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Head Loss Characteristics of a Fibrous Bed in a PWR Chemical Environment

Ashok K. Ghosh, Kerry J. Howe, Arup K. Maji, Bruce C. Letellier, Russell C. Jones

Nuclear Technology / Volume 157 / Number 2 / February 2007 / Pages 196-207

Technical Paper / Thermal Hydraulics

This paper examines the generation and effect of secondary materials created by chemical reactions between dislodged fiberglass insulation debris and simulated cooling system water that would be present within the containment of a pressurized water reactor following a loss-of-coolant accident (LOCA). Corrosion and subsequent precipitation of metals (aluminum, iron, zinc, and calcium) pose an important safety concern because the surface area of exposed metal inside containment represents a large potential source term of chemical debris products that may be capable of blocking the recirculation sump. The Advisory Committee on Reactor Safeguards (ACRS) cited the presence of gelatinous material recovered from the Three Mile Island containment pool after its 1979 accident and noted that the formation of adverse chemical products had not been previously examined under Generic Safety Issue 191 (GSI-191) research program.

Based on small-scale tests, the following key issues related to corrosion and precipitation were investigated:

1. Do credible corrosion mechanisms exist for leaching metal ions from bulk solid surfaces, and if so, what are the typical reaction rate constants?

2. Can corrosion products accumulate in the containment pool water to the extent that they might precipitate as new chemical species at pH and temperature levels that are relevant to the LOCA accident sequence?

3. How do chemical precipitants affect the head loss across an existing fibrous debris bed?

Findings from these tests confirmed that corrosion of metal can occur and that artificially induced metallic precipitants can cause substantial additional head loss.

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