Answers have been edited for length and clarity.

Searchlight: Is there any scientific need for weapons testing in our time?

Dylan Spaulding: There is absolutely no scientific need for new explosive testing to maintain the safety and reliability of existing U.S. nuclear weapons. For the past 30 years, the U.S. has maintained its nuclear arsenal and annually certified its reliability, using a science-based approach that does not require explosive nuclear testing. All the weapons in our current stockpile were tested at full scale when they were originally produced, and the U.S. maintains the largest trove of nuclear testing data of any nuclear-armed country, including Russia.

Throughout the Cold War, the U.S. conducted 1,030 nuclear tests, and data from those tests continues to be analyzed using ever-improving techniques. In addition, the U.S. national laboratories have advanced experimental facilities and some of the most powerful computers in the world, which allow scientists to understand the physics and materials science of nuclear weapons at a level that wasn’t possible when the U.S. last conducted underground nuclear explosions. As a result, scientists now understand weapons performance better than could have been imagined in the era of explosive testing.

A minority of weapons scientists argue that testing would allow validation of certain aspects of computer codes used to study weapons that are still out of reach with other experimental tools. However, the geopolitical costs of testing far, far outweigh the minimal technical benefits. It is more likely that a return to testing would come from a desire to make a political statement, and a desire to break this long-held moratorium.

The costs of doing that would be a huge gift to U.S. adversaries. It would invite other countries who don’t have extensive testing experience or the same level of data as the U.S. to catch up, stoking fears of new weapons development internationally. It would also make any future efforts to reduce nuclear dangers with arms control agreements much harder. 

Searchlight: What about testing the new weapons that are currently in the works? 

Spaulding: No, I don’t think that they need to test, even for the W87-1 or W93 warheads that are currently being developed. As far as we know, these designs represent only minor departures from tested designs. Up to half of the W93s will likely re-use existing pits, according to Jill Hruby, the current head of the National Nuclear Security Administration. The knowledge of material properties for the components within weapons is better now than it was at the end of the Cold War. That allows much better computer modeling and other quantitative assessments to be done, so we’re sure we understand how any changes could affect performance. In most cases, for any potential alterations to a design, the question is not “Will it work?” The question is: “What is the minute uncertainty that is introduced by that change?” 

Furthermore, any change to components that are outside the nuclear explosive package — the part containing the primary and secondary stage, or the “nuclear” part of the warhead — can be tested. That includes things like the firing and fusing system, sensors, valves and other components.

Searchlight: If testing suddenly resumes, should this country be concerned about frontline communities?

Spaulding: Underground tests would typically pose much less risk than above-ground tests, which can result in fallout that travels downwind, and which in the past settled over populations near where testing occurred. In the U.S., people are currently fighting for compensation from harms experienced because of testing under the Radiation Exposure Compensation Act. To those who are still fighting for recognition and support for the harms of testing during the Cold War, even raising the idea of testing again is unthinkable and can feel like further betrayal by their own government. At the end of the day, any form of testing comes with the potential for human harm, which is a strong argument for why it should never be resumed, particularly given the lack of any technical benefit and the guarantee of international repercussions.