ML20141K318
| ML20141K318 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 05/23/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20141K316 | List: |
| References | |
| NUDOCS 9705280441 | |
| Download: ML20141K318 (5) | |
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UNITED STATES s
j NUCLEAR REGULATORY COMMISSION t
WASHINGTON, D.C. 30806 4001 j
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 83 TO FACILITY OPERATING LICENSE NO. NPF-72 COMMONWEALTH EDISON COMPANY BRAIDWOOD STATION. UNIT NO. 1 DOCKET NO. STN 50-456
1.0 INTRODUCTION
By two letters dated May 23, 1997, Commonwealth Edison Company (Comed, the licensee). requested an emergency license amendment for Braidwood, Unit 1; the second letter superseded the first in its entirety. During discussions with the NRC concerning a plugged emergency core cooling system (ECCS) pump vent line at Byron, Unit 2, the licensee was made aware that their practices for venting chemical and volume (CV) control system (CVCS) discharge piping high points did not reflect precise compliance with Technical Specification (TS) 4.5.2.b.1.
The purpose of venting is to verify that the piping is full of water.
The CVCS high point vent is in a section of piping that is pressurized by the CV pump (s) and should not be opened during plant operation.
Following the discussion with the NRC staff, the licensee submitted a change to the TS to include an alternate method (ultrasonic examination) as a means to ensure that the ECCS is completely full of water.
2.0 EVALUATION TS 4.5.2.b.1 requires that the ECCS pump casings and discharge piping high points outside of containment be vented at least once per 31 days. The ECCS is comprised of the CV pumps, Safety Injection (SI) system pumps, Residual l
Heat Removal (RH) pumps and associated piping. The SI and RH pumps are provided with pump casing vents. The CV pumps are of a self-venting design with both suction and discharge piping on the top of the pump casing. No casing vents were provided with the CV pumps in this design. The ECCS discharge piping for Braidwood, Unit 1, is provided with vents located at high points throughout the system; both inside and outside containment.
During power operations, one CV pump is in operation and the other pump is in standby. The operating pump is continuously vented via flow through the system. The non-operating pump is designed to be self-venting since both the suction and discharge piping are located at the top of the pump casing. The discharge piping containing the high point vent (1/25I045) is at full CV pump discharge pressure and, therefore, it is not appropriate from an equipment reliability' and personnel safety standpoint to open the valve for venting purposes.
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9705280441 970523 PDR ADOCK 05000456 P
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By letters dated March 17, 1989, August 25, 1989, March 12, 1990, and June 10, 1991, Comed submitted a TS amendment request to discontinue the performance of 1
4 the venting surveillance requirement (SR) for the ECCS piping inside l
containment for Braidwood. The staff reviewed and approved that request in the June 22, 1992, Safety Evaluation (SE) related to Amendt.ent No. 36 for each of the Braidwood Units.
1 In the submittals, the licensee provided results of water hammer analyses that were performed to support the proposed changes. Based on their analyses, the licensee concluded that if air is present in the ECCS piping inside containment, the system is capable of withstanding the resulting water hammer event. However, the Illinois Department of Nuclear Safety (IDNS) had concerns regarding the consequences of the licensee's proposed changes. An analysis performed by IDNS determined the maximum pressure peak as a function of voided pipe volume. The analysis indicated that when a relatively small void volume exists (approaching the zero limit), the peak pressures experienced by the piping during a water hammer event are similar to those caused by the sudden opening of valves, pump startups, etc., and are of no concern. However, the worst case scenario is represented by a voided volume of approximately 12 j
l cubic feet. At this volume, the peak pressure was calculated to exceed 600 psig, the setpoint of the discharge relief valve of the RH system. A loss of low head ECCS capability or an intersystem loss-of-coolant accident may result if the relief valve opens and fails to reseat once the pressure is relieved.
While the above is an example related to the RH system, in the June 22, 1992, staff SE, the staff concluded that, in general, the calculations and
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analytical methods used in determining the effects of water hammer for any system are uncertain in nature due to computer code limitations. Therefore, l
the staff did not base approval of the amendments on the water hammer analyses, but instead, on operational experience.
In approval of that request, the staff considered the small likelihood of air intrusion in the piping system and the adequacy of licensee controls to ensure a water filled system (e.g., maintenance practices, operational experience, and procedural controls). Therefore, the staff again notes that conclusions reached in this evaluation are based on the licensee's 7ther justifications (i.e., ultrasonic testing) and not on the licensee's water hammer analyses.
