ENERGY

Explaining Japan’s Nuclear Crisis

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National Journal
Amy Harder
March 17, 2011, 2 a.m.

In light of Ja­pan’s nuc­le­ar crisis, the en­tire world is either get­ting an im­promptu nuc­le­ar phys­ics les­son or com­pletely con­fused about what’s go­ing on in­side the four rocked re­act­ors at the Fukushi­ma Daii­chi plant. More ac­cur­ately, it’s prob­ably both.

Here’s a primer on what is””and is not””go­ing on with the re­act­ors (with the un­der­stand­ing that ma­jor de­vel­op­ments are hap­pen­ing con­stantly).

The dis­aster un­fold­ing at the plant, which in­cludes four re­act­ors with ma­jor prob­lems and two without, is at the start of the nuc­le­ar power gen­er­a­tion cycle and at the end. Par­tial nuc­le­ar melt­downs and co­in­cid­ing ex­plo­sions have oc­curred in at least two of the re­act­ors after the double whammy of the earth­quake and tsunami knocked out the plant’s elec­tri­city. Those prob­lems have aris­en with the ac­tu­al gen­er­a­tion of the nuc­le­ar power. The news of the day Wed­nes­day fo­cused on prob­lems with the fourth re­act­or’s spent-fuel pool, the nuc­le­ar waste left over once power has been gen­er­ated.

The terms nuc­le­ar melt­down and spent fuel””and the dozens of oth­ers also crop­ping up in me­dia re­ports””can be com­plex on pa­per and even more con­fus­ing to ima­gine. But one ba­sic point is that the most im­port­ant piece of the puzzle is wa­ter. And in Ja­pan’s case, that piece of the puzzle has been miss­ing.

What’s a melt­down?

Former Nuc­le­ar Reg­u­lat­ory Com­mis­sion Chair­man Dale Klein de­scribed a nuc­le­ar melt­down like a car ac­ci­dent: It can be as minor as a fend­er bend­er or as ma­jor as a head-on col­li­sion. Three of the four dam­aged re­act­ors at Ja­pan’s plant have ex­per­i­enced what can best be de­scribed as “par­tial melt­downs.” A nuc­le­ar melt­down is a bad thing, to be sure, but it’s bad only if the bar­ri­ers en­cas­ing the re­act­or’s core break down. That has ap­peared to have happened in at least two of the four crippled re­act­ors, which caused ex­plo­sions.

A nuc­le­ar melt­down oc­curs with­in a re­act­or’s core when pel­lets about the size of a pen­cil eraser con­tain­ing the ra­dio­act­ive ma­ter­i­al heat up, melt, and form a mol­ten blob. The pel­lets are in­side thou­sands of 10-feet long, pen­cil-thin, shiny met­al tubes called fuel rods. And those fuel rods make up the re­act­or’s core.

An ex­plo­sion oc­curs if that mol­ten blob””which in­cludes hy­dro­gen””es­capes some or all of the re­act­or’s bar­ri­ers and com­busts with air. The re­act­ors at Ja­pan’s plant have three ma­jor bar­ri­ers.

So what causes a re­act­or’s core to heat up in the first place? The lack of wa­ter mov­ing around the re­act­or’s core. In Ja­pan’s case, the earth­quake and tsunami knocked out elec­tri­city and pre­ven­ted the plant from us­ing its backup dies­el gen­er­at­ors to en­sure wa­ter can keep get­ting pumped in­to the core to keep the rods cool.

In a sim­pli­fied ana­logy, pro­du­cing nuc­le­ar power is like boil­ing wa­ter on a hot stove, where the flame un­der­neath the tea kettle is the source of en­ergy. In a nor­mal scen­ario wa­ter boils and steam goes out of the kettle. At a nor­mal nuc­le­ar plant, nuc­le­ar fis­sion in the fuel is the source of en­ergy that heats the wa­ter to pro­duce steam, which gen­er­ates elec­tri­city.

