ML20012B451
| ML20012B451 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 03/09/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20012B440 | List: |
| References | |
| NUDOCS 9003140432 | |
| Download: ML20012B451 (3) | |
Text
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ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO STEAM GENERATOR INTRU5 ION EVENT SOUTH CAROLINA ELECTRIC & GAS COMPANY VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO. 50-395 INTRODUCTION j
On February 14, 1989, steam generator blowdown system demineralizer resin beads were discharged into the condenser hot well due to operator error. Subsequently, resin beads were transported to the steam generators via the condensate and feed system, where themal decomposition resulted in increased cation conductivity, sulfate, chloride, silica and sodium concentrations and decreased pH levels.
Upon exceeding action level 3 (greater than 7 p S/cm cation conductivity) the plant was shot downwithin four hours, as recomended in the PWR Secondary Water Chemistry Guidelines. After th* steam generator secondary water was cleaned up 1
by feed and bleed to less thm T pS/cm cation conductivity, at recommended by the Guidelines, the plant went back to power. Additional resin beads may have l
been flushed into the steam generators where thermal decomposition again caused i
the chtion conductivity to exceed the Guideline action level 3 value.
Instead of shuting down, as reconsnended in the Guidelines, the licensee decided to stay on line at 30 to 45% power for 19 days to clean up the resin from the steam generators. The licensee considere6'that high* condensate and feedwater flow velocities, coupled with maximum steam generator blowdown flows,would effectively clean up the resin. However, on March 10 the plant was shut down and cooled down to ac'hieve resin cleanup of the condensate and feed systems and steam generators.
By letter dated March 28, 1989, the licensee comitted to-1-
Infom NRC within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following any deviation from the PWR Secondary Water Chemistry Guidelines including corrective action being taken to regain confomance with the Guidelines.
2-Evaluate its operating procedures concerning steam generator tube rupture to confim their adequacy.
i The licensee has also taken corrective action to preclude a future reoccurrence of resin intrusion.
EVALUATION In addition to exceeding cation conductivity Guideline action levels, the licensee exceeded the sulfate action level of 20 ppb.
From the time of the resin intrusion on February 14 until plant shutdown and cooldown on March 10, the sulfate concentration remained above the 20 ppb action level. The sulfate concentration exceeded 1000 ppb for about 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br /> during this time. The Guidelines state that the steam generators should be drained and refilled when sulfate concentrations exceed 1000 ppb.
In addition, the Guidelines indicate sulfates promote intergranular attack of Alloy 600 in both acid and alkaline environments. Sulfates are also implicated in pitting attack of Alloy 600 and,
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. 1 along with chlorides, promote the growth of non-protective magnetite in crevices (denting). During the 19 days of power operation for resin cleanup, the cation conductivity exceeded 7 pS/cm (Guideline Action Level 3 which recomends shut-down) for about 75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br />. The Guidelines indicate that denting has occurred in plants operating at full power at 2-7 pS/cm. The staff is in agreement with the l
Guideline action levels and corresponding actions to prevent rapid steam generator corrosion during continued operation.
I The licensee committed to informing NRC within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following any deviations from the Guidelines. The licensee indicated that the cation conductivity action levels may be exceeded due to boric acid treatment (corrective action to mitigate steam generator tube denting and caustic inteFgranular attack of Alloy 600 tubing).
i Revision 2 of the PWR Secondary Water Chemistry Guidelines EPRI NP-6239, dated December 1988,provides information for the correction of cation conductivity for boric acid effects. The staff does not anticipate that the licensee should have to make a decision to deviate from the Guidelines if the resin cleanup was adequate. Should the licensee notify NRC that it has deviated from the Guidelines, the staff intends to evaluate the basis for the deviation and corrective action to regain conformance.
CONCLUSION The staff concurs in the licensee's commitments to inform NRC within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following any deviation from the PWR Secondary Water Chemistry Guidelines and to evaluate the operating procedures to confirm adequacy in responding to i
steam generator tube ruptures and thd corrective action taken to prevent future resin intrusions. The staff also recomends adherence to the Guidelines.
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