APR: your source for nuclear news and analysis since April 16, 2010

Sunday, March 20, 2011

Recovery of water damaged electrical equipment

Since TEPCO continues to be unable to restore power inside the flood ravaged Fukushima Daiichi nuclear plants, let's take a moment (while we are waiting for news that the power is back available in the plants, as well as waiting for other news) and look at a very interesting and relevant volume in the APRA library. This book is titled "Westinghouse Electrical Maintenance Hints" and was published by Westinghouse Electric Corporation in 1974. Relevant to us is the chapter on recovery of flood damaged electrical equipment; we'll use this, and experience, to give some brief idea of what TEPCO is doing.

The first thing that will have to be done is to check that any equipment to be energized is totally dry, and this includes the insulation. Many kinds of insulation do not insulate at all when wetted. Runs of cable may have to be totally replaced, which includes connecting new terminals; this might be better done outside the normal cable ways if they cannot be assured dry throughout.

Equipment must also be cleaned of deposits if they exist, as in the inside of switchboards or motor controller cabinets. Steam can be used to blast out sediment; it may air dry, or be dried by forced heated air, or be dried in a temporary drying oven set up on site. This dry-out applies to all motors or other components that are to be reused. It seems that replacement of many components is the method of choice at Fukushima Daiichi.

Once all equipment to be energized has been opened, cleaned, dried and inspected it must be tested for resistance to ground with a meg-ohm meter ("megger" is the familiar term) before being actually energized. Of course grounds will be found in the equipment and these must be found and eliminated. Certainly, proper protection in the form of circuit breakers is vital in the improvised electrical network set up locally in the area of Nos. 1 through 4 reactor plants at the site.

Electronic equipment can be expected to be damaged as well, and it may prove true that complete spares of I&C (instrumentation and control) equipment might be needed to get any real operability of remote plant indications in the control room.

It should be noted that in the past, various kinds of solvents were commonly used to clean electrical equipment and these produce noxious, sometimes toxic and sometimes flammable vapors - something to be reckoned with in enclosed spaces where there might be arcs and sparks if they're used.

Electric motors of all kinds (DC, AC all types) are normally seriously damaged or ruined if submerged in salt water and would normally be replaced.

This is just the electrical aspect; radiation fields will probably limit times that crews can work in some areas, while contamination may have to be cleaned up or avoided / bypassed when performing the electrical work.

The days are probably gone when Westinghouse can mount the kind of effort it closes the chapter in the HINTS book with -- a plant owned by American Cyanamid was flooded and Westinghouse mounted a massive effort by bringing in 40 foot trailers and about forty men who worked around the clock disassembling and cleaning electrical parts. Many parts depots were contacted for spares that were flown in starting 48 hours after the first requests. Many loads of parts, solvents, and expendables were shipped in and used. The engineers converted a shed into a drying oven for parts that had been cleaned by steam or solvent methods; rigs for this were also constructed. From the flooded plant over 1500 motors were shipped out to Westinghouse and General Electric repair centers while over 2000 components were cycled through the newly constructed (rigged) onsite plant. The plant was back in partial operation for its owner only 16 days after the flood actually hit.

That's one example of what a maximum effort can do. TEPCO and its contractors are right now confronting a dilemma of another, higher order of magnitude and are exerting their own maximum efforts.

9:20 PM Eastern Sunday 3/20


  1. Nice post; suggest that TEPCO and others are going to be working to get the RICS system operational (if indeed it can be operated) in the reactor building itself then go from there (spent fuel pools et al) without actually getting the control rooms operational (if they have been flooded) ... do we know for a fact what was flooded?

    Tnx for the blog BTW -txrxqa

  2. Thank you. TEPCO seems insistent on using the control room and has now cooked up plans to filter the air. No actual word of what was flooded and what wasn't that I've seen.