ML16138A808
| ML16138A808 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/07/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16138A807 | List: |
| References | |
| NUDOCS 9602120296 | |
| Download: ML16138A808 (5) | |
Text
UNITED STATES C,
NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 214 TO FACILITY OPERATING LICENSE DPR-38 AMENDMENT NO. 214 TO FACILITY OPERATING LICENSE DPR-47 AND AMENDMENT NO. 211 TO FACILITY OPERATING LICENSE DPR-55 DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter dated February 6, 1996, Duke Power Company (the licensee), submitted a request for changes to the Oconee Nuclear Station, Units 1, 2, and 3, Technical Specifications (TS).
The amendments revise TS Section 3.16, "Containment Hydrogen Control Systems."
The change adds a footnote to TS 3.16.3.b. to allow a one-time outage duration extension in regard to the Containment Hydrogen Control System flow path. This extension is necessary to install and test plant modifications, which will allow the Containment Hydrogen Control System to perform as designed, without the potential for inoperability due to water accumulation in the flow path.
2.0 BACKGROUND
Oconee Nuclear Station consists of three 2568 Mwt pressurized water reactors located in Seneca, South Carolina and operated by Duke Power Company (the licensee).
The Containment Hydrogen Recombiner System (CHRS) is the primary method for controlling post-accident hydrogen generation at Oconee Nuclear Station. The Reactor Building Hydrogen Purge System (RBHPS) is intended as a backup to the CHRS. However, the licensee has stated in conversations with the staff that the RBHPS would not be immediately available as a backup. The CHRS consists of a portable hydrogen recombiner, control panel for the recombiner, and a portion of the Penetration Room Ventilation System (PRVS).
When needed, the recombiner is moved to the affected unit, anchored to a foundation designated for this.purpose, and connected to the PRVS piping which runs to and from containment penetrations.
On February 1, 1996, at 1:30 p.m., Oconee Nuclear Station declared the CHRS and RBHPS inoperable due to the potential condensation of steam from the containment atmosphere following a loss-of-coolant accident (LOCA) in the piping to and from the CHRS or RBHPS. If the affected flow paths are not restored to an operable status within 7 days, Technical Specification 3.16.3.b requires that the affected unit shall be in hot shutdown within the next 960212029o6 960207 PDR ADCPK 500269
_PDR__
0 0
-2 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and at cold shutdown within an additional 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The condensation phenomenon is common to all three Oconee units. The NRC was notified of this condition via a 10 CFR 50.72 notification at approximately 4:30 p.m. on February 1, 1996.
The flow path from containment to the hydrogen recombiner consists of approximately 250 feet of three inch diameter stainless steel piping.
Similarly, the return flow path from the.recombiner to containment is also approximately 250 feet in length. The routed piping contains several low points. Following an accident, the gas mixture flowing through this piping will include saturated steam. Recent calculations by the licensee determined that steam condensation will create loop seals in the low points of the piping that will interrupt flow to the hydrogen recombiner. These loop seals may inhibit the ability of the recombiner to reduce the post-accident hydrogen concentration.
The licensee is considering a long-term solution to this problem. Because this long term solution will take some time to implement, the licensee proposed an interim solution which satisfies the Technical Specifications and the intent of the design basis of the system, and which could be implemented under the criteria of 10 CFR 50.59. The licensee has estimated that the interim design will then be in place for approximately 60 days before the long-term design modification is operable. However, the licensee has determined that more time may be required to complete installation and testing of this interim solution than is permitted by the current Technical Specifications allowed outage time for the CHRS. The licensee has therefore requested, by letter dated February 6, 1996, changes to the Oconee Nuclear Station Technical Specifications to permit a one-time extension of the 7-day allowable outage time for the CHRS to 14 days.
Until the completion of ongoing installation and testing of the interim modification, the CHRS will continue to be inoperable.
Even though the work is being performed on an expedited basis, the licensee will not be able to complete the modification within the allowed time frame of 7 days.
3.0 EVALUATION The staff finds the licensee's proposed change to the Technical Specifications to increase the allowed outage time for the CHRS to be acceptable for the following reasons.
First, the probability of a loss-of-coolant accident occurring during the additional time CHRS is inoperable while implementing the interim design is low. Within 14 days (7 days in addition to that permitted by the existing LCO allowed outage time) the licensee intends to have in place an interim design which will maintain the OPERABILITY of the CHRS.
The increase in risk due to an inoperable CHRS and RBHPS for 14 days is not significant. Neither the CHRS nor the RBHPS performs a required core cooling function; therefore, there will be no increase in the core damage frequency.
Furthermore, structural integrity of the Oconee containment would be maintained, even with concentrations of hydrogen that would be present should
-3 no hydrogen be removed for 30 days following a LOCA, as discussed in the licensee's February 6, 1996, submittal.
