monday: The fear that prices will soon start to fall is starting to overcome the optimism spawned by the recently rising prices.

Investors are wondering how long the good times can continue. And they're taking some profits from their Cameco stock just in case the answer is "not much longer."