But even if the nuc­le­ar plant stops, the ra­dio­act­ive ma­ter­i­al with­in the nuc­le­ar re­act­or’s core con­tin­ues to pro­duce en­ergy and re­quires wa­ter to cool it down. “They [fuel rods] have a mind of their own,” said Gil­bert Brown, a nuc­le­ar en­gin­eer­ing pro­fess­or at the Uni­versity of Mas­sachu­setts. “They’re still pro­du­cing heat.” It’s like a tea kettle on a stove where the flame is only slowly turned down, but not en­tirely off after you tried to turn it off.  In nor­mal gen­er­a­tion of nuc­le­ar power, “you con­stantly have to be put­ting wa­ter in and tak­ing en­ergy out” to cool down the fuel, Brown said. But if there is no wa­ter (be­cause there is no elec­tri­city) that’s not an op­tion and the fuel can be­come dan­ger­ously over­heated. 

Story Con­tin­ues Be­low Graph­ic

 

What’s the spent-fuel pool?

It’s es­sen­tially a massive swim­ming pool full of wa­ter and spent fuel en­closed in a con­crete and steel con­tain­er. “It’s a very ro­bust swim­ming pool,” Klein said. In Ja­pan’s case, the con­tain­er was el­ev­ated next to the re­act­ors, Klein said. Cur­rent NRC Chair­man Greg Jaczko told law­makers Wed­nes­day that he be­lieved the pool had run dry of wa­ter and was left with the ex­posed fuel rods. Klein and oth­er in­dustry ex­perts who spoke with Na­tion­al Journ­al Wed­nes­day said the re­ports are mixed. But the con­sequences of los­ing wa­ter in a spent pool are bad, Klein said.

“If you lose wa­ter then the spent-fuel pools are out­side con­tain­ment and so you could have ra­dio­act­ive re­lease if you have a prob­lem with los­ing wa­ter in those pools,” Klein said. “I think the worst-case scen­ario is the in­ab­il­ity to keep the spent-fuel pool covered with wa­ter.”

How does it stack up to oth­er nuc­le­ar dis­asters?

“I would ima­gine that after everything sta­bil­izes this will be more sig­ni­fic­ant than Three Mile Is­land,” Klein said, ref­er­en­cing the par­tial melt­down that oc­curred at a Pennsylvania plant in 1979. The Three Mile Is­land dis­aster res­ul­ted from re­act­or mal­func­tions and op­er­at­or er­ror, while Ja­pan’s crisis stems from just not be­ing pre­pared to re­spond to the nat­ur­al dis­aster double-head­er. “I think they know what they want to do, it’s not hav­ing the abil­ity to do it,” Klein said.

The Chernobyl dis­aster in the former So­viet Uni­on, con­sidered the worst nuc­le­ar dis­aster in his­tory, was vastly dif­fer­ent and Ja­pan’s crisis isn’t likely to rise to that level, Klein and oth­er ex­perts said. That re­act­or didn’t have any ma­jor sec­ond­ary con­tain­ment, which al­lowed ra­dio­act­ive ma­ter­i­al to be re­leased in­to the at­mo­sphere freely after an ex­plo­sion.

The big pic­ture

The re­act­ors at the Ja­pan­ese plant were built by Gen­er­al Elec­tric and faced what the nuc­le­ar power in­dustry de­scribes as a “bey­ond-design” cata­strophe. In oth­er words, the double whammy of an earth­quake and a tsunami lar­ger than an­ti­cip­ated was not something the re­act­or design was cap­able of with­stand­ing.

Ra­dio­act­ive ma­ter­i­al that has been in­ter­mit­tently re­leased from the crippled re­act­ors is not in and of it­self a great cause of pub­lic con­cern, ex­perts say. It de­pends on wheth­er the ma­ter­i­al goes any­where oth­er than right near it and how much is re­leased. “Just be­cause there is ra­di­ation, un­less you’re sit­ting in a hot air bal­loon over the top of the build­ing, you’re prob­ably not go­ing to get ra­di­ated,” Brown said.

But sci­entif­ic as­sess­ments aside, the idea of ra­di­ation is not a good one and that’s what got the en­tire world stirred up.

“You would not know you were be­ing ra­di­ated,” said Ar­thur Motta, chair of the Nuc­le­ar En­gin­eer­ing pro­gram at Penn State Uni­versity. “That’s the scary part. I could be sit­ting here and I wouldn’t know it.”

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