A. Scheduling of Lift Adjustments for Service Water Pumps

Currently, the regular period between overhauls for the Service Water Pumps at Cooper Nuclear Station is 2 years. The primary limiting condition that requires this relatively short turn-around period is wear on the impeller and pump bowl. The wear observed or measured on the other expendable pump components, such as the pump bearings, Cutlass bearings, the check valve, the pump shafts and shaft couplings, pump wear rings, and so on, do not prevent the pumps from being safely run longer periods of time between turn-arounds. In fact, an informal telephone survey of several nuclear plants, some with the same type and manufacturer of vertical pumps, found that the turn-around time associated with the Service Water pumps at the Cooper Nuclear Station was the shortest. The usual turn-around time was four years; some were longer.

In the past, lift adjustments on the Service Water pumps at Cooper Nuclear Station have only been done once or perhaps twice a year. As shown previously in this report, because of differential expansion, one or even two lift adjustments per year is not enough to ensure that the pump operates within the recommended clearance range.

More importantly, one or even two lift adjustments per year are not enough to ensure that the impeller will not contact the bowl and grind itself into the casing causing accelerated wear and degraded performance. As noted previously, about 42 mils of material may be ground off each year of operation if only one or two lift adjustments are made. After two years of operating this way, up to 84 mils of bowl and impeller materials could be ground off. In short, the largest contributor to impeller-bowl wear in the Service Water pumps has been the lack of timely lift adjustments.

Inspection of the bowl and impeller when they have been routinely removed for inspection and maintenance confirms that such grinding damage has occurred. Re-machining of the impeller and bowl due to excessive wear is typically required in a Service Water pump overhaul, and examination of the wear has found that it not only consists of rounded and smooth erosive cuts associated with water flow and sand abrasion, but also of hard, sharp striations parallel with the rotational plane of the impeller.

Thus, to insure that the pump is operated within reasonable clearance dimensions and to insure that the impeller does not inadvertently grind itself into the bowl, it is necessary to perform four pump lifts per year on the Service Water Pumps at CNS: one lift per quarter. Since performance surveillances (CNS Procedures 6.1SW.101 and 6.2SW.101) are required to be done directly after a lift adjustment is made to re-establish the baseline characteristics of a pump, it is expedient to simply perform a lift adjustment and surveillance at the same time. For this reason, it is recommended that lift adjustments followed by surveillance runs be done on each pump on a quarterly basis during a calendar year.

3. Change in Service Water Pump Turn-Around Periods

Since much of the accelerated wear observed on the bowl and impeller has been caused by not adjusting the lift enough times in a year, if lifts are done according to a regular schedule, the time between overhauls for the Service Water Pumps can be significantly increased.

As noted in various inspections done when a Service Water Pump has been dismantled after two years of service, wear in the expendable parts has been minimal. In fact, when these parts have only been used for one 2 year service period, they have been found to be within tolerance with sufficient margin to be re-usable a second time as is.

Thus, it is recommended that the turn-around period for Service Water pumps be changed from a two year turn-around period to a four year turn-around period.

4. Economic Assessment of Service Water Maintenance Costs

Prior to summer of 1999, typical costs for a Service Water pump turn-around were approximately $198,000 per pump. On an annualized basis, this is $99,000 per year per pump. Thus, it was costing Cooper Nuclear Station approximately $396,000 per year, or $792,000 every two years, to maintain the four Service Water pumps.

This remarkably high cost for the maintenance of the Service Water vertical mixed flow pumps was due to several factors. One factor is the fact that new intermediate pump shafts purchased from the OEM on a non-competitive basis cost $15,000 each, and each pump required four of them. This was an annualized cost per pump of $30,000 just for pump intermediate shafts.

Since summer of 1999, the cost for intermediate shafts, however, has been reduced to about $2000 per intermediate shaft. This was possible because the machine shop at Cooper Nuclear Station is now making replacement intermediate shafts for the Service Water pumps from heat treated bar stock readily available from competitive suppliers. Further, since it has been found that a new shaft is not needed every two years; an intermediate shaft can be re-used at least once, if not more. Thus, the annualized cost for these shafts per pump has dropped from $30,000 to less than $2,000.

The other major factor in causing high maintenance costs has been the relatively short turn around time for the Service Water pumps. This relatively short turn around time was necessitated by the high amount of wear observed in the bowl and impeller. As noted in the previous portions of this report, this wear was primarily caused by a lack of timely administered lift adjustments. Thus, it can be significantly reduced by performing lift adjustments on a quarterly basis. By doing so, it is estimated that the wear on the pump and bowl will be at least halved. Consequently, this allows the scheduled turn-around period to be increased from two years to four years.

Table 4, which follows on the next page, indicates the reduction in costs in present constant dollars of maintaining the Service Water Pumps since early 1999. The first column indicates typical turn-around maintenance costs prior to summer 1999 when intermediate shaft replacement parts were bought from the OEM. The second column indicates the savings accrued due to making the intermediate shafts in-house. The last column indicates the total saving accrued if the turn-around period is lengthened from two to four years. As Table 4 shows, the savings are significant. Instead of spending nearly 4 million dollars for routine Service Water Pump maintenance, only 1.42 million dollars will be spent.

Annualized Basis

Post proposed

Item pre-1999 summer 1999 4 year PM

Labor to change out pump 5,000 5,000 2,500

3 men – 3 days

90 mhrs @ $111/hr

intermediate shafts 30,000 2,000 2,000

check valve 19,000 19,000 8,500

other parts and misc 30,000 30,000 15,000

machining bowl and 15,000 15,000 7,500

impeller/weld build up ______ ______ ______