ML20199L387
| ML20199L387 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 01/20/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20199L384 | List: |
| References | |
| NUDOCS 9901270216 | |
| Download: ML20199L387 (5) | |
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i UNITED STATES s
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 20066 0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.119TO FACILITY OPERATING LICENSE NO. NPF-62 lLLINOIS POWER COMPANY CLINTON POWER STATION. UNIT 1 l
DOCKET NO. 50-461 i
1.0 INTRODUCTION
j By letter dated August 24,1998, Illinois Power (the licensee) proposed a change to clarify that operator action, in lieu of an automatic design feature, is required to reset the govemor for the Division 3 diesel generator (DG) to establish ready-to-load operation should an accident signal occur during DG testing while parallel to the offsite grid at the Clinton Power Station (CPS). The licensee provided a new paragraph to be added to the CPS Updated Safety Analysis Report (USAR) regarding the change. The CPS Technical Specification (TS) Bases will also be changed to reflect the operator action.
Following a telephone discussion with the staff, the licensee in a letter dated November 20, 1998, provided additional information including a revised proposed TS Bases discussion and a revised USAR discussion. This letter did not change the requested action or affect the NRC staff's finding of proposed no significant hazards consideration determination (63 FR 48529).
2.0 BACKGROUND
Surveillance Requirement (SR) 3.8.1.17 in Section 3.8.1 of the TS requires, with the Division 3 DG operating in the test mode, verification that an actual or simulated emergency core cooling system (ECCS) initiation signal automatically overrides the test mode and retums the DG to ready-to-load operation. On June 26,1998, the licensee determined that this surveillance requirement was not being adequately satisfied for the Division 3 DG since the Clinton design (for Division 3 DG only) requires operator action, in lieu of an automatic design feature, to establish ready-to-load operation should an ECCS signal occur during DG testing.
The plant's TS Bases pertaining to SR 3.8.1.17 states that an automatic switchover design is required by paragraph 6.2.6(2) of IEEE Std. 308-1980, "lEEE Standard Criteria for Class 1E Power Systems for Nuclear Power Generating Stations" (endorsed by Regulatory 9901270216 990120 PDR ADOCK 05000461 P
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s Guide 1.32, " Criteria for Safety-Related Electric Power Systems for Nuclear Power Plants").
During the NRC's Special Evaluation of the Clinton Power Station conducted during the fall of 1997, the NRC team discussed with the licensee a concem associated with this requirement.
Specifically, the team observed that the Division 3 DG was operated in the droop mode during testing when parallel to the offsite power system and manual action would be required to restore the DG to isochronous operation (droop =0) for an ECCS demand. Licensee Event Report (LER)96-012 r,tated thm the DG was inoperable in this condition during testing because, without manual restoration, the resulting frequency of the DG output would not be sufficient for the high pressure core spraf (HPCS) pump to produce required flow should a loss-of-offsite power with a loss-of-coolant acWent (LOOP /LOCA) occur. The NRC team determined that this aspect of the Clinton Division 3 DG design was contrary to Regulatory Guide 1.108, " Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants," and Regulatory Guide 1.9, " Selection, Design, and Qualification of Diesel-Generator Units Used as Standby (Onsite) Electric Power Systems at Nuclear Power Plants,"(which endorses IEEE Std 387, "lEEE Standard Criteria for Diesel-Generator Units Applied as Standby Power Supplies for Nuclear Power Generating Stations") which require automatic restoration from the test mode for an accident demand as does IEEE Std 308-1980. Also, it appeared that the licensee implied, during original plant licensing reviews, that the plant's design for the emergency DG's (including the Division 3 DG) provided this feature and was in compliance with the regulatory guides. In response to the evaluation team's concern, the licensee opened a condition report to address this issue.
As a result, the licensee proposed a change to the USAR and the TS Bases discussion related to SR 3.8.1.17 to eliminate the conflict between the surveillance requirement and the actual d sign of Division 3 DG control circuitry. Because of the concern over the Division 3 DG design's apparent deviation from staff guidance and historical position contained in the regulatory guides and IEEE standards mentioned above, the NRC staff questioned the licensee's approach and supporting documentation for the proposed change. As a result, the staff (during an October 1,1998, conference call) requested the licensee to provide additional supporting information which was provided in the supplementalletter.
3.0 EVALUATION The licensee's proposed change to the TS Bases follows:
1.
On Page B 3.8.13 following the first two paragraphs under Surveillance Requirements add:
In general, surveillances performed for each of the required DGs are similar, with one notable difference due to the fact that the Division 3 DG utilizes a mechanical govemor, while the Division 1 and 2 DGs utilize an electronic govemor. As such, the Division 1 and 2 DGs are capable of operating in both an isochronous mode as well as a " droop" mode for when the DGs are paralleled to the offsite source during testing. The Division 3 DG, on the other hand, is capable of operating only in the droop mode (though a droop setting of zero can be utilized). This difference may affect the Division 3 DG's capability to achieve rated frequency l
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following automatic switchover from the test mode to ready-to-load operation upon receipt of a LOCA initiation signal (as verified per SR 3.8.1.17).
