Parametric study of the potential for BWR ECCS strainer blockage due to LOCA generated debris. Final report

Abstract

This report documents a plant-specific study for a BWR/4 with a Mark I containment that evaluated the potential for LOCA generated debris and the probability of losing long term recirculation capability due ECCS pump suction strainer blockage. The major elements of this study were: (1) acquisition of detailed piping layouts and installed insulation details for a reference BWR; (2) analysis of plant specific piping weld failure probabilities to estimate the LOCA frequency; (3) development of an insulation and other debris generation and drywell transport models for the reference BWR; (4) modeling of debris transport in the suppression pool; (5) development of strainer blockage head loss models for esbunating loss of NPSH margin; (6) estimation of core damage frequency attributable to loss of ECCS recirculati~on capability following a LOCA. Elements 2 through 5 were combined into a computer code, BLOCKAGE 2.3.A point estimate of overall DEGB pipe break frequency (per Ih-year) of 1.59E-04 was calculated for the reference plant, with a corresponding overall ECCS loss of NI'SH frequency (per Rx-year) of 1.58E-04. The calculated point estimate of core damage frequency (per Rx-year) due to blockage related accident sequences for the reference BWR ranged from 4.2E-06 to 2.5E-05. The results of this study show that unacceptable strainer blockage and loss of NPSH margin can occur within the first few minutes after ECCS pumps achieve maximum flows when the ECCS strainers are exposed to LOCA generated fibrous debris in the presence of particulates (sludge, paint chips, concrete dust). Generic or unconditional extrapolation of these reference plant calculated results should not be undertaken.

Experimental study of pressure drops through LOCA-generated debris deposited on a fuel assembly

“…The cut pieces were then shredded in a leaf shredder/chipper, and produced fiberglass as 'fine' debris. Most of the bypass fiber was classified as 'Class 1 which is described in the NUREG/CR-6224 (Zigler et al, 1995). Fig.…”

Final report, BWR drywell debris transport Phenomena Identification and Ranking Tables (PIRTs)

“…The panel was fortunate that prior work [2] provided a consistent framework for partitioning the drywell into the four components pictorially illustrated in Figure 2 and described below: Boundary conditions -Based on discussions related to the opinion that break flow was adequately characterized by the proposed methodology, and that the development of debris generation models was already well focused, it was determined these sources were best characterized as boundary conditions to the PIRT work. Therefore, there was no need to define components for these regions.…”

“…Information from the NRC research [2] (including those informally documented efforts given in Appendix C), and to a limited extent from the BWROG work, constitutes the baseline for the PIRT project described herein.…”

Permeability and compression of fibrous porous media generated from dilute suspensions of fiberglass debris during a loss of coolant accident

“…In nuclear engineering, NUREG/CR-6224 (Zigler et al, 1995) predicted the head loss across the fibrous debris bed formed on the strainer for Boiling Water Reactors (BWRs) as shown in Eq. (13).…”

“…Based on modified conditions, Lee et al (2014a,b) proposed an empirical Kozeny constant model for viscous flow, Eq. (15), for NUKON fibrous debris prepared using the shredder method (Zigler et al, 1995), based on Lord's model.…”