The goal of these studies was to determine whether we could avoid nuclear proliferation problems associated with current LWR and LMFBR fuel cycles by developing alternative fuel cycles that do not produce nuclear materials in forms suitable for use in a nuclear weapon. The studies concluded that proliferation-proof, diversion-proof fuel cycles are unattainable and that the urgent need of some countries for nuclear power will result in the continued growth of the uranium-based nuclear power industry. In fact, some countries see a need not only for nuclear power facilities, but for their own reprocessing plants and centrifuge enrichment plants in order to assure an adequate, economical supply of nuclear fuel for power production. From a safeguards point of view, reprocessing plants that recover weapons-usable uranium and plutonium from burnt or spent reactor fuel and centrifuge plants that enrich uranium are the most vulnerable elements in the nuclear fuel cycle. Not only do they produce weapons-grade uranium and plutonium in large quantities, but the safeguards technologies necessary to account for the materials on a timely basis are in the development stages prior to test and evaluation. The 1980 General Accounting Office report on problems of nuclear fuel reprocessing concludes that "new technology is needed if the United States is to further its own goals of preventing the spread of nuclear weapons and influence other countries to adopt strengthened safeguards at reprocessing facilities."

As the Department of Energy's lead laboratory for research and development in special nuclear material control and accountability, LASL has made major contributions to these and other safeguards technology problems. We have developed nondestructive assay instrumentation for timely measurement of sensitive nuclear materials in all stages of processing. We have also designed near-real-time material control and accountability systems based on the use of these measurement techniques and are now demonstrating such a system at our Plutonium Processing Facility. Further we have developed the systems methodology necessary to design similar systems for new facilities and to evaluate their detection sensitivities. These integrated systems are necessary to deter and detect diversion of sensitive nuclear material by a knowledgeable insider. With regard to materials accountability for reprocessing, the appropriate measurement instruments are under development at LASL. Based on projected measurement capabilities our design analyses suggest that adequate safeguards accountability systems can be implemented in reprocessing facilities. However, the final assurance can come only after instrument development is complete and measurement systems are tested and evaluated at an operating plant. Whether or not commercial reprocessing is carried out in this country, I believe that in order to fulfill our commitment to international safeguards, we

must continue to develop, test, and evaluate the materials con trol and accountability technology needed to safeguard all types of nuclear facilities including reprocessing plants.

Los Alamos also has the principal responsibility for transferring this developing technology to industry, the Nuclear Regulatory Commission, International Atomic Energy Agency, and other countries. In this role, the Laboratory sponsors an extensive program of special training courses and participates directly in the design of new facilities and the addition of new safeguards to existing facilities.

To meet national goals for the prompt recovery of lost or stolen materials, Los Alamos also plays a lead role in defining and organizing DOE's nuclear emergency search team (NEST). The Laboratory's unique capabilities in weaponrelated fields are applied to development and operational deployment of search, hazard-assessment, and render-safe equipment and procedures that may be needed to deal with improvised nuclear devices and nuclear terrorism. Nondestructive assay techniques contribute significantly to these NEST capabilities. The weapons development program continues to integrate protective measures into the design of nuclear weapons to deny malefactors the ability to achieve a nuclear yield without resorting to extraordinary measures.

For the future, Los Alamos is developing cost-effective methods to integrate material control and accountability with physical protection. The Laboratory is also taking initiatives

to

⚫ develop the NEST technology and organization for extension to nuclear sabotage and reactor accidents. develop special international safeguards technology for application to gas-centrifuge plants, advanced isotope separation plants, the fast-breeder fuel cycle, and highthroughput, spent-fuel reprocessing plants.

develop safeguards systems for away-from-reactor spentfuel storage.

However, technology only augments the institutional controls on nuclear materials and weapons technology. Institutional developments must proceed in parallel with technology if we are to achieve the level of deterrence we require. To that end, three proposals are under consideration: an international plutonium storage supported by about 85% of the nations participating in the INFCE, international or multinational nuclear fuel cycle facilities, and nuclear power parks that close the fuel cycle within their borders. These institutional initiatives promise to address some of the vulnerabilities of the current nuclear economy. Advanced technology must be developed to make them even more effective in order that nuclear energy may be retained as an alternative for the future.

SCIENCE IDEAS

by Bob Riecker

D

uring your lifetime, North America and Europe will separate by the average height

of a person; the Pacific Ocean will shrink by the average width of a singlefamily home. Next year, Los Angeles will move closer to San Francisco by the length of your little finger. Last year, some 100 cubic kilometers of new earth crust were born at crests of ocean ridges. In the last 76 million years, the north magnetic pole has reversed its polarity at least 171 times, and in the last 100 million years, an area equal to the size of the Pacific Ocean basin has disappeared beneath surrounding continents.

Plate tectonics is the unifying concept in geosciences. The Earth's surface is divided into a mosaic of possibly 10 to 12 large (and many smaller) rigid, moving plates, varying from 10 to 100 kilometers thick and often many thousands of kilometers wide. The plates that move apart on our globe must collide somewhere, and when they do, earthquakes and volcanism remind us of turmoil. In an ocean chain over 30,000 kilometers long, new earth crust forms to add rock to continents. At other places, mountains rise because of plate collisions.

