August 2013 Plutonium Mountain Inside the 17-year mission to secure a dangerous legacy of Soviet nuclear testing By Eben Harrell & David E. Hoffman Project on Managing the Atom

Belfer Center for Science and International Affairs  |  

Harvard Kennedy School

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unguarded, on the test site and in the 

tunnels.

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As a result of Hecker’s visits, the Rus-

sians began to cooperate. It took years 

for them to reveal everything, but in 

June 1999, Hecker invited Ilkaev to a 

NATO-sponsored conference on non-

proliferation and environmental issues 

in Almaty, Kazakhstan. Hecker orga-

nized the conference with Kadyrzhanov 

of the Institute for Nuclear Physics. 

Ilkaev brought several of his special-

ists from Arzamas-16, including the key 

scientists who performed the experi-

ments at the test site, Styazhkin and 

Stepanyuk, whom Hecker had met with 

on his trip to Russia. The Russians’ attendance was a watershed—only a year or so earlier, Ilkaev 

had declared that they were never going back to discuss remediation efforts. 

At the margins of the conference in Almaty, Hecker, Ilkaev and Kadyrzhanov signed a three-way 

agreement for a series of field studies that would determine the scope of the problem at Semi-

palatinsk. The three countries divided up their duties. The United States, through Los Alamos 

National Laboratory, would fund the effort; Russia agreed to loan the scientists and provide the 

vital information; Kazakhstan would do the fieldwork and provide necessary permissions. The 

U.S. government would fund both the Kazakh and Russian work. Hecker had brought Dr. Phil 

Hemberger, a Los Alamos colleague, with him to lead the scientific aspects of the project. Hecker 

described Hemberger’s role as “essential in providing the trusted link to the Russian scientists, in 

helping to evaluate the seriousness of the proliferation risk posed, and in connecting to the Ka-

zakhs to get the initial fieldwork started.” Hecker recalled that during the first trilateral meetings, 

the Russians revealed that the problem at Semipalatinsk was much more extensive than anticipat-

ed. The most pressing concern was not the nuclear test tunnels, but rather the “equation-of-state” 

tests in shallow bore holes close to the Degelen Mountain area. 

Hecker, in a talk to participants at the NATO conference, emphasized the importance of scientists 

working together. “It was said some time ago that ‘religion preaches the brotherhood of man, but 

science practices it.’ I believe that,” he said. The three signers of the trilateral document and their 

colleagues celebrated with vodka and several rounds of toasts to the project. What they didn’t 

know is that the plan they discussed that evening would take more than a decade to complete. 

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   The 200 kilogram estimate is from Hecker’s trip report.

Source: Siegfried Hecker

From left: Kairat Kadyrzhanov (Kazakhstan), Radi Ilkaev 

(Russia), and Siegfried Hecker (United States), together in Almaty, 

Kazakhstan, 1999.

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Plutonium Mountain: Inside the 17-year mission to secure a dangerous legacy of Soviet nuclear testing

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The Project Begins

Officials from the Russian Atomic Energy agency, then known as Minatom, remained deeply 

suspicious that the United States would use cooperation at Degelen Mountain to collect intel-

ligence about Russian nuclear weapons. Specifically, Russian scientists were concerned that the 

spectrometry equipment needed to verify the presence of plutonium in shafts and tunnels could 

also be used to reveal the mix of different plutonium isotopes used in Soviet—and now Rus-

sian—nuclear bombs. The isotopic composition of Russia’s weapons-grade plutonium was still a 

closely guarded secret.

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Meanwhile, the initial assessments of whether or not the situation in the shallow bore holes was 

a proliferation problem involved an enormous amount of work. Hemberger of Los Alamos was 

on the phone almost daily with Styazhkin and the head of the Kazakh nuclear center, Shamil 

Tukhvatulin. That field work, conducted by the Kazakhs under the direction of the Russians and 

Americans, convinced any remaining skeptic in the U.S. that the proliferation threat was real. 

Hecker went to the U.S. Defense Threat Reducation Agency looking for more help, and they 

agreed. Hecker also sought support from Andy Weber, then in the Office of the Secretary of De-

fense, and from Rose Gottemoeller, an assistant secretary of energy. 

Next, an effort was launched to conclude an official, three-nation agreement to govern the effort. 

In May, 2000, Gottemoeller went to Moscow to meet Russian and Kazakh officials. The Rus-

sian representative was Lev D. Ryabev, first deputy minister of atomic energy, accompanied by 

Styazhkin. Hecker went as Gottemoeller’s technical adviser. All three sides expressed a desire to 

move forward with work on the Semipalatinsk test site, but still struggled with the spectrometer 

issue. A breakthrough came in a technical agreement between Los Alamos and Arzamas-16 sci-

entists in which Russia would allow the United States to use equipment to verify the presence of 

plutonium, but only if U.S. scientists promised to immediately erase all readings on the device, 

and then bury any samples of material taken during testing.

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  U.S. scientists could take a quick 

look at the spectrometer—long enough to verify the presence of plutonium—but not long enough 

to determine the isotopic composition of that plutonium.  

Russian and U.S. officials also disagreed on the important issue of how to dispose of the plutoni-

um. U.S. officials felt it should be dug up and returned to a secure storage in Russia.  Russia was 

not interested in taking it.

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   Most combinations of plutonium isotopes—the different forms of an element, having different numbers of neutrons in their 

nuclei—can be used to make a nuclear weapon. Not all combinations, however, are equally convenient or efficient, which is why 

Russia was concerned about sharing information about the isotopic composition of its bomb fuel.  Nonetheless, given the sophis-

tication of both U.S. and Russian nuclear weapons, the very modest difference between different mixes of isotopes still dominat-

ed by Pu-239, the isotope most suited for weapons, and the immense destructive effects of even unsophisticated nuclear weapons, 

it seems strange that the mixture of plutonium should be such a closely guarded secret in Russia.  A similar concern, however, has 

cropped up again and again in bilateral discussions ranging from plutonium disposition (where the U.S.-Russian agreement al-

lows Russia to mix its weapons plutonium with some reactor-grade plutonium to hide its original isotopic content), to verification 

of stored plutonium (where Russia has been similarly reluctant about letting U.S. experts take measurements). The United States, 

by contrast, has declassified the isotopic composition of its weapons plutonium. Russia may also have been concerned about 

protecting chemical information about gallium added to the plutonium to stabilize it in the desired crystalline form.  The United 

States declassified the fact that gallium is used for this purpose in the 1990s, but Russia did not – and none of the weapon states 

has declassified the exact percentages used. 

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   Viktor Stepanyuk, “Liquidation of Consequences of Nuclear Tests at the Semipalatinsk Test Site (STS) in Trilateral Collabora-

tion,” presentation, Sarov, February 2012. 

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