ML20247K788
| ML20247K788 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/21/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20247K766 | List: |
| References | |
| NUDOCS 8908010061 | |
| Download: ML20247K788 (5) | |
Text
e
',. psp %9 p
k UNITED STATES NUCLEAR REGULATORY COMMISSION 7.
ej WASHINGTON, D. C. 20555
\\... +,#
j j
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 114 TO FACILITY OPERATING LICENSE NO. DP,R-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271
1.0 INTRODUCTION
By letter dated December 7, 1987, the Vermont Yankee Nuclear Power Corpora-tion, the licensee for the Vermont Yankee Nuclear Power Station, submitted information on the alternate testing requirements of the emergency core cooling 1
system (ECCS) and the standby liquid control (SLC) system and requested that
{
these requirements be eliminated (Refs. 1, 2 and 6). The ECCS includes the diesel generators, the automatic depressurization systems, the high and low pressure core injection systems, containment cooling, core spray, the residual heat removal system, the service water and uninterrupted power supply.
The initial request (Ref. 1) was based on an unquantified expectation that the unavailability for all these systems will improve with the elimination of the prescribed daily tests. The staff reouested a quantification of the unavail-ability to justify the claimed improvement. The licensee submitted the additional information in Reference 2 which is a joint report with Pickard, Lowe and Garrick, Inc., and is based on probabilistic risk assessment methods with generic and plant-specific data.
In Reference 6 the licensee added to the proposed change a requirement that within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following an ECCS failure the redundant train of ECCS be tested and within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following an SLC component failure the redundant SLC component be tested.
The staff reviewed the proposal and the methodology and the date bases for the quantification of the unavailability.
Our review and evaluation follows.
2.0 EVALUATION 2.1 Introductjnn The current Vennont Yankee technical specifications require alternate testing of ECCS and SLC system or subsystems when other engineered safeguards systems or subsystems are out of service.
These tests are required innediately when a system / subsystem is declered inoperable and daily thereafter. The following technical specifications and systems are involved:
1 1
8908o10061 890721 PDR ADOCK 00000271 l
p PDC 1
., [. o 2
2
/
. Technical. Specification Inoperable. System / Subsystem 4.4.B Standby Liquid Control 4.5.A.2 Core Spray 4.5.A.3 Low Pressure Core Injection Pump 4.5.A.4 Low Pressure Core Injection System 4.5.8.2 Containment Cooling 4.5.C.2 Residual Heat Removal Service Water 4.5.C.3 Residual Heat Removal System 4.5.D.2 Service Water 4.5.D.3 Alternate Cooling 4.5.E.2 High Pressure Core Injection 4.5.F.2 Automatic Depressurization System 4.5.G.2 Reactor Core Isolation Cooling 4.5.H.I Diesels 4.5.B.3.C Standby Gas Treatment System 4.10.B.4 Uninterrupted Power Supply System 2.2 Type s. c f. C omp o oe o t. a o d. Sy s tem. Uc av a i l a b i l i t i e s In the context of this analysis, the term unavailability means the probability that a component or system is unable to accomplish its intended function. The causes of component unavailabilities are:
failure, test override, repair, scheduled maintenance and human error. System unavailability can be caused by component unavailability and/or system alignment.
Component failures can be time-related, demand-related or test-related. Correspondingly, systems have time, demand or test-related failures.
The licensee submitted quantification of the unavailabilities for the systems to perform their intended function upon demand. Two systems were chosen for detailed analysis: Core Spray System and the Diesel Generators.
The other systems involved were reviewed in the context of the results obtained for the components of the Core Spray and the Diesel Generators.
The benefits and drawbacks of testing have been quantified; 1.e., the decreased potential for an undetected failure and the increased unavailability and unavailability due to repair of demand-related and test-related failures.
However, other alternate testing drawbacks such as:
reduced reliability due to degradation from testing potential of plant. transients initiated from surveillance testing potential for plant shutdown due to such transients diversion of maintenance personnel for testing, and potential increase in personnel radiation exposure from testing have not been quantified; thus, the estimated benefit is conservative.
2.3 The. Core Spray. System The system provides two trains of core spray for cooling during a loss-of-coolant accident.
The main active components include the core spray pump and the following valves: pump suction, manual pump suction, test bypass, pump discharge bypass, inboard discharge, outboard discharge and manual isolation.
1 The system alignments are:
standby, injection, flow test and valve test.
)
1 I
i i
e o *.
3
~
Three data bases were used in this study:
Generic data from a Pickard, Lowe and Garrick, LWR data base, Reference 3 Vermont Yankee plant-specific data, and Human error data from NUREG/CR-1278 (Ref. 4)
The plant-specific demands and observed failures are small; thus, general data were " updated" with plant-specific data using Bayesian calculations (Ref. 3).
The result is a probability of failure (unavailability) distribution that reflects the Vermont Yankee failure data base.
In this manner, it was shown that for time and demand-related failures, daily testing produced unavail-abilities at least a factor of 4 greater for daily testing versus monthly testing. Similar results were obtained for time and test-related failures.
In addition, the effect of the test interval change on the unavailability of both core spray trains was studied with and without common cause failures.
The results again show unavailability improvement by a factor of about 4.
