Nuclear, Reactors

Steam generator replacements continue

Issue 4 and Volume 101.

Steam generator replacements continue

By Teresa Hansen, Assoicate Editor

One of the biggest challenges facing utilities with pressurized water reactors (PWR) is how to keep the steam generators (SG), which are essential to their design, from deteriorating permanently. SG degradation has been the greatest cause of PWRs` capacity factor loss, and as plants age, new types of problems are appearing.

In 1993, Portland General Electric Co.`s Trojan nuclear plant became the first PWR to be decommissioned primarily because of SG problems. Other utilities with similar problems have elected to invest in new SGs to keep their plants in service. The following tables, provided by the Electric Power Research Institute (EPRI), give information on SG replacement through 1995. 1996 data, which should be released in October, have not yet been compiled. Although some of this information may have changed in the past 15 months, it still provides an accurate indication of the increasing SG replacement activity occurring within the nuclear utility industry. This information also shows that the impact of a utility having to replace SGs is still substantial.

Table 1 shows that replacement duration has ranged from 38 days to 365 days. Replacement costs have ranged from $37 million to $230 million dollars, excluding replacement power costs. The table also shows that operation before SG replacement ranged from seven to 24 years. However, effective full power years of operation (EFPY) has ranged from 3.6 to 19.5, with the SGs replaced in 1995 having an average of 11.2 EFPY.

Total personnel radiation doses during the replacement process have been as low as 60 and as high as 2,141 man REM. The 1995 replacements on average required only 33 percent of the time and 8 percent of the exposure as the first replacement at Surry 2.

Table 2 shows the SG orders that had been announced through the end of 1995. These orders indicate that SG replacement activity will continue to remain high over the next several years z

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Table 1

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Table 1 continued