We ride northwestward on Our namesake, the North American plate,

which extends from the Pacific coast to the middle Atlantic Ocean. We grind against the Pacific plate along the San Andreas Fault in California. Plate motion insures that, in 50 million years, Los Angeles will become a western suburb of San Francisco. That trip is not easy geologically, as major earthquakes attest periodically.

The gurus of plate tectonics predicted at the paradigm's inception, about 15 years ago, that the new theory would require rewriting of geology textbooks. In fact, that's happened. But we are just now beginning to understand how dynamic and changing the Earth's surface really is.

Problems remain. The simple model of 100-kilometer-thick, rigid plates, or rafts, floating about on "greasy skids" of the Earth's upper mantle looks naive. Seismic research based on study of propagation of elastic waves through the Earth suggests that continents have much deeper roots. Also, we don't really know yet what makes the plates go! Certainly the Earth's natural heat engine drives the rafts, but how, and over what vertical dimensions? The Earth loses heat, generated mainly by radioactive decay, at a rate about five times more than the rate at which man uses energy (2 × 1012 calories/second). How long

have plates moved over the Earth's surface since the planet's birth? As the Earth's heat engine cools, are plate motions slowing, and is mountain building ceasing? Often earthquakes and sometimes volcanism appear in the interior of plates, not only along their edges as predicted by the theory.

Normally the hottest spots are where the action is. That's where plates originate or where they collide or are consumed. At ocean spreading centers, new crust forms and enlarges the plates.

One such hot zone centers along the Rio Grande rift. A rift is a long, narrow, usually down-faulted valley in the Earth's crust. The Rio Grande rift extends from Leadville, Colorado, through New Mexico, and across the border into northern Mexico. Along this 800kilometer rift, significant volcanism, earthquake activity, uplift, and separation have occurred during the last 30 million years.

For the preceding hundreds of millions of years, the entire zone along which the Rocky Mountains stand had been an active mountain-building region. Then 30 million years ago, regional separation initiated rifting. The rift opened along a series of northward and northeastward flaws or lineaments, which reach down through the overlying

sedimentary cover. The series of deep basins that eventually formed in the rift now contain thousands of meters of sediment and volcanic fill.

The deeply cutting flaws that cross the rift are zones of weakness that probably extend deep into the Earth's mantle. They leak vast quantities of molten rock into and through the crust. The Jemez lineament, which extends across the Jemez caldera northeast, was especially active volcanically during the last 10 million years as indicated by large volumes of young volcanic rocks blanketing the surface. Many of these volcanics, silicic in composition, erupted during violent explosions much larger than modern man has seen. Layers of fine ash from some of the eruptions reached as far east as Iowa and Illinois before falling from the atmosphere. The giant scale of these events can be imagined as one rides past the Jemez caldera in the center of the Jemez mountains. This grassy pastureland, more than 15 kilometers in diameter, is the remnant of a large volcano.

The scale of the Rio Grande rift is also quite large. Separation across the rift is as wide as 10 kilometers and uplift exceeds many thousand meters. Does this mean that the North American plate is being torn asunder in the southwestern United States? Some geoscientists believe so, and in their jargon, the rift represents an incipient spreading center where new earth crust forms and shoves aside older rock.

Major crustal stretching occurred not only along the Rio Grande rift but over the entire southwestern portion of the United States. We see evidence of the stretching in the patterns of faulting and the appearance of volcanic rocks in the Basin and Range provinces in Arizona. and Nevada to the west and in the High Lava Plains of Oregon and California to the north. The exact cause of the

SCIENCE IDEAS

stretching remains obscure and controversial. It must involve interactions during the last fraction of geologic time among the North American and Pacific plates and the Farallon plate, which lay between them, but since has been consumed as the southwestern part of our raft overrode it. These interactions also produced and now drive the San Andreas fault splitting California.

There is no question that episodic rifting continues today in New Mexico, as evidenced by the abundant fault scarps, earthquakes, high heat flow, modern elevation changes, recent volcanism, and the geophysical evidence of an anomalous thin crust beneath the rift.

The earliest written record of earthquake activity in New Mexico is of an earthquake swarm described by an army surgeon camping near Socorro in late 1849. Most of the recent earthquakes have occurred in a 150-kilometer section between Belen and Socorro, New Mexico. During the last 20 years, seismic recording suggests a very low level of activity. The level is surprising in view of major crustal movements in the past and the presence of modern fault scarps along the edges of the rift. The rift now appears quiet, but seismically pregnant.

Detailed seismic studies continue in New Mexico with measurements performed by LASL, the New Mexico Institute of Mining and Technology, and the Albuquerque Seismological Laboratory of the U.S. Geological Survey. Each group installed seismometers for different reasons, but all cooperate closely in trying to learn more about seismic activity in New Mexico. One motivation for LASL's seismic research has been to study natural earthquake activity near the hot dry rock geothermal energy experiment at Fenton Hill, so that manmade and natural events can be distinguished. Also construction of new