Session: OAC-03-01/04-01 Monitoring, Diagnostics & Inspection and Storage and Transportation of Radioactive and other Hazardous Materials I

Paper Number: 60533

Start Time: Wednesday, July 14, 2021, 08:00 PM

60533 - 30 CM Horizontal Drop of a Surrogate 17x17 PWR Fuel Assembly 

The 30 cm drop is the remaining NRC normal conditions of transport (NCT) regulatory requirement (10 CFR 71.71) for which there are no data on the response of spent fuel. While obtaining data on the spent fuel is not a direct requirement, it allows for quantifying the risk of fuel breakage resulting from a cask drop from a height of 30 cm or less. Because a full-scale cask and impact limiters are very expensive, 3 consecutive drop tests were conducted to obtain strains on a full-scale surrogate 17x17 PWR assembly. The first step was a 30 cm drop of a 1/3 scale cask loaded with dummy assemblies. The second step was a 30 cm drop test of a full-scale dummy assembly. The results of these tests were published in MRS Advances (2020). The third step was a 30 cm drop of a full-scale surrogate assembly. The results of this final test are presented in this paper.

The 30 cm drop test of a full-scale surrogate assembly was conducted in May 2020. The acceleration pulses observed on the surrogate assembly instrumented with 13 accelerometers were in good agreement with the expected pulses derived from steps 1 and 2. This confirmed that during the 30 cm drop the surrogate assembly experienced the same conditions as it would have if it had been dropped in a full-scale cask with impact limiters.

The surrogate assembly was instrumented with 27 strain gauges. Pressure paper was inserted between the rods within the two long spacer grid spans (top and bottom end of the assembly) and within two shorter spacer grid spans (mid-part of the assembly) prior to the test. The purpose of the pressure paper was to register the pressure in case of rod-to-rod contact. The pressure paper range was from 7.2 to 7,100 psi.

The maximum observed peak strain on the surrogate assembly was 1,724 microstrain. The next two highest values were 1,169 and 1,067 microstrain. The corresponding strain gauges were located at the bottom (slap down) end of the assembly that hit the target a few milliseconds later than the top end.

The pressure paper sheets from the two short spans were blank, indicating no rod-to-rod contact in these spans. All pressure paper sheets from the two long spans between spacer grids, except a few middle layers, showed marks indicating rod-to-rod or rod-to-guide tube contact. The maximum estimated contact pressure was 4,100 psi. The points of the maximum pressure were located in the middle of the span where bending was maximum.

The longitudinal bending stress corresponding to the maximum observed strain value (calculated from the stress-strain curve for low burnup cladding) was 22,230 psi. The maximum estimated rod-to-rod contact pressure was 4,100 psi. Both values are significantly below the yield strength of the cladding. The major conclusion that can be drawn from the 30 cm drop test is that the fuel rods will maintain their integrity following a 30 cm drop inside of a transportation cask. 

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. The SNL review and approval number is SAND2020-11963 A.

Presenting Author: Elena Kalinina Sandia National Laboratories

Authors:

Elena Kalinina Sandia National Laboratories
Douglas Ammerman Sandia National Laborartories
Carissa Grey Sandia National Laboratories
Gregg Flores Sandia National Laboratories
Lucas Lujan Sandia National Laboratories
Sylvia Saltzstein Sandia National Laboratories
Danielle Michel Sandia National Laboratories