ML17199F807
| ML17199F807 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/06/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17199F806 | List: |
| References | |
| GL-83-28, NUDOCS 8606200327 | |
| Download: ML17199F807 (4) | |
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SAFETY EVALUTION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO GENERIC LETTER 83-28, SALEM ATWS ITEM 1.2 (POST-TRIP REVIEW-DATA AND INFORMATION CAPABILITY)
COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER STATION, UNIT NOS. 2 AND 3 DOCKET NOS. 50-237 AND 50-249 I.
INTRODUCTION On February 25, 1983, both of the scram circuit breakers at Unit 1 of the Salem Nuclear Power Plant (SNPP) failed to open upon an automatic reactor trip signal from the reactor protection system. This incident occurred during the plant start-up and the reactor was tripped manually by the operator about 30 seconds after the initiation of the automatic trip signal.
The failure of the circuit breakers has been determined to be related to the sticking of the undervoltage trip attachment.
On February 22, 1983, during start-up of SNPP, Unit 1, an automatic trip signal occurred as the result of steam generator low-low level. In this case, the reactor was tripped manually by the operator almost coincidentally with the automatic trip. Following these incidents, on February 28, 1983, the NRC Executive Director for Operations (EDO) directed the staff to investigate and report on the generic implications of these occurrences. The results of the staff's inquiry into these incidents are reported in NUREG-1000, "Generic Implications of ATWS Events at the Salem Nuclear Power Plant.
11 As a result of this investigation, the Conunission requested {by Generic Letter 83-28 dated July 8, 1983) all licensees of operating reactors, applicants for an operating license, and holders of construction permits to respond to certain generic concerns. These concerns are categorized into four areas:
(1) Post-Trip Review, (2) Equipment Classification and Vendor Interface, (3) Post-Maintenance Testing, and {4) Reactor Trip System Reliability Improvements.
The first action item, Post-Trip Review, consists of Action Item 1.1, "Program Description and Procedure" and Action Item 1.2, "Data and Infor-mation Capability." This safety evaluation report {SER) addresses Action Item 1.2 only.
II.
REVIEW GUIDELINES The following review guidelines were developed after initial evaluation of the various utility responses to Item 1.2 of Generic Letter 83-28 and incorporate the best features of these submittals.
As such, these review guidelines in effect represent a "good practices" approach to post-trip review.
The staff has reviewed the licensee's response to Item 1.2 against these guidelines:
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The equipment that provides the digital sequence of events (SOE) record and the analog time history records of an unscheduled shutdown should provide a reliable source of the necessary information to be used in the post-trip review.
Each plant variable which is necessary to deter-mine the cause and progression of the events following a plant trip should be monitored by at least one recorder (such as a sequence-of-events recorder or a plant process computer) for digital parameters; and strip charts, a plant process computer or analog recorder for analog (time history) variables. Performance characteristics guidelines for SOE and time history recorders are as follows:
- o Each sequence of events recorder should b~ capable of detecting and recording the sequence of events with a sufficient time discrimina-tion capability to ensure that the time responses associated with_
each monitored safety-related system can be ascertained, and that a determination can be made as to whether the time response is within acceptable limits based on FSAR Chapter 15 Accident Analyses.
The recommended guidelines for the SOE time discrimination is approximately 100 milliseconds. If current SOE recorders do not have this time discrimination capability, the licensee should show that the current time discrimination capability is sufficient for an adequate reconstruction of the course of the reactor trip and post-trip events.
As a minimum, this should inclu.de the ability to adequately reconstruct the transient and accident scenarios pre-sented in Chapter 15 of t~e plant FSAR.
o Each analog time history data recorder should have a sample interval
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sm~ll enough so that the incident.can be accurately reconstructed following a reactor trip. As a minimum, the licensee should be able to reconstruct the course of the transient and accident sequences evaluated in the accident analysis of Chapter 15 of the plant FSAR.
The recommended guideline for the sample interval is 10 seconds.
