Information Notice 1986-48, Inadequate Testing of Boron Solution Concentration in the Standby Liquid Control System
| ML031220694 | |
| Person / Time | |
|---|---|
| Issue date: | 06/13/1986 |
| From: | Jordan E NRC/IE |
| To: | |
| References | |
| IN-86-048 | |
| Download: ML031220694 (4) | |
118 ORIGINAL SSINS No.: 6835 IN 86-48 UNITED STATES RECEIVED
NUCLEAR REGULATORY COMMISSION Bart D. Withers
OFFICE OF INSPECTION AND ENFORCEMEN Vice President, Nuclear
WASHINGTON, D.C. 20555 IJL!N, 3 1986 Route To:,
June 13, 1986 ________
IE INFORMATION NOTICE NO. 86-48: INADEQUATE TESTING OF BORON SOLUTION
CONCENTRATION IN THE STANDBY LIQUID
CONTROL SYSTEM
Addressees
All boiling water reactor (BWR) nuclear power facilities holding an operating
license (OL) or a construction permit (CP).
Purpose
This notice is to alert recipients to a potentially significant problem that
has been observed with the sampling and testing of the sodium pentaborate
solution concentration in the standby liquid control system (SLC) at several
BWR nuclear power plants. It is expected that recipients will review the
information for applicability to their facilities and consider action, if
appropriate, to preclude a similar problem at their facilities. However, suggestions contained in this information notice do not constitute NRC require- ments; therefore, no specific action or written response is required.
Description of Circumstances
Review of licensee event reports (LERs) over the past several years indicates
continuing problems in maintaining volume and concentration of the solution
within Technical Specification (TS) limits. Inspections have also revealed
inadequate preoperational testing which failed to prevent operational problems
with concentration. Several of the problems caused plants to initiate shut- downs as required by TS limits. Usually, the proper level and concentration
was recovered in less than 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> but in one case recovery took twice that
time. Values both lower and higher than the TS requirements were reported.
Low boron concentration or low tank level reduces protection against an
anticipated-transient-without-scram (ATWS) event due to reduced negative
reactivity worth of the boron solution. High boron concentration increases the
risk of forming crystals of boron that could render the system inoperable.
However, none of the LERs or inspections reported situations in which the SLC
would be rendered inoperable by boron crystallization or not capable of shut- ting down the reactor as required.
Discussion:
Eight LERs reported boron solution concentration too low (ranging from 94 percent to 99 percent of the TS limit) while 6 reported concentration too high
Copies to: Withers, Yundt, Lentsch, Orser, Steele, E. Burton, E. Jordan, A. Holm, LIS, C. A. Olmstead, S. Hoag, S. Sautter, TNP:GOV REL F:NRC CHRONO,
TNP:GOV REL F:NRC IE Information Notice 86-48 PGE OAR Action - M. H. Malmros
-, - A "No OAR to be issued - Applicable to BWR's only"
IN 86-48 June 13, 1986 (ranging from 100.1 percent to 106 percent of the TS limit). The causes
reported included incorrect tank levels, inadequate accounting for system
leakage, inadequate accounting for the specific gravity of sodium pentaborate, inferred loss of boron, and increased water evaporation rate with increased
solution temperature. The problems of tank level measurement and mixing and
testing procedures are discussed below in more detail.
Storage Tank Level
At LaSalle 2, NRC inspection revealed that the operations group and the
chemistry group used 3 different methods to measure the tank level and
results were in frequent disagreement. In some instances, the disagreement
was as large as 200 gallons (about 4 percent). The 3 methods involved
level meter readings, sight glass readings, and readings of a measuring
tape attached to a plumb bob. As a corrective measure, the licensee is
sr-cifying the use of tne last m because it is apparently the most
reliable method.
At Susquehanna 2, level was reported to be 8 percent less than the TS
requirement (about 17 percent error in volume). Level was measured using
a steel tube from which air bubbles continuously exited near the bottom of
the tank and tank level was inferred from the air pressure. This approach
was rendered inaccurate by tube blockage built up by the alternate wetting
and drying of the tip of the tube. The licensee modified this system for
periodically cleaning the tube with a brush and Is establishing an addi- tional alternative method of level measurement using an ultrasonic device.
