How to Build an Ice Wall Around a Leaking Nuclear Reactor

Alexis C. Madrigal, The Atlantic
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Alexis C. Madrigal, The Atlantic
Aug. 14, 2013, 6:02 a.m.

SAN FRAN­CISCO — Here’s the crazy thing about the plan to build an al­most mile long, 90-foot deep, sub­ter­ranean ice wall around the Fukushi­ma nuc­le­ar plant: It’s not really very crazy at all. Build­ing cryo­gen­ic bar­ri­ers sounds like the spe­cialty of an ob­scure su­pervil­lain, but it’s a well-es­tab­lished tech­nique in civil en­gin­eer­ing, used reg­u­larly for tun­nel bor­ing and min­ing. Ground freez­ing was even tested as a way of con­tain­ing ra­dio­act­ive waste in the 1990s at Oak Ridge Na­tion­al Labor­at­ory and per­formed ad­mir­ably.

Joe Sop­ko, the civil en­gin­eer­ing firm More­trench’s dir­ect­or of ground freez­ing, has spoken with sev­er­al con­sult­ants about the de­tails of the pro­ject, and he’s con­vinced it’s cer­tainly pos­sible. “This is not a com­plic­ated freeze job. It really isn’t,” he told me. “However, the in­stall­a­tion, be­cause of the ra­di­ation, is.”

Ed Yar­mak of Arc­tic Found­a­tions, which in­stalled the sys­tem at Oak Ridge, agreed. “It’s a large sys­tem, but I don’t think it’s out there, where people can’t do it and can’t do it ef­fi­ciently.”

Here’s the prob­lem this tech­no­logy could solve. The Fukushi­ma nuc­le­ar plant, which was dev­ast­ated by an earth­quake and tsunami in March of 2011, is loc­ated on a slope. This fact of to­po­logy means that ground­wa­ter run­ning down from the Abukuma plat­eau to the east pass right in­to the site.


Fukushi­ma’s geo­graph­ic­al loc­a­tion. Box not to scale (Google Earth)

 

Ja­pan­ese of­fi­cials es­tim­ate that 400 tons of wa­ter reach the plant every day and mix with wa­ter used to cool the re­act­ors. That’s roughly 96,000 gal­lons of ra­dio­act­ive wa­ter. About 300 tons (or 72,000 gal­lons) of con­tam­in­ated wa­ter flow out to sea daily, ac­cord­ing to Ja­pan’s Na­tion­al Re­sources and En­ergy Agency.

TEPCO, the Ja­pan­ese util­ity, has been try­ing to deal with these prob­lems, but the volume of wa­ter poses a for­mid­able lo­gist­ic­al chal­lenge, and some of it con­tin­ues to leak out to the ocean.

So, what to do? En­gin­eers have been pump­ing and treat­ing the wa­ter, but the scale has made that too dif­fi­cult and pre­ven­ted oth­er cleanup work from hap­pen­ing. They’ve con­tem­plated di­vert­ing ground­wa­ter ap­proach­ing the site in­to the sea or build­ing clay walls, too. But it ap­pears that of­fi­cials have settled on the ice-wall con­tain­ment strategy, as sug­ges­ted by Ja­pan­ese con­tract­or Kajima.

In news stor­ies, this op­er­a­tion was presen­ted as dif­fi­cult on ac­count of the scale. “The tech­no­logy has been used be­fore in the con­struc­tion of tun­nels, but nev­er on the massive scale that the Fukushi­ma plant would re­quire,” CNN wrote. Even Cab­in­et Sec­ret­ary Yoshi­hide Suga told re­port­ers, “There is no pre­ced­ent in the world to cre­ate a wa­ter-shield­ing wall with frozen soil on such a large scale.”

But the more I dug in­to ground freez­ing, the more I real­ized it was one of those corners of en­gin­eer­ing that’s been quietly help­ing the world’s in­fra­struc­ture get built for dec­ades. There are journ­al art­icles about it and books, too. There’s J.S. Har­ris’ Ground Freez­ing in Prac­tice and the defin­it­ive text­book, Frozen Ground En­gin­eer­ing by Or­lando An­der­s­land and Branko Lada­nyi. There have been hun­dreds of ground-freez­ing pro­jects, an eval­u­ation by the De­part­ment of En­ergy, and dozens of in­ter­na­tion­al con­fer­ences.


Draw­ings of two com­mon ground freez­ing uses: shaft min­ing and tun­nel bor­ing from Frozen Ground En­gin­eer­ing


Here’s how it works. Freeze pipes, made from nor­mal steel, are sunk in­to the ground at reg­u­lar in­ter­vals. The spa­cing is nor­mally about one meter. Then, some type of coolant is fed in­to the pipes. Sop­ko uses a brine — salty li­quid which can be cooled far be­low the freez­ing point of fresh wa­ter without turn­ing in­to a sol­id. On the sur­face, a big re­fri­ger­at­or chills the li­quid, which is pumped in­to the pipes. The li­quid ex­tracts heat from the ground, and re­turns to the chiller, where it is re­cooled and sent back down. It’s not a fast pro­cess and can take many months. (Some­times, for speed’s sake an ex­pend­able re­fri­ger­ant like li­quid ni­tro­gen is used, but it re­quires truck­ing in tanks full of the stuff.)

