[cdn-nucl-l] Update from Japan

["Adam McLean" <adam.mclean@utoronto.ca>]

Posted on Asahi.com on December 16, 2001 and at:
http://www.asahi.com/english/national/K2001121400463.html

Adam

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Hamaoka nuclear probe zeroes in on hydrogen gas

The Asahi Shimbun

Plants have already installed valves to release accumulations of the highly
inflammable gas.

An explosion caused by accumulated hydrogen gas likely ruptured a pipe last
month at the Hamaoka Nuclear Power Plant in Shizuoka Prefecture, nuclear
safety officials said Thursday.

The finding has already prompted four power companies, including Chubu
Electric Power Co., the operator of the Hamaoka plant, and Tokyo Electric
Power Co., to install pressure release valves to allow the escape of
hydrogen gas at 14 reactors with similar cooling systems nationwide.

The Ministry of Economy, Trade and Industry's Agency for Nuclear and
Industrial Safety had earlier circulated its report on the findings among
the firms.

Agency officials said Chubu Electric had inspected pipes at another reactor
at Hamaoka, in addition to another system at the No. 1 reactor, where the
Nov. 7 rupture occurred. The company found hydrogen in pipes on the No. 2
reactor in concentrations of about 1 million times greater than that found
in the atmosphere.

An analysis of the ruptured pipe also led investigators to rule out a
phenomenon known as water hammering-in which steam coming into contact with
liquid water causes shock waves-as the cause of the rupture.

Officials are still trying to determine how the hydrogen, which they believe
accumulated after the steam in the pipes cooled, was generated, as well as
how it was ignited.

The rupture occurred in an inverted U-shaped section of pipe through which
the steam flows before reaching a valve, and which is designed to allow
light gases such as hydrogen to accumulate.