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Title: The probability of containment failure by direct containment heating in Zion. Supplement 1

Abstract

Supplement 1 of NUREG/CR-6075 brings to closure the DCH issue for the Zion plant. It includes the documentation of the peer review process for NUREG/CR-6075, the assessments of four new splinter scenarios defined in working group meetings, and modeling enhancements recommended by the working groups. In the four new scenarios, consistency of the initial conditions has been implemented by using insights from systems-level codes. SCDAP/RELAP5 was used to analyze three short-term station blackout cases with Different lead rates. In all three case, the hot leg or surge line failed well before the lower head and thus the primary system depressurized to a point where DCH was no longer considered a threat. However, these calculations were continued to lower head failure in order to gain insights that were useful in establishing the initial and boundary conditions. The most useful insights are that the RCS pressure is-low at vessel breach metallic blockages in the core region do not melt and relocate into the lower plenum, and melting of upper plenum steel is correlated with hot leg failure. THE SCDAP/RELAP output was used as input to CONTAIN to assess the containment conditions at vessel breach. The containment-side conditions predicted by CONTAIN are similarmore » to those originally specified in NUREG/CR-6075.« less

Authors:
; ; ;  [1];  [2]
+ Show Author Affiliations
  1. Sandia National Labs., Albuquerque, NM (United States)
  2. Idaho National Engineering Lab., Idaho Falls, ID (United States)
Publication Date:
Research Org.:
Nuclear Regulatory Commission, Washington, DC (United States). Div. of Systems Research; Sandia National Labs., Albuquerque, NM (United States)
Sponsoring Org.:
Nuclear Regulatory Commission, Washington, DC (United States)
OSTI Identifier:
10106612
Report Number(s):
NUREG/CR-6075-Suppl.1; SAND-93-1535-Suppl.1
ON: TI95005274; BR: GB0103012
DOE Contract Number:
AC04-94AL85000
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Dec 1994
Country of Publication:
United States
Language:
English
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; ZION-1 REACTOR; CONTAINMENT; ZION-2 REACTOR; C CODES; S CODES; R CODES; RADIATION HEATING; REACTOR ACCIDENTS; REACTOR SAFETY; PROBABILITY; MATHEMATICAL MODELS; MELTDOWN; PRESSURE DEPENDENCE; PRESSURIZATION; FAILURES; EVALUATION; DOCUMENTATION; BLACKOUTS; 220900; 210200; 990200; POWER REACTORS, NONBREEDING, LIGHT-WATER MODERATED, NONBOILING WATER COOLED; MATHEMATICS AND COMPUTERS

