Partial loss of post-trip cooling

Print View Posted on: 29 April 2024

Event Date: 15 November 2023 Event Type: Power Reactor
Event Location: United Kingdom, TORNESS-2 INES Rating: 2 (Final)

The planned reactor trip triggered switching of the reactor’s eight Gas Circulators' (GC) power supply from “nominal - 11kV” to “variable speed – 3.3kV”. The 3.3kV power supply is provided by four Variable Frequency Convertors (VFC) and four Variable Speed Drives (VSD). In this case two VFC failed to start, and one VFC and one VSD tripped shortly after starting. Reactor cool down was safely provided by the remaining four GCs for 6 hours when the two failed VFCs were brought into service, which improved cooling margins.

INES Rating: 2 - Incident (Final) as per 26 April 2024
Release beyond authorized limits? No
Overexposure of a member of the public? No
Overexposure of a worker? No
Contamination spread within the facility? No
Damage to radiological barriers (incl. fuel damage) within the facility? No
Degradation of Defence In-Depth Yes
Person injured physically or casualty? No
Is there a continuing problem? No

Ivaylo Stanev
Office for Nuclear Regulation (ONR)
Ivaylo.Stanev@onr.gov.uk
http://www.onr.org.uk
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