ML20076B434
| ML20076B434 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 06/27/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20076B428 | List: |
| References | |
| NUDOCS 9107110234 | |
| Download: ML20076B434 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELAiCD TO AMENDMENT NO. 46 TO FACILITY OPERATING LICENSE NO. NPF-42 WOLF CREEK NUCLEAR OPERATING CORPORATION WOLF CREEK GENERATING STATION DOCKET NO. 50 48_2
1.0 INTRODUCTION
Wolf Creek Nuclear Operating (Appendix A to Corporation By application dated March 20, 1991, (the licensee) requested changes to the Technical Specifications Facility Operating License No. NPF-42) for the Wolf Creek Generating Station.
The proposed changes would revise Technical Specification (TS) 3.1.3.2 and its associated Bases to add a new Action Statement to address the situation where more than one digital rod position indicator per control rod bank may be inoperable. The new Action Statement would avoid unnecessary plant shutdowns per TS 3.0.3, yet is consistent with the overall protection provided by related TS. Additionally, a proposed change to TS 3.1.3.1 corrects an erroneous reference.
2.0 BACKGROUND
The Wolf Creek Generating Station has 53 full-length rod cluster control assemblies (RCCAs). The RCCAs are designated by function as the control bank and the shutdown banks.
The shutdown banks are always in the fully withdraun position during normal power operation whereas the control rods can be manipulated for reactivity control.
The digital rod position indication (DRPI) system measures the actual position of each control rod using a detector which consists of discrete coils mounted concentrically with the red drive pressure housing. The coils are located axially along the pressure housing and magnetically sense the entry and presence of'the rod drive shaft througl its centerline.
For each detector, the coils are interlaced into two data channels, and are connected to the containment electronics (Data A and B) by separate multi-conductor cables.
By employing two separate channels of information, the DRPI system can continue to function (at reduced accuracy) when one channel fails. The current technical specifications address the situation when one DRPI per bank is inoparable.
In this case, continued plant operation is permitted provided that increased surveillance is performed using the movable incore detectors to verify rod position.
However, the existing TS 3.1.3.2 does not add-ess loss of both DRPI channels in one bank. Consequently, the licensee must initiate the actions prescribed by TS 3.0.3, which, in this case, would require the 9107110234 910627 PDR ADOCK 05000402 P
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.;, operators to begin reducing reactor power within I hour after losing both channels of the control rod pasition monitoring capability.
That is, the operators would be challenged to use the control rod control system with degraded control rod monitoring capabilities.
2.0 EVAltar!0N 2.1 Digital Rod Position Indication System The licensee proposed modifying TS 3.1.3.2 to include a 24-hour allowed outage time to facilitate repairs when both DRPI channels in a bank become inoperable.
This will allow time to repair at least one inoperable DRPI channel before entering TS 3.0.3.
The licensee justifies this request based upon the assumptions it used in its safety analyses.
In these analyses, the postulated worst case reactivity transient assumes the operators ignore the RCCA position indication. The licensee contends that whether the operator ignores the RCCA position indication or is not aware of the RCCA position is irrelevent with regard to the results of the bounding safety analyses. Additionally, the reactivity insertion rates used in the licensee's safety analyses are based on conservative, worst-case scenarios, independent of whether they are caused by operator error or equipment malfunctior.. Consequently, the safety analyses bound DRPI failure modes. The staff agrees with this justification.
The existing limiting condition for operation for loss of a single DRPI channel is justified because tho cperators can continue to assess the position of the control rod group with the remaining DP?! :.hannel and the movable incore detector. With the less of both D.7) channels in a bank, however, the operator's primary e :nad of monitoring control rod group position becomes degraded. The licensee c W ends that a 24-hour ailowed outage time provides sufficient time to troublest oot and restore the DRPI system to operation while avoiding challenges associated with a plant shutdown. The licensee further states that overall plant safety would be enhanced by maintaining steady state operatior,,
as compared with the large control rod movements required during the plant shutdown process in conjunction with the loss of DRPl. The staff agrees with this justification.
The TS Bases states that TS 3.1.3.2 ensures that:
a.
Acceptable power distribution limits are maintained, b.
The minimum SHUTDOWN MARGIN is maintained, and c.
The potential effects of rod misalignment in associated accident analyses are limited.
The licensee's compensatory actions require that rod position be determined incirectly via the movable incore flux detectors and that reactor coolant system temperatures be monitored and recorded.
Also, rod control is placed in
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manual and rod motion is limited. Since the licensee's FSAR analyses for this class of events do not assume a dependence on the operator for monitoring the position of the rods, the staff agrees that these actions will sufficiently ensure the FSAR minimum departure from nucleate boiling ratio will not be decreased.
The licensee's requested modifications were evaluated in accordance with the Standard Review Plan guidelines.
The requested modifications correct an over-sight in the licensee's existing TS that would require operation of a system important to safety without availability of the preferred monitoring capability.
The staff concludes that the requested modifications are acceptable.
2.2 Movable Control Assemblies Specification 3.1.3.1 requires that all full length shutdown and controi rods be operable and positioned within 12 steps (indicated position) of their group step counter demand position in Modes 1 and 2.
Action 3 of this TS contains a reference to Figures 3.1-1 and 3.1-2.
However, the Wolf Creek TS have never contained a Figure 3.1-2.
This discrepancy has existed since the technical specifications were originally issued by the NRC. The licensee has proposed deleting the reference to this figure.
Since the proposed modification deletes an incorrect reference, the staff fincs this change acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Kansas State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The an.endment changes a requirement with respect to installation or use of a f acility corponent located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (56 FR 20047). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment, r
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6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Conmission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Douglas V. Pickett Date:
June 27,1991 i