This disposal concept is based on the Tumulus design developed by the French at the La Manche facility. Waste units are stacked above-grade on a concrete pad. The facility currently under development at the Oak Ridge National Laboratory (ORNL) involves sealing waste in concrete vaults, placing the vaults on a grade level concrete pad, and covering the pad and vaults with a soil cover after vault emplacement is complete. Emplacement is expected to continue until the facility exhausts its approximate 800 m/sup 3/ (28,000 ft/sup 3/) capacity. The facility incorporates engineered barriers to radionuclide migration; a monitoring system to ensure barrier performance; and a newly developed set of Demonstration Waste Acceptance Criteria to reduce the likelihood of groundwater contamination.

The Microwave Tokamak Experiment (MTX) at LLNL will investigate electron heating in the MTX tokamak (formerly Alcator-C) at high density (up to 6 x 10/sup 20/ m/sup -3/) and high power by using a free electron laser (FEL). Parameters of the FEL are a peak power up to 8 GW and 50 ns duration, with average power 1 to 2 MW, at a frequency of 250 GHz. The planned input driver for the FEL is a gyrotron oscillator. The FEL output will be transported quasi-optically, inside a 50 cm evacuated pipe, to the input port of the tokamak by means of a four-mirror system. Launch polarization is the ordinary mode. This experiment will test the FEL technology at short wavelength and high peak and average power levels. Important physics issues to be explored are the effects of intense pulse heating (electric field up to 500 kV/cm) on nonlinear wave absorption and bulk heating, plasma confinement, plasma impurities, and parametric instabilities. Because the FEL technology is scalable to higher frequency and power, success of these experiments has importance for next-generation tokamaks.

Two of eight differently prepared copper stabilizer samples, previously irradiated in the RTNS-II at LLNL, the IPNS-1 and the BSR at ORNL, have been irradiated to a fluence of 1.33 /times/ 10/sup 22/ n/m/sup 2/ at RTNS-II. During the course of the irradiation the samples were periodically removed (without warming) for measurements of the transverse magnetoresistance and returned for continued irradiation. This experiment extends the range of neutron-irradiation-induced resistivity by a factor of five over the previous experiments. A simple model is developed which reproduces the magnetoresistance results of all the experiments to an accuracy of 2.5%. 13 refs., 6 figs.

The existing 2.2-m-radius Nova aluminum target chamber, coated and lined with boron-seeded carbon shields, is proposed for use with 1000-MJ-yield targets in the next laser facility. The laser beam and diagnostic holes in the target chamber are left open and the desired 10/sup -2/ Torr vacuum is maintained both inside and outside the target chamber; a larger target chamber room is the vacuum barrier to the atmosphere. The hole area available is three times that necessary to maintain a maximum fluence below 12 J/cm/sup 2/ on optics placed at a radius of 10 m. Maximum stress in the target chamber wall is 73 MPa, which complies with the intent of the ASME Pressure Vessel Code. However, shock waves passing through the inner carbon shield could cause it to comminute. We propose tests and analyses to ensure that the inner carbon shield survives the environment. 13 refs.

We calculated thermal stresses in Nova glass laser disks having light-absorbing edge cladding glass attached to the periphery with an epoxy adhesive. Our closed-form solutions indicated that, because the epoxy adhesive is only 25 ..mu..m across, it does not significantly affect the thermal stress in the disk or cladding glass. Our numerical results showed a peak tensile stress in the cladding glass of 24 MPa when the cladding glass had a uniform absorption coefficient of 7.5 cm/sup -1/. This peak value is reduced to 19 MPa if surface parasitic oscillation heating is eliminated by tilting the disk edges. The peak tensile stresses exceed the typical 7 to 14-MPa working stress for glass; however, we have not observed any disk or cladding glass failures at peak Nova fluences of 20 J/cm/sup 2/. We have observed delamination of the epoxy adhesive bond at fluences several times that which would occur on Nova. Replacement laser disks will incorporate cladding with a reduced absorption coefficient of 4.5 cm/sup -1/. Recent experiments show that this reduced absorption coefficient is satisfactory.

The vaporization of core-concrete mixtures is being measured using a transpiration method. Mixtures of stainless steel, concrete (limestone or basaltic) and urania (doped with La/sub 2/O/sub 3/, SrO, BaO, and ZrO/sub 2/) are vaporized at 2150 - 2400 K from a zirconia crucible into flowing He - 6% H/sub 2/ gas. Up to 600 ppM H/sub 2/O is added to the gas to fix the partial molar free energy of oxygen in the range -420 kJ to -550 kJ. The fraction of the sample that is vaporized is determined by weight change and by chemical analyses on the condensates that are collected in an Mo condenser tube. The results are being used to test the thermodynemic data base and the underlying assumptions of computer codes used for prediction of release during the severe accident. 13 refs., 2 tabs.