Search

The physical state of the debris cloud generated by the interaction of a projectile with a thin target depends on the energy balance associated with the impact event. At impact velocities well above the sound speeds of the materials involved, the cloud is expected to consist of material in solid, liquid, and vapor phases. A series of numerical calculations using the multi-dimensional finite-difference hydrocode CTH has been used to evaluate the effect of phase changes ( i.e. , different vapor fractions) on these clouds, and on their subsequent interaction with backwall structures. In the calculations, higher concentrations of vapor are achieved either by (1) increasing the initial temperature of both the projectile and the thin shield while keeping the impact velocity constant, or (2) by actually increasing the impact velocity. The nature of the debris cloud and its subsequent loading on the protected structure depend on both its thermal and physical state. This interaction can cause rupture, spallation, or simply bulging of the backwall. These computational results are discussed and compared with new experimental observations obtained at an impact velocity of ∼ 10 km/s. In the experiment, the debris cloud was generated by the impact of a plate-shaped titanium projectile with a thin titanium shield.

A systematic study is described which has led to the successful launch of thin flier plates to velocities of 16 km/s. The energy required to launch a flier plate to 16 km/s is approximately 10 to 15 times the energy required to melt and vaporize the plate. The energy must, therefore, be deposited in a well-controlled manner to prevent melt or vaporization. This is achieved by using a graded-density assembly to impact a stationary flier-plate. Upon impact, time-dependent, structured, high pressure pulses are generated and used to propel the plates to hypervelocities without melt or fracture. In previous studies, a graded-density impact of 7.3 km/s was used to launch a 0.5 mm thick plate to a velocity of over 12 km/s. If impact techniques alone were to be used to achieve flier-plate velocities approaching 16 km/s, this would require that the graded-density impact occur at - 10 km/s. In this paper, we describe a new technique that has been implemented to enhance the performance of the Sandia hypervelocity launcher. This technique of creating an impact-generated acceleration reservoir, has allowed the launch of 0.5 mm to 1.0 mm thick plates to record velocities up to 15.8 km/s. In these experiments, both titanium (Ti-6A1-4V) and aluminum (6061-T6) alloy were used for the flier-plate material. These are the highest metallic projectile plate velocities ever achieved for masses in the range of 0.1 g to 1 g.

A systematic study is described that has led to the successful launch of thin flier plates to velocities of 16 km/s. In this paper, we describe a novel technique that has been implemented to enhance the performance of the Sandia Hyper Velocity Launcher (HVL). This technique of creating an impact-generated acceleration reservoir, has allowed the launch of 0.5 mm to 1.0 mm thick titanium (Ti-6Al-4V) and aluminum (6061-T6) alloy plates to record velocities up to 15.8 km/s. These are the highest metallic projectile plate velocities ever achieved for macroscopic masses in the range of 0.1 g to 1 g.

To gain a better understanding of the risk significance of low power and shutdown modes of operation, the Office of Nuclear Regulatory Research at the NRC established programs to investigate the likelihood and severity of postulated accidents that could occur during low power and shutdown (LP&S) modes of operation at commercial nuclear power plants. To investigate the likelihood of severe core damage accidents during off power conditions, probabilistic risk assessments (PRAs) were performed for two nuclear plants: Unit 1 of the Grand Gulf Nuclear Station, which is a BWR-6 Mark III boiling water reactor (BWR), and Unit 1 of the Surry Power Station, which is a three-loop, subatmospheric, pressurized water reactor (PWR). The analysis of the BWR was conducted at Sandia National Laboratories while the analysis of the PWR was performed at Brookhaven National Laboratory. This multi-volume report presents and discusses the results of the BWR analysis. The subject of this part presents the deterministic code calculations, performed with the MELCOR code, that were used to support the development and quantification of the PRA models. The background for the work documented in this report is summarized, including how deterministic codes are used in PRAS, why the MELCOR code is used, what the capabilities and features of MELCOR are, and how the code has been used by others in the past. Brief descriptions of the Grand Gulf plant and its configuration during LP&S operation and of the MELCOR input model developed for the Grand Gulf plant in its LP&S configuration are given.

MELCOR is a fully integrated, engineering-level computer code, being developed at Sandia National Laboratories for the USNRC, that models the entire spectrum of severe accident phenomena in a unified framework for both BWRs and PWRS. As part, of an ongoing assessment program, the MELCOR computer code has been used to analyze a series of containment spray tests performed in the Containment Systems Experiment (CSE) vessel to evaluate the performance of aqueous sprays as a means of decontaminating containment atmospheres. Basecase MELCOR results are compared with test data, and a number of sensitivity studies on input modelling parameters and options in both the spray package and the associated aerosol washout and atmosphere decontamination by sprays modelled in the radionuclide package have been done. Time-step and machine-dependency calculations were done to identify whether any numeric effects exist in these CSE assessment analyses. A significant time-step dependency due to an error in the spray package coding was identified and eliminated. A number of other code deficiencies and inconveniences also are noted.

