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| Issue date: | 04/03/1981 |
| From: | Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | Kuzmycz G Office of Nuclear Reactor Regulation |
| References | |
| P-81112, NUDOCS 8104210342 | |
| Download: ML20008F592 (8) | |
Text
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^ April 3,1931 f
m) Fort St. Vrain I
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i?! nrn 20198* g Unit No.1 P-ali 2 s '1
/* .. , C8A8'M C
M y* i J Mr. George Ku:mycz, Project Manage U. S. Nuclear Regulatory Commission
$O 8
Division of Special Projects Washington, D.C. 20555
SUBJECT:
Fort St. Vrain, Unit No. 1, Steam Generator Penetration Leakage
REFERENCE:
P-80139
Dear Mr. Kuzmycz:
By the above referenced letter we ide.1tified a problem concerning a high leakage rate in the Loop 2 Steam Generator Penetrations. At the time of our original correspondence we had not been able to identify the number of steam generator penetrations that were experiencing this leakage, and on that basis we conservatively extended LCO 4.2.9 to cover the leakage, although we felt the type of leakage being experienced was not addressed by LCO 4.2.9 as such. We have since conducted a series of tests on the six (6) steam generator penetrations in Loop 2. The tests confirmed the postulated leak path described in P-80139 (see attachments for further familiarization) and we were able to confirm that only two (2) of the six (6) modules were involved in the leakage. Module B-2-2 has a very small leak in the area described (on the order of 2 to 3 pounds per day). Module B-2-3 was defined as the module which is contributing to the excessive leak rate. Prior to the unit shutdown on March 28, 1981, the overall leak rate was approximately 1,350 pounds per day. Because we had extended LCO 4.2.9 to cover this leak, and based on the leak rate exceeding 700 pounds per day, the unit was shutdown. Based on the tests we have conducted the leak path is definitely from thepenetrationinterspace,@,downtheACMEthreadsofcoldreheat pipe, @ , past the "0" ring seal, @, into the annulus, @, and then past the seas weld, into the cold reheat system (see Figures 1 and 1). Tha lea @kratevarieswithtemperatureandpressure conditions as would be expected. 810.42103 @ $
I We are presently investigating variou's alternatives to repair the seal weld as well as other alternatives for sealing or reducing the leak rate. These alternatives consist of the following:
- 1. Rewelding the seal weld. We are presently investigating necessary modifications to the remote tube plugging machine that would permit making fusion weld repairs to the seal weld area. We are also investigating the possibilities of manually repairing the seal weld area.
- 2. Establish an active seal. Utilizing the purge lines, 6, (see Figure 1) it is possible to establish an active sea n the annulus perhaps utilizing steam injected into the annulus under controlled pressure and temperature conditions.
- 3. Establish a passive seal. Again utilizing the purge lines, 6 , (see Figure 1) it is possible to fill the annulus with scme type of sealant material that would seal the leak path or at least significantly reduce the leak rate.
- 4. Establish a dified passive seal. Again utilizing the purge lines, , (see Figure 1) it is possible to inject sealant mate 1 into the annulus and extrude this material into the leaking area and then remove the main body of- the material from the annulus similar to the repair that was made on the core support floor cooling tubes.
All of these alternatives will require considerable time to develop, test, and evaluate, and most certainly we are proceeding with the necessary work to develop and test these alternatives. Based on our investigation of leak path and our recent tests, l however, it is our opinion that the presently defined leak path is not defined by LCO 4.2.9 and therefore the criteria of LCO 4.2.9 should not be applied to this particular leak path. We have reached this conclusion based on the following:
- 1. LCO 4.2.9 was primarily established for an unidentified leak in the penetration with the primary concern that the leak path may involve the primary closure. We have demonstrated the integrity of the primary closure and in fact have defined the leak path.
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- 2. LCO 4.2.9 addresses leakage through the secondary closure seals of the penetration with the primary purpose of meeting LCO 4.2.7.c which requires pressurization of the penetration interspace to a pressure higher than reactor vessel pressure. The defined leak path does not involve the secondary closure seals as such, and is, in fact, internal to the penetrations. In addition we have demonstrated that with the leakage rate all conditions of LC0 4.2.7.c can be met.
Based on the pecularities of the defined leak path we intend to proceed as follows:
- 1. To control the amount of helium in the ccid reheat system and to control the leak rate as effectively as possible we are installing the system shown in Figure 3. With this system we can effectively control the pressure in the annulus, 4 in Figure 2 slightly above cold reheat steam pressure. y controlling this pressure differential we will be able to significantly reduce the amount of helium leaking into the cold reheat steam system. The purified helium leaking into the annulus from the penetration interspace will be vented through a pressure control system to either the low pressure separator or the low pressure bottles.
The system is designed such that if the volume of helium cannot be handled in the low pressure separator the helium will be automatically directed to the low pressure bottles. This system will permit us to recover the helium from the leak path in the penetration and return this helium to the system.
- 2. This interim system is being installed on a temporary basis to determine the feasibility of the systc1
- 3. While in operation with this system, and to ensure that we can meet the intent of LCO 4.2.9 with reference to the primary closure, we will be monitoring the total leakage of the defined leak path, and, of course, will have to meet the conditions of LCO 4.2.7.c for penetration pressurization capability.
i
- 4. We will continue to conduct the pressure decay tests for the steam generator penetrations in Lcop 2 as indicated in P-80139 and will continue to apply the criteria of LCO 4.2.9 to the remaining five (5) steam generator penetrations (B-2-1, B-2-2, B-2-4, B-2-5, and B-2-6) applying the 700 pounds per day maximum leak rate provided by your letter of June 5, 1930.
- 5. A radiation monitor will be installed on the line venting helium to the low pressure bottles. The. low pressure separator and steam system already have permanent radiation monitors. As long as the conditions of LC0 4.2.7.c are met, there really isn't any mechanism to get primary coolant leakage into the defined leak path, but never-the-less should there be any activity in the leak path it~can be readily detected.
- 6. The purge line from the annulus is 7/32" inside diameter and is isolatable. In the event of a sudden failure of the primary closure coupled with the inability to maintain conditions of LCO 4.2.7.c the annulus purge line can be manually isolated and the secondary steam side would be automatically isolated. The radiological consequences of any leakage from the penetration would be bounded by previously analyzed accidents in the Final Safety Analysis Report.
- 7. Provided that all the above conditions can be maintained we would intend to operate the reactor under these conditions until the scheduled outage for the helium loop split presently scheduled for September, 1981. At that time we plan to have developed one of the alternatives indicated previously for repairing the defined leak path.
Unless you should disagree with our proposed program we intend to proceed with the program as outlined. Based on our-present schedule we would plan to conduct our initial feasibility tests early next week. Pending favorable results of these tests we would propose to continue with reactor operations and attempt 'to complete the fluctuation test program above 70% power. Based on our presert schedules we should have the fluctuation tests completed and be prepared for refueling by late May, 1981.
e
~If you should have any problem'with our proposed program or require, any additional information please let'me know as soon as possible.
Very truly yours,- hDonW Wen _ ' A:! W. Warembourg-Manager, Nuclear Production Fort St. Vrain Nuclear
- Generating ~ Station ,
DWW/alk Attachments ,
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