ML19309G541
| ML19309G541 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/08/1980 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Ferguson J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 8005070121 | |
| Download: ML19309G541 (2) | |
Text
v e
- ps navy
!E; g[kj NUCLEAR REGULATORY COMMISSION UNITED STATES 800 070 / 2!
5 7
sM/
E WASHING TON, D. C. 20555
'.....'j' April 8,1980 Mck2t No. 50-338 Mr. J. H. Ferguson Executive Vice President - Power Virginia Electric and Power Company Post Office Box 26666 Richmond, Virginia 23261
Dear Mr. Ferguson:
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION REGARDING STEAM GENERATOR CHEMISTRY AND CORROSION - NORTH ANNA POWER STATION, UNIT NO. 1 (NA-1)
The first refueling inspection'of t'he steam generators at NA-1 was documented in your report dated December 10, 1979.
In your report you also provide corrective actions to be taken based on the results of the inspection. Our safety evaluation report for the inspection and subsequent corrective actions for the steam generators was issued on February 4, 1980.
In our report we stated that you had implemented conservative maintenance and corrective actions commensurate with the findings of the steam generator inspection.
We have been continuing our review of your corrective actions regarding tube integrity, tube support plate corrosion and changes in the steam generator chemistry which may occur as a result of boric acid addition.
Our review of these matters has been conducted with an emphasis on long term operation of the steam generators at NA-1.
Based on our review of your corrective actions, w9 find that we require additional information in order to complete our review of these matters.
Our concerns and basis for the need for the additional information is provided below.
Long term steam generator tube integrity is dependent on your success in the control of three parameters, (1) hideout return of acid sulphates due to previous contamination from condensate polisher resins, (2) oxygen control, and (3) boric acid treatment.
Laboratory experiments have provided evidence that the boric acid treatment will reduce corrosion of the tube support plates and retard tube denting by formation of a ferro-borate " barrier" in the crevice region between the nonprotective magnetite and the carbon steel support plates. Also, electrochemical behavior, pitting, stress corrosion cracking, and corrosion fatigue testing on the effects of boric acid carry-over on steam turbine
s.
Mr. J. H. Ferguson Virginia Electric and Power Company April 8, 1980 materials indicates no significant identifiable effects. Although it has been claimed that the turbine materials will not be affected by the boric acid treatment, there is the underlying concern about the relevance of residual boron in the condensate and its effect on non-stainless steel ferrous components in the feedwater train of the secondary system.
A reduction in oxygen level should reduce crevice corrosion, provided the original ionic impurities are non-reactive.
Any residual sulphates not removed from the tube annuli by the flushing program proposed by you, could cause intergranular attack of the Inconel 600 tubing.
The potential high stresses in the dented tube with the presence of sulphates in the crevice would lead to str5ss corrosion cracking, even with a reduced oxygen level in the steam generator water.
Hence, successful removal of the sulphate impurities in the tube / tube support plate annuli is important for long term tube integrity.'
Therefore, in order to complete our review, we request the following information:
1.
The results of the flushing program to reduce the sulphate contaminates, in particular, data on hideout return after 50".
load reduction and prior to returning to full power.
2.
The effects of boric acid treatment on the non-stainless steel ferrous components in the feedwater train of the secondary system.
3.
Preliminary data on the effectiveness of the boric acid treatment to stop tube support plate corrosion; i.e.,
(a) results of the low power soak treatment, (b) boron analysis on condensate, feedwater, blowdown, main steam and heater drains, and (c) hydrogen, oxygen, ammonia, pH, and cation conductivity analysis.
We request that your response to our request for additional information be submitted within 30 days receipt of this letter.
Please inform us within 7 days after receipt of this letter of your confirmation of our requested response date or the date you will be able to meet.
Sincerely, l
r u b'l$ $ &
A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors cc: See next page T
Mr. J. H. Ferguson Virginia Electric and Power Cocpany April 8,1980 cc: Richard M. Foster, Esquire 1230 A Pearl Street Denver, Colorado 80203 Michael W. Maupin, Esquire Hunton, Willians, Gay and Gibson P. O. Box 1535 Richmond, Virginia 23212 Alderman Library Manuscripts Department University of Virginia Charlottesville, Virginia 22901 Mr. Edvard Kube Board of Supervisors Louisa County Courthouse P. O. Box 27 Louisa Virginia 23093 Ellyn R. Weiss, Esquire t
Sheldon, Harmon, Roisman and Weiss t
1725 I Street, N.W., Suite 506 Washington, D. C.
20006 Mr. J. B. J ack s on, J r.
Commonwealth of Virginis Council cn the Environment 903 Ninth Street Office Building 4
Richmond, Virginia 23129 Mr. Michael S. Kidd U. S. Nuclear Regulatory Commission Post Office Box 128 Spotsylvania, Virginia 22553 Mr. W. R. Cartwright Station Manager P. O. Box 402 Mineral, Virginia 23117
.