ML20128H393
| ML20128H393 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 02/22/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20127C509 | List: |
| References | |
| NUDOCS 8507090513 | |
| Download: ML20128H393 (3) | |
Text
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s Enclosure SAFETY EVALUATION REPORT Introduction By memorandum dated May 29, 1984 (R. Starostecki (Region I) to D. G. Eisenhut (NRC), IE Region I requested an assessment by NRR of the (regulatory) position set forth in Standard ReviewPlan(SRP)6.2.1.1.C. The issue relates to the allowable bypass leakage via the vacuum breakers between the drywell and the wetwell air space region for Susquehanna Steam Electric Station Units 1 and ?
1 (SSES). As stated in the May 29, 1084 memorandum, the region's concern dealt with the lack of test acceptance criteria for the set points of the position indication switches that are mo;nted on the drywell-to-suppression chamber vacuum breakers.
I Rackground Both SSES Units 1 and ? are equipped with five sets of drywell to wetwell vacuum breaker valves. A set consists of two 24" valves in series attached to selected downcomers. The inboard vacuum breakers are connected to a common alarm; sim-Ilarly, each outboard vacuum breaker is connected to another comon alarm. The alarm in the control room indicates when any valve is not fully closed. Addi-tionally, there exists individual vacuum breaker position indication in the main control room.
Item 3.a of Appendix A to SRP 6.2.1.1.C states in part that the indicators should have adequate sensitivity to detect a total valve opening, for all valves, that is less than the bypass capability (A/fR=0.0Sft8 for SSES Units 1 and ?).
Evaluation As stated in the FSAR, the SSES switches have a hysteresis of 0.025." However, this hysteresis is multiplied through the mechanical linkage to the valve disk so that the inboard valve can be as much as 0.3?" off the seat before the "not fully closed" light comes on. The outboard valve has a better tolerance, but can be off the seat by as much as 0.7," under similar conditions. These set point tolerances could result in an equivalent steam bypass leakage path of A/VT = 0.23 f t8 for the vacuum relief system. This bounding condition would yield a leakage path which is four times arcater than the recomendation of the SRP. Therefore, the information available to the operator is not sufficient to make a positive determination of the leak tight integrity of the vacuum breakers. We note that these valves are located inside the wetwell air space region, which is nonrally inerted. Therefore, visual inspection is eot a viable option to correct this deficiency. Accordingly, use of properly calibrated limit switches is the only practical means for determining adequate vacuum breaker closure.
Conclusions and planned Actions Pased on our review, we conclude that compliance with the provision of SRP 6.2.1.1.C regarding the sensitivity of the linit switches would be sufficient to assure containment integrity. However, the licensee is not comitted to meet this SRP in their current licensing status. To renuire such compliance would involve a backfit declaration with a supporting value impact appraisal.
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An assessment of the importance of the above discussed issue to other plants with RWR containments was also requested in the May 29, 1984 memorandum. Since the Standard Technical. Specification does not have a surveillance requirement on these indicators, we find that similar situations can exist at other BWR facilities.
In addition, since the position in Appendix A to SRP Section 6.2.1.1.C only applies in the review of all Cp and OL applications with Mark I, Mark II and Mark III containments, we cannot backfit this as a requirement for operating BWRs. However, considering the consequence of exceeding the bypass capability of the plant on the overall plant safety, due to inadequate indicator sensitivity, we are considering recommending the issuance of an IE Infomation Notice to all operating plants with BWR containments. This infomation Notice would describe the nature of problems encountered to date and their significance to plant safety.
It would also provide guidance by reference to staff's recomendations set forth in SRP 6.2.1.1.C.
In the interim (pending completion of the aforementioned planned actions), con-tinued operation of all BWR Plants (including SSES Units 1 and ?) is,iustified on the following bases:
l.
The vacuum breaker valves are tested monthly to assure free movement. Openino of the valves with the air actuators and closing them by venting the air assures that the valves will be functional.
2.
It is very unlikely that a11 vacuum breaker disks would be off the seat by the bounding amount corresponding to the "not fully closed light indication.
3.
For the ma,iority of Mark I plants that are operating with adP between the drywell and wetwell, valves disk displacement will be detected by a loss of the A P.
4.
Spring force holding the valve in the closed position results in a large torque acting on the valve seat.
5.
The bypass leakage test conducted at 18 month intervals insures that i
the drywell to wetweII leakape is within the bypass capability of the I
plant.
6.
For Mark !! plants, the vacuun breakers are mounted two in series.
The likelihood of both valve disks in the same line being off the seat is further reduced.
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