This report summarizes the results from MELCOR calculations of severe accident sequences in the ABWR and presents comparisons with MAAP calculations for the same sequences. MELCOR was run for two low-pressure and three high-pressure sequences to identify the materials which enter containment and are available for release to the environment (source terms), to study the potential effects of core-concrete interaction, and to obtain event timings during each sequence; the source terms include fission products and other materials such as those generated by core-concrete interactions. Sensitivity studies were done on the impact of assuming limestone rather than basaltic concrete and on the effect of quenching core debris in the cavity compared to having hot, unquenched debris present.

MELCOR is a fully integrated, engineering-level computer code, being developed at Sandia National Laboratories for the USNRC. This code models the entire spectrum of severe accident phenomena in a unified framework for both BWRs and PWRs. As part of an ongoing assessment program, the MELCOR computer code has been used to analyze a station blackout transient in Surry, a three-loop Westinghouse PWR. Basecase results obtained with MELCOR 1.8.2 are presented, and compared to earlier results for the same transient calculated using MELCOR 1.8.1. The effects of new models added in MELCOR 1.8.2 (in particular, hydrodynamic interfacial momentum exchange, core debris radial relocation and core material eutectics, CORSOR-Booth fission product release, high-pressure melt ejection and direct containment heating) are investigated individually in sensitivity studies. The progress in reducing numeric effects in MELCOR 1.8.2, compared to MELCOR 1.8.1, is evaluated in both machine-dependency and time-step studies; some remaining sources of numeric dependencies (valve cycling, material relocation and hydrogen burn) are identified.

Two sets of MELCOR calculations have been completed studying the effects of air ingression on the consequences of various severe accident scenarios. One set of calculations analyzed a station blackout with surge line failure prior to vessel breach, starting from nominal operating conditions; the other set of calculations analyzed a station blackout occurring during shutdown (refueling) conditions. Both sets of analyses were for the Surry plant, a three-loop Westinghouse PWR. For both accident scenarios, a basecase calculation was done, and then repeated with air ingression from containment into the core region following core degradation and vessel failure. In addition to the two sets of analyses done for this program, a similar air-ingression sensitivity study was done as part of a low-power/shutdown PRA, with results summarized here; that PRA study also analyzed a station blackout occurring during shutdown (refueling) conditions, but for the Grand Gulf plant, a BWR/6 with Mark III containment. These studies help quantify the amount of air that would have to enter the core region to have a significant impact on the severe accident scenario, and demonstrate that one effect, of air ingression is substantial enhancement of ruthenium release. These calculations also show that, while the core cladmore » temperatures rise more quickly due to oxidation with air rather than steam, the core also degrades and relocates more quickly, so that no sustained, enhanced core heatup is predicted to occur with air ingression.« less

MELCOR is a fully integrated, engineering-level computer code, being developed at Sandia National Laboratories for the USNRC, that models the entire spectrum of severe accident phenomena in a unified framework for both BWRs and PWRS. As part of an ongoing assessment program, the MELCOR computer code has been used to analyze several of the IET direct containment heating experiments done at 1:10 linear scale in the Surtsey test facility at Sandia and at 1:40 linear scale in the corium-water thermal interactions (CWTI) COREXIT test facility at Argonne National Laboratory. These MELCOR calculations were done as an open post-test study, with both the experimental data and CONTAIN results available to guide the selection of code input. Basecase MELCOR results are compared to test data in order to evaluate the new HPME DCH model recently added in MELCOR version 1.8.2. The effect of various user-input parameters in the HPME model, which define both the initial debris source and the subsequent debris interaction, were investigated in sensitivity studies. In addition, several other non-default input modelling changes involving other MELCOR code packages were required in our IET assessment analyses in order to reproduce the observed experiment behavior. Several calculations were done to identify whethermore » any numeric effects exist in our DCH IET assessment analyses.« less

Calculations have been performed with the HULL hydrocode to study ground shock effects for multiple earth penetrator weapon (EPW) bursts in hexagonal-close-packed (HCP) arrays. Several different calculational approaches were used to treat this problem. The first simulations involved two-dimensional (2D) calculations, where the hexagonal cross-section of a unit-cell in an effectively-infinite HCP array was approximated by an inscribed cylinder. Those calculations showed substantial ground shock enhancement below the center of the array. To refine the analysis, 3D unit-cell calculations were done where the actual hexagonal cross-section of the HCP array was modelled. Results of those calculations also suggested that the multiburst array would enhance ground shock effects over those for a single burst of comparable yield. Finally, 3D calculations were run in which an HCP array of seven bursts was modelled explicitly. In addition, the effects of non-simultaneity were investigated. Results of the seven-burst HCP array calculations were consistent with the unit-cell results and, in addition, provided information on the 3D lethal contour produced by such an array.

