Radioc­ti­ve? Cae­si­um? Lost? That may rai­se more than an eye­brow or two.

So befo­re anyo­ne gets high blood pres­su­re: no need to. Not­hing and nobo­dy is end­an­ge­red and that won’t chan­ge.

Simi­lar case in Aus­tra­lia

The sto­ry reminds one of a case in Aus­tra­lia in Janu­ary 2023 when a very small cap­su­le of radio­ac­ti­ve cae­si­um was lost during road trans­port over 1400 kilo­me­t­res. If hand­led irre­spon­si­bly, cae­si­um can inde­ed be a very dan­ge­rous sub­s­tance. Hence, a major search was initia­ted and the cae­si­um cap­su­le was found only two days later.

Cae­si­um cap­su­le lost in 1984

A simi­lar cap­su­le was lost on the moun­tain Brein­osa near mine 7 east of Lon­gye­ar­by­en in Spits­ber­gen. The inci­dent hap­pen­ed in 1984, no less than 40 years ago. Now the sto­ry sur­faced again in a report in the con­text of pre­pa­ra­ti­ons to clo­se mine 7 in 2025, as Sval­bard­pos­ten recent­ly repor­ted.

The dif­fe­rence to the case in Aus­tra­lia: the cae­si­um cap­su­le in Spits­ber­gen is still whe­re it was lost in 1984. And it will stay the­re.

Mine 7 and the moun­tain Brein­osa: cae­si­um cap­su­le under 300 met­res of solid rock
(pho­to taken during a sche­du­led flight to Lon­gye­ar­by­en).

Radio­ac­ti­ve cae­si­um 137 in mining

So what hap­pen­ed? A source of radia­ti­on such as a cap­su­le of cae­si­um 137 is used for exam­p­le during pro­s­pec­ting mine­ral resour­ces: it can be appli­ed to get infor­ma­ti­on about the com­po­si­ti­on of rocks. The idea is that the inten­si­ty of radia­ti­on recei­ved by a mea­su­ring device from a source of known inten­si­ty and in a known distance yields infor­ma­ti­on aboutn the den­si­ty of the rocks bet­ween the source and the mea­su­ring device and this again tells geo­lo­gists some­thing about the poten­ti­al pre­sence (or absence) of mate­ri­als such as coal that have a dif­fe­rent den­si­ty than, say, sand­stone.

But it is not a good thing when someone drops the cae­si­um cap­su­le into a bore­hole more than 300 met­res deep. This is not to say that someone actual­ly drop­ped it manu­al­ly, a cae­si­um cap­su­le is not some­thing you just hold in your hand, obvious­ly. But any­way, somehow the cap­su­le dis­ap­peared into that 300 m deep, nar­row hole near mine 7 on the moun­tain Brein­osa during pro­s­pec­ting work.

The cae­si­um cap­su­le will stay whe­re it is

It is tech­ni­cal­ly not pos­si­ble to retrie­ve the cae­si­um cap­su­le from more than 300 m depth at the bot­tom of a nar­row bore­hole wit­hout crea­ting an enti­re­ly new way of access, some­thing that would obvious­ly invol­ve mas­si­ve effort. On the other hand, a rock cover of 300 m pro­vi­des a pret­ty safe place for a small amount of cae­si­um. Ground­wa­ter flow lea­king to the sur­face is ruled out by experts, and ero­si­on of more than 300 m of solid rock would requi­re more than one gla­cia­ti­on peri­od, rough­ly equi­va­lent to 100,000 years, and even lon­ger time in case the­re won’t be any future peri­ods of major gla­cia­ti­on. In other words, it can be ruled out that the cae­si­um cap­su­le will appear at the sur­face due to natu­ral pro­ces­ses for a very long time.

Ano­ther fac­tor of the risk assess­ment is the half life of cae­si­um 137 which is 30.1 years. This means that alre­a­dy now the acti­vi­ty of the cae­si­um is redu­ced by more than 50 %. After a total of 10 half life peri­ods, a good 300 years in total, the remai­ning radia­ti­on is under the the­shold of detec­tion thres­hold and far from levels that might be a risk for health of envi­ron­ment. Con­side­ring all this, aut­ho­ri­ties and mining com­pa­ny have deci­ded to let the cae­si­um cap­su­le rest in peace whe­re it is. The only mea­su­re taken is to docu­ment the inci­dent and the whe­re­a­bouts so it is known to future gene­ra­ti­on that it might be a bad idea to dig a deep hole in that very posi­ti­on.