K-Basin spent nuclear fuel characterization data report

Abstract

SummaryAn Integrated Process Strategy has been developed to package, condition, transport, and store in an interim storage facility the spent nuclear fuel (SNF) currently residing in the K-Basins at Hanford. Information required to support the development of the conditioning process and to support the safety analyses must be obtained fiom characterization testing activities conducted on fuel samples from the Basins. Some of the information obtained in the testing was reported in PNL-10778, K-Basin Spent Nuclear Fuel Characterization Data Report (Abrefah et al. 1995).That report focused on the physical, dimensional, metallographic examinations of the first K-West (KW) Basin SNF element to be examined in the Postirradiation Testing Laboratory (PTL) hot cells; it also described some of the initial SNF conditioning tests.This second of the series of data reports covers the subsequent series of SNF tests on the first fuel element. These tests included optical microscopy analyses, conditioning (drying and oxidation) tests, ignition tests, and hydrogen content tests.The results of the conditioning, hydrogen content, and ignition testing of the element sections An SNF specimen w i t h added water was cold vacuum dried (CVD) at 60 Torr and 323 K, hot vacuum dried (HVD) at 60 Torr and 573 K, and then conditioned at 473 K in 2% oxygen/98% argon mixture. The added water came off during the first 3 hours of the CVD cycle. Relatively little moisture evolved during the HVD cycle. A small oxygen pickup was noted during passivation. may be summarized as follows: 0Two SNF specimens with free water added were CVD at 60 Torr and 323 K, HVD at 60 Torr and 573 K, and then conditioned at 523 K in 2% oxygen/98% argon mixture at 1 atm. Most of the added water came off during the CVD cycle. Relatively little moisture was observed during the HVD cycle. A total of 27 mg of oxygen was picked up during passivation. The two specimens lost a total of 505.6 mg of weight as a result of oxide spalling. Analysis of the spalled residue indicated that U,O, and U,O, were the predominant chemical phases. -The moisture content in the off-gas stream during the passivation cycle in this run was higher than in tests when water was not added to the specimens Hydrogen release was measured from a decladded fuel specimen at 573 K for about 24 hours and at 623 K for 96 hours in an argon gas flow of 100 cdmin. System pressure was about one atmosphere. The concentration of hydrogen gas peaked during the temperature ramp. The total hydrogen measured was 0.12 mg. An appreciable amount of moisture was also detected in the gas stream. a Significant amounts of both moiswre and hydrogen were released fiom cladding material peeled off the damaged end of the element. These values peaked sharply (about 260 ppm moisture and 75 ppm hydrogen in the gas stream) during the temperature ramp but, remained fairly high throughout the run.iii Hydrogen release was measured from a decladded fuel specimen sectioned from the uncorroded mid-length of N-reactor fuel element. A total of ...

DSNF and Other Waste Form Degradation Abstraction

“…The Magnox SNF did not exhibit the kind of physical damage that much of the N Reactor SNF showed, and therefore the uranium metal did not have the prolonged direct exposure to water that the N Reactor SNF has had. This fuel had burnups ranging from 1,100 to 9,850 MWd/t (reasonably typical of the N Reactor SNF), but had displayed more extensive localized irradiation swelling (ranging from 5% to 50%) compared to swelling of approximately a few percent observed on the N Reactor SNF (Abrefah et al 1995 The degradation of all uranium metal-based DSNF is taken to be similar to that observed by Gray and Einziger (1998 [DIRS 109691] , although the absolute rates were higher for the N Reactor SNF (see Table 6-4). Table 6 A significant fraction of the N Reactor fuel has been stored in a damaged condition under water at the K-basins at Hanford, and the metallic uranium has been exposed to the water environment.…”

Waste Form Features, Events, and Processes

“…Examination and testing conducted at PNNL on damaged N Reactor zirconium-clad uranium metal fuel showed small but discernable amounts of uranium hydride formed as precipitates within the metal (Marschman et al 1997 , the chance of spontaneous ignition will be considered in this analysis to support the screening argument of low consequence of pyrophoric event to the postclosure TSPA-LA. Because the fraction of N Reactor SNF with cladding that is damaged enough to expose the metallic uranium core is quantitatively unknown but potentially significant (Abrefah et al 1995 [DIRS 151125]), all the SNF elements will be regarded as damaged for the purposes of this analysis.…”

DSNF and other waste form degradation abstraction

“…A significant fraction of the N-reactor fuel is visibly damaged, and much of the rest could have small pinholes/cracks in the cladding. The exposed uranium metal surfaces of the N-reactor fuel elements show extensive corrosion resulting from the many years of direct exposure to the K-basin water (Abrefah et al 1995;Abrefah et al 1999, Figure 3 where k is the corrosion rate, A is the activation energy for dissolution (66.4 f 2.0 kJ/mol), R is the gas constant (8.3 14 J/mol-K), and TK is the temperature in kelvins.…”