ML20028H049
| ML20028H049 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 09/27/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20028H048 | List: |
| References | |
| NUDOCS 9010050311 | |
| Download: ML20028H049 (4) | |
Text
l
, &q %q$*,,
[1
+
UNITED sT ATES t
ic( 'g NUCLEAR REGULATORY COMMISSION 5k...+}E WASHINGTON, D. C. 20666 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RFLATED TO AMENDMENT NO.
49 TO FACILITY OPERATING LICENSE NO. NPF-62 ILLIN0l$ POWER COMPANY. ET AL.
CLINTON POWER STATION. UNIT NO. 1 DOCKET NO. 50-461
1.0 INTRODUCTION
By letter dated July 11,1990, the 11' inch Power Company (IP), et al.
(the licensee), requested three P.:..endr.ents to Facility 0)erating License No NPF-62 for the Clinton Power Station, Unit 1.
The t1ird proposed amendment in that submittal would revise the footnote concerning test frequencyforthedieselgeneratorsinTechnicalSpecification(TS) Table 4.8.1.1.2-1 and would modify the reporting requirements of TS 4.8.1.1.3 to be on a per-diesel-generator basis rather than a per-nuclear-unit basis.
2.0 EVALUATION TS Table 4.8.1.1.2-1, " Diesel Generator Test Schedule " is a table which defines test frequency of the individual diesel generators based on the number of valid failures in the last 20 and last 100 valid tests. A note to the table explains that for the case of 2 or more failures in the last 20 valid tests, the increased test frequency shall be maintained until 7 consecutive failure-free demands have been performed and the numoer of failures in the last 20 valid demands has been reduceTTo less than or equal to one.
No such provision currently exists for exiting from the
%reased testing frequency requirements required when 5 or more failures occur in the itst 100 valid tests. Thus, a diesel generator which experienced 5 or more failures in the last 100 valid tests could be required to maintain-the in:reased testing frequency significantly longer than in the previous case after repairs had restored the diesel generator to its former reliability. The licensees' proposed change seeks to use the same criteria for demonstration of restored reliability regardless of the circumstances which resulted in the increased testing frequency requirement, p
OnJuly2,1984,thestaffissuedGenericLetter84-15(G.L.84-15)toall f
licensees of operating reactors, ap)1icants for an operating license, and holders of construction permits. Tie intent of G.L. 84-15 was to provide licensees with guidance on improving diesel generator reliability by reducing the number of cold fast starts for diesel generators, obtaining diesel generator rel hbility data, and attaining and maintaining a diesel generator reliability goal. Enclosure 1 to G.L. 84-15 described the basis for reducing cold fast starts and its resultant improvement in diesel 9010050311 900927 PDR ADOCK 05000461' P
PNU
1
[
) generator reliability and also discussed the correlation between excessive diesel generator testing (other than cold fast starts) and its resultant i
degradation of diesel engines. This was primarily aimed at some older plants whose TS required testing of diesel generators each time subsystems of the emergency core cooling system became inoperable.
Enclosurt 3 to G.L. 84-15 described an acceptable example of a performance program for attaining and maintaining diesel generator reliability above the threshold level of concern.
It included increastd surveillance frequency where previous testing indicated failure counts in excess of a specified value until restored reliability was demonstrated.
It also considered disqualification and subsequent requalification of the diesel j
generator in accordance with a prescriptive testing program, including 7 consecutive successful demands without a failure within 30 days, and 14 successful consecutive demands within 75 days of the diesel generator being restored to operable status.
Certain more restrictive criteria applied should a i C 1ure occur during the above testing.
I While incrused testing frequency was and still is determined by the staff j
to be an acceptable method to demonstrate restored reliability of the diesel generator, the discussions in Enclosure 1 to G.L. 84-15 regarding reduction of unnecessary testing and changes to the Standard TS as described in Appendix A of G.L. 84-15, such as changing the previous 3-day q
test frequency to 7 days, clearly indicate that unneccessary diesel generator testing sho"1d be avoided if other methods of demonstrating and/or restoring diesel generator reliability exist.
