Dynamic behavior of a subcooled BWR core during a rod-drop accident

The techniques and models used in the study of rapid reactivity insertion in a BWR have ranged from approximate conservative methods with simple feedback models to detailed representations of coupled neutronic thermal-hydraulic mechanisms. In a recent paper Cheng and Diamond presented a detailed evaluation of the control rod drop accident (CRDA). Their calculations suggested that the effect of inlet subcooling and rod drop speed may play an important role in determining the severity of the rod drop accident. The purpose of the work summarized in this paper has been to determine in detail the dynamic behavior of a BWR core as the inlet moderator temperature and the speed of the dropped rod are varied

Pressure-vessel-damage fluence reduction by low-leakage fuel management. [PWR]

As a result of neutron-induced radiation damage to the pressure vessel and of an increased concern that in a PWR transient the pressure vessel may be subjected to pressurized thermal shock (PTS), detailed analyses have been undertaken to determine the levels of neutron fluence accumulation at the pressure vessels of selected PWR's. In addition, various methods intended to limit vessel damage by reducing the vessel fluence have been investigated. This paper presents results of the fluence analysis and the evaluation of the low-leakage fuel management fluence reduction method. The calculations were performed with DOT-3.5 in an octant of the core/shield/vessel configuration using a 120 x 43 (r, theta) mesh structure

Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields

We analyze in details the standard Primordial Nucleosynthesis scenario. In particular we discuss the key theoretical issues which are involved in a detailed prediction of light nuclide abundances, as the weak reaction rates, neutrino decoupling and nuclear rate modeling. We also perform a new analysis of available data on the main nuclear processes entering the nucleosynthesis reaction network, with particular stress on their uncertainties as well as on their role in determining the corresponding uncertainties on light nuclide theoretical estimates. The current status of theoretical versus experimental results for 2H, 3He, 4He and 7Li is then discussed using the determination of the baryon density as obtained from Cosmic Microwave Background anisotropies.Comment: LaTeX, 83 pages, 30 .pdf figures. Some typos in the units of R-functions in appendix D and relative plots fixe

Low Genetic Variation in the Heath Hen Prior to Extinction and Implications for the Conservation of Prairie-Chicken Populations

Low genetic variation is often considered to contribute to the extinction of species when they reach small population sizes. In this study we examined the mitochondrial control region from museum specimens of the Heath Hen ( Tympanuchus cupido cupido ), which went extinct in 1932. Today, the closest living relatives of the Heath Hen, the Greater ( T. c. pinnatus ), Attwater’s ( T. c. attwateri ) and Lesser ( T. pallidicinctus ) Prairie-chicken, are declining throughout most of their range in Midwestern North America, and loss of genetic variation is a likely contributor to their decline. Here we show that 30 years prior to their extinction, Heath Hens had low levels of mitochondrial genetic variation when compared with contemporary populations of prairie-chickens. Furthermore, some current populations of Greater Prairie-chickens are isolated and losing genetic variation due to drift. We estimate that these populations will reach the low levels of genetic variation found in Heath Hens within the next 40 years. Genetic variation and fitness can be restored with translocation of individuals from other populations; however, we also show that choosing an appropriate source population for translocation can be difficult without knowledge of historic population bottlenecks and their effect on genetic structure.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42596/1/10592_2005_Article_7856.pd

Two-dimensional dynamic analysis of a BWR rod-drop accident

BNL-TWIGL has enabled us to determine the dependence of the CRDA peak power and fuel enthalpy on the core inlet subcooling and rod drop speed. The results show that the peak power and fuel enthalpy increases rapidly with inlet subcooling up to a subcooling of approx. 20/sup 0/F and become relatively insensitive at higher subcoolings. Furthermore, as the rod drop speed is increased, the calculations show that the peak fuel enthalpy increases by less than or equal to 30%. It must be pointed out that in all cases studied the peak fuel enthalpy was found to be well below the 280 cal/gm criterion

Neutron-induced fission of weapons plutonium in an accelerator/target/blanket system

A proliferation-proof method for the disposition of weapons-grade plutonium using an intermediate-energy proton accelerator is presented in this paper. The method makes use of a spallation neutron source and a subcritical plutonium-loaded blanket assembly surrounding it. The neutron source consists of a heavy water-colled lead target, bombarded by a uniform-intensity 1 GeV, 100 mA proton beam. Plutonium is loaded in small graphite spheres (beads) which are enclosed in helium-colled zircalloy pressure tubes. A subcritical configuration of these tubes blankets the spallation neutron source. Uniformly-distributed erbium is used to control reactivity. The system, operating at constant power, is capable of burning 300 kg of plutonium in a six-month period

Effects of subcooling and rod drop speed on the BWR rod drop accident

The techniques and models used in the analysis of the control rod drop accident (CRDA) in a BWR have ranged from approximate conservative methods with a simple feedback model to detailed representations of the thermal-hydraulic and neutronic mechanisms. In a recent paper Cheng and Diamond presented a detailed evaluation of the CRDA and the effects of varying a number of important accident parameters. Their calculations performed with the BNL-TWIGL core dynamics code, have shown that the effect of inlet subcooling and rod drop speed play an important role in determining the severity of the rod drop accident. The purpose of the work summarized in this paper has been to determine in detail the dependence of the rod drop accident parameters on the (1) inlet subcooling; and (2) rod drop speed

Pressure-vessel fluence reduction through selective fuel-assembly replacement

The nil-ductility transition temperature (RT/sub NDT/) of a PWR pressure vessel (PV) increases during its lifetime due to neutron-induced radiation damage. If during a pressurized thermal shock (PTS) event the PV is cooled below its RT/sub NDT/ and then repressurized, the vessel may undergo brittle fracture. For several operating reactors it may be necessary to reduce this neutron-induced vessel damage in order to maintain the vessel RT/sub NDT/ below the range of concern. In this study the potential fluence (and hence damage) reduction achievable by selective replacement of peripheral fuel assemblies in which the fuel rods have been replaced by stainless steel rods is considered

PIUS core performance analysis

A detailed evaluation of the fuel-burnup dependent power distribution and the scram reactivity for the PIUS reactor design has been performed. The analyses were carried out using the CPM lattice physics and NODE-P2 core neutronics/thermal-hydraulics codes, and are based on the information provided in the PIUS Preliminary Safety Information Document. Cycle depletion calculations were performed for a set of nine representative initial core loadings and the three-dimensional core power distributions were determined. These calculations indicate that the PIUS radial F{sub {Delta}h} and total F{sub Q} power peaking is stronger than that indicated by the PIUS reference-design values. The scram reactivity resulting from the injection of highly borated pool water was calculated for a series of time-dependent linear ramp and square-wave pool flows. The three-dimensional distribution of the borated pool water throughout the core was modeled and the spatial reactivity effects of the distributed boron were determined. For pool flows that increase as a linear ramp, the spatial reactivity effects of the distributed boron were very small. In this case, a constant core-average boron reactivity coefficient can be used to model the PIUS scram reactivity