[en] The W-2 SLSF (Sodium Loop Safety Facility) experiment was an instrumented in-reactor test performed to characterize the failure response of full-length, preconditioned LMFBR prototypic fuel pins to slow transient overpower (TOP) conditions. Although the test results were expected to confirm analytical predictions of upper level failure and fuel expulsion, an axial midplane failure was experienced. Extensive post-test analyses were conducted to understand all of the unexpected behavior in the experiment. (1) The initial post-test effort focused on the temperature oscillations recorded by the 54 thermocouples used in the experiment. In order to synthesize the extensive data records and identify patterns of behavior in the data records, a computer-generated film was used to present the temperature data recorded during the experiment

[en] The United States Enrichment Corporation (USEC) controls two uranium enrichment facilities that produce enriched uranium for both military and commercial use. The process requires both feed and withdrawal operations. The withdrawal process requires both product (enriched uranium) withdrawal stations and tails (depleted uranium) withdrawal stations. A previous prototype system, ''X-330 Tails Cylinder Assay Monitor,'' was developed as a demonstration for the tails withdrawal station at the Portsmouth Gaseous Diffusion Plant (PORTS). The prototype system was done in response to potential problems with the original method for determining the hourly weighted assay averages that are used to calculate the final weighted assay of the cylinder. In the original method the ²³⁵U assay of uranium hexaflouride withdrawn from PORTS cascade into tails cylinders is determined every 5 min by measurements from an in-line assay mass spectrometer. An average value for a 1-h period is then calculated by area control room personnel and assigned to the accumulated weight in the cylinder for the period. A potential problem with this method is that cylinder weight is not automatically recorded as often as the assay. The assay and withdrawal rate can both vary during the given period. This variation results in inaccuracies in the hourly weighted assays that are used to calculate the final weighted assay of the cylinder. Laboratory analysis is considered to be the most accurate method for determining the final cylinder assay; however, the cost and safety considerations of redundant cylinder handling limit the number of cylinders sampled to less than 10%

[en] It has been postulated that the use of annular fuel provides an inherent safety shutdown mechanism during hypothetical LMFBR accidents by providing a pathway for molten fuel to be ejected from the active core region to the fission gas plenum. Although this mechanism has been demonstrated to be effective for rapid overpower transients, previous work has been unable to demonstrate the viability of the mechanism for slower ramp rate cases in the range of 10 to 50 cents/s. An axial blanket internal hole size design variation (DP-1) significantly improved the viability of internal fuel motion to act as an inherent safety shutdown mechanism for high ramp rate cases on the order of 2 to 3$/s. However, when evaluated for a 50 cents/s TOP case, this design variation did not prove viable. A further design variation (DP-2) reported proved viable for a 50 cents/s TOP case. Case DP-3, a limiting variation, proved viable for a 10 cents/s TOP case. The basic fuel pin design used dual fission gas plena. The base case assumed a 50 cents/s TOP accident with a 3$ reactivity insertion for a 2550 MWt Large Development Plant (LDP) heterogeneous core design. All cases were analyzed using the coupled MELT-IIIB/FUMO-E code

No abstract available

[en] In this paper, the whole-core reactivity consequences of internal fuel motion in three annular fuel designs during a hypothetical 3 dollars/s transient overpower (TOP) accident are compared to determine the effect of geometric design variations. The PINEX-2 and PINEX-3 experiments were performed in the TREAT reactor using annular fuel pins irradiated in GETR. This paper investigates three combinations of solid and annular axial blankets and fission gas plena: top annular blanket and plenum, bottom annular blanket and plenum, and both top and bottom (dual) annular blankets and plena. The dual plena design case showed a significant decrease in internal fuel motion over the single plenum design cases

[en] It has been postulated that the use of annular fuel provides an inherent safety shutdown mechanism during hypothetical LMFBR accidents by providing a pathway for molten fuel to be ejected from the active core region to the fission gas plenum. Previous work evaluating internal fuel motion for whole-core, transient overpower accident cases has been unable to demonstrate the viability of the mechanism for ramp rate cases of $3/s with 3$ total reactivity insertion and below. Continued work reported here has identified an axial blanket internal hole size design variation which does significantly improve the viability of internal fuel motion to act as an inherent safety shutdown mechanism. The size of axial blanket central hole studied was 0.356 cm diameter (large), double the 0.178 cm diameter (small) used previously. Three combinations of annular axial blankets and fission gas plena have been analyzed with the large size central hole: top annular blanket and plenum, bottom annular blanket and plenum, and both top and bottom (dual) annular blankets and plena. The base case assumed a 3$/s transient overpower (TOP) accident with a $3 reactivity insertion for a 2550 MWt Large Development Plant (LDP) heterogeneous core design. The cases were analyzed using the coupled MELT-IIIB/FUMO-E code

[en] The W-2 SLSF experiment was an instrumented in-reactor test performed to characterize the failure response of full-length, preconditioned LMFBR prototypic fuel pins to slow transient overpower (TOP) conditions. Although the test results were expected to confirm analytical predictions of upper level failure and fuel expulsion, an axial midplane failure was experienced. Extensive post-test analyses were conducted to understand all of the unexpected behavior in the experiment. The initial post-test effort focused on the temperature oscillations recorded by the 54 thermocouples used in the experiment. In order to display the patterns of behavior in the data records, a computer-generated film was used to present the temperature data recorded in the test section during the experiment. Results are presented

[en] The use of annular fuel can provide an inherent safety shutdown mechanism during hypothetical LMFBR accidents by providing a pathway for molten fuel to be ejected from the active core region to the fission gas plenum. This effect can result in sufficient negative reactivity to shut down a reactor prior to fuel pin cladding failure during a transient overpower (TOP) accident. The whole-core reactivity consequences of internal fuel motion were studied in six cases to determine the effect of geometric design variations

[en] The W-2 SLSF experiment was an instrumented in-reactor test performed to characterize the failure response of full-length preconditioned LMFBR prototypical fuel pins to slow transient overpower (TOP) conditions. Although the test results were expected to confirm analytical predictions of upper-level failure and fuel expulsion, an axial midplane failure was experienced. Preliminary interpretations of the cause and implications of midplane failure have been revised. Extensive analyses were conducted in order to understand the unexpected behavior of the experiment. The results of the analyses and their interpretations are presented

[en] The FUMO-E internal fuel motion model for annular fuel was developed to assess the viability of internal fuel motion as an inherent safety shutdown mechanism during the initiation phase of hypothetical LMFBR accidents. This concept involves the ejection of molten fuel through the central hole away from the active fuel core region during a transient overpower event to provide a prompt negative reactivity feedback. The principal role of the FUMO-E model is to quantitatively assess the driving force for fuel ejection by transient fission-gas release, fuel density changes, and fuel-vapor pressure, and also to determine the effect of fuel refreezing and plugging in the central hole on limiting the fuel ejection. After completion of the assessment and of a validation process, the FUMO-E model will be incorporated into the MELT-III whole-core accident analysis code to perform the assessment of the internal fuel motion concept as a viable safety shutdown mechanism