Operational Experience with and Postirradiation Examinations on Boiling Water Reactor Control Rods

On-line monitoring of control rod integrity in BWRs using a mass spectrometer

“…However this boron would have the natural isotopic ratio of 19.9% 10 B and 80.1% 11 B. Since boron carbide only dissolves in water after having reached a 10 B depletion of about 50% or more [8], boron that leaked out from a control rod will be significantly depleted in 10 B. Therefore measuring the isotopic ratio 10 B/ 11 B in the reactor water gives information about the origin of the boron.…”

“…A fraction of the formed helium diffuses through the boron carbide structure into the inner free volume of the rod, contributing to the build-up of the rod's internal pressure [7]. Due to the consolidation, which is initiated already at a very low burn up, the propagation of the swelling neutron absorber into the free volume of a rod is impeded, causing the increase of stress on the stainless steel of control rod walls [8]. The contents of helium in the rod and, subsequently, the swelling of the neutron absorber and the internal pressure are increasing with the depletion of boron.…”

“…Coolant may eventually enter the rod and cause a disintegration of the neutron absorber leading to a release of the helium which was captured in the boron carbide lattice. Furthermore, small particles that are produced due to the disintegration of the absorber material might be washed out into the reactor coolant [8].…”

Verhalten von Tritium in B4C‐Absorbermaterial

“…(1 a) aus dem Reaktionsprodukt 'Li beginnt bei Null und hat steigende Tendenz, die Bildung (2) beginnt bei einem Hochstwert und geht mit fortschreitendem "B-Abbrand gegen Null. (1 a) aus dem Reaktionsprodukt 'Li beginnt bei Null und hat steigende Tendenz, die Bildung (2) beginnt bei einem Hochstwert und geht mit fortschreitendem "B-Abbrand gegen Null.…”

“…Es wies keine HuBerlich erkennbaren Schaden auf [2].Abb. Es wies keine HuBerlich erkennbaren Schaden auf [2].Abb.…”