First, ice forms in columns around the freeze pipes. Then, as time goes on, the ice spreads out, link­ing the columns. Fi­nally, an im­per­meable wall forms. For con­tain­ment, it’s im­port­ant that the ice ex­tend all the way down to the bed­rock, so that the walls of ice form a box with the bed­rock at the bot­tom. If an earth­quake cracks the ice or the power goes out for a peri­od of times, re­fri­ger­at­ing the ground again re-seals the wall.

“You have all this cold frozen soil that wa­ter wants to leak through,” Yar­mak said. “But as the wa­ter leaks its way through, it freezes, and the wall heals it­self back up.”

All this to say: As crazy as it sounds, hu­mans reg­u­larly freeze vast chunks of Earth… be­cause we can. (I am re­minded of our un­of­fi­cial motto: This is your world. Look at it.)

The Fukushi­ma plant is not even the largest ice wall ever at­temp­ted. Sop­ko, An­der­s­land’s last PhD stu­dent at Michigan State, told me that in the 1990s, he’d de­signed and in­stalled a 3.5 kilo­met­er peri­met­er wall that re­quired 1,950 pipes, 159,000 meters of drilling, and eight 1,500 horsepower com­pressors for the Aquar­i­us gold mine in Ontario, Canada. Un­for­tu­nately, while the pipes were be­ing in­stalled, the price of gold plummeted and the sys­tem was nev­er switched on.

“Right now, we’re cur­rently in­volved in a pi­lot test in the oil sands. The pro­posed job would be 8 kilo­met­ers,” Sop­ko told me. “We’re right in the middle of freez­ing a pi­lot test.”

While some tech­no­lo­gies need to change a lot as they scale up, ground freez­ing isn’t one of them. As Har­ris notes in Ground Freez­ing in Prac­tice, “The meth­od is not lim­ited by prob­lems of scale.”

“The three really large jobs that I’ve looked at, the only thing that makes those dif­fer­ent than the small [min­ing] shaft is the coolant dis­tri­bu­tion sys­tem, be­ing able to pump enough coolant through the pipes,” Sop­ko said. “It’s pretty easy to do, though. The pipes are the same and the com­pressors are the same.”

What’s really sur­pris­ing is that the op­er­a­tion does not take that massive an amount of power. Sop­ko walked me through how much power one might need to get the job done. Ja­pan­ese au­thor­it­ies have said the wall’s peri­met­er would be roughly 1,400 meters at a depth of 30 meters. We as­sumed they’d place a freez­ing pipe every meter and want the wall to be 2 meters thick. With those num­bers in mind, Sop­ko made the back-of-the-en­vel­ope cal­cu­la­tion that TEPCO would need about 6,000 horsepower of com­pressor to do the re­fri­ger­a­tion dur­ing the act­ive freez­ing peri­od, which would prob­ably take a couple of months. After that, the main­ten­ance of the ice wall would re­quire about 3,000 horsepower. Yar­mak thought 6,000 horsepower was a pretty good “guess­tim­ate,” as well.

In elec­tric­al terms, that’s about 4.5 mega­watts of power, which is sub­stan­tial, but less than a per­cent of a large power plant’s out­put.

The key prob­lem ground freez­ing pro­jects can run in­to, Sop­ko said, was fast flow­ing ground­wa­ter. Flow rates above 1 meter per day can make it dif­fi­cult for the freeze wall to form. But he said that he’d spoken with people with know­ledge of the site, who said the rate was a tenth of that, or about 10 cen­ti­meters per day.

The most dif­fi­cult thing, as in all cryo­gen­ic bar­ri­er con­struc­tion, is the drilling.

“The holes have to go in straight. They have to be par­al­lel to each oth­er,” Sop­ko said. “If the pipes de­vi­ate too far apart from each oth­er, then, you don’t get clos­ure between the two.” In oth­er words, you’d have holes in your wall.

Arc­tic Found­a­tion’s Yar­mak also noted that the dif­fi­culty of the drilling would vary. The in­stall­a­tion of the pipes on the in­land side of the com­plex would be re­l­at­ively easi­er be­cause the wa­ter you’d en­counter would be less con­tam­in­ated. It’s on the oth­er side, after the wa­ter has passed through the plant, that the drilling could get tricky.

“If it’s con­tam­in­ated ma­ter­i­al, then everything gets really ex­pens­ive, and things slow down. And you have to make sure you’re keep­ing your people safe and not screw­ing up the en­vir­on­ment more than it already is,” Yar­mak said.

However, if the en­gin­eers can get the in­land and wing walls to form, then the amount of wa­ter flow­ing through the plant could drop enough to make drilling on the ocean side a little easi­er.

Still, work­ing on a con­tam­in­ated site is just dif­fi­cult. At Oak Ridge, Yar­mak’s crew had to stay on a patch of pave­ment that had been plopped down over an old cool­ing pond. “You couldn’t walk off the pave­ment. The pave­ment was clean, but the woods were not. You couldn’t go in­to the woods. If the leaves came down, you had to blow them away be­cause they were con­tam­in­ated,” he said. “It was quite an in­ter­est­ing job, but it was a little stress­ful. You wanted to make sure your crew stayed safe.”

At Fukushi­ma, those prob­lems will be even more ex­treme, but the cost of do­ing noth­ing is even high­er.

Re­prin­ted with per­mis­sion from the At­lantic. The ori­gin­al story can be found here.

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