For the Division 1 and 2 DGs, DG operation is retumed to the isochronous mode upon switchover such that rated speed / frequency is automatically attained. For the Division 3 DG, however, with the DG govemor initially operating in the droop condition during the test mode, operator action may be required to reset the govemor for ready-to-load operation at the required frequency. This difference is acknowledged in the Bases for SR 3.8.1.17 to address compliance with that SR. Notwithstanding, the condition also requires the Division 3 DG to be considered inoperable if it cannot be ensured that the required frequency would be attained in the event of a LOCA and a loss of offsite power concurrent with the Divisior 3 DG being operated or tested with the existing droop setting in effect.
Thus, the Division 3 DG is generally considered inoperable while the droop setting is in effect during performance of SRs that require the DG to be paralleled to the offsite source.
2.
On Page B 3.8-27 revise the first paragraph under SR 3.8.1.17 as follows with the change shown in italics:
Demonstration of the test mode override ensures that the DG availability under accident conditions is not compromised as a result of testing.
Except as clarified below for the Division 3 DG, interlocks to the LOCA sensing circuits cause the DG to automatically reset to ready-to-load operation if an ECCS initiation signalis received during operation in the test mode. Ready-to-load operation is defined as the DG running at rated speed and voltage with the DG output breaker open. These provisions for automatic switchover are required by IEEE-308 (Ref.13), paragraph 6.2.6(2), as further amplified by IEEE 387, sections 5.6.1 and 5.6.2.
(Clarification regarding conformance of the Division 3 DG design to these standards is provided in the USAR, Chapter 8 (Reference 2).)
3.
Add the following as a new second paragraph to the Bases discussion for SR 3.8.1.17:
Automatic switchover from the test mode to ready-to-load operation for the Division 3 DG is also c emonstrated, as described above, by ensuring that DG control logic automatically resets in response to a LOCA signal during the test mode and confirming that ready-to-load operation is attained (as evidenced by the DG running with the output breaker open).
However, with the DG govemor initially operating in a " droop" condition during the test mode, operator action may be required to reset the governor for ready-to-load operation in order to complete the surveillance for the Division 3 DG. Resetting the govemor ensures that the DG will supply the Division 3 bus at the required frequency in the event of a
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LOCA and a loss of offsite power while the DG is in a droop condition during the test mode.
The staffs view of the key points in the information provided by the licensee is summarized as follows:
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As stated above, the safety concem is that the Division 3 DG requires manual j
testoration from the droop mode during testing before it can provide power at an adequate frequency to meet the HPCS flow requirements for an accident demand. To assess the risk associated with this concem, the licensee made the following conservative assumptions / estimations:
The reduction in HPCS flow due to the droop setting not being restored to zero is only a problem for medium and large break LOCAs which have an estimated probability of occurrence of 9.05E-5/ year.
The concern is only related to events involving a LOCA with a LOOP.
The licensee estimated the conditional probability of a LOOP occurring concurrent with a LOCA to be 6.0E-2.
The surveillances that require the DG to be operated parallel to the grid are the monthly 1-hour load test and the 18-month 24-hour load test. The licensee conservatively estimated the fraction of time per year that the DG would be operated during those tests in a droop mode that represented a vulnerability / risk in that adequate frequency would not be provided for an accident demand without reliance upon operator action. That estimate was 2.74E-3.
The licensee multiplied the above three numbers to obtain an overall probability for the event of 1.5E-8/ year which does not represent a significant risk.
2.
During testing of the DG in parallel with the offsite grid, an operator is typically nearby and can perform the simple operator action locally to restore the DG to zero droop operation should an accident demand occur. Also the operator in the main control room can take action to overcome the droop setting if required.
3.
The licensee stated that the Division 3 DG is considered inoperable when the droop setting is not equal to zero and that its removal from service for testing is controlled and limited by the plant's Technical Specifications.
Based on the above, the staff finds the proposed changes to the Technical Specification Bases acceptable. Revisions to the TS Bases are made by the licensee and provided to the NRC staff i
in accordance with TS 5.5.11, " Technical Specification (TS) Bases Control Program."
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Along with the above proposed TS Bases changes, the licensee submitted revisions to various sections of the USAR to clarify the plant's compliance with Regulatory Guides 1.9,1.32, and i
1.108 and IEEE Std 387 as pertaining to the Division 3 DG's restoration to the ready-to-load operation from the test mode. The NRC staff also finds the revisions to the USAR to be
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5 acceptable based on the evaluation presented above. The USAR shall be updated in j
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accordance with 10 CFR 50.71(e).
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4.0 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.
l 5.0 ENVIRONMM l
This amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes a surveillance requirement. 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 public j
comment on such finding (63 FR 48529). Accordingly, the amendment meets the eligibility l
criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b),
i no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 CONCLUSION
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, (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 j
common defense and security or to the health and safety of the public.
Principal Contributor: F. Burrows i
Date: January 20, 1999 l
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