https://crsreports.congress.gov
Updated August 18, 2025
U.S. Nuclear Weapons Tests
The United States has observed a voluntary moratorium on
nuclear explosive testing since 1992, although it has
maintained the ability to resume these tests at the Nevada
National Security Site (NNSS). Since 1993, it has used a
program known as Science-Based Stockpile Stewardship to
maintain confidence in the “safety, security, and
effectiveness” of its nuclear arsenal. Press reports in May
2020 indicated that Trump Administration officials had
discussed whether to conduct an explosive test of a U.S.
nuclear weapon. Since then, the first Trump Administration
and subsequent Biden Administration statements have
reaffirmed the moratorium.
In an August 2024 video, the Department of Energy (DOE)
National Nuclear Security (NNSA) Administrator stated
that the United States has “no technical reasons” to conduct
nuclear tests. Some analysts have expressed concerns that
NNSA development of new warhead designs could “result
in demands to resume explosive testing.” Congress may
continue to face these issues as it considers authorizing and
appropriating funds for the stockpile stewardship program,
as well as modernization of the nuclear security enterprise.
Limits on U.S. Nuclear Tests
By its own count, the United States conducted 1,054
explosive nuclear tests between 1945 and 1992. Of these,
NNSS hosted 928 tests, including 100 atmospheric tests. In
1990, Congress created a program to compensate some
individuals whose health may have been affected by this
testing. DOE also engages in environmental remediation at
NNSS.
The United States has been a party since 1963 to the
Limited Test Ban Treaty, under which it is obligated to
refrain from conducting nuclear weapons test explosions in
the atmosphere, outer space, or under water. The United
States is also party to the Threshold Test Ban Treaty of
1974, which bans underground nuclear weapons tests
having an explosive force of more than 150 kilotons.
In 1992, Congress passed and President George H.W. Bush
signed into law the Hatfield-Exon-Mitchell Amendment
establishing a temporary unilateral moratorium on
underground nuclear testing (P.L. 102-377, §507; 50 U.S.C.
§2530). It states that “no underground test of nuclear
weapons may be conducted by the United States after
September 30, 1996, unless a foreign state conducts a
nuclear test after this date, at which time the prohibition on
United States nuclear testing is lifted.” Several foreign
states have conducted nuclear tests since 1996.
The United States then participated in negotiations on the
Comprehensive Test Ban Treaty (CTBT). This multilateral
treaty, which opened for signature in 1996, would ban all
nuclear explosions. President Clinton signed and submitted
the treaty to the Senate for advice and consent to ratification
in 1997. Amid expressions of concern among some
Members of Congress about CTBT’s potential national
security implications, the Senate rejected the treaty on
October 13, 1999, by a vote of 48 for, 51 against, and 1
present.
As of August 2025, 187 states parties had signed the CTBT
and 178 had ratified it. The treaty’s entry into force requires
ratification by 44 specific states listed in the CTBT. Of the
44 required states, 35 have ratified, 3 have not signed
(India, North Korea, and Pakistan), and another 5 have not
ratified (China, Egypt, Iran, Israel, and the United States).
Russia revoked its ratification of the treaty in November
2023. In the years since the treaty opened for signature,
India, Pakistan, and North Korea have conducted explosive
nuclear tests.
Although the CTBT has not entered into force, each
subsequent U.S. President has indicated that the United
States will continue to observe the unilateral moratorium.
Most recently, this moratorium was articulated in the
Trump Administration’s 2018 Nuclear Posture Review
(NPR) and the Biden Administration’s 2022 NPR.
The CTBT contains a “zero-yield” standard, which requires
states to refrain from conducting “any test that produces a
self-sustaining, supercritical chain reaction of any kind,”
according to a 2019 U.S. State Department report. Such a
reaction is necessary for a nuclear detonation. Neither the
CTBT nor the U.S. unilateral test moratorium prohibits
subcritical experiments (i.e., those that do not produce a
nuclear yield).
Foreign Countries
The United Kingdom and France also adhere to a zero-yield
nuclear testing standard in line with their CTBT
commitments. U.S. government official statements and
reports to Congress have questioned the Russian
Federation’s and the People’s Republic of China (PRC’s)
adherence to their respective testing moratoria and the zero-
yield standard. The unclassified 2024 version of the State
Department’s annual arms control Compliance Report to
Congress notes concerns “due to the lack of transparency
with regard to their respective nuclear testing activities and
previously identified adherence issues.” Since 2019 this
report has stated that Russia had previously conducted
nuclear weapons-related experiments with more than zero
yield. Department of Defense statements and reports outline
PRC efforts to expand “its nuclear warhead research,
development, testing, and production capacity to support
the size and pace of its nuclear stockpile expansion,” as
well as “the PRC’s possible preparation to operate its Lop
Nur nuclear test site year-round.”
