ML20147A513
| ML20147A513 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 05/26/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-010-00 | |
| Download: ML20147A513 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
160846 Date:
March 20, 1980
Title:
Loss of 24 Volt dc Nonnuclear Instrument Power Supply at Crystal River 3 The failure sequence was:
- 1. With the reactor at 100% power, the 24 V dc nonnuclear instrumentation "X" power supply was lost due to a failed voltage buffer card.
- 2.
Because of this, the integrated control system received erroneous signals and demanded (1) a reactor power increase, (2) a feedwater
- runback, and (3) the opening of the power-operated relief valve.
- 3.
The open PORV did not prevent reactor coolant pressure from reaching the over-pressure trip set point, which initiated a
- 4.
The loss of power caused the PORV to stay open.
Primary coolant was discharged into the reactor coolant drain tank and then into the reactor containment building (43,000 gal) after the drain tank rupture disk opened.
RCS pressure dropped resulting in high pressure injection being automatically actuated at 3 min (HPI continued for 84 min).
- 5.
At 4 min the operator tripped the reactor coolant pumps as required by the HPI initiation.
- 6.
The "A" once through steam generator effectively boiled dry at approximately 8 min.
- 7.
The operator shut the block valve which stopped the loss of reactor coolant through the PORV at 2 to 5 min.
- 8.
The operator initiated emergency feedwater at approximately 9 min.
- 9.
The RCS pressure increased due to continued HPI at 1100 gpm, and a code safety valve opened at 10 min.
- 10.
Power was restored to the nonnuclear instrumentation about 21 min into the transient.
- 11.
At 29 min the operator throttled the HPI flow to about 250 gpm.
- 12.
Until about 2 h after the incident began, the safety valve periodi-cally released coolant at 2300 psi to the containment.
About 40,000 gal of coolant was dumped into the reactor building.
- 13.
At about 5 h 7 min into the transient, decay-heat closed-cycle cooling pump DCP-IA failed, rendering the "A" decay-heat closed-cycle cooling loop inoperable.
The failure was due to failure of the pump motor coupling.
- 14.
The plant was stabilized and maintained in hot standby on natural circulation until forced RCS flow was initiated about 6 h 16 min
into the transient.
The plant was subsequently taken to cold shutdown.
- 15.
Throughout the event, core coverage was maintained; no fuel damage occurred, and the RCS remained within code allowable limits.
Corrective action:
The plant was shut down for resolution of the problem and implemen-tation of corrective actions.
These actions included:
Complete testing and inspection of the nonnuclear instrumentation system for similar failures.
Installation of new redundant channels for indication of twenty-three key plant parameters to provide more reliable information to the operator.
Comprehensive operator training in response actions for NNI and ICS failures.
Installation of positive position indication on the power operated relief valve and the two code safety valves.
Modification of the NNI power supply to provide more reliable power.
Evaluation of NNI power supply reliability in response to IE Bulletin 79-27 (Loss of Non-Class 1E Instrumentation and Control Power System Bus During Operation).
Modification of the control circuitry for the PORV and pressurizer spray valves so that the valves will not open in the event of loss of NNI power.
The NRC initiated an extensive review program regarding the effect of the Crystal River event.
Design purpose of failed system or component:
The nonnuclear process instrumentation provides the required input signals of process variables for the reactor protection, regulating, and auxiliary systems.
It performs the required process control functions in response to those systems and provides instrumentation for startup, operation, and shutdown of the reactor system under normal and emergency conditions.
Inputs to the reactor protective system by the nonnuclear instrumentation are reactor outlet temperature, coolant flow, and pressure.
Inputs provided to the integrated control system are reactor outlet temperature, inlet differential temperature, coolant flow, feedwater temperature, feedwater flow, steam generator level, steam generator outlet pressure, and turbine header pressure.
Reactor at Consequent Reactor trip Safety Injection Operator closes Opeeator Power rotored HPI throttled Decay heot Shutdown delayed Potential power and erroneous sig-due to high Initiated due to block valve and manually to 00I train XI to miniie cloned cycle chile pep ICP-i Pvoer lost of vaIn to ICS RCS pressurv decreasing RCS Isolates open Initiates discharge of cooling pumps is repaired rre NNI train X resulting in pressuren POl emergency containment DCP-IA 1avall-Damage power supply increased power feedwater able due to due to
- demand, feed-failed motor failed volt-water runback, coupling age buffer and opened PORV cord No No - single decay heat loop oavailable No No
/
No Possible -
If HPI throttled to point that subcooling No is lost No (POR cloure)Possihle If HPI throttled to point that subcooling is lost
ýosure)
Possible -
Itf PI throttled to point that subcooling is lost No Yes Yes NSIC 160846 - Actual Occurrence for Loss of 24-V Nonnculear Instrument Power Supply at Crystal River 3
Small Reactor Auxiliary High Low Pressure LOCA*
Trip Feedwater and Pressure Recirculation Secondary Injection and LPR/HPI Heat Removal Cross-Connect Potential Severe Core Damage Sequence No.
No I
Yes Yes 2
3 No 4
Yes Yes Yes 5
6 7
NSIC 160846 -
Sequence of Interest for Loss of 24-V dc Nonnuclear Instrumentation Power Supply at Crystal River 3
- due to loss of NNI-X power supply
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
160846 LER NO.:
80-010 Rev.
1 DATE OF LER:
March 20, 1980 DATE OF EVENT:
February 26, 1980 SYSTEM INVOLVED:
Nonnuclear instrumentation COMPONENT INVOLVED:
24 V dc power supply CAUSE:
A combination of misaligned connector pins on printed circuit boards and a technician working on saturation meter circuit utilizing these boards resulted in loss of the power SEQUENCE OF INTEREST:
Loss of NNI-X power supply ACTUAL OCCURRENCE:
Failure of nonnuclear instrumentation power supply, reactor trip, turbine trip, and engineered safeguards actuation REACTOR NAME:
Crystal River Unit 3 DOCKET NUMBER:
50-302 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
825 MWe REACTOR AGE:
3.1 years VENDOR:
Babcock & Wilcox ARCHITECT-ENGINEERS:
Gilbert Associates OPERATORS:
Florida Power Corporation LOCATION:
7 miles NW of Crystal River, Florida DURATION:
N/A PLANT OPERATING CONDITION:
100% power TYPE OF FAILURE:
Inadequate performance; made inoperable DISCOVERY METHOD:
Operational event COMMENT: