ML20097H426
| ML20097H426 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 06/08/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20097H424 | List: |
| References | |
| NUDOCS 9206260324 | |
| Download: ML20097H426 (4) | |
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UNITED STATES c
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.i NUCLEAR REGULATORY COMMISSION a
wAsmuoson. o.c. nu SAFETY EVALVATION BY THE JFFICE OF NUCLEAR REACTOR REGULATIO3 REtATED TO AMENDMENT NO. 10 TO FACILITY OPERallNG LICENSE NO. NPF-81 TE0 ! VIILITits ELECTRIC COMPANY. ET AL.
.(.WANCHE PlAK STEAM ELECTRl(_jilATION. UNIT 1 MCKU_80. 50-445
1.0 INTRODUCTION
By letter dated February 28, 1992, Texas Utilities Electric Company (the licensee) requested an amendment to the Technical Specifications (Appendix A to Facility Operating License No. NPF-87)d changes would remove the Boron for the Comanche Peak Steam Electric Station (CPSES), Unit No. 1.
The propose Dilution Mitigation System (BDMS) setpoints from the Technical Specifications (TS).
The BDMS was developed to detect and mitigate a boron rlilution event in Modes 3, 4 and 5 prior to a complete loss of shutdown margin.
The system detects a boron dilution event by monitoring the output of the source range neutron flux detectors to determine if the neutron flux has incrr,ied by a specified multiplication factor over a prescribed time period.
-n a dilution event is detected, the BDMS isolates known dilution pt
.o the reactor coolant system and realigns the reactor makeup water systs to the refueling water storage tank so that any additional makeup will result in boration of the reactor coolant.
Technical Specification 3.3.1, Table 3.3-1, Functional Unit 6.b, " Boron Dilution Flux Doubling," requires that this function be operable in Modes 3, 4, and 5.
If not operable when required, Action 5 applies.
Th action requires, in part, that the reactor trip breakers be open, that all operations involving positive reactivity changes be suspanded, and that the sources of possible dilution be isolated.
Since changirig the plant temperature is an operation which could add positive reactivity, this action statement could require that plant cooldown or heatup be suspended.
As a result of a recent review of the analyses for the licensing basis boron dilution event for CPSES Unit 1, the licansee identified certain noncoriservatisms related to the input assumptions and boundary conditions used by Westinghouse in the original design of the system.
Specifically, the inverse count rate ratio (ICRR) and flux multiplication setpoint used in the analyses are not bounding.
As a result, the licensing basis boron dilution event analysis, which shows that the BOMS response will prevent a return to critical, may not be applicable to CPSES Unit 1.
Because of this, TV Electric has declared the boron dilution flux doubling channels inoperable. With the current TS and action statement described above, this could prevent a plant 9206260324 920608 PDR ADOCK 05000445 P
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- restart following entry into Mode 3, 4, or 5.
Therefore, the licensee proposed the aforementioned revised TS which would remove the boron dilution flux doubling rentrements.
Or. Marc 5 23, 1992, a meeting was held at NRC Headquarters and was attended by representatives from the NRC, TU E) ectr'c, and Westinghouse.
According to 10 Electric, the most plausible long-term solution would be to relocate the source assemblies in the core during the second refueling outage, currently scheduled for the f all of 1992.
The NRC did not feel that it was appropriate to approve the proposed amendment as a permanent change because of the cnntradiction with the staff position that requires positive actions to prevent an unplanned criticality due to boron dilution events.
The potential generic implication to certain other Westinghouse plants is also being reviewed.
However, the NRC did recognize that temporary relief was necessary for CPSES Unit I until the issue could be researched further and an acceptable long-term solution could be identified with more certainty.
Therefore, the licensee was requested to provide a supplemental letter which prJposed 4 time limitation for the revised TS and a discussion of the compensatory actions that TV Electric would take during this time period.
The licensee submitted these proposed TS revisions in a letter dated April 6, 1992.
The licensee subsequently submitted additional changes to the preposed TS revir.ons to delete reference to Unit 2 in a letter dated May 26, 1992.
The additional information contained in the supplemental letters dated April 6, 1992 and May 26, 1992, was clarifying in nature and, thus, within the scope of the initial Federal Reoister notice and did not affect the staff's proposed no significant hazards consideration determination.
2.0 EVALUATION TU Electric has requested that the TS revisions proposed by their May 26, 1992, letter remain in effect for Unit I until six months after criticality following the second refueling outage. After this time interval, the baron dilution flux doublin; requirements would again become effective.
These durations are expecteo to allow sufficient time to research the issues involved, verify the conclusion during testing following core (re) load, propose a permanent resolution, and for the NRC to review and approve the permanent resolution.
The proposed modifications to the TS adequately addrcst, these time limits.
The staff concurs with these proposed time limits and concurrently is preparing an Information Notice to alert all pressurized water reactor licensees of the CPSES problem since the same inadequacies may exist in similar systems.
The following compensatory action is proposed for the duration of this temporary revision of the Technical Specification:
- 1) Within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of entry into MODES 3, 4, or 5 from MODES 1, 2, or 6, (and once per every 14 days thereafter while in MODES 3, 4, or 5), TV Electric will verify (unless startup is in progress) that either valve CS-8455 or valves CS-8560, FCV-lll8, CS-8439, C5-8441, and CS-8453 are closed and secured in position; or 1
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- 2) Following entry into MODES 3, 4, or 5 from MODES 1, 2, or 6, each crew of the Control Room Staff will receive a briefing to discuss the type of reactivity changes-that could occur during a dilution event; the indication of a dilution event; and the actions required to stop dilution, commence immediate boration and establish the required shutdown margin.
For extended shutdowns, this briefing will be repeated for each crew prior to resumption of control room duties following an off duty period which exceeds 7 days. During time periods when this option is used, the source range will be monitored for indication of unexplained increasing counts and inadvertent boron dilution every fifteen (15) minutes.
In addition, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of enterino MODE 5, TV Electric will ensure that only one Reactor Makeup bater P..ap (dilution source) is aligned to tl.a supply header.
These administrative actions will serve to isols dlution flow paths by locking out valves from dilution sources or will rewrict the maximum dilution flow rate by ensuring that no more than-one reactor makeup water pump can supply water to the reactor coolant system (RCS) during Mode 5 operation. The NRC cnncurs that these administrative controls will reduce the probability of an inadvertent boron dilution event during the proposed temporary time interval for the revised TS.
In addition, the NRC believes that the proposed interim actions will provide appropriate operator vigilance to reduce the probability of an inadvertent boron dilution in all threc. shutdown modes during the proposed time interval for the revised TS.
New analyses have been performed by Westinghouse for CPSES Unit I with no credit for the BDMS that show at least 15 minutes exist from the initiation of an inadvertent boron dilution while operating in Modes 3, 4, or 5 before shutdown margin is lost.
These analyses, documented ir. a letter from J. L.
Vota (Westinghouse) to W. J. Cahill, Jr. (TV Electric) WPT-14386, dated February 25, 1992, provide reasonable confidence that the reactor operators have sufficient tin,c during performance of their routine duties to identify and mitigate an inadvertent boron dilution event. The licensee has committed to perform similar ana'Ns tir CPSES Unit 2 prior to licensing.
Even though credit is not maken for the BDMS, its use daring CPSES Unit 1 operation provide 3 additional assurs.nce that an inadvertent dilution event will be detected and mitigated prior to a return to critical.
In addition, other alarms and indications (as provided in Sectior. 15.4.6.1 of the CPSES FSAR) are available to the operator which allow for the detection of an inadvertent baron dilution.
In view of these alarms and indications, tagether with the procedures, training, and activities previously mentioned, the NRC believes that l
reasonable assurance has been provided to minimize the likelihood of an inadvertent boron dilution event during the time interval proposed for the temporary TS revisions.
Should such an event occur, these actions provide reasonable assurance of timely detection and mitigation.
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The staff has reviewed the proposed temporary TS changes for CPSES which assume no credit for the BDMS and which will remain in effect for Unit I until six months after criticality following the second refueling outage. Similar changes will_ be addressed separately for Unit 2 to allow a six-month evaluation period of the BDMS following initial criticality.
Based on the above safety evaluation, we find these proposed changes acceptable during the proposed time interval.
3.0 STATE CONSULTATIO3 In accordance with the Commission's regulations, the Texas State official was notified of the proposed issuance of the amendment.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment. changes a req 1 rement 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 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 pub
comment on such finding (57 FR 8941). Accordingly, the amendment meets th t
. bility criteria for categorical exclusion set forth in 10 CFR 51
).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or
+cs wamo tal astrssment need be prepared in connection with the issuance of t'
wah nnt.
5.c (fhg 21LON The Commission has concluded, based on the consideration 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 Contributor:
L. Kopp Date:
June 8, 1992
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