ML20156A220
| ML20156A220 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/04/2020 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1981-021-00 | |
| Download: ML20156A220 (5) | |
Text
PRECURSOR DESCRIPTION AND DATA NSIC Accession Number:
167611 Date:
June 30, 1981
Title:
Inadvertent Spray Initiation and Draining of Reactor Coolant System at Sequoyah 1 The failure sequence was:
- 1.
The unit was in cold shutdown on RHR train and preparing to bring RHR train B on line.
- 2.
To effect this, the unit operator sent an assistant unit operator (AUO) to open locally operated valves 1-HCV-74-37 and 531.
Because the RHR containment spray valve 1-FCV-72-40 had been tested for operability earlier in the day, the auxiliary unit operator was also instructed to check it for closure.
- 3.
A later telephone conversation between the unit operator and aux-iliary unit operator apparently confused the AUO regarding the valves to be opened, and he opened all three valves which resulted in initiation of containment spray.
- 4.
The RCS began to blow down through the B RHR train and spray line to the containment.
- 5.
RCS pressure and pressurizer level decreased rapidly.
- 6.
The operators, believing a LOCA had possibly occurred, tripped the operating RC pumps.
- 7.
The containment was evacuated.
- 8.
Standard emergency (LOCA) procedures were implemented:
- a.
containment purge was terminated,
- b.
the charging pumps were aligned to the RWST,
- c.
RHR suction valve to the RWST was opened.
- 9.
Pressurizer level began to increase.
- 10. Forty three minutes after the event began, the operators learned that the AUO had opened the spray valves and verified its being open from the control board indicators.
The valve was closed and the RCS stabilized.
- 11.
During the event, approximately 105,000 gallons of water had been sprayed into the containment; 40,000 gallons from the RCS and 65,000 gallons from the RWST.
Corrective action:
An extensive initial investigation subsequently resulted in the following actions:
- 1.
In order to clarify the duties and responsibilities of the shift employees including the shift engineer, the structure of the operating shift was revised and issued.
The general responsibilities and authorities of each position are described in the job description provided to the individuals when they are appointed, to the position.
Administrative Instruction AI-2 has been revised to describe the responsibilities and authorities of each operating station.
- 2.
In order to improve communications between shift personnel and between shift personnel and management, clearer lines of communica-tion were provided between operating positions within a shift as well as between operating shifts and other sections by revising the shift structure, clarifying the communication paths, establishing work location routines, improving the maintenance of telephones, and investigating additional or different radio communications.
- 3.
The environment in the main control room was improved by closer supervision and compliance with established policies regarding con-duct, access, and housekeeping.
- 4.
The Assistant Superintendent and Operations Supervisor met with each shift crew before restart to emphasize the conduct required by AI-2.
These discussions stressed clear communications, control room atmosphere, authorities and responsibilities of operating personnel, and status control of safety-related systems.
Discussions were also held with all key supervisors emphasizing the requirements to keep the shift engineer informed of work in progress and his responsibility to keep control of activities affecting safety.
- 5.
An in-plant on-the-job training and certification system of non-licensed operating personnel was established.
- 6.
All future nonlicensed operating employees will, upon assignment to Sequoyah, receive on-the-job break-in training and examinations before assuming responsibility for any job position.
A Sequoyah Standard Practice describing this break-in was issued and implemented.
- 7.
In order to ensure that only qualified employees are assigned to perform functions that can affect the safety of operations, TVA evaluated nonlicensed operating employees, specifically the assistant unit operators and fourth-period student operators, to determine each individual's qualifications and competence in regard to performing operating functions that can affect the safety of operations.
The result of this evaluation is a qualification status list which reflects the spectrum of nonlicensed operating personnel's operating experience at Sequoyah.
This list will be used to fill vacant shift positions.
Design purpose of failed system or component:
The spray system provides water to the containment atmosphere for containment depressurization and radionuclide scavenging.
The RHR system provides core cooling during plant shutdown.
Reactor at Assistant unit After opening Rapid RCS Charging Spray cold shutdown operator sent RHR valves, pressure and pumps valve with RHR to open RHR AUO opened pressurizer aligned to discovered train A in train B valves spray valve level decrease RWST; RHR opened and operation 1-HCV-74-37 and in lieu of results in suction closed
-531 to prepare checking it initiation of valves to for starting closed, ini-LOCA emergency RWST train B and tiating con-procedure opened to check closed tainment spray containment through RHR spray valve system I 1-FCV-72-40 I
I
_II Potential Severe Core Damage No N
No -
A Plant in cold shutdown and sump recirculation capability available A
Possible -
if RCS drained and core cooling not eventually restored Possible -
if RCS drained and core cooling not eventually restored A
No
-No NSIC 167611 -
Actual Occurrence for Inadvertent Spray Initiation and Draining of Reactor Coolant System at Sequoyah 1
Reactor Containment RHR Pumps LOCA Procedures Spray Charging Recently Spray Valve Continue Initiated; Valve Pumps Placed in Inadvertently to Operate Charging Pumps Found Provide RHR Follow-Opened in After Loss Aligned to RWST Opened Adequate ing Shutdown Lieu of of NPSH and Started, and RCS Makeup From Power Checking Following RHR RWST Closed Closed RCS Depres-Isolation surization Valves I Opened Potential Severe Core Damage Sequence No.
No No Yes No No Yes No Yes No NSIC 167611 -
Sequence of Interest for Inadvertent Spray Initiation and Draining of Reactor Coolant System at Sequoyah 1
CATEGORIZATION OF ACCIDENT SEQUENCE PRECURSORS NSIC ACCESSION NUMBER:
167611 LER NO.:
81-021 Rev.
1 DATE OF LER:
June 30, 1981 DATE OF EVENT:
February 11, 1981 SYSTEM INVOLVED:
Residual heat removal and containment spray COMPONENT INVOLVED:
Spray isolation valve CAUSE:
Operator error SEQUENCE OF INTEREST:
Small break LOCA while on RHR ACTUAL OCCURRENCE:
Inadvertent spray initiation and RCS draining REACTOR NAME:
Sequoyah 1 DOCKET NUMBER:
50-327 REACTOR TYPE:
PWR DESIGN ELECTRICAL RATING:
1128 MWe REACTOR AGE:
0.6 year VENDOR:
Westinghouse ARCHITECT-ENGINEERS:
Tennessee Valley Authority OPERATORS:
Tennessee Valley Authority LOCATION:
9.5 miles NE of Chattanooga, Tennessee DURATION:
N/A PLANT OPERATING CONDITION:
Cold shutdown TYPE OF FAILURE:
Made inoperable DISCOVERY METHOD:
Operational event COMMENT: