ML20112C612
| ML20112C612 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/05/1985 |
| From: | Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | Johnson E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| P-85071, NUDOCS 8503220042 | |
| Download: ML20112C612 (8) | |
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- 2420 W. 26th Avenue, Suite 1000, Denver, CO 80211 Denver, CO 80201- 0840 (303) 571 -7511 March 5, 1985 Fort St. Vrain Unit No. 1 P-85071 Regional Administrator 3@M0W2 %
Region IV U.S. Nuclear Regulatory Commission g g 2E 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011 y
Attn: Mr. Eric Johnson DOCKET N0. 50-267
SUBJECT:
Fort St. Vrain Unit No. 1 Revised Tendon Surveillance Program
REFERENCES:
- 1) P-85039, Gahm to Johnson, dated January 31, 1985
- 2) P-84523, Warembourg to Johnson, dated December 14, 1984
Dear Mr. Johnson:
As a result of our porposal for a PCRV tendon surveillance program presented at the February 20-22, 1985 site meetings and subsequent telephone conversations, we are transmitting herewith our written description of this program.
The basis for our proposal is as follows:
A.
Surveillance Frequency and Tendon Population Our original interim surveillance program as proposed by P-85039, established an 18 month frequency for the visual inspection and liftoff test programs. While it is felt that this program would provide adequate monitoring of the prestressing system, we recognize that the present data base is not sufficient to define a corrosion rate. Based on present information, the corrosion rate appears to be relatively slow, but we feel it is l
necessary to develop a more sufficient data base.
On this basis yGO{ y we have proposed the accelerated inspection / testing program for HIV Official Fila Copy l
/r 8503220042 850305 tb PDR ADOCK 05000267 fL i
6 P
PDR TO
P-85071
-Page 2
-the next three (3) year period or until-such time that effective corrosion control is established.
The program changes the
- previously proposed 18, month frequency for visual inspection to a six :(6) month frequency. The proposed program also establishes a larger control group of. tendons to permit a better assessment of corrosion rate. '
The liftoff frequency for the new. tendon population remains the same as'previouslyl proposed; however, a control group has been established to fprovide a liftoff assessment every six (6)
. months for tendons in this group.
i This substantial. increase in the surveillance program together with a'very high percentage of tendons that we have i'
already inspected / tested provides the necessary assurance that PCRY:prestressing system is capable of performing its design
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function.
B.
Engineering Evaluations / Failed Wire Criteria 4
As indicated in the proposed surveillance program, we will l
be continuously assessing the PCRV prestressing system from an engineering ~ viewpoint as data is obtained in.the surveillance
=
. program. We expect the surveillance program. to be continuous over the frequency cycle specified.
4 Within the' proposed program, we did specify a mandatory engineering evaluation based on > 15%
failed wires for circumferential barrel' tendons ani -> 20% failed wires for all other tendons.
It should be noted that the program outlined on
- February 22, 1985, during the NRC site meetings established a general criteria'of > 20% failed wires for all tendons.
That i.
' original criteria Hid not recognize the two sub-groups of circumferential tendons,- one of which is the 152-wire circumferential barrel tendons. As_a result, this surveillance program has established a > 15% failed wire criteria for the circumferential barrel tenTons.
4 Design Criteria DC-11-1 (FSAR, Appendix E) requires the PCRV be designed to resist a cavity pressure of 2.1 RP (1775 psig) for Limit Condition 2 which is the governing case..The allowable stress / strength limits for this condition are:
4 Longitudinal tendons --Guaranteed ultimate tensile. strength provided that strain compatibility is satisfied.
Circumferential. tendons in-barrel - Same as above.
Top and bottom head tendons (circumferential and crosshead)
- 0.9 fsy where fsy is the minimum guaranteed steel yield-strength at 1% elongation, and is equal to 204 ksi (FSAR, Fig. 5.6-1).
I
.. _ _ _. -,. _ - _ -... ~ _. _. - -. _. _,...
., _. - ~ -
P-85071 Page 3 In this calculation, in order to assure the participation of rebars, the allowable stress for the longitudinal tendons and the circumferential tendons in the barrel section is limited to fsy.
The PCRV ultimate load analysis (FSAR Section 5.3.3.3 and Appendix E, Section E.10, Figs. E.10-23 through E.10-25) indicates that at a cavity pressure of 1775 psig the stresses in typical tendons are still elastic as given below:
1.
Longitudinal tendons:
156 ksi.
2.
Circumferential tendons at barrel:
170 ksi.
3.
Circumferential tendons at heads:
138 ksi.
4.
Crosshead tendons = 139.5 ksi.
These tendon stresses expressed as ratios of the respective allowable stress / strength limits are as follows:
1.
Longitudinal tendons:
156/204 = 0.76 2.
Circumferential tendons at barrel:
170/204 = 0.83 3.
Circumferential tendons at heads:
138/(0.9 x 204) = 0.75 4.
Crosshead tendons:
139.5/(0.9 x 204) = 0.76 It follows that the minimum acceptable tendon steel areas to resist the overpressure condition expressed as ratios of original areas specified in design are as follows:
Wire Failure Area Permissable Evaluation Required Loss Criteria Longitudinal Tendons 76%
24%
20%
Circumferential Barrel 83%
17%
15%
Circumferential Head 75%
25%
20%
Crosshead, Top or Bottom 76%
24%
20%
Based on the above percentages, we established the > 15% and
> 20% wire failure criteria as a conservative point for iiiandatory Engineering evaluation. The conservative nature of the criteria is based on the following:
1.
Although the above calculations are based on minimum guaranteed yield strengths, they are also based on a hypothetical reactor vessel pressure of 2.1 Reference Pressure (1775 psig).
The plant protective system action which monitors reactor pressure, trips the reactor at 107.5% of the normal working pressure of 688 psig.
In addition, two redundant safety relief valves provide overpressure protection with setpoints of ~ 812 psig and 832 psig respectively.
r 2.
The criteria assumes uniform degradation of all tendons. This is obviously not representative of how
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P-85071 Pagn 4 corrosion will proceed, and is most certainly ultra conservative based on our inspection findings.
The criteria will be utilized to provide a trigger for engineering evaluations on a tendon by tendon basis.
3.
The design of the prestressing system (see FSAR Appendix E
Section E.14.2.5) permits complete detensioning and removal of a tendon at power operation which represents a 100% loss of wires for that tendon when applied to the prestressing system as a whole.
Obviously an evaluation of an individual tendon using the proposed criteria if > 15% and > 20% is conservative.
4.
The inspection findings to date do not reveal any specific tendency for tendon corrosion on a cluster basis.
The corrosion is random in nature and there is no inmediate concern for cluster failure of several tendons that would result in localized PCRV concrete tension.
C.
Overall Conclusion It is our opinion that the proposed surveillance program will provide adequate monitoring of the PCRV prestressing system to permit assessment of the PCRV integrity on a continuous basis to ensure the health and safety of the public.
Very truly yours,
$ 7Y /Tw Don W. Warembourg Manager Nuclear Engineering Division DWW:pa
P-85071 Page 4 corrosion will proceed, and is most certainly ultra conservative based on our inspection findings.
The criteria will be utilized to provide a trigger for engineering evaluations on a tendon by tendon basis.
3.
The design of the prestressing system (see FSAR Appendix E
Section E.14.2.5) permits complete detensioning and removal of a tendon at power operation which represents a 100% loss of wires for that tendon when applied to the prestressing system as a whole.
Obviously an evaluation of an individual tendon using the proposed criteria if > 15% and > 20% is conservative.
4.
The inspection findings to date do not reveal any specific tendency for tendon corrosion on a cluster basis.
The corrosion is random in nature and there is no immediate concern for cluster failure of several tendons that would result in localized PCRV concrete tension.
C.
Overall Conclusion It is our opinion that the proposed surveillance program will provide adequate monitoring of the PCRV prestressing system to permit assessment of the PCRV integrity on a continuous basis to ensure the health and safety of the public.
