The Economist 14Mar2020

The EconomistMarch 14th 2020 Science & technology 65

O

ccasionally,a fossilturnsupthat

remindspeopleofhowlittleisreally

knownaboutthepast.This,perhaps,is

sucha discovery.It istheskull,a mere

7mmlong,ofa tiny,yetfull-growndino-

saur,preservedinamberfroma deposit

innorthernMyanmarwhichis99myears

old.Thatdatesit tothemiddleofthe

Cretaceous,morethan30myearsbefore

thisperiod’smorefamousdinosaurian

denizens,Ankylosaurus,Triceratopsand

Tyrannosaurus, bestrodewhatisnow

NorthAmerica.

Extrapolatingfromitsskull,Oculu-

dentaviskhaungraaewouldhavebeen

aboutthesizeofa beehummingbird,the

smallestbirdnowalive.And—confus-

inglytomodernsensibilities,whichare

usedtothinkingof“dinosaurs”and

“birds”asseparatecategories—itwasa

bird,too.It belongedtoa groupcalledthe

Enantiornithes,whichweresimilarto

modernbirds,theNeornithes,except

thatevolutiondidnotdeprivethemof

eithertheirteethortheclawsontheir

forelimbs,eventhoughthoseforelimbs

werefullyfunctionalwings.

TheEnantiornithesperishedalong

withmostotherdinosaurs(andabout

three-quartersoftherestoftheplanet’s

animalandplantspecies)ina collision,

66myearsago,betweenEarthandan

asteroid.TheNeornithes,though,sur-

vivedthiscatastropheandwentonto

become,in1758,theclassofanimals

calledAvesinLinnaeus’s“SystemaNatu-

rae”.Thisclassificationpredatedthe

discoveryoffossildinosaurs(indeed,it

predatedtherealisationthatEarthisfar

olderthansuggestedbyBiblicaland

othermythicaltraditions).That,andthe

everydayfamilarityofbirds,hasmadeit

hardtograspthattheAvestrulyarea

groupofdinosaurs.

TheformaldescriptionofO.khaun-

graaewaspublishedthisweekinNature

byXingLidaoftheChinaUniversityof

Geosciences,inBeijing,whohasmany

previousdiscoveriesfromthenorth-

Burmeseambertohisname.Thereis

evidencethattheareainwhichit lived

was,atthetime,anislandinanarchipel-

agoina vanishedoceancalledTethys.Dr

Xingandhiscolleaguesthereforespecu-

latethatit mayhavebeena productof

islanddwarfism—atendencyofinsular

speciestoshrink,comparedtotheir

mainlandrelatives.Whatevertheexpla-

nationforitssize,though,O.khaungraae

nowshareswiththebeehummingbird

(whichisnota productofislanddwar-

fism,butratherofitshabitoffeedingon

thenectarofflowers)thetitleof“small-

estdinosaurknown”.

Thesmallestdinosaur?

Palaeontology

AnotherintriguingdiscoveryfromtheamberminesofMyanmar

Small,butperfectlypreserved

W

ar zones are dangerous places.

Where better, then, for a nuclear reac-

tor? On March 9th America’s government

awarded a trio of firms $39.7m to design

“microreactors” that can supply a few

megawatts of power to remote military

bases, and be moved quickly by road, rail,

sea and air.

The idea of small reactors is as old as nu-

clear power itself. In July 1951, five months

before a reactor in Idaho became the first in

the world to produce usable electricity

through fission, America began building

uss Nautilus, a nuclear-powered subma-

rine. In the 1960s and 1970s small reactors

powered bases in Alaska and Greenland, a

radar facility in Wyoming, a research sta-

tion in Antarctica and—from a cargo ship—

the Panama Canal Zone. America still uses

nuclear-powered submarines and aircraft-

carriers. But land-based mini-reactors

proved unreliable and expensive and have

fallen out of favour.

Interest has been revived by recent

wars, in which American forces proved ex-

traordinarily hungry for energy. Early in

the Iraq war, fuel made up over a third of

the tonnage transported to the region. Be-

tween 2001 and 2010, over half of American

casualties in Iraq and Afghanistan oc-

curred during land-transport missions,

many involving fuel deliveries to remote

outposts. Portable reactors could substi-

tute for unreliable power grids or the gen-

erators that often take their place.

America’s armed forces use about 30

terawatt-hours of electricity per year—

about the same as Ireland—and more than

35m litres of fuel per day. In 2016 a report by

the Defence Science Board, a committee of

experts, concluded that demand would

surge as new power-hungry weapons, like

lasers and rail-guns, come to maturity. Ve-

hicles are also moving away from fossil fu-

els: America expects to have all-electric bri-

gades within the decade. A report by the

army in 2018 said that Holos, a prototype

mobile nuclear reactor, would be 62%

cheaper than using liquid fuel.

It is not just American troops experi-

menting with mobile nuclear power. nasa

is developing smaller “Kilopower” reactors

for space missions, designed to power

small lunar outposts. Russia already uses

larger floating reactors for its nuclear-pow-

ered icebreakers. China plans to install

similar devices on disputed islands in the

South China Sea.

But the planned microreactors would

be distinct in several ways. They are in-

tended to be assembled in a factory and

shipped in one piece, doing away with the

need for tricky engineering in remote

places. They should weigh under 40 tonnes

and fit onto the back of an articulated lorry.

And they are supposed to run themselves,

with “minimal monitoring” from afar.

The risks are manageable, say propo-

nents. Designs feature “passive safety” sys-

tems, which keep working even if electric-

ity is lost or a component breaks. Cooling

pumps can be replaced by natural convec-

tion currents, for instance. The reactors

use “tristructural isotropic particle fuel”, in

which blobs of fissile uranium (along with

oxygen and carbon) are wrapped in layers

of carbon and silicon carbide. The pellets

can withstand high temperatures, contain

radioactive contamination and limit the

impact of accidents. The reactors them-

selves “would be shielded and protected,

and possibly placed in a hole in the

ground”, says Bill Lee, a nuclear engineer

and materials scientist at Bangor Universi-

ty, in Wales. A nuclear meltdown should be

“physically impossible”, says the Pentagon.

The grunts on the ground will be hoping

that is right. 7

Nuclear power plants are coming to a

battlefield near you

Atomic energy

Fun-sized fission