United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 77-04: Calculational Error Affecting The Design Performance of a System For Controlling pH of Containment Sump Water Following a LOCA

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

                             November 4, 1977  

                                                         IE Bulletin 77-04 

CALCULATIONAL ERROR AFFECTING THE DESIGN PERFORMANCE OF A SYSTEM FOR 
CONTROLLING pH OF CONTAINMENT SUMP WATER FOLLOWING A LOCA 

Description of Circumstances: 

On September 29, 1977, the Baltimore Gas and Electric Company reported that 
for Calvert Cliffs Unit 1 and Unit 2, the amount of trisodium phosphate 
dodecahydrate (TSP) specified in the technical specifications may not be 
sufficient under all operating conditions to perform its intended design 
function. 

The TSP is used to control the pH of the containment sump water following a 
LOCA in order to reduce the probability of chloride stress corrosion 
cracking leading to equipment failure or,loss of containment integrity and 
to ensure low volatility of dissolved radioiodines. At Calvert Cliffs, 
the,TSP is stored in three dissolving baskets located on the lowest level of 
the containment. Original design specifications (FSAR) required a sufficient
quantity of TSP to raise the pH of the sump water to approximately 7.0. The 
more recent guidance provided by the Standard Review Plan (SRP) states that,
for Post Accident Chemistry, the optimum pH control consists of stabilizing 
pH between 7 and 8 within four hours. 

For the Calvert Cliffs facilities, the quantity of TSP required to meet the 
FSAR design specifications was initially calculated to be 75 cubic feet. 
However, these calculations were not based on maximum boron concentrations 
and water volumes permitted by the technical specifications for the 
containment sump water sources, e.g., Refueling Water Tank (RWT), Safety 
Injection Tanks (SIT), Boric Acid Tanks (BAT) and the Reactor Coolant System
(RCS). Revised calculations indicated that the quantity of TSP required to 
meet design specifications under worst case conditions was approximately 82 
cubic feet. 


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IE Bulletin 7704                                         November 4, 1977 

As a result, administrative controls have been implemented at the Calvert 
Cliffs facilities to limit the maximum boron concentration in the RWT and 
SITs to 2200 ppm. The minimum boron concentration specified in the technical
specifications will still apply. Although the problem described above 
occurred at a facility utilizing TSP for pH control of containment sump 
water, this problem may be applicable to facilities utilizing different 
methods of pH control of containment sump water e.g., sodium hydroxide 
(NaOH). This would be the case if chemical requirements for pH control were 
based on values less than the maximum values for boron concentrations and 
water volume permitted by the technical specifications for the containment 
sump water sources. 

Action to be Taken by Licensees and Permit Holders: 

For all PWR Power Reactor Facilities with an operating license or a 
construction permit: 

1.   If your facility utilizes or plans to utilize a system for pH control 
     of containment sump post LOCA solution, describe what action you have 
     taken or plan to take to assure that the system design specifications 
     will be met for all operating conditions permitted by the technical 
     specifications, as applicable to the containment sump water sources. 

2.   Report in writing within 45 days for facilities with an operating 
     license and within 60 days for facilities with a construction pe mit, 
     your plan of action and schedule with regard to Item I. Reports should 
     be submitted to the Director of the appropriate NRC Regional Office and
     a copy should be forwarded to the NRC Office of Inspection and 
     Enforcement, Division of Reactor Operations Inspection, Washington, D. 
     C. 20555. 

Approved by GAO, B180225 (R0072); clearance expires 7-31-80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

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