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Seaweed shuts down reactor at Leningrad nuclear plant via Bellona

ST. PETERSBURG – Seaweed caused almost three days’ downtime at Unit 3 of Leningrad Nuclear Power Plant (LNPP), on the Gulf of Finland, near St. Petersburg, after a storm blew bay bottom sediments into the plant’s water intake structures, clogging the intakes that supply water to the unit’s cooling system. The blockage had to be manually removed before the reactor could resume operation.

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Nuclear plants’ water supply: A whale of trouble

Adverse weather, grass, seaweed, or ice are known to have caused emergency reactor shutdowns both in Russia and other countries. For instance, in January 2010, ice in the Delaware River forced shutdown at Unit 2 and power reduction at Unit 1 of the New Jersey-based Salem Nuclear Power Plant, which uses the river for water supply.

In fact, the owner of Unit 1 at the Salem plant had previously been fined for an incident involving water intake blockage. In 1994, the Nuclear Regulatory Commission levied a $500,000 fine for “violations stemming from an event on April 7, 1994, when marsh grass floating in the Delaware River blocked the traveling screens at the intake structure,” says an issue brief by the U.S. Union of Concerned Scientists.

The operators, who reduced the reactor power level, made a series of mistakes along the way and the reactor automatically shut down for safety reasons, the brief says. The 2007 brief, entitled Got Water?, explains the cooling water needs of nuclear power plants and cites numerous incidents where personnel’s violations or issues with maintaining proper water supply threatened a plant’s safety.

In August 2010 – when an unprecedented heat wave hit European Russia – raging wildfires were taking down high-voltage transmission lines around Novovoronezh Nuclear Power Plant, near Voronezh, and a malfunction in the plant’s outdoor switchgear, which was attributed to heat, brought on a turbogenerator shutdown and a reactor trip at Unit 3. In December that year, black ice and glaze ice conditions, as well as ice buildup tearing down power lines, led to power shutdowns and other utility interruptions in Dimitrovgrad, in Ulyanovsk Region, where one research reactor was scrammed and five more were taken offline preventively.

In more extravagant cases, a bird scrammed a reactor at Ukraine’s Rovno (Rivne) Nuclear Power Plant in April 2011, in June that year two reactors at Torness Nuclear Power Plant in Scotland were stopped by a swarm of jellyfish – a risk factor that has also affected operation of nuclear power plants in Japan and California, and that same month an Atlantic gray seal wandered into the water intake chamber of the Hinkley Point B station in Somerset in Great Britain and was trapped there for five days before staff managed to rescue and release it nearby.

Vulnerability to external factors is a known cause of nuclear energy’s unreliability. These risks make unplanned downtime a common occurrence at nuclear reactors. This time, on account of fine seaweed risen by a storm and clogging water intake structures, a 1,000-megawatt reactor stayed down for 61 hours and had to operate at a reduced power level after that. Some 70 million kilowatt-hours was undersupplied to the Russian Northwest’s grid as a result.

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