Citation Formats

Pilch, M.M., Allen, M.D., Stamps, D.W., Tadios, E.L., and Knudson, D.L. The probability of containment failure by direct containment heating in Zion. Supplement 1. United States: N. p., 1994. Web. doi:10.2172/10106612.
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Pilch, M.M., Allen, M.D., Stamps, D.W., Tadios, E.L., & Knudson, D.L. The probability of containment failure by direct containment heating in Zion. Supplement 1. United States. doi:10.2172/10106612.
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Pilch, M.M., Allen, M.D., Stamps, D.W., Tadios, E.L., and Knudson, D.L. Thu . "The probability of containment failure by direct containment heating in Zion. Supplement 1". United States. doi:10.2172/10106612. https://www.osti.gov/servlets/purl/10106612.
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@article{osti_10106612,
title = {The probability of containment failure by direct containment heating in Zion. Supplement 1},
author = {Pilch, M.M. and Allen, M.D. and Stamps, D.W. and Tadios, E.L. and Knudson, D.L.},
abstractNote = {Supplement 1 of NUREG/CR-6075 brings to closure the DCH issue for the Zion plant. It includes the documentation of the peer review process for NUREG/CR-6075, the assessments of four new splinter scenarios defined in working group meetings, and modeling enhancements recommended by the working groups. In the four new scenarios, consistency of the initial conditions has been implemented by using insights from systems-level codes. SCDAP/RELAP5 was used to analyze three short-term station blackout cases with Different lead rates. In all three case, the hot leg or surge line failed well before the lower head and thus the primary system depressurized to a point where DCH was no longer considered a threat. However, these calculations were continued to lower head failure in order to gain insights that were useful in establishing the initial and boundary conditions. The most useful insights are that the RCS pressure is-low at vessel breach metallic blockages in the core region do not melt and relocate into the lower plenum, and melting of upper plenum steel is correlated with hot leg failure. THE SCDAP/RELAP output was used as input to CONTAIN to assess the containment conditions at vessel breach. The containment-side conditions predicted by CONTAIN are similar to those originally specified in NUREG/CR-6075.},
doi = {10.2172/10106612},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 01 00:00:00 EST 1994},
month = {Thu Dec 01 00:00:00 EST 1994}
}
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Technical Report:
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DOI:  10.2172/10106612
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  • ; ;
    This report is the first step in the resolution of the Direct Containment Heating (DCH) issue for the Zion Nuclear Power Plant using the Risk Oriented Accident Analysis Methodology (ROAAM). This report includes the definition of a probabilistic framework that decomposes the DCH problem into three probability density functions that reflect the most uncertain initial conditions (UO{sub 2} mass, zirconium oxidation fraction, and steel mass). Uncertainties in the initial conditions are significant, but our quantification approach is based on establishing reasonable bounds that are not unnecessarily conservative. To this end, we also make use of the ROAAM ideas of envelopingmore » scenarios and ``splintering.`` Two causal relations (CRs) are used in this framework: CR1 is a model that calculates the peak pressure in the containment as a function of the initial conditions, and CR2 is a model that returns the frequency of containment failure as a function of pressure within the containment. Uncertainty in CR1 is accounted for by the use of two independently developed phenomenological models, the Convection Limited Containment Heating (CLCH) model and the Two-Cell Equilibrium (TCE) model, and by probabilistically distributing the key parameter in both, which is the ratio of the melt entrainment time to the system blowdown time constant. The two phenomenological models have been compared with an extensive database including recent integral simulations at two different physical scales. The containment load distributions do not intersect the containment strength (fragility) curve in any significant way, resulting in containment failure probabilities less than 10{sup {minus}3} for all scenarios considered. Sensitivity analyses did not show any areas of large sensitivity.« less

  • ; ; ; ...
    The Integral Effects Test (IET) series was designed to investigate the effects of subcompartment structures on direct containment heating (DCH). Scale models of the Zion reactor pressure vessel (RPV), cavity, instrument tunnel, and subcompartment structures were constructed in the Surtsey Test Facility at Sandia National Laboratories. The RPV was modelled with a melt generator that consisted of a steel pressure barrier, a cast MgO crucible, and a thin steel inner liner. The melt generator/crucible had a hemispherical bottom head containing a graphite limiter plate with a 4 cm exit hole to simulate the ablated hole in the RPV bottom headmore » that would be formed by tube ejection in a high pressure melt ejection (HPME) accident. The reactor cavity model contained an amount of water (3.48 kg) that was scaled to condensate levels in the Zion plant. Iron oxide, aluminum, chromium thermite (43 kg) was used to simulate molten corium. The driving gas was 440 g{center dot}moles of steam at an initial absolute pressure of 7.1 MPa in IET-1 and 477 g{center dot}moles of steam at an initial pressure of 6.3 MPa in IET-1R. Steam blowdown entrained debris into the Sorts vessel resulting in a peak pressure increase in Sorts of 98 kPa in IET-1 and 110 kPa in IET-1R. The total debris mass ejected into the Sorts vessel was 43.0 kg in IET-1, compared to 36.2 kg in IET-1R. The Sorts vessel had been previously inerted with N{sub 2}. The total quantity of hydrogen produced by steam/metal reactions was 223 g{center dot}moles in IET-1 and 252 g{center dot}moles in IET-1R.« less

