Upon return to service from a refueling outage, the 1150 MW SONGS Unit 3 was at 39% reactor power when a circuit breaker fault resulted in a fire, a partial loss of AC off-site power, and a reactor shutdown. The failure of a circuit breaker to function properly resulted in the unavailability of the DC driven turbine emergency lubricating oil pump, causing extensive damage to the turbine generator. The power supply crisis in California at this time highlighted the need for an urgent understanding of the seriousness of the damage to the turbine generator, the consequences for the repair and timely return of the unit to service. Initial inspections indicated that all rotor line bearings had suffered from loss of white metal and most of the housings were distorted. Rotor journals were scored from solid contact and subject to excessive heat damage. Rotor steam seals had suffered rubbing damage. In view of the component sizes associated with such a large machine, and the need to minimize the outage duration, a large proportion of the repair work was undertaken on site. This enabled SCE to project manage the work themselves ‘in-house’. It was decided that the HP and the three LP turbine rotors would remain on site, with only the Generator rotor and the complete Exciter being shipped to the OEM’s workshops for repair. Specialist sub-contractors were employed for site machining and heat treatment. Consultants were hired for specialist technical matters, primarily related to metallurgical issues, to complement the in-house expertise of both SCE and ALSTOM. The serious nature of the damage required close cooperation between SCE and ALSTOM the OEM. It was important to understand the design margins and therefore the scope for repair, and long term integrity of the solutions. The detailed repair instructions were prepared and controlled jointly between ALSTOM and SCE engineers on site, with extensive technical back-up provided from the OEM engineering design departments. Similar close co-operation on the re-design of components and fast track supply of spare parts was crucial to the success of the project.

I. THE NEED. A. In high pressure feedwater heaters, a tube leak quickly claims several neighboring tubes as collateral victims. B. Prompt detection of the initial leak would save the neighboring tubes from damage and preclude a potential turbine water induction incident. II. EXAMPLE. A. A Midwest generating station replaced 12 old high pressure heaters. The new heaters contained 304N SS tubes. In one of the new heaters, an unknown localized contaminant caused a single tube leak within the first year. This single leak went undetected until several surrounding tubes were lost due to impingement from the initial leak. And even the conservatively sized normal and emergency drains were overwhelmed, causing the heater to trip on high level. III. CAPABILITY OF SMART LEVEL CONTROLS. A. There are three known possibilities that would cause high drain-flow conditions in a feedwater heater. 1. High Unit Load. 2. The upstream feedwater heater is out of service. 3. A tube leak. B. Traditional Local level controls can sense high flow conditions, but cannot tell why. Most systems will alarm the opening of the emergency drain valve, but by that time, the collateral tube damage is usually severe. “Smart” Level Controls have the capability to distinguish between these conditions, thus allowing it to give early notification of a tube leak, before collateral damage becomes severe.