ML20209E199

Submits Status Rept Re Natural Circulation Boron Mixing Test.Ss Diab Will Witness Test at San Luis Obispo,Ca Scheduled for 850329.Trip Rept & Seminar Re Observations Will Be Prepared

ML20209E199
Person / Time
Site:	05000000, Diablo Canyon
Issue date:	03/25/1985
From:	Diab S Office of Nuclear Reactor Regulation
To:	Sheron B Office of Nuclear Reactor Regulation
Shared Package
ML082410749	List: ML20209A984 ML20209B531 ML20209B624 ML20209B724 ML20209B847 ML20209B894 ML20209C131 ML20209C225 ML20209C292 ML20209C320 ML20209C516 ML20209C643 ML20209C669 ML20209C675 ML20209C698 ML20209C705 ML20209C710 ML20209C715 ML20209C720 ML20209C836 ML20209C847 ML20209C848 ML20209C876 ML20209C881 ML20209C908 ML20209C921 ML20209C969 ML20209C975 ML20209C981 ML20209C993 ML20209D004 ML20209D012 ML20209D018 ML20209D030 ML20209D038 ML20209D044 ML20209D045 ML20209D071 ML20209D089 ML20209D114 ML20209D127 ML20209D130 ML20209D135 ML20209D139 ML20209D146 ML20209D154 ML20209D211 ML20209D218 ML20209D230 ML20209D235 ... further results
References
FOIA-86-197 TAC-51638, NUDOCS 8504080337
Download: ML20209E199 (2)

Text

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MEMORANDUM FOR:

Brian W.'Sheron, Chief f

Reactor; Systems Branch, DSI I

THRU:

Ledyard'B. Marsh, Section Leader Section'D Reactor Systems Branch, DSI 3

l FROM:

Sammy S. Diab, Section D l

Reactor; Systems Branch, DSI e

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SUBJECT:

-.3 DIABLO CANYON UNIT 1 - STATUS OF THE NATURAL CIRCULATION BORON MIXING TEST, This is a status report intended ',o document some last minute information obtained about the Diablo Canyon dnit 1 Natural Circulation Test.

This will aid to maintain the continuity of staff review of the test after it has been conducted.

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I have recently' completed review of the Diablo Canyon Unit 1 Natural Circulation Baron Mixing test procedure No. 42.7, and the Natural Circulation Pretest Report (menc from B.' Sheron to G. Knighton, tiarch 14,vl985).

During that review two RSB cc.ncerns required extensive resolution effort.

These two concerns are related to:

(a) the method of boration chosen to demonstrate the plant's capability to borate the reactor coolant to the cold shutdown concentration, and (b) the reactor coolant pumps (RCPs) delayed trip after the reactor has been tripped.

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In relation to the first item (a) above, the licensee will attempt to demonstrate coron mixing'under natural circulation (NC) conditions.

Given the test results, the licensie should demonstrate that the reactor can be borated to the cold shutdown concentration using only safety related boron sources and flow paths.

The licensee should consider the potential change in mixing rate that results from the reactor water cooldown.

In~ relation to item (b),.since the staff's objective is simulation of RCS temperatures including those in thfucper head region, we have accepted a delayed RCPs trip subject to some procedural changes (see memo, Sheron to Knighton, March 14,1985).

The licensee accepted to implement such changes.

Therefore, we concluded that the test procedure is acceptable as revised.

However, after cur memo was drafted, the licensee informed us that 6 of the 11 magnetically attached head thermocouples became inoperable.

Of the remaining 5, two are attached on reactr>rfvessel head (RVHA st':ds..

Therefore, only.3 TCs are expected to provide RVH, surf ace temperature simulation.

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B. Sheron.

Since the licensee plans to utilize the control rod drive mechanism (CRDM) fans to cool the RVH surface throughout high temperature operation (for upper head temperature > 350*F), and since these fans are not safety related it is important that measurements be made to determine the effects on the reactor -

coolant system if these fans were not available, as required by RSB 5-1.

One approximate, but adequate, way to determine the heat removal rate due to the operation of the CRDM fans can be obtained by measuring the temperatures both inside the upper head region and on the RVH surface during the cooldown.

The failure mechanism of the magnetic RVH TCs as explained by the licensee appears to be caused by system vibrations leading to damage in signal transmission lines, i.e. a common mode failure.

After these findings, I held several discussions with the licensee's representatives to assess the situation.

The alternatives discussed were as follows:

(a) Repair the 11 TCs, or 4

(b)If any of the crucial 3 TCs are failed prior to, or during the Diablo

' Canyon Unit 1 NC test so that insufficient information was available, e

measurements should be planned on Unit 2 to provide similar information.

Since 3 TCs remain operable the licensee chose to pursue alternative (b).

The licensee proposed to obtain such measurements during the precriticality testing at Unit 2 with RCPs running, i.e. forced flow with TCs magnetically attached on the-RVH, surface and non inside the upper head region. The licensee argues that with' forced flow the core exit temperature would provide an adequate indirect indication of the upper head region temperature.

I indicated to the. licensee that the validity of his argument was not obvious and if such an argument is not substantiated the staff will require measurement of the upper head temperatures directly.

I plan to witness the test at San Luis Obispo, California, scheduled for Friday March 29, 1985.

After the test I will write a trip report noting my observations about the test.

I will also be prepared to hold a seminar for the branch if'there is suffficient interest.

J Sammy S. Diab, Section D Reactor Systems Branch Division of Systems Integration cc:

C. Liang RSB Sections Leaders R. Bernero D. Langford R. W. Houston l

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