ML17055B221
| ML17055B221 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 01/27/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17055B220 | List: |
| References | |
| GL-83-28, NUDOCS 8602050373 | |
| Download: ML17055B221 (20) | |
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATISN RELATING TO GENERIC LETTER 83-28, ITEM 1.2 - POST-TRIP REVIEW DATA AND INFORMATION CAPABILITY NIAGARA MOHAWK POWER CORPORATION NINE MILE POINT UNIT 1 DOCKET NO. 50-220 K"9 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 under voltage 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."
As a result I
of this investigation, the Comission 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:
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(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 Information Capability."
This safety evaluation (SE) addresses Action Item 1.2 only.
- 2. 0 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.
We have reviewed the licensee's response to Item 1.2 against these guidelines:
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 determine 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:
Each sequence of events recorder should be capable of detecting and recording the sequence of events with a sufficient time discrimination 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 include the ability to adequately reconstruct the transient and accident scenarios presented in Chapter 15 of the plant FSAR.
Each analog time history data recorder should have a sample interval small 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 minutes after the trip.
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 information to determine the root cause of the unscheduled
- shutdown, the progression of the reactor trip, and the response of the plant parameters and protection and safety systems to the unscheduled shutdowns.
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 design envelope are presented in Table 1.
They were selected on the basis of staff engineering judgment following a complete evaluation 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 show that the existing set of monitored 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.
C.
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 presented in a readable and meaningful format, taking into consideration good human factors practices such as those outlined in NUREG-0700.
D.
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 shutdowns.
Information gathered during the post-trip review is to be
retained for the life of the plant for post-trip review comparisons of subsequent events.
3.0 EVALUATION AND CONCLUSION By letter dated November 8, 1983, Niagara Mohawk Power Corporation provided information regarding its post-trip review program data and information capabilities for Nine Mile Point Unit 1.
We have evaluated the licensee s
submittal against the review guidelines described in Section 2,0.
Deviations from the Guidelines of Section 2.0 were discussed with representatives of the licensee by telephone on November 26, 1985.
A brief description of the licensee's responses and the staff's evaluation of'he response 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 our review of the licensee's submittal, we find that the sequence of events recorder characteristics conform to the guidelines described in Section 2,A;, and. are acceptable.
The time-history recorder for Nuclear Steam Supply System (NSSS) data also conforms to these guidelines.
The time-history recorder for Balance of Plant (BOP) data conforms to these guidelines except that the analog points recorded on this post-trip log are output only once per 30 seconds.
Parameters recommended for time-history recording in Section 2.B should not be recorded on the BOP log.
B.
The licensee has established and identified the parameters to be monitored and recorded for post-trip review.
Based on our telephone
- review, we find that the parameters selected by the licensee include all but two of those identified in Table I and conform to the guidelines described in Section 2.B.
One additional parameter is recorded on the BOP recorder at a slower-than-recommended frequency.
The licensee reports that control rod position is not recorded by either the sequence of events recorder or the time-history recorder.
Rod position information will be printed-out on demand by the operators, but will not provide position vs. time data.
Operators are trained to demand rod position data after any reactor trip from criticality.
We find this approach satisfactory.
The licensee reports that containment isolation status as recorded by the sequence of events recorder is limited to Main Steam Isolation Valve (MSIV) position only.
However, recorded flow data for other systems is available, and can be used to establish the status of other isolation valves.
Also, demand signals for containment isolation are recorded, and isolation can be confirmed from the control room status light panels.
We believe that enough data and information will be recorded to permit adequate post-trip review of containment isolation.
The licensee also reports that neutron flux (power) is recorded on the BOP time-history recorder.
With a 30-second output interval, it might not be possible to record flux change following a
'I trip signal.
However, the licensee reports that this parameter is also recorded on a strip chart recorder.
We find this satisfactory, provided that the recorder is powered from a non-interruptible power source.
Otherwise, this parameter should be input to the NSSS time-history recorder.
C.
The licensee has described the means for storage and retrieval of the information gathered by the sequence of events and time-history recorders, and for the presentation of this information for post-trip review and analysis.
Based on our review, we find 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 2.C.
D.
The licensee has committed to retaining the data and information used during post-trip reviews in an accessible manner for the life of the plant.'ased on information obtained during our telephone
- review, we find that the licensee's program for data retention conforms to the guidelines of Section 2.D, and is acceptable.
Based on our review, we conclude that the licensee's post-trip review data and information capabilities for Nine Mile Point Unit 1 are acceptable, but recommend that the licensee upgrade recording capability for neutron flux as described in Section 3.B.
Principal contributor:
R. Froelich Date:
January '27, 1986.
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TABLE 1
BWR PARAMETER LIST SOE Recorder x (I) x (I)
(2) x (I)
(2) x (I) x (I) x (I)
Time History Recorder Parameter/Si nal Reactor Trip Safety Injection Containment Isolation Turbine Trip Control Rod Position Neutron Flux, Power Main Steam Radiation Containment (Dry Well) Radiation Drywell Pressure (Containment Pressure)
Suppression Pool Temperature Primary System Pressure Primary System Level MSIV Position Turbine Stop Valve/Control Valve
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Position (3) x (I) x (I)
Turbine Bypass Valve Position Feedwater Flow-Steam Flow Recirculation;
- Flow, Pump Status Scram Discharge Level Condenser Vacuum
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4 SOE Recorder (3) (4)
Time History Recorder Parameter/Si nal AC and DC System Status (Bus Voltage)
Safety Injection; Flow, Pump/Valve Status Diesel Generator Status (on/Off, Start/Stop)
(I)
Trip parameters (2)
Parameter may be recorded by either an SOE or time history recorder.
(3)
Acceptable recorder options are:
(a) system flow recorded on an SOE
- recorder, (b) system flow recorded on a time history recorder, or (c) equipment status recorded on an SOE recorder.
(4)
Includes recording of parameters for all applicable systems from the following:
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