'Test Divider' on 23 September 1992 at the Nevada Test Site:
The last nuclear testnig conducted by the United States

23 September 1992 - Last U.S. nuclear test

The ‘Divider’ – device being lowered into the shaft. Image courtesy of Los Alamos National Laboratory.

This nuclear test’s code-name – Divider – was well-chosen (perhaps unwittingly), as it marked the last U.S. nuclear test to date. The 20 kilotons underground nuclear test, which was conducted at the test site in Nevada on 23 September 1992, was the last of 1,032 nuclear tests carried out by the country. The first U.S. test - Trinity - had been detonated 47 years earlier on 16 July 1945.

The United States conducted more nuclear tests than all other countries combined. While the early  nuclear tests were carried out at remote islands in the Pacific Ocean, starting with the Able and Baker tests in July 1946 at the Bikini atoll, the brunt of the U.S. nuclear tests  - 928 - were conducted at the Nevada Test Site. In an attempt to minimize nuclear fallout on large populations in Las Vegas, Los Angeles and San Francisco, the tests usually took place when westerly winds prevailed. The effects of nuclear testing for downwinders especially in smaller towns in Nevada and Utah, however, were severe.

“It does not constitute a serious hazard to any living thing outside the test site.” 1955 United States Atomic Energy Brochure on the fallout.

Before the advent of nuclear testing in Nevada in 1951, the U.S. government had conducted extensive studies on the effects of radioactive contamination on humans, particularly after the Hiroshima and Nagasaki bombings (the results, including the extensive film and photo material taken at the time, remained classified for decades). Nonetheless, residents close to the Nevada Test Site were assured by the U.S. Atomic Energy Commission that the tests were harmless; see 1955 brochure Atomic Test Effects in the Nevada Test Site Region.

We can expect many reports that ‘Geiger counters were going crazy here today.’ Reports like this may worry people unnecessarily. Don't let them bother you.1955 United States Atomic Energy Brochure
"Atomic Test Effects in the Nevada Test Site Region”
The tower for the cancelled "Icecap" nuclear test planned for late-1992. Photo: NNSA/Nevada Site Office

Shortly after Divider, and following a months-long national grassroots lobbying campaign led by disarmament groups, U.S. President George Bush (Rep.) finally signed Congressional legislation approved by both House and Senate that mandated a 9-month moratorium on U.S. nuclear weapon testing, which was subsequently extended. Senator Mark Hatfield (Rep.) had played a key role in this bipartisan initiative. One year before, Soviet Secretary General Mikhail Gorbachev had unilaterally declared a halt on all Soviet nuclear tests (see Gorbachev’s contribution to the September 2011 issue of CTBTO Spectrum, “Helping to create a truly global community”). Plans for U.S. underground tests initially scheduled for 1993 were abandoned and the 1992 moratorium was subsequently extended by President Bush’s successors.

Activists during protests in the Nevada desert in September 1992.

Important factors leading to the moratorium were the end of the Cold War and the growing public pressure at home. From the mid-1980s, the Nevada desert witnessed a constant increase in protests against nuclear testing. Five months prior to the Divider test, around 500 protesters were arrested on misdemeanour charges after clashing with guards at the annual Easter demonstration against nuclear testing.

In May 2006, an initiative spearheaded by downwinders in St. George against the non-nuclear, high explosive ‘Divine Strake’  test, was successful in achieving its cancellation. Today, there is an ongoing debate on the future use of the Nevada National Security Site, as the Nevada Test Site is now called.

The United States is committed to the ratification of the Comprehensive Nuclear Test Ban Treaty and to its early entry into force, and we will work with the United States Senate to help achieve advice and consent to this important international agreement. U.S. President Barack Obama, May 2010

In 1996, the United States was the first country to sign the Comprehensive Nuclear-Test-Ban Treaty (CTBT) which bans all forms of nuclear explosions. However, the United State has yet to ratify the Treaty, a step that is mandatory for its entry into force. The same applies to seven other nuclear-capable States: China, the Democratic People’s Republic of Korea, Egypt, India, Israel, Iran and Pakistan.