Very truly yours,
/[A.JY /Twn$n~p Don W Warembourg Manager Nuclear Engineering Division DWW:pa hviewed By :
~
J
Fort St. Vrain PCRV Tendon Surveillance Program CONDITIONS The following PCRV Tendon Surveillance Program is to be implemented, effective April 22, 1985, for a period of three (3) years or until such time that effective tendon corrosion control is established, whichever occurs first.
An ongoing PCRV Tendon Surveillance Program will be established thereafter, subject to NRC review and approval.
DEFINITIONS For the purpose of this surveillance test, the following definitions are applicable:
VISUAL INSPECTION:
Removal of the tendon end cap and an in-place visual examination of the anchor assembly to include tendon wire button
LIFT 0FF TESTS:
A physical liftoff of the tendon to determine the load being carried by that tendon. Liftoff tests for tendons that have not previously been lifted off would include removal of the shim plates to permit visual examination and as necessary reapplication of grease to the accessible areas of the tendon.
Repetitive liftoff tests on the same tondon not in a control group may not include removal of shim plates for visual examination.
Liftoff tests for tendons in designated control groups will include removal of shim plates and visual examination.
NEW TENDONS:
A tendon population selected at random for visual inspection or liftoff testing over the next specified surveillance period.
Selection shall be such that the total population of accessible tendons in that group shall be inspected / tested before beginning any repeat inspections / tests.
CONTROL' TENDONS:
A population of tendons in each tendon group that will be selected and will remain constant for each inspection / test surveillance cycle. The criteria for selection of these tendons shall be to select those tendons which represent conditions in which corrosion is most pronounced tempered by ready accessibility.
Selection must necessarily be based on inspection data available on or before April 15, 1985.
TENDON GROUP:
Four tendon population groups defined as 1.
Circumferential-----310 ea 2.
Top Cross Head------ 24 ea 3.
Bottom Cross Head--- 24 ea 4.
Longitudinal-------- 90 ea The circumferential tendon group consists of two subgroups.
consisting of 210 Circumferential Barrel Tendons and 100 Circumferential Head Tendons.
In-tenns of inspection / testing, there will be no attempt to address these subgroups as separate entities in selecting inspection / test population.
NUMBER OF TENDONS:
The number of tendons to be inspected or tested shall represent a predesignated number of tendons in that group.
With the exception'of the longitudinal tendon
- group, all tendons designated for inspection or liftoff testing shall be inspected or lifted off to include both end anchor assemblies if accessible.
Longitudinal-tendons will be inspected and lifted off only from the top end.
(Inaccessible tendons have been designated as such in PSC letter P-84523 dated December 14,1984).
ENGINEERING EVALUATION: A technical evaluation based on visual examinations, liftoff
- tests, load cells and other pertinent information to determine tendon acceptability and PCRV performance.
~
FAILED WIRES:
Wires within a ttndon bundle that have failed as identified by raised button heads in the anchor assembly or as may have been previously identified as failed by visual inspection.
For tendons which are not accessible on both ends, it shall be assumed that 20% of the number of failed wires identified on the accessible end have failed on the inaccessible end in determining the total population of failed wires.
VISUAL INSPECTION PROGRAM Once every six (6) months visual inspection shall be performed for the following tendon population.
Total Total Total Number of Number of Number of Tendon Groups Tendons New Tendons Control Tendons Circumferential 16 13 3
Top Cross Head 2
1 1
Bottom Cross Head 8
6 2
Longitudinal 30 24 6
LIFT 0FF PROGRAM Liftoff tests shall be performed on all "new" tendons once every 18 months and on all control tendons once every six (6) months as follows:
Total Total Total Number of Number of Number of Tendon Group Tendons New Tendons Control Tendons Circumferential 16 13 3
Top Cross Head 2
1 1
Bottom Cross Head 4
3 1
Longitudinal 15 12 3
ENGINEERING EVALUATION Engineering evaluations will be made on a continuous basis as the tendon inspection / testing program progresses with the intent of ensuring that the prestressing system is performing its design function.
Specific engineering evaluations will be mandatory for any circumferential barrel tendon with > 15% failed wires and for any tendon in any of the remaining tendon groups with > 20% failed wires.
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