Unit-2 functional after being shut since 2016

MUMBAI: A conclusive report by the country’s nuclear watchdog revealed impurity in carbon dioxide gas corroded the outer surface of coolant channels, resulting in leakage of heavy water in units 1 and 2 of Kakrapar Atomic Power Station (KAPS), Gujarat, in 2015 and 2016.

On Monday, KAPS-2 attained criticality at 2.22am after completion of renovation and modernisation work that included replacement of coolant channel and feeder. Reaching criticality is the initiation of controlled selfsustaining fission chain reaction in the reactor.

However, there is no word on when will KAPS-1 start

“Based on the findings, it has been concluded that unlisted impurity [hydrocarbons] in the carbon dioxide gas used in the annulus gas system of these reactors. This resulted in shallow localised corrosion spots on the outer surface of coolant channels and corresponding generation of hydrogen,” reads the report released on August 31 by Atomic Energy Regulatory Board (AERB).

It adds, “Shallow localised corrosion spots led to gradual absorption of hydrogen by coolant channels, which affected material properties and resulted in leakage.”

To ascertain the cause of leakage, both the failed and some fit coolant channels from KAPS-1 and 2 units were examined and analysed at Bhabha Atomic Research Centre, Trombay.

While inspections in pressurised heavy water reactors (PHWRS) across India revealed localised corrosion was specific to only KAPS-1 and 2 units, AERB has made specifications for carbon dioxide gas and its

quality assurance checks more stringent for every operating PHWR.

“Scope of coolant channel in-service inspection programme has been enhanced by including requirement for detection of localised corrosion during periodic inspections,” said AERB.

CASE HISTORY

On March 11, 2016, 220 megawatt KAPS-1 underwent an automatic shut down after a heavy water leakage from its coolant system following which a “plant emergency” was declared.

The previous year, on July 1, 2015, unit 2 of the 220 megawatt indigenous PHWR was shut down after a similar leakage from its coolant channels.

Heavy water, used in nuclear reactors, is formed when hydrogen molecules are partly or wholly replaced by the isotope deuterium.

Heavy water is the key to one type of reactor in which plutonium can be bred from natural uranium.