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From: "Emergency Drill"
To: bnpp@nppd.co.ir
Sent: Wednesday, October 3, 2018 6:32:51 PM
Subject: Emergency drill terminated - No action required

THIS IS A DRILL – THIS IS NOT A REAL EVENT –

THIS IS A DRILL NO ACTION REQUIRED

Event Notification Report – Plant name Notification 3 – Date: 03-10-2018

Reactor tripped due to failure of SG relief valve & primary to secondary leakage in SG-4 with atmosphere release

Plant name: Busher

Busher NPP

Plant owner:

Click here to enter text.

Unit(s) affected:

Unit 1

Reactor type(s):

PWR -WWER

Event date:

03/10/20018

Event time (UTC/local time):

06:55/10:25

What happened:

At 06:07 UTC/09:37 local time -Due to spurious opening of Steam Generator SG#4 relief valve and failure to close it, secondary coolant was evaporating from SG#4.

Reactor protection system tripped the reactor.

At 06:38/10:08 due to a rupture of the hot collector of SG#4 a primary-to-secondary leak occurred. Radioactive primary coolant is flowing into SG#4 secondary side and then being released as radioactive steam into the atmosphere via the open SG#4 relief valve.

At 06:55/10:25 station declared general emergency

Due to the primary-to-secondary lead, automatic RCS cooldown started via the intact SG#1,2,3 at a rate of 60 degrees C per hour. Additional boron injection pump started to inject into the pressuriser to reduce the primary pressure quickly. 2 staff suffered injury their hands during the attempt to close relief valve manually.

Plant personnel and protective area are evacuated.

( protective area – it is the area around the plant site, where protective measures in case of emergency are to be performed)

By 11:20/14:50 maintenance personnel successfully closed the relief valve by forcefully blocking the pilot valves (at that moment the RCS pressure was 1.5 MPa and the RCS temperature was 110 degrees Centigrade. The radioactive release was terminated.

12:57 (16:27 local time) The operators continued to cool down the RCS using the healthy SGs#1, 2, 3, with the respective RCP#1,2,3 and normal feedwater pumps running and steam being released to the condenser via the turbine bypass valves.

SG#4 was completely filled up with reactor coolant. The RCS coolant inventory is being maintained by use of the low-pressure safety injection pumps charging 16 g/kg borated water from the containment sump into the RCS. After the RCS was cooled down to 100 degrees Centigrade the operators switched over to cool down the RCS via the RHR system. At the moment the RCS temperature is 80 degrees Centigrade.

Further immediate planned actions:

• cool down the RCS to cold shutdown via the residual heat removal system

• initiate an outage to repair/replace SG#4 and the failed SG#4 relief valve

• continue radiological surveys and area cleaning activities as needed

• make a decision as to further personnel and population protection activities per the current radiological conditions.

The emergency drill has been terminated

Reactor status:

Subcritical

Consequence(s) of the event:

Atmospheric release through failed SG-4 relief valve. Dose rate on-site is 1.23 mSv/hour

Event classification:

Off-site emergency/General Emergency

Why this event notification?

You are receiving this event notification report because you are a WANO member and are on the WANO event notification distribution list. This report is classified as Limited Distribution .

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--
Sincerely Yours
Rasoul Mahmoudi
Manager of Managing Director Office,
Public Relations & International Affairs

Add: Nuclear Power Plant, Bushehr, Iran
P.O.Box: 75181/111
Tel: +98 77 3111 2585
Fax: +98 77 3111 2710
Personal Email: Mahmoudi@nppd.co.ir