Therefore, the staff finds the licensee's proposed increase in the allowed outage time of the CHRS to a total of 14 days to be acceptable.
4.0 STATEMENT OF EMERGENCY CIRCUMSTANCES The licensee's application for the TS change has been timely. An engineering review of the Containment Hydrogen Control System (CHCS) identified a condition where condensation may accumulate in the flow path to the hydrogen recombiner, potentially rendering the system inoperable. This potential inoperability was identified on February 1, 1996, and had not been previously known. The NRC was promptly notified and the licensee aggressively pursued the development and implementation of corrective actions to restore the system to operable status. The current allowable outage time for the CHCS is seven (7) days. Although the licensee has expedited the development and installation of a temporary modification to restore the system to operable status, they are unable to complete the installation and testing of the modification within the allowable 7 days.
The NRC staff finds that failure to grant the proposed changes in a timely manner would result in shutdown of Oconee, Units 1, 2, and 3. The staff also finds that the licensee has responded in a timely manner, and has not delayed its application to take advantage of the Emergency License Amendment provisions of the 10 CFR 50.91. Accordingly, the staff concludes that the licensee has satisfied the requirements of 10 CFR 50.91(a)(5), and that a valid emergency exists.
5.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission's regulations in 10 CFR 50.92 state that the Commission may make a final determination that a license amendment involves no signficant hazards considerations, if operation of the facility, in accordance with the amendment would not (1) involve a significant increase in the probability or consequences of any accident previously evaluated; or (2) create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) involve a significant reduction in a margin of safety.
The amendments have been evaluated against the three standards in 10 CFR 50.92(c). In its analysis of the issue of no significant hazards consideration, as required by 10 CFR 50.91(a), the licensee has provided the following:
(1) Involve a significant increase in the probability or consequences of an accident previously evaluated:
No. The Containment Hydrogen Control System is not an accident initiator. The Containment Hydrogen Control System functions following a loss of coolant accident (LOCA) to control combustible gas concentration accumulating inside containment.
-4 This one-time, seven day extension of the allowable outage time for the Containment Hydrogen Control System flow path does not increase the probability of a LOCA or any other previously evaluated accident.
The hydrogen generation which occurs following a design basis LOCA is a slow process driven by sump radiolysis and metal corrosion. Calculations have shown that many days are required to reach the regulatory limit of 4 v/o. A hydrogen concentration slightly above 4 v/o is generally accepted as the lower flammability limit. Furthermore, assuming no credit for the CHRS or RBHPS, the concentration thirty days following a design basis LOCA, is approximately 5.5 v/o. Studies of containment structural capacity and the effects of hydrogen combustion have shown that concentrations much higher than 4 v/o are required to threaten the integrity of a large dry containment like the Oconee containment. Concentrations in excess of 12 v/o would be required to present a challenge to the integrity of the Oconee containment. Concentrations of this magnitude are only expected during core damage accidents like those studied in probabilistic risk analyses. Therefore,_
this proposed change does not increase the consequences of an accident previously evaluated.
(2) Create the possibility of a new or different kind of accident from any kind of accident previously evaluated:
No. As stated previously, the Containment Hydrogen Control, System is not an accident initiator. Rather it provides mitigation functions post-accident.
Increasing the allowable outage extension time does not introduce any new credible failure modes. Therefore, this proposed change does not create the possibility of a new or different kind of accident from any kind of accident previously evaluated.
(3) Involve a significant reduction in a margin of safety:
No. The margin of safety is not significantly reduced by a one-time fourteen (14) day allowable outage time for the Containment Hydrogen Control System flow path. As stated above, hydrogen generation following a design basis LOCA is a slow process which will not reach concentrations which would be required to threaten containment integrity within thirty days. For large, dry containments, the fact that hydrogen generation following a design basis event is not a significant safety concern has been recognized for several years. In 1993, the NRC hosted a workshop on the elimination of requirements marginal to safety. One of the items discussed was the requirements for hydrogen recombiners. Since it has been recognized that the
-5 requrements concerning the hydrogen recombiner are incidental to safety, this one-time increase in the allowed outage time does not represent a significant reduction in the margin of safety.
The NRC staff has reviewed the licensee's analysis and, based on this review, finds that the three standards of 10 CFR 50.92(c) are satisfied. Therefore, the NRC staff has determined that the amendment request involves no significant hazards consideration.
6.0 STATE CONSULTATION
Based upon the written notice of the proposed amendments, the South Carolina State official had no comments.
7.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to 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 amendments involve 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. Accordingly, the amendments meet 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 amendments. The Commission has made a final no significant hazards consideration finding with respect to the amendments.
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 amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: R. Lobel Date: February 7, 1996