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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