ML19319B945

Safety Evaluation Supporting Revision of Tech Spec 3.4.2 to Commit to Operability Decay Heat Removal Sys Pressure Relief Valve DH-4849 & to Remove Control Power from DH-11 & DH-12 When Open to Assure Overpressure Protection of RCS

ML19319B945
Person / Time
Site:	Davis Besse
Issue date:	03/20/1978
From:	TOLEDO EDISON CO.
To:
Shared Package
ML19319B942	List: ML19319B941 ML19319B944 ML19319B945
References
NUDOCS 8001290682
Download: ML19319B945 (1)

Text

~

DB-1 SAFETY EVALUATION To provide the reactor coolant system (RCS) overpressure protection when

, the RCS temperature is less than 280 F,0 DH-ll and DH-12 are open and the valve operator control power removed to provide assurance that pres-sure relief capacity is available using the relief valve on the decay heat removal (DHR) system. The interlock in the pressurizer heater control circuit prevents the pressurizer heaters from being energized when DH-ll or DH-12 are opened and the RCS pressure is above the set-point which automatically closes DH-11 and DH-12. This prevents pres-surization of the RCS above the interlock setpoint if DH-il or DH-12 is closed and the control power has been inadvertently left off from the other valve. This pressurizer interlock was described in a letter to the NRC, dated April 7, 1977.

The removal of the control power from DH-ll and DH-12 after they are opened assures that these valves will remain open, providing overpressure protection to the RCS through the DHR relief valve. This control power removal also prevents damage to both decay heat pumps due to the inad-vertent closure of either DH-il or DH-12. The circuit for the removal of control power from the control room will be similar to that for DH-1A and DH-1B as shown on drawing No. 7749 E52B, sheet 60A and 60B. An alarm is actuated when DH-11 is opened and has control power to the motor operator. A second alarm is provided similarly for DH-12.

The trip setpoint and allowable valve for the decay heat isolation valve and pressurizer heaters are <438 psig and4 443 psig, respectively.

Referenced to the centerline of valves DH-11 and DH-12. Table 3.3-3 and the Associated Action Statements Nos. 12 and 13 Table 4.3-2, Table 3.3-4 and Surveillance requirement 4.5.2d need to be revised to reflect these new setpoints and functions. These technical specifica-tion limits assure that even with the total possible instrument string drift and inaccuracies of 51 psi, the DHR system will be isolated from the RCS before the design overpressure of the DHR system is reached.

With the above instrumentation, the requirement that both decay heat removal pumps not be operated si=ultaneously can be modified. License condition 2.C(3)(j) can ce deleted and page 3/4 4-2 of technical specific-ations can be modified by deleting " decay heat removal pump switch oper-ations", and consitting to not operating more than one decay heat removal pump with their sole suction flow path through DH-il and DH-12 unless the control power has been removed from the DH-ll and DH-12 valve operators, or manual valves DH-21 and DH-23 are opened.

Specification 3.4.2 should be changed to co=mit to operability of the i decay heat removal system pressure relief valve DH-4849 and to removal of control power from DH-il and DE-12 when they are open to assure the overpressure protection of the RCS. The pressurizer code safety valve is no longer required operable in modes 4 and 5 so this requirement can l be deleted. I l

I ks e/9 l l

go o l c24 OGM