US plans a flying Chernobyl

Wednesday, May 22, 1991

By Eve Sinton

AUCKLAND — The United States is planning to test a nuclear-powered rocket in the South Pacific which, if it fails, could spread radioactivity over New Zealand.

Copies of the ultra-secret Star Wars Timberwind project have been obtained by Auckland University peace researcher Dr Peter Wills. A map shows that the rocket would be tested by firing it across the southern Pacific Ocean on a path very close to New Zealand. Variations in winds or rocket thrust, or inaccuracies in its guidance system, could send it crashing into New Zealand, most likely around Dunedin or Invercargill.

"Any such crash would make Chernobyl look like a controlled release", Wills said.

It is intended to make the rocket circle Antarctica, just north of the 60th parallel. The Antarctic Treaty forbids military activity south of this latitude. The region in which the rocket could come down in the event of its nuclear-powered engine failing is very large, highlighting the uncertainties in the proposed test.

In a ground test some time ago, a one-twentieth scale version of the reactor-driven rocket engine failed after 24 seconds. The risk to New Zealand would be greatest if failure occurred after 75 seconds in the proposed suborbital test. Assuming that the Timberwind engine fails and the rocket crashes at random, the chances of it hitting New Zealand are placed at 4.3 in 10,000 by scientists at the Sandia National Laboratory.

The new, as yet unproven, nuclear rocket propulsion technology is based on a type of reactor known as a "particle bed reactor". It uses nuclear fuel in the form of individually coated particles which are only half a millimetre across. Each particle has a core of uranium and carbon alloy and is coated by layers of carbon and a sealant. A covering of zirconium carbide is designed to prevent chemical reaction with the hydrogen rocket fuel.

In particulate form, nuclear fuel is able to transfer its heat much more effectively than when it is compacted in the form of rods, as in conventional reactors. To maximise efficiency, the reactor would be operated at 2500° Celsius, near the fuel melting temperature, raising concerns over fission product release during operation.

The rocket designers admit that the engine could emit radioactivity in its exhaust, and spent fuel would present a radiation threat if it deteriorated more rapidly than expected.

Previously, particle bed reactors have been studied for commercial, high-temperature, gas-cooled reactors, and as a means of generating electricity for Star Wars. To drive a rocket, the heat is transferred to liquid hydrogen which is heated up to serve as the propellant.

During the first ground test, a blockage developed in the porous tubes which hold the fuel particles and the test was declared "unsatisfactory". It is thought that tests are continuing in the middle of the Nevada nuclear test site.

So far about US$40 million has been spent. Project Timberwind is funded within the US Department of Defense "black budget", which is kept secret.

About 1500 people are allowed to know details of the Timberwind program. These include key staff from the Congressional committees who authorise the funding and various staff from the Department of Defense who lobby Congress.