If the time history equipment does not meet this guideline, the licensee should show that the time history capability is sufficient to accurately reconstruct the transient and accident sequences presented in Chapter 15 of the FSAR.
To support the post-trip analysis of the cause of the trip and the proper functioning of involved safety related equipment, each analog time history data recorder should be capable of updating and retaining information from approximately five minutes prior to the trip until at least ten minut~s after the trip.
o All equipment used to record sequence of events and time history information should be powered from a reliable and non-interruptible power source. The power source used need not be Class IE.
B.
The sequence of events and time history recording equipment should monitor sufficient digital and analog parameters, respectively, to assure that the course of the reactor trip and post-trip events can be reconstructed.
The parameters monitored should provide sufficient
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3 information to detennine the root cause of the unscheduled shutdown, the progression of the reactor trip, and the response* of the plant parameters and protection an~ safety systems to the unscheduled shut-downs.
Specifically, all input parameters associated with reactor trips, safety injections and other safety-related systems as well as output parameters sufficient to record the proper functioning of these systems should be recorded for use in the post-trip review.
The parameters deemed necessary, as a minimum, to perform a post-trip review that would determine if the plant remained within its safety limit desiqn envelope are presented jn Table 1.
They were selected on the basis of staff engineering,iud9fTlent following a complete evalua-tion of utility submittals. If the licensee's SOE recorders and time history recorders do not monitor all of the parameters suggested in these tables, the licensee should sho~ that the existing set of moni~ored
. parameters are sufficient to establish that the plant remained within the design envelope for the accident conditions analyzed in Chapter 15 of the plant FSAR.
The information gathered by the sequence of events and time history recorders should be stored in a manner that will allow for data retrieval and analysis. The data may be retained in either hardcopy,
{e.g., computer printout, strip chart record), or in an accessible memory (e.g., magnetic disc or tape). This information should be presentecf in a readable and meaningful fonnat, takinq into considera-tion good human factors practices such as those outlined in NURF.G-0700.
Retention of data from all unscheduled shutdowns provides a valuable reference source for the determination of the acceptability of the plant vital parameter and equipment response to subsequent unscheduled shut-downs.
Information gathered durinq the post-trip review is to be ret.aine~ for the life of the plant for post-trip review comparisons of subsequent events.
I I I.
EVALUATION By letters dated November 5, 1983 and April 29, 1986, Conunonwealth Edison Company provided information regarding its post-trip review program data and information capabilities for Dresden Nuclear Power Station. The staff has evaluated the licensee's submittals aqainst the review guidelines described in Section IJ. Deviations from the guidelines of Section II were discussed with representatives of the licensee by telephone on January 8, 1986. A brief description of the licensee's responses and the s~aff's evaluation of the responses against each of the review guidelines follows:
A.
The licensee has described the performance characteristics of.the equipment used to record the sequence of events and time history data needed for post-trip review.
Based on a review of the licensee's submittals, the staff finds that the sequence of events recorder and time history recorder characteristics conform to the guidelines described in Section II A, and are, therefore, acceptable.
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B.
The licensee has established and identified the parameters to he monitored and recorded for post-trip review.
The staff finds that the parameters selected by the licensee include all of those identified in Table 1 and conform to the guidelines described in Section II R and are, therefore, acceptable.
C.
The licensee described the means for storaqe and retrieval of the infor-mation gathered b.v the sequence of events and time history recorders, and for the presentation of this information for post-trip review and analysis. The staff finds that this information will be presented in a readable and meaningful format, and that the storage, retrieval and presentation conform to the guidelines of Section II C and are, there-fore, acceptable.
D *. The licensee's April 29, 1986, submittal indicates that the data and information used during post-trip reviews are being retained in an accessible manner for the life of the olant. Based on this information, the staff finds that the licensee's program for data retention conforms to the guidelines of Section II D, and is, therefore, acceptable.
CONCLUSION Based on a review of the licensee's submittals, the staff concludes that the licensee's post-trip review data and information capabilities for Dresden Nuclear Power Station are acceptable.
Princip_~l Contributor: J. Kramer Dated:
June 6, 1986