Private bunker demand is exploding in France, driven by fears of a nuclear conflict. Yet the scientific reality of the risk and radioactivity is often misunderstood, particularly when it comes to how long danger lasts.
Appearing on RMC on April 5, 2026, Patrice Roussel, head of the France Bunker company, said he had, for the first time, a wave of quote requests like never before.
Don’t forget the concept of radioactive half-life: all told, radioactivity falls quickly
Requests for quotes on private bunkers are surging in France, underscoring growing anxiety about a nuclear strike on the country. To understand the risk of contamination in such a scenario, you have to recall the half-life concept: the half-life is the time required for a radioactive element’s activity to drop by half. In practical terms, after one half-life, 50% of the initial radioactivity remains; after two half-lives, 25%; after three, 12.5%; and so on. This process follows an exponential law: radioactivity plunges rapidly at first, then more gradually.
In the case of a nuclear explosion, the challenge is that there isn’t a single radioactive element, but more than 300 different isotopes, with half-lives ranging from a few seconds to many decades. The half-life of iodine-131 is about 8 days, while cesium-137 peaks at around 30 years, for example. There are also isotopes with very short half-lives (only a few hours). Thus, in a nuclear strike, the immediate danger is dominated by short-lived, highly radioactive elements that vanish quickly, while the long-term danger comes from long-lived elements that are less intense but persist.
In the event of a nuclear strike on national soil, a few days in a bunker may suffice
So it’s essential to know that radioactivity drops very quickly: seven hours after an attack, radiation levels are reduced by a factor of 10. And 48 hours after, only about 1% of the initial level remains. Additionally, more than 50% of the radioactive energy is released in the first hour.
If a strike occurs a few hundred kilometers away (i.e., within the country), the particles arrive within a few hours to a day. How long should you shelter? The first 24 hours are absolutely critical—you must be indoors with protection; surviving outside without protection is not feasible. Days 1 to 3 constitute a very dangerous phase: even though radioactivity falls sharply, levels can still be potentially lethal. Finally, during the transition phase (days 3 to 14), radioactivity drops to about 1% of the initial level: the risk falls sharply.
By contrast, in a scenario where a strike hits thousands of kilometers away, on another continent, the radioactive elements arrive late and with much weaker radioactivity, so sheltering becomes far less worthwhile.
This wave of requests, which Patrice Roussel of France Bunker described on RMC, reflects a concern about a strike on national territory. Moreover, French clients who contacted him are mainly seeking bunkers with multi-week autonomy: either they don’t grasp how quickly radioactivity declines, or they want absolute protection from any radiation—no matter how low—and thus are willing to invest substantial sums to secure such a sophisticated bunker.
Did you know? How long do you really need to shelter?
Contrary to common belief, you generally don’t have to stay confined for weeks.
- After 7 hours, radioactivity is reduced by a factor of 10
- After 48 hours, it falls to about 1% of the initial level
- The majority of the danger concentrates in the first 24 to 72 hours
That means a temporary shelter can be enough in many cases, especially if you’re far from the impact zone.