The licensees' proposal seeks to avoid the possibility of a situation
)
occurring which would require continued diesel generator testing even after demonstration that reliability has been restored.
Such testing is deemed by the licensees to be excessive and not in keeping with the intent of G.L. 84-15.
The staff's April 25, 1985 Safety Evaluation (SE) related to issuance of Amendment No. 48 to the North Anna Unit 2 operating license discusses the i
reliability goals, the accelerated testing frequency and the incentives for engine overhaul and their relation to improvement in reliability. As stated in the SE, the original accelerated testing frequency for North Anna
)
was based upon number of failures in the last 100 starts. The expansion of
)
the accelerated test frequency table to include the number of failures in the last 20 starts was to provide early indication (of 2 or more failures in the last 20 starts) of a.90 or lower reliability.
To enter accelerated testing at this point would provide a better sensi-tivity to the possibility of abrupt diesel generator degradation and provide l
a timely response.
Increasing the test frequency would provide a faster accumulation of test data upon which to judge the reliability of the diesel.
This additional data could then be used to distinguish between failures which occur close together simply due to random chance and such failures that are indicative of an abrupt decline in the actual reliability.
The weekly test L
i
.i t,.
2, i
. schedule would be continued until two conditions have been satisfied.
- First, seven consecutive successful tests have been accumulated. Second, the j
failures in the most recent 20 tests have been reduced to one. Seven suc-cessful tests indicate a reliability of at least 0.90/ demand but at only the 50% confidence lavel. Continuing the accelerated testing until the number of failures is 1 out of 20 adds further assurance that the diesel generator i
has not degraded below the 0.90/ demand level. This relaxation to the normal testing interval of once per 31 days upon satisfying the two conditions above was only applicable to the case where 2 or more failures occurred in the last 20 starts, not the case where 5 or more failures occurred in the last 100 starts.
The licensee has stated that the resolution of diesel generator reliability l
problems are taken very seriously and are vigorously pursued at Clinton.
Although the existing TS allow for a reduction in testing when a diesel
)
overhaul has been performed, a complete overhaul of a niesel generator may not significantly contribute to a reduction of the mosN statistically prevalent failures if they are not related to the inte'nals of the engine.
In the case of the recent slow starts of the Clinton d usel generator IA, i
the root cause was determined to be related to the engit.e governors.
l Therefore, the licensee has propesed that monthly testine of the diesel should be allowed when, in lieu of a complete overhaul, a:ceptable reliability of the diesel generator has been demonstrated to have been h
restored by the successful performance of seven consecutive failure-free damands and the diesel generator has demonstrated a reliability of greater than 0.90 over its last 20 valid tests.
Based on the previous discussion, the staff finds the licensees' proposed change to be acceptable.
The licensees' request to modify the reporting requirements of TS 4.8.1.1.3 from a per-nuclear-unit basis to a per-diesel-generator basis is in keeping with the guidance of G.L. 84-15 for determining failure rates on each diesel generator at a site. The test failures are determined on a per-diesel-generator basis to avoid excessive testing on otherwise reliable diesel generators because of failures on one generator at a site. The change in reporting criteria to a per-diesel-generator requirement would be consistent I
with the testing criteria and would avoid the need for a dual countilig system, one for f>ilures and one for reports. The staff considers this change i
act: noble.
3.0 - ENylRONMENTAL CONSIDERATION This amendment involves a change to a requirement with respect to the instal-lation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or a change to a surveillance requirement. The 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 tnis amendment involves no significant hazards
1 it :..
criteriaforcategoricalexclusionsetforthin30CFR51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact 1:stement nor environmental assess-ment need be prepared in connection with the issuance of this amendment.
4.0 CONCLUSION
{
The staff has concluded, based on the considerations discussed above, that:
l (1) there is reasonable assurance that the health and safety of the will not be endangered by operation in the proposed manner; and (2) public such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.-
Prinicipal contributor:
J. Hickman Dated: September 27, 1990 1
I
.--