Abstract: A storage tank for radioactive fissile material solutions. The tank comprises at least one cell containing a radioactive solution and a solid neutron-absorbing material while preventing any risk of criticality. A network of substantially vertical tubes is arranged within said cell and metal walls completely separate the radioactive solution from the solid neutron absorbing material. Said tubes contain the neutron absorbing material and are located in compartments defined by the metal walls throughout the radioactive solution. Said tank occupies a reduced floor space.