MELCOR analyses of severe accident scenarios in Oconee, a B&W PWR plant

This paper presents the results and insights gained from MELCOR analyses of two severe accident scenarios, a Loss of Coolant Accident (LOCA) and a Station Blackout (TMLB) in Oconee, a Babcock & Wilcox (B&W) designed PWR with a large dry containment, and comparisons with Source Term Code Package (STCP) calculations of the same sequences. Results include predicted timing of key events, thermal-hydraulic response in the reactor coolant system and containment, and environmental releases of fission products. The paper also explores the impact of varying concrete type, vessel failure temperature, and break location on the accident progression, containment pressurization, and environmental releases of radionuclides

A simplified model for calculating atmospheric radionuclide transport and early health effects from nuclear reactor accidents

During certain hypothetical severe accidents in a nuclear power plant, radionuclides could be released to the environment as a plume. Prediction of the atmospheric dispersion and transport of these radionuclides is important for assessment of the risk to the public from such accidents. A simplified PC-based model was developed that predicts time-integrated air concentration of each radionuclide at any location from release as a function of time integrated source strength using the Gaussian plume model. The solution procedure involves direct analytic integration of air concentration equations over time and position, using simplified meteorology. The formulation allows for dry and wet deposition, radioactive decay and daughter buildup, reactor building wake effects, the inversion lid effect, plume rise due to buoyancy or momentum, release duration, and grass height. Based on air and ground concentrations of the radionuclides, the early dose to an individual is calculated via cloudshine, groundshine, and inhalation. The model also calculates early health effects based on the doses. This paper presents aspects of the model that would be of interest to the prediction of environmental flows and their public consequences

ALK-positive histiocytosis: a new clinicopathologic spectrum highlighting neurologic involvement and responses to ALK inhibition

ALK-positive histiocytosis is a rare subtype of histiocytic neoplasm first described in 2008 in three infants with multisystemic disease involving the liver and hematopoietic system. This entity has subsequently been documented in case reports and series to occupy a wider clinicopathologic spectrum with recurrent KIF5B-ALK fusions. The full clinicopathologic and molecular spectra of ALK-positive histiocytosis remain, however, poorly characterized. Here, we describe the largest study of ALK-positive histiocytosis to date, with detailed clinicopathologic data of 39 cases, including 37 cases with confirmed ALKrearrangements. The clinical spectrum comprised distinct clinical phenotypic groups: infants with multisystemic disease with liver and hematopoietic involvement, as originally described (Group 1A: 6/39), other patients with multisystemic disease (Group 1B: 10/39), and patients with single-system disease (Group 2: 23/39). Nineteen patients of the entire cohort (49%) had neurologic involvement (seven and twelve from Groups 1B and 2, respectively). Histology included classic xanthogranuloma features in almost one third of cases, whereas the majority displayed a more densely cellular, monomorphic appearance without lipidized histiocytes but sometimes more spindled or epithelioid morphology. Neoplastic histiocytes were positive for macrophage markers and often conferred strong expression of phosphorylated-ERK, confirming MAPK pathway activation. KIF5B-ALK fusions were detected in 27 patients, while CLTC-ALK, TPM3-ALK, TFG-ALK, EML4-ALK and DCTN1-ALK fusions were identified in single cases. Robust and durable responses were observed in 11/11 patients treated with ALK inhibition, ten with neurologic involvement. This study presents the existing clinicopathologic and molecular landscape of ALK-positive histiocytosis, and provides guidance for the clinical management of this emerging histiocytic entity.Molecular tumour pathology - and tumour genetic

MELCOR Verification, Benchmarking, and Applications experience at BNL

This paper presents a summary of MELCOR Verification, Benchmarking and Applications experience at Brookhaven National Laboratory (BNL), sponsored by the US Nuclear Regulatory Commission (NRC). Under MELCOR verification over the past several years, all released versions of the code were installed on BNL`s computer system, verification exercises were performed, and defect investigation reports were sent to SNL. Benchmarking calculations of integral severe fuel damage tests performed at BNL have helped to identify areas of modeling strengths and weaknesses in MELCOR; the most appropriate choices for input parameters; selection of axial nodalization for core cells and heat structures; and workarounds that extend the capabilities of MELCOR. These insights are explored in greater detail in the paper, with the help of selected results and comparisons. Full plant applications calculations at BNL have helped to evaluate the ability of MELCOR to successfully simulate various accident sequences and calculate source terms to the environment for both BWRs and PWRs. A summary of results, including timing of key events, thermal-hydraulic response, and environmental releases of fission products are presented for selected calculations, along with comparisons with Source Term Code Package (STCP) calculations of the same sequences. Differences in results are explained on the basis of modeling differences between the two codes. The results of a sensitivity calculation are also shown. The paper concludes by highlighting some insights on bottomline issues, and the contribution of the BNL program to MELCOR development, assessment, and the identification of user needs for optimum use of the code

Independent assessment of MELCOR as a severe accident thermal-hydraulic/source term analysis tool

MELCOR is a fully integrated computer code that models all phases of the progression of severe accidents in light water reactor nuclear power plants, and is being developed for the US Nuclear Regulatory Commission (NRC) by Sandia National Laboratories (SNL). Brookhaven National Laboratory (BNL) has a program with the NRC called ``MELCOR Verification, Benchmarking, and Applications,`` whose aim is to provide independent assessment of MELCOR as a severe accident thermal-hydraulic/source term analysis tool. The scope of this program is to perform quality control verification on all released versions of MELCOR, to benchmark MELCOR against more mechanistic codes and experimental data from severe fuel damage tests, and to evaluate the ability of MELCOR to simulate long-term severe accident transients in commercial LWRs, by applying the code to model both BWRs and PWRs. Under this program, BNL provided input to the NRC-sponsored MELCOR Peer Review, and is currently contributing to the MELCOR Cooperative Assessment Program (MCAP). This paper presents a summary of MELCOR assessment efforts at BNL and their contribution to NRC goals with respect to MELCOR

Analysis of loss-of-flow transients in a pool-type LMFBR using SSC-P

In order to have a general analytical capability for the safety evaluation of any proposed LMFBR system, the USNRC is sponsoring the development and validation of computer codes for both pool- and loop-type plants. The computer code for pool-type LMFBRs is designated SSC-P. This paper is concerned with the application of SSC-P to simulate loss-of-flow accident transients in a pool-type LMFBR. The models required for dynamic plant simulation are briefly highlighted. The system response is calculated for (1) a complete loss of electric power event, with scram, leading the plant into buoyancy-induced natural circulation, (2) a protected pipe rupture accident in the primary pump discharge line, and (3) an unprotected loss of off-site power event. For the last case, the predicted results from SSC-P are compared with the published results of Phenix behavior by NOVATOME