Tackling tritium

Exelon Nuclear is launching an initiative across its ten-station nuclear fleet to assess systems that handle tritium and take the necessary actions to minimise the risk of inadvertent discharge of tritium to the environment.

The assessments will take place in 2006 and will cover pipes, pumps, valves, tanks and other pieces of equipment that carry tritiated water in and around the plants.

According to a statement, the initiative is intended to significantly reduce the possibility of a tritium release of the type that occurred in the past involving the lake “blowdown” line at Braidwood Generating Station near Braceville, Ill. While the Braidwood leak poses no health or safety threat to the environment or the public, “we recognise that inadvertent releases are unacceptable and we are committed to eliminating them,” said Exelon Nuclear Chief Operating Officer Charles Pardee.

Exelon said the initiative will also establish new standards for inspections, responses to, and remediation of tritium releases that have the potential to affect the environment or the public.

Standards for responses to tritium releases would be modelled, in part, after a recent response at the Dresden Generating Station, where intensified monitoring and inspection detected a small underground tritium leak shortly after it occurred. The small leak, which was confirmed by test data over this past weekend, dripped at a rate of about a half-cup per minute and was discovered within a few weeks after it began.

In this case, the suspect pipe was scheduled for replacement as part of a repair and monitoring program undertaken at Dresden. The leak was confined to shallow ground in a small area near the center of the plant property alongside the plant structure and inside the protected security area. It is not expected to approach the edges of the plant property and poses no health or safety threat.

“Our purpose is to ensure that we have a full understanding of the health of our systems that handle tritium, and that we have satisfied ourselves, our stakeholders and the communities in which we are members, that our equipment has a high degree of integrity,” Pardee said. “Just as important, we want to ensure that we are fully prepared to properly respond to a leak should one occur.”
Tritium is a radioactive isotope of hydrogen that is found naturally in small concentrations in most surface water. It is produced in higher concentrations in water used in nuclear reactors and is a normal byproduct of commercial nuclear power production. Tritium is typically discharged into the environment under strict federal guidelines.

The US Environmental Protection Agency has established a safe drinking water limit of 20,000 picocuries of tritium per liter of water.

At Dresden, tritium found in one test well near the center of the plant property measured 500,000 picocuries per liter. Surrounding test wells 10 to 20 feet away showed tritium concentrations of 20,000 picocuries per liter or less, indicating a small area of tritium that dissipates rapidly at the edges. The affected area is believed to be about 30 feet across near the centre of the plant’s 1,782 acres, adjacent to the plant structure and inside the protected security area. Testing along the site boundary confirmed that no tritium has approached the property edge.

The equipment inspection program has already been initiated at the Byron Nuclear Generating Station in Ogle County, Ill., which is similar to Braidwood in its design. As does Braidwood, Byron uses a blowdown line to release tritium to a nearby river – the Rock River – as part of normal permitted plant operations.

Recent inspections at Byron initiated in response to the Braidwood issue found standing water inside concrete vaults in the ground that are part of the Byron blowdown line, which runs along a strip of company property to the river. The vaults house valves known as “vacuum breakers” that can malfunction and leak.

Water in the vaults was tested last week and found to contain a tritium concentration of 86,000 picocuries per liter. Additional engineering work and environmental sampling is being undertaken this week to determine if tritium has migrated into the ground outside the vaults.