ML19256F243
| ML19256F243 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point, Prairie Island  |
| Issue date: | 11/28/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19256F233 | List: |
| References | |
| NUDOCS 7912180358 | |
| Download: ML19256F243 (3) | |
Text
2.0 EXPERIENCE 2.4 Prairie Island Unit 1 2.4.3 Licenses Remedial Actions and Regulatory Actions 2.4.3.1 Plant System Modifications None 2.4.3.2 Operations Modifications Steam Generator Tube Rupture Procedure A note of caution should be added to the steam generator tube rupture procedure to have the operator stop the turbine-driven auxiliary feed pump as soon as possible and to shut the steam supply valve from the affected steam generator.
This was done even through this caution had not been in the procedure.
Isolate Steam Generator Add a note of emphasis to the operator to isolate the leaking steam generator as soon as possible and to keep in mind that the MSIV bypass can be used to protect the steam generator from overpressure.
Also, reducing the RCS pressure quickly, while maintaining adequate RCS subcooling; (which was done curing this event) will help prevent overpressure of the secondary side.
Reacter Coolant Pump Operation Operation of the reactor coolant pumps during a steam generator tube break should be considered.
This would allow use of the spray valves in the depressurization process, which could minimize the chance of blowing the pressurizer relief tank rupture disc.
It should be pointed out that even though the disc failed, there was little discharge to the containment.
Considerations for the Industry The industry should consider the problems associated with a tube break recovery, in particular -
(a) Increasing reactor coolant pressure indicates level has probably reactie'd its lowest point and that pressurizer level is recovering (even if C05 off-scale low), and (b) bringing pressure up in the pressurizer to greater than 2000 psig 4
leads to increasing flow OUT of the break (thus slower recovery) and E
decreasing makeup flow from the SI pumps (due to pump-head curve characteristics) 1608 047 7912180 3N
. Isolation of Instrument Air The feasibility of not isolating instrument air to the containment should be evaluated, since the PORV's are used to reduce RCS pressure in this event.
Under current logic and procedures, containment isolation must be reset to repressurize the PORV accumulators.
Material Control Procedures The procedures for control of material into and out of the steam generator and other enclosed spaces should be upgraded.
2.4.3.3 Steam Generator Modifications REMEDIAL ACTIONS In addition to the failed tube, and the tube with a 65% wall reduction, the remaining four tubes adjacent to the failed tube were plugged.
This action was taken to preclude additional leaks in the event that the burst tube should fail at its weakened section during operation and damage the adjacent tubes.
2.4.3.4 Regulatory Actions Technical Specifications The Prairie Island Plant Technical Specifications comply with Reculatory Guide 1.83.
NRC Requests The NRC staff requested that a meeting be held prior to return to power 3peration of Unit 1.
On October 12, 1979, representatives of NSP met with the staff to present the details of the steam generator tube rupture; cause, inspections performed, remedial actions, and plans to return to power, etc.
NRC Requirements The staff concluded that the following requirements would be necessary:
1.
In regard to corrective measures applied to the ruptured tube, NSP must either.
2 plug sii tubes (a total of twelve plugs including the corresponding a.
cold leg tubes); the ruptured tube, the 65% degraded tube and the four other tubes bounding the ruptured tube, or b.
plug two tubes (a total of four plugs, including the corresponding cold leg tubes); the ruptured tube first having been stiffened to prevent it from breaking loose and causing further damage to surrounding tubes.
1608 048
. Option b was elected by NSP.
In addition, the ruptured and damaged tubes must be inspected at the next refueling shutdown and the results reported to the NPC.
A careful consideration of occupational exposures should b.. factored into the above choice.
2.
Documentation of the information presented at this meeting must be made prior to restart of Prairie Island Unit 1.
3.
Coolant Technical Specifications as given by the Standard Technical Specifications must be submitted to the NRC in thirty days.
In the interim period, but to be in effect before the startup of Prairie Island Unit 1, interim procedures shall be in effect for the reactor coolant and secondary coolant activity limiting conditions of operation.
4.
Three copies of the pertinent pictures taken during the inspections which show the location of the springs, eroded and ruptured tubes, etc.
1608 049
.