Question

After the Chernobyl nuclear accident, the Pripyat River in Ukraine received 5.0 ×10¹¹ Bq yr^?1 of ⁹⁰Sr from around the Chernobyl nuclear plant through runoff water and groundwater seepage, totaling 1.0 × 10⁷ m³ yr^?1 of the effluent discharge. The Pripyat River width under a normal (mean annual) flow condition is 200 m. The nearest resident is living at the town of Chernobyl, which is 10 km downstream on the same (south) side of the river as the nuclear plant. Determine the ⁹⁰Sr concentration in the river at the town of Chernobyl.

Answer 1

The Pripyat River width under a normal flow condition is 200 m.

The width of the river can be represented in terms of annual flow rate as;

where is the river mean annual flow rate.

so,

It is recommanded to consider 30 year low annual flow rate for river discharge. Assuming 30 year low river flow rate is one third of the mean annual flow rate. So the 30 year low river flow rate is;

Now the river width taking 30 year low annual river flow rate would be;

and river depth in 30 year low annual river discharge would be;

The river velocity for discharge is given by;

[The minimum distance required to have complete vertical mixing is; which is less than 10 km (distance of chernobyl town from nuclear plant).]

The 90Sr release rate by the plant is

Half life of 90Sr is 28.79 yr, so the dicay constant for 90Sr is;

So the 90Sr concentration in the river at the town of Chernobyl is;