ML20151D320
| ML20151D320 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 04/08/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20151D317 | List: |
| References | |
| NUDOCS 8804140135 | |
| Download: ML20151D320 (5) | |
Text
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SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.150 TO FACILITY OPERATING LICENSE NO. DPR-62 CAROLINA POWER A LIGHT COMPANY et al.
BRUNSWICK STEAM ELECTRIC PLANT, UNIT 2 DOCKET h0. 50-324
1.0 INTRODUCTION
l By application dated September 29, 1987, Carolina Power & Light Company l
(the licensee) requested an amendment to the Technical Specifications for i
Facility Operating License No. DPR-62 for the Brunswick Steam Electric Plant, Unit 2 (Unit 2). The proposed Technical Specification (TS) changes l
would incorpnrate revised instrument numbers in TS Tables 3.3.6.1-1, 3.3.6.1-2 a:
1.3.6.1-1 and revise TS Section 3/4.3.6 to reflect the new instruments...at have been installed for the Alternate Rod injection (ARI) and the Recirculation Pump Trip (RPT System to mitigate postulated anticipated transient without scram (ATWS)) events. This system was presented to the staff for review by letters dated April 14, June 18 July 24, and August 24, 1987, in accordance with the requirements of 10 l
CFR 50.62.
In response to the staff's request for additional information, the licensee stated in Enclosure 2, Item 4, of its April 14, 1987 letter that l
the instrument channel components, including the sensors, signal condi-l tioning and isolation devices, will be diverse from the existing l
Reactor Trip System (RTS) Components.
Based on this information, the staff accepted the Brunswick design and issued a Safety Evaluation on August 31, 1987.
2.0 EVALUATION AND CONCLUSION l
The ATWS Rule (10 CFR 50.62) requires specific improvements in the design and operation of comercial nuclear power facilities to reduce the likelihood of failure to shut down the reactor following anticipated transients, and to mitigate the consequences of an ATWS event.
The ATWS mitigation system components are required to be diverse from the reactor trip system, from sensor output to the final actuation oevice.
1 G804140135 080408 PDR ADOCK 05000324 P
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The Safety Evaluation Report on the BWROG Topical Report NEDE-31096-P states that equipment diversity to the extent reasonable and prac-ticable, to minimize the potential for connon cause failures, is required.
This should include all diverse reactor trip system instrument channel components, excluding sensors, but including all signal conditioning.
In the submittal dated September 29, 1987, CP&L states that they plan to replace the existing digital reactor vessel pressure switches of the ATWS-RPT system with an analog pressure transmitter / master trip unit.
Based on the information reviewed to date, the staff believes that the analog transmitter / master trip units installed for the ARI/RPT system are identical to the analog transmitter / master trip units installed in i
the Reactor Trip System.
Identical components used in both the existing RTS and the ARI/RPT system are subject to potential connon
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mode failures and do not meet the functional requirements of 10 CFR 50.62. Therefore, the staff concludes that the t tioning (Rosemount analog transmitter / trip units)ype of signal condi-provided for the i
Brunswick ATWS design does not meet the diversity requirements of 10 CFR 50.62 in that diversity, to the extent reasonable and practicable, has not been provided.
Instrumentation is available from other manu-facturers that would provide the required degree of diversity. A more complete discussion of the staff's position on diversity require-4 ments is stated in Appendix 1 (attached).
In telephone conversations with the licensee, we have learned that the Rosemount analog transmitter / trip units have heen installed during the ongoing Unit 2 refueling outage. The TS changes requested in the September 29, 1987 submittal must, therefore, be issued to permit startup of the plant in the current configuration.
Because startup from this outage is scheduled for mid-April 1988, we recognize that there is not sufficient time available to redesign, purchase and install equipment that will satisfy the functional requirements of the design and meet the diversity requirements of the ATWS Rule before restart.
However, 10 CFR 50.62 (the ATWS Rule) requires that the specified equipment be installed before startup from the second refueling outage af ter July 26, 1984, or by a later date agreed upon by the Connission and the licensee.
Although the installation of the Rosemount analog transmitters / trip units does not satisfy the requirements of 10 CFR 50.62, that rule does not establish an inflexible deadline for compliance.
It provides that a schedule beyond the second refueling outage after July 1984 can be 4
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established if justified and mutually agreed upon by the Connission and the licensee. The licensee's explanation of the circumstances con-cerning the Rosemounts provides a reasonable justification for an extension to the deadline until not later than the end of the next l
i refueling outage and the Connission has granted such extension.
Therefore, the installation of the Rosemount analog transmitter / trip j
units and the issuance of the associated TS change does not assure
I I t compliance with the fur.ctional requirements of the Rule, but neither are these actions in violation of the Rule. Based on the above, we l
find that the proposed TS changes are acceptable until a date l
agreed upon by the staff and licensee for full compliance with 10 CFR 50.62. At that time, further changes may be required to these TS sections to reflect the installation of diverse signal conditioning l
units.
3.0 ENVIRONMENTAL CONSIDERATION
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l An Environmental Assessment has been prepared pursuant to 10 CFR 51.32 l
and published in the FEDERAL REGISTER on April 7, 1988 at 53 FR 11576.
4.0 _ CONCLUSION The Comission made a proposed determination that this amendment involves no significant hazards consideration which was published in the FEDERAL REGISTER (52 FR 42048) on November 2, 1987, and consulted with the State of North Carolina.
No public coments or requests for hearing were received, and the State of North Carolina did not have any coments.
The staff 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, and (2) such activities will be conducted in compliance with the Comission's regulations, and the issuance of the amendment will not be inimical to the comon defense and security or to the health and safety of the public.
Principal Contributor:
H. Li l
l Dated: April 8,1988 l
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APPENDIX 1:
THE STAFF POSITION ON DIVERSITY REQUIREMENTS The basic premise behind the ATWS rule as documented in SECY-83-293, "Amendments to 10 CFR 50 Related to Anticipated Transients Without Scram (ATWS) Events" is to require systems / equipment that are diverse (and independent) to those portions of the existing reactor trip system (RTS) where only minimal diversity is currently provided, and which are capable of preventing or mitigating the consequences of an ATWS event. An ATWS event is defined as an expected operational transient (such as loss of feedwater, loss of condenser vacuum, or loss of offsite power) which is accompanied by a failure of the RTS to shutdown the reactor. The failure mechanism of concern is a comon mode failure of identical components within j
the RTS (e.g., logic channels, actuation devices and instrument channels, excluding sensors),
Comon mode failures (CHF) are failures of identical components due to the same failure mechanism (e.g., manufacturing defect, design defect, calibra-tion or maintenance error). Comon cause failures are a broader class of failures consisting of the failure of multiple components, not necessarily identical in design, due to the same cause, typically environmental in nature (e.g., extreme temperature, numidity induced corrosion, vibration).
Existing RTS are considered to have, by design, sufficient redundancy and testability features to prevent random failures from leading to system unavailability. However, because the redundant components are in general identical in manufacturer and design, they are subject to potential comon mode failures. Existing reactor trip systems are typically located in controlled environments; and, thus, the potential for many types of comon cause failures is minimized. Comon mode failures are a subset of comon cause failures. Comon mode failures, but not necessarily comon cause failures, can be eliminated by providing total / absolute diversity. The diversity required by the ATWS rule is intended to ensure that comen mode failures which disable the electrical portion of the existing reactor trip system will not affect the capability of systems / equipment installed in I
accordance with ATWS rule requirements (to prevent or mitigate the conse-quences of ATWS events) to perform their design functions. Therefore, the i
diversity required by the ATWS rule is hardware / component diversity (to l
prevent CHF from disabling both the existing RTS and ATWS preventive /
i mitigative systems).
It is recognized that total / absolute component / hardware diversity can be difficult and sometimes impossible to achieve.
For these instances, acceptable level of component / hardware diversity can be achieved in accordance with combinations of allowable methods such as energization states, AC versus DC power, functional capability, and the use of components from dif.ferent manufacturers.
The concept of equipment / hardware diversity has been firmly established and well documented throughout the history of the ATWS issue and rulemaking process. Appendix C (ATWS Equipment Requirements) to NUREG-0460, "Antici-pated Transients Without Scram for Light Water Reactors " Volume 3 (publishedinDecember1978),statesthattheequipment(installedto
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> l prevent / mitigate the consequences of ATWS events) shall be independent and separate from corponents for systems that initiate the anticipated transient (s) being analyzed and diverse from the normal scram system l
(postulated to fail) to minimize the probability of the ATWS disabling its operation.
The supplementary information provided with the FEDERAL REGISTER notifica-tion of the ATWS rule includes guidance concerning the diversity required of diverse reactor trip systems (diverse scram systems) and mitigating j
systems from the existing reactor trip system.
The guidance states that i
equipment diversity to minimize the potential for common cause failures is i
required from sensor output to and including the components used to interrupt control rod power (circuit breakers from different manufacturers l
alone is not sufficient to provide the required diversity for interruption of control rod power) for diverse scram systems, and from sensor output to.
l but not including, the final actuation device for mitigating systems (e.g., diverse turbine trip and diverse auxiliary feedwater actuation).
Therefore, all diverse scram system and mitigating systems instrument channel components (excluding sensors) and logic channel components, and all diverse scram system actuation devices must be diverse from the existing RTS i
l in accordance with the methods of achieving required equipment diversity identified above to obtain a level of diversity acceptable to satisfy the i
l requirements of the ATWS rule.
Identical components used in both the existing RTS and the diverse scram system or mitigatirig systems are subject to potential common mode failures, and therefore, are not acceptable.
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