2.4 Diese3. Generators The same method was applied to estimate the diesel generator unavailability versus the test frequency. The generic data base was updated to reflect the observed Vermont Yankee failure rates.
The results for a single diesel, show a reduction of unavailability by a factor of about 3.
More importantly, however, they show that the improvement is due to the reduction of test-induced failures. This is clear evidence against daily testing of diesel generators.
Similar conclusions have been drawn from industry studies of fast starts of diesel generators which caused accelerated degradation (Ref. 5).
2.5 Application.to.0ther. Systems As we have seen above, there are more systems involved in this application than the core spray and the diesel generators. The remaining systems can be classified into two functional categories:
those not related to supply of water: uninterruptible power supply, the automatic depressurization and the standby gas treatment and all others which either pump or route cooling or
~
borated water.
Uninterruptible Power Supply (UPS)
The UPS provides ac power to the inverter when ac power is not available for the operation of the low pressure core injection valve. However, the battery banks are reliable and are not subject to the alternate ECCS requirements. The valve operation system is discussed below:
Automatic Depressurization System (ADS)
When the high pressure core injection is declared inoperable, the ADS must be tested immediately and daily thereafter.
Because the valves
)
e
. l. o,
e cannot be tested without causing a trip, only the ADS logic is subjected to the' test. However, the actuation logic is very reliable. Under normal conditions, the ADS logic test is performed once each operating cycle. During the test, the valves must be deenergized, thus, increasing ADS unavailability, without benefit from the test.
Standby Gas Treatment System (SGTS)
The SGTS handles gas with fans and dampers for which the generic failure rates are equivalent to those of the pumps and motor-operated valves of the core spray system (Ref. 3). Therefore, it is expected that it should behave in a similar manner with respect to the effect from test frequency (i.e., higher unavailability for daily versus monthly testing).
Other Water Pumping and Routing Systems In these types of systems, their unavailability is dominated by the failure of active components, i.e., pumps and valves. Therefore, these systems behave in a manner similar to the core spray we have examined above. Because the failure rates of their components are similar to those of the core spray it is reasonable to conclude that their unavailability decreases with decreasing testing frequency.
We have reviewed the information submitted by Vemont Yankee pertaining to the quantification of the unavailability of ECCS and SLC versus testing frequency.
The method was based cnly on test and demand-related unavailabilities, thus, is conservative.
The estimates were based on plant-specific modifications of generic data bases.
Two systems (i.e., core spray and diesel generators) were explicitly analyzed.
In addition, similarities were established for the other systems so that conclusions could be drawn regarding the expected behavior of system unavailability versus testing frequency. We find the methods and the data bases employed for these estimates te be acceptable.
The results of the licensee's study demonstrated that the unavailability of the SLC and ECCS systems decreases by e factor of at least 3 for a change of testing frequency from daily to monthly. We conclude that the elimination of H
the alternate testing requirements for Vermont Yankee will contribute to the increase of the SLC and ECCS system reliability; therefore, we find the proposed changes acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
Notice of Consideration by the staff of issuance of the proposed amendment was published in the Federal Register on January 26, 1988 (53 FR 2114) and requests for a hearing were received from the State of Vemont and the Commonwealth of Massachusetts. By a filing dated May 15, 1989, to the Atomic Safety and l
Licensing Board, the two interveners and the licensee filed a joint motion to dismiss the proceeding. The Board granted the motion to dismiss in an Order dated May 23, 1989. An Environmental Assessment (EA) and Finding of No Significant Impact was published in the Federal Register on July 21, 1989 (54 FR 30619). Based upon the EA, the staff has determined not to prepare an environmental impact statement for the proposed license amendment, and has j
concluded that the proposed action will not have a significant adverse effect on the quality of the human environment.
l
a
- f., h o j
- 5 i
4;0 CONCLUSION-L We have concluded, based on the considerations discussed above,.that (1) there l
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) issuance of this amendment will not be inimical. to the common defense and security or to the health and safety of the public..
5.0, REFERENCES 1.
Letter from W. P. Murphy, Vermont Yankee Nuclear Power Corporation to USNr.C. " Surveillance Testing of the ECCS and the SLC Equipment," (FVY 87-112), dated December 7, 1987.
2.
Letter from R. W. Capstick, Vcmont Yankee Corporation to USNRC, "VY Response to RAI - Surveillance Testing of ECCS and SLC Equipment," (FVY 88-58), dated July 15, 1988.
3.
PLG-500, "Probabilistic Risk Assessment Dato Base for Light Water Reactors," Pickard, Lowe and Garrick, Inc., to be published August 1988.
4.
.NUREG/CR-1278, "Handbock of Human Reliability Analysis with Emphasis.on Nuclear Power Plant Applications," by A. D. Swain and H. H. Guttman.
5.
NUREG-1024, " Technical Specifications - Enhancing the Safety Impact,"
prepared by the task group on Technical Specification, dated November 1983..
6.
Letter from W. P. Murphy, Vermont Yankee Nuclear Power Corporation, to USNRC, " Surveillance Testing of ECCS and SLC Equipment, Supplement 2 to Proposed Change No. 85," (BVY 89-49), dated July 8, 1989.
Principal Contributor:
L. Lois Dated: July 21, 1989 l
l