ML20205F555
| ML20205F555 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/25/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20205F543 | List: |
| References | |
| NUDOCS 8703310195 | |
| Download: ML20205F555 (4) | |
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UNITED STATES f' 7, NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D. C. 20555 N..
f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACT 0P REGULATION RELATING TO PCRV TENDON INTERIM SURVEILLANCE PUBLIC SERVICE COMPANY OF COLORADO FORT ST. VRAIN NUCLEAR GENERATING STATION DOCKET NO. 50-267
1.0 BACKGROUND
As a result of discovered deterioration of tendons at the Fort St. Vrain PCRV in 1984, the licensee embarked on a surveillance program to monitor any further corrosion of tendons. Under the requirements of this program, the licensee will file semiannual reports of their findings related to tendon surveillance perfonned during the past six-month period. The interim surveillance program requires liftoff or visual surveillance to be performed on a given number of selected tendons over six-month intervals.
This program was established for a period of three years or until such time that effective corrosion control has been established.
The Safety Evaluation addresses the second six-month tendon surveillance report covering the period of January 5, 1986 through June 20, 1986.
Also included are the findings of the liftoff tests performed on the new tendon group selected for the first eighteen-month interim surveillance, which covers the period of January 1985 through June 1986.
2.0 LICENSEE'S FINDINGS The licensee's report provides the pertinent information regarding control tendons (tendons within each of the four tendon types which will remain the same throughout the surveillance period), and the new tendons of a given population selected at random during each inspection / test period.
It also describes the results of both the visual inspection and the liftoff tests for both groups of tendons. Additionally, the report contains information regarding the supplemental tests (visual and liftoff) performed in an effort te complete at least one surveillance on all accessible PCRV tendons in a timely manner.
These tendons have been surveilled over and above the control and new tendons scheduled for the interim surveillance during the past six-month period. The results of the i
six-month surveillance are sumarized below.
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2 2.1 New Tendor Surveillance Forty-four.(44) new tendons were selected for this 6-month surveillance and subjected to both visual and liftoff tests._ The report indicates
'that there was some discoloration or corrosion on anchor assembly parts or in the wire bundles of 42 of the 44-tendons examined. The breakdown of the affected tendons is as follows:
Number of the Tendon Group Affected Tendons Circumferential 12 out of 13 Top crosshead 1 out of 1 Bottom crosshead 6 out of 6 Longitudinal 23 out of 24 Out-of the total of 44-new tendons examined in this surveillance, 34 have had at least one surveillance prior to the start of the interim surveillance program. Out of these 34 tendons,16 had noneffective wires during the previous examination:
2 circumferential, 4 bottom crosshead, and 10 longitudinal. There is no indication that corrosion is continuing in 33 of these 34 new tendons. This conclusion is drawn because there has been no increase in the number of noneffective broken wires in these 33 new tendons when this surveillance data is compared to the previous surveillances. One tendon, BILU3, did show an increase from 16 to 18 noneffective wires in a 14-month period. The noneffective wires are defined as wires which no longer carry any load.
Of the 10 new tendons which had not been previously examined, 2 tendons were observed with noneffective wires. These are tendon CM9.5 with I noneffective wire and tendon CM4.6 with 20 noneffective wires.
The remaining eight tendons did not have any noneffective wires.
The licensee reported that on March 13, 1986, during a routine surveillance of tendon CM4.6, approximately ?8 gallons of water were drained from the tube and end caps. This finding, included postulations as to the source of the water and the corrective action to date. The finding was reported in the Licensee Event Report (LER) number 84-055-04, dated June 16, 1986. Since the submittal of this LER, the tendon end caps were again removed from tendon CM4.6. During this second inspection, approximately 0.45 gallons of additional water was collected from the end caps. The licensee believes that the water could be a result of evaporation from the interior intersitices of the tendon wire bundle, which did not fully drain during the original opening. This was followed by a recondensation of the water in the cooler regions of the end caps.
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. 1 2.3 Supplemental Tendon Surveillance Nineteen tendons were subjected to surveillance in this group. Of there, IP were selected for a liftcff test and 7 for visual inspection. All of these tendons, except two, have no record of previous surveillance since the original installation. Only 1 of the 19 supplemental tendons surveilled, CM7.5, was observed to have a noneffective wire. All supplemental tendons which had a liftcff test possess preloads which are well above the minimum design preload for each tendon.
2.4 Tendon load Cell Surveillance Twenty-seven (27) tenden load cells are being monitored monthly for signs of excessive relaxation or preload loss. Data have been recorded monthly from May 1984 through June 1986.
The report indicates that from May 1984 through June 1985 there were no signs in any of the load-cell tendons of a general trend toward relaxatior.
or preload loss. Moreover, all load-cell tendons continue to possess a substantial preload margin above the minimum design preload for each respective tendon type.
2.5 Number and Percentage of Tendons Surveillance to Date The licensee reported that 319 of the total 448 PCRV tendons, or 71.2
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percent, have had at least a visual inspection on at least one end at least one time since March 1, 1984. This is an increase of 6.9 percent of total tendons surveilled since the January 1986 tendon surveillance report.
The licensee indicated that eventually all accessible pCRV tendons will be surveilled.
3.0 EVALUATION The staff has reviewed the report for the PCRV tendon interim surveillance dated July 1986.
Indicated below are the observations and conclusions reached by the staff resulting from this review.
The fact that discoloration or corrosion was observed in a relatively large percentage of tendons has been noted. This fact by itself does not render the tendons as noneffective, but calls for increased attention in the future. The staff is directing the licensee's attention to this issue during future surveillances. Also, accumulation of water in the tendon tube and end cap of tendon CM4.6 remains unexplained. The staff finds the licensee's conclusion contained in the report is conjecture, and not supported by facts. The staff requests further inquiry to determine the cause of this incident and, if necessary, measures be taken to prevent its further occurrence. More frequent examination of this tendon for water accumulations should be considered.
F The staff will undertake an effort to study the overall structural integrity of the PCRV, taking into consideration the percentage of the corroded tendons, the remedial action taken, the original design margins, and the conclusions from the present surveillance program. These considerations would also include the projected long-range deterioration of the tendons, and other factors which could potentially affect the PCRV structual integrity. The primary purpose of this study will be a long-range assessment of the margins of safety inherent in the PCRV. This approach is in contrast with an evaluation on the basis of a surveillance report, which is addressing an "as is" condition.
In sunnary, the licensee demonstrated that there are many tendons which require attention during future surveillances because of discoloration observed on washers. Examination of Table 2.1-1 of the subject report disclosed that these tendons did not have any discoloration during previous surveillances. Also, accumulation of water in one of the tendons requires further investigation to determine the cause. Because many tendons are not accessible and, therefore, cannot be surveilled, there is a possibility that water may have been accumulated in other tendons as well. We regest a more definitive evaluation of this water accumulation, including an assessment of possible pathways, consequences, and remedies. This evaluation should be included in the next surveillance report.
On the other hand, the report indicates that the number of noneffective wires increased only in the case of one tendon, BILU3, which might be construed as an indication that the rate of degradation of the tendons was slowing down.
Future surveillance should confirm or negate this conclusion.
On the basis of the above, the staff concludes that,although further investigation and surveillances are required, the present state of the PCRV is such that operation of the plant should not present a risk to the public safety at this time. Our future evaluation of the PCRV will be based on the review of the forthcoming PCRV tendon surveillance reports and other evaluations.
Reviewer: R. Lipinski, DPWRL-B Dated: March 25, 1987 1