Mixing
Over the course of 3 inspections of preoperational testing of the SLC at
LaSalle, Perry, and Clinton, the NRC has identified apparent noncompliance
related to whether the SLC can generate a uniform solution. The involved
licensees did not adequately meet their commitment to implement Regulatory
Guide 1.68, "Initial Test Programs for Water-Cooled Nuclear Power Plants."
In particular, the air sparger subsystem was not tested properly. Also, the sampling methodology (dip samples were or might be taken from near the
liquid surface at these plants) necessary to satisfy surveillance require- ments of TS was not demonstrated to yield valid results.
Concerning preoperational testing of the SLC, Appendix A of Regulatory
Guide 1.68 gives in part:
(3) Standby Liquid Control System Tests. Demonstrate proper operation
of the system with demineralized water. Verify proper mixing of
solution and adequacy of sampling system. . . .
Verify operability of. . . air spargers. . .
The testing observed consisted of filling the solution tank with deminer- alized water, commencing air flow through the sparger, and verifying that
IN 86-48 June 13, 1986 the distribution of air bubbles was even. This procedure does not demon- strate uniform mixing of the solution and it does not determine what sparging
time is required to ensure that dip samples represent the tank's contents.
The sodium pentaborate solution stratifies over time. Because TS surveil- lance tests are performed on a monthly basis, the solution may not be wella
mixed at the time of the test. If the solution is not adequately mixed, sample will be unrepresentative of the tank's contents. This may lead to
accepting the inferred concentration erroneously or diluting or strength- be
ening the solution erroneously and thus allowing the concentration to
outside the TS requirement.
The licensees at LaSalle, Perry, and Clinton have found that an adequate
way to verify proper mixing is to initially fill the tank to the concen- tration required by the facility's TS, allow a settling period equal toof
the maximum allowed time between surveillances, and apply air sparging
the solution at a given rate with periodic axial sampling until theprede- difference in concentration between the axial samples is within a
termined variance (e.g., twice the sampling accuracy). The cumulative
time
sparging time that yields this variance then is the minimum spargingrate.
to be used for all future surveillances for the specified sparging
Any decrease from the sparging rate used in the above test would necessi- tate retesting to determine an acceptable sparging time.
For those plants past the preoperational test phase, if the original TS
testing performed on the SLC air sparger subsystem was inadequate, the
surveillance tests may not be yielding valid results.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Jdwaorn D r
Division of Emergency Preparedness
and E gineering Response
Office of Inspection and Enforcement
Technical Contacts: Vernon Hodge, IE
(301) 492-7275 Roger D. Lanksbury, RIII
(312) 790-5579 Attachment: List of Recently Issued IE Information Notices
t I
4.
Attachment 1 IN 86-48 June 13, 1986 LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information Date of
Notice No. Subject Issue Issued to
86-47 Feedwater Transient With 6/9/86 All BWRs and PWRs
Partial Failure Of The facilities holding
Reactor Scram System an OL or CP
86-46 Improper Cleaning And Decon- 6/12/86 All power reactor
tamination Of Respiratory facilities holding
Protection Equipment an OL or CP and
fuel fabrication
facilities
86-45 Potential Falsification Of 6/10/86 All power reactor
Test Reports On Flanges facilities holding
Manufactured By Golden Gate an OL or CP and
Forge And Flange, Inc. research and test
facilities
86-44 Failure To Follow Procedures 6/10/86 All power reactor
When Working In High Radiation facilities holding
research and test
reactors
86-43 Problems With Silver Zeolite 6/10/86 All power reactor
Sampling Of Airborne Radio- facilities holding
86-42 Improper Maintenance Of 6/9/86 All power rector
Radiation Monitoring Systems facilities holding
86-41 . Evaluation Of Questionable 6/9/86 All byproduct
Exposure Readings Of Licensee material licensees
Personnel Dosimeters
86-32 Request For Collection Of 6/6/86 All power reactor
Sup. 1 Licensee Radioactivity facilities holding
Measurements Attributed To an OL or CP
The Chernobyl Nuclear Plant
Accident
OL = Operating License
CP = Construction Permit