ML17252A271

Transmittal of Reportable Occurrence Report No. 50-249/1977-9

ML17252A271
Person / Time
Site:	Dresden
Issue date:	04/21/1977
From:	Stephenson B Commonwealth Edison Co
To:	Kappler J NRC/RGN-III
References
50-249/1977-9
Download: ML17252A271 (3)

Text

Commonwe4t Edison Dresden Nuclear Power Station R.R. #1 Morris, Illinois* 60450 Telephone 815/942-2920 BBS Ltr. # 334 April 21, 1~77 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operation - Region JI I U. S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, 111 inois 60137 Enclosed please find Reportable Occurrence report number 50-249/1977-9.

This report is being submitted to your office in accordance with the Dresden Nuclear Power Station Technical Specifications, Section 6.6.B.

Stephenson tation Superintendent Dresden Nuclear Power Station BBS:skm Enclosure cc:

Director of Inspection & Enforcement Director of Management Information & P~ogram Control Fi 1 e/NRC APR 2 G 1977

L l1

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.. *CONTROL BLOCK: l 1

LICENSE.E EVENT REPORT 91 I I I I

• .dASE PRINT ALL REQUIRED INFORMATION) 6 LICENSEE UC EN SE EVENT NAME LICENSE NUMBER TYPE TYPE

~I I I LI 0 1 '-~

11135 1 31 I 01 ° 1.:... I 0 I 0 I 0 I 0 I 0 1-1° I 0 I.14 *1 1 11 I 1 I 1 I I 0 1 11 7

89 14 15 25 26 30

31 32 CATEGORY REPORT.

REPORT*

TYPE SOURCE DOCKET NUMBER EVENT DATE REPORT DATE

@TI]coN'T I I I L!J L!:J I 01 s 1 o 1~1 o 12 14 I 9 I I 0 I 4 1 1 I o I 71 7 I I 01 4j 212117 17 I 1 * *0 57 58 59 60 61 68 69 74 75 80 EVENT DESCRIPTION

[filfil I During control rod withdrawal operations at approximately 44% power, the unit 7

8 9 lo131 I 013erato.r discovered that Rod Block Monitor (RBM) channels 7 and 8 were automatically 81 7 8 9!:-'.---------------------------------~....;._----------__.J*

lol41.!;l __

.b_y.;..p_a~s_s_e~d=-a_n_d_i_n_d_i_c_a_te_d_

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1_

1

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__ r_c_o_n_t_r_o_l_r_o_d_s_w_e_re_t_h_e_n_s_e_l,....e_c_t_e_d_t_.o_c_h.,...e_c_k_t_h_e_f:..,.u_n_c_t.:....* i-'o_n_i_n_g--

8

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s_Jl 7

8' 9 PRIME.

(continued) 80

. SYST.EM CAUSE COMPONENT.

COMPONENT COOE

.. COOE COMPONENT CODE SUPPUER MANUFACTURER VDLATlJN

(§0 I I I B I LlJ I II N I s I Tl R I u I

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I G I 0 I 8 I 0 I

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7 8 9 10 11 12 17 43 44 47 48 CAUSE DESCRIPTION (olal I Investigation revealed that a shorted diode in the control rod select circuitry I

7 8 9 80 lolsl 1~*--w_a_s ___ t_h_e....,....c_a_u_s_e_.~o-f_t_h_e_._s... pu ___

r_ro_u~s--R_B_M_b_y_p_a_s_~_a_n_d ___

1 1

e_d_g_e_r_o:..,.d __ s_e_1_e_c_t_e __ d_

11_i_nd-ic_a_t_io_n_f_o_r ____

~I j1ioj j~_b_.~_*t_h __ c_o_n_t_r_o_l_r_o_d_s_B_-_7_a_n_d_B_-_s_. __

T_h_e_d_e_f_e_c_t_iv_e_d_io_d_e_._w_a_s_r_e_p_l_a_c_e_d_,_a __

nd_p_r_o_p_e_r_R_B_M ___

8

~l 7

8 9 80 FACIUTY METHOD OF.

('continued)

• . STATUS POWER OTHER STATUS DISCOVERY DISCOVERY DESCRIPTION l_Ll I 0 I 4 I 4 I

• 1.___N_A ____ -"

~ I See 11Eve*nt Descr i pt i on 1

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12 13 44 45 46 80

.FORM OF

.ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT. OF ACTIVITY

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11 44 rn 7

8 NA LOCATION OF RELEASE 45 80 PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION

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13.

BO PERS.ONNEL

• 1NJURIES NUMBER OESCRl°PTION

[ill] I 0 I 01 01.';::-* -* __._NA_*---------------~---~--~

7 a*s 11 12 00 OFFSITE, CONSEQUENCES

. E~L NA 7

8 9 80 LOSS OR DAMAGE TO FACILITY TYPE

. DESCRIPTION EID lLl NA 7

8 9 10!::--------------------'--....--....;._--------------......:.--------8~0 PUBLICITY

[fill NA

. 7 8 9 80 ADDITIONAL FACTORS Eifil 7

8 9

• N 60

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.. NA-'\\1E~.~. _,_ __ J_e_f_f_e_r_y....,.R_. _w_o_J_* n_a_r_o_w""'s_k_i -------- PHONE: __

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GPO a 111.* a 117

EVENT DESCRIPTION (continued) found to cause :a oypass of the RBM system.

Withdrawal of control rods B-7 and B-8 was suspended and an investigation was initiated.

The safety significance of this event was minimal because the RBM backs up p~ocedural rod selections.

Although the Tech Specs require the RBM to be

• operab 1 e above 30% power, the Tech Spec bases indicate that the RBM function is not necessary below 70% power.

The significance was further mitigated by the core location of B-7 and B~8, since both control rods are located one position i~side the core periphery.

This is not a repetitive occurrence.

(50-249/1977-9)

CAUSE DESCRIPTION (continued) operation was verif1ed before further withdrawals of control rods B-7 and B-8 were performed.

All other interior control rods have been successfu(ly checked for similar problems.

This is the first rep0,r_ted failure of any of these diodes.

No further corrective action was deem~d~)warranted. The Rod Block Monitoring system. was supplied by the General Electric Company.