George S. Stanford

Fuel motion in overpower tests of metallic integral fast reactor fuel

In this paper results from hodoscope data analyses are presented for transient overpower (TOP) tests M5, M6, and M7 at the Transient Reactor Test Facility, with emphasis on transient feedback mechanisms, including prefailure expansion at the tops of the fuel pins, subsequent dispersive axial fuel motion, and losses in relative worth of the fuel pins during the tests. Tests M5 and M6 were the first TOP tests of margin to cladding breach and prefailure elongation of D9-clad ternary (U-Pu-Zr) integral fast reactor-type fuel. Test M7 extended these results to high-burnup fuel and also initiated transient testing of HT-9-clad binary (U-Zr) Fast Flux Test Facility driver fuel. Results show significant prefailure negative reactivity feedback and strongly negative feedback from fuel driven to failure.

Loss-of-flow transient reactor test facility tests l6 and l7 with irradiated liquid-metal fast breeder reactor type fuel

This paper describes Transient Reactor Test Facility tests L6 and L7, in which a loss-of-flow accident sequence was simulated using three fuel elements containing (Pu,U)O/sub 2/. Fuel dispersal rates at 10 and 20 times nominal power were measured using the 1.2-m fast neutron hodoscope. The measured axial fuel density variations were weighted with typical liquid-metal fast breeder reactor fuel-worth distributions so that the significance of the fuel motion could be assessed. The experimental fuel-worth changes were also compared with the fuel-worth changes computed by fuel motion models SLUMPY and LEVITATE. 11 refs.

Reprocessing method could allay weapons fear.

SIR — Your News story “Experts plan to reclaim the web for pop science” (Nature 439, 516–517; 2006) describes a project called the Digital Universe, which aims to create, and provide links to, trustworthy peer-reviewed content on the Internet. As suggested by critics in your News story, it seems wasteful to try to reproduce content that already exists in an open, accessible and improvable form. I would encourage those working on projects such as the Digital Universe to consider a strategy that truly leverages the power of the Internet. For example, the free and editable encyclopedia Wikipedia (en.wikipedia.org) contains innumerable articles that are scientifically accurate, although it obviously contains errors, omissions and some articles of low quality. But MediaWiki, the software upon which Wikipedia is based (see www.mediawiki. org), allows one to link to specific versions of articles. Thus, expert peer reviewers could analyse articles, improve them and provide links to the trusted version of that article. A web portal that provided a ‘filtered’ version of the Internet, with links to the most trustworthy available article on a given subject, would be a boon to scientists and science enthusiasts alike. Kevin Yager Department of Chemistry, McGill University, Lab 406, Otto Maass Chemistry Building, 801 Sherbrooke Street West, Montréal, Québec H3A 2K6, Canada

Transient-overpower test E8 on FFTF-type low-power-irradiated fuel

Test E8 simulated a hypothetical

TREAT Test E8 simulating liquid-metal fast breeder reactor /3/s overpower accident with irradiated Fast Test Reactor type fuel

3/s transient overpower accident in an LMFBR using seven (plutonium, uranium) oxide fuel elements of the FTR type. The test elements were pre-irradiated in the PNL-10 assembly in EBR-II to 5 at.% burnup at 30 kW/m. The pre-irradiation in EBR-II caused a fuel-restructuring range characteristic of a low-to-moderate power microstructure for FTR. Failure predictions indicated that fuel with this microstructural characteristic would fail at a lower energy deposition than fuel irradiated at higher power. Data from test-vehicle sensors, hodoscope, and postmortem examinations were used to construct the sequence of events occurring within the test zone. The sequence occurred incoherently across the test cluster, the initial event occurring abruptly at about 29 times nominal power level at an estimated stored energy of about 925 kJ/kg with 50% of the fuel above the solidus at the suspected failure site. After the initial failure, about 2% of the total mass of test fuel was ejected above the original top of the active fuel column. Sodium voiding occurred rapidly. A fuel-debris blockage also apparently prevented further fuel dispersal. Inherent test-vehicle limitations, loss of flow-tube geometry, and nontypical power generation after failure may have caused a departure from the fuel motion predicted for FTR conditions. No violent fuel-coolant interaction or associated work-energy conversion to the coolant was observed.

Smarter Use of NUCLEAR WASTE

In a transient overpower (TOP) accident, the fuel element failure threshold is a function of the rate of reactivity increase and the fuel microstructure. In Transient Reactor Test Facility (TREAT) Test E8, seven mixed-oxide PNL-10 elements from the Experimental Breeder Reactor II (EBR-II) subassembly X093 were used in a simulation of an unprotected /3/s transient overpower (TOP) accident in a liquid-metal fast breeder reactor (LMFBR). This paper presents the results of Test E8. Experimental hardware is also described. 9 refs.