ML20206T444
| ML20206T444 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 05/26/1989 |
| From: | Hodges M Office of Nuclear Reactor Regulation |
| To: | Berkow H Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20206S598 | List: |
| References | |
| FOIA-99-28 NUDOCS 9902110382 | |
| Download: ML20206T444 (2) | |
Text
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MEMORANDUM FOR:
H. Berkow, Project Director Project Directorate II-2
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Division of Reactor Projects I/II FROM:
M. Wayne Hodges, Chief Reactor Systems Branch Division of Engineering & Systems Technology
SUBJECT:
CRYSTAL RIVER REACTOR VESSEL LEVEL INDICATION SYSTEM 4
(RVLIS)
REFERENCE:
Letter, W. C. Stewart (Virginia Electirc and Power Co.) to g
USNRC, Serial No.87-507, dated October 8, 1987.
.R Florida Power has recently questioned the staff about the usefulness of RYLIS and proposed not to include RVLIS in the Crystal River Technical Specifications or procedures. The Reactor Systems Branch reiterated our strong belief that RVLIS is a very useful instrument and that Technical Specifications and procedures are required for RYLIS.
k The addition of a reactor coolant inventory system will improve the reliability of plant operators to diagnose the approach of ICC and to assess the adequacy of responses taken to restore core cooling. The benefit will be preventive in nature in that the instrumentation will assist the operator in avoidance of a degraded or melted core when voids in the reactor coolant system and saturation conditions result from over cooling, steam generator 4
g tube rupture, and small break loss of coolant events. The addition of a reactor coolant inventory system, coupled with upgraded in-core thermocouple instruments and a subcooling margin monitor, provides an ICC instrumentation package which could reduce significantly the likelihood of incorrect operator diagnosis and errors for events such as steam generator tube ruptures, loss of instrument bus or control system upsets, pump seal failures, or overcooling events originating from disturbances in the secondary coolant side of the plant. For low probability events, involving coincidental multiple faults or more rapidly' developing small break LOCA conditions, the ICC instrumentation could also reduce the probability of incorrect operator diagnosis and subsequent errors leading to a degraded core.
The staff also cautions the licensee about the difficulty in using the probabilistic risk assessment of a loss of inventory event to show the benefits of RVLIS.
It is very important that such an assessment be properly adjusted to include the incremental improvement which might result from the inclusion of RVLIS. For example, if it is assumed that RVLIS does not provide any new infomation but only redundant to existing information or if RVLIS is not fully utilized in procedure for a given scenario, such a scenario would be virtually unaffected by the addition of RVLIS. Such an assumption gives no credit for early detection of ICC with vessel water level indication and the
Contact:
G. Schwenk, SRX8 x20878 KELLY 99-28 PDR
- h 99021103s2 990203 PDR FOIA
e H. Berkow 2-corresponding potential for corrective operator action or for benefits for using RVLIS when the other instruments give failed or misleading readings.
It is also important to recognize that the staff believes thatJwing able to ascertain re. actor water level is of funCamental importance as a safeguard in dealing with beyond design bases events end potential sequences which have not been previously considered or analysed.
The staff also believes that it is important that RVLIS be fully utilized in the plant procedures and will review l
this area in depth during our review of the Babcock & Wilcox Owners Group l
Abnormal Transient Operating Guidelines.
RVLIS has already been shown to be a useful instrument in operating reactors.
For example, at North Anna Unit 1 (Reference 1) during the time frame between June.17, 1987,and June 21, 1987, approximately 17,000 gallons of RCS inventory was removed from the Reactor Coolant System (RCS). The pathway for the loss was through the pump backseat of the "A" Reactor Coolant Pump (RCP), up the shaft, and out through the seals into the containment sump. The pump had been decoupled from the motor for stator replacement. The inventory loss was not detected because the pressurizer had been allowed to cool down and go into a vacuum and a bubble had formed in the reactor vessel head.
In this condition, pressurizer level indication did not provide an adequate representation of RCS inventor Indication was available via the Reactor Vessel Level Indication System (y.RYLIS) portion of the Integrated Core Cooling Monitoring (ICCM) System l
which had been installed during the refueling outage. Even though the RVLIS I
had not been declared operational and operator action to terminate the condition was not taken based on that information, it did alert the operators l
and action was finally taken when vacuum in the pressurizer was also detected. At that time RVLIS was used to trend the vessel level during ventino of the reactor head and rystem refill.
The staff has also identified other design basis events where RVLIS (if it had been installed) could have resulted in better operator response. These included a natural circulation cooldown event with a bubble in the vessel head at St. Lucie 1 and a Steam Senerator Tube Rupture event with a bubble in the reactor vessel head even thwgh there was continued indication of adequate i
subcooling margin at Ginna.
- h. Wayne odges, Chief Reactor Systems Branch Division of Engineering & Systems Technology H. Silver (14H-22))
cc:
S. Newberry (7E-12 R. Jones M. Lyon i
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