distinction between the technology of a nuclear explosive device that would be used as a weapon and one that would be used for a peaceful purpose. For this reason, any TTBT limits on weapons tests had to apply equally to tests for peaceful purposes. Similarly, the basic monitoring requirement of the TTBT and the PNET is the same to determine whether explosions with yields in excess of 150 kilotons have occurred. In assessing the U.S. Government's ability to do this, it does not matter whether the explosion in question is considered a weapons test or a PNE.

BACKGROUND TO THE COMMITTEE'S FINDINGS When the TTBT and PNET were signed in 1974 and 1976, respectively, U.S. policymakers planned to rely on "national technical means of verification" to verify compliance with the TTBT. This meant using sites outside the Soviet Union to record the seismic waves generated by an explosion and then estimating the yield of the explosion based on the size of the seismic signal.

Successive Administrations judged, however, that such means were insufficient to verify Soviet compliance with high confidence, largely because of inherent uncertainties in seismic estimates of Soviet test yields. Moreover. serious concerns arose about possible Soviet violations of the TTBT and the risk of undetected evasion. As a consequence, the Senate did not provide its advice and consent to ratification and the Executive branch worked to improve its monitoring capabilities and, since the mid-1980's, to develop new verification Protocols to the Treaties.

In recent years, U.S. Government experts have gained increasing knowledge of the geology of the Soviet test sites. have developed new analytical methods and have calibrated their seismic efforts with on-site measurements, all of which have reduced their uncertainties and resulted in lower seismic estimates of the yields of current and past Soviet tests. In addition, the new verification Protocols to the Treaties address both the uncertainty problem associated with estimating nuclear yields and the risks of Soviet evasion.

With regard to the uncertainty problem, on-site inspection will provide geological data that are crucial to the analysis of how well seismic signals will be generated and transmitted from an explosion site. In-country seismic monitoring will improve U.S. collection of regional seismic signals, although this may make only a minor contribution to U.S. monitoring confidence. On-site (hydrodynamic) monitoring will provide an independent and, generally, a more accurate estimate of explosive yield, which will reduce the uncertainty in "all-source" estimates of yield and also contribute to the refinement of seismic equations. thus lowering the uncertainty attached to yield estimates that are based only on seismic data.

The Protocols will also make evasion much more difficult. Thus, on-site inspectors will be able to detect the use of large cavities or porous material to reduce the size of the seismic signals emitted by a nuclear explosion. This means that any evasion scheme using those methods would have to depress the apparent yield of an explosion to near 35 kilotons, rather than merely to near 150 kilotons a much more

daunting challenge. On-site hydrodynamic monitoring similarly protects against evasion, by forcing the evader to contend with more than just seismic monitoring. A scheme that might reduce a test's apparent yield in seismic monitoring will be fruitless unless it can either depress the apparent yield to near 50 kilotons or also fool the hydrodynamic monitors that measure the shock wave as close as 35 feet from the explosion.

Several other Protocol provisions are specifically designed to thwart evasion: a limit on the size of cavities for nuclear tests; limits on closely-spaced nuclear tests; local seismic monitoring of group PNEs with a declared aggregate yield over 150 kilotons, to detect any undeclared explosion; and the requirement that the Verifying Party agree to verification measures for any group PNE with that large a declared aggregate yield.

There will still be some uncertainties in U.S. monitoring, although U.S. experts could not think of a reason why the Soviets would want to engage in the minor violations of the 150-kiloton limit that exploitation of those uncertainties (without a major evasion effort) would with some risk permit. There are also still evasion scenarios that one could envision (as described in this report), although they are much more time-consuming, costly and risky than without the new Protocols. Finally, there may well be means of evading the 35-kiloton and 50-kiloton trigger levels, if the only goal of the Soviets is to avoid U.S. access to a test that exceeds those limits but is still well below 150 kilotons.

KEY FINDINGS AND RECOMMENDATIONS

Basic Monitoring Judgments

1. As a result of the cooperative monitoring and inspection measures negotiated with the Soviets and recent improvements in U.S. analytical methodologies, the overall U.S. capability to monitor Soviet compliance with the 150-kiloton limits in the Threshold Test Ban Treaty (TTBT) and the Peaceful Nuclear Explosions Treaty (PNET) has been significantly improved.

2. The Committee concludes that unilateral U.S. capabilities and the cooperative measures provided for in the verification Protocols are sufficient to monitor Soviet compliance with the 150-kiloton limits.

3. The Soviets could conduct tests slightly above the 150-kiloton limits without the U.S. Government being certain that they had done so. The Soviets could not evade the 150-kiloton limits by a significant amount. however, without a lengthy. costly and risky covert evasion effort.

4. It will be more difficult to monitor Soviet compliance with the 35-kiloton and 50-kiloton "trigger levels” for on-site inspection and hydrodynamic or in-country seismic monitoring. These trigger levels will still serve their primary purpose, however, of making any major evasion of the 150-kiloton limits a much more daunting task for the Soviets.

Soviet Incentives to Comply or to Evade

5. The primary motivations for Soviet evasion would be to conduct full-yield tests to validate the performance, reliability or safety of old or new weapons, or to preclude U.S. knowledge of Soviet exotic weapons programs.

6. These motivations are offset by Soviet reliance on proven nuclear weapon designs; by the fact that most nuclear testing needs can be met by tests under 150 kilotons; by the high costs of covert evasion; by the uncertainty that any evasion scenarios would work as intended; and by the risk of detection by the United States or revelation by an increasingly open and anti-nuclear Soviet press and society. The cost, risk and uncertainty factors would all increase if more than one illegal test were attempted.

Evasion Scenarios

7. Although the motivations and risks described above did not lead any Executivę branch witnesses to expect the Soviet Union to attempt any evasion of the Treaties, the following evasion scenarios were presented as examples of the most feasible approaches:

a. The Soviets could attempt an unannounced 300-kiloton explosion in a large cavity to reduce the seismic signal generated by the explosion, and thus the estimated yield, to near the 35-kiloton trigger level for on-site inspection. Covert construction of such a cavity would be a major activity costing hundreds of millions of dollars. requiring years to create and still running the risk of being detected.

b. Because the TTBT Protocol does not restrict the timing or separation of any tests below 35 kilotons. the Soviets could conduct multiple tests that would degrade seismic estimates of yield. Multiple-explosion evasion scenarios appear more feasible regarding the trigger levels than for any significant evasion of the 150-kiloton limit.

c. Testing in deep space, a violation primarily of the Limited Test Ban Treaty of 1963. is the only technically feasible method of completely concealing the occurrence of a large nuclear explosion. The Soviets would not only have to fly a nuclear payload and testing equipment deep into space and be willing to pay the cost, but would also have to develop an adequate cover story for the mission and for their retrieval of testing data at a time when they are increasingly open about their scientific space missions.

Past Soviet Compliance

8. Given current U.S. Government estimates of the yields of past nuclear tests. the Committee can rule out any major Soviet violation of the 150-kiloton limits of 1976. The pattern of past Soviet testing is consistent with either of two other hypotheses: Soviet compliance with the 150-kiloton limit: or a few slight violations of it. The military rationale for slight violations remains in doubt.

9. The inability of the U.S. Government to determine whether the Soviets had or had not violated the 150-kiloton limits was sufficient reason for the United States to negotiate more stringent verification protocols.

Implementation and Counterintelligence

10. The Executive branch has made sensible decisions on organization and policy for implementing the verification Protocols, analyzing the resulting data, producing monitoring estimates and reaching verification judgments.

11. There is a threat of Soviet intelligence exploitation of the inspection process. including efforts to compromise the secrecy of U.S. nuclear weapons and defense programs and to target U.S. inspectors in the Soviet Union.

12. No comprehensive interagency risk assessment has yet been completed. The risks at the Nevada Test Site and at potential locations for housing Soviet inspectors have not been fully evaluated, partly because not all relevant Executive branch elements have participated adequately in the assessments.

13. The Executive branch has not yet resolved major issues of funding for implementation and counterintelligence. While the President could postpone exchanging instruments of ratification until funds for implementation are available, the mere availability of funds will not guarantee that the several agencies involved will have the needed counter- intelligence resources in place before the first inspection occurs.

Protocol Changes

14. The TTBT Protocol contains not only the basic monitoring rights, but also other provisions affecting monitoring capabilities that are essential for effective verification. They include those that specify data to be provided by the Testing Party; assure the reliability of CORRTEX monitoring; set the criteria for "standard" nuclear tests; and list the permitted activities and equipment of inspectors and monitors.

15. The TTBT Protocol also contains provisions that are essential for effective counterintelligence. They include provisions requiring the use of anti-intrusiveness devices and giving the United States the right to escort Soviet personnel at all times; to control the travel and contacts of Soviet personnel; to examine any equipment brought to the United States; and to inspect the baggage, personal belongings and packages brought or mailed by Soviet personnel.

16. These provisions are subject to change by the Bilateral Consultative Commission established pursuant to paragraphs 2-4 of Section XI of the TTBT Protocol. Executive branch statements thus far do not provide sufficient assurance that changes in such essential provisions will be subject to the advice and consent of the Senate.

Recommendations

1. The Executive branch should provide firm assurances that any changes in the TTBT Protocol regarding provisions that are essential for effective U.S. monitoring. counterintelligence or security - such as those listed above - will be treated as amendments to the Protocol that are subject to the advice and consent of the Senate. The Committee recommends that a condition to the instrument of ratification be enacted to buttress those assurances.

2. The Executive branch should also assure the Senate that it will provide the Senate Intelligence Committee prior notice of any other proposed change in the TTBT Protocol that may have a negative impact on U.S. monitoring, counterintelligence or security capabilities, to enable the Committee to voice an objection in appropriate cases, before the issue becomes moot. The Committee recommends that a condition to the instrument of ratification be enacted to protect the interests of all relevant Committees of the Senate.

3. The Parties agree, in paragraph 3 of Article I of the TTBT, to "continue ... negotiations with a view toward achieving a solution to the problem of the cessation of all underground nuclear tests." The Committee did not consider whether the United States should negotiate further constraints on nuclear tests, but supports further research into technologies that may contribute to verification of compliance with any new obligations the United States may undertake.

4. The Executive branch should complete a comprehensive risk assessment immediately. In conjunction with that assessment, relevant agencies should inform the Intelligence Committees of their plans for effective counterintelligence and security countermeasures.

5. The Committee recommends that a condition to the instrument of ratification be enacted requiring that the President not exchange instruments of ratification until he certifies to the Senate that sufficient resources and time are available to prepare for TTBT implementation. including counterintelligence and security countermeasures.