The analysis of Ghoniem and Kulcinski of a single radiation pulse has been extended to include the effects of temperature oscillations and multiple pulses by coupling six simultaneous nonlinear ordinary differential equations for point defect concentrations and sink strengths with a heat equation governing radiation-produced temperature fluctuations. The pulsed irradiation considered is that of the 800 MeV proton beam at the Clinton P. Anderson Meson Physics Facility (LAMPF), and numerical calculations have been done for aluminum and molybdenum. The model material is assumed to have been irradiated to a specific microstructure, and the calculation is begun after the material has returned to thermal equilibrium conditions. Void growth is seen to proceed at a nearly linear rate after initial transients (caused by the assumption of initial thermal equilibrium) in both vacancy concentration and vacancy loop size and number density. The temperature pulses associated with cyclic rather than steady irradiation generally enhance void growth if the ambient temperature is below the material peak swelling temperature, and conversely decrease void growth when the ambient temperature is above peak swelling temperature. The exception seen occurs when the temperature pulse is great enough that thermal emission of vacancies, rather than radiation production, is dominant.

The analysis of Brailsford and Bullough on radiation-produced point defect transport to lattice sinks and the analysis of Ghoniem and Kulcinski of pulsed radiation have been extended to include the effects of radiation-induced temperature oscillations. We have already shown in earlier papers that these temperature pulses enhance void growth if the ambient temperature is below the peak swelling temperature and, conversely, decrease void growth when the ambient temperature is above the peak swelling temperature. When the temperature pulses were suppressed, no difference was seen between void growth under steady and pulsed irradiation. In this paper, we show that the same effects on void growth can be obtained by superposing externally-produced temperature pulses on material under steady irradiation. Calculations have been done for aluminum and molybdenum for sinusoidal temperature pulses of many amplitudes and frequencies.

The RELAP5 independent assessment project at Sandia National Laboratories is part of an overall effort funded by the NRC to determine the ability of various systems codes to predict the detailed thermal; hydraulic response of LWRs during accident and off-normal conditions. The RELAP5/MOD1 code is being assessed at SNLA against test data from various integral and separate effects test facilities. As part of this assessment matrix, a turbine trip rapid cooldown transient performed at the LOFT test facility has been analyzed. The results show that RELAP5/MOD1 can predict the experimental behavior of LOFT test L6-7/L9-2 in detail. However, careful selection of modeling options and adjustment of boundary conditions within the experimental uncertainties is required.

An analytic model for a solar receiver boiler panel has been developed, using the RELAP4 nuclear plant systems thermal-hydraulic computer code. Results are compared to other computer calculations and experimental data from tests conducted by McDonnell-Douglas. The test panels were prototypes of panels to be used in the Barstow 10 MWe solar-electric pilot power plant central receiver. Results are also compared to analytic studies done by Combustion Engineering as part of the test data evaluation. Steady state operating conditions for a given incident heat flux were calculated from a zero-power cold-water startup. The effects of incident flux axial profile shape and of lateral flux gradients were studied, as was the dynamic response of the model to flux and flow transients. The nodalization detail required for accurate simulation was also determined.

Calculations were performed with the CTH and HULL finite difference wavecodes to evaluate computational capabilities for predicting depth and diameter of target cavities produced in high velocity penetration events. The calculations simulated selected tests in a set of armor penetration experiments conducted by the US Army Ballistic Research Laboratory and reported earlier in the literature. The tests and simulations involved penetration of semi-infinite targets by long rod projectiles over a range of impact velocities from 1.3 to 4.5 km/sec. Comparisons are made between the calculated and measured dimensions of the target cavities, and the sensitivity of the predicted results to target property variations is investigated. 9 refs., 18 figs., 3 tabs.

Postirradiation radiochemistry analysis of 800-MeV proton irradiated ultrahigh purity aluminum has been done with standard gamma-ray counting equipment determining the Na/sup 22/ activity in the activated aluminum. Results are compared to predicted values obtained from CINDER, a general nuclide depletion and fission-product code. This program can be used easily to calculate the activity of materials under arbitrary irradiation, provided that the source terms for the various radionuclides produced are known. The required production cross sections have been calculated by using the nucleon-meson transport code NMTC to determine the nuclear reactions produced by the protons, and the theory of Lindhard et al. to evaluate the resultant damage energy deposited in the target.

Utilization of a pulsed radiation source such as the Clinton P. Anderson Meson Physics Facility (LAMPF) for materials science studies requires knowledge of the time--temperature history of a subject metal foil. An analytic solution was derived to a two-dimensional heat flow equation, incorporating the LAMPF time structure and the LAMPF Gaussian beam spot profile. This calculational method is useful in designing experimental systems for materials science studies and can be done on a Hewlett--Packard model 97 desk-top calculator. The results were compared with an equivalent numerical solution of the same two-dimensional heat flow problem done on a digital computer.