As an alternative to venting, the license performed ultrasonic testing which verified that the piping was full of water at the high point of the piping between the pump discharge and the normally closed containment isolation valves. The testing was performed in accordance with Comed approved procedure NDT-C-28, Revision 0, " Ultrasonic Pulse Echo Detection of Water Levels in Piping," which requires use of acceptable techniques and personnel qualified to the American Society of Nondestructive Testing ASNT-TC-1A, " Recommended Practice for Nondestructive Testing, Personnel Qualifications and Certification." Ultrasonic testing equipment is calibrated using a pipe full of water.
If gas voids exist at the top of the pipe, the liquid level in the horizontal pipe is determined by taking the ratio of the sweep length to the
reflection of the liquid surface to the sweep length of the calibration pipe diameter back-reficction.
Based upon the testing performed by the licensee to ensure the SR intent is met and that the piping is filled with water, the staff concluded that the p eposed change is acceptable. This is consistent with the Standard Technical Specifications Westinghouse Plants, NUREG-1431, Revision 1, issued April 1995, which includes SR 3.5.2.3 to " Verify ECCS piping is full of water." Both the SR and the basis for the SR are performance based and not prescriptive on how the licensee is to perform the verification. The licensee requested the proposed changes for one operating cycle. The staff found this acceptable because it is considering the generic aspects of gas intrusion into piping, and intends to address this issue generically.
3.0 TECHNICAL SPECIFICATION CHANGES TS 4.5.2.b.1 is revised to require that each ECCS subsystem be demonstrated cperable at least once per 31 days by venting the ECCS pump casings and discharge piping high points outside of containment that are equipped with i
high point vent valves for subsystems not in direct communication with operating systems. An expanded bases discussion will be added to clarify that only the RH and SI pumps are equipped with pump casing vent valves.
Additionally, the bases will note that the CV subsystem will not normally be vented, and the operating train of RH will not be vented while shutdown cooling is in operation. Additionally, a new TS requirement is added to ultrasonically examine the discharge piping of the idle centrifugal pump and the portion of the piping upstream of the High Head Safety Injection isolation valves (ISI8801A&B) on a monthly basis adjacent to the vent valve ISIO45.
4.0 EMERGENCY CIRCUMSTANCES Promptly after identifying the venting question, the licensee completed testing to verify the actual conditions in the flow path and submitted the amendment request in a timely manner. Further, the licensee requested emergency processing to allow the plant to resume operation.
Braidwood, Unit 1, is about to restart from its sixth refueling outage and is in Mode 3.
Failure to grant the amendment would prevent resumption of operation.
Accordingly, the Commission finds that an emergency situation exists pursuant to 10 CFR 50.90(a)(5).
Throughout this process, the licensee acted promptly and kept the staff informed regarding the status of its activities. The staff finds that the licensee did not create the emergency situation and acted i
promptly once it became aware of the venting question.
5.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION As required by 10 CFR 50.91(a), the licensee has provided their analysis of the issue of no significant hazards consideration. The NRC staff has reviewed
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the' licensee's analysis against the standards of 10 CFR 50.92(c). The staff's review is presented below.
Since the level of surveillance performed to date has provided confidence that no significant voiding has occurred and the ultrasonic examinations have confirmed that the water solid conditions exist in the piping, operation of the facility under the proposed amendment would not involve a significant increase in the probability or consequences of an accident previously evaluated.
The purpose of the SR is to verify that the flow path does not contain noncondensibles to ensure that previously identified accident scenarios are minimized. The licensee has implemented adequate controls to assure that air intrusion is unlikely. This change will not result in a new failure mode because no new equipment is installed, and installed equipment is not operated in a new or different manner. Therefore, this change does not create the possibility of a new or different kind of accident from any accident previously evaluated.
Since the licensee has determined by an alternate means of verification that a significant volume of noncondensibles has not accumulated, this change does not involve a significant reduction in a margin of safety.
Accordingly, the staff has made a final determination that the proposed amendment involves no significant hazards consideration.
6.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendment. The State official had no comments.
7.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to the installation or use of a facility component 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 made a final no significant hazards finding with respect to this amendment. 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.
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8.0 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 Commission'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 Contributors: M. Shuaibi M. Chatterton L. Gundrum G. Dick Date: May 23, 1997