ML17199T427
| ML17199T427 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, 05000000 |
| Issue date: | 11/13/1987 |
| From: | Morgan W COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation |
| References | |
| 3829K, GL-87-05, GL-87-5, NUDOCS 8711190125 | |
| Download: ML17199T427 (5) | |
Text
... - *----
-~!:1 CommonvAlth Edison One First Natl~Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 - 0767 Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Conunission Attn:
Document Control Desk Washington, DC 20555 November 13, 1987
Subject:
Dresden Station Units 2 & 3 Quad Cities station Units 1 & 2 Supplemental Response to Generic Letter 87-05 NRC Docket Nos. 50-237/249 & 50-254/265
Reference:
M. S. Turbak letter to Office of Nuclear Reactor Regulation dated May 11, 1987.
Dear Sir:
The referenced letter transmitted Conunonwealth Edison's response to Generic Letter 87-05.
Included in this response were statements responding to Questions 1 and 2 that stated that both Dresden and Quad Cities Stations would attempt to demonstrate that their drain lines are open and functioning.
Additionally, Dresden and Quad Cities were currently in the process of performing a surveillance examination in their reactor building basements to determine if water was draining from the expansion gap through other paths. It was stated that if water was found, an investigation into the source of in-leakage and corrective action was to be initiated.
The following attachment provides additional information regarding those statements.
To the best of my knowledge and belief, the statements contained within are true and correct.
In some respect these statements are not based on my personal knowledge, but obtained information furnished by other Commonwealth Edison employees, contractor employees, and consultants.
Such information has been reviewed in accordance with company practice, and I believe it to be reliable.
~-----
8711190125 871113
~DR ADOCK 05000237 PDR
US NRC November 13, 1987 Please address any questions that you or your staff may have concerning this response to this office.
Very truly yours,
~~g:~
Nuclear Licensing Administrator Attachments cc:
Region III Administrator Resident Inspector - Quad Cities Resident Inspector - Dresden 3829K/bs
ATTAC:HMENT 1 DRESDEN AND QUAD CITIES SUPPLEMENTAL RESPONSE TO GENERIC LETTER 87-05 QUESTIONS 1 & 2 QUAD CITIES Unit 1 drywell liner drains were found with no significant amount of water.
One drain line was found with approximately 1/2 gallon of water which was assumed to have been stagnant at the other end of the drain pipe.
Another drain on Unit 1 was found to have been plugged and a roto-roter type drain cleaner was used to clear the drain, this effort was unsuccessful. It was assumed that the bottom of the drain was being blocked by concrete.
Since the other three drains were found to be clear it was concluded that any water present would be able to drain out of the sand pocket area.
Unit 2 drywell liner drains were found with no water present and were found unplugged in three of th_e_c;lrains and undetermined in the fourth.
The fourth drain, was physically too short to hook up equipment to unplug the line, therefore the drain was untested. It was believed that if water was present the other three drains would drain the sand pocket area.
DRESDEN The sand cushion drain lines originally were found dry on both units.
However, the lines were tested and determined to contain blockage.
Eventually, each line was cleared, and to various degrees, each line displayed leakage.
A sampling and testing program was inunediately undertaken, and the effluent was evaluated for chemistry, biological, and radiological activity.
(See Attachment 2)
The total amount of leakage for Unit 2 was approximately 1900 gallons and Unit 3 approximately 1100 gallons.
The source of water tentatively has been identified as refuel cavity leakage.
After evaluating the most likely paths, the station believes the source to be past the refueling bellows drain line expansion joints.
The existing method utilized to plug the drain lines during refueling is the installation of an expanding stop plug, which if incorrectly placed in the expansion joint, could produce leakage.
The plug design is being altered to preclude incorrect placement and should eliminate leakage.
To verify this, a surveillance procedure has been established to monitor sand cushion drain lines during refuel activities. If during refuel flood-up, leakage is detected, an inspection of the refuel bellows will take place.
Based on the findings at Dresden and Quad cities, a technical evaluation was performed by Edison's Production Services Department with input from our architect/engineer (AE) and the Electric Power Research Institute.
It was concluded that there was no inunediate safety concern.
_ The evaluation of the Dresden I containment was based on a worst case corrosion rate of 10 Mils per year for fresh river water and a tolerance of at least 1/4 inch corrosion of the steel plate without loss of its structural integrity.
Qxygenated river water corrosion is typically in the range of 1-14 mils per year and increases with increasing acidity.
However, collected water samples show a basic, 8.5 - 9.0 ph.
Corrosion rates also increase with increasing oxygen concentration and increasing temperature.
The oxygen level in the sand pockets is gradually decreasing from its original level since there is no aeration.
However, for added conservatism we assumed a corrosion of 10 mpy without any decreases due to anaerobic conditions. The temperature is assumed constant.
Utilizing the most conservative value for the containment steel plate thickness, of 1 inch with a 1/4 inch corrosion tolerance, one could expect a life of 0.25/0.010 years or 25 years, without loss of integrity.
However, because this evaluation was based on conservative assumptions, inspection of the drywell liner will be conducted to demonstrate additional safety margin.
The May 1987 letter stated our plan was to perform UT thickness measurements during the next refueling outages.
However, Conunonwealth Edison believes the existing evaluation is justification for operation for at least one more fuel cycle.
The only inspection technique which can be ready for the upcoming Dresden Unit 3 outage is removal of concrete from the drywell floor and direct UT thickness measurements.
This inspection method has a potentially high economic impact, high personnel radiation exposure and would not definitively resolve the issue for life of the plant. Initial investigation by the structural engineers at our AE suggest that there are viable options which will simultaneously minimize economic impact, minimize personnel radiation exposure and solve the root cause of drywell liner degradation as hypothesized in Generic Letter 87-05.
For these reasons the current plan is not to take UT measurements during the Dresden Unit 3 refueling outage that has now been re-scheduled from December 1987 to February 1988.
A number of inspection options are currently being considered and a final plan for inspection activities and schedule for implementation will be prepared by June 1, 1988.
ATTACHMENT 2 WATER SAMPLE EVALUATION D2 Samples:
A)
Conductivity-730 Micro-mho B) pH-8.97 C)
Chloride-33 ppm D)
Nitrite-24 ppm E)
Biological Activity-Sulfate reducing bacteria-1 to 10 cells/cc Acid producing bacteria-10 to 100 cells/cc F)
Total Activity-7.5 E3 pCi/L G)
Radio Nuclide Analysis-Mn-54 1.3E- 07 UCl/G Co-60 3.4E-06 UCl/G Cs-137
- 6. lE-06 UCl/G D3 Samples~
A) Conductivity-620 Micro-mho B) pH-8.47 C)
Chloride-37 ppm D)
Nitrite-9 ppm E)
Biological Activity-None recordable F)
Total Activity-3.0E3 pCi/L G)
Radionuclide Analysis Mn-54 4.5E-08 UCl/G Co-60 5.6E-07 UCl/G Xe-133 8.lE-08 UCl/G Xe-135 9.5E-08 UCl/G