United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-48: Inadequate Testing of Boron Solution Concentration in the Standby Liquid Control System

                                                          SSINS No.: 6835  
                                                          IN 86-48         

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                                June 13, 1986

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 
requirements; 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 hours 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 shutting 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  


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                                                            IN 86-48 
                                                            June 13, 1986 
                                                            Page 2 of 3 

(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 specifying the use of the last method, 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 additional 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 requirements 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 
     demineralized water, commencing air flow through the sparger, and 
     verifying that  
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                                                            IN 86-48 
                                                            June 13, 1986 
                                                            Page 3 of 3 

     the distribution of air bubbles was even. This procedure does not 
     demonstrate 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 
     surveillance tests are performed on a monthly basis, the solution may 
     not be well mixed at the time of the test. If the solution is not 
     adequately mixed, a sample will be unrepresentative of the tank's 
     contents. This may lead to accepting the inferred concentration 
     erroneously or diluting or strengthening the solution erroneously and 
     thus allowing the concentration to be 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 concentration required by the facility's TS, allow a settling 
     period equal to the maximum allowed time between surveillances, and 
     apply air sparging of the solution at a given rate with periodic axial 
     sampling until the difference in concentration between the axial 
     samples is within a predetermined variance (e.g., twice the sampling 
     accuracy). The cumulative sparging time that yields this variance then 
     is the minimum sparging time to be used for all future surveillances 
     for the specified sparging rate. Any decrease from the sparging rate 
     used in the above test would necessitate retesting to determine an 
     acceptable sparging time. 

     For those plants past the preoperational test phase, if the original 
     testing performed on the SLC air sparger subsystem was inadequate, the 
     TS 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. 


                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contacts: Vernon Hodge, IE 
                    (301) 492-7275 

                    Roger D. Lanksbury, RIII 
                    (312) 790-5579 

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