The assembly IFA-534 contained 4 rods base irradiated for 4 cycles in the Swiss Goesgen PWR up to a burn-up of ~52 MWd/kg. The rods were re-instrumented with either pressure transducers or clad elongation detectors and re-irradiated between January and May 1998 in the Halden HBWR to a final discharge burn-up of ~55 MWD/kg. The purpose of the experiment was to investigate the effect of fuel grain size on irradiation performance. The rods included in this data sets are rods 18 (22 micron grain size) and 19 (8.5 micron grain size) fitted with pressure transducers from which Fission Gas Release (FGR) was measured both in-pile and during final PIE.
In the Goesgen reactor, the rods were irradiated as segments manufactured by Siemens KWU, clad with Zr-4 and filled with UO2 pellets manufactured by GE. Information about the base irradiation is sparse; only the range of powers in each of the 4 cycles was given:
cycle 1 25.5-26.5 kW/m
cycle 2 26.5-27.5 kW/m
cycle 3 20.0-21.0 kW/m
cycle 4 20.0 kW/m
In preparing the histories it has been assumed that each cycle comprised two periods of equal duration with powers (in kW/m) distributed as follows:
Cycle no. first period second period
1 26.5 25.5
2 27.5 26.5
3 21.0 20.0
4 20.0 20.0
Small modification were made to individual rod powers based on fuel weight in order to achieve 52 MWd/kg at start of the Halden irradiation.
The Halden irradiation was recorded on their Test Fuel Data Bank with measurements recorded every 15 mins of reactor time. The histories were condensed to manageable size by amalgamating adjacent data points if the power changed by less than 1 kW/m. Care was taken that the resulting condensed history faithfully represented the raw data. In-pile measurements of rod internal pressure are given as a function of burn-up as well as a conversion to FGR versus burn-up.
Pre-characterization was not extensive but what is available is given here. No interim measurements were made during re-fabrication, only at the end of life. Measurements were made of rod internal pressure and volume, and detailed isotopic composition of the released fission gas. A single radial cross section was cut and examined from each rod. Metallography revealed the presence of high burn-up restructuring at the pellet rim; the grain size and pore size distribution was measured across the pellet diameter and the results reported as average values in 3 additional radial zones.
The results of the experiment successfully demonstrated the effect of grain size on FGR.