Office for Nuclear Regulation

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Inspection of Progress with Electrical, Control & Instrumentation Aspects of PGDSC Preparation Following Final Shutdown of Reactor 1

Executive summary

Purpose of intervention

The purpose of this intervention was to inspect Electrical, Control and Instrumentation (EC&I) engineering aspects of Wylfa power station’s preparations for transition to a Post Generation and Defueling (PGD) phase of operation. This follows the cessation of generation by Reactor 2 (R2) in April 2012 and Reactor 1 (R1) on 30th December 2015.

This intervention was one of a series of planned interventions that will collectively inform a judgement on station’s readiness to implement PGD Operating Rules that are set out in a Post Generation and Defueling Safety Case (PGDSC).

Interventions Carried Out by ONR

The scope of this intervention by ONR Electrical and C&I Specialist Inspectors covered the EC&I engineering activities that station are undertaking in preparation for the PGDSC implementation. These activities included those described within Wylfa document ‘NP/SC 4899 Revision 1 Addendum 2 (Post Generation and Defueling Safety Case: Confirmation of Continued Validity and Update of Proposed RSOIs)’ and also any related developments or emergent issues.

This intervention was an inspection of the licensee’s progress in implementing Licence Condition 24 arrangements in respect of the development of Referenced Station Operating Instructions (RSOI) in support of the PGDSC.

Explanation of Judgement if Safety System Not Judged to be Adequate

The current inspection was not a safety system inspection, and therefore this section is not applicable.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

The majority of electrical modifications were found overall to be progressing adequately. However, station have identified that some protection settings on the electrical distribution system may not be optimised for the proposed emergency backup generation arrangements in the PGD phase. Station are taking action to remediate this aspect, but in the meantime it has justifiably adopted a conservative approach by retaining the extant configuration of emergency back-up generation going into the PGD phase.

Station’s C&I modifications were found to be progressing to plan.

The intervention identified a number of areas for potential improvement, and although none gave rise to significant concern, two issues have been entered onto the ONR Issues Database in order to monitor station’s action to address them. ONR will monitor progress with addressing these issues through normal regulatory business.

In summary, the outcome from the inspection of EC&I engineering work activity is that implementation of the LC24 arrangements from the perspective of PGDSC preparations are deemed adequate, in relation to the activities sampled. Therefore an inspection rating of 3 (Adequate) was assigned.

Conclusion of Intervention

From the information gathered and evidence obtained during this intervention, no matters were identified that are likely to have a significant impact on nuclear safety at present.

At present, no additional regulatory action is needed over and above ONR’s planned interventions of Wylfa power station, as set out in the intervention strategy, which will continue as planned.


Archwiliad o Gynnydd gydag Agweddau Trydanol, Rheoli ac Offeryniaeth o’r Paratoad PGDSC yn Dilyn Cau Adweithydd 1 yn Derfynol

Crynodeb gweithredol

Diben yr Ymyrraeth

Diben yr ymyrraeth hon oedd archwilio agweddau peirianyddol Trydanol, Rheoli ac Offeryniaeth (EC&I) paratoadau gorsaf bwer Wylfa ar gyfer y trawsnewid i’r cyfnod o weithredu Ôl Gynhyrchu a Gwagio Tanwydd (PGD). Mae hyn yn dilyn dwyn i ben y cynhyrchu gan Adweithydd 2 (R2) yn Ebrill 2012 ac Adweithydd 1 (R1) ar 30ain Rhagfyr 2015.

Roedd yr ymyrraeth hon yn un o gyfres o ymyraethau a gynlluniwyd fydd ar y cyd yn hysbysu’r farn ar barodrwydd yr orsaf i roi’r Rheolau Gweithredu PGD a nodir mewn Achos Diogelwch Ôl Gynhyrchu a Gwagio Tanwydd (PGDSC) ar waith.

Ymyraethau a Gyflawnwyd gan yr ONR

Roedd cwmpas yr ymyrraeth hon gan Arolygwyr Arbenigol Trydanol a C&I yr ONR yn cynnwys gweithgareddau peirianyddol y mae’r orsaf yn eu gweithredu wrth baratoi ar gyfer rhoi’r PGDSC ar waith. Roedd y gweithgareddau hyn yn cynnwys y rhai a ddisgrifir o fewn dogfen yr Wylfa ‘NP/SC 4899 Revision 1 Addendum 2 (Post Generation and Defueling Safety Case: Confirmation of Continued Validity and Update of Proposed RSOIs)’ a hefyd unrhyw ddatblygiadau cysylltiedig neu faterion oedd yn codi.

Archwiliad o’r symud ymlaen gan y trwyddedai i roi trefniadau Amod Trwydded 24 ar waith oedd yr ymyrraeth hon parthed datblygu Cyfarwyddiadau Gweithredu Gorsaf Cyfeirnodedig (RSOI) i ategu’r PGDSC.

Esboniad o’r Dyfarniad os Nad oedd y System Ddiogelwch wedi cael ei Barnu yn Ddigonol.

Nid archwiliad o’r system ddiogelwch oedd yr archwiliad cyfredol, ac felly nid yw’r adran hon yn berthnasol.

Casgliadau Allweddol, Barnau’r Arolygydd a Rhesymau dros Wneud

Dyfarniadau

Gwelwyd bod y rhan fwyaf o addasiadau trydanol yn datblygu’n ddigonol ar y cyfan. Fodd bynnag, mae’r orsaf wedi canfod nad oedd rhai gosodiadau diogelu ar y system dosbarthu trydanol o bosib wedi eu mwyafu ar gyfer y trefniadau cynhyrchu wrth gefn mewn argyfwng arfaethedig yn y cyfnod PGD. Mae’r orsaf yn cymryd camau i wella ar yr agwedd hon, ond yn y cyfamser mae’n haeddiannol wedi mabwysiadu ymagwedd geidwadol drwy gadw’r cyfluniad presennol o gynhyrchu wrth gefn mewn argyfwng wrth fynd i mewn i’r cyfnod PGD.

Gwelwyd bod addasiadau C&I’r orsaf yn datblygu yn ôl y cynllun.

Canfyddodd yr ymyrraeth sawl maes y gellid gwella arno, ac er nad oedd yr un yn achosi pryder sylweddol, mae dau fater wedi eu rhoi ar Fasdata Materion yr ONR er mwyn monitro camau gweithredu’r orsaf i fynd i’r afael â nhw. Bydd yr ONR yn monitro cynnydd wrth fynd i’r afael â’r materion hyn drwy waith rheoleiddiol arferol.

I grynhoi, canlyniad yr archwiliad ar weithgaredd peirianyddol EC&I yw bod y gweithredu ar drefniadau LC24 o safbwynt paratoadau PGDSC yn cael eu hystyried yn ddigonol, yn ôl y gweithgareddau a samplwyd. Felly rhoddwyd gradd archwilio o 3 (Digonol).

Casgliad yr Ymyrraeth

O’r wybodaeth a gafwyd a’r dystiolaeth a gasglwyd yn ystod yr ymyrraeth hon, ni chanfyddwyd unrhyw faterion sy’n debygol o gael effaith sylweddol ar ddiogelwch niwclear ar hyn o bryd.

Ar hyn o bryd, nid oes angen gweithredu rheoleiddiol yn ychwanegol at yr ymyraethau a gynlluniwyd gan yr ONR ar orsaf bwer Wylfa, fel y’u nodir yn y strategaeth ymyrraeth, fydd yn parhau yn ôl y cynllun.