  • ; ; ; ...
    The Integral Effects Test (IET) series was designed to investigate the effects of subcompartment structures on direct containment heating (DCH). Scale models of the Zion reactor pressure vessel (RPV), cavity, instrument tunnel, and subcompartment structures were constructed in the Surtsey Test Facility at Sandia National Laboratories. The RPV was modelled with a melt generator that consisted of a steel pressure barrier, a cast MgO crucible, and a thin steel inner liner. The melt generator/crucible had a hemispherical bottom head containing a graphite limiter plate with a 4 cm exit hole to simulate the ablated hole in the RPV bottom headmore » that would be formed by tube ejection in a high pressure melt ejection (HPME) accident. The reactor cavity model contained an amount of water (3.48 kg) that was scaled to condensate levels in the Zion plant. Iron oxide, aluminum, chromium thermite (43 kg) was used to simulate molten corium. The driving gas was 440 g{center_dot}moles of steam at an initial absolute pressure of 7.1 MPa in IET-1 and 477 g{center_dot}moles of steam at an initial pressure of 6.3 MPa in IET-1R. Steam blowdown entrained debris into the Sorts vessel resulting in a peak pressure increase in Sorts of 98 kPa in IET-1 and 110 kPa in IET-1R. The total debris mass ejected into the Sorts vessel was 43.0 kg in IET-1, compared to 36.2 kg in IET-1R. The Sorts vessel had been previously inerted with N{sub 2}. The total quantity of hydrogen produced by steam/metal reactions was 223 g{center_dot}moles in IET-1 and 252 g{center_dot}moles in IET-1R.« less

  • ; ; ; ...
    In a light-water reactor core melt accident, if the reactor pressure vessel (RPV) fails while the reactor coolant system (RCS) at high pressure, the expulsion of molten core debris may pressurize the reactor containment building (RCB) beyond its failure pressure. A failure in the bottom head of the RPV, followed by melt expulsion and blowdown of the RCS, will entrain molten core debris in the high-velocity steam blowdown gas. This chain of events is called a high-pressure melt ejection (HPME). Four mechanisms may cause a rapid increase in pressure and temperature in the reactor containment: (1) blowdown of the RCS,more » (2) efficient debris-to-gas heat transfer, (3) exothermic metal-steam and metal-oxygen reactions, and (4) hydrogen combustion. These processes, which lead to increased loads on the containment building, are collectively referred to as direct containment heating (DCH). It is necessary to understand factors that enhance or mitigate DCH because the pressure load imposed on the RCB may lead to early failure of the containment.« less

  • ; ; ; ...
    For some core meltdown accident sequences in light water reactors (LWRs) it is possible for the primary system to remain at high pressure. Under these circumstances, as the molten core debris penetrates the reactor vessel, the core debris would be ejected under high pressure and, subsequently, dispersed into the containment atmosphere. During the process, thermal and chemical energies are directly transferred from the core debris to the containment atmosphere. This phenomenon has become known as direct containment heating (DCH). This report presents the results of a series of calculations at Brookhaven National Laboratory (BNL) to provide estimates of the DCHmore » containment pressure loading in the Zion plant subject to a wide range of initial conditions and phenomenological assumptions. The containment loading calculations were performed using a version of the CONTAIN code with update modifications, which parametrically characterize DCH phenomena (CONTAIN-DCH, Version 1.10). The range of calculation parameters was selected to represent many of the current uncertainties in DCH initial conditions and uncertainties in modeling DCH phenomena. The choice of CONTAIN calculation input parameters is discussed and results are presented for both a seven-cell nodalization of the Zion containment building. The seven-cell calculations incorporate all the features of the CONTAIN-DCH model. The single-cell calculations are included only for comparison purposes and represent upper-bound estimates of DCH loads, assuming complete mixing, adiabatic conditions and thermal equilibrium between the gas and core debris. Calculation results are presented and discussed. 16 refs., 12 figs., 8 tabs.« less