US company Holtec International has completed a series of free drop-tests on its HI-STAR ATB-1T waste cask, also known as the HI-STAR 330. It is designed for transportation of radioactive non-fuel waste and hardware from reactor operations and decommissioning and has a rectangular footprint, unlike cylindrical fuel-bearing transport casks. Holtec submitted its safety analysis report for US Nuclear Regulatory Commission (NRC) approval in October 2015, planning to start production in 2017.
To earn certification, a transport cask must pass a series of "free drop" tests in which a scaled replica of the loaded cask is dropped from a height of 9 metres on to an unyielding surface without any significant damage. US and international regulations require the cask's orientation at impact with the target surface to cause maximum damage.
A quarter-scale model of the ATB-1T cask, fabricated by Holtec's manufacturing division and instrumented by the New Mexico Sandia National Laboratory (SNL), was subjected to three successive drops in three discrete orientations according to a plan reviewed by NRC. The tests were carried out at SNL’s Albequerque drop test facility. The direct collisions included a top down oblique drop, a centre-of-gravity-over-corner drop, and a puncture drop test. The cask met the structural sufficiency criteria and sustained no damage to its containment boundary or dislodging of its closure lid, Holtec said.
The cask exhibited physical deformation contours in line with those predicted by computer simulations, and data collected during the tests will be assessed. It is expected to confirm the successful structural performance of the cask. The computer simulations will also provide a valuable benchmark for the computer code, validated under Holtec’s quality assurance programme, routinely used to simulate impact phenomena in a variety of nuclear plant systems, structures, and components.
The ATB-1T cask’s large rectangular footprint (3.7 metres by 1.8 metres), with several corners, facets and edges, render it vulnerable to a crushing impact loading. With its payload, it weighs more than 120t, and has no impact limiter to cushion its impact upon its collision with the target, unlike cylindrical casks which are fitted with impact limiters. Avoiding the need for impact limiters simplifies operations and reduces operational dose associated with impact limiter installation, Holtec says. The cask is also equipped with an innovative quick connect/disconnect controlled cask locking system rather than a conventional bolted lid.
