ML17252B027

Letter Reporting a 08/12/1972 Occurrence of Two of Eight Electrohydraulic Control (EHC) Oil Low Pressure Scram Switches Setpoints Drifting Beyond the Technical Specifications - Dresden Units 2 and 3

ML17252B027
Person / Time
Site:	Dresden
Issue date:	08/23/1972
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
Download: ML17252B027 (2)

Text

ONE FIRST NATIONAL PLAZA *CHICAGO. ILL.:(NOIS. __ -

Address Reply to' P 0 ST 0 FF ICE B0 X 7 6 7

• CH I.CA G 0, ILL IN 0 IS 60 69 0 Dresden Nuclear Power Station R. R. 111 I]. .l.C'fttt':IES-~

Mr. A. Giambu_sso . .. . . .

- Deputy Director for* Reactor Projec Directorate of Licensing U. s. Atomic Energy Commission Washington, D.C. 20545

Subject:

- Licenses DPR-19 and *nPR-25, Dresden Nuclear Power Station Units 2 and 3, Section 3.1 of the Technical Specifications

Dear Mi:

'. Giambusso:

This is.to report a con~ition relating to the operation of Units 2 and 3, in which on August p, 1972, two of the eight "electrohydraulic control (EHC) oil low pressure: scram switches" setpoints drifted beyond the setpoints established in the Technical Specifications.

As reported in our letter of July 27, 1972, it was found that during July's routine calibration of the EHC switches (required every three months by Technical Specification Table 4.1.2) six of th~ C:!ight subject switches setpoints were found to have drifted beyond the setpoir,t

.of 900 psig decreasing. As part of the investigative proceedings, all of the EHC switches were calibrated this month rather than just functionally checked as required by the Technical Specifications (once per month -

Technical Specification Tabl_e l~.1.1). As a result of this calibration one switch on Unit ff2 was found* t() have drifted to 885 psig, and one switch on Unit #3 drifted to 884 psig.

INVESTIGATION All of the EHC switch internals were inspec*ted l.ast month and revealed that one switch had slight internal leakage, while the other*

seven switches displayed no abnormalities. A similar inspection this month of the two subject switches revealed no abnormalities.

-2..: , August 23, 1972 The leaking switch has be~n replaced with a certified Barksdale Co. model TC-9622-2 switch with a setpoint range of 250-1500 psig versus the original Barksdale model TC-9622-3 with a setpoint range of 250-3000 psig. 'Tilis new switch is being observed for setpoint drift and accuracy *.

CORRECTIVE. ACTION.

The two switches on Unit 112 and Unit 113 were recalibrated for 910 psig and 908 psig respectively; they are not considered to be failures

. as they remained within the instrument scale accuracy of +/- 1% corresponding to + 30 psi..

The replaced switch. has been s.ent back. to the manufacturer for evaluation. If the new 250-1500 p~igswitchproves to. have better appli-cability to the system, all of the, -remaining* switches will be replaced with this device.

Sincerely,

_ W. P. Worden Superintendent WPW~sds