ML20214C665
| ML20214C665 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 11/17/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20214C635 | List: |
| References | |
| NUDOCS 8611210189 | |
| Download: ML20214C665 (10) | |
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UNITED STATES e8 NUCLEAR REGULATORY COMMISSION a
WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO 10 CFR 50.62 - ANTICIPATED TRAN5IENT5 WITHOUT SCRAM COMMONWEALTH EDISON COMPANY ZION NUCLEAR POWER STATION, UNITS 1 AND 2 DOCKET N05. 50-295 AND 50-304 I.
BACKGROUND On July 26, 1984, the Code of Federal Regulations (CFR) was amended to include Section 10 CFR 50.62, " Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants" (known as the ATWS Rule). The requirements of this section apply to
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all commercial light-water-cooled nuclear power plants.
An ATWS is 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 reactor trip system (RTS) to shutdown the reactor. The ATWS rule requires specific improvements in the design and operation of commercial nuclear power facilities to reduce the likelihood of failure to shutdown the reactor following anticipated transients, and to mitigate the consequences of an ATWS event.
Paragraph (c) (6) of the rule requires that information sufficient to demonstrate compliance with the requirements of the rule be submitted to the Director, Office of Nuclear Reactor Regulation.
The submittal by Commonwealth Edison Company (CECO) by letter dated June 5,1986 (Reference 1) provided a description of the ATWS modifications proposed for the Zion Nuclear Power Station, Units 1 and 2.
The staff reviewed the submittal using
" Safety Evaluation of Topical Report (WCAP-10858)- AMSAC Generic Design Package,"
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. d dated July 7, 1986 (Reference 2) as the basis for the review. The-submittal did not permit the staff to complete its review or in all cases to assess the licensee's compliance with the diversity, electrical independence, reliability, and testability at power requirements of the ATWS rule.
On August 13, 1986, the staff and its contractor (EG&G) held a telephone con-ference with the licensee during which issues requiring further information were discussed. The information required by the staff to complete its review of the implementation of the ATWS rule at the Zion Station, linits 1 and ? is forwarded by Attachrent 1, Request for Additional Information (RAI).
II. DISCUSSION AND EVALUATION The staff's acceptance letter (Ref. P1 for Westinghouse topical report WCAP-10858, "AMSAC Generic Design Package," contained 14 key elements to be resolved in the plant-specific design. The following paragraphs discuss the licensee's submittal with respect to these plant-specific elements.
1.
Diversity The plant submittal should indicate the degree of diversity that exists between the AMSAC equipment and the existing Reactor Protection System (DPS).
The licensee's proposed nodifications regarding diversity are adequate and are acceptable to the staff.
I 2.
Logic Power Supplies 3
Logic power need not be Class IE, but should cone from a power sou'rce that is independent from the RPS power supplies. The licensee proposes to use the RPS power source to power the ATWS mitigation system. The staff views this lack of an independent power source to be unacceptable. During telecon on August 13, 1986, the type and number of power supplies and the capacity of the ATWS UPS were discussed. The power-supply discussion centered around using one power supply for the four logic loops or u' sing four power supplies, one for each logic loop. This discussion was not resolved. This key element is addressed in the
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RAI.
3.
Safety-Related Interface The licensee's response to this key element is acceptable, as the existing protection system continues to meet all applicable safety criteria.
4.
Quality Assurance The licensee did not specifically address Generic Letter 85-06; however, the response stated that CECO has elected to procure and install the ATWS modifications as safety-related. This is acceptable to the staff.
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5.
Maintenance Bypasses Maintenance-bypass indications should be incorporated into the continuous indication of bypass status in the control room. The licensee's response stated that these bypasses are indicated both at the control room and at the relay / matrices / testing (RMT) cabinet. The staff finds this acceptable.
6.
Operatino Bypasses The operating bypasses should be indicated continuously in the control room.
The basis for the 70% bypass should be provided, and the diversity and independence of the C-20 permissive signal should be discussed. The licensee's response prop.erly addressed the operating bypasses and the basis
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for the 70% power arming level.
-r-The submittal also indicated that the ATWS modifications would use the existing P-8 power permissive instead of the C-20 permissive signal, as stated in WCAP-10858. This deviation from the topical report needs to be further clarified, and is addressed in the RAI.
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5 7.
Means for Bypassing Bypasses should be accomplished by means of switches or similar devices. The licensee's response indicated that switches were being used to effect the necessary bypasses, but did not specifically state that lifted leads, jumpers, pulled fuses, etc., were not being employed as bypasses. The RAI will address this element in more detail.
8.
Manual Initiation Manual control should be provided for turbine trips and auxiliary feedwater actuation. The licensee's response that the existing manual controls are satisfactory is acceptable.
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Electrical Independence From Existing Reactor Protection System This key element addresses the electrical isolation between Class IE systems and the non-Class 1E ATWS mitigating system. The licensee stated that Westinghouse 7300 series isolators are being used. These isolators are l
reported on in WCAP-8892-A, and have been accepted by the staff.
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- 10. Physical Separation From Existing Reactor Protection System _
The implementation of the ATWS mitigating system must be such that the separation criteria applied to the existing protection system are not violated.
The licensee has made a positive statement to this effect, and the staff finds
- the response acceptable.
11.
Environmental Oualification
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The environmental qualification of ATWS equipment for anticipated operational occurrence needs to be addressed. The licensee's response did not address this subject, and it will be brought up in the RAI.
- 12. Testability at Power The equipment required by 10 CFR 50.6? to reduce the risk associated with an ATWS event must be designed to perform its functions in a reliable manner.
Measures to test the ATWS mitigating system prior to installation, as well as periodically, are to be established.
The licensee's response to this element did not receive the staff's full approval and additional discussions are necessary. The PAI will address this element in more detail.
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- 13. Completion of Mitigative Action Plant-specific submittals should verify that (1) the protective action, once initiated, goes to completion and (2) the subseouent return to operation requires deliberate operator action. The licensee's response did not specifically address this element, and it will be brought up in the RAI.
14 Technical Specifications
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The equipment required by the ATWS rule to reduce the risk associated with an ATWS event must be designed to perform its functions in a reliable manner.
A method acceptable to the staff for demonstrating that the equipment satisfies the reliability requirements of the ATWS rule is to provide AMSAC technical
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specifications including operability and surveillance requirements. The staff will provide details regarding this concern in a separate document.
In addition, another concern (non-key element) with respect to the stean gener-ator sampling and blowdown valves was raised by the staff. A statement by the licensee that the sampling and blowdown valves are not being closed is not a key element, but does require further clarification. This statement is in opposition i
to those contained in WCAP-10858. The RAI will ask for clarification concerning the operation of these valves.
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III. CONCLUSION Based upon a review of the licensee's submittal, the conclusions of the staff are as follows.
1)
The licensee is performing in good faith, as related to the ATWS Rule.
2)
The RAI must be answered in detail and reviewed by the staff before
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final design approval can be granted.
3)
The licensee may continue with the implementation of Zion Station's ATVS mitigating system pending final staff approval.
IV. REFERENCES 1.
Letter dated June 5,1986, from P. C. LeBlond (CECO) to H. R. Denton (NRC),
" Zion Nuclear Power Station Units 1 and 2 ATWS Protection - 10 CFR 50.62."
2.
Letter dated July 7, 1986, from C. E. Rossi (NRC) to L. D. Butterfield (CECO-WOG), " Acceptance for Referencing of Licensing Topical Report."
ATTACPMENT 1 s
REQUEST FOR ADDITIONAL INFORMATION w
ZION NUCLEAR POWER STATIONS, llNITS 1 AND 2 ANTICIPATED TRANSIENTS WITHOUT SCRAM The staff has reviewed the submittal provided by Commonwealth Edison Company (Letter dated. lune 5,1986, From P. C. LeBlond (CECO) to H. R. Dentoni, " Zion Nuclear Power Station Units 1 and ? ATWS Protection - 10 CFR 50.6?.") and con-cluded that additional information will be required to complete its review.
The staff's review was based on the' generic safety evaluation presented in a letter dated tluly 7,1986, from C. E. Rossi (NRC) to L. D. Butterfield (CECO-WOG1,
" Acceptance for Referencing of Licensing Topical Report." The information needed by the staff is defined below:
1.
Provide a statement that the ATWS logic power supplies are independent from the RPS power supply.
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The function of the C-20 permissive is both to arm the ATWS mitigating system and to defeat the block of AMSAC.
Figure 1 of the submittal shows the P-8 permissive entering the system up-stream of the block test switch.
Proviite a discussion as to why the P-8 permissive is a technically adequate substitution for the C-20 permissive and how the function
" defeats the block of AMSAC" is accomplished.
u 3.
Provide a discussion delineating the use of lifted leads, pulled fuses, tripped breakers or blocked relays as a means of effecting a bypass.
In addition, provide a response to the question "how are forgotten bypasses detected or prevented."
4 Provide a discussion addressing the environmental qualification of all proposed ATWS equipment for anticipated operational occurrences.
- 5. of the licensee's submittal described "At-Power" and
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"Zero-Power" tests of the proposed ATWS moaification. The tests as described were examples of what a test might consist of. The tests were not definitive enough and did not address the key element " Testability at Power" contained in the staff's generic safety evaluation.
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Provide a test procedure and test program that address such topics as end-to-end tests, testing intervals, at power tests, circuit calibration (set points), and maintenance. The information should be sufficient to demonstrate that the systems and equipment required by the ATWS rule will be adequately maintained and capable of performing their design functions in a reliable manner when required.
6.
Provide a statement addressing the completion of mitigative action once started.
7.
Provide a discussion as to why the steam generator sampling and blowdown valves are not being closed. These non-closures are in opposition to the